Patent Description:
Silicon carbide (carborundum) sawing wires are mainly used to cut silicon chips, gemstones, and the like. Among them, the silicon chips are main raw materials for the photovoltaic and electronic industries. In order to improve the cutting efficiency, the silicon carbide (carborundum) sawing wires require an ultrafine specification typically having a diameter of <NUM>-<NUM>, which is thinner than human hair. The ultrafine specification puts forward strict requirements on the control of inclusions in steel. The width of all inclusions contained in the steel should be less than <NUM>, and cannot include brittle aluminum inclusions.

In the prior art, some Japanese enterprises conduct production through the process of converter-refining furnace-continuous casting-primary rolling-wire rolling. In the smelting process, inclusions are controlled mainly by strictly controlling the aluminum content of refractory materials and the denaturation treatment of inclusions to achieve inclusion refinement so that the wire rod has a deformation ability. Even so, the steel wire rod produced by this process still has the phenomenon of wire breakage during the drawing process of silicon carbide (carborundum) sawing wires, and the main cause of wire breakage is large particulate silica-alumina inclusions. Wire breakage has a great impact on the drawing production, and the wire connection time will exceed <NUM> hours after the wire breakage.

Those enterprises that do not have the capability to produce steel for silicon carbide (carborundum) sawing wires using converter process and electric furnace process face a main problem that they cannot control a complete absence of brittle alumina inclusions and high content of magnesia inclusions. If such inclusions are controlled by improving the refractory material, the production cost of the whole process will be greatly increased.

However, the demand for silicon carbide (carborundum) sawing wires is small, and its profit cannot offset the increase in the cost of refractory materials in the whole process. Therefore, the production of the silicon carbide (carborundum) sawing wires by the converter process or the electric furnace process cannot achieve economic benefits. In order to ensure that the silicon carbide (carborundum) sawing wire can provide enough breaking force and cut the silicon chips efficiently, the requirement for the carbon content in steel is high. Generally, the carbon content in percentage by mass is required to be at least <NUM>% or more, preferably more than <NUM>%; in addition, the nitrogen content is required to be less than 50ppm, and such amounts of components cannot be used in other steel grades. In the process of large-scale production of steel for silicon carbide (carborundum) sawing wires by the converter process or the electric furnace process, once the control of inclusions is not up to standard, steel in the whole batch will face the risk of being scrapped, and at the same time, the steel cannot be continuously produced in the continuous casting process. From the perspective of market demand, because of its strong durability, the consumption of the silicon carbide (carborundum) sawing wires during service is not large, for example, the market demand in China is maintained at <NUM>,<NUM>-<NUM>,<NUM> tons, and silicon carbide (carborundum) sawing wire manufacturers typically order no more than <NUM> tons each time from steel manufacturers. In this case, production with an electric furnace process or converter process of <NUM> tons or more will cause the problem that the production cannot be organized. <CIT> concerns a superfine extra-high-strength steel wire, a steel wire rod for the superfine extra-high-strength steel wire, and a production method of the steel wire rod.

In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a small-scale process for smelting steel for ultrafine silicon carbide (carborundum) sawing wires having high requirements, as defined in the appended set of claims. This process can control inclusions to produce ultrafine silicon carbide (carborundum) sawing wires without occurring wire breakage during the drawing process of the silicon carbide (carborundum) sawing wire.

The technical problems to be solved can be implemented by the following technical solutions.

Provided is a process for smelting steel for ultrafine silicon carbide (carborundum) sawing wires, of which the production process can be summarized as smelting in a vacuum induction furnace-electroslag-forging-wire rolling, and the main steps comprised in the process are as follows:.

The steel wire rod produced by the present invention can finally be drawn into a silicon carbide (carborundum) sawing wire having an ultrafine specification with a diameter of <NUM>-<NUM>, which will not occur wire breakage in the drawing process, and suitable for high efficiency cutting of silicon chips, gemstones and the like.

As a further improvement of the present technical solution, in step <NUM>), it is further required that at the end of the smelting in the vacuum induction furnace, the molten steel comprises the following elemental components in percentage by mass: [C]: <NUM>-<NUM>%, [Si]: <NUM>-<NUM>%, [Mn]: <NUM>-<NUM>%, [Al]: less than <NUM>%, [N]: less than <NUM>%, [S]: less than <NUM>%, [P]: less than <NUM>%, and the balance of iron and unavoidable impurities. Specifically, considering that silicon will be further attenuated during the electroslag process, the silicon content after the smelting in the vacuum induction furnace should be higher; moreover, since aluminum will be further attenuated during the electroslag process, [Al]<<NUM>%, if required, would be difficult to achieve at this stage, so the content of Al is configured to [Al]<<NUM>%.

The temperature of the molten steel at the end of the smelting in the vacuum induction furnace is controlled at <NUM>-<NUM>; after the %, smelting in the vacuum induction furnace, argon is properly blown as a protective atmosphere, so that the pressure in the furnace is adjusted to 10000Pa-20000Pa, and then casting under the protective atmosphere. The protective atmosphere is, for example, but not limited to, argon, and the casting mold adopts a cast iron mold.

At the end of the smelting in the vacuum induction furnace, the content of carbon, silicon and aluminum in the molten steel will be slightly higher than that in steel after remelting and smelting in the electroslag furnace, which is mainly due to a certain attenuation of carbon, silicon and aluminum in the molten steel during remelting and smelting in the electroslag furnace. The temperature of the molten steel at the end of the smelting in the vacuum induction furnace is controlled to be <NUM>-<NUM>, which mainly considers that the superheat degree of casting is <NUM>-<NUM>, which can cast an electrode bar capable of electroslag smelting. In practical production, if only one ingot is cast, the end point temperature can be controlled close to the lower limit, that is, close to <NUM>; if two ingots are cast, the end point temperature can be controlled close to the upper limit, that is, close to <NUM>, otherwise casting of the second ingot may not be completed. Vacuum protective casting is to prevent nitrogen absorption and secondary oxidation during the casting process.

As a further improvement of the present technical solution, in step <NUM>), after the iron raw materials (the iron raw materials include pure iron and low-phosphorus pig iron) are completely melted, <NUM>-<NUM> of lime is added per ton of the iron raw materials for slag making, dephosphorization and desulfurization. During the smelting in the vacuum induction furnace, it is not advisable to add too much slagging material (in this technical solution, the slagging material is lime), otherwise it will cause problems such as difficulty in melting the slagging material and affecting degassing. However, since the raw materials inevitably contain sulfur and phosphorus, in order to ensure that the desulfurization and dephosphorization are sufficiently performed, a small amount of lime can be added to meet the requirements for sulfur and phosphorus contents of the product.

As a further improvement of the present technical solution, in step <NUM>), the electroslag process needs to be carried out under a protective atmosphere including but not limited to argon; and the step of remelting and smelting in the electroslag furnace are remelting and smelting at a constant melting rate.

The step of remelting and smelting in the electroslag furnace under the protective atmosphere is mainly for preventing oxidation. If the secondary oxidation is serious, it will easily lead to serious attenuation of silicon and carbon in the molten steel due to oxidation; and at the same time, secondary oxidation of the molten steel will form more silica inclusions, which is unfavorable for the control of inclusions in the molten steel.

The present invention develops a brand-new process path, that is, through the steps of smelting in the vacuum induction furnace-electroslag-forging-wire rolling to produce the steel wire rod for the silicon carbide (carborundum) wire. The adoption of such process path is mainly based on the characteristics of low demand and high requirements for the steel for the silicon carbide (carborundum) wire, which can facilitate small-scale production of the steel for the silicon carbide (carborundum) wire, and solve the problem of excessive quantity of extra steel that cannot be utilized because of the adoption of massive converter process or an electric furnace process which produce far more weight of steel in each batch than the ordered quantity. This process completely removes large particulate inclusions and brittle inclusions through the electroslag process, and can control the composition of the inclusions within the required range of inclusion plasticization, so as to achieve decontamination of all inclusions in the steel and avoid wire breakage during drawing of the silicon carbide (carborundum) wire. In this process, production may be performed at night, which can make full use of the power grid capacity during the low-peak period.

The process provided by the above technical solution has the following beneficial effects:
small-scale flexible and stable production of the steel for ultrafine silicon carbide (carborundum) sawing wires can be achieved, and the widths of inclusions in the obtained final steel wire rod are all less than <NUM>, which ensures that no wire breakage due to the inclusions will occur for the steel wire rod in each drawing process of the silicon carbide (carborundum) wire.

The present invention provides a process for smelting steel for ultrafine silicon carbide (carborundum) sawing wires through a new steel-making process path design to produce high-end steel for the ultrafine silicon carbide (carborundum) sawing wires, which can realize the flexible and stable production of the steel for the silicon carbide (carborundum) sawing wires, and fundamentally solves the problem of wire breakage in the subsequent silicon carbide (carborundum) wire drawing process caused by poor control of inclusions.

The process includes main steps as follows:.

The steel wire rod can be drawn into a silicon carbide (carborundum) wire having a diameter of <NUM>-<NUM> while no wire breakage caused by poor control of inclusions will occur in the drawing process.

The process of smelting in a vacuum induction furnace-electroslag-forging-wire rolling provided by the present application is used to produce steel for silicon carbide (carborundum) sawing wires, and the main process steps thereof are as follows:.

The steel wire rod produced in this example can finally be drawn into a silicon carbide (carborundum) master wire with a diameter of <NUM> while no wire breakage will occur in the drawing process and the silicon carbide (carborundum) wire can be used for high efficiency cutting of silicon chips, gemstones and the like.

The steel wire rod includes the following chemical elements in percentage by mass: [C]: <NUM>%, [Si]: <NUM>%, [Mn]: <NUM>%, [Al]: <NUM>%, [N]: <NUM>%, [S]: <NUM>%, [P]: <NUM>%, and the balance of iron and unavoidable impurities. Inclusions in the steel wire rod are detected as a CaF<NUM>-CaO-SiO<NUM>-Al<NUM>O<NUM>-Na<NUM>O-K<NUM>O composite inclusion, and a SiO<NUM>-Al<NUM>O<NUM>-MnO-CaO-MgO-Na<NUM>O-K<NUM>O composite inclusion (the SiO<NUM> contents in both composite inclusions are greater than <NUM>%). These two series of inclusions have good plasticity, and the widths of the inclusions are all less than <NUM>, which are harmless inclusions and will not cause wire breakage in the steel wire rod drawing process.

The steel wire rod produced in this example can finally be drawn into a silicon carbide (carborundum) master wire with a diameter of <NUM> while no wire breakage will occur in the drawing process, and the silicon carbide (carborundum) wire can be used for high efficiency cutting of silicon chips, gemstones and the like.

Claim 1:
A process for smelting steel for ultrafine silicon carbide (carborundum) sawing wires, comprising the following steps of:
<NUM>) melting a raw material into liquid molten steel under the protection of argon in a vacuum induction furnace, the raw material uses carbon-free pure iron and low-phosphorus pig iron having a carbon content of <NUM>%-<NUM>% by mass; then vacuumizing to perform vacuum smelting, the vacuum smelting is performed under a condition of less than 300Pa to degas for <NUM>-<NUM>, and performing deoxygenation with high-purity silicon iron as a deoxidizer to adjust components of the molten steel; and after the adjustment of the components of the molten steel, casting circular ingots under vacuum condition, wherein each ingot has a mass of <NUM>-<NUM> tons, a diameter of <NUM>-<NUM> and a length of <NUM>-<NUM>;
<NUM>) cleaning the surface of the circular ingots to manufacture electrode bars for electroslag smelting;
<NUM>) remelting and smelting the electrode bars as raw materials in an electroslag furnace, wherein an electroslag protecting slag comprises the following in percentage by mass:
CaF<NUM>: <NUM>-<NUM>%, Al<NUM>O<NUM>: <NUM>-<NUM>%, SiO<NUM>: <NUM>-<NUM>%, Na<NUM>O: <NUM>-<NUM>%, and K<NUM>O: <NUM>-<NUM>%; and
smelting the electrode bar in the electroslag furnace into a cylindrical electroslag ingot having a diameter of <NUM>-<NUM>;
<NUM>) forging the electroslag ingot into a forged billet for wire rolling, wherein the forged billet is a square billet having a cross section of square with a side length of <NUM>-<NUM>, and the forged billet has a length of greater than <NUM>; and
<NUM>) rolling the forged billet into a steel wire rod having a diameter of <NUM>-<NUM> by the wire rolling process, wherein the steel wire rod comprises the following chemical elements in percentage by weight: [C]: <NUM>-<NUM>%, [Si]: <NUM>-<NUM>%, [Mn]: <NUM>-<NUM>%, [Al]: less than <NUM>%, [N]: less than <NUM>%, [S]: less than <NUM>%, [P]: less than <NUM> %, and the balance of iron and unavoidable impurities,