Martensitic stainless steel material and method for producing the same

Abstract

A martensitic stainless steel material having the following composition: C: 0.30-0.60%, Si: 0.05-1.00%, Mn: 0.05-1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0-18.0%, Ni: 0.01-0.30%, Mo: 0.01-1.00%, Al: 0.030% or less, N: 0.010-0.350%, Ca: 0.0001-0.0030%, O: 0.001-0.010%, 2.5C+N is 1.10% or more, and the remainder comprises Fe and impurities. The average particle size of carbides in this martensitic stainless steel material is 0.50 μm or less. In addition, the number of carbides larger than 10 μm is 0.20 per cm 2 the following.

Description

Technical Field

[0001] The present invention relates to a martensitic stainless steel material and a method for manufacturing the same. Background Art

[0002] Stainless steel materials used for various knives such as razors, scissors, and kitchen knives are required to have high hardness, and therefore martensitic stainless steel materials having a high C content have been used (for example, Patent Document 1).

[0003] However, if the C content is high, it will form carbides with alloying elements such as Cr, and will easily precipitate as coarse eutectic carbides during the manufacturing process. These eutectic carbides are difficult to completely dissolve even through annealing processes, and the amount of C dissolved in the solid solution decreases during quenching, causing excessive softening. In addition, these eutectic carbides become corrosion starting points, thereby not only reducing corrosion resistance, but also causing chipping and irregular patterns during processing.

[0004] Therefore, Patent Document 2 proposes a martensitic stainless steel material for cutting tools, characterized in that it contains, in mass%, C: 0.40-0.50%, Si: 0.05-0.60%, Mn: 0.5-1.5%, P: 0.035% or less, S: 0.010% or less, Cr: 11.0-15.5%, Ni: 0.01-0.30%, Cu: 0.01-0.30%, and Mo: 0.01-0. 30%, V: 0.01-0.10%, Al: 0.02% or less, Sn: 0.002-0.10%, N: 0.010-0.035%, Ca: 0.0001-0.0010%, O: 0.001-0.01%, the remainder contains Fe and unavoidable impurities, and satisfies Cu+Ni+Mo=0.05-0.30%, and the number of inclusions larger than 10 μm is 0.2 / cm 2 the following.

[0005] In addition, Patent Document 3 proposes a method for producing a grain-refined martensitic stainless steel material, which is characterized by comprising the following steps: a step of preparing a base material having a composition comprising 13.0 to 14.0 wt% of Cr, 1.15 to 1.35 wt% of Mo, 0.35 to 0.55 wt% of C, 0.20 to 0.50 wt% of Si, 0.20 to 0.50 wt% of Mn, 0.025 wt% or less of P, 0.020 wt% or less of S, and the remainder being Fe and inevitable impurity elements; a step of subjecting the base material to at least one of a high-density dislocation introduction method and a super-sudden cooling solidification method, and then annealing the base material to obtain a fine-structured ferrite steel; and a step of subjecting the ferrite steel to cold rolling, annealing, and, if necessary, plastic working into a predetermined shape, and then quenching the ferrite steel to obtain a grain-refined martensitic stainless steel material.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-273587

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-9231

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2003-313612 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] However, the martensitic stainless steel material described in Patent Document 2 does not have a controlled average particle size of inclusions (particularly carbides), and therefore may have insufficient workability or may produce irregular patterns.

[0013] Furthermore, the martensitic stainless steel described in Patent Document 3 is not suitable for mass production because it uses special processes such as high-density dislocation introduction and ultra-rapid solidification. Furthermore, the martensitic stainless steel contains a high Mo content, resulting in high costs.

[0014] Conventional martensitic stainless steel materials having a reduced C content in this manner have the aforementioned problems.

[0015] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a martensitic stainless steel material having good workability, high hardness and corrosion resistance after quenching or quenching and tempering, and capable of suppressing the generation of irregular patterns, and a method for producing the same.

[0016] Means for solving problems

[0017] The present inventors conducted in-depth research on martensitic stainless steel and found that inclusions, especially carbides, are closely related to corrosion resistance, workability, and irregular patterns. By controlling the number of carbides larger than 10 μm and the average particle size of the carbides in addition to the steel composition, the above-mentioned problems can be completely solved, thus completing the present invention.

[0018] That is, the present invention is a martensitic stainless steel having the following composition: containing, by mass, C: 0.30-0.60%, Si: 0.05-1.00%, Mn: 0.05-1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0-18.0%, Ni: 0.01-0.30%, Mo: 0.01-1.00%, Al: 0.030% or less, N: 0.010-0.350%, Ca: 0.0001-0.0030%, O: 0.001-0.010%, 2.5C+N is 1.10% or more, and the remainder comprises Fe and impurities.

[0019] The average particle size of carbides is less than 0.50 μm.

[0020] The carbides with a size of 10 μm or larger are 0.20 pieces / cm 2 the following.

[0021] Furthermore, the present invention provides a method for producing a martensitic stainless steel material, comprising a hot rolling step of subjecting a slab to heat treatment at a temperature of T or higher represented by formula (1) for 1 to 5 hours and then hot rolling the slab, wherein the slab has the following composition: C: 0.30-0.60%, Si: 0.05-1.00%, Mn: 0.05-1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0-18.0%, Ni: 0.01-0.30%, Mo: 0.01-1.00%, Al: 0.030% or less, N: 0.010-0.350%, Ca: 0.0001-0.0030%, O: 0.001-0.010%, 2.5C+N being 1.10% or more, and the remainder comprising Fe and impurities,

[0022] T[℃]=6500 / (4-logC[%])-273 (1).

[0023] Effects of the Invention

[0024] According to the present invention, it is possible to provide a martensitic stainless steel material having good workability, high hardness and corrosion resistance after quenching or quenching and tempering, and capable of suppressing the generation of irregular patterns, and a method for producing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a graph showing the relationship between 2.5C+N and hardness in Examples and Comparative Examples. DETAILED DESCRIPTION

[0026] The following describes the embodiments of the present invention in detail. The present invention is not limited to the following embodiments, and it should be understood that within the scope of the present invention, the following embodiments may be modified or improved based on the common knowledge of those skilled in the art without departing from the scope of the present invention.

[0027] In addition, the expression "%" about a component in this specification means "mass %" unless otherwise specified.

[0028] The martensitic stainless steel material according to an embodiment of the present invention has a composition comprising C: 0.30-0.60%, Si: 0.05-1.00%, Mn: 0.05-1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0-18.0%, Ni: 0.01-0.30%, Mo: 0.01-1.00%, Al: 0.030% or less, N: 0.010-0.350%, Ca: 0.0001-0.0030%, O: 0.001-0.010%, 2.5C+N is 1.10% or more, and the balance comprises Fe and impurities.

[0029] In this specification, "steel" refers to various materials such as steel plates. In addition, "steel plate" is a concept that includes steel strips. Furthermore, "impurities" refer to components that are mixed in during the industrial production of stainless steel due to various factors such as raw materials such as ore and scrap iron, and the manufacturing process, and are allowed within the range that does not adversely affect the present invention. Examples of impurities include Zn, Pb, Se, Sb, H, Ga, Ta, Mg, and Zr. When these elements are included as impurities, Zn≤100ppm, Pb≤100ppm, Se≤100ppm, Sb≤500ppm, H≤100ppm, Ga≤500ppm, Ta≤500ppm, Mg≤120ppm, and Zr≤120ppm.

[0030] Furthermore, the martensitic stainless steel material according to the embodiment of the present invention may further contain one or more of V: ​​0.50% or less, Nb: 0.30% or less, Ti: 0.3% or less, Cu: 4.0% or less, Sn: 0.100% or less, B: 0.0050% or less, and Co: 0.30% or less.

[0031] Hereinafter, each component will be described in detail.

[0032] <C:0.30~0.60%>

[0033] C is an element necessary to obtain a specified hardness (Vickers hardness) after quenching or quenching and tempering. In order to stably obtain a hardness of 500 HV or more, the content of C must be set at 0.30% or more. If C is added excessively, sensitization during quenching is promoted, resulting in deterioration of corrosion resistance, and the toughness after quenching or tempering is also reduced due to un-solubilized carbonitrides. Therefore, the content of C must be set at 0.60% or less. Considering the reduction of hardness or toughness caused by changes in heating conditions during quenching or quenching and tempering, the lower limit value of the content of C is preferably 0.32%, and the upper limit value is preferably 0.58%.

[0034] <Si: 0.05 - 1.00%>

[0035] Si is an element that is necessary not only for deoxidation during melting and refining but also useful for suppressing the formation of scale during quenching. In addition, if the Si content is low, deoxidation tends to be insufficient, more carbides are formed, and sometimes it becomes a starting point for rusting, resulting in a reduction in corrosion resistance. Therefore, the content of Si must be set at 0.05% or more. On the other hand, Si narrows the austenite single-phase temperature region and impairs quenching stability. Therefore, the content of Si must be set at 1.00% or less. From the viewpoint of stably obtaining the above effects brought by Si, the lower limit value of the Si content is preferably 0.07%, and the upper limit value is preferably 0.98%.

[0036] <Mn: 0.05 - 1.50%>

[0037] Mn is an element added as a deoxidizer and expands the austenite single-phase region, contributing to an improvement in hardenability. If Mn is not added sufficiently, the two-phase region expands and the α-phase increases. As a result, Cr carbonitrides also increase, and a Cr-deficient layer is formed around them, so it easily becomes a starting point for rusting and the corrosion resistance is reduced. Therefore, the content of Mn must be set at 0.05% or more. From the viewpoint of stably obtaining the above effects brought by Mn, the lower limit value of the Mn content is preferably 0.07%. On the other hand, excessive Mn reduces corrosion resistance, promotes the formation of scale during quenching, and increases the subsequent grinding load, etc. Therefore, the content of Mn must be set at 1.50% or less. If the reduction of corrosion resistance due to sulfides such as MnS is also considered, it is preferably 1.45% or less.

[0038] <P: 0.040% or less>

[0039] P is an element contained as an impurity in main raw materials such as hot metal or ferrochrome used as raw materials. It is an element harmful to the toughness and corrosion resistance of hot-rolled annealed plates or quenched materials. Therefore, the content of P must be set to 0.040% or less, preferably 0.038% or less. On the other hand, the lower limit value of the content of P is not particularly limited, but excessive reduction will cause problems such as the necessity to use high-purity raw materials, resulting in an increase in cost. Therefore, the lower limit value of the content of P is preferably 0.010%.

[0040] <S: 0.030% or less>

[0041] S forms sulfide-based inclusions, deteriorating the general corrosion resistance (general corrosion or pitting corrosion) of steel. In addition, S reduces hot workability and increases the edge cracking sensitivity of hot-rolled plates. Therefore, the content of S must be set to 0.030% or less, preferably 0.025% or less. It should be noted that the lower limit value of the content of S is not particularly limited, but the less the content of S, the better the corrosion resistance. On the other hand, the greater the desulfurization load, the greater the manufacturing cost. Therefore, the lower limit value of the content of S is preferably 0.001%.

[0042] <Cr: 13.0 - 18.0%>

[0043] Cr is an element used to maintain the necessary corrosion resistance in the main uses of martensitic stainless steel. Therefore, the content of Cr must be set to 13.0% or more. On the other hand, from the perspective of suppressing the formation of retained austenite after quenching, the Cr content must be set to 18.0% or less. From the perspective of stably obtaining the above effects brought by Cr, the lower limit value of the content of Cr is preferably 13.1%, and the upper limit value is preferably 17.8%.

[0044] <Ni: 0.01 - 0.30%>

[0045] Ni, like Mn, is an austenite stabilizing element and also has the effect of improving the toughness after quenching or quenching and tempering. On the other hand, if a large amount of Ni is contained, there may be a decrease in press formability due to solid solution strengthening in hot-rolled annealed plates, and since it is a high-cost element, the manufacturing cost increases. Therefore, the content of Ni must be set to 0.30% or less. On the other hand, Ni is an element effective in suppressing the progress of pitting corrosion. From the perspective of stably obtaining the above effects brought by Ni, the lower limit value of the content of Ni is preferably 0.02%, and the upper limit value is preferably 0.27%.

[0046] <Mo: 0.01 - 1.00%>

[0047] Mo is an element effective in improving the corrosion resistance of a martensitic structure containing δ-ferrite. From the viewpoint of obtaining this effect, the content of Mo must be set at 0.01% or more. On the other hand, Mo is a stabilizing element of the ferrite phase, and excessive addition will damage the quenching characteristics by narrowing the single-phase austenite temperature range. Therefore, the content of Mo must be set at 1.00% or less. From the viewpoint of stably obtaining the above effect brought by Mo, the lower limit value of the content of Mo is preferably 0.02%, the upper limit value is preferably 0.50%, and more preferably 0.30%.

[0048] <Al: 0.030% or less>

[0049] Al is an element that improves oxidation resistance in addition to being added as a deoxidizing element. However, if a large amount of Al is contained, the carbides tend to become large. Therefore, the content of Al must be set at 0.030% or less, preferably 0.025% or less, and more preferably 0.020% or less. On the other hand, the lower limit of the content of Al is not particularly limited, and Al may not be contained. However, from the viewpoint of obtaining the above effect brought by Al, the lower limit value of Al is preferably 0.001%. Here, Al is T.Al.

[0050] <N: 0.010 - 0.350%>

[0051] N, like C, is an element necessary to obtain a specified hardness (Vickers hardness) after quenching or quenching and tempering. Particularly in the embodiment of the present invention, in order to reduce the content of C, N must be contained as a substitute. In addition, N also has the effect of improving corrosion resistance when it is dissolved. From the viewpoint of obtaining these effects, the content of N must be set at 0.010% or more. However, N sometimes forms Cr nitrides to generate a Cr-deficient layer, and in this case, the corrosion resistance is reduced. In addition, if N is added in excess, the control in the steelmaking stage becomes difficult, and it becomes easy to form bubble system defects. If bubble system defects are formed, not only does it become easy to be a starting point for rusting and reduce the corrosion resistance, but there is also a concern about reducing the yield. Therefore, the content of N must be set at 0.350% or less. From the viewpoint of stably obtaining the above effect brought by N, the lower limit value of the content of N is preferably 0.020%, more preferably 0.025%, further preferably 0.036%, the upper limit value is preferably 0.300%, and more preferably 0.290%.

[0052] <Ca: 0.0001 - 0.0030%>

[0053] Ca is added during the steelmaking stage to adjust the composition, but acts as a strong deoxidizer and has the effect of promoting deoxidation. However, since Ca is a strong deoxidizing element, most of it floats out in the molten steel as inclusions and hardly remains in the steel. However, if a large amount of Ca is added, CaO is included in the steelmaking inclusions, which is highly likely to become the starting point of rusting and reduces the corrosion resistance. Therefore, the content of Ca must be set to 0.0030% or less, preferably 0.0010% or less. On the other hand, since it is impossible to remove even fine inclusions, it is difficult in the manufacturing process to set the content of Ca below 0.0001%. Therefore, the content of Ca is set to 0.0001% or more.

[0054] <O: 0.001 - 0.010%>

[0055] To reduce inclusions, O, together with Al and Ca, becomes an important element. If a large amount of O is added, the number of large inclusions (especially carbides) remaining in the steel increases, which has an adverse effect on the corrosion resistance. Therefore, the content of O must be set to 0.010% or less. In addition, O is preferably reduced as much as possible, but excessive reduction will lead to an increase in cost. Therefore, the content of O is set to 0.001% or more. From the perspective of the balance between cost and corrosion resistance, the lower limit value of the O content is preferably 0.002%, and the upper limit value is 0.009%.

[0056] <2.5C + N is 1.10% or more>

[0057] As described above, C and N are elements necessary to obtain a specified hardness (Vickers hardness) after quenching or quenching and tempering. In the embodiment of the invention, N is contained as an alternative to reducing the content of C, and C contributes to this hardness at 2.5 times that of N. Therefore, from the perspective of obtaining a specified hardness, 2.5C + N must be set to 1.10% or more, preferably 1.25% or more. It should be noted that the upper limit value of 2.5C + N is not particularly limited, but preferably 1.80%, more preferably 1.70%, and further preferably 1.60%.

[0058] <V: 0.50% or less>

[0059] V is an element that forms fine carbonitrides and contributes to the improvement of corrosion resistance, and is added as needed. However, if V is added in excess, it may cause coarsening of precipitates, and as a result, the toughness after quenching decreases. Therefore, the content of V is 0.50% or less, preferably 0.30% or less, and more preferably 0.20% or less. It should be noted that the lower limit value of the content of V is not particularly limited, but V is sometimes mixed into the alloy raw materials as an unavoidable impurity, and it is difficult to remove in the refining process. In addition, from the viewpoint of obtaining the above effects, the lower limit value of the content of V is preferably 0.01%, more preferably 0.02%, and further preferably 0.03%.

[0060] <Nb: 0.30% or less>

[0061] Nb is an element that forms carbonitrides and suppresses sensitization or reduction of corrosion resistance caused by precipitation of Cr carbonitrides, and is added as needed. However, if Nb is added in excess, the martensite phase becomes unstable and the hardness decreases. Therefore, the content of Nb is 0.30% or less, preferably 0.28% or less, and more preferably 0.25% or less. It should be noted that the lower limit value of the content of Nb is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0062] <Ti: 0.3% or less>

[0063] Ti is an element that forms carbonitrides and suppresses sensitization and reduction of corrosion resistance caused by precipitation of Cr carbonitrides, and is added as needed. However, if Ti is added in excess, coarse TiN is formed, resulting in the occurrence of hot rolling defects or reduction of toughness. Therefore, the content of Ti is set to 0.3% or less, preferably 0.25% or less. It should be noted that the lower limit value of the content of Ti is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.06%, and further preferably 0.10%.

[0064] <Cu: 4.0% or less>

[0065] Cu is an element that is effective in improving the corrosion resistance of a martensite structure containing δ ferrite and also contributes to the improvement of hardenability as an austenite stabilizing element, and is added as needed. However, excessive addition of Cu may cause a decrease in hot workability or an increase in raw material cost. Therefore, the content of Cu is set to 4.0% or less, preferably 3.8% or less, and more preferably 3.5% or less. It should be noted that the lower limit value of the content of Cu is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 1.0%, more preferably 1.3%, and further preferably 1.5%.

[0066] <Sn: 0.100% or less>

[0067] Sn is an element effective in improving the corrosion resistance after quenching or quenching and tempering, and is added as needed. However, excessive addition of Sn promotes edge cracking during hot rolling. Therefore, the Sn content is set to 0.100% or less, preferably 0.090% or less. It should be noted that the lower limit value of the Sn content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.002%, preferably 0.050%.

[0068] <B: 0.0 weight percent or less>

[0069] B is an element effective in improving hot workability, and is added as needed. However, excessive addition of B may reduce the hardenability due to the composite precipitation of borides and carbides. Therefore, the B content is set to 0.0050% or less, preferably 0.0045% or less. It should be noted that the lower limit value of the B content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.0002%.

[0070] <Co: 0.30% or less>

[0071] Co is an element that improves heat resistance, and is added as needed. However, since Co is expensive, if the Co content is too much, it will lead to an increase in manufacturing cost. Therefore, the Co content is set to 0.30% or less, preferably 0.10% or less, more preferably 0.05% or less. It should be noted that the lower limit value of the Co content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%.

[0072] The average grain size of the carbides in the martensitic stainless steel material of the embodiment of the present invention is 0.50 μm or less, preferably 0.48 μm or less. By controlling the average grain size of the carbides within such a range, the workability of the martensitic stainless steel material is improved, chipping during tool manufacturing (especially during edge grinding) is suppressed, and the generation of irregular patterns is also suppressed. It should be noted that the lower limit value of the average grain size of the carbides is not particularly limited, but it is preferably 0.01 μm, more preferably 0.05 μm, and further preferably 0.10 μm.

[0073] Here, the carbides with a specified average grain size are targeted at both the eutectic carbides generated during casting and the precipitated carbides generated during the rolling process.

[0074] In addition, the average grain size of the carbides can be calculated by observing the cross section of the martensitic stainless steel material using SEM, measuring the equivalent circle diameter of each carbide in the observation field of view, and calculating the average value thereof.

[0075] In the martensitic stainless steel material according to the embodiment of the present invention, the number of carbides with a size of 10 μm or more is 0.20 pieces / cm 2 Below, preferably 0.19 pieces / cm 2 Carbides larger than 10 μm are prone to rusting, so by controlling the number of carbides larger than 10 μm to this range, rust can be suppressed and corrosion resistance can be improved. It should be noted that the fewer carbides larger than 10 μm, the better, so there is no particular limit, but it is generally 0.01 pieces / cm 2 above.

[0076] Here, the predetermined number of carbides having a size of 10 μm or more mainly refers to eutectic carbides formed during casting. In addition, the size of the carbide refers to (long axis + short axis) / 2 of the carbide.

[0077] The number of carbides with a size of 10 μm or larger can be calculated by observing a cross section of a martensitic stainless steel material with an optical microscope to determine the number of carbides with a size of 10 μm or larger and dividing the number by the area of ​​the measurement region.

[0078] The hardness (Vickers hardness) of the martensitic stainless steel material according to an embodiment of the present invention after quenching or quenching and tempering is 500 HV or higher. In particular, when the martensitic stainless steel material is used as a cutting tool, the hardness is preferably 550 HV or higher. It should be noted that the upper limit of the hardness is not particularly limited, but is preferably 900 HV, and more preferably 800 HV.

[0079] Here, quenching is performed at 1000 to 1100° C. Tempering is performed at 100 to 400° C. After quenching, cryogenic treatment is preferably performed at -200 to -50° C.

[0080] In addition, hardness refers to the value measured at room temperature (25° C.) using a Vickers hardness tester.

[0081] The martensitic stainless steel material according to the embodiment of the present invention is not particularly limited, but is preferably a hot-rolled sheet, a hot-rolled annealed sheet, a cold-rolled sheet, or a cold-rolled annealed sheet.

[0082] The martensitic stainless steel material according to an embodiment of the present invention includes a hot rolling process in which a slab having the same composition as the above-mentioned martensitic stainless steel material is heat-treated at a temperature of T or higher represented by formula (1) for 1 to 5 hours and then hot-rolled. This hot rolling process can produce a hot-rolled sheet.

[0083] T[℃]=6500 / (4-logC[%])-273 (1)

[0084] By performing heat treatment under such conditions, eutectic carbides generated during casting can be completely dissolved, and thus the average particle size of carbides and the number of carbides having a size of 10 μm or greater can be controlled within the above-mentioned ranges.

[0085] The conditions for hot rolling are not particularly limited, but the steel sheet is preferably finished to a thickness of 2 to 8 mm by rough rolling and finish rolling.

[0086] After hot rolling, the hot-rolled sheet is coiled at a coiling temperature of 800° C. to 900° C. The coiled hot-rolled sheet is in the form of a coil.

[0087] After the hot rolling process, the hot rolled sheet in coil form is subjected to a softening process of annealing at a temperature of Ac1 point to (Ac1 point - 50°C) for 1 to 5 hours. By performing this softening process, a hot rolled annealed sheet can be obtained. In addition, by performing annealing under such conditions, the coarsening of carbides can be suppressed, so that the average particle size of carbides and the number of carbides with a size of 10 μm or more can be stably controlled within the above range. Annealing is performed by keeping the heated hot rolled sheet in coil form at a temperature of Ac1 point to (Ac1 point - 50°C). Therefore, for annealing, it should be noted that the hot rolled sheet in coil form is not temporarily cooled and then heated to this temperature. In addition, annealing is performed in a batch annealing furnace.

[0088] Here, the Ac1 point is calculated by the following formula (2).

[0089] Ac1=-250C+73Si-66Mn-115Ni+35Cr+60Mo-18Cu+620Ti+750Al-280N+410 (2)

[0090] In the formula, the symbol of each element is the mass % of each element.

[0091] It should be noted that the hot-rolled annealed sheet obtained in the softening step may be pickled as needed.

[0092] After the softening step, a cold rolling step is performed on the hot-rolled annealed sheet, which has been pickled as needed. A cold-rolled sheet can be obtained by performing the cold rolling step.

[0093] The conditions for cold rolling are not particularly limited and may be appropriately adjusted according to the desired cold-rolled sheet.

[0094] After the cold rolling process, the cold rolled sheet is subjected to an annealing process in which the sheet is heated at a temperature range of 100°C to the Ac1 point (Ac1 point - 50°C) at a heating rate of 50°C / second or more, preferably at a heating rate of 100°C / second or more. It should be noted that annealing can be started when the cold rolled sheet is in a temperature range of above room temperature (25°C) and below 100°C. By performing this annealing process, a cold rolled annealed sheet can be obtained. In addition, by performing the annealing process under such conditions, the coarsening of carbides can be suppressed, so that the average particle size of the carbides and the number of carbides with a size of 10 μm or more can be stably controlled within the above range.

[0095] The martensitic stainless steel material according to the embodiment of the present invention manufactured as described above has excellent workability, high hardness and corrosion resistance after quenching or quenching and tempering, and can suppress the occurrence of irregular patterns because, in addition to the steel composition, the number of carbides with a size of 10 μm or more and the average particle size of the carbides are controlled within a predetermined range.

[0096] Example

[0097] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

[0098] The steel having the steel composition shown in Table 1 was melted and cast into a 200 mm thick slab. After the slab was heat treated at the temperature and time shown in Table 2, it was hot rolled (rough rolling and finish rolling) to form a hot rolled plate with a thickness of 3 mm, which was coiled into a coil at a coiling temperature of 850°C. Next, the hot rolled plate in the coiled state was transferred to a batch annealing furnace and subjected to a softening process at the temperature and time shown in Table 2. Next, the hot rolled annealed plate obtained in the softening process was cold rolled, and then the cold rolled plate was heated in a temperature range from 100°C to the temperature shown in Table 2 at a heating rate shown in Table 2 to perform an annealing process. It should be noted that annealing starts from the state where the cold rolled plate is at room temperature (25°C). Thereafter, pickling was performed. The following evaluation was performed on the obtained cold rolled annealed plate (martensitic stainless steel).

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103] (hardness)

[0104] The resulting cold-rolled annealed sheet was heated to 1000-1100°C and quenched. The surface was then polished with #80 and the JIS surface hardness (quenching hardness) was measured using a Vickers hardness tester. The measurement temperature was set at room temperature (25°C). A hardness of 500 HV or higher was considered acceptable.

[0105] (Corrosion resistance)

[0106] The resulting cold-rolled annealed sheets were heated to 1000-1100°C and quenched. The surfaces were then polished with #600 and subjected to a 24-hour salt spray test according to JIS Z2371:2015 "Salt spray test method" to measure the rust area percentage. In this evaluation, a rust area percentage of less than 10% was considered acceptable (◯), while a rust area percentage of 10% or greater was considered unacceptable (×).

[0107] (Average particle size of carbide)

[0108] The cross section of the obtained cold-rolled annealed sheet parallel to the rolling direction and the thickness direction is observed using an SEM. The equivalent circle diameter (μm) of all carbide particles observed in the observation field, excluding carbide particles with an equivalent circle diameter of less than 0.10 μm and carbide particles whose particles partially overflow from the observation field, is measured as the measurement object. The value obtained by dividing the sum of the equivalent circle diameters of the carbide particles of the measurement object by the total number of the carbide particles of the measurement object is set as the average particle size (μm) of the carbide. Among them, the total number of the carbide particles of the measurement object is set to 100 or more by randomly selecting multiple non-repeating observation fields. The equivalent circle diameter of the carbide particles is calculated by processing the SEM image using image processing software and calculating the area of ​​the carbide particles.

[0109] (Number of carbides larger than 10 μm in size)

[0110] The cross section of the obtained cold-rolled annealed sheet parallel to the rolling direction and the sheet thickness direction was visually observed using a 50x optical microscope at 20 locations in a 50 mm x 50 mm area. The average number of spots was calculated by dividing by the area of ​​the observed area.

[0111] (Processability)

[0112] The resulting cold-rolled annealed sheet was punched into a tool shape to collect steel, which was then heated at 1000-1100°C for quenching. Next, the steel surface was ground, and one of the longitudinal end faces was wet-ground for sharpening, yielding a test piece (tool). Test pieces that did not experience chipping during this sharpening process were rated as acceptable (◯), while those that did experience chipping were rated as unacceptable (×).

[0113] (Irregular pattern)

[0114] By the same method as for the machinability, a test material (knife) was obtained. The test material was visually observed for appearance, and the test material with no irregular pattern on the blade surface was set as qualified (◯), and the test material with irregular pattern on the blade surface was set as unqualified (×).

[0115] Table 3 shows the above-mentioned evaluation results.

[0116] Table 3

[0117]

[0118] As shown in Table 3, the cold-rolled annealed sheets (martening stainless steel materials) of Examples 1 to 23 exhibited excellent hardness and corrosion resistance after quenching. Furthermore, these cold-rolled annealed sheets exhibited excellent workability, with no chipping during sharpening, due to the small average carbide particle size and the small number of carbides larger than 10 μm. Furthermore, the formation of irregularities on the tool surface was suppressed, as evidenced by the small average carbide particle size and the small number of carbides larger than 10 μm.

[0119] In contrast, the cold-rolled annealed sheets of Comparative Examples 1 to 14 exhibited insufficient hardness and corrosion resistance after quenching due to any of the following: steel composition, average carbide grain size, or number of carbides with a size of 10 μm or greater falling outside the specified ranges. In particular, the cold-rolled annealed sheets with a large average carbide grain size and a high number of carbides with a size of 10 μm or greater experienced chipping during sharpening, resulting in insufficient workability and irregularities on the tool surface.

[0120] Here, a graph showing the relationship between 2.5C+N and hardness in the above-mentioned examples and comparative examples is shown in FIG. Figure 1 In. Figure 1 As shown in , it is known that there is a proportional relationship between 2.5C+N and hardness, and that increasing 2.5C+N tends to increase hardness. In particular, it is known that controlling 2.5C+N to 1.10% or more can achieve hardness of 500 HV or more.

[0121] As apparent from the above results, the present invention can provide a martensitic stainless steel material having good workability, high hardness and corrosion resistance after quenching or quenching and tempering, and capable of suppressing the generation of irregular patterns, and a method for producing the same.

Claims

1. A martensitic stainless steel material having the following composition: comprising, by mass, 0.30-0.60% C, 0.05-1.00% Si, 0.05-1.50% Mn, 0.040% or less P, 0.030% or less S, 13.0-18.0% Cr, 0.01-0.30% Ni, 0.01-1.00% Mo, 0.030% or less Al, 0.010-0.350% N, 0.0001-0.0030% Ca, 0.001-0.010% O, 2.5C+N being 1.10% or more, and the remainder being Fe and impurities. The average particle size of carbides is less than 0.50 μm. The number of carbides larger than 10 μm is 0.20 per cm 2 the following.

2. The martensitic stainless steel material according to claim 1, wherein: The alloy further contains, on a mass basis, one or more of V: ​​0.50% or less, Nb: 0.30% or less, Ti: 0.3% or less, Cu: 1.0 to 4.0%, Sn: 0.100% or less, B: 0.0050% or less, and Co: 0.30% or less.

3. The martensitic stainless steel material according to claim 1 or 2, wherein the hardness after quenching or quenching and tempering is 500 HV or higher.

4. The martensitic stainless steel material according to claim 1 or 2, wherein: The martensitic stainless steel is used for cutting tools.

5. A method for producing a martensitic stainless steel material, comprising a hot rolling step of subjecting a slab to a heat treatment at a temperature of T or higher represented by formula (1) for 1 to 5 hours and then hot rolling the slab, wherein the slab has the following composition: C: 0.30-0.60%, Si: 0.05-1.00%, Mn: 0.05-1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0-18.0%, Ni: 0.01-0.30%, Mo: 0.01-1.00%, Al: 0.030% or less, N: 0.010-0.350%, Ca: 0.0001-0.0030%, O: 0.001-0.010%, 2.5C+N is 1.10% or more, and the remainder is Fe and impurities, T[℃]=6500 / (4-logC[%])-273 (1) The manufacturing method further comprises the following steps: In the hot rolling step, the hot rolled sheet is coiled at a coiling temperature of 800°C to 900°C and then subjected to a softening step of annealing at a temperature of Ac1 point to (Ac1 point - 50°C) for 1 to 5 hours; A cold rolling step of cold rolling the hot-rolled annealed sheet obtained in the softening step; and The cold-rolled sheet obtained in the cold-rolling step is annealed in a temperature range from 100° C. to Ac1 point to (Ac1 point−50° C.) at a heating rate of 50° C. / second or higher.

6. The method for producing a martensitic stainless steel material according to claim 5, wherein: The slab further contains, on a mass basis, one or more of V: ​​0.50% or less, Nb: 0.30% or less, Ti: 0.3% or less, Cu: 4.0% or less, Sn: 0.100% or less, B: 0.0050% or less, and Co: 0.30% or less.

Images