Martensitic stainless steel material and its manufacturing method

Abstract

This martensite-based stainless steel material has a compositional makeup which includes, in mass basis, 0.30-0.60% of C, 0.05-1.00% of Si, 0.05-1.50% of Mn, 0.040% or less of P, 0.030% or less of S, 13.0-18.0% of Cr, 0.01-0.30% of Ni, 0.01-1.00% of Mo, 0.030% or less of Al, 0.010-0.350% of N, 0.0001-0.0030% of Ca, and 0.001-0.010% of O, and in which 2.5C+N equals 1.10% or more and the remaining portion is Fe and impurities. In this martensite-based stainless steel material, the average particle diameter of carbides is 0.50 μm or less. Further, carbides having a size equal to or more than 10 μm are included in an amount of 0.20 particles / cm2 or less.

Description

[Technical Field]

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

[0002] Stainless steel materials used in various cutting tools such as shavers, scissors, and kitchen knives require high hardness, and therefore martensitic stainless steel materials with a high C content are used (for example, Patent Document 1). 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 by annealing, and the amount of dissolved C decreases during quenching, causing excessive softening. Furthermore, these eutectic carbides act as corrosion initiation sites, reducing corrosion resistance and causing chipping and irregular patterns during processing.

[0003] Therefore, Patent Document 2 describes the following composition in mass %: C: 0.40 to 0.50%, Si: 0.05 to 0.60%, Mn: 0.5 to 1.5%, P: 0.035% or less, S: 0.010% or less, Cr: 11.0 to 15.5%, Ni: 0.01 to 0.30%, Cu: 0.01 to 0.30%, Mo: 0.01 to 0.30%, V: 0.01 to 0.10%, The alloy contains Al: 0.02% or less, Sn: 0.002 to 0.10%, N: 0.010 to 0.035%, Ca: 0.0001 to 0.0010%, O: 0.001 to 0.01%, the balance being Fe and unavoidable impurities, and satisfies Cu+Ni+Mo=0.05 to 0.30%, and further, the number of inclusions with a size of 10 μm or more is 0.2 pieces / cm 2 A martensitic stainless steel material for cutlery has been proposed, characterized in that:

[0004] Patent Document 3 proposes a method for producing a grain-refined martensitic stainless steel material, comprising the steps of: preparing a base material having a composition consisting of 13.0 to 14.0 wt.% Cr, 1.15 to 1.35 wt.% Mo, 0.35 to 0.55 wt.% C, 0.20 to 0.50 wt.% Si, 0.20 to 0.50 wt.% Mn, 0.025 wt.% or less P, 0.020 wt.% or less S, and the balance being Fe and unavoidable impurity elements; subjecting this base material to at least one of a high-density dislocation introduction method and an ultra-rapid solidification method, followed by annealing to obtain a fine-structured ferritic steel; and cold-rolling, annealing, and, if necessary, plastically working the ferritic steel into a predetermined shape, followed by quenching to obtain a grain-refined martensitic stainless steel material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-273587 [Patent Document 2] Japanese Patent Application Publication No. 2018-9231 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-313612 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the martensitic stainless steel material described in Patent Document 2 does not have a controlled average grain size of inclusions (particularly carbides), and therefore may have insufficient workability or may develop irregular patterns. Furthermore, the martensitic stainless steel material described in Patent Document 3 is not suitable for mass production because it requires special processes such as high-density dislocation introduction and ultra-rapid solidification. Furthermore, this martensitic stainless steel material contains a large amount of Mo, which makes it expensive. Conventional martensitic stainless steel materials with reduced C content have had the above-mentioned problems.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a martensitic stainless steel material that has good workability, high hardness and corrosion resistance after quenching or quench-tempering, and is capable of suppressing the occurrence of irregular patterns, and a method for manufacturing the same. [Means for solving the problem]

[0008] As a result of extensive research into martensitic stainless steel materials, the inventors discovered that among inclusions, carbides in particular are closely related to corrosion resistance, workability, and irregular patterns, and that all of the above problems can be solved by controlling the number of carbides with a size of 10 μm or more and the average particle size of the carbides in addition to the steel composition, which led to the completion of the present invention.

[0009] That is, the present invention provides a composition containing, by mass, C: 0.30 to 0.60%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.030% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, 2.5C+N is 1.10% or more, and the balance is Fe and impurities, The average grain size of the carbide is 0.50 μm or less, The carbides having a size of 10 μm or more are 0.20 pieces / cm 2 The following is a martensitic stainless steel material.

[0010] The present invention also provides A method for producing the martensitic stainless steel material, A slab having a composition containing, by mass, C: 0.30 to 0.60%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.030% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, 2.5C+N is 1.10% or more, and the balance is Fe and impurities, represented by formula (1): T[℃]=6500 / (4-log C[%])-273 ··· (1) The hot rolling process includes a step of performing a heat treatment at a temperature equal to or higher than T for 1 to 5 hours and then hot rolling. How to eat It is the law. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a martensitic stainless steel material that has good workability, high hardness and corrosion resistance after quenching or quench-tempering, and is capable of suppressing the occurrence of irregular patterns, and a method for manufacturing the same. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the relationship between 2.5C+N and hardness in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following is a detailed description of the embodiments of the present invention. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements made to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention are also within the scope of the present invention. In this specification, the "%" designation for components means "% by mass" unless otherwise specified.

[0014] A martensitic stainless steel material according to an embodiment of the present invention has a composition containing C: 0.30 to 0.60%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.030% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, with 2.5C+N being 1.10% or more, and the balance being Fe and impurities.

[0015] In this specification, "steel" refers to various types of materials, such as steel plates. Furthermore, "steel plates" encompasses steel strips. Furthermore, "impurities" refer to components that are mixed in during the industrial production of stainless steel materials due to various factors, such as raw materials like ores and scraps, or during the manufacturing process, and are acceptable within a 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 present as impurities, the following limits are satisfied: Zn≦100 ppm, Pb≦100 ppm, Se≦100 ppm, Sb≦500 ppm, H≦100 ppm, Ga≦500 ppm, Ta≦500 ppm, Mg≦120 ppm, and Zr≦120 ppm.

[0016] In addition, the martensitic stainless steel material according to an 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. Each component will be described in detail below.

[0017] <C:0.30~0.60%> C is an essential element for obtaining a predetermined hardness (Vickers hardness) after quenching or quench-tempering. In order to consistently obtain a hardness of 500 HV or more, the C content must be 0.30% or more. Excessive addition of C promotes sensitization during quenching, impairing corrosion resistance, and also reduces toughness after quenching or tempering due to undissolved carbonitrides. Therefore, the C content must be 0.60% or less. Considering the reduction in hardness and toughness due to fluctuations in heating conditions during quenching or quench-tempering, the lower limit of the C content is preferably 0.32% and the upper limit is preferably 0.58%.

[0018] <Si:0.05~1.00%> Si is necessary for deoxidation during melting and refining, and is also a useful element for suppressing oxide scale formation during quenching. Furthermore, a low Si content tends to result in insufficient deoxidation, resulting in an increase in carbides, which may become the starting point for rusting, resulting in reduced corrosion resistance. Therefore, the Si content must be 0.05% or more. On the other hand, Si narrows the austenite single-phase temperature range and impairs quenching stability, so the Si content must be 1.00% or less. To stably obtain the above-mentioned effects of Si, the lower limit of the Si content is preferably 0.07%, and the upper limit is preferably 0.98%.

[0019] <Mn:0.05~1.50%> Mn is added as a deoxidizer and expands the austenite single-phase region, contributing to improved hardenability. Insufficient Mn content expands the two-phase region and increases the α phase. As a result, Cr carbonitrides also increase, forming Cr-depleted zones around them, which are prone to rusting and reduce corrosion resistance. Therefore, the Mn content must be 0.05% or more. To ensure the above-mentioned effects of Mn are consistently achieved, the lower limit of the Mn content is preferably 0.07%. However, excessive Mn reduces corrosion resistance, promotes the formation of oxide scale during hardening, and increases subsequent grinding loads. Therefore, the Mn content must be 1.50% or less. Considering the reduced corrosion resistance caused by granular particles such as MnS, a Mn content of 1.45% or less is preferred.

[0020] <P: Below 0.040%> P is an element contained as an impurity in the main raw materials such as hot metal and ferrochrome which are raw materials. It is a harmful element to the toughness and corrosion resistance of hot-rolled annealed plates and materials after quenching. Therefore, it is necessary to make the content of P 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 causes problems such as making the use of high-purity raw materials essential, leading to an increase in cost. Therefore, the lower limit value of the content of P is preferably 0.010%.

[0021] <S: Below 0.030%> S forms sulfide-based inclusions and deteriorates the general corrosion resistance (general corrosion and pitting corrosion) of steel materials. Also, S reduces the hot workability and increases the ear cracking sensitivity of hot-rolled plates. Therefore, the content of S needs to be 0.030% or less, preferably 0.025% or less. Note 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, while the desulfurization load increases and the manufacturing cost increases. Therefore, the lower limit value of the content of S is preferably 0.001%.

[0022] <Cr: 13.0 - 18.0%> Cr is an element for maintaining the corrosion resistance required in the main applications of martensitic stainless steel materials. Therefore, it is necessary to make the content of Cr 13.0% or more. On the other hand, from the viewpoint of suppressing the formation of retained austenite after quenching, it is necessary to make the Cr content 18.0% or less. From the viewpoint of stably obtaining the above effects by Cr, the content of Cr preferably has a lower limit value of 13.1% and an upper limit value of preferably 17.8%.

[0023] <Ni: 0.01 - 0.30%> Ni, like Mn, is an austenite stabilizing element and also has the effect of improving toughness after quenching or quenching and tempering. On the other hand, if a large amount of Ni is contained, there is a risk of reducing the press formability due to solid solution strengthening in the hot-rolled annealed sheet, and the manufacturing cost increases because Ni is an expensive element. Therefore, the Ni content needs to be 0.30% or less. On the other hand, Ni is an element effective in suppressing the progress of pitting corrosion. From the viewpoint of stably obtaining the above effects of Ni, the Ni content preferably has a lower limit value of 0.02% and an upper limit value preferably of 0.27%.

[0024] <Mo: 0.01~1.00%> Mo is an element effective in improving the corrosion resistance of a martensite structure containing δ-ferrite. From the viewpoint of obtaining this effect, the Mo content needs to be 0.01% or more. On the other hand, Mo is a stabilizing element of the ferrite phase, and excessive addition impairs the quenching characteristics by narrowing the austenite single-phase temperature range. Therefore, the Mo content needs to be 1.00% or less. From the viewpoint of stably obtaining the above effects of Mo, the Mo content preferably has a lower limit value of 0.02%, an upper limit value preferably of 0.50%, and more preferably of 0.30%.

[0025] <Al: 0.030% or less> Al is added as a deoxidizing element and is also an element that improves oxidation resistance. However, when a large amount of Al is contained, carbides tend to grow larger. Therefore, the Al content needs to be 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 Al content is not particularly limited, and it may not contain Al. However, from the viewpoint of obtaining the above effects of Al, the lower limit value of Al is preferably 0.001%. Here, Al is T.Al.

[0026] <N: 0.010~0.350%> Like C, N is an essential element for achieving a predetermined hardness (Vickers hardness) after quenching or quench-tempering. In particular, since the C content is reduced in the embodiment of the present invention, N must be added instead. Furthermore, N also has the effect of improving corrosion resistance when dissolved in solid solution. To achieve these effects, the N content must be 0.010% or more. However, N may form Cr nitrides, resulting in a Cr-deficient zone, which reduces corrosion resistance. Furthermore, excessive addition of N is difficult to control during steelmaking, and pore defects are likely to form. The formation of pore defects can easily become the starting point for rusting, reducing corrosion resistance and potentially reducing yield. Therefore, the N content must be 0.350% or less. From the viewpoint of stably obtaining the above-mentioned effects of N, the lower limit of the N content is preferably 0.020%, more preferably 0.025%, and even more preferably 0.036%, and the upper limit is preferably 0.300%, and more preferably 0.290%.

[0027] <Ca:0.0001~0.0030%> Ca is added during the steelmaking process to adjust the composition, but it also acts as a powerful deoxidizer, promoting deoxidation. However, because Ca is such a powerful deoxidizing element, most of it floats to the surface in the molten steel as inclusions, with very little remaining in the steel. However, adding large amounts of Ca results in the inclusions containing CaO, which is likely to become the starting point for rusting and reduce corrosion resistance. Therefore, the Ca content must be 0.0030% or less, and preferably 0.0010% or less. On the other hand, because it is impossible to remove even the smallest inclusions, it is difficult in the manufacturing process to limit the Ca content to less than 0.0001%. Therefore, the Ca content is set to 0.0001% or more.

[0028] <O:0.001~0.010%> In order to reduce inclusions, O becomes an important element together with Al and Ca. When 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 corrosion resistance. Therefore, the O content needs to be 0.010% or less. Also, although it is preferable to reduce O as much as possible, excessive reduction leads to an increase in cost, so the O content should be 0.001% or more. From the perspective of the balance between cost and corrosion resistance, the lower limit of the O content is preferably 0.002%, and the upper limit is 0.009%.

[0029] <2.5C + N is 1.10% or more> As described above, C and N are essential elements for obtaining a predetermined hardness (Vickers hardness) after quenching or quenching and tempering. In an embodiment of the invention, N is contained instead of reducing the C content, and C contributes 2.5 times that of N to the hardness. Therefore, from the perspective of obtaining a predetermined hardness, 2.5C + N needs to be 1.10% or more, preferably 1.25% or more. The upper limit of 2.5C + N is not particularly limited, but is preferably 1.80%, more preferably 1.70%, and still more preferably 1.60%.

[0030] <V: 0.50% or less> 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 excessively, there is a risk of coarsening of precipitates, and as a result, the toughness after quenching decreases. Therefore, the V content is 0.50% or less, preferably 0.30% or less, more preferably 0.20% or less. The lower limit of the V content is not particularly limited, but V may be mixed as an inevitable impurity in the alloy raw material and is difficult to remove in the refining process. Also, from the perspective of obtaining the above effects, the lower limit of the V content is preferably 0.01%, more preferably 0.02%, and still more preferably 0.03%.

[0031] <Nb: 0.30% or less> Nb forms carbonitrides and suppresses sensitization and corrosion resistance degradation caused by the precipitation of Cr carbonitrides. It is added as needed. However, if Nb is added excessively, the martensite phase becomes unstable and the hardness decreases. Therefore, the Nb content is 0.30% or less, preferably 0.28% or less, more preferably 0.25% or less. Note that the lower limit value of the Nb content is not particularly limited, but from the perspective of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0032] <Ti: 0.3% or less> Ti forms carbonitrides and suppresses sensitization and corrosion resistance degradation caused by the precipitation of Cr carbonitrides. It is added as needed. However, if Ti is added excessively, coarse TiN is formed, leading to the occurrence of hot rolling defects and a decrease in toughness. Therefore, the Ti content is 0.3% or less, preferably 0.25% or less. Note that the lower limit value of the Ti content is not particularly limited, but from the perspective of obtaining the above effects, it is preferably 0.01%, more preferably 0.06%, still more preferably 0.10%.

[0033] <Cu: 4.0% or less> Cu is effective in improving the corrosion resistance of a martensite structure containing δ-ferrite and also contributes to improving hardenability as an austenite stabilizing element. It is added as needed. However, excessive addition of Cu leads to a decrease in hot workability and an increase in raw material costs. Therefore, the Cu content is 4.0% or less, preferably 3.8% or less, more preferably 3.5% or less. Note that the lower limit value of the Cu content is not particularly limited, but from the perspective of obtaining the above effects, it is preferably 1.0%, more preferably 1.3%, still more preferably 1.5%.

[0034] <Sn: 0.100% or less> Sn is an element effective in improving the corrosion resistance after quenching or quenching and tempering, and is added as necessary. However, excessive addition of Sn promotes ear cracking during hot rolling. Therefore, the Sn content is set to 0.100% or less, preferably 0.090% or less. The lower limit 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%.

[0035] <B: 0.0050% or less> B is an element effective in improving hot workability and is added as necessary. However, excessive addition of B may reduce hardenability due to the combined precipitation of borides and carbides. Therefore, the B content is set to 0.0050% or less, preferably 0.0045% or less. The lower limit of the B content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.0002%.

[0036] <Co: 0.30% or less> Co is an element that improves heat resistance and is added as necessary. However, since Co is expensive, if the Co content is too high, it will lead to an increase in manufacturing costs. Therefore, the Co content is set to 0.30% or less, preferably 0.10% or less, more preferably 0.05% or less. The lower limit of the Co content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%.

[0037] The martensitic stainless steel material according to the embodiment of the present invention has an average carbide particle size of 0.50 μm or less, preferably 0.48 μm or less. By controlling the average carbide particle size within such a range, the workability of the martensitic stainless steel material is improved, chipping during tool manufacturing (especially during edge attachment processing) is suppressed, and the occurrence of irregular patterns is also suppressed. The lower limit of the average carbide particle size is not particularly limited, but is preferably 0.01 μm, more preferably 0.05 μm, and still more preferably 0.10 μm. Here, the carbides defining the average particle size target both eutectic carbides generated during casting and precipitation carbides generated during the rolling process. The average grain size of the carbides can be calculated by observing the cross section of the martensitic stainless steel material with an SEM, measuring the circle-equivalent diameter of each carbide in the observed field of view, and finding the average value.

[0038] In the martensitic stainless steel material according to the embodiment of the present invention, the number of carbides having a size of 10 μm or more is 0.20 / cm 2 Less than or equal to 0.19 particles / cm 2 Carbides with a size of 10 μm or more are likely to become the starting point of rusting, so by controlling the number of carbides with a size of 10 μm or more within this range, rusting can be suppressed and corrosion resistance can be improved. The fewer carbides with a size of 10 μm or more, the better, so there are no particular limitations, but generally it should be 0.01 particles / cm. 2 That's all. Here, the number of carbides with a size of 10 μm or more refers mainly to eutectic carbides formed during casting. The size of a carbide is defined as (longer diameter + shorter diameter) / 2 of the carbide. The number of carbides with a size of 10 μm or more can be calculated by observing the cross section of the martensitic stainless steel material with an optical microscope to determine the number of carbides with a size of 10 μm or more, and then dividing that number by the area of ​​the measurement region.

[0039] The martensitic stainless steel material according to the embodiment of the present invention has a hardness (Vickers hardness) of 500 HV or more after quenching or quench-tempering. In particular, when the martensitic stainless steel material is used for cutting tools, the hardness is preferably 550 HV or more. The upper limit of the hardness is not particularly limited, but is preferably 900 HV, more preferably 800 HV. Here, quenching is performed at 1000 to 1100°C, and tempering is performed at 100 to 400°C. After quenching, it is desirable to perform sub-zero treatment at -200 to -50°C. The hardness refers to a value measured at room temperature (25° C.) using a Vickers hardness tester.

[0040] 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.

[0041] The martensitic stainless steel material according to an embodiment of the present invention includes a hot rolling step in which a slab having the same composition as the martensitic stainless steel material described above is heat treated at a temperature equal to or higher than T represented by formula (1) for 1 to 5 hours, and then hot rolled. By carrying out this hot rolling step, a hot-rolled sheet can be obtained. T[℃]=6500 / (4-log C[%])-273 ··· (1) By performing heat treatment under these conditions, the eutectic carbides formed during casting can be completely dissolved, making it possible to control the average grain size of the carbides and the number of carbides with a size of 10 μm or more within the above ranges.

[0042] The conditions for hot rolling are not particularly limited, but it is preferable to finish the sheet to a thickness of 2 to 8 mm by rough rolling and finish rolling. 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.

[0043] After the hot rolling process, the coiled hot-rolled sheet is subjected to a softening process in which it is annealed at a temperature of Ac1 point to (Ac1 point - 50°C) for 1 to 5 hours. This softening process allows for the production of a hot-rolled annealed sheet. Furthermore, by performing annealing under these conditions, coarsening of carbides is suppressed, making it possible to stably control the average grain size of carbides and the number of carbides with a size of 10 μm or more within the above ranges. Annealing is performed by holding the heated coiled hot-rolled sheet at a temperature of Ac1 point to (Ac1 point - 50°C). Therefore, it should be noted that annealing is not performed by cooling the coiled hot-rolled sheet once and then reheating it to the same temperature. Furthermore, annealing is performed in a batch annealing furnace. Here, the Ac1 point is calculated by the following formula (2). Ac1=-250C+73Si-66Mn-115Ni+35Cr+60Mo-18Cu+620Ti+750Al-280N+410... (2) In the formula, each element symbol represents the mass % of each element. The hot-rolled annealed sheet obtained in the softening step may be pickled as needed.

[0044] After the softening step, the hot-rolled annealed sheet, which has been pickled as necessary, is subjected to a cold rolling step, whereby a cold-rolled sheet can be obtained. The conditions for cold rolling are not particularly limited and may be adjusted appropriately depending on the required cold-rolled sheet.

[0045] After the cold rolling step, the cold-rolled sheet is subjected to an annealing step in which the cold-rolled sheet is heated at a temperature rising rate of 50°C / sec or more, preferably 100°C / sec or more, in a temperature range from 100°C to the Ac1 point to (Ac1 point - 50°C). The annealing can be started when the cold-rolled sheet is in a temperature range of room temperature (25°C) or more and less than 100°C. By performing this annealing step, a cold-rolled annealed sheet can be obtained. Furthermore, by performing the annealing step under these conditions, coarsening of carbides is suppressed, making it possible to stably control the average grain size of the carbides and the number of carbides with a size of 10 μm or more within the above ranges.

[0046] The martensitic stainless steel material according to the embodiment of the present invention manufactured as described above has the number of carbides having a size of 10 μm or more and the average grain size of the carbides controlled within a predetermined range in addition to the steel composition, and therefore has good workability, high hardness and corrosion resistance after quenching or quench-tempering, and can suppress the occurrence of irregular patterns. [Example]

[0047] The present invention will be described in detail below with reference to examples, but the present invention should not be construed as being limited to these examples.

[0048] Steel having the steel composition shown in Table 1 was melted and cast into a 200 mm thick slab. This slab was heat treated at the temperature and time shown in Table 2, and then hot rolled (rough rolling and finish rolling) to obtain a hot-rolled sheet having a thickness of 3 mm, which was then coiled at a coiling temperature of 850°C. Next, this coiled hot-rolled sheet 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 sheet obtained in the softening process was cold-rolled, and then the cold-rolled sheet was heated at 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. Note that annealing was started when the cold-rolled sheet was at room temperature (25°C). Thereafter, pickling was performed. The obtained cold-rolled annealed sheet (martensitic stainless steel material) was evaluated as follows.

[0049] [Table 1]

[0050] [Table 2]

[0051] (hardness) The obtained cold-rolled annealed sheets were heated to 1000 to 1100°C and quenched, then the surface was polished with #80 sandpaper, and the JIS surface hardness (quenched hardness) was measured using a Vickers hardness tester. The measurement temperature was room temperature (25°C). A hardness of 500 HV or more was considered acceptable.

[0052] (corrosion resistance) The obtained cold-rolled annealed sheets were heated to 1000 to 1100°C and quenched, then the surface was polished with a #600 grit, and a salt spray test was performed for 24 hours in accordance with JIS Z2371:2015 "Salt Spray Test Method" to measure the rust area ratio. In this evaluation, a rust area ratio of less than 10% was rated as pass (◯), and a rust area ratio of 10% or more was rated as fail (×).

[0053] (average particle size of carbide) Cross sections of the resulting cold-rolled and annealed sheets parallel to the rolling and thickness directions were observed using an SEM. The circle-equivalent diameters (μm) of all carbide particles observed within the observation field were measured, excluding those with a circle-equivalent diameter of less than 0.10 μm and those partially extending beyond the observation field. The average carbide particle size (μm) was determined by dividing the sum of the circle-equivalent diameters of the measured carbide particles by the total number of measured carbide particles. The total number of measured carbide particles was set to 100 or more, using multiple randomly selected, non-overlapping observation fields. The circle-equivalent diameters of the carbide particles were calculated from the area of ​​the carbide particles obtained by image processing of the SEM images using image processing software.

[0054] (Number of carbides with a size of 10 μm or more) A cross section of the obtained cold-rolled annealed sheet parallel to the rolling direction and the sheet thickness direction was visually observed at 20 locations in a 50 mm x 50 mm area using an optical microscope at 50x magnification to determine the average number of defects, and the number was calculated by dividing the average number by the area of ​​the observed area.

[0055] (processability) The resulting cold-rolled annealed sheet was punched into the shape of a blade to obtain steel material, which was then heated to 1000-1100°C and quenched. Next, the surface of the steel material was polished, and one end face in the longitudinal direction was wet polished to sharpen the blade, obtaining a test material (blade). Materials that did not suffer from chipping during this sharpening process were evaluated as passing (◯), and materials that suffered from chipping were evaluated as failing (×).

[0056] (irregular pattern) Test pieces (knives) were obtained in the same manner as for workability. The appearance of these test pieces was visually observed, and those that did not have irregular patterns on the blade surface were rated as passing (◯), and those that had irregular patterns on the blade surface were rated as failing (×). The results of the above evaluations are shown in Table 3.

[0057] [Table 3]

[0058] As shown in Table 3, the cold-rolled annealed sheets (martensitic stainless steel materials) of Examples 1 to 23 had good hardness and corrosion resistance after quenching. Furthermore, these cold-rolled annealed sheets had small average carbide grain sizes and few carbides with sizes of 10 μm or more, so no chipping occurred during sharpening, and workability was good, while the occurrence of irregular patterns on the blade surface was also suppressed. In contrast, the cold-rolled annealed steel sheets of Comparative Examples 1 to 14 were outside the specified ranges for the steel composition, the average grain size of the carbides, or the number of carbides with a size of 10 μm or more, and therefore had insufficient hardness or corrosion resistance after quenching. In particular, steel sheets with a large average grain size of carbides and a large number of carbides with a size of 10 μm or more suffered from chipping during sharpening, resulting in insufficient workability and irregular patterns on the blade surface.

[0059] Here, a graph showing the relationship between 2.5C+N and hardness in the above-mentioned Examples and Comparative Examples is shown in Figure 1. As shown in Figure 1, there is a proportional relationship between 2.5C+N and hardness, and it was found that increasing 2.5C+N tends to increase hardness. In particular, it was found that by controlling 2.5C+N to 1.10% or more, it is possible to achieve hardness of 500HV or more.

[0060] As can be seen from the above results, the present invention can provide a martensitic stainless steel material and a manufacturing method thereof that has good workability, high hardness and corrosion resistance after quenching or quench-tempering, and can suppress the occurrence of irregular patterns.

Claims

1. The composition contains, on a mass basis, C: 0.30 to 0.60%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.030% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, and O: 0.001 to 0.010%, with 2.5C+N being 1.10% or more and the balance being Fe and impurities; The average particle size of the carbide is 0.50 μm or less, The carbides having a size of 10 μm or more are 0.20 pieces / cm 2 The martensitic stainless steel material is as follows:

2. The martensitic stainless steel material according to claim 1, further comprising, 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.

3. A martensitic stainless steel material according to claim 1 or 2, having a hardness of 500 HV or more after quenching at 1000 to 1100°C, or after quenching at 1000 to 1100°C and tempering at 100 to 400°C.

4. The martensitic stainless steel material according to any one of claims 1 to 3, wherein the martensitic stainless steel material is for use in cutlery.

5. A method for producing the martensitic stainless steel material according to claim 1, comprising: A slab containing, on a mass basis, C: 0.30 to 0.60%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.030% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, wherein 2.5C + N is 1.10% or more, and the balance is Fe and impurities, and the slab has a composition represented by formula (1): T[℃]=6500 / (4-log C[%])-273... (1) The method includes a hot rolling step of performing a heat treatment at a temperature equal to or higher than T for 1 to 5 hours, followed by hot rolling.

6. A method for producing the martensitic stainless steel material according to claim 2, comprising: By mass, C: 0.30 to 0.60%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.030% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.003 0%, O: 0.001 to 0.010%, and further containing 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, and 2.5C+N is 1.10% or more, and the balance is Fe and impurities, and a slab having a composition represented by formula (1): T[℃]=6500 / (4-log C[%])-273... (1) The method includes a hot rolling step of performing a heat treatment at a temperature equal to or higher than T for 1 to 5 hours, followed by hot rolling.

7. 7. The method according to claim 5 or 6, further comprising a softening step of annealing the hot-rolled sheet at a temperature of Ac1 point to (Ac1 point - 50°C) for 1 to 5 hours after coiling the hot-rolled sheet at a coiling temperature of 800 ° C to 900 ° C in the hot rolling step.

8. a cold rolling step of cold rolling the hot-rolled annealed sheet obtained in the softening step; An annealing process in which the cold-rolled sheet obtained in the cold rolling process is heated at a temperature rising rate of 50 ° C. / second or more in a temperature range from 100 ° C. to Ac1 point to (Ac1 point - 50 ° C.); The method of claim 7 further comprising:

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