A STEEL STRIP AND A TOOL MADE THEREOF

Abstract: In a laminated steel strip a first layer consists of a high allow steel containing in weight-%: 1.0-2.5 C, 0.2-1.0 Si, O.1-2.0 Mn, 4-15 Cr, 0.7-18 Mo, 0-1 Ni, 0-10 W, 0-10 (V + Ta/Nb + Ti + N) the total content of Cr + Mo + W + V + Ta/Nb + Ti + N being at least 12 weight-%, balance substantially iron and impurities in normal amounts, while a second layer consists of a low alloy steel containing 0.2-0.6 C, 0.2-2.0 Si, 0.2-1.5 Mn, 0-5 Cr, 0-0.2 V, 0-1.0 Mo, balance substantially iron and impurities in normal amounts.

Description: A STEEL STRIP AND A TOOL MADE THEREOF TECHNICAL FIELD This invention relates to a laminated steel strip consisting of at least two layers. The invention also relates to tools made of the laminated material, such as knives, cutters, saws, doctor blades and other scraping tools which are subjected to heavy wear. BACKGROUND ART Many compound products are since long made of special steels. Compound steels are made for the chemical industry and the cellulose industry, where a backing material of carbon steel is provided with a coating of stainless steel. It is also known in the art to alloy the backing material with carbide- and nitride-forming elements, particularly titanium, and to hot-roll the compound material and subject it to annealing operations during so long periods of time that the carbon in the stainless cromium steel coating by diffusion into the backing material is reduced to extremely low contents which further improves the corrosion resistance of the stainless surface layer. In the field of compound materials one can also find the traditional Mora-knife, which has an edge layer of carbon steel with a high carbon content covered on both sides with carbon steel with a lower carbon content, which provides a combination of good edge sharpness and toughness of the knifeblade. Also knifeblades consisting of stainless, austenitic and martensitic layers are known in the art as well as knifeblades consisting of combinations of layers of carbon steels and stainless steels. Those knife materials which have stainless, martensitic edge layers have some significant advantageous features as compared to knife materials where the edge layer consists of carbon steel. An example of a tool which is designed in this way is described in US-A-3537 828. BRIEF DISCLOSURE OF THE INVENTION It is an object of the invention to provide a laminated steel strip with better features than have been achieved according to known art. Particularly there is an object of the invention to combine a very high hardness of those parts of the tool which are subjected to wear with a good toughness. These and other objects can be achieved by a suitable combination of the alloys in the various layers in the steel strip. According to the invention a first layer consists of a high alloy steel containing in weight-% 1.0-2.5 C, 0.2-1.0 Si, 0.1-2.0 Mn, 4-18 Cr, 0.7-10 Mo, 0-1 Ni, 0-10 W, in total 0-10 V + Ta/Nb + Ti + N, the total content of Cr + Mo + + V + Ta/Nb + Ti + N being at least 12 weight-%, balance substantially iron and impurities in normal contents, while a second layer consists of a low alloy steel containing 0.2-0.6 C, 0.2-2.0 Si, 0.2-1.5 Mn, 0-5 Cr, (preferably 1-5 Cr), 0-0.2 V, 0-1.0 Mo, balance substantially iron and impurities in normal contents. Normally the steel strip consists of a laminate consisting of three layers. In case the steel strip is intended for the manufacturing of knives or other edge-tools or saws, the edge or the saw teeth, respectively, are provided in the high alloy layer which can be provided either in the center or in the surface layers, respectively. Laminates with high alloy surface layers are adapted for being surface coated by titanium nitride or other hard materials in vacuum or by chemical methods due to the high carbon volume and the composition of the surface layers. Further features of the invention will be apparent from the appending claims and from the following description of some embodiments chosen by way of example. BRIEF^DESCRIPTION OF DRAWINGS In the following description of some embodiments chosen by way of example reference will be made to the attached drawings, in which Fig. 1A shows a steel strip having the high alloy layer in the center, Fig. IB shows a knife made of the steel strip in Fig. 1A, Fig. 2A shows a three-layer laminate, in which the two surface layers consist of a high alloy material, Fig. 2B shows a knife made of the material in Fig. 2A, Fig. 2C shows a perforating knife made of the same material, Fig, 2D shows a doctor blade made of the steel blade shown in Fig. 2A, Fig. 2E shows an edge swaged three-layer laminate suitable for particularly saws. DESCRIPTION OF EMBODIMENTS AND ALLOY COMBINATIONS Example 1 This example concerns a laminated steel strip for knives with a hard and wear resistant edge but without requirements as far as high resistance to tempering is concerned. The layer intended to form the edge or the edges consisted of a steel with a carbon content which varied between about 1.5 and about 2.0 % over the cross section of the centre layer between the two surface layers, about 0.5 Si, about 13.5 Cr, about 1.0 Mo, and about 0.3 V, balance essentially only iron and impurities in normal contents. The variation in above all the carbon content depends on the diffusion of carbon from the low alloy layer to the high alloy edge layer during heating. The low alloy layer contained between 0.2 and 0.6 % C, 0.6 Mn and about 0.3 Cr, the latter also providing a good hardenability to this layer. Hardening from 980°C and fast cooling gave a hardness in the high alloy material of 63-65 HRC. Part of the carbides in the material were dissolved during hardening which facilitates the achievement of a high martensite hardness and a considerable corrosion resistance. In an alternative embodiment the low alloy layer according to this example also contained 0.010 V and 0.5 Mo. Example 2 The high alloy layer had the same composition as in Example 1, while the low alloy layer contained 0.2 C, 0.6 Mn, 3.0 Cr and 0.5 Mo. Example 3 In this example the high alloy layer had the following nominal composition: 1.0-1.7 C, 0.9-1.0 Si, 4.0 Cr, 9.0 Mo, 2.5 V, 1.8 W. The low alloy steel had the same composition as in Example 1. This material combination is intended for applications which also require a high resistance to tempering. The addition of tungsten promotes the formation of fine carbides such that the steel obtains features comparable to those of high speed steels mads from powder. In the drawings the high alloy steel has been designated by the numeral 1 and the low alloy steel by the numeral 2. The thickness of the steelstrip may be between 0.1 and 3 mm. The lamination is carried out by forge (roll) welding.

Claims: CLAIMS 1. Laminated steel strip consisting of at least two layers, c h a r a c t e r i z e d in that a first layer consists of a high alloy steel containing in weight-%: 1.0 - 2.5 C 0.2 - 1.0 Si 0.1 - 2.0 Mn 4 - 15 Cr 0.7 - 18 Mo 0 - 1 Ni 0 - 10 W 0 - 10 (V + Ta/Nb + Ti + N) the total content of Cr + Mo + W + V + Ta/Nb + Ti + N being at least 12 weight-%, balance substantially iron and impurities in normal amounts, and that a second layer consists of a low alloy steel containing 0.2-0.6 C, 0.2-2.0 Si, 0.2-1.5 Mn, 0-5 Cr, 0-0.2 V 0-1.0 Mo, balance substantially iron and impurities in normal amounts. 2. Steel strip according to claim 1, c h a r a c t e r i z e d in that the second layer has a Cr-content of between 1 and 5 % Cr. 3. Steel strip according to claim 1, c h a r a c t e r i z e d in that the first layer consists of a steel having the composition: 1 - 2 C, preferably 1.3-2.0 C 0.2 - 1.0 Si 0.1 - 2.0 Mn 12 - 14 Cr 1 - 2 Mo max 2.0 V max 1.0 Ni, preferably 0.2-1.0 Ni, balance essentially only iron and impurities in normal amounts. 4. Steel strip according to claim 1, c h a r a c t e r i z e d in that the first layer consists of a steel having the composition: 1.2 - 2.0 C 0.2 - 1.0 Si 0.1 - 2.0 Mn 3 - 7 Cr 5 - 10 Mo 1.5 - 3.5 V 1 - 4 W max 1.0 Ni, preferably 0.2-1.0 Ni, balance essentially only iron and impurities in normal amounts. 5. Steel strip according to any of claims 1-3, c h a r a c - t e r i z e d in that it has a total thickness of 0.1-3 mm. 6. Cutting tool or tool subjected to wear, c h a r a c t e r i z e d in that it is made according to any of claims 1-4. 7. Tool according to claim 5, c h a r a c t e r i z e d in that it has an edge in that layer or those layers which consist of the high alloy first layer. 8. Tool according to claim 6, c h a r a c t e r i z e d in that it consists of a toothed perforating knife, and that the two surface layers consist of the high alloy first steel. 9. Tool according to claim 5, c h a r a c t e r i z e d in that it is a saw. 10. Tool according to claim 5, c h a r a c t e r i z e d in that it is a doctor blade.

Inventors: LUNNERFJORD ALLAN, SUNDBERG ROLAND, LUNNERFJORD, ALLAN, SUNDBERG, ROLAND
Applicants: SWEDEV AKTIEBOLAG
Application year: 1985
Main classification: B32B15
IPC codes: B23D61, B32B15, C23C28, C23C30