METHOD FOR THERMALLY TREATING A FLAT STEEL PRODUCT, THERMALLY TREATED FLAT STEEL PRODUCT AND USE THEREOF

Abstract

A method for thermally treating a flat steel product, a thermally treated flat steel product and use thereof. The method includes providing a flat steel product with a structure with a first hardness. The flat product is heated at least in sections to an austenitizing temperature. The heated flat product is cooled at least in sections so that a structure with a second hardness is formed within the flat product at least in sections, the second hardness having a higher level of hardness in comparison to the structure with the first hardness. The heating and the cooling down of the flat product are coordinated with each other such that the structure with the second hardness is formed across the thickness of the flat product and at least in one of said sections, the structure with the first hardness remains constant across the thickness of the flat product.

Claims

1.-19. (canceled)

20. A method for thermally treating a flat steel product comprising the following steps: providing a flat steel product with a structure with a first hardness, heating the flat product at least in sections to an austenitizing temperature, and cooling the flat product heated at least in sections so that a structure with a second hardness is formed within the flat product at least in sections, the second hardness having a higher level of hardness in comparison to the structure with the first hardness, wherein the heating and the cooling down of the flat product are coordinated with each other such that the structure with the second hardness is formed across the thickness of the flat product in sections and, at least in one of said sections, the structure with the first hardness remains constant across the thickness of the flat product.

21. The method of claim 20, wherein the heating takes place at least on one side with the use of at least one heat source, wherein the structure with the second hardness is at least formed within one edge section of the flat product.

22. The method of claim 20, wherein at least one inductor is used as a heat source.

23. The method of claim 20, wherein at least one edge section of the flat steel product is heated to at least a temperature of at least A.sub.c3+20 K during the heating process and is held at this temperature for at least 1 s up to a maximum of 60 s.

24. The method of claim 20, wherein the cooling takes place by quenching the flat product with water.

25. The method of claim 20, wherein the heating takes place on both sides with the use of at least one heat source respectively, wherein the structure with the second hardness is formed in both edge sections of the flat product or an edge section with a structure with the second hardness is formed on one side of the flat product and an edge section with a structure with a third hardness is formed on the other side of the flat product, wherein the structure with the third hardness has a lower level of hardness than the structure with the second hardness and a higher level of hardness than the structure with the first hardness.

26. The method of claim 25, wherein at least between an edge section with the structure with the second hardness and/or third hardness and the section with the structure with the first hardness, an annealing section with a structure with a fourth hardness is formed, which has a lower level of hardness than the section with the structure with the first hardness.

27. The method of claim 26, wherein at least in one of the edge sections with the structure with the second hardness and/or third hardness, a decarburized edge layer or an edge layer with a fifth hardness and a lower level of hardness in comparison to the edge section with the structure with the second hardness and/or third hardness is formed.

28. The method of claim 20, including forming across the thickness of the flat product, a symmetric or asymmetric hardness profile.

29. The method of claim 20, wherein the flat steel product consists of the following components in % by weight: TABLE-US-00002 0.15 C 0.6, 0.1 Si 1.2, 0.3 Mn 1.8, 0.1 Cr 1.8, 0.05 Mo 0.6, 0.05 Ni 3.0, 0.0005 B 0.01, Al 0.15, Ti 0.04, P 0.04, S 0.03, N 0.03, wherein the remainder is iron and impurities.

30. The method of claim 20, including forming and/or cutting the flat product into a final product.

31. A thermally treated flat steel product made according to the method of claim 20, wherein within the flat product, a structure is formed with the second hardness in sections across the thickness of the flat product and, at least in one section, a structure with the first hardness is formed across the thickness of the flat product, wherein the structure with the second hardness has a higher level of hardness in comparison to the structure with the first hardness and is thermally treated.

32. The flat steel product of 31, wherein the structure with the second hardness is formed in an edge section of the flat product, wherein the layer thickness of the edge section is at least 5% up to a maximum of 80% of the total thickness of the flat product and the remaining thickness of the total thickness of the flat product consists of the section with the structure with the first hardness.

33. The flat steel product of claim 31, the structure with the second hardness is formed within both edge sections of the flat product or one edge section with a structure with the second hardness is formed on one side of the flat product and one edge section with a structure with a third hardness is formed on the other side of the flat product, wherein the structure with the third hardness has a lower level of hardness than the structure with the second hardness, and a higher level of hardness than the structure with the first hardness, wherein the layer thickness of the edge section varies between at least 5% and a maximum of 45% of the total thickness of the flat product respectively and the remaining thickness is formed by the section with the structure with the first hardness.

34. The flat steel product of claim 33, wherein the flat product has a hardness difference of at least 100 HV10 between the at least one edge section with the structure with the second hardness and/or third hardness and the section with the structure with the first hardness.

35. The flat steel product of claim 33, wherein the flat product at least between one edge section with the structure with the second hardness and/or third hardness and the section with the structure with the first hardness comprises an annealing section with a structure with a fourth hardness, which has at least a 10 HV10 lower level of hardness in comparison with the section with the structure with the first hardness.

36. The flat steel product of claim 35, wherein the flat product at least in one of the edge sections with the structure with the second hardness and/or third hardness comprises a decarburized edge layer or an edge layer with a structure with a fifth hardness, which has a lower level of hardness in comparison to the edge section with the structure with the second hardness and/or third hardness.

37. The flat steel product of claim 31, wherein the flat product has a total thickness between 3 and 80 mm.

38. The flat steel product of claim 31, wherein the flat product has a total thickness between 6 and 20 mm.

Description

[0030] The invention is explained in detail in the following based on a drawing showing exemplary embodiments. Identical parts are referenced with same reference numbers. The figures show:

[0031] FIG. 1a) a first exemplary embodiment for thermally treating a flat product in a schematic view,

[0032] FIG. 1b) an illustration of the hardness progression across the thickness of the thermally treated flat product according to the first exemplary embodiment,

[0033] FIG. 2a) a second exemplary embodiment for thermally treating a flat product in a schematic view,

[0034] FIG. 2b) an illustration of the hardness progression across the thickness of the thermally treated flat product according to the second exemplary embodiment,

[0035] FIG. 3a) a schematic cross section through a thermally treated flat product according to a third exemplary embodiment,

[0036] FIG. 3b) an illustration of the hardness progression across the thickness of the thermally treated flat product in FIG. 3a),

[0037] FIG. 4a) a schematic cross section through a thermally treated flat product according to a fourth exemplary embodiment,

[0038] FIG. 4b) an illustration of the hardness progression across the thickness of the thermally treated flat product in FIG. 4a),

[0039] FIG. 5a) a schematic cross section through a thermally treated flat product according to a fifth exemplary embodiment,

[0040] FIG. 5b) an illustration of the hardness progression across the thickness of the thermally treated flat product in FIG. 5a),

[0041] FIG. 6a) a schematic cross section through a thermally treated flat product according to a sixth exemplary embodiment,

[0042] FIG. 6b) an illustration of the hardness progression across the thickness of the thermally treated flat product in FIG. 6a).

[0043] A first exemplary embodiment for thermally treating a flat product (1) is shown in FIG. 1a) in a schematic view. The flat product (1) consists of a ferromagnetic steel with a primarily homogeneous structure with a first hardness (1.1), for example, of a thermally treatable steel material with a ferritic/perlitic structure with a thickness between 3 and 80 mm, preferably between 6 and 20 mm, which is preferably made of a heavy plate. The flat product (1) has a length (L), a width, which is not shown here because of the sectional view and, for example, is many times smaller than the length (L) with regard to the dimension, and has a thickness and a total thickness (D). The flat product (1) is preferably thermally treated within the scope of a continuous process at least in sections, preferably across the entire width of the flat product (1) and at least in sections, preferably across the entire length (L) of the flat product (1). As is shown in FIG. 1a), the flat product (1) is, for example, located on a roller conveyor (R) and is moved in the direction of a thermal treatment unit (W), symbolized by the arrow shown. The thermal treatment unit (W) comprises at least one heat source for the one-sided heating of the flat product (1), wherein at least one inductor (I) is preferably used as a heat source, and at least one cooling unit to cool down the heated flat product (1), which preferably comprises at least one water shower or water spray (B). The flat product (1) is heated to at least a temperature of at least A.sub.c3+20 K via the inductor (I) during the heating process and held at this temperature for at least 1 s up to a maximum of 60 s, preferably a maximum of 10 s, wherein the area to be hardened (2.1) is fully austenitized within the flat product (1). Due to the heat conduction inside the flat product (1), it must be ensured that the area (2.1) to be hardened does not exceed the desired final thickness. Depending on the thermal treatment depth, the austenitized area to be hardened (2.1) is quenched via a water spray (B), wherein the cooling speed >30 K/s is selected in order to configure a hardening structure, for example, a martensitic or a martensitic/bainitic structure (2.2) in the edge section (2). Thereby, the heating (I) and the cooling (B) of the flat product (1) are coordinated with each other in such a way that a structure with a second hardness (2.2) is formed in sections across the thickness (D) of the flat product (1), namely in the edge section (2), and the structure with the first hardness (1.2) remains the same at least in one section (1.1) across the thickness (D) of the flat product (1), meaning that the section (1.1) is not or is not significantly influenced by the thermal treatment in a negative manner. As an alternative and not shown here, the thermal treatment unit and/or its units can be individually arranged in a movable manner across the flat product. The hardness profile across the thickness of the flat product (1) is shown in FIG. 1b) and shows that the edge section (2) comprises a structure with a second hardness (2.2), which is higher than the section (1.1) with the structure with the first hardness (1.2), wherein the hardness difference is preferably at least 100 HV10.

[0044] A second exemplary embodiment for thermally treating a flat product (1) is shown in FIG. 2a) in a schematic view. In order to avoid repetitions, only the differences in comparison with the first exemplary embodiment will be explained. The flat product (1) shown on a roller conveyor (R) is moved in the direction of a thermal treatment unit (W), as is shown in FIG. 1a). On the side facing away from the thermal treatment unit (W), there is a second thermal treatment unit (W), which comprises at least one heat source, preferably at least one inductor (I) to heat the flat product (1) and at least one cooling unit, preferably at least one water shower or spray (W) to cool down the heated flat product (1). The heating takes place on both sides via at least one inductor (I, I) respectively, which preferably completely extends across the entire width of the flat product in order to cover the entire width of the flat product (1) and to completely austenitize the areas to be hardened (2.1, 2.1) within the flat product (1). Depending on thermal treatment depth, the austenitized areas to be hardened (2.1, 21) are quenched via water sprays (B, B), wherein, for example, a martensitic or a martensitic/bainitic structure (2.2, 2.2) is configured in each case in the edge sections (2, 2). Thereby, the heating (I, I) and the cooling (B, B) of the flat product (1) are coordinated with each other in such a way that a structure with a second hardness (2.2, 2.2) is formed in sections across the thickness (D) of the flat product (1), namely in the edge sections (2), and the structure with the first hardness (1.2) remains the same at least in one section (1.2) across the thickness (D) of the flat product (1), meaning that the section (1.1) is not or is not significantly influenced by the thermal treatment in a negative manner and this forms the core layer (1.1) of the flat product (1). Thereby, thermal treatment takes place simultaneously on both sides. Alternatively and not shown here, the thermal treatment units can also be arranged offset to one another, whereby both edge sections can be created in a temporally offset manner. The hardness profile across the thickness of the flat product (1) is shown in FIG. 2b) and shows that the edge sections (2, 2) have a structure with a second hardness (2.2, 2.2), which are higher than the section (1.2) or the core layer with the structure with the first hardness (1.2). Preferably, the hardness difference is at least 100 HV10.

[0045] In FIGS. 3a), 4a), 5a) and 6a), cross sections through flat products (1) manufactured according to the invention with the related hardness profiles across the respective thickness (D) in FIGS. 3b), 4b), 5b) and 6b) are shown.

[0046] In a schematic cross section through a flat product (1) thermally treated according to a third exemplary embodiment, a section (1.1), in particular a core layer with a structure with a first hardness (1.2), two edge sections (2, 2) with a structure with a second hardness (2.2, 2.2), and, respectively, an annealing section (3, 3) with a structure with a fourth hardness (3.2, 3.2) between the edge sections (2, 2) and the section (1.1) are shown. The annealing sections (3, 3) have in each case a lower hardness by at least 10 HV10 in comparison to the section (1.1). The section (1.1) and the edge sections (2, 2) each correspond to 30% of the total thickness (D) of the flat product (1) and the annealing sections (3, 3) take up another 5% respectively; FIG. 3a). The symmetrical hardness profile across the thickness (D) is shown in FIG. 3b).

[0047] In a schematic cross section through a flat product (1) thermally treated according to a fourth exemplary embodiment, in comparison to the third exemplary embodiment, the difference exists in the fact that the upper edge section (2) with a structure with a second hardness (2.2) is designed to be thicker, which corresponds to 50% of the total thickness (D) for example, and the lower edge section (2) with a structure with a second hardness (2.2) is designed to be thinner, which, for example, corresponds to 10% of the total thickness (D); FIG. 4a). The asymmetrical hardness profile across the thickness (D) is shown in FIG. 4b).

[0048] In a schematic cross section through a flat product (1) thermally treated according to a fifth exemplary embodiment, a section (1.1), in particular, a core layer with a structure with a first hardness (1.2), and two edge sections (2, 2) with a structure with a second hardness (2.2, 2.2) are shown. In both edge sections (2, 2), the flat product (1) comprises a decarburized edge layer respectively or comprises an edge layer (4, 4) with a structure with a fifth hardness (4.2, 4.2) respectively, which has a lower level of hardness in comparison to the edge section (2, 2). The section (1.1) is 30% and the edge sections (2, 2) each correspond to 35% of the total thickness (D) of the flat product (1), wherein the decarburized edge section or the edge layer (4, 4) can be present up to a maximum thickness of 5% with reference to the total thickness (D) of the flat product (1); FIG. 5a). The symmetrical hardness profile across the thickness (D) is shown in FIG. 5b).

[0049] In a schematic cross section through a flat product (1) thermally treated according to a sixth exemplary embodiment, a section (1.1) with a structure with a first hardness (1.2), an edge section (2) with a structure with a second hardness (2.2), and an annealing section (3) with a structure with a fourth hardness (3.2) between the edge section (2) and the section (1.1) are shown. In the edge section (2), the flat product (1) comprises a decarburized edge layer or comprises an edge layer (4.2) with a structure with a fifth hardness (4.2). The section (1.1) has a thickness of 35%, the annealing section (3) has a thickness of 5%, the edge section (2) has a thickness of 60%, from which a thickness of a maximum of 5% can be omitted for the edge layer (4.2), with reference to the total thickness (D) of the flat product (1); FIG. 6a). The asymmetrical hardness profile across the thickness (D) is shown in FIG. 6b).

[0050] The design of the sections with various levels of hardness is not limited to the exemplary embodiments shown. Rather, for example, one of the edge layers can comprise a structure with a third hardness, wherein the structure with the third hardness can have a lower level of hardness than the structure with the second hardness, however, a higher level of hardness than the structure with the first hardness. In particular, due to the manufacturing process, the flat steel products can be used in the as-rolled condition as well as alternatively or cumulatively already with a homogeneous initial hardness of at least 300 HV10 for example. The flat products according to the invention, which can be optionally formed and/or cut into an end product, are either used as a part or component of an armoring or as a part or a component with special characteristics, in particular, against the effect of wear influences. Other application fields are also conceivable, in which flat products or end products with at least one section with a structure with a first hardness across the thickness and at least one section with a structure with a second hardness across the thickness of the flat or end product can be used, wherein the second hardness is greater than the first hardness.

REFERENCE LIST

[0051] 1 flat product

[0052] 1 thermally treated flat product

[0053] 1.1 section, core layer

[0054] 1.2 structure with a first hardness

[0055] 2, 2 edge section

[0056] 2.1, 2.1 austenitized, heated area to be annealed

[0057] 2.2, 2.2 structure with a second hardness

[0058] 3, 3 annealing section

[0059] 3.2, 3.2 structure with a fourth hardness

[0060] 4, 4 decarburized edge layer, edge layer

[0061] 4.2, 4.2 structure with a fifth hardness

[0062] B, B cool-down spray

[0063] D thickness, total thickness

[0064] 1, 1 inductor

[0065] W, W thermal treatment unit