Martensitic stainless steel material and method for producing same, and quenching or quenching and tempering material of martensitic stainless steel

Abstract

To provide a martensitic stainless steel material which, after quenching or quenching and tempering, has high hardness and corrosion resistance, excellent wear resistance, and can suppress the occurrence of irregular patterns.SOLUTION: A martensitic stainless steel material having a composition comprising, in terms of mass, C: 0.305-0.600%, Si: 0.05-1.00%, Mn: 0.10-1.50%, P: 0.0085-0.0400%, S: 0.0300% or less, Cr: 13.0-18.0%, Ni: 0.01-0.30%, Mo: 0.01-1.00%, Al: 0.300% or less, N: 0.010-0.350%, Ca: 0.0001-0.0030%, and O: 0.001-0.010%, the balance being Fe and impurities, wherein 2.5C+N (where C and N are the contents of C and N, respectively) is 0.85% or more. In a cross section of the martensitic stainless steel material, the average grain diameter of carbide is more than 0.50 μm and 2.00 μm or less, the number of carbides having a size of 10 μm or more is 0.20 / cm2 or less, and the area ratio of carbide is 15.0-20.0%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a martensitic stainless steel material, a method for producing the same, and a quenched or quenched and tempered martensitic stainless steel material. [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, a high C content can easily form carbides with alloying elements such as Cr, resulting in the precipitation of coarse eutectic carbides during the manufacturing process. These eutectic carbides are difficult to completely dissolve, even through annealing, and the amount of C dissolved in the material decreases during quenching or quench-tempering, resulting in excessive softening. These eutectic carbides also act as corrosion initiation sites, reducing corrosion resistance and causing chipping and the formation of irregular streak-like or island-like patterns during machining. Furthermore, because C is a strong austenite-stabilizing element, if a large amount of retained austenite remains after quenching or quench-tempering due to C segregation, this can lead to reduced hardness, poor sharpness, and the formation of irregular streak-like or island-like patterns.

[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.

[0005] Patent Document 4 also describes a method for producing a stainless steel sheet having a thickness of 0.1 mm or less, which has a composition of, by mass, 0.25 to 0.45% C, 1.0% or less Si, 0.1 to 1.5% Mn, 12.0 to 15.0% Cr, 0.5 to 3.0% Mo, 0.30 to 0.45% N, and the balance being Fe and impurities, and which is subjected to a heat treatment in which the sheet is heated in a nitrogen atmosphere to a temperature exceeding 1000°C for 1 to 10 minutes and then cooled, thereby reducing the number density of carbides having a circle equivalent diameter of 0.5 μm or more to 0 to 50 / 1000 μm. 2 A method for manufacturing a martensitic stainless steel material (martensitic stainless steel sheet) with controlled hardness has been proposed. It is described that the martensitic stainless steel material manufactured by this method can obtain high hardness from the surface to the center of the sheet thickness when quenched and tempered, and also has good corrosion resistance.

[0006] Furthermore, Patent Document 5 discloses a method for manufacturing a hot-rolled steel sheet, which includes a first step of holding a steel slab having a composition containing, by mass%, C: 0.45 to 0.60%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, P: 0.05% or less, S: 0.020% or less, Cr: 13.0% or more but less than 16.0%, Ni: 0.10 to 1.00%, and N: 0.010 to 0.200%, with the balance being Fe and unavoidable impurities, at 1200 to 1350°C for 30 minutes or more; A method for producing a martensitic stainless steel material (stainless steel sheet) has been proposed, which includes a second step of coiling the steel sheet and a third step of annealing the hot-rolled steel sheet to produce a hot-rolled annealed steel sheet, wherein the hot rolling in the second step includes three or more rolling passes with an end temperature of 1050°C or higher and a reduction of 20% or higher, the coiling temperature of the hot-rolled steel sheet is 600°C or higher, and the holding temperature in the hot-rolled sheet annealing in the third step is 750 to 900°C, and the holding time is 10 minutes or longer.The martensitic stainless steel material produced by this method is described as having high hardness and good surface quality.

[0007] However, the martensitic stainless steel material described in Patent Document 2 may develop irregular patterns because the average grain size of inclusions (particularly carbides) is not controlled. 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. In addition, this martensitic stainless steel material contains a large amount of Mo, which makes it expensive. The martensitic stainless steel material described in Patent Document 4 is expensive because it is subjected to a nitrogen absorption treatment in which heat treatment is performed in a nitrogen atmosphere to increase nitrogen and dissolve coarse carbides. The martensitic stainless steel material described in Patent Document 5 dissolves coarse carbides by heating the steel slab at high temperatures of 1200 to 1350°C, but this heating alone cannot suppress the segregation of C, which causes the coarse carbides. As a result, the reprecipitation of coarse carbides and the generation and softening of retained austenite due to the segregation of C occur, leading to a decrease in hardness and the occurrence of irregular patterns. Furthermore, heating the slab at an excessively high temperature is likely to cause deformation of the slab due to its own weight.

[0008] Furthermore, blades such as kitchen knives are required to have a long lifespan (durability of the sharpness) in addition to sharpness. The sharpness of a blade depends on the hardness of the material, and the lifespan depends on the hardness and wear resistance of the material. The martensitic stainless steel materials described in Patent Documents 2 to 5 do not particularly address the issue of blade lifespan, and there is no mention of any means for improving it.

[0009] On the other hand, Patent Document 6 proposes a martensitic stainless steel material for cutlery that can maintain a long service life, characterized in that it contains, by mass%, one or more of C: 0.50 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, P: 0.008% or less, S: 0.010% or less, Cr: 13.00 to 18.00%, Ni: 0.01 to 1.20%, Mo: 0.01 to 1.20%, and V: 0.01 to 1.20%, with the balance being Fe and unavoidable impurities. By reducing the P content of the martensitic stainless steel material to 0.008% or less, the service life of cutlery can be maintained long. [Prior art documents] [Patent documents]

[0010] [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 [Patent Document 4] International Publication No. 2019 / 146743 [Patent Document 5] International Publication No. 2021 / 220754 [Patent Document 6] Japanese Patent Publication No. 2020-45511 Summary of the Invention [Problem to be solved by the invention]

[0011] The martensitic stainless steel material described in Patent Document 6 is expensive because it requires the use of special raw materials with an extremely low P content in order to reduce the P content to 0.008% or less. Furthermore, this martensitic stainless steel material does not particularly address the issue of irregular patterns.

[0012] The present invention has been made to solve the above-mentioned problems, and aims to provide a martensitic stainless steel material that has high hardness and corrosion resistance after quenching or quench-tempering, excellent wear resistance, and can suppress the occurrence of irregular patterns, and a method for manufacturing the same. Another object of the present invention is to provide a quenched or quenched and tempered martensitic stainless steel material that has high hardness and corrosion resistance, excellent wear resistance, and is capable of suppressing the occurrence of irregular patterns. [Means for solving the problem]

[0013] As a result of extensive research into martensitic stainless steel materials, the inventors have discovered that while carbides in martensitic stainless steel materials cause a decrease in corrosion resistance and hardenability (hardness) and the occurrence of irregular patterns, they also contribute to improving wear resistance. They have also discovered that all of the above problems can be solved by controlling the average grain size of the carbides, the number of carbides with a size of 10 μm or more, and the area ratio of the carbides, in addition to the composition of the martensitic stainless steel material, and have thus completed the present invention.

[0014] That is, the present invention provides a martensitic stainless steel material having a composition containing, by mass, C: 0.305 to 0.600%, Si: 0.05 to 1.00%, Mn: 0.10 to 1.50%, P: 0.0085 to 0.0400%, S: 0.0300% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.300% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, the balance being Fe and impurities, and 2.5C+N (C and N are the contents of C and N) is 0.85% or more, In the cross section of the martensitic stainless steel material, the average grain size of the carbides is more than 0.50 μm and not more than 2.00 μm, and the number of the carbides having a size of 10 μm or more is 0.20 / cm 2 The following relates to a martensitic stainless steel material in which the area ratio of the carbides is 15.0 to 20.0%.

[0015] The present invention also provides a quenched or quenched and tempered martensitic stainless steel material having a composition, by mass, containing C: 0.305 to 0.600%, Si: 0.05 to 1.00%, Mn: 0.10 to 1.50%, P: 0.0085 to 0.0400%, S: 0.0300% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.300% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, the balance being Fe and impurities, and having 2.5C+N (C and N are the contents of C and N) of 0.85% or more, The present invention relates to a quenched or quenched and tempered martensitic stainless steel material, in which, in a cross section of the quenched or quenched and tempered material, the average grain size of the carbides is 0.10 to 0.50 μm, the area ratio of the carbides is 2.0 to 15.0%, and the area ratio of retained austenite is 15.0% or less.

[0016] Furthermore, the present invention provides a breakdown rolling process for obtaining a breakdown material by rough rolling a slab having a composition, by mass, containing 0.305 to 0.600% C, 0.05 to 1.00% Si, 0.10 to 1.50% Mn, 0.0085 to 0.0400% P, 0.0300% or less S, 13.0 to 18.0% Cr, 0.01 to 0.30% Ni, 0.01 to 1.00% Mo, 0.300% or less Al, 0.010 to 0.350% N, 0.0001 to 0.0030% Ca, and 0.001 to 0.010% O, with the balance being Fe and impurities, and having a 2.5C+N content of 0.85% or more, wherein C and N are the contents of C and N, respectively; a hot rolling step of hot rolling the breakdown material to obtain a hot rolled material; A softening process in which the hot-rolled material is heated at a temperature above the Ac1 point (Ac1 point + 100 ° C.) for 2 to 10 hours and then cooled at a cooling rate of 0.100 ° C. / second or less; The present invention relates to a method for producing a martensitic stainless steel material, including: [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a martensitic stainless steel material that has high hardness and corrosion resistance after quenching or quench-tempering, has excellent wear resistance, and is capable of suppressing the occurrence of irregular patterns, and a method for manufacturing the same. Furthermore, according to the present invention, it is possible to provide a quenched or quenched and tempered martensitic stainless steel material that has high hardness and corrosion resistance, excellent wear resistance, and is capable of suppressing the occurrence of irregular patterns. DETAILED DESCRIPTION OF THE INVENTION

[0018] 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.

[0019] (1. Martensitic stainless steel) A martensitic stainless steel material according to an embodiment of the present invention has a composition containing C: 0.305-0.600%, Si: 0.05-1.00%, Mn: 0.10-1.50%, P: 0.0085-0.0400%, S: 0.0300% or less, Cr: 13.0-18.0%, Ni: 0.01-0.30%, Mo: 0.01-1.00%, Al: 0.300% or less, N: 0.010-0.350%, Ca: 0.0001-0.0030%, O: 0.001-0.010%, the balance being Fe and impurities, and 2.5C+N (C and N are the contents of C and N) being 0.85% or more.

[0020] 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.

[0021] In addition, the martensitic stainless steel material according to an embodiment of the present invention may further contain one or more elements selected from Ti: 0.30% or less, Nb: 0.50% or less, Cu: 4.0% or less, B: 0.005% or less, V: 0.50% or less, Sn: 0.10% or less, and Co: 0.30% or less. Each component will be described in detail below.

[0022] <C:0.305~0.600%> Carbon (C) is an essential element for obtaining a predetermined hardness (Vickers hardness) after quenching or quench-tempering. In particular, to consistently obtain a hardness of 500 HV or more, the C content must be 0.305% or more. Excessive addition of C promotes sensitization during quenching, impairing corrosion resistance, and also reduces toughness after quenching or quench-tempering due to undissolved carbonitrides. Therefore, the C content must be 0.600% 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 0.320% or more, more preferably 0.330% or more, and the upper limit is preferably 0.590% or less, more preferably 0.580% or less.

[0023] <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. A low Si content can lead to insufficient deoxidation, resulting in an increase in carbides, which can become the starting point for rusting, thereby reducing 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% or more, more preferably 0.10% or more, and the upper limit is preferably 0.98% or less, more preferably 0.90% or less.

[0024] <Mn:0.10~1.50%> Mn is an element added as a deoxidizer and contributes to improving hardenability by expanding the austenite single-phase temperature range. 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-depleted layer forms around them, making it easier to become the starting point of rusting and reducing corrosion resistance. Therefore, it is necessary to set the content of Mn to 0.10% or more. From the viewpoint of stably obtaining the above effects of Mn, the content of Mn is preferably 0.15% or more, more preferably 0.20% or more. On the other hand, excessive Mn reduces corrosion resistance, promotes the formation of oxidation scale during quenching, increases the subsequent polishing load, etc., and in addition, the amount of retained austenite may increase. Therefore, it is necessary to set the content of Mn to 1.50% or less. Considering the reduction of corrosion resistance caused by particulate matter such as MnS, the content of Mn is preferably 1.30% or less, more preferably 1.00% or less.

[0025] <P: 0.0085~0.0400%> P is an element contained as an impurity in main raw materials such as hot metal and ferrochrome. Also, P is an element harmful to the toughness and corrosion resistance of the material after quenching or quenching and tempering. Therefore, it is necessary to set the content of P to 0.0400% or less, preferably 0.0380% or less, more preferably 0.0350% or less. On the other hand, excessive reduction of P causes problems such as the use of high-purity raw materials being essential, leading to an increase in cost. Therefore, the content of P is 0.0085% or more, preferably 0.0090% or more, more preferably 0.0100% or more.

[0026] <S: 0.0300% or less> S forms sulfide-based inclusions, which deteriorate the general corrosion resistance (general corrosion and pitting corrosion) of steel materials. S also reduces hot workability and increases the susceptibility of hot-rolled sheets to edge cracking. Therefore, the S content must be 0.0300% or less, preferably 0.0200% or less, and more preferably 0.0150% or less. While there are no particular restrictions on the lower limit of the S content, the lower the S content, the better the corrosion resistance becomes, but the greater the desulfurization load and the higher the manufacturing costs become. Therefore, the lower limit of the S content is preferably 0.0001% or more.

[0027] <Cr:13.0~18.0%> Cr is an element that maintains the corrosion resistance required for martensitic stainless steel materials. Therefore, the Cr content must be 13.0% or more. On the other hand, Cr easily forms carbides, and adding a large amount of Cr not only causes the formation of coarse carbides but also increases the amount of retained austenite after quenching or quench-tempering. Therefore, in order to suppress these issues, the Cr content must be 18.0% or less. In order to stably obtain the above effects of Cr, the lower limit of the Cr content is preferably 13.1% or more, more preferably 13.2% or more, and the upper limit is preferably 17.8% or less, more preferably 17.5% or less.

[0028] <Ni:0.01~0.30%> Like Mn, Ni is an austenite-stabilizing element and also has the effect of improving toughness after quenching or quench-tempering. However, a large amount of Ni may cause a decrease in press formability due to solid solution strengthening in hot-rolled annealed steel, may increase the amount of retained austenite after quenching or quench-tempering, and, since Ni is an expensive element, increases manufacturing costs. Therefore, the Ni content must be 0.30% or less. On the other hand, since Ni is an effective element for suppressing the progression of pitting corrosion, the Ni content must be 0.01% or more. To stably obtain the above-mentioned effects of Ni, the lower limit of the Ni content is preferably 0.02% or more, more preferably 0.03% or more, and the upper limit is preferably 0.28% or less, more preferably 0.25% or less.

[0029] <Mo: 0.01 to 1.00%> Mo is an element effective for improving the corrosion resistance of a martensite structure containing δ-ferrite. From the viewpoint of obtaining this effect, it is necessary to set the content of Mo to 0.01% or more. On the other hand, Mo is a stabilizing element of the ferrite phase, and excessive addition will impair the hardening characteristics by narrowing the austenite single-phase temperature range. Therefore, it is necessary to set the content of Mo to 1.00% or less. From the viewpoint of stably obtaining the above effects by Mo, the lower limit of the content of Mo is preferably 0.02% or more, more preferably 0.03% or more, and the upper limit is preferably 0.80% or less, more preferably 0.70% or less.

[0030] <Al: 0.300% or less> Al is added as a deoxidizing element and is also an element for improving oxidation resistance. However, when a large amount of Al is contained, carbides tend to become large. In addition, since Al is a ferrite stabilizing element, it hinders austenite transformation and raises the Ac1 line. Therefore, the content of Al needs to be 0.300% or less, preferably 0.250% or less, more preferably 0.200% or less. On the other hand, the lower limit of the content of Al is not particularly limited, but from the viewpoint of obtaining the above effects by Al, it is preferably 0.001% or more, more preferably 0.002% or more. Here, Al is T.Al.

[0031] <N: 0.010 to 0.350%> Like C, N is an essential element for achieving a predetermined hardness (Vickers hardness) after quenching or quench-tempering. In particular, in the embodiment of the present invention, since the C content is reduced, 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-based nitrides, resulting in a Cr-deficient layer, 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 0.012% or more, more preferably 0.013% or more, and the upper limit is preferably 0.300% or less, more preferably 0.250% or less, and even more preferably 0.150% or less.

[0032] <Ca:0.0001~0.0030%> Ca is added during the steelmaking process to adjust the composition. In particular, Ca acts as a powerful deoxidizer and has the effect of promoting deoxidation. However, because Ca is a powerful deoxidizing element, most of it floats to the surface in the molten steel as inclusions, and very little remains in the steel. However, if a large amount of Ca is added, the steelmaking inclusions contain 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, preferably 0.0029% or less, and more preferably 0.0028% or less. On the other hand, since 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.

[0033] <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 content of O needs to be 0.010% or less. Also, although it is preferable to reduce O as much as possible, excessive reduction will increase the cost. Therefore, the content of O should be 0.001% or more. From the perspective of the balance between cost and corrosion resistance, the lower limit of the content of O is preferably 0.002% or more, and the upper limit is preferably 0.009% or less.

[0034] <2.5C + N: 0.85% 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 present invention, N is contained instead of reducing the content of C, and C contributes 2. : 5 times that of N to the hardness. Therefore, from the perspective of obtaining a predetermined hardness, 2.5C + N should be 0.85% or more, preferably 0.90% or more. Also, if 2.5C + N is excessively increased, the hardness before quenching may become too high, which may lead to a decrease in workability and polishing properties. Therefore, the upper limit of 2.5C + N is preferably 1.60% or less, more preferably 1.50% or less.

[0035] <Ti: 0.30% or less> Ti is an element that forms carbonitrides and suppresses sensitization and corrosion resistance deterioration due to the precipitation of chromium carbonitrides, and is added as needed. However, when Ti is added excessively, coarse TiN is formed, leading to the occurrence of hot rolling defects and a decrease in toughness. Therefore, the content of Ti should be 0.30% or less, preferably 0.25% or less. The lower limit of the content of Ti is not particularly limited, but from the perspective of obtaining the above effects, it is preferably 0.01% or more, more preferably 0.06% or more, and even more preferably 0.10% or more.

[0036] <Nb: 0.50% or less> Nb forms carbonitrides and suppresses sensitization and reduction of corrosion resistance due to precipitation of chromium carbonitrides, and is added as needed. However, if Nb is added in excess, it destabilizes the martensite phase and reduces hardness. Therefore, the content of Nb is 0.50% or less, preferably 0.35% or less, more preferably 0.30% or less, and still more preferably 0.25% or less. The lower limit of the Nb content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01% or more, more preferably 0.05% or more.

[0037] <Cu: 4.0% or less> Cu is effective in improving the corrosion resistance of a martensitic structure containing δ-ferrite and also contributes to improving hardenability as an austenite stabilizing element, and 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 content of Cu is 4.0% or less, preferably 3.8% or less, more preferably 3.5% or less. The lower limit of the Cu content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 1.0% or more, more preferably 1.3% or more, and still more preferably 1.5% or more.

[0038] <B: 0.005% or less> B is an element effective in improving hot workability and is added as needed. However, excessive addition of B may reduce hardenability due to the composite precipitation of borides and carbides. Therefore, the content of B is 0.005% or less, preferably 0.004% 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% or more.

[0039] <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 necessary. However, if V is added in excess, there is a risk of coarsening of precipitates, and as a result, the toughness after quenching or quenching and tempering decreases. Therefore, the content of V is 0.50% or less, preferably 0.30% or less, more preferably 0.20% or less. The lower limit of the content of V is not particularly limited, but V may be mixed as an impurity in the alloy raw material and it may be difficult to remove it in the refining process. Also, from the viewpoint of obtaining the above effects, the lower limit of the content of V is preferably 0.01% or more, more preferably 0.02% or more, and still more preferably 0.03% or more.

[0040] <Sn: 0.10% or less> Sn is an element effective for 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 content of Sn is 0.10% or less, preferably 0.09% or less. The lower limit of the content of Sn is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.002% or more, more preferably 0.05% or more.

[0041] <Co: 0.30% or less> Co is an element that improves heat resistance and is added as necessary. However, since Co is an expensive element, if the content of Co is too high, it will lead to an increase in production cost. Therefore, the content of Co is 0.30% or less, preferably 0.10% or less, more preferably 0.05% or less. The lower limit of the content of Co is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01% or more.

[0042] In the martensitic stainless steel material according to an embodiment of the present invention, the average grain size of the carbides in the cross section is greater than 0.50 μm and not greater than 2.00 μm. By controlling the average grain size of the carbides to be greater than 0.50 μm, wear resistance is improved, and the life (durability of sharpness) of a manufactured blade can be extended. Furthermore, by controlling the average grain size of the carbides to be not greater than 2.00 μm, a decrease in corrosion resistance and the occurrence of irregular patterns can be suppressed. From the viewpoint of stably ensuring these effects, the average grain size of the carbides is preferably 0.55 to 1.80 μm, more preferably 0.60 to 1.50 μm. Here, the carbides for which the average particle size is specified include both eutectic carbides formed during casting and precipitated carbides formed 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.

[0043] 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 in its cross section. 2 Less than or equal to 0.15 particles / cm 2 Less than or equal to 0.10 particles / cm 2 The number of carbides with a size of 10 μm or more is less than 0.00 pieces / cm. Since carbides with a size of 10 μm or more are likely to become the starting point of rusting, 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. Furthermore, since carbides with a size of 10 μm or more can also cause irregular patterns, controlling the number of these carbides can also suppress the occurrence of irregular patterns. The fewer carbides with a size of 10 μm or more, the better, with a minimum of 0.00 pieces / cm. 2 may be. 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.

[0044] In the martensitic stainless steel material according to the embodiment of the present invention, the area ratio of carbides in the cross section is 15.0 to 20.0%, more preferably 15.5 to 19.8%, or 16.0 to 19.5%. By controlling the area ratio of carbides to 15.0% or more, hardness and wear resistance are improved, so that when a blade is manufactured, the initial sharpness can be improved and its life (durability of sharpness) can be extended. Furthermore, by controlling the area ratio of carbides to 20.0% or less, a decrease in corrosion resistance and the occurrence of irregular patterns can be suppressed. Here, the carbides for which the area ratio is specified include both eutectic carbides formed during casting and precipitated carbides formed during the rolling process. The area ratio of carbides can be calculated by observing the cross section of the martensitic stainless steel material with an SEM, measuring the area of ​​each carbide in the observed field, dividing the area by the area of ​​the observed field, and multiplying the result by 100.

[0045] 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.

[0046] The martensitic stainless steel material according to the embodiment of the present invention has high hardness and corrosion resistance after quenching or quench-tempering, excellent wear resistance, and can suppress the occurrence of irregular patterns, and therefore can be used in various applications requiring these properties. Among these, this martensitic stainless steel material is suitable for use in blades. When this martensitic stainless steel material is used in blades, in addition to improving corrosion resistance and suppressing the occurrence of irregular patterns, it is possible to improve the sharpness (initial sharpness) of the blade and extend its lifespan (sharpness durability).

[0047] (2. Manufacturing method of martensitic stainless steel material) The martensitic stainless steel material according to an embodiment of the present invention can be manufactured by a method including a breakdown rolling process, a hot rolling process, and a softening process (hot rolling annealing process) using a slab having the same composition as the above-described martensitic stainless steel material.

[0048] The breakdown rolling process is a process in which the slab is roughly rolled to obtain a breakdown material. The conditions for the breakdown rolling process are not particularly limited. Preferably, the slab is heat-treated at a temperature of 1000°C or higher but lower than 1200°C for 1 to 10 hours, followed by rough rolling under conditions resulting in a total rolling reduction of 30 to 70%. Furthermore, it is preferable to perform the rough rolling in two or more passes. By performing the breakdown rolling process under these conditions, the eutectic carbides formed during casting can be dissolved during the high-temperature heat treatment (holding) of the slab. Furthermore, the rough rolling reduces the width of macrosegregation and promotes carbon diffusion by introducing dislocations extending to the center of the breakdown material, thereby eliminating carbon segregation that occurred during casting. Furthermore, it can also suppress the formation of retained austenite due to a decrease in the Ms point caused by carbon segregation. As a result, the average particle size of carbides, the number of carbides with a size of 10 μm or higher, and the area ratio of carbides can be easily controlled within the above-mentioned ranges. These effects can be effectively achieved by combining the subsequent hot rolling process and a soaking treatment process, which is performed as needed.

[0049] If the heat treatment time in the breakdown rolling step is less than 1 hour or the heat treatment temperature is less than 1000°C, it may be difficult to obtain the effects of solution of eutectic carbides and reduction of carbon segregation. Also, if the heat treatment time in the breakdown rolling step exceeds 10 hours or the heat treatment temperature is 1200°C or higher, sagging deformation occurs due to the weight of the slab, making it difficult to carry out subsequent steps. Furthermore, if the total rolling ratio in the breakdown rolling step is less than 30%, the introduction of dislocations is insufficient and the width of macrosegregation is difficult to reduce, so that the effects of solution of eutectic carbides and reduction of carbon segregation may not be sufficiently obtained.Also, if the total rolling ratio in the breakdown rolling step exceeds 70%, the rolling ratio in the subsequent hot rolling may be insufficient.

[0050] The hot rolling step is a step in which the breakdown material is hot rolled to obtain a hot rolled material. The conditions for hot rolling are not particularly limited, but it is preferable to perform hot rolling after heat treatment of the breakdown material at a temperature of 1000 to 1200°C for 1 to 5 hours. By performing heat treatment under such conditions, the eutectic carbides formed during casting can be completely dissolved, making it easier to control the average grain size of the carbides, the number of carbides with a size of 10 µm or more, and the area ratio of the carbides within the above ranges. The hot rolling conditions are not particularly limited, but it is preferable to finish the sheet to a thickness of 2 to 8 mm.

[0051] If the heat treatment time in the hot rolling step is less than 1 hour or the heat treatment temperature is less than 1000°C, the effects of solution of eutectic carbides and reduction of carbon segregation may not be sufficiently obtained. Also, if the heat treatment time in the hot rolling step exceeds 5 hours or the heat treatment temperature is 1200°C or higher, sagging deformation may occur due to the weight of the breakdown material, making it difficult to carry out subsequent steps. From the viewpoint of stably ensuring the above effects, the heat treatment time in the hot rolling step is preferably 1.5 to 3 hours.

[0052] The softening process (hot rolling annealing process) is a process in which the hot rolled material is heated at a temperature above the Ac1 point (Ac1 point + 100°C) or lower for 2 to 10 hours, and then cooled at a cooling rate of 0.100°C / second or lower. By heating at a temperature above the Ac1 point (Ac1 point + 100°C) for 2 to 10 hours, the martensite structure is transformed into austenite, and carbides can be dispersed in the austenite phase. Furthermore, when heating above the Ac1 point, the austenite phase that normally forms during heating transforms into martensite and hardens. However, by controlling the cooling rate to 0.100°C / sec or less, the austenite phase is decomposed into a soft ferrite phase and carbides, and softening can be achieved while precipitating a large amount of carbides that are of a certain amount and size.

[0053] The softening step is preferably carried out in a batch annealing furnace after the hot-rolled material has been coiled. That is, the coiled hot-rolled sheet is preferably placed in the batch annealing furnace and heated at a temperature above the Ac1 point (Ac1 point + 100°C) for 2 to 10 hours. Here, the Ac1 point is calculated by the following formula (1). Ac1=-250C+73Si-66Mn-115Ni+35Cr+60Mo-18Cu+620Ti+750Al-280N+410... (1) In the formula, each element symbol represents the mass % of each element. The softened material obtained in the softening step may be pickled as needed.

[0054] A soaking treatment step may be carried out between the breakdown rolling step and the hot rolling step, if necessary. The soaking treatment step is a step in which the breakdown material is held at a temperature of 1000 to 1200° C. for 1 to 48 hours. By carrying out the soaking treatment step under such conditions, it is possible to enhance the effects of solution of eutectic carbides and reduction of carbon segregation.

[0055] If the heat treatment time in the soaking step is less than 1 hour or the heat treatment temperature is less than 1000°C, the effects of solutionizing the eutectic carbide and reducing carbon segregation will not be sufficiently achieved. Furthermore, if the heat treatment time in the soaking step exceeds 48 hours or the heat treatment temperature exceeds 1200°C, sagging deformation will occur due to the weight of the breakdown material, making it difficult to carry out subsequent steps. To stably ensure the above effects, the heat treatment time in the soaking step is preferably 3 to 30 hours, more preferably 3 to 24 hours.

[0056] After the softening step, a cold rolling step and an annealing step may be carried out as necessary. The cold rolling step is a step in which the softened material obtained in the softening step is cold rolled to obtain a cold-rolled material. The conditions for cold rolling are not particularly limited and may be adjusted appropriately depending on the required cold rolled material.

[0057] The annealing step is a step of heating the cold-rolled material to a temperature equal to or lower than the Ac1 point. By carrying out this annealing step, a cold-rolled annealed material can be obtained. The lower limit of the heating temperature is not particularly limited, but is preferably (Ac1 point - 50°C). Annealing of the cold-rolled material may be started at a temperature of 25 to 100°C. By performing the annealing process under the above conditions, coarsening of carbides is suppressed, and it becomes possible to stably control the average particle size of the carbides, the number of carbides with a size of 10 μm or more, and the area ratio of the carbides within the above ranges.

[0058] (3. Quenched or quenched and tempered martensitic stainless steel) The quenched or quenched-tempered martensitic stainless steel material according to an embodiment of the present invention (hereinafter abbreviated as "quenched or quenched-tempered material") is obtained by quenching or quenching-tempering the above-mentioned martensitic stainless steel material. The conditions for quenching are not particularly limited, but quenching is preferably carried out at 1000 to 1200° C. The conditions for tempering are also not particularly limited, but quenching is preferably carried out at 100 to 400° C. After quenching, sub-zero treatment is preferably carried out at -200 to -50° C. The quenched or quenched and tempered material according to the embodiment of the present invention has the same composition as the martensitic stainless steel material described above, and therefore, a description of the composition will be omitted.

[0059] In the quenched or quenched and tempered material according to the embodiment of the present invention, the average grain size of the carbide is 0.10 to 0.50 μm in its cross section. By controlling the average grain size of the carbide to 0.10 μm or more, wear resistance is improved, and the life (durability of sharpness) of the blade when manufactured can be extended. Furthermore, by controlling the average grain size of the carbide to 0.50 μm or less, a decrease in corrosion resistance and the occurrence of irregular patterns can be suppressed. From the viewpoint of stably ensuring these effects, the average grain size of the carbide is preferably 0.11 to 0.49 μm, more preferably 0.11 to 0.48 μm. The average particle size of carbides can be calculated by observing the cross section of a quenched or quenched and tempered material by SEM, measuring the circle equivalent diameter of each carbide in the observed field of view, and finding the average value.

[0060] In the quenched or quenched and tempered material according to the embodiment of the present invention, the area ratio of carbides in the cross section is 2.0 to 15.0%, more preferably 2.5 to 14.5%, or 3.0 to 14.0%. By controlling the carbide area ratio to 2.0% or more, hardness and wear resistance are improved, so that when a blade is manufactured, the initial sharpness can be improved and its life (sharpness durability) can be extended. Furthermore, by controlling the carbide area ratio to 15.0% or less, a decrease in corrosion resistance and the occurrence of irregular patterns can be suppressed. The area ratio of carbides can be calculated by observing the cross section of a quenched or quenched and tempered material with an SEM, measuring the area of ​​each carbide in the observed field, dividing the result by the area of ​​the observed field, and multiplying the result by 100.

[0061] In the quenched or quenched and tempered material according to the embodiment of the present invention, the area ratio of retained austenite in its cross section is 15.0% or less, preferably 14.5% or less, and more preferably 14.0% or less. Retained austenite occurs when austenite generated during quenching remains without transforming into martensite during subsequent treatments (e.g., subzero treatment, tempering treatment). Retained austenite is particularly likely to occur in areas where carbon, a strong austenite-stabilizing element, is segregated. Because retained austenite is softer than martensite, the desired hardness cannot be obtained if a large amount is present. The area ratio of retained austenite is not particularly limited since the smaller the better, but it is typically 1.0% or more, and preferably 1.5% or more.

[0062] Because carbon segregation occurs primarily as center segregation during casting, retained austenite is often produced in large quantities in the center of the thickness direction of quenched or quenched and tempered material. Since the center of the thickness direction of such quenched or quenched and tempered material becomes the cutting edge when blades are formed, the presence of soft retained austenite at the cutting edge can cause chipping or a deterioration in the sharpness of the blade.

[0063] The area fraction of retained austenite can be calculated as follows. First, a cross section of a quenched or quenched and tempered material is observed using EBSD to distinguish between the BCC and FCC crystal structure phases and determine their respective areas. Next, based on these areas, the ratio of the area of ​​the FCC crystal structure phase to the total area of ​​the BCC and FCC crystal structure phases (i.e., the area fraction of the FCC crystal structure phase) is calculated. The area fraction of the FCC crystal structure phase calculated in this way is taken as the area fraction of retained austenite.

[0064] In the central carbon segregation portion described above, coarse carbides are likely to be generated in rows, which causes irregular patterns (striped patterns or island patterns). Therefore, reducing the central segregation is also effective in reducing these irregular patterns.

[0065] The quenched or quenched and tempered material according to the embodiment of the present invention preferably has a Vickers hardness of 500 to 900 HV, more preferably 520 to 850 HV, and even more preferably 540 to 800 HV. A Vickers hardness within this range can ensure the strength and initial sharpness particularly required for blades. In this specification, the Vickers hardness refers to a value measured at room temperature (25° C.) using a Vickers hardness tester.

[0066] The quenched or quenched and tempered material according to the embodiment of the present invention has a specific wear rate of preferably 0.0020 mm 3 / N·m or less, preferably 0.0019mm 3 If the wear rate is within this range, wear resistance, particularly durability of the sharpness required for blades, can be ensured. In this specification, the specific wear rate means a rate determined by a pin-on-disk friction and wear test described in the examples below.

[0067] The quenched or quenched and tempered material according to the embodiment of the present invention has high hardness and corrosion resistance, excellent wear resistance, and can suppress the occurrence of irregular patterns, and can therefore be used in a variety of applications requiring these properties. Among these, this quenched or quenched and tempered material is particularly suitable for use in blades. When this quenched or quenched and tempered material is used in blades, in addition to improving corrosion resistance and suppressing the occurrence of irregular patterns, it is possible to improve the blade's sharpness (initial sharpness) and extend its lifespan (sharpness durability).

[0068] (4. Manufacturing method of blades)

[0069] The method for manufacturing a blade according to an embodiment of the present invention includes a quenching step in which the martensitic stainless steel material is worked into a predetermined shape, then heated at a temperature of 1000 to 1200°C for 5 to 60 minutes, and cooled at a cooling rate of 3°C / sec or more, preferably 10°C / sec or more, and more preferably 20°C / sec or more. By performing the quenching process under the above conditions, precipitates such as carbides and nitrides are sufficiently dissolved, increasing the amounts of solute C and N, making it possible to obtain high hardness. Furthermore, by controlling the cooling rate within the above range, it is possible to suppress the reprecipitation of Cr carbonitrides during the quenching process, suppress sensitization, and obtain high corrosion resistance.

[0070] The method for processing the martensitic stainless steel material is not particularly limited, and known methods such as forging and polishing can be used. After the quenching step, a tempering step and a sub-zero treatment step can be carried out as necessary. The tempering step is preferably carried out at a temperature of 100 to 400°C, and the sub-zero treatment step is preferably carried out at a temperature of -200 to -50°C.

[0071] The blades manufactured by the above manufacturing method can improve corrosion resistance and prevent the occurrence of irregular patterns, as well as improve the sharpness (initial sharpness) of the blades and extend their lifespan (durability of sharpness). [Example]

[0072] 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.

[0073] (Examples 1 to 21 and Comparative Examples 1 to 16) Steels having the compositions shown in Table 1 were melted and cast into 200 mm thick slabs. These slabs were subjected to a breakdown rolling step, a hot rolling step, a softening step, a cold rolling step, and an annealing step in this order. The conditions for the breakdown rolling step, the hot rolling step, the softening step, and the annealing step are shown in Table 2. In Example 20, a soaking treatment step was further carried out between the breakdown rolling step and the hot rolling step. In Comparative Example 14, the breakdown rolling step was not carried out. In the breakdown rolling process, the total rolling ratio was set to 40%. In the hot rolling process, the final product was a hot-rolled sheet with a thickness of 3 mm. In the softening step, the hot-rolled sheet obtained in the hot rolling step was wound into a coil, and then this coiled hot-rolled sheet was transferred to a batch annealing furnace, where the softening step was carried out under the conditions shown in Table 2. In the cold rolling step, the softened plate obtained in the softening step was cold rolled to a thickness of 2.0 mm. After the annealing process, pickling was carried out.

[0074] The cold-rolled annealed sheets (martensitic stainless steel materials) obtained as described above were evaluated as follows. Note that, for Comparative Example 16, quenching occurred during the cooling in the softening step, and as a result, cold rolling was not possible, making it unmanufacturable. Therefore, the following evaluations could not be performed.

[0075] [Table 1]

[0076] [Table 2]

[0077] (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 × 50 mm area using an optical microscope at 50x magnification to determine the average number of carbides, and the average number was calculated by dividing the number by the area of ​​the observed area.

[0078] (Average particle size and area ratio of carbide particles) Cross sections of the resulting cold-rolled annealed sheets parallel to the rolling direction and thickness direction were observed using an SEM. The equivalent circle diameters (μm) of all carbides observed within the observation field were measured, excluding those with equivalent circle diameters of less than 0.10 μm and those with portions of the particles extending beyond the observation field. The average particle size (μm) of the carbides was determined by dividing the sum of the equivalent circle diameters of the carbides measured by the total number of carbides measured. The total number of carbides measured was 100 or more, using multiple randomly selected, non-overlapping observation fields. The equivalent circle diameters of the carbides were calculated from the area of ​​the carbides obtained by image processing the SEM images using image processing software. The area ratio of carbides was determined by measuring the area of ​​the carbides in the above observation, dividing the area by the area of ​​the observation field, and multiplying the result by 100.

[0079] The evaluation results are shown in Table 3.

[0080] [Table 3]

[0081] As shown in Table 3, the cold-rolled annealed sheets (martensitic stainless steel materials) of Examples 1 to 21 had the specified composition, and the average grain size of carbides, carbides with a size of 10 μm or more, and carbide area ratio were controlled within the specified ranges. In contrast, the cold-rolled annealed sheets (martensitic stainless steel materials) of Comparative Examples 4, 7, and 11 to 12 were able to control the average grain size of carbides, carbides with a size of 10 μm or more, and carbide area ratio within the specified ranges, but did not have the specified composition. Furthermore, the cold-rolled annealed sheets (martensitic stainless steel materials) of Comparative Examples 1 to 3, 5, 6, and 8 to 10 did not have the specified composition, and in addition, one or more of the average particle size of carbides, the number of carbides with a size of 10 μm or more, and the area ratio of carbides could not be controlled within the specified range. Furthermore, although the cold-rolled annealed sheets (martensitic stainless steel materials) of Comparative Examples 13 to 15 had the specified composition, the manufacturing conditions were not appropriate, and therefore it was not possible to control one or more of the average particle size of carbides, the number of carbides with a size of 10 μm or more, and the area ratio of carbides within the specified range.

[0082] Next, the cold-rolled annealed sheet was quenched by heating at 1050°C for 10 minutes and air-cooling (cooling rate of 3°C / sec or more), and then tempered by heating at 200°C for 30 minutes to obtain a quenched and tempered sheet. Furthermore, to evaluate it as a blade, the cold-rolled annealed sheet was punched out, polished, and processed into a blade shape, and then quenched and tempered in the same manner as above. The portion that would become the cutting edge was then roughly polished and finish-polished to form the cutting edge, thereby obtaining a blade. The quenched and tempered plates and blades obtained as described above were evaluated as follows.

[0083] (Vickers hardness) The Vickers hardness of the quenched and tempered plates was measured using a Vickers hardness tester at room temperature (25°C).

[0084] (corrosion resistance) The surfaces of the quenched and tempered plates were polished with a #600 grit sandpaper and subjected to the JIS Z2371:2015 "Salt Spray Test." In this evaluation, a rust area rate of less than 10% was rated as passing (◯), and a rate of 10% or more was rated as failing (×). Furthermore, among those with a rust area rate of less than 10%, those with a rust area rate of 0% were rated as particularly excellent (◎).

[0085] (Average particle size and area ratio of carbide particles) The average grain size and area ratio of carbides were determined in the same manner as above, except that a quenched and tempered sheet was used instead of a cold-rolled annealed sheet.

[0086] (area ratio of retained austenite (γ)) Cross sections of the quenched and tempered plates parallel to the rolling direction and plate thickness direction were measured using EBSD, and then the BCC and FCC crystal structure phases were distinguished and their areas were calculated. Next, based on these areas, the ratio of the area of ​​the FCC crystal structure phase to the total area of ​​the BCC and FCC crystal structure phases (i.e., the area fraction (%) of the FCC crystal structure phase) was calculated, and the calculated area fraction of the FCC crystal structure phase was taken as the area fraction of retained austenite.

[0087] (specific wear rate) A 5 mm diameter test piece was cut out from the quenched and tempered plate and attached to the tip of a 5 mm diameter base pin to create a pin, after which the specific wear rate was evaluated using a pin-on-disk friction and wear tester. The disk, which served as the mating wear material, was made of emery paper (#400) with hard SiC particles attached. This wear test was carried out by fixing the pin to a sample holder, and pressing the surface of the pin's test piece against the rotating disk with a test load of 20 N, at a sliding speed of 0.66 m / s for 5 minutes. The volume of material lost due to wear was calculated from the difference in thickness of the test piece before and after the test, and this was taken as the wear loss (mm 3 ) The specific wear rate was calculated using the following formula: Specific wear rate [mm 3 / N·m] = wear loss [mm 3 ] / (Test load [20N] x friction distance [200m])

[0088] (Initial sharpness of blade) The sharpness of the blades was evaluated using a Honda sharpness tester. For the sharpness test, the blade was fixed in place and stacked with 7.5 mm wide sheets of paper equivalent to newspaper (approximately 70 μm thick), and a load of approximately 750 g was applied while the blade was moved back and forth 20 mm. One cycle was counted, and the number of sheets of paper completely cut in one cycle was counted. In this evaluation, if 10 or more sheets of paper were cut, the blade was judged to have good initial sharpness.

[0089] (Durability of blade sharpness) In the above-mentioned sharpness test, 500 cycles were carried out and the number of sheets of paper that were completely cut was counted. In this evaluation, if the number of sheets of paper that were cut was 3 or more, it was judged that the sharpness durability of the blade was good.

[0090] (Surface pattern of blade) The blades were visually inspected for irregular patterns on the surface of the blade, and evaluated. In this evaluation, those with no irregular patterns were rated as excellent (◎), those with only slight irregular patterns were rated as pass (◯), and those with irregular patterns were rated as fail (×).

[0091] The results of the above evaluations are shown in Table 4.

[0092] [Table 4]

[0093] As shown in Table 4, the quenched and tempered plates (quenched and tempered materials) of Examples 1 to 21 had a predetermined composition, and the average grain size of carbides, the area ratio of carbides, and the area ratio of retained austenite were able to be controlled within predetermined ranges. As a result, the quenched and tempered plates of Examples 1 to 21 had high hardness and corrosion resistance, and a low specific wear rate (excellent wear resistance). Furthermore, the blades of Examples 1 to 21 had good initial sharpness and durability of sharpness, and the occurrence of irregular patterns was also suppressed.

[0094] In contrast, the quenched and tempered plate of Comparative Example 1 had a small area ratio of carbides because the C content and the amount of 2.5C+N were too low. Furthermore, this quenched and tempered plate had low hardness, which resulted in insufficient initial sharpness of the blade, and also had an increased specific wear rate, which resulted in insufficient durability of the sharpness of the blade. The quenched and tempered plate of Comparative Example 2 had a high C content, so although it had high hardness, the area ratios of carbides and retained austenite were large. As a result, the retained austenite and carbides became the starting points for chipping, resulting in insufficient sharpness durability of the blade and the inability to suppress the occurrence of irregular patterns. This quenched and tempered plate also had low corrosion resistance. The quenched and tempered plate of Comparative Example 3 had too high a content of C, Si, and Ni, resulting in a large average grain size and area ratio of carbides, which resulted in the carbides becoming the starting point for chipping, resulting in insufficient durability of the cutting edge and the occurrence of irregular patterns.

[0095] The quenched and tempered plate of Comparative Example 4 had a large area ratio of retained austenite due to an excessively high Mn content. Furthermore, this quenched and tempered plate had low hardness and a high specific wear rate. As a result, the initial sharpness and durability of the cutting tool were insufficient, and the occurrence of irregular patterns could not be suppressed. The quenched and tempered plate of Comparative Example 5 had a low Cr content, resulting in a small area ratio of carbides and a large area ratio of retained austenite. This quenched and tempered plate also had low hardness and corrosion resistance, and a high specific wear rate. As a result, the initial sharpness and durability of the blade were insufficient, and the occurrence of irregular patterns could not be suppressed. The quenched and tempered plate of Comparative Example 6 had an excessively high Cr content, resulting in a large average grain size and area ratio of carbides. This quenched and tempered plate also had low hardness. Therefore, even though the specific wear rate was sufficient, the blade dulled quickly, resulting in insufficient initial sharpness and durability of the blade, and the occurrence of irregular patterns could not be suppressed.

[0096] The quenched and tempered plate of Comparative Example 7 had a high Ni content, resulting in a large area ratio of retained austenite. This quenched and tempered plate also had low hardness and a high specific wear rate. As a result, the initial sharpness and durability of the blade were insufficient, and the occurrence of irregular patterns could not be suppressed. The quenched and tempered plate of Comparative Example 8 had low hardness and a high specific wear rate due to an excessively high Mo content, which resulted in insufficient initial sharpness and durability of the cutting edge, and the occurrence of irregular patterns could not be suppressed. The quenched and tempered plate of Comparative Example 9 had a low hardness and a high specific wear rate due to an excessively high Al content, which resulted in insufficient initial sharpness and durability of the cutting tool, and the occurrence of irregular patterns could not be suppressed.

[0097] The quenched and tempered plate of Comparative Example 10 had a large area ratio of retained austenite because the N content was too low. Furthermore, this quenched and tempered plate had low hardness and corrosion resistance, and a high specific wear rate. Therefore, the initial sharpness and durability of the cutting tool were insufficient, and the occurrence of irregular patterns could not be suppressed. The quenched and tempered plate of Comparative Example 11 had a low corrosion resistance due to an excessively high Ca content. The quenched and tempered plate of Comparative Example 12 had an excessively high O content, and therefore had reduced corrosion resistance.

[0098] The quenched and tempered plate of Comparative Example 13 had a large specific wear rate because the average particle size of the carbide was too small, which resulted in insufficient durability of the cutting edge. The quenched and tempered plate of Comparative Example 14 had a high specific wear rate because the average particle size of the carbide was too large, which resulted in insufficient durability of the cutting edge and the occurrence of irregular patterns. The quenched and tempered plate of Comparative Example 15 had a large average grain size and area ratio of carbides, resulting in a high specific wear rate, and therefore insufficient durability of the cutting edge.

[0099] As can be seen from the above results, the present invention can provide a martensitic stainless steel material and a method for manufacturing the same that have high hardness and corrosion resistance, excellent wear resistance, and can suppress the occurrence of irregular patterns after quenching or quench-tempering. Furthermore, the present invention can provide a quenched or quench-tempered martensitic stainless steel material that has high hardness and corrosion resistance, excellent wear resistance, and can suppress the occurrence of irregular patterns.

Claims

1. A martensitic stainless steel material having a composition containing, on a mass basis, C: 0.305 to 0.600%, Si: 0.05 to 1.00%, Mn: 0.10 to 1.50%, P: 0.0085 to 0.0400%, S: 0.0300% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.300% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, the balance being Fe and impurities, and having 2.5C+N (C and N are the contents of C and N) of 0.85% or more, In the cross section of the martensitic stainless steel material, the average grain size of the carbides is more than 0.50 μm and 2.00 μm or less, and the number of the carbides having a size of 10 μm or more is 0.20 / cm 2 Hereinafter, a martensitic stainless steel material in which the area ratio of the carbides is 15.0 to 20.0%.

2. The martensitic stainless steel material according to claim 1, further comprising, on a mass basis, one or more selected from Ti: 0.30% or less, Nb: 0.50% or less, Cu: 4.0% or less, B: 0.005% or less, V: 0.50% or less, Sn: 0.10% or less, and Co: 0.30% or less.

3. The martensitic stainless steel material according to claim 1 or 2, which is for use in cutlery.

4. A quenched or quenched and tempered martensitic stainless steel material having a composition containing, on a mass basis, C: 0.305 to 0.600%, Si: 0.05 to 1.00%, Mn: 0.10 to 1.50%, P: 0.0085 to 0.0400%, S: 0.0300% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.300% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, the balance being Fe and impurities, and having a 2.5C+N (C and N are the contents of C and N) of 0.85% or more, A quenched or quenched and tempered martensitic stainless steel material, wherein in a cross section of the quenched or quenched and tempered material, the average grain size of the carbides is 0.10 to 0.50 μm, the area ratio of the carbides is 2.0 to 15.0%, and the area ratio of retained austenite is 15.0% or less.

5. 5. The quenched or quenched-tempered martensitic stainless steel material according to claim 4, further comprising, by mass, one or more selected from Ti: 0.30% or less, Nb: 0.50% or less, Cu: 4.0% or less, B: 0.005% or less, V: 0.50% or less, Sn: 0.10% or less, and Co: 0.30% or less.

6. The quenched or quenched and tempered martensitic stainless steel material according to claim 4 or 5, having a Vickers hardness of 500 to 900 HV.

7. Specific wear rate: 0.0020 mm 3 6. The quenched or quenched and tempered martensitic stainless steel material according to claim 4 or 5, wherein the tensile strength is 1 / N·m or less.

8. 6. The quenched or quenched and tempered martensitic stainless steel material according to claim 4 or 5, wherein the quenched or quenched and tempered martensitic stainless steel material is for use in cutlery.

9. a breakdown rolling process in which a slab having a composition containing, by mass, C: 0.305 to 0.600%, Si: 0.05 to 1.00%, Mn: 0.10 to 1.50%, P: 0.0085 to 0.0400%, S: 0.0300% or less, Cr: 13.0 to 18.0%, Ni: 0.01 to 0.30%, Mo: 0.01 to 1.00%, Al: 0.300% or less, N: 0.010 to 0.350%, Ca: 0.0001 to 0.0030%, O: 0.001 to 0.010%, the balance being Fe and impurities, and 2.5C+N (C and N are the contents of C and N) being 0.85% or more is rough rolled to obtain a breakdown material; a hot rolling step of hot rolling the breakdown material to obtain a hot rolled material; A softening step in which the hot-rolled material is heated at a temperature higher than the Ac1 point (Ac1 point + 100 ° C.) for 2 to 10 hours and then cooled at a cooling rate of 0.100 ° C. / second or less; A method for producing a martensitic stainless steel material, comprising:

10. 10. The method for producing a martensitic stainless steel material according to claim 9, wherein the slab further contains, by mass, one or more selected from Ti: 0.30% or less, Nb: 0.50% or less, Cu: 4.0% or less, B: 0.005% or less, V: 0.50% or less, Sn: 0.10% or less, and Co: 0.30% or less.

11. The method for producing a martensitic stainless steel material according to claim 9 or 10, further comprising a soaking treatment step of holding the breakdown material at a temperature of 1000 ° C to 1200 ° C for 1 to 48 hours between the breakdown rolling step and the hot rolling step.

12. a cold rolling step of cold rolling the softened material obtained in the softening step to obtain a cold-rolled material; an annealing step of heating the cold-rolled material to a temperature equal to or lower than the Ac1 point; The method for producing a martensitic stainless steel material according to claim 9 or 10, further comprising:

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