Patent Description:
Welding is a fabrication process used to join two or more materials together. Welding is utilized in almost every industry, including manufacturing processes and process control plants. In general, welding involves melting two work pieces together and adding a filler material to form a pool of molten material that cools or dries to form a joint. The work pieces are often compositions of metals or metal alloys and the filler material is often a metal or metal alloy. Many different types of welding exist such as, for example, gas tungsten arc welding, gas metal arc welding, flux-cored arc welding, shielded metal arc welding, etc..

When welding together two dissimilar metals and/or metal alloys, metallurgical problems can arise. For example, when welding two work pieces of steel alloy, such as grade <NUM> steel (e.g., ASTM A387) and grade <NUM> steel, a steep gradient exists with regard to the chromium content or concentration in the different steels. Grade <NUM> steel has a chromium content of about <NUM> percent (%) by weight while grade <NUM> steel has a chromium content of about <NUM>% by weight. During post-weld heat treatment and/or during service of the work pieces in a relatively high temperature area, carbon diffusion occurs between the grade <NUM> steel and the grade <NUM> steel due to the different chromium contents. Carbon diffusion causes a reduction in strength and/or creep resistance in the lower-chromium metal (i.e., the grade <NUM> steel). Even when using a filler material having a chromium content that is between the chromium contents of the grade <NUM> steel and the grade <NUM> steel, the chromium content gradient still results in carbon diffusion between the grade <NUM> steel and the grade <NUM> steel. Document <CIT> describes two welding layers to be weld directly in situ or to be remotely manufacture and two base supports are therefore needed. Document <CIT> discloses disposing a plurality of layered weldments on a ring member of increasing chromium weight percentage. Document <CIT> is directed to a weld filler composition for joining different alloy steel pieces. Document <CIT> discloses a weld joint that allegedly reduces the chromium gradient between a low alloy steel and a high alloy steel.

The figures are not to scale. Instead, to clarify multiple layers and regions, the thickness of the layers may be enlarged in the drawings. Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts.

The present invention is directed to a method for assembling two work pieces and to a corresponding piece assembly, the main and subsidiaries aspects of which are defined by the appended claims. Embodiments and examples in the following description that are deemed not covered by the appended claims are considered as being not part of the invention, and are provided for the purpose of understanding.

When welding together dissimilar metals and/or metal alloys, metallurgical problems often arise. Steel, which is generally composed of iron and carbon, is commonly alloyed with other elements (e.g., metallic elements) or constituents (e.g., alloyants) such as manganese, nickel, chromium, molybdenum, vanadium, silicon and boron. The content or percentage by weight (or mass) of these elements may be varied to produce different types of steel alloys. However, when welding steel alloys having different compositions (e.g., different contents of particular elements), metallurgical problem often arise. For example, when welding two work pieces (e.g., two end pieces or parts to be coupled) of steel alloy, such as grade <NUM> steel and grade <NUM> steel, a steep gradient (e.g., a relatively large change) exists with regard to the chromium content in the steels. Grade <NUM> steel has a chromium content of about <NUM> percent (%) by weight, which is lower than the chromium content in grade <NUM> steel, which has a chromium content of about <NUM>%by weight. A steep chromium content gradient is the driving force for carbon diffusion, and during post-weld heat treatment and/or during service in a relatively high temperature/stress environment, carbon diffusion occurs between the different steels as a result of the chromium content gradient. In other words, carbon from the lower-chromium metal (e.g., grade <NUM> steel) diffuses into the higher-chromium metal (e.g., the grade <NUM> steel). Carbon diffusion causes a reduction in strength and/or creep resistance in the lower-chromium metal (i.e., the grade <NUM> steel).

In general, welding involves melting a filler material with the metals/metal alloys of two work pieces to form a molten pool of material that cools to form a weld (e.g., a bead, a weld layer, etc.) that bonds the work pieces together. A filler material may be, for example, a covered electrode, a bare electrode wire and/or a tubular electrode wire. A filler material may have a different composition than the work pieces being welded. For example, the filler material may be a metal alloy having a chromium content that is between the chromium contents of the first and second work pieces (e.g., about <NUM>% chromium by weight). However, even when using such a filler material, a chromium gradient is still present between the lower-chromium metal and the higher-chromium metal and, thus, carbon diffusion occurs.

Example methods and apparatus disclosed herein reduce and/or substantially eliminate adverse effects of welding two work pieces (e.g., two components to be coupled together) having different compositions or contents of elements (e.g., a metallic element, an alloyant). The example methods and apparatus may be used to, for example, reduce and/or substantially eliminate carbon diffusion between two work pieces having different chromium contents. In general, the example methods disclosed herein include depositing weld layers between two work pieces, where the weld layers have compositions (e.g., chemistries) with contents (e.g., by mass or weight percentage) of one or more element(s) (e.g., a metallic element) that falls between the range of compositions or contents of the element(s) in the two work pieces. The resulting weld layers produce a composition that transitions less abruptly from one of the work pieces to the other work piece. For example, with work pieces having different chromium contents (e.g., the weight percentages of chromium are different), the weld layers may have chromium contents that more gradually transition across the weld layers. In other words, the composition of the weld layers at one end are substantially more similar to the composition of one of the work pieces to be welded, while the composition of weld layers at the other end are substantially more similar to the composition of the other work piece to be welded. As a result, the gradient of the chromium content of the weld layers (e.g., the change in the chromium content) between the two work pieces is more gradual. This gradual transition forms a chromium content gradient that may be below a threshold that typically results in carbon diffusion. Therefore, the likelihood of carbon diffusion between the work pieces and the adjacent weld layers and/or across the weld layers is reduced and/or substantially eliminated.

According to the invention, there is disclosed a transitional piece that is to be welded between two work pieces. The transitional piece includes a base that may be the same material and has the same chromium content as a first one of the work pieces. Three weld layers are disposed on the end of the base that is to be coupled to the second one of the work pieces having a different composition (e.g., the work piece having a different chromium content). The three weld layers may have compositions with contents of one or more element(s) (e.g., a metallic element) that increases or decreases in content (e.g., the weight percentage of the element) to provide a transition to the second work piece. The weld layers have increasing or decreasing chromium contents that result in a relatively less steep (e.g., more gradual or moderate) chromium content gradient across the weld layers. The transitional piece is welded between the two work pieces by welding a first end of the base to the first work piece and welding the three weld layers (e.g., at a second end of the base) to the second work piece. The three weld layers create a chromium content that transitions more gradually across the weld layers. The resulting chromium gradient is relatively gradual and, thus, the likelihood of carbon diffusion is reduced and/or substantially eliminated.

The example methods and apparatus disclosed herein may be implemented using any type of welding process that utilizes filler material such as, for example, gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), electroslag welding (ESW), submerged arc welding (SAW), shielded metal arc welding (SMAW) (i.e., stick welding), flux-cored arc welding (FCAW), etc. Other types welding that use a filler material may also be implemented (e.g., gas or oxy acetylene welding with a filler material).

When depositing weld layers using the example methods disclosed herein and/or creating an example transitional piece as disclosed herein, different filler materials having different contents of an element (e.g., a metallic element) may be employed. In some examples disclosed herein, the filler materials are implemented as two or more rods or wires (e.g., wire electrodes or electrode wires) that are twisted or braided together to form a filler material having a composition with a desired content of the metallic element. Using combinations of two or more wires or rods having different contents enables a welder to form a plurality of different weld layers, having a plurality of different possible contents, while employing a few types of commercially-available wire grades. In some examples, a wire feed welder having two wire electrodes is used to create the example weld layers. The wire electrodes may have different contents of the element and the speeds or feed rates of the wires may be adjusted to result in different element contents for the resulting weld layers, for example. Although many of the examples disclosed herein are described in relation to reducing the gradient of the content of a metallic element, such as chromium, between two metal alloys, the example methods and apparatus disclosed herein may be implemented to provide a transition between any different materials that may have adverse effects when welded together. In other words, the examples disclosed herein may be used to join materials having different contents (e.g., mass or weight percentages) of any element (e.g., a metal, a non-metal, a metalloid) that may otherwise produce negative or undesired effects if welded together (e.g., a decrease in strength).

Turning now to the figures, <FIG> illustrates an example weld <NUM>, implemented in accordance with example welding methods disclosed herein, to reduce and/or eliminate adverse or negative effects produced when welding two work pieces having different compositions or contents of an alloyant or metallic element (e.g., a transition metal such as vanadium, tungsten, titanium, niobium, etc.). For example, the weld <NUM> may be used to reduce and/or substantially eliminate carbon diffusion between two work pieces having different chromium contents. In the illustrated example, a first work piece <NUM> is coupled (e.g., joined) to a second work piece <NUM> via the example weld <NUM>. The first work piece <NUM> may be a metal alloy having a first chromium content and the second work piece <NUM> may be another metal alloy having a second chromium content that is higher than the first chromium content of the first work piece <NUM>. For example, the first work piece <NUM> may be grade <NUM> steel alloy, which has a chromium content (e.g., a nominal chromium content) of about <NUM>% by weight, and the second work piece <NUM> may be grade <NUM> steel alloy, which has a chromium content of about <NUM>% by weight. Therefore, if the first and second work pieces <NUM>, <NUM> were welded together using known techniques, a chromium content gradient would exist across the weld between the first and second work pieces <NUM>, <NUM>. As a result, carbon in the first work piece <NUM> (e.g., the lower-chromium work piece) would diffuse or migrate toward the second work piece <NUM> (e.g., the higher-chromium work piece) and, thus, the strength and/or creep resistance in the first work piece <NUM> would be reduced.

To reduce carbon diffusion between the first and second work pieces <NUM>, <NUM>, the example weld <NUM> includes a first weld layer <NUM> and a second weld layer <NUM>. The first weld layer <NUM> is deposited (e.g., "buttered," patterned, laid) on a first end <NUM> of the first work piece <NUM> and has a chromium content that is higher than the first chromium content of the first work piece <NUM> and lower than the second chromium content of second work piece <NUM>. The second weld layer <NUM>, which is deposited between the first weld layer <NUM> and a second end <NUM> of the second work piece <NUM>, has a chromium content that is higher than the chromium content of the first weld layer <NUM> (and/or the first work piece <NUM>) and lower than the second chromium content of the second work piece <NUM>. For example, the first weld layer <NUM> may have a chromium content of about <NUM>% by weight and the second weld layer <NUM> may have a chromium content of about <NUM>% by weight. In other words, the chromium content gradually increases between the first end <NUM> of the first work piece <NUM> and the second end <NUM> of the second work piece <NUM>. As a result, the gradient of the chromium content formed between the first end <NUM> of the first work piece <NUM> and the second end <NUM> of the second work piece <NUM> is less steep or more gradual than produced with known techniques and, thus, the likelihood of carbon diffusion is reduced or substantially eliminated.

In the illustrated example of <FIG>, two weld layers form the example weld <NUM>. However, in other examples, more than two weld layers may be used to form the example weld <NUM>. In such an example, each of the weld layers, beginning with weld layer closest to the first work piece <NUM>, has a progressively increasing chromium content. As a result, the chromium content gradient between the first and second work pieces <NUM>, <NUM> is reduced or lessened. Further, although this method is described as starting with the lowest chromium content weld layer, this process may be performed in reverse. In other words, the second weld layer <NUM> may be deposited on the second end <NUM> of the second work piece <NUM> and then the first weld layer <NUM> may be deposited between the second weld layer <NUM> and the first end <NUM> of the first work piece <NUM> to couple the first and second work pieces <NUM>, <NUM> together.

<FIG> illustrates an example transitional piece <NUM> that may be used to couple two work pieces having different compositions or contents of an alloyant or metallic element (e.g., a transition metal) and to reduce negative or adverse effects of welding such work pieces together. The transitional piece <NUM> is used to reduce the carbon diffusion between the work pieces having different chromium contents. In the illustrated example, a first work piece <NUM> is to be coupled to a second work piece <NUM>. Similar to the work pieces described in <FIG>, the first work piece <NUM> may be a metal alloy (e.g., grade <NUM> steel) having a first chromium content and the second work piece <NUM> may be another metal alloy (e.g., grade <NUM> steel) having a second chromium content that is higher than the first chromium content of the first work piece <NUM>.

To couple or join the first and second work pieces <NUM>, <NUM>, the transitional piece <NUM> is welded between the first and second work piece <NUM>, <NUM>. In the illustrated example, the transitional piece <NUM> includes a base <NUM> having a first end <NUM> and second end <NUM>. In the illustrated example, the base <NUM> is implemented as substantially the same material as the first work piece <NUM> and/or a material having a chromium content that is substantially similar to the first chromium content of the first work piece <NUM>. The first end <NUM> of the base <NUM> may be welded to the end <NUM> of the first work piece <NUM> using a filler material (e.g., an electrode wire) that has substantially the same chromium content as the first work piece <NUM> and/or the base <NUM>. As a result, no substantial chromium gradient is produced and, thus, no carbon diffusion would occur between the first work piece <NUM> and the base <NUM> of the transitional piece <NUM>. To reduce the likelihood of carbon diffusion between the base <NUM> and the second work piece <NUM> (e.g., which has a relatively higher chromium content), the transitional piece <NUM> includes a first weld layer <NUM>. In the illustrated example, the first weld layer <NUM> has a chromium content that is higher than the chromium content of the base <NUM> and lower than the second chromium content of the second work piece <NUM>. To couple the transitional piece <NUM> to the second work piece <NUM>, a weld layer having a chromium content that is higher than the chromium content of the first weld layer <NUM> and less than the chromium content of the second work <NUM> may be deposited between the first weld layer <NUM> and the end <NUM> of the second work piece <NUM>. As a result, the chromium content gradient is relatively less steep or more gradual and, thus, the likelihood carbon diffusion is reduced and/or substantially eliminated.

<FIG> illustrates the example transitional piece <NUM> welded between the first and second work pieces <NUM>, <NUM>. In the illustrated example, a second weld layer <NUM> is deposited between the first weld layer <NUM> and the end <NUM> of the second work piece <NUM>. As described above, the second weld layer <NUM> may have a chromium content that is higher than first weld layer <NUM> and lower than the second chromium content of the second work piece <NUM>. Therefore, the chromium content gradient between the second end <NUM> of base <NUM> and the second work piece <NUM> is relatively less steep and, thus, the likelihood of carbon diffusion is reduced and/or substantially eliminated. Additionally, to couple the first work piece <NUM> to the transitional piece <NUM>, a third weld layer <NUM> is deposited between the first end <NUM> of the base <NUM> of the transitional piece <NUM> and the end <NUM> of first work piece <NUM>. As described above, the third weld layer <NUM> is a material that is substantially similar to and/or has a chromium content that is substantially similar to the first work piece <NUM> and/or the base <NUM>. As a result, no carbon diffusion would occur between the first work piece <NUM> and the base <NUM> (e.g., because the materials and/or chromium contents of the first work piece <NUM>, the third weld layer <NUM> and the base <NUM> are all the substantially the same).

In some examples, many different types of example transitional pieces may be manufactured so that instead of depositing each of the weld layers between the two dissimilar work pieces, a transitional piece may be coupled between the two work pieces via one weld at each end of the transitional piece. For example, transitional pieces having different base materials and/or weld layers with different metallic element contents (e.g., different chromium contents) may be manufactured for different combinations of work pieces. An appropriate transitional piece may be selected and welded between the two work pieces to couple the two work pieces together.

In the illustrated example of <FIG>, and according to the invention, the base <NUM> of the transitional piece <NUM> is implemented as a material that is substantially similar to and/or has a chromium content that is substantially similar to the first work piece <NUM>. However, in other examples, the base <NUM> of the transitional piece <NUM> may instead be implemented as a material that is substantially similar to and/or has a chromium content that is substantially similar to the second work piece <NUM>. In such an example, one or more weld layers may instead be deposited on the first end <NUM> of the base <NUM> to reduce and/or substantially eliminate the carbon diffusion between the base <NUM> and the first work piece <NUM>. In some examples, the base <NUM> may be a material having a chromium content that is different than the first work piece <NUM>. For example, the base <NUM> may have a chromium content that is higher than the first chromium content of the first work piece <NUM>. In such an example, the third weld layer <NUM> may have a chromium content that is between the first chromium content of the first work piece <NUM> and the chromium content of the base <NUM>. As a result, the chromium content gradient between the first work piece <NUM> and the second work piece <NUM> is relatively less steep and, thus, the likelihood of carbon diffusion is reduced and/or substantially eliminated.

Additionally, although only two weld layers (e.g., the first weld layer <NUM> and the second weld layer <NUM>) are employed in <FIG> between the base <NUM> of the transitional piece <NUM> and the second work piece <NUM>, in other examples, more than two weld layers may be deposited between the base <NUM> and the second work piece <NUM>. According to the invention, three weld layers are deposited between the base <NUM> and the second work piece <NUM>.

Although the example work pieces <NUM>, <NUM>, <NUM>, <NUM> illustrated in <FIG> are substantially planar (e.g., sheets of metal), the disclosed methods and/or transitional pieces may be used with any type of work pieces having any desired shapes or geometries.

For example, <FIG> illustrates a cross-section of walls of two pipes that are to be joined. An example plurality of weld layers <NUM> is implemented to couple a first work piece or pipe <NUM> to a second work piece or pipe <NUM>. The first work piece <NUM> has a first chromium content and the second work piece <NUM> has a second chromium content, which is higher than the first chromium content of the first work piece <NUM>. A butt weld is typically used to join two pipes together and involves beveling the exterior of the both of the pipe ends to form a groove at the abutted pipe ends where a weld layer can be deposited. In the illustrated example, an end <NUM> of the first work piece <NUM> is to be coupled to an end <NUM> of the second work piece <NUM>. The weld layers <NUM> are deposited onto the end <NUM> of the first work piece <NUM>. In the illustrated example, the weld layers <NUM> include a first weld layer <NUM>, a second weld layer <NUM>, a third weld layer <NUM>, a fourth weld layer <NUM>, a fifth weld layer <NUM> a sixth weld layer <NUM> and a seventh weld layer <NUM>. To produce a relatively low chromium content gradient, each of the successive layers <NUM>-<NUM> (from left to right in <FIG>) has an increasing chromium content relative to the previous or adjacent weld layer. For example, the first weld layer <NUM> has a chromium content that is higher than the first chromium content of the first work piece <NUM>, the second weld layer <NUM> has a chromium content that is higher than the first weld layer <NUM>, the third weld layer <NUM> has a chromium content that is higher than the second weld layer <NUM>, the fourth weld layer <NUM> has a chromium content that is higher than the third weld layer <NUM>, the fifth weld layer <NUM> has a chromium content that is higher than the fourth weld layer <NUM>, the sixth weld layer <NUM> has a chromium content that is higher than the fifth weld layer <NUM>, and the seventh weld layer <NUM> has a chromium content that is higher than the sixth weld layer <NUM>. In the illustrated example, the seventh weld layer <NUM> is formed by a plurality of passes. In other examples, more or fewer passes may be performed.

In the illustrated example, the example weld layers <NUM> are beveled (e.g., angled, tapered) to form a groove between the weld layers <NUM> and the end <NUM> of the second work piece <NUM>, which is also beveled. In some examples, the weld layers <NUM> are deposited onto the end <NUM> of the first work piece <NUM> and then ground or cut to form the bevel. Additionally or alternatively, the weld layers <NUM> may be deposited at a decreasing width on the end <NUM> of the first work piece <NUM> to form the bevel. For example, when depositing the seventh weld layer <NUM> with a plurality of passes, each of the passes (from left to right in <FIG>) may deposit a narrower weld layer than the previous pass to form the bevel.

In the illustrated example of <FIG>, a final weld layer <NUM> is deposited between the plurality of welds <NUM> and the end <NUM> of the second work piece <NUM> to couple the first work piece <NUM> to the second work piece <NUM>. The final weld layer <NUM> may have a chromium content that is substantially similar to the seventh weld layer <NUM> and/or the second chromium content of the second work piece <NUM>. In some examples, the final weld layer <NUM> has a chromium content that is higher than the seventh weld layer <NUM> and lower than the second chromium content of the second work piece <NUM>. As a result, the chromium content gradient between the end <NUM> of the first work piece <NUM> and the end <NUM> of the second work piece <NUM> is less steep and, thus, the likelihood of carbon diffusion is reduced and/or substantially eliminated.

In some examples, the first work piece <NUM> and the plurality of weld layers <NUM> form a transitional piece that may be welded between two pipes to couple two pipes together. For example, an opposite end of the first work piece <NUM> may be welded to another pipe (e.g., an upstream pipe), and the end <NUM> with the plurality of weld layers <NUM> may be welded to the second work piece <NUM> (e.g., a downstream pipe), to couple the pipes together.

In the illustrated examples of <FIG>, the example weld layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <NUM> are formed by melting a filler material onto or between adjacent materials. In some examples, the filler materials may have different contents of the alloyant or metallic element (e.g., chromium). In some examples, multiple filler materials may be combined to produce a resultant filler material having a composition with a desired metallic element content for the corresponding weld layer. For example, <FIG> illustrates a first example filler material <NUM> and a second example filler material <NUM> that may be used to form one or more of the example weld layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <NUM> of <FIG>. In the illustrated example, the first filler material <NUM> includes a first wire or rod <NUM> and a second wire or rod <NUM> that are twisted or braided together. The first filler material <NUM> may be deposited using, for example, GTAW. In the illustrated example, the first wire <NUM> and the second wire <NUM> have different chromium contents. However, when melted together via the GTAW process, the resulting chromium content is based on the chromium contents of the first and second wires <NUM>, <NUM>. In the illustrated example, the second filler material <NUM> is also formed of a first wire or rod <NUM> and a second wire or rod <NUM>, having different chromium contents, and twisted or braided together. The first filler material <NUM> and the second filler material <NUM> may be used to form the respective first and second weld layers <NUM>, <NUM> of the example weld <NUM> of <FIG>.

For example, the first work piece <NUM> of <FIG> may be grade <NUM> steel, which has a chromium content of about <NUM>% by weight and the second work piece <NUM> may be grade <NUM> steel, which has a chromium content of about <NUM>% by weight. The first wire <NUM> and/or the second wire <NUM> of the first filler material <NUM> may have a chromium content that is higher than the first chromium content of the first work piece <NUM>. As a result, the first weld layer <NUM> would have a chromium content that is higher than the first chromium content of the first work piece <NUM>. For example, the first wire <NUM> may have a chromium content of about <NUM>% by weight and the second wire <NUM> may have a chromium content of about <NUM>% by weight. When the first filler material <NUM> is melted to produce the first weld layer <NUM>, the resulting first weld layer <NUM> has a chromium content of about <NUM>% by weight, for example. Therefore, the first weld layer <NUM> would have a chromium content that is higher than the first chromium content (e.g., about <NUM>% by weight) of the first work piece <NUM>. Further, the first wire <NUM> and/or the second wire <NUM> of the second filler material <NUM> may have a chromium content that is higher than either or both of the first and second wires <NUM>, <NUM> of the first filler material <NUM> and/or lower than the second chromium content of the second work piece <NUM>. As a result, the second weld layer <NUM> would have a chromium content that is higher than first weld layer <NUM> and lower than the second chromium content of the work piece <NUM>. For example, the first wire <NUM> may have a chromium content of about <NUM>% and the second wire <NUM> may have a chromium content of about <NUM>% by weight. When the second filler material <NUM> is melted to produce the second weld layer <NUM>, the resulting second weld layer <NUM> would have a chromium content of about <NUM>% by weight, for example. Therefore, the second weld layer <NUM> would have a chromium content that is higher than the first weld layer <NUM> and lower than the second chromium content (e.g., about <NUM>% by weight) of the second work piece <NUM>. This example method can be repeated multiple times depending on the number of weld layers that are to be used. Therefore, a plurality of weld layers can be formed with a few wires or rods, each having a different content of the alloyant or metallic element (e.g., chromium), by combining the wires in different combinations to form filler materials having desired alloyant or metallic element contents for the corresponding weld layers.

<FIG> illustrates another example filler material <NUM> that may be used to produce one or more of the example weld layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <NUM> of <FIG>. The example filler material <NUM> includes a first wire or rod <NUM>, a second wire or rod <NUM> and a third wire or rod <NUM> that are twisted or braided together. Similar to the example first and second filler materials <NUM>, <NUM> of <FIG>, different combinations of wires may be used to form the filler material <NUM>.

For example, the first work piece <NUM> of <FIG> may be grade <NUM> steel, which has a chromium content (e.g., a nominal chromium content) of about <NUM>% by weight, and the second work piece <NUM> may be grade <NUM> steel, which has a chromium content of about <NUM>% by weight. Table <NUM> below illustrates example combinations of three types of wires (e.g., wire electrodes, filler materials) that may be used to form the filler material <NUM> for each of the example weld layers <NUM>-<NUM> of <FIG>.

"-B3" may be, for example, ER90S-B3, which has a chromium content in the range of about <NUM> - <NUM>% by weight, "-B6" may be, for example, ER80S-B6, which has a chromium content in the range of about <NUM> - <NUM>% by weight and "-B8" may be, for example, ER80S-B8, which has a chromium content in the range of about <NUM> - <NUM>% by weight. As illustrated in Table <NUM>, to form the filler material <NUM> for the first weld layer <NUM>, all three of the wires <NUM>-<NUM> are implemented as -B3. The resulting first weld layer <NUM> has a chromium content of about <NUM>% by weight. Therefore, the first weld layer <NUM> may have a higher chromium content than the chromium content of the first work piece <NUM>, which may range have a range of about <NUM> - <NUM>%, for example. To form the filler material <NUM> for the second weld layer <NUM>, as illustrated in Table <NUM>, two of the wires <NUM>-<NUM> are implemented as -B3 and one of the wires <NUM>-<NUM> is implemented as -B6. The resulting second weld layer <NUM> has a chromium content of about <NUM>% by weight. Therefore, the chromium content of the second weld layer <NUM> (e.g., about <NUM>% by weight) is higher than the chromium content of the first weld layer <NUM> (e.g., about <NUM>% by weight). As illustrated in the example Table <NUM>, this process can continue for each of the weld layers <NUM>-<NUM>. Each of the layers has an increasing chromium content (e.g., <NUM>%, <NUM>%, <NUM>%, etc.) the further away from the first work piece <NUM>. To form the filler material <NUM> for the seventh weld layer <NUM>, as illustrated in Table <NUM>, all three of the wires <NUM>-<NUM> are implemented as -B8, which results in a weld layer with a chromium content of about <NUM>% by weight. Thus, the chromium content of the seventh weld layer <NUM> is below the chromium content of the second work piece <NUM>, which may have a range of about <NUM> - <NUM>%, for example. By creating a plurality of weld layers in which successive weld layers have gradually increasing chromium contents, the chromium content gradient across the weld layers <NUM>-<NUM> is less than a threshold that causes carbon diffusion. Thus, the carbon diffusion is reduced and/or substantially eliminated.

In this example, three wires or rods are used to form the filler material <NUM>. However, in other examples, more or fewer types of wires or rods may be employed to form the filler materials for the different weld layers <NUM>-<NUM>. Additionally, the wires <NUM>-<NUM> may be other types of wires or rods having different compositions.

<FIG> illustrates an example system <NUM> for reducing and/or substantially eliminating negative or adverse effects of coupling two work pieces having different compositions or contents of an alloyant or metallic element (e.g., a transition element) via welding. The example system <NUM> may be used to produce any of the example weld layers of <FIG>. The example system <NUM> may be used, for example, to reduce the carbon diffusion between two work pieces joined by a weld.

In the illustrated example, a wire feed welder <NUM> is used to deposit a plurality of example weld layers <NUM> on a work piece <NUM>. The first work piece <NUM> may have a first content of a metallic element such as chromium. The wire feed welder <NUM> may be, for example, a GMAW welder, a flux core welder, etc. The wire feed welder <NUM> includes a handle or gun <NUM>. In the illustrated example, the wire feed welder <NUM> includes two spools <NUM>, <NUM> of filler materials (e.g., wire electrodes) that are fed through a tip <NUM> of the gun <NUM>. The first spool <NUM> feeds a first wire <NUM> and the second spool <NUM> feeds a second wire <NUM>. The first and second wires <NUM>, <NUM> may have different contents of the metallic element (e.g., different contents of chromium).

The wire feed welder <NUM> of the illustrated example is used to deposit weld layers formed by the first wire <NUM> and/or the second wire <NUM>. To provide weld layers having different contents of the metallic element, the feed rates of the first and second wires <NUM>, <NUM> of the example system <NUM> are independently adjustable. For example, during a first pass to form a first weld layer <NUM>, a first feed rate for the first wire <NUM> may be relatively high and a second feed rate for the second wire <NUM> may be relatively low. As a result, more of the first wire <NUM> is melted to form the first weld layer <NUM>. If the first wire <NUM> has a lower content of the metallic element than the second wire <NUM>, for example, then the first weld layer <NUM> also has a relatively lower content of the metallic element. For example, if the metallic element is chromium, then the resulting first weld layer <NUM> has a relatively lower chromium content. The resulting chromium content of the first weld layer <NUM> may be higher or lower than the chromium content of the work piece <NUM>, depending on the contents of the chromium in the first and second wires <NUM>, <NUM>. During a second pass to form a second weld layer <NUM>, the feed rates of the first and second wires <NUM>, <NUM> may be altered. For example, a first feed rate of the first wire <NUM> may be lower than the feed rate of the first wire <NUM> during the first pass for the first weld layer <NUM>. Additionally or alternatively, a second feed rate for the second wire <NUM> may be higher than the feed rate of the second wire <NUM> during the first pass for the first weld layer <NUM>. If the second wire <NUM> has a relatively higher content of the metallic element than the first wire <NUM>, for example, then the second weld layer <NUM> also has a relatively higher content of the metallic element (e.g., higher than the first weld layer <NUM>). For example, if the metallic element is chromium, the resulting second weld layer <NUM> has a relatively higher chromium content. This method may be used to deposit multiple weld layers having desired contents of the metallic element.

The example system <NUM> may employ a control system <NUM> to operate the feed rates of the first and second wires <NUM>, <NUM>. The control system <NUM> of the illustrated example includes a microprocessor <NUM>, an input/output module <NUM>, a comparator <NUM> and a wire speed controller <NUM>. For example, a welding technician may input a desired chromium content or speed rate for the first and second wires <NUM>, <NUM> to produce a weld layer with a particular chromium content. The chromium content may be based on a plurality of factors including, for example, the type of material of the first and second wires <NUM>, <NUM>, the speeds of the first and second wires <NUM>, <NUM>, the type of shielding gas used, the voltages applied to the first and second wires <NUM>, <NUM>, the type of material to be welded, etc. As the first and second wires <NUM>, <NUM> are fed, a signal corresponding to the target or desired speeds is provided to the microprocessor <NUM> via the input/output module <NUM>. The control system <NUM> may determine if the speed rates of the first and second wires <NUM>, <NUM> are within a certain range or threshold to produce the desired weld layer. For example, the comparator <NUM> may compare the speed rates of the first and second wires <NUM>, <NUM> with a threshold provided by, for example, reference data. The reference data may include, for example, a table of threshold speed rates for different types of wires based on a number of factors including, for example, the type of material being welded, the type of shielding gas, etc. If the feed rates of the first and second wires <NUM>, <NUM> are too fast and/or too slow, the wire speed controller(s) <NUM> may adjust the speeds of the spools <NUM>, <NUM>, which changes the feed rates of the first and second wires <NUM>, <NUM>. This operation may be performed for each weld layer the welding technician desires to deposit. In some examples, the welding may be performed by a welding robot. In such an example, the feed rates of the first and second wires <NUM>, <NUM> may be stored in the software or coding of a program that is executed to automatically control the robot to produce the desired weld layers.

A flowchart representative of an example method for coupling two work pieces having different compositions or contents of an alloyant or metallic element and for reducing and/or substantially eliminating negative or adverse effects of coupling the work pieces by a weld is shown in <FIG>. The example method illustrated in <FIG> may be used to create any of the example welds of <FIG> and <FIG> and/or implement the example system <NUM> of <FIG>. In this example, at least a portion of the method may be implemented using machine readable instructions that comprise a program for execution by a processor such as the processor <NUM> shown in the example processor platform <NUM> discussed below in connection with <FIG>. The program may be embodied in software stored on a tangible computer readable storage medium such as a CD-ROM, a floppy disk, a hard drive, a digital versatile disk (DVD), a Blu-ray disk, or a memory associated with the processor <NUM>, but the entire program and/or parts thereof could alternatively be executed by a device other than the processor <NUM> and/or embodied in firmware or dedicated hardware. Further, although the example program is described with reference to the flowchart illustrated in <FIG>, many other methods of producing the example welds of <FIG> and <FIG> and/or implementing the example system <NUM> of <FIG> may alternatively be used. For example, the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, or combined.

As mentioned above, at least a portion of the example method of <FIG> may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a tangible computer readable storage medium such as a hard disk drive, a flash memory, a read-only memory (ROM), a compact disk (CD), a digital versatile disk (DVD), a cache, a random-access memory (RAM) and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term tangible computer readable storage medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, "tangible computer readable storage medium" and "tangible machine readable storage medium" are used interchangeably. Additionally or alternatively, the example method of <FIG> may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a non-transitory computer and/or machine readable medium such as a hard disk drive, a flash memory, a read-only memory, a compact disk, a digital versatile disk, a cache, a random-access memory and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term non-transitory computer readable medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, when the phrase "at least" is used as the transition term in a preamble of a claim, it is open-ended in the same manner as the term "comprising" is open ended.

<FIG> illustrates an example flowchart representative of an example method <NUM> for coupling two work pieces having different compositions or contents of an alloyant or metallic element (e.g., a transition metal) and for reducing and/or substantially eliminating negative or adverse effects of coupling the work pieces by a weld. The example method <NUM> may be used to create one or more of the example welds in <FIG> and/or implement the example system <NUM> of <FIG>. The example method <NUM> may be implemented to deposit one or more weld layers between two work pieces having dissimilar compositions such as, for example, a first work piece having a chromium content that is lower than a chromium content of a second work piece. The example method <NUM> includes depositing a first weld layer on a first end of a first work piece (block <NUM>). In the illustrated example, the first weld layer has a content of a metallic element that is higher than a content of the metallic element in the first work piece. For example, in the illustrated example of <FIG>, the first weld layer <NUM> has a higher chromium content than the first chromium content of the first work piece <NUM>. In the example method <NUM>, the first weld layer may be deposited using any type of welding process including, for example, GTAW, GMAW, flux-core, etc. The example first weld layer may be deposited using a filler material having a desired content of the metallic element (e.g., chromium). In some examples, the filler material is formed by two or more wires or rods that are twisted or braided together such as, for example, the filler materials <NUM>, <NUM>, <NUM> of <FIG>. The wires or rods may have different contents of the metallic element and, when melted together, form a resulting content of the metallic element. For example, as illustrated in <FIG>, the filler materials <NUM>, <NUM>, <NUM> may be used to produce weld layers having different contents of chromium. Additionally or alternatively, a wire feed welder may be utilized to produce the first weld layer. For example, in the example system <NUM>, the wire feed welder <NUM> feeds the first and second wires <NUM>, <NUM> at different rates to produce weld layers of having differing contents of the metallic element. In such an example, the method <NUM> may include wire feed welding a first wire and a second wire to the first end of the first work piece.

The example method <NUM> includes determining whether to deposit another weld layer on the first weld layer (block <NUM>). If another weld layer is not to be deposited, the example method <NUM> includes depositing a second weld layer between the first weld layer and a second end of a second work piece (block <NUM>). The second work piece has a higher content of the metallic element than the first work piece, and the second weld layer may have a higher content of the metallic element than the first weld layer. As a result, the gradient of the metallic element content between the first end of the first work piece and the second end of the second work piece is relatively gradual and, thus, the likelihood of adverse affects is reduced and/or substantially eliminated. For example, in <FIG>, the first and second weld layers <NUM>, <NUM> provide a gradual transition of the chromium content between the first and second work pieces <NUM>, <NUM>. As a result, the gradient of the chromium content between the first and second work pieces <NUM>, <NUM> is relatively more gradual and, thus, the likelihood of carbon is reduced and/or substantially eliminated. The second weld layer may be deposited similar to the first weld layer. For example, the second weld layer may be deposited using any type of welding process including, for example, GTAW, GMA, flux-core, etc. The example second weld layer may be deposited using a filler material having a desired content of the metallic element. In some examples, the filler material of the second weld layer is formed by two or more wires or rods that are twisted or braided together such as, for example, the filler materials <NUM>, <NUM>, <NUM> of <FIG>. One or more of the wires for the filler material of the second weld layer may be similar to the one or more of the wires of the filler material for the first weld layer (block <NUM>). In an example where a wire feed welder is used, the speed or feed rates of the first and second wires may be adjusted to produce the desired content of the metallic element for the second weld layer. For example, in the example system <NUM>, the wire feed welder <NUM> may feed the first wire <NUM> (e.g., which has a relatively lower chromium content) at a first rate and the second wire <NUM> (e.g., which has a relatively higher chromium content) at a second rate to produce the first weld layer <NUM>. When producing the second weld layer <NUM>, the wire feed welder <NUM> may feed the first wire <NUM> at a third rate, lower than the first rate, and/or the may feed the second wire <NUM> at a fourth rate, higher than the second rate. The resulting second weld layer <NUM> has a higher content of the metallic element (e.g., chromium) than the first weld layer <NUM>.

In some examples, a plurality of weld layers may be deposited to gradually change the metallic element content between the ends of the first and second work pieces. In the example method <NUM>, if another weld layer is to be deposited on the first weld layer (block <NUM>), the method <NUM> includes depositing another weld layer (e.g., a second weld layer) on a previous weld layer (e.g., the first weld layer) (block <NUM>). The additional weld layer may be deposited in a manner similar to the first weld layer (block <NUM>). The additional weld layer has a higher content of the metallic element than the previous weld layer (e.g., the first weld layer). For example, in <FIG>, the second weld layer <NUM> (e.g., an additional weld layer) is deposited on the first weld layer <NUM> and has a higher chromium content than the first weld layer <NUM>. In some examples, the additional weld layer is formed using a filler material with a different composition than the first weld layer. The filler material may be formed by braiding or twisting combinations of wires or rods such as, for example, as illustrated in Table <NUM>, to produce a desired metallic element content. In some examples, such as in the example system of <FIG>, the weld layers are formed by adjusting the feed rates of the first and second wires <NUM>, <NUM>. The example method <NUM> may include adjusting the feed rates of the first and second wires <NUM>, <NUM> to result in the desired metallic element contents of the corresponding weld layers.

The example method <NUM> includes determining whether another weld layer is to be deposited (block <NUM>). If another weld layer is to be deposited, the method <NUM> includes depositing another weld layer (e.g., a third weld layer) on the previous weld layer (e.g., the second weld layer) (block <NUM>). The additional weld layer has a higher content of the metallic element than the previous weld layer (e.g., the second weld layer). The process of depositing an additional weld layer (blocks <NUM>, <NUM>) may be performed any number of times to produce a plurality of weld layers. Each time another weld layer is deposited, the additional weld layer has a higher content of the metallic element than the previous layers. Thus, as the weld layers are stacked on top of each other, the gradient of the metallic element content across the weld layers becomes more gradual.

If another weld layer is not to be deposited onto the previous weld layer (block <NUM>), the example method <NUM> includes depositing a final weld layer between the previous weld layer and a second end of a second work piece (block <NUM>). The second work piece has a higher content of the metallic element than the first work piece. The final weld layer has a higher chromium content than the first work piece and/or the previous weld layer. In some examples, the final weld layer has the same metallic element content as the previous weld layer. For example, the final weld layer <NUM> is deposited between the seventh weld layer <NUM> and the end <NUM> of the second work piece <NUM>. The final weld layer <NUM> has a chromium content that is higher than the first chromium content of the first work piece <NUM> and/or the chromium content of the seventh weld layer <NUM>. In some examples, the final weld layer <NUM> may have the same chromium content as the seventh weld layer <NUM>. In this manner, weld layers are deposited between the first and second work pieces to couple the first and second work pieces together. Each of the weld layers has a metallic element content that is between the metallic element contents of the first and second work pieces. As a result, the gradient or change in the metallic element content between the first and second work pieces is more gradual and, thus, the likelihood of adverse welding effects is reduced and/or eliminated. In some examples, post-weld treatment may be performed on the weld (e.g., heat treatment).

The example method <NUM> may also be performed in reverse. In other words, the weld layers may be deposited onto the second end of the second work piece, starting with a weld layer having a lower content of the metallic element than the second work piece. In some examples, one or more weld layers may be deposited on each of the first and second work pieces, and a final weld layer may be deposited between the weld layers to couple the first and second work pieces together.

<FIG> is a block diagram of an example processor platform <NUM> capable of executing instructions to implement at least a portion of the method of <FIG> and to produce one or more of the example welds of <FIG> and <FIG> and/or implement the control system <NUM> of <FIG>. The processor platform <NUM> can be, for example, a server, a personal computer, a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), a personal digital assistant (PDA), an Internet appliance or any other type of computing device.

The input device(s) <NUM> permit(s) a user to enter data and commands into the processor <NUM>.

The output devices <NUM> can be implemented, for example, by display devices (e.g., a light emitting diode (LED), an organic light emitting diode (OLED), a liquid crystal display, a cathode ray tube display (CRT), a touchscreen, a tactile output device, a printer and/or speakers). The interface circuit <NUM> of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip or a graphics driver processor.

Coded instructions <NUM> to implement at least a portion of the method of <FIG> may be stored in the mass storage device <NUM>, in the volatile memory <NUM>, in the non-volatile memory <NUM>, and/or on a removable tangible computer readable storage medium such as a CD or DVD.

Claim 1:
A method comprising:
welding a first end (<NUM>) of a base (<NUM>) to a first end (<NUM>, <NUM>) of a first work piece (<NUM>, <NUM>, <NUM>, <NUM>) having a first content of a metallic element, the base (<NUM>) having a same content of the metallic element as the first work piece (<NUM>, <NUM>, <NUM>, <NUM>);
depositing a first weld layer (<NUM>, <NUM>, <NUM>, <NUM>) on a second end (<NUM>) of the base (<NUM>) opposite the first end (<NUM>);
depositing a second weld layer (<NUM>, <NUM>, <NUM>, <NUM>) between the first weld layer (<NUM>, <NUM>, <NUM>, <NUM>) and a second end (<NUM>, <NUM>) of a second work piece (<NUM>, <NUM>, <NUM>) to couple the first work piece (<NUM>, <NUM>, <NUM>, <NUM>) to the second work piece (<NUM>, <NUM>, <NUM>), the second work piece having a second content of the metallic element higher than the first content, the first weld layer (<NUM>, <NUM>, <NUM>, <NUM>) having a third content of the metallic element higher than the first content and lower than the second content, and the second weld layer (<NUM>, <NUM>, <NUM>, <NUM>) having a fourth content of the metallic element higher than the third content and lower than the second content;
and
before the deposition of the second weld layer (<NUM>, <NUM>, <NUM>, <NUM>), depositing a third weld layer on the first weld layer (<NUM>, <NUM>, <NUM>, <NUM>), the second weld layer (<NUM>, <NUM>, <NUM>, <NUM>) to be deposited between the third weld layer and the second end (<NUM>, <NUM>) of the second work piece (<NUM>, <NUM>, <NUM>), the third weld layer having a fifth content of the metallic element higher than the third content and lower than the fourth content.