Martensitic stainless steel material, method for producing same, and method for producing tool

Abstract

A martensitic stainless steel material having a composition containing, by mass, 0.305 to 0.600% of C, 0.05 to 1.00% of Si, 0.05 to 2.50% of Mn, 0.0085 to 0.0400% of P, 0.0300% or less of S, 13.0 to 18.0% of Cr, 0.01 to 1.00% of Ni, 0.01 to 1.00% of Mo, 0.100% or less of Al, 0.010 to 0.350% of N, 0.0001 to 0.0050% of Ca, and 0.001 to 0.010% of O, with the remainder being Fe and impurities. The martensitic stainless steel material has an average particle diameter of carbides of 0.50 [mu] m or less, an amount of carbides having a size of 10 [mu] m or more of 0.10 particles / cm2 or less, a Vickers hardness of 320 HV or less before quenching or quenching / tempering, and a retained austenite amount of 10.0 vol% or less after quenching or quenching / tempering, and when the solid solution amount (mass%) of C is denoted as [C] and the solid solution amount (mass%) of N is denoted as [N] after quenching or quenching / tempering, the average particle diameter of the carbides is less than 0.50 [mu] m and the average particle diameter of the carbides is less than 0.10 particles / cm2. And the amount of [C] + 0.3 [N] is 0.15 mass% or more.

Description

Technical Field

[0001] The present invention relates to a martensitic stainless steel material, a manufacturing method thereof, and a manufacturing method of a cutting tool. Background Art

[0002] Since stainless steel materials used for various knives such as razors, scissors, and kitchen knives require high hardness, martensitic stainless steel materials with a high C content are used (for example, Patent Document 1).

[0003] However, if the C content is high, it will generate carbides with alloying elements such as Cr, which are easily precipitated as coarse eutectic carbides during the manufacturing process. Even if an annealing process is used, it is difficult to completely dissolve the eutectic carbides, which causes the solid solubility of C to decrease during quenching or quenching and tempering, thereby causing excessive softening. In addition, the eutectic carbides become the starting point of corrosion, thereby reducing corrosion resistance. In addition, they also become the cause of chipping and irregular patterns such as ribs and islands during processing. Moreover, since C is a strong austenite stabilizing element, if a large amount of retained austenite remains after quenching or quenching and tempering due to the segregation of C, it will also lead to a reduction in hardness, deterioration of sharpness, and the generation of irregular patterns such as ribs and islands.

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

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

[0006] In addition, Patent Document 4 proposes a method for producing a martensitic stainless steel material (martensitic stainless steel sheet), wherein a raw material of a stainless steel sheet having a thickness of 0.1 mm or less and containing, by mass%, C: 0.25-0.45%, Si: 1.0% or less, Mn: 0.1-1.5%, Cr: 12.0-15.0%, Mo: 0.5-3.0%, N: 0.30-0.45%, and the balance being Fe and impurities, is subjected to a heat treatment in a nitrogen atmosphere at a temperature exceeding 1000° C. for 1 to 10 minutes and then cooled, thereby controlling the number density of carbides having an equivalent circle diameter of 0.5 μm or more to 0 to 50 per 1000 μm. 2 It is described that a martensitic stainless steel material produced by this method can obtain high hardness from the surface to the center of the plate thickness when quenched and tempered, and also has good corrosion resistance.

[0007] Furthermore, Patent Document 5 proposes a method for producing a martensitic stainless steel material (stainless steel plate), the method comprising: a first step of holding a steel slab at a temperature of 1200 to 1350° C. for 30 minutes or more, the steel slab containing, in 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 and less than 16.0%, Ni: 0.10 to 1.00%, and N: 0.010 to 0.00%. The invention discloses a martensitic stainless steel material produced by this method, comprising a first step of hot rolling a steel slab to produce a hot-rolled steel sheet, and a second step of coiling the hot-rolled steel sheet. Furthermore, the invention discloses a third step of hot-rolling the hot-rolled steel sheet to produce a hot-annealed steel sheet. The second step includes three or more hot-rolling passes with a finish temperature of 1050°C or higher and a reduction ratio of 20% or higher. Furthermore, the hot-rolling temperature is 600°C or higher, and the third step includes a hot-rolling annealing hold temperature of 750-900°C for a hold time of 10 minutes or longer. The invention discloses that the martensitic stainless steel material produced by this method has high hardness and good surface quality.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-273587

[0011] Patent Document 2: Japanese Patent Application Publication No. 2018-9231

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 2003-313612

[0013] Patent Document 4: International Publication No. 2019 / 146743

[0014] Patent Document 5: International Publication No. 2021 / 220754 Summary of the Invention

[0015] However, the martensitic stainless steel material described in Patent Document 2 has insufficient workability and may produce irregular patterns because the average particle size of inclusions (particularly carbides) is not controlled.

[0016] The martensitic stainless steel described in Patent Document 3 is not suitable for mass production due to the introduction of special processes such as high-density dislocation introduction and ultra-rapid solidification. In addition, the martensitic stainless steel has a high Mo content and is expensive.

[0017] The martensitic stainless steel described in Patent Document 4 is expensive because it undergoes a nitrogen absorption treatment in a nitrogen atmosphere for high nitridation and dissolution of coarse carbides. Furthermore, since this martensitic stainless steel is limited to thin plates with a thickness of 0.1 mm or less, it is difficult to use for knives such as kitchen knives.

[0018] The martensitic stainless steel described in Patent Document 5 dissolves coarse carbides by heating the steel slab at a high temperature of 1200-1350°C. However, this heating alone cannot suppress the segregation of carbon, which causes the coarse carbides. Consequently, this leads to the reprecipitation of coarse carbides, the formation of retained austenite due to carbon segregation, softening, reduced hardness, and the development of irregular patterns. Furthermore, excessively heating the slab at high temperatures increases the likelihood of deformation due to its own weight.

[0019] Thus, conventional martensitic stainless steel materials having a high C content have the problems described above.

[0020] Furthermore, kitchen knives and other knives are primarily manufactured using the following method: martensitic stainless steel is forged and ground, formed into the desired shape, then hardened by quenching and cold treatment, and tempered to ensure toughness. However, if the martensitic stainless steel is excessively hardened before quenching, its workability during forging and grinding is reduced, making it difficult to form into the desired shape.

[0021] The present invention has been made to solve the above-mentioned problems, and its object is to provide a martensitic stainless steel material and a method for producing the same, which has good workability because it is soft before quenching or quenching and tempering, and has high hardness and corrosion resistance after quenching or quenching and tempering, and can suppress the generation of irregular patterns.

[0022] Another object of the present invention is to provide a method for manufacturing a cutting tool that is easy to process, has high hardness and corrosion resistance, good sharpness, and can also suppress the generation of irregular patterns.

[0023] The present inventors have conducted intensive research on martensitic stainless steels and have discovered that the average carbide particle size, the number of carbides with a size of 10 μm or greater, the Vickers hardness before quenching or quenching and tempering, the amount of retained austenite after quenching or quenching and tempering, and the amount of carbon and nitrogen dissolved therein after quenching or quenching and tempering are closely related to workability, corrosion resistance, and irregularity. Furthermore, the present inventors have discovered that by controlling, in addition to the steel composition, the average carbide particle size, the number of carbides with a size of 10 μm or greater, the Vickers hardness before quenching or quenching and tempering, the amount of retained austenite after quenching or quenching and tempering, and the amount of carbon and nitrogen dissolved therein after quenching or quenching and tempering, all of the above-mentioned problems can be overcome, leading to the completion of the present invention.

[0024] That is, the present invention relates to a martensitic stainless steel material having a composition containing, by mass, C: 0.305-0.600%, Si: 0.05-1.00%, Mn: 0.05-2.50%, P: 0.0085-0.0400%, S: 0.0300% or less, Cr: 13.0-18.0%, Ni: 0.01-1.00%, Mo: 0.01-1.00%, Al: 0.100% or less, N: 0.010-0.350%, Ca: 0.0001-0.0050%, O: 0.001-0.010%, with the balance being Fe and impurities, wherein the average particle size of carbides is 0.50 μm or less, and the number of carbides having a size of 10 μm or more is 0.10 particles / cm 2 The Vickers hardness before quenching or quenching and tempering is 320 HV or less, the amount of retained austenite after quenching or quenching and tempering is 10.0 volume % or less, and when the solid solution amount (mass %) of C after quenching or quenching and tempering is represented as [C] and the solid solution amount (mass %) of N after quenching or quenching and tempering is represented as [N], [C] + 0.3 [N] is 0.15 mass % or more.

[0025] The present invention also relates to a method for producing a martensitic stainless steel material, comprising a blooming and rolling step, a hot rolling step, and a softening step.

[0026] In the bloom rolling process, the slab is heat treated at a temperature of 1000° C. or higher and lower than 1200° C. for 1 to 10 hours, and then rough rolled at a total reduction of 30 to 70%, including two or more passes with a reduction of 10% or more per pass, to obtain a bloom material. The slab contains, by mass, C: 0.305 to 0.600%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, and Mn: 0.05 to 1.00%. 2.50%, P: 0.0085~0.0400%, S: 0.0300% or less, Cr: 13.0~18.0%, Ni: 0.01~1.00%, Mo: 0.01~1.00%, Al: 0.100% or less, N: 0.010~0.350%, Ca: 0.0001~0.0050%, O: 0.001~0.010%, and the balance is Fe and impurities,

[0027] In the hot rolling process, the slab is heat treated at a temperature of 1000° C. or higher and lower than 1200° C. for 1 to 5 hours, and then hot rolled to obtain a hot-rolled material.

[0028] In the softening step, the hot-rolled material is coiled at a coiling temperature of 800° C. to 900° C., and then heated at a temperature of Ac1 point to (Ac1 point −50° C.) for 1 to 5 hours.

[0029] Furthermore, the present invention relates to a method for manufacturing a cutting tool, comprising: processing the martensitic stainless steel material, heating it at a temperature of 1000° C. to 1200° C. for 5 to 60 minutes, and cooling it at a cooling rate of 3° C. / second or more to quench it.

[0030] The present invention provides a martensitic stainless steel material having good workability due to being soft before quenching or quenching and tempering, high hardness and corrosion resistance after quenching or quenching and tempering, and capable of suppressing the generation of irregular patterns, and a method for producing the same.

[0031] Furthermore, according to the present invention, it is possible to provide a method for manufacturing a cutting tool that is easy to process, has high hardness and corrosion resistance, and has good sharpness, while also being able to suppress the generation of irregular patterns. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This graph shows the relationship between [C]+0.3[N] (the solid solution amount (mass %) of C after quenching or quenching and tempering is expressed as [C], and the solid solution amount (mass %) of N is expressed as [N]) and Vickers hardness in Examples and Comparative Examples. DETAILED DESCRIPTION

[0033] The embodiments of the present invention are described in detail below. The present invention is not limited to the following embodiments, and it should be understood that within the scope of the present invention, based on the common knowledge of those skilled in the art, the following embodiments may be appropriately modified, improved, etc. to obtain embodiments that are also within the scope of the present invention.

[0034] In addition, in this specification, "%" about a component means "mass %" unless otherwise specified.

[0035] The martensitic stainless steel material according to an embodiment of the present invention has a composition comprising C: 0.305-0.600%, Si: 0.05-1.00%, Mn: 0.05-2.50%, P: 0.0085-0.0400%, S: 0.0300% or less, Cr: 13.0-18.0%, Ni: 0.01-1.00%, Mo: 0.01-1.00%, Al: 0.100% or less, N: 0.010-0.350%, Ca: 0.0001-0.0050%, O: 0.001-0.010%, with the balance being Fe and impurities. In this composition, 2.5C+N is preferably 0.80-1.20%.

[0036] Here, in this specification, the so-called "steel material" refers to various materials such as steel plates. In addition, the so-called "steel plate" is a concept that includes steel strips. In addition, the so-called "impurities" refer to components that are mixed in during the industrial production of stainless steel materials due to various factors such as raw materials such as ores and scraps, and the manufacturing process, and are allowed within the range that does not adversely affect the present invention. Examples of impurities include Zn, Pb, Se, Sb, H, Ga, Ta, Mg, Zr, etc. When these elements are included as impurities, Zn≤100ppm, Pb≤100ppm, Se≤100ppm, Sb≤500ppm, H≤100ppm, Ga≤500ppm, Ta≤500ppm, Mg≤120ppm, and Zr≤120ppm.

[0037] Regarding the content of each element, the phrase "containing xx% or less" means xx% or less, but includes an amount exceeding 0% (particularly, an amount exceeding an impurity level).

[0038] The martensitic stainless steel material according to the embodiment of the present invention may further contain one or more selected from V: 0.50% or less, Nb: 0.50% or less, Ti: 0.30% or less, Cu: 4.0% or less, Sn: 0.10% or less, B: 0.005% or less, and Co: 0.30% or less.

[0039] Each component is described in detail below.

[0040] <C:0.305~0.600%>

[0041] C is an element necessary to obtain a specified hardness (Vickers hardness) after quenching or quenching and tempering. In order to stably obtain a hardness of 500 HV or more, the C content needs to be set to 0.305% or more. If C is added excessively, sensitization during quenching is promoted, which impairs corrosion resistance. In addition, the toughness after quenching or quenching and tempering is also reduced due to undissolved carbonitrides. Therefore, the C content needs to be set to 0.600% or less. Considering the reduction in hardness and toughness caused by changes in heating conditions during quenching or quenching and tempering, the lower limit of the C content is preferably 0.320%, and the upper limit is preferably 0.580%.

[0042] <Si:0.05~1.00%>

[0043] Si is an element that is useful not only for deoxidation during melting and refining but also for suppressing the formation of scale during quenching. Additionally, if the Si content is low, deoxidation tends to be insufficient, carbides increase, and in some cases, rusting may occur starting from these carbides, reducing corrosion resistance. Therefore, the Si content needs to be set at 0.05% or more. On the other hand, since Si narrows the austenite single-phase temperature range and impairs quenching stability, the Si content needs to be set at 1.00% or less. From the perspective of stably obtaining the above effects brought by Si, the lower limit value of the Si content is preferably 0.07%, and the upper limit value is preferably 0.98%.

[0044] <Mn: 0.05 - 2.50%>

[0045] Mn is an element added as a deoxidizer, and it expands the austenite single-phase temperature range, contributing to improving hardenability. If Mn is not added sufficiently, the duplex region expands and the α-phase increases. As a result, Cr carbonitrides also increase, and a Cr-depleted layer forms around them, so it easily becomes a starting point for rusting and corrosion resistance decreases. Therefore, the Mn content needs to be set at 0.05% or more. From the perspective of stably obtaining the above effects brought by Mn, the lower limit value of the Mn content is preferably 0.10%. On the other hand, excessive Mn reduces corrosion resistance, promotes the formation of scale during quenching, increases the subsequent grinding load, etc., and there is a possibility of an increase in the amount of retained austenite. Therefore, the Mn content needs to be set at 2.50% or less. If considering the reduction in corrosion resistance caused by particles such as MnS, it is preferably 1.50% or less.

[0046] <P: 0.0085 - 0.0400%>

[0047] P is an element contained as an impurity in the main raw materials such as molten iron and ferrochrome. Additionally, P is an element harmful to the toughness and corrosion resistance of the material after quenching or quenching and tempering. Therefore, the P content needs to be set at 0.0400% or less, preferably 0.0380% or less. On the other hand, excessive reduction of P causes problems such as the need to use high-purity raw materials, resulting in increased costs. Therefore, the lower limit value of the P content is 0.0085%.

[0048] <S: 0.0300% or less>

[0049] S forms sulfide-based inclusions, deteriorating the general corrosion resistance (general corrosion, pitting corrosion) of the steel. Additionally, S reduces hot workability and increases the edge cracking sensitivity of hot-rolled sheets. Therefore, the S content needs to be set at 0.0300% or less, preferably 0.0200% or less. Furthermore, the lower limit value of the S content is not particularly limited. The lower the S content, the better the corrosion resistance, but on the other hand, the desulfurization load increases and the manufacturing cost increases. Therefore, the lower limit value of the S content is preferably 0.0001%.

[0050] <Cr: 13.0 - 18.0%>

[0051] Cr is an element used to maintain the corrosion resistance required in the main applications of martensitic stainless steel. Therefore, the Cr content needs to be set at 13.0% or more. On the other hand, Cr easily forms carbides. When a large amount of Cr is added, in addition to being a cause of the formation of coarse carbides, the amount of retained austenite increases after quenching or quenching and tempering. Therefore, from the viewpoint of suppressing these situations, the Cr content needs to be set at 18.0% or less. From the viewpoint of stably obtaining the above effects brought by Cr, the lower limit value of the Cr content is preferably 13.1%, and the upper limit value is preferably 17.8%.

[0052] <Ni: 0.01 - 1.00%>

[0053] Ni, like Mn, is an austenite stabilizing element and also has the effect of improving the toughness after quenching or quenching and tempering. On the other hand, if a large amount of Ni is contained, there is a risk of reducing the press formability due to solid solution strengthening in hot-rolled annealed materials, and there is a possibility that the amount of retained austenite increases after quenching or quenching and tempering. In addition, since it is a high-cost element, the manufacturing cost increases. Therefore, the Ni content needs to be set at 1.00% or less. On the other hand, since Ni is an element effective in suppressing the progress of pitting corrosion, the Ni content needs to be set at 0.01% or more. From the viewpoint of stably obtaining the above effects brought by Ni, the lower limit value of the Ni content is preferably 0.02%, the upper limit value is preferably 0.80%, and more preferably 0.50%.

[0054] <Mo: 0.01 - 1.00%>

[0055] Mo is an element effective in improving the corrosion resistance of martensitic structures containing δ-ferrite. From the viewpoint of obtaining this effect, the Mo content needs to be set at 0.01% or more. On the other hand, Mo is a stabilizing element of the ferrite phase, and excessive addition will narrow the austenite single-phase temperature range, thereby impairing the quenching characteristics. Therefore, the Mo content needs to be set at 1.00% or less. From the viewpoint of stably obtaining the above effects brought by Mo, the lower limit value of the Mo content is preferably 0.02%, the upper limit value is preferably 0.80%, and more preferably 0.60%.

[0056] <Al: 0.100% or less>

[0057] Al is an element added as a deoxidizing element and is also an element that improves oxidation resistance. However, if Al is contained in large quantities, carbides tend to become larger. In addition, since Al is a ferrite-stabilizing element, it hinders austenite transformation and increases the Ac1 line. Therefore, the Al content needs to be set to 0.100% or less, preferably 0.050% or less, and more preferably 0.030% or less. On the other hand, the lower limit of the Al content is not particularly limited, but from the perspective of obtaining the above-mentioned effects brought about by Al, the lower limit of Al is preferably 0.001%. Here, Al refers to total aluminum (total Al).

[0058] <N:0.010~0.350%>

[0059] Like C, N is an essential element for achieving a specified hardness (Vickers hardness) after quenching or quenching and tempering. In particular, in embodiments of the present invention, since the C content is reduced, N must be included to compensate for this. Furthermore, when N is dissolved, it also has the effect of improving corrosion resistance. To achieve these effects, the N content must be set to 0.010% or above. However, N can form Cr-based nitrides, resulting in a Cr-depleted layer, which reduces corrosion resistance. Furthermore, excessive N addition makes it difficult to control during steelmaking and can easily lead to the formation of blister defects. If blister defects form, they can easily become the starting point of rust, reducing corrosion resistance and also risking a decrease in yield. Therefore, the N content must be set to 0.350% or below. To stably achieve the aforementioned effects of N, the lower limit of the N content is preferably 0.015%, more preferably 0.018%, and the upper limit is preferably 0.300%, more preferably 0.290%.

[0060] <Ca:0.0001~0.0050%>

[0061] Ca is added during the steelmaking stage to adjust the composition. In particular, Ca acts as a strong deoxidizer and has the effect of promoting deoxidation. However, since Ca is a strong deoxidizing element, it generally floats in the molten steel as an inclusion and hardly remains in the steel. However, if a large amount of Ca is added, CaO will be contained in the steelmaking inclusions, which is likely to become the starting point of rust and reduce corrosion resistance. Therefore, the Ca content needs to be set to 0.0050% or less, preferably 0.0045% or less, and more preferably 0.0040% or less. On the other hand, since it is impossible to remove even fine inclusions, it is difficult to reduce the Ca content to less than 0.0001% in the manufacturing process. Therefore, the Ca content is set to 0.0001% or more.

[0062] <O:0.001~0.010%>

[0063] In order to reduce inclusions, O, together with Al and Ca, is an important element. If a large amount of O is added, the number of large inclusions (especially carbides) remaining in the steel increases, which has an adverse effect on corrosion resistance. Therefore, the O content needs to be set to 0.010% or less. In addition, O is preferably reduced as much as possible, but excessive reduction will lead to an increase in cost. Therefore, the O content is set to 0.001% or more. From the viewpoint of the balance between cost and corrosion resistance, the lower limit value of the O content is preferably 0.002%, and the upper limit value is preferably 0.009%.

[0064] <2.5C + N: 0.80 - 1.20%>

[0065] C and N are elements necessary to obtain a specified hardness (Vickers hardness) after quenching or quenching and tempering as described above. In an embodiment of the present invention, N is contained as a compensation for reducing the C content, and the contribution of C to this hardness is 2.5 times that of N. Therefore, from the viewpoint of obtaining a specified hardness, 2.5C + N needs to be set to 0.80% or more, preferably 0.85% or more. In addition, if 2.5C + N is too high, the hardness before quenching is too high, and there is a risk of reduced machinability and grinding performance. Therefore, the upper limit value of 2.5C + N is preferably less than 1.20%, more preferably 1.10%.

[0066] <V: 0.50% or less>

[0067] V is an element that forms fine carbonitrides and helps improve corrosion resistance, and is added as needed. However, if an excessive amount of V is added, there is a risk of coarsening of the precipitates, and as a result, the toughness after quenching or quenching and tempering is reduced. Therefore, the V content is 0.50% or less, preferably 0.30% or less, more preferably 0.20% or less. Furthermore, the lower limit value of the V content is not particularly limited, but V sometimes混入as an unavoidable impurity in the alloy raw materials and is difficult to remove in the refining process. In addition, from the viewpoint of obtaining the above effects, the lower limit value of the V content is preferably 0.01%, more preferably 0.02%, and further preferably 0.03%.

[0068] <Nb: 0.50% or less>

[0069] Nb is an element that forms carbonitrides and inhibits sensitization and reduction of corrosion resistance caused by the precipitation of chromium carbonitrides, and is added as needed. However, if an excessive amount of Nb is added, the martensitic phase becomes unstable and the hardness decreases. Therefore, the Nb content is 0.50% or less, preferably 0.35% or less, more preferably 0.30% or less, and further preferably 0.25% or less. Furthermore, the lower limit value of the Nb content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0070] <Ti: Below 0.30%>

[0071] Ti is an element that forms carbonitrides, inhibits sensitization caused by the precipitation of chromium carbonitrides, and reduces the decrease in corrosion resistance, and is added as needed. However, if Ti is added in excess, coarse TiN is formed, leading to the generation of hot rolling defects and a decrease in toughness. Therefore, the Ti content is set to 0.30% or less, preferably 0.25% or less. Furthermore, the lower limit value of the Ti content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.06%, and further preferably 0.10%.

[0072] <Cu: 4.0% or less>

[0073] Cu is an element that is effective in improving the corrosion resistance of a martensitic structure containing δ-ferrite and also contributes to improving the hardenability as an austenite stabilizing element, and is added as needed. However, excessive addition of Cu causes a decrease in hot workability and an increase in raw material costs. Therefore, the Cu content is set to 4.0% or less, preferably 3.8% or less, and more preferably 3.5% or less. Furthermore, the lower limit value of the Cu content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 1.0%, more preferably 1.3%, and further preferably 1.5%.

[0074] <Sn: 0.10% or less>

[0075] Sn is an element that is effective in improving the corrosion resistance after quenching or quenching and tempering, and is added as needed. However, excessive addition of Sn promotes edge cracking during hot rolling. Therefore, the Sn content is set to 0.10% or less, preferably 0.09% or less. Furthermore, the lower limit value of the Sn content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.002%, more preferably 0.05%.

[0076] <B: 0.005% or less>

[0077] B is an element that is effective in improving hot workability and is added as needed. However, when B is added in excess, there is a risk of reducing the hardenability due to the composite precipitation of borides and carbides. Therefore, the B content is set to 0.005% or less, preferably 0.0045% or less. Furthermore, the lower limit value of the B content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.0002%.

[0078] <Co: 0.30% or less>

[0079] Co is an element that improves heat resistance and is added as needed. However, since Co is an expensive element, 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, and more preferably 0.05% or less. Furthermore, the lower limit of the Co content is not particularly limited, but from the viewpoint of obtaining the above-mentioned effect, it is preferably 0.01%.

[0080] In the martensitic stainless steel material according to the embodiment of the present invention, the average carbide particle size is 0.50 μm or less, preferably 0.48 μm or less. By controlling the average carbide particle size within this range, the workability of the martensitic stainless steel material is improved and the generation of irregular patterns is 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 even more preferably 0.10 μm.

[0081] Here, the carbides having the specified average grain size are targeted at both eutectic carbides generated during casting and precipitated carbides generated during the rolling process.

[0082] The average particle size of carbides can be calculated by observing a cross section of a martensitic stainless steel material using an SEM, measuring the equivalent circle diameter of each carbide in the observation field, and finding the average value.

[0083] In the martensitic stainless steel material according to the embodiment of the present invention, the number of carbides with a size of 10 μm or more is 0.10 pieces / cm 2 Below, preferably 0.05 pieces / cm 2 Since carbides larger than 10 μm are likely to become the starting point of rust, controlling the number of carbides larger than 10 μm within this range can suppress rust and improve corrosion resistance. In addition, since carbides larger than 10 μm also cause irregular patterns, controlling the number of these carbides can also suppress the generation of irregular patterns. Furthermore, the fewer carbides larger than 10 μm, the better. Although there is no particular limit, it is generally 0.01 per cm 2 above.

[0084] Here, the predetermined number of carbides with a size of 10 μm or larger is mainly eutectic carbides formed during casting. The carbide size is defined as (longer diameter + shorter diameter) / 2 of the carbide.

[0085] The number of carbides having a size of 10 μm or larger can be calculated by observing a cross section of the martensitic stainless steel material with an optical microscope, determining the number of carbides having a size of 10 μm or larger, and dividing the obtained number by the area of ​​the measurement region.

[0086] The martensitic stainless steel material according to an embodiment of the present invention has a Vickers hardness of 320 HV or less, preferably 300 HV or less, and more preferably 290 HV or less before quenching or quenching and tempering. A Vickers hardness within this range indicates softness, thereby improving workability during forging, grinding, and the like. The lower limit of the Vickers hardness is not particularly limited, but is preferably 150 HV, and more preferably 200 HV.

[0087] Here, in this specification, Vickers hardness means a value measured at room temperature (25° C.) using a Vickers hardness tester.

[0088] In the martensitic stainless steel material according to an embodiment of the present invention, the amount of retained austenite after quenching or quenching and tempering is 10.0% by volume or less, preferably 8.0% by volume or less, and more preferably 5.0% by volume or less. Retained austenite is formed when austenite formed during quenching does not undergo martensitic transformation during subsequent treatments (e.g., cold treatment and tempering) and remains. Retained austenite is particularly prone to formation in areas where carbon, a strong austenite-stabilizing element, segregates. Since retained austenite is softer than martensite, its presence in large quantities prevents the desired hardness from being achieved.

[0089] Since carbon segregation occurs primarily as central segregation during casting, retained austenite often forms in large quantities in the center of the thickness of martensitic stainless steel. This center of the thickness of the martensitic stainless steel becomes the blade edge during tool forming. The presence of soft retained austenite at the blade edge can lead to chipping and reduced sharpness.

[0090] The amount of retained austenite can be calculated as follows. First, EBSD is performed on a cross-section of a martensitic stainless steel material to distinguish between BCC and FCC phases, and the areas of each are calculated. Next, based on these areas, the ratio of the area of ​​the FCC phase to the total area of ​​the BCC and FCC phases (i.e., the area ratio of the FCC phase) is calculated. The area ratio of the FCC phase thus calculated is considered the amount of retained austenite (volume %).

[0091] Furthermore, in the aforementioned central segregation portion of carbon, coarse carbides are likely to be generated in rows, which causes irregular patterns (ribbed patterns, island patterns). Therefore, reducing central segregation is also effective in reducing these irregular patterns.

[0092] In the martensitic stainless steel material according to an embodiment of the present invention, when the carbon solid solution content after quenching or quenching and tempering is denoted as [C] and the nitrogen solid solution content is denoted as [N], [C] + 0.3 [N] is 0.15% or greater. In particular, when the martensitic stainless steel material is used as a cutting tool, [C] + 0.3 [N] is preferably 0.20% or greater. Within this range of [C] + 0.3 [N], strength for use as a cutting tool can be ensured. The upper limit of [C] + 0.3 [N] is not particularly limited, but is preferably 1.00%, and more preferably 0.80%.

[0093] The solid solution amounts of C and N ([C] and [N]) can be measured by the following electrolytic extraction residue method.

[0094] A test piece approximately 20 mm square was cut from the center of the width of the martensitic stainless steel. The entire surface of the test piece, corresponding to the surface of the martensitic stainless steel, was wet-polished using #600 water-resistant abrasive paper. After polishing, the test piece substrate (stainless steel substrate) was dissolved by electrolysis in a methanol solution containing 10% maleic anhydride and 2% tetramethylammonium chloride at a constant potential of -100 mV. After electrolysis, the undissolved residue (precipitate) remaining in the solution was captured using a filter with a mesh size of 200 nm. The captured precipitate was washed with pure water and dried. The precipitate was then dissolved using aqua regia and perchloric acid, and elemental analysis was performed using ICP emission spectrometry in accordance with JIS G1258:2014 to determine the mass of carbon in the precipitate. The obtained mass was divided by the mass change of the test piece due to electrolysis ("mass of the test piece before electrolysis" - "mass of the test piece after electrolysis") to obtain a value expressed as a percentage, which was used as the "precipitation amount C p ” (%). The solid solution amount [C] (=C0-C p ). The solid solution [N] can also be calculated using the same method.

[0095] The martensitic stainless steel material according to an embodiment of the present invention preferably has a Vickers hardness of 500 HV or higher after quenching or quenching and tempering. In particular, when the martensitic stainless steel material is used as a cutting tool, the Vickers hardness is more preferably 550 HV or higher. A Vickers hardness within this range ensures sufficient strength for use as a cutting tool. The upper limit of the hardness is not particularly limited, but is preferably 900 HV, and more preferably 800 HV.

[0096] Here, quenching is performed at a temperature of 1000 to 1200° C. Tempering is performed at a temperature of 100 to 400° C. After quenching, it is preferably subjected to a cold treatment at a temperature of -200 to -50° C.

[0097] 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.

[0098] The martensitic stainless steel material according to the embodiment of the present invention can be produced by using a slab having the same composition as the above-mentioned martensitic stainless steel material, by a method including a bloom rolling step, a hot rolling step, and a softening step.

[0099] The bloom rolling process involves heat treating the slab at a temperature of 1000°C to less than 1200°C for 1 to 10 hours, followed by rough rolling at a total reduction of 30 to 70%, including two or more passes with a reduction of 10% or more per pass, to produce a bloomed product. The upper limit of the heat treatment temperature is preferably 1180°C or lower, more preferably 1160°C or lower, and even more preferably 1150°C or lower.

[0100] By carrying out the slab rolling process under such conditions, the following effects can be obtained. First, the eutectic carbides generated during casting can be dissolved in the high-temperature heat treatment (holding) of the slab. In addition, the width of the macrosegregation is reduced by rough rolling, and the diffusion of carbon is promoted by the introduction of dislocations throughout the center of the slab, so that the carbon segregation generated during casting is eliminated. Moreover, the formation of retained austenite caused by the reduction of the Ms point due to carbon segregation can also be suppressed. As a result, the average particle size of the carbides, the number of carbides with a size of 10μm or more, and the amount of retained austenite after quenching or quenching and tempering can be controlled within the above-mentioned ranges. These effects can be effectively obtained by combining with the subsequent hot rolling process and the soaking treatment process performed as needed.

[0101] If the heat treatment time in the bloom rolling process is less than 1 hour or the heat treatment temperature is less than 1000°C, the effect of solid solution formation of eutectic carbides and reduction of carbon segregation cannot be fully achieved. In addition, if the heat treatment time in the bloom rolling process exceeds 10 hours or the heat treatment temperature is above 1200°C, the slab will sag due to its own weight, making it difficult to carry out subsequent processes.

[0102] Furthermore, if the total reduction ratio in the blooming rolling process is less than 30%, the introduction of dislocations is insufficient, and the width of macrosegregation is difficult to reduce. Therefore, the effect of solid solution of eutectic carbides and reduction of carbon segregation cannot be fully achieved. In addition, if the total reduction ratio in the blooming rolling process exceeds 70%, the reduction ratio in the subsequent hot rolling will be insufficient. In addition, if the reduction ratio in each pass during blooming is low, the strain does not reach the center of the plate, and the effect of eliminating macrosegregation is weakened. Therefore, it is necessary to perform two passes with a reduction ratio of 10% or more.

[0103] The number of passes in the bloom rolling process is not particularly limited as long as it is 2 or more, but is preferably 2 to 9, more preferably 2 to 6. Furthermore, the position of the pass with a reduction ratio of 10% or more is also not particularly limited, but the reduction ratio of the final pass and the preceding pass is preferably set to 10% or more.

[0104] The hot rolling step is a step of subjecting a slab to heat treatment at a temperature of 1000° C. or higher and lower than 1200° C. for 1 to 5 hours and then hot rolling the slab to obtain a hot-rolled material.

[0105] By performing heat treatment under such conditions, the eutectic carbides generated during casting can be completely dissolved, so the average particle size of the carbides, the number of carbides with a size of 10 μm or more, and the amount of retained austenite after quenching or quenching and tempering can be controlled within the above ranges.

[0106] The conditions for hot rolling are not particularly limited, but the plate is preferably finished to a thickness of 2 to 8 mm.

[0107] If the hot rolling heat treatment time is less than 1 hour or the heat treatment temperature is less than 1000°C, the effects of solid solution formation of eutectic carbides and reduction of carbon segregation cannot be fully achieved. Furthermore, if the hot rolling heat treatment time exceeds 5 hours or the heat treatment temperature is above 1200°C, sagging deformation occurs due to the weight of the open billet, making subsequent processes difficult. To stably ensure the above effects, the hot rolling heat treatment time is preferably 1.5 to 3 hours.

[0108] The softening process is a process in which the hot-rolled material is coiled at a coiling temperature of 800°C to 900°C and then heated at a temperature between the Ac1 point and (Ac1 point - 50°C) for 1 to 5 hours.

[0109] This softening step yields a soft, highly workable, softened material (martensitic stainless steel) with a Vickers hardness of 320 HV or less before quenching or quenching and tempering. Furthermore, heating under these conditions suppresses the coarsening of carbides in segregated areas, thereby stably controlling the average carbide particle size and the number of carbides with a particle size of 10 μm or greater within the aforementioned ranges.

[0110] Heating is performed by maintaining the heated coiled hot-rolled sheet at a temperature between the Ac1 point and (Ac1 point - 50°C). Therefore, it should be noted that heating is not performed by temporarily cooling the coiled hot-rolled sheet and then heating it to this temperature. Furthermore, heating is performed in a batch annealing furnace.

[0111] Here, the Ac1 point is calculated using the following formula (1).

[0112] Ac1=-250C+73Si-66Mn-115Ni+35Cr+60Mo-18Cu+620Ti+750Al-280N+410···(1)

[0113] In the formula, the symbol of each element is the mass % of each element.

[0114] Furthermore, the softened material obtained in the softening step may be pickled as needed.

[0115] A soaking treatment process may be performed between the bloom rolling process and the hot rolling process as needed.

[0116] The soaking step is a step of maintaining the raw material at a temperature of 1000°C or higher and lower than 1200°C for 1 to 24 hours.

[0117] By performing the soaking treatment step under such conditions, the effects of solubilizing eutectic carbides and reducing carbon segregation can be enhanced.

[0118] If the soaking step's heat treatment time is less than 1 hour or the heat treatment temperature is less than 1000°C, the effects of solid solution formation of eutectic carbides and reduction of carbon segregation cannot be fully achieved. Furthermore, if the soaking step's heat treatment time exceeds 24 hours or the heat treatment temperature is above 1200°C, sagging deformation occurs due to the weight of the raw material, making subsequent steps difficult to perform. To stably ensure the above-mentioned effects, the soaking step's heat treatment time is preferably 3 to 20 hours, more preferably 3 to 15 hours.

[0119] After the softening step, a cold rolling step and an annealing step may be performed as needed.

[0120] The cold rolling step is a step of cold-rolling the softened material obtained in the softening step to obtain a cold-rolled material.

[0121] By performing the cold rolling step, a cold-rolled material can be obtained.

[0122] The conditions for cold rolling are not particularly limited and may be appropriately adjusted according to the desired cold-rolled material.

[0123] The annealing step is a step of heating the cold-rolled material from 100°C to a temperature between the Ac1 point and (Ac1 point - 50°C) at a heating rate of 50°C / s or higher. The heating rate is preferably 100°C / s or higher.

[0124] This annealing step produces a cold-rolled annealed material. Annealing of the cold-rolled material begins at a temperature between 25°C and 100°C. The temperature from the Ac1 point to (Ac1 point - 50°C) is the annealing temperature in the annealing step. The heating rate can be calculated by subtracting 100°C from the annealing temperature (annealing temperature - 100°C) and dividing it by the time (s) from 100°C until the annealing temperature is reached.

[0125] By performing the annealing process under the above conditions, the coarsening of carbides is suppressed, thereby stably controlling the average carbide particle size and the number of carbides with a size of 10 μm or greater within the above ranges. Furthermore, due to the softening caused by strain recovery and fine carbide precipitation during cold rolling, a soft and highly workable cold-rolled annealed material (martensitic stainless steel) with a Vickers hardness of 320 HV or less before quenching or quenching and tempering can be obtained.

[0126] The martensitic stainless steel material according to the embodiment of the present invention manufactured as described above is soft and has good workability before quenching or quenching and tempering, and has high hardness and corrosion resistance after quenching or quenching and tempering, because, in addition to the steel composition, the average particle size of carbides, the number of carbides with a size of 10 μm or more, the Vickers hardness before quenching or quenching and tempering, the amount of retained austenite after quenching or quenching and tempering, and the amount of solid solution of C and N after quenching or quenching and tempering are controlled. Furthermore, after quenching or quenching and tempering, the martensitic stainless steel material is high in hardness and corrosion resistance, and the generation of irregular patterns can be suppressed.

[0127] The method for manufacturing a cutting tool according to an embodiment of the present invention includes a quenching step of processing the aforementioned martensitic stainless steel material, heating the material at a temperature of 1000°C to 1200°C for 5 to 60 minutes, and cooling the material at a cooling rate of 3°C / second or greater. The cooling rate is preferably 10°C / second or greater, and more preferably 20°C / second or greater.

[0128] By performing the quenching process under the above conditions, precipitates such as carbides and nitrides are fully dissolved, the amount of dissolved C and dissolved N increases, and high hardness can be achieved. In addition, by controlling the cooling rate within the above range, the reprecipitation of Cr carbonitrides during the quenching process can be suppressed, sensitization can be suppressed, and high corrosion resistance can be achieved.

[0129] The processing method of the martensitic stainless steel material is not particularly limited, and known methods such as forging and grinding can be used.

[0130] After the quenching step, a tempering step or a cold treatment step may be performed as needed. The conditions for the tempering step and the cold treatment step are not particularly limited, but the tempering step is preferably performed at a temperature of 100 to 400°C, and the cold treatment step is preferably performed at a temperature of -200 to -50°C.

[0131] The cutting tool manufactured by the above-mentioned manufacturing method is easy to process, has high hardness and corrosion resistance, good sharpness, and can also suppress the generation of irregular patterns.

[0132] Example

[0133] The present invention will be described in detail below with reference to the following examples, but the present invention is not limited to these examples.

[0134] Steels with the compositions shown in Table 1 were melted and cast into 200 mm thick slabs. These slabs were sequentially subjected to bloom rolling, hot rolling, softening, cold rolling, and annealing. The conditions for bloom rolling, hot rolling, softening, and annealing are shown in Tables 2 and 3. In some examples (Examples 21 and 22), a soaking step was performed between the bloom rolling and hot rolling steps.

[0135] In the hot rolling process, a hot-rolled sheet having a thickness of 3 mm was finally obtained.

[0136] In the softening step, the hot-rolled sheet obtained in the hot rolling step was coiled at a coiling temperature of 850° C., and then the coiled hot-rolled sheet was transferred to a batch annealing furnace and softened under the conditions shown in Tables 2 and 3.

[0137] In the cold rolling step, the softened sheet obtained in the softening step was cold rolled to a thickness of 2.0 mm.

[0138] After the annealing step, pickling was performed.

[0139] The cold-rolled annealed sheets (marteningeal stainless steel materials) obtained as described above were evaluated as follows.

[0140]

[0141]

[0142] (solid solution [C] + 0.3 [N])

[0143] The obtained cold-rolled annealed sheets were quenched under the conditions shown in Tables 2 and 3, cold-treated at -70°C, and tempered at 200°C. The solid solution amounts of C and N were measured by the electrolytic extraction residue method, and [C] + 0.3 [N] was calculated.

[0144] The solid solution amounts of C and N were measured according to the above-mentioned method.

[0145] (Vickers hardness)

[0146] The Vickers hardness (Vickers hardness before quenching or quenching and tempering) of the obtained cold-rolled annealed sheet was measured using a Vickers hardness tester. The measurement temperature was set to room temperature (25° C.). A Vickers hardness of 320 HV or less was evaluated as acceptable.

[0147] The resulting cold-rolled annealed sheets were quenched under the conditions shown in Tables 2 and 3, cold-treated at -70°C, tempered at 200°C, and then surface-polished with #80 steel. JIS surface hardness (Vickers hardness after quenching or quenching and tempering) was measured using a Vickers hardness tester. The measurement temperature was room temperature (25°C). A Vickers hardness of 500 HV or higher was considered acceptable.

[0148] (Corrosion resistance)

[0149] The resulting cold-rolled annealed sheets were quenched under the conditions shown in Tables 2 and 3, cold-treated at -70°C, and tempered at 200°C. The surfaces were then polished with #600 and subjected to the JIS Z2371:2015 "Salt Spray Test." In this evaluation, a rust area ratio of less than 10% was rated as acceptable (○), while a rust area ratio of 10% or greater was rated as unacceptable (×). Among samples with a rust area ratio of less than 10%, samples with a rust area ratio of 0% were rated as particularly excellent (◎).

[0150] (Average particle size of carbides)

[0151] The cross section of the cold-rolled annealed sheet, parallel to the rolling direction and the thickness direction, was observed using a SEM. The equivalent circle diameter (μm) of all carbide particles observed within the observation field, excluding those with an equivalent circle diameter of less than 0.10 μm and those with a portion extending beyond the observation field, was measured. The average carbide particle size (μm) was calculated by dividing the sum of the equivalent circle diameters of the measured carbide particles by the total number of measured carbide particles. However, multiple, randomly selected, non-overlapping observation fields were used to ensure that the total number of measured carbide particles was 100 or more. The equivalent circle diameter of the carbide particles was calculated from the area of ​​the carbide particles determined by image processing of the SEM image using image processing software.

[0152] (Number of carbides larger than 10 μm)

[0153] The cross section of the obtained cold-rolled annealed sheet parallel to the rolling direction and the sheet thickness direction was visually observed using a 50x optical microscope at 20 locations in a 50 mm x 50 mm area, the average number of spots was determined, and the average number was divided by the area of ​​the observed area for calculation.

[0154] (Retained austenite amount)

[0155] The resulting cold-rolled annealed sheets were quenched under the conditions shown in Tables 2 and 3, cold-treated at -70°C, and tempered at 200°C. Cross-sections of the tempered samples obtained in this manner, parallel to the rolling and thickness directions, were measured using EBSD. The BCC and FCC phases were distinguished, and their respective areas were determined. Based on these areas, the ratio of the FCC phase area to the total area of ​​the BCC and FCC phases (i.e., the FCC phase area ratio (%)) was calculated. The calculated FCC phase area ratio was used as the retained austenite amount (volume %).

[0156] Table 4 shows the above-mentioned evaluation results.

[0157]

[0158] As shown in Table 4, the cold-rolled annealed sheets (marteneous stainless steel materials) of Examples 1 to 22 were able to control [C] + 0.3 [N] to 0.15% or more, control the Vickers hardness before quenching or quenching and tempering to 320 HV or less, control the average particle size of carbides to 0.50 μm or less, and control the number of carbides with a size of 10 μm or more to 0.10 pieces / cm 2 The retained austenite content after quenching and tempering was controlled to 10.0% by volume or less. Furthermore, the cold-rolled annealed sheets of Examples 1 to 22 exhibited excellent hardness (Vickers hardness) and corrosion resistance after quenching or quenching and tempering. Furthermore, due to the small average particle size of the carbides, workability was excellent, and the formation of irregular patterns was suppressed. While Examples 21 and 22 included soaking treatment steps, corrosion resistance was improved by setting the soaking treatment temperature to a value between 1000°C and less than 1200°C and controlling the heating time to 1 to 24 hours.

[0159] In contrast, the cold-rolled annealed sheets of Comparative Examples 1 to 17 had any of the following outside the specified ranges: composition, [C] + 0.3 [N], Vickers hardness before quenching or quenching and tempering, average carbide particle size, number of carbides with a size of 10 μm or greater, and retained austenite after quenching and tempering. Therefore, the cold-rolled annealed sheets of Comparative Examples 1 to 17 did not achieve the desired properties.

[0160] Here, the relationship between [C] + 0.3 [N] (the amount of C solid solution (mass %) after quenching or quenching and tempering is expressed as [C], and the amount of N solid solution (mass %) is expressed as [N]) and Vickers hardness in some examples and comparative examples is shown in the figure. Figure 1 .like Figure 1As shown, there is a proportional relationship between [C] + 0.3 [N] and Vickers hardness, and as [C] + 0.3 [N] increases, the Vickers hardness tends to increase. In particular, it is found that by controlling [C] + 0.3 [N] to 0.15% or more, the Vickers hardness can be increased to 500 HV or more.

[0161] Next, a cutting tool was produced as follows using the obtained cold-rolled annealed sheet.

[0162] First, the obtained cold-rolled annealed sheet was punched and then ground into a tool shape. The sheet was then quenched under the conditions shown in Tables 2 and 3, cold-treated at -70°C, and tempered at 200°C. The surface was then ground, and the portion that would become the blade edge was then rough-ground and finish-ground to form a blade edge. The tools thus obtained were evaluated as follows.

[0163] (Tool machinability)

[0164] When the tool was ground into a tool shape before quenching, the case where no burn marks were generated was evaluated as acceptable (○), and the case where burn marks were generated and the tool was heated and scale was generated was evaluated as unacceptable (×).

[0165] (Sharpness of the knife)

[0166] The sharpness of the knives was evaluated using a Bendo sharpness tester.

[0167] For the sharpness test, the blade was fixed, and a 7.5mm wide sheet of paper (approximately 70μm thick) similar to newspaper was stacked on top of the blade. A load of approximately 750g was applied while the blade was moved back and forth 20mm. One back and forth motion was considered one cycle, and 100 cycles were performed. The number of sheets of paper completely cut was counted. Sharpness was considered good if 50 or more sheets of paper were cut.

[0168] (Surface pattern of the tool)

[0169] The resulting cutting tools were visually observed for irregularities on their surfaces and evaluated. Cutting tools with no visible irregularities were rated excellent (◎), those with very slight irregularities were rated (○), and those with visible irregularities were rated unacceptable (×). The evaluation results are shown in Table 5.

[0170]

[0171] As shown in Table 5, cutting tools made from the cold-rolled, annealed sheets (martensitic stainless steel) of Examples 1-22 and Comparative Examples 11 and 12 exhibit excellent workability and sharpness, while also suppressing the formation of irregular patterns. In particular, Examples 21 and 22, which undergo a soaking treatment, achieve improved sharpness and significantly suppress irregular patterns by controlling the soaking temperature to between 1000°C and 1200°C and the heating time to 1-24 hours. However, based on the above results, it is believed that Comparative Examples 11 and 12 exhibit insufficient corrosion resistance.

[0172] In contrast, the cutting tools made from the cold-rolled annealed sheets of Comparative Examples 1, 15, and 16 exhibited insufficient workability. Furthermore, the cutting tools made from the cold-rolled annealed sheets of Comparative Examples 1 to 10, 13, and 14 exhibited insufficient sharpness and were unable to suppress the generation of irregular patterns. Furthermore, the cutting tool made from the cold-rolled annealed sheet of Comparative Example 17 exhibited insufficient sharpness.

[0173] As can be seen from the above results, the present invention can provide a martensitic stainless steel material that exhibits excellent workability due to its softness before quenching or quenching and tempering, and exhibits high hardness and corrosion resistance after quenching or quenching and tempering, thereby suppressing the formation of irregular patterns, and a method for manufacturing the same. Furthermore, the present invention can provide a method for manufacturing a cutting tool that exhibits ease of processing, high hardness and corrosion resistance, excellent sharpness, and also suppresses the formation of irregular patterns.

Claims

1. A martensitic stainless steel material, Having a composition containing, on a mass basis, C: 0.305-0.600%, Si: 0.05-1.00%, Mn: 0.05-2.50%, P: 0.0085-0.0400%, S: 0.0300% or less, Cr: 13.0-18.0%, Ni: 0.01-1.00%, Mo: 0.01-1.00%, Al: 0.100% or less, N: 0.010-0.350%, Ca: 0.0001-0.0050%, O: 0.001-0.010%, with the balance being Fe and impurities, The average particle size of carbides is less than 0.50 μm. The number of carbides with a size of 10 μm or more is 0.10 per cm 2 the following, The Vickers hardness before quenching or quenching and tempering is below 320HV. The amount of retained austenite after quenching or quenching and tempering is less than 10.0 volume%, When the solid solution amount of C in mass % after quenching or quenching and tempering is represented as [C] and the solid solution amount of N in mass % is represented as [N], [C]+0.3[N] is 0.15 mass % or more.

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

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

4. The martensitic stainless steel material according to any one of claims 1 to 3, The martensitic stainless steel is used for cutting tools.

5. A method for manufacturing a martensitic stainless steel material, It includes slab rolling process, hot rolling process and softening process. In the bloom rolling process, the slab is heat treated at a temperature of 1000° C. or higher and lower than 1200° C. for 1 to 10 hours, and then rough rolled at a total reduction of 30 to 70%, including two or more passes with a reduction of 10% or more per pass, to obtain a bloom material. The slab contains, by mass, C: 0.305 to 0.600%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, and Mn: 0.05 to 1.00%. 2.50%, P: 0.0085~0.0400%, S: 0.0300% or less, Cr: 13.0~18.0%, Ni: 0.01~1.00%, Mo: 0.01~1.00%, Al: 0.100% or less, N: 0.010~0.350%, Ca: 0.0001~0.0050%, O: 0.001~0.010%, and the balance is Fe and impurities, In the hot rolling process, the slab is heat treated at a temperature of 1000° C. or higher and lower than 1200° C. for 1 to 5 hours, and then hot rolled to obtain a hot-rolled material. In the softening step, the hot-rolled material is coiled at a coiling temperature of 800° C. to 900° C., and then heated at a temperature of Ac1 point to (Ac1 point −50° C.) for 1 to 5 hours.

6. The method for producing a martensitic stainless steel material according to claim 5, A soaking treatment step of holding the bloom material at a temperature of 1000° C. or higher and lower than 1200° C. for 1 to 24 hours is further included between the bloom rolling step and the hot rolling step.

7. The method for producing a martensitic stainless steel material according to claim 5 or 6, The slab further contains, by mass, one or more selected from the group consisting of V: ​​0.50% or less, Nb: 0.50% or less, Ti: 0.30% or less, Cu: 4.0% or less, Sn: 0.10% or less, B: 0.005% or less, and Co: 0.30% or less.

8. The method for producing a martensitic stainless steel material according to any one of claims 5 to 7, It also includes cold rolling and annealing processes. In the cold rolling step, the softened material obtained in the softening step is cold rolled to obtain a cold rolled material. In the annealing step, the cold-rolled material is heated from 100° C. to a temperature ranging from the Ac1 point to (Ac1 point−50° C.) at a heating rate of 50° C. / s or higher.

9. A method for manufacturing a cutting tool, comprising: processing the martensitic stainless steel material according to any one of claims 1 to 4, followed by a quenching step of heating the material at a temperature of 1000°C to 1200°C for 5 to 60 minutes, and cooling the material at a cooling rate of 3°C / s or higher.

Images