Martensitic stainless steel sheet and method for manufacturing the same and brake disc

Abstract

To provide a martensitic stainless steel sheet having excellent wear resistance and corrosion resistance as well as excellent toughness and a method for manufacturing the same and a brake disc.SOLUTION: There is provided a martensitic stainless steel sheet which comprises 0.030 to 0.090% or less of C, 0.05 to 0.80% of Si, 0.20 to 1.50% of Mn, 0.035% or less of P, 0.015% or less of S, 11.00 to 13.50% of Cr, 0.01 to 0.50% of Ni, 0.01 to 0.70% of Cu, 0.01 to 0.50% of Mo, 0.05% or less of Al, 0.01 to 0.10% of V, 0.010 to 0.060% of N and the balance Fe with impurities, wherein the hardness is 31.0 HRC to 39.0 HRC, the crystal orientation of the central part of the sheet is 1.2 or more to random orientations at the integration degree in (200) ND orientation and the Charpy impact value at 0°C is 40 J / cm2 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a martensitic stainless steel sheet, a method for manufacturing the same, and a brake disk.

Background Art

[0002] For brake disks of motorcycles and the like, since wear resistance and corrosion resistance are required, martensitic stainless steel sheets such as SUS410, SUS410S, and SUS420J2 are used as materials for brake disks. After the steel sheet is punched into a disk shape, only the outer peripheral portion is heated to 950 to 1050 ° C by high-frequency induction heating and then quenched in a mold to build up the required hardness. However, these days, in major industrial products such as automobiles and motorcycles, reduction of carbon dioxide emissions during material production and component production is required. Therefore, in the manufacturing process of brake disks, reduction of CO2 by omitting the quenching process is desired. There are several reports on the omission of quenching of martensitic stainless steel.

[0003] Patent Document 1 shows that in order to obtain a hardness of HV = 250 to 300 without performing a quenching treatment, a hot-rolled steel sheet is made into a ferrite single-phase structure by hot-rolled sheet annealing and then cold-rolled with a rolling reduction of 15 to 70%. However, in this method, it is necessary to anneal, pickling, and cold-roll the hot-rolled steel sheet, and problems such as a decrease in productivity and an increase in cost due to additional processes are pointed out.

[0004] Further, Patent Document 2 shows that a martensitic stainless steel strip is heated to the austenite temperature range and cooled after cold rolling to obtain a quenched steel strip. In the case of Patent Document 2, the hot-rolled sheet annealing, pickling, and cold-rolling processes are added, and since quenching is performed by cold-rolled sheet annealing, it is more productive than quenching a brake disk subjected to punching press working. However, since there is carbon dioxide emission in the annealing process, the effect of reducing the CO2 emission amount is poor.

[0005] On the one hand, Patent Document 3 discloses a method for manufacturing a high-toughness martensitic stainless steel plate, which involves heating a martensitic stainless steel containing a ferrite phase in a temperature range of 1150°C or lower, then performing hot rolling with a reduction ratio of 10% or more at a temperature of at least 1000°C or lower and finishing in a temperature range of 800°C or higher, and immediately after the hot rolling, cooling at a cooling rate of 5°C / sec or more to a temperature range of 100°C or lower. In this method, hot rolling is performed in the two-phase temperature range of austenite and ferrite, and quenching is carried out during the cooling process after hot rolling. Therefore, it is considered an effective means for CO2 reduction without adding additional processes. However, cooling to 100°C or lower after hot rolling is difficult to achieve in a general hot rolling mill in a thin plate manufacturing process due to warping of the plate shape and an increase in surface defects caused thereby, even though it may be relatively easy in a thick plate factory. In addition to surface defects, the hot rolled steel strip that has martensitic transformation is prone to brittle cracking during rewinding, shape correction, blanking, and drilling processes.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a martensitic stainless steel plate having excellent wear resistance and corrosion resistance as well as excellent toughness, a method for manufacturing the same, and a brake disk.

Means for Solving the Problems

[0008] In order to reduce CO₂ emissions during the production of steel sheets as well as during the quenching of martensitic stainless steel sheets, the hot-rolled steel strip immediately after finish hot rolling at a finish temperature that results in a partially recrystallized austenite structure is rapidly cooled, for example, on a run-out table (ROT), and then coiled as an austenite single-phase structure or a partially martensitic structure, with the idea of obtaining a hot-rolled coil with a martensitic structure at room temperature without ferrite transformation during the cooling process of the hot-rolled coil.

[0009] In order to coil with austenite as the main structure and prevent ferrite transformation from austenite during the cooling process of the hot-rolled coil, it is necessary to set the coiling temperature to 550°C or lower. Also, when cooling the hot-rolled steel strip with an ROT, in order to prevent the occurrence of defects during coiling without disturbing the sheet shape, it is necessary to set the coiling temperature to 300°C or higher. Since the Ms point of SUS410 is approximately around 400°C, it is preferable to set the coiling temperature to 400°C or higher and 550°C or lower in order to make the cooling conditions of the steel strip uniform over the entire length and obtain a uniform material.

[0010] Also, during coiling, although it is a hot-rolled coil that is almost austenite single-phase, since bainite transformation must not occur during the cooling process of the coil, alloy design to delay the transformation is required. By optimizing the contents of Cr, Mn, Si, Ni, Mo, Cu, C, and N as the main alloying elements, it becomes possible to delay bainite transformation. On the other hand, excessive inclusion of these main elements causes various problems in addition to an increase in alloy cost, such as a decrease in hardness and corrosion resistance due to the formation of δ ferrite during hot rolling heating and a decrease in hardness due to an increase in retained austenite, so optimization of the composition is necessary.

[0011] The martensitic stainless steel sheet manufactured in this way has a hardness of 35 ± 4 HRC, and it is less likely to cause brittle cracking during additional processes such as rewinding and shape correction, and also during punching. However, in order to ensure stable toughness throughout the year regardless of seasonal variations, a part of the austenite structure before ROT cooling is made into a recrystallized structure, and it was conceived that most of the prior austenite grains are elongated grains and a part are equiaxed grains. Therefore, as a result of investigating the influence of the finish rolling temperature of hot rolling on the toughness of the hot rolled strip of martensitic structure, it was found that the toughness can be improved by setting the finish rolling temperature to 900 °C or higher and 1000 °C or lower.

[0012] The gist of the present invention is as follows. [1] The chemical composition is, by mass%, C: 0.030 to 0.090%, Si: 0.05 to 0.80%, Mn: 0.20 to 1.50%, P: 0.035% or less, S: 0.015% or less, Cr: 11.00 to 13.50%, Ni: 0.01 to 0.50%, Cu: 0.01 to 0.70%, Mo: 0.01 to 0.50%, Al: 0.05% or less, V: 0.01 to 0.10%, N: 0.010 to 0.060% is contained, the balance consists of Fe and impurities, the hardness is 31.0 HRC to 39.0 HRC, the crystal orientation at the center of the plate thickness has an integration degree in the (200) ND orientation of 1.2 or more with respect to the random orientation, the Charpy impact value at 0 °C is 40 J / cm 2 or more, and is a martensitic stainless steel sheet. [2] Furthermore, the martensitic stainless steel sheet according to [1], characterized in that it contains one or two or more groups of elements of the following Group A, Group B, Group C or Group D. (Group A) One or two elements of Sn: 0.001% or more and 0.1% or less, Co: 0.001% or more and 0.1% or less. (Group B) One or more elements of Nb: 0.005% or more and 0.2% or less, Ti: 0.005% or more and 0.05% or less, Zr: 0.005% or more and 0.1% or less. (Group C) B: 0.0003% or more and 0.003% or less. (Group D) One or more elements of Ca: 0.0001 - 0.0040%, Mg: 0.0001 - 0.0040%, REM: 0.001 - 0.020%. [3] A step of heating a slab having the chemical composition described in [1] or [2] and having a thickness of 150 - 250 mm to 1100 - 1250 °C, A hot rolling step of performing hot rolling on the heated slab so that the finish rolling temperature is 900 - 1000 °C to make the plate thickness 3.0 - 8.0 mm, A step of starting cooling immediately after the end of hot rolling and cooling at an average cooling rate of 20 °C / s or more, A step of coiling at 300 - 550 °C, and a method for manufacturing a martensitic stainless steel sheet, characterized by comprising the above steps. [4] The chemical composition is in mass%, C: 0.030 - 0.090%, Si: 0.05 - 0.80%, Mn: 0.20 - 1.50%, P: 0.035% or less, S: 0.015% or less, Cr: 11.00 - 13.50%, Ni: 0.01 - 0.50%, Cu: 0.01 - 0.70%, Mo: 0.01 - 0.50%, Al: 0.05% or less, V: 0.01 - 0.10%, Contains N: 0.010 - 0.060%, The balance consists of Fe and impurities, The hardness is 31.0 HRC - 39.0 HRC, The crystal orientation at the center of the plate thickness has an integration degree in the (200) ND orientation of 1.2 or more with respect to the random orientation, and the Charpy impact value at 0 °C is 40 J / cm 2 The brake disc is made of the above-mentioned martensitic stainless steel. [5] Furthermore, the brake disc according to [4], characterized by containing one or more groups of elements from the following Group A, Group B, Group C, or Group D. (Group A) One or two elements of Sn: 0.001% or more and 0.1% or less, Co: 0.001% or more and 0.1% or less. (Group B) One or more elements of Nb: 0.005% or more and 0.2% or less, Ti: 0.005% or more and 0.05% or less, Zr: 0.005% or more and 0.1% or less. (Group C) B: 0.0003% or more and 0.003% or less. (Group D) One or more elements of Ca: 0.0001 to 0.0040%, Mg: 0.0001 to 0.0040%, REM: 0.001 to 0.020%.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide a martensitic stainless steel plate, a manufacturing method thereof, and a brake disc that are excellent in wear resistance and corrosion resistance and also excellent in toughness. In particular, the martensitic stainless steel plate of the present invention can be suitably used as a material for brake discs of two-wheeled or four-wheeled vehicles. In addition, since the martensitic stainless steel plate of the present invention has sufficient hardness, it is possible to omit the quenching process in the manufacturing process of the brake disc, contributing to CO2 reduction. Also, since it has sufficient hardness, it is excellent in wear resistance, and the martensitic stainless steel plate of the present invention can be suitably used as a material for brake discs. Furthermore, since the martensitic stainless steel plate of the present invention is excellent in toughness, even if a hot-rolled coil made of the steel plate is unwound and shape correction, blanking, hole punching, etc. are performed, brittle fracture does not occur, and the defective rate of brake discs can be reduced. Furthermore, since the martensitic stainless steel sheet of the present invention has corrosion resistance such that no flow rust occurs in the salt spray test, it has excellent appearance, and thus can improve the appearance of the brake disk. In addition, according to the method for manufacturing the martensitic stainless steel sheet of the present invention, the hot-rolled sheet annealing process can be omitted, so it can also contribute to the reduction of CO2. Furthermore, since the brake disk of the present invention is excellent in wear resistance, corrosion resistance and toughness, it can be suitably used as a brake disk for a two-wheeled vehicle or a four-wheeled vehicle.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0015] In order to solve the above problems, the present inventors conducted various experiments. The outlines of each experiment are shown below.

[0016] <Experiment 1> In order to omit the hot rolling and subsequent quenching processes of the martensitic stainless steel sheet, the inventors investigated the effect of the coiling temperature on the cross-sectional hardness of the hot-rolled steel strip in order to increase the strength of the hot-rolled steel strip in the hot rolling process. Fig. 1 shows the relationship between the coiling temperature and the surface hardness (HRC hardness) of a 12.3%Cr-0.3%Si-1.2%Mn-0.04%C-0.02%N steel. As shown in Fig. 1, it was found that a hardness of about 35 HRC can be obtained by setting the coiling temperature to 550°C or lower.

[0017] The heating temperature before hot rolling was 1160°C, the thickness of the steel strip after hot rolling was 3.7 mm, the finish rolling temperature was 950°C, and the average cooling rate of ROT was about 30°C / s.

[0018] <Experiment 2> It is generally considered that the toughness of martensitic stainless steel sheets decreases due to quenching. Therefore, the effect of the coiling temperature on the toughness of the steel strip was investigated. As shown in Fig. 2, by setting the coiling temperature of a 12.3%Cr-0.3%Si-0.8%Mn-0.03%C-0.05%N steel to 550°C or lower, the impact value was improved to 40 J / cm 2 or more, and it was found that the impact value was higher than that of the quenched material.

[0019] The heating temperature before hot rolling was 1160°C, the thickness of the steel strip after hot rolling was 3.7 mm, the finish rolling temperature was 950°C, and the average cooling rate of ROT was about 30°C / s.

[0020] It was considered that the toughness was improved by setting the coiling temperature to 550°C or lower because carbide precipitation at the grain boundaries was suppressed, reducing the initiation points of fracture. On the other hand, the reason why the impact value was higher than that of the quenched material was considered to be that the crystal orientation of the martensite structure in the center and surface layers of the plate thickness changed due to the shear strain from the surface layer to the 1 / 4 plate thickness part during hot rolling, suppressing the propagation of fracture.

[0021] <Experiment 3> The toughness of the hot-rolled martensitic stainless steel plate varies depending on the crystal orientation and was expected to be affected by the austenite structure before transformation. Therefore, the effect of the finish rolling temperature on the Charpy impact value at 0 °C of the steel plate after hot rolling was investigated. A slab of 12.3% Cr - 0.3% Si - 1.2% Mn - 0.04% C - 0.02% N steel was heated to 1160 °C, hot rolled to a thickness of 3.7 mm while changing the finish temperature in hot rolling, cooled at an average cooling rate of about 30 °C / s by ROT, and a steel strip was produced by coiling at 500 °C. Then, the Charpy impact value at 0 °C of the obtained steel strip was measured. The results are shown in Fig. 3.

[0022] As shown in Fig. 3, it was found that when the finish rolling temperature exceeds 1000 °C or is less than 900 °C, the Charpy impact value decreases. When the finish rolling temperature exceeds 1000 °C, it is considered that the austenite structure that has accumulated the strain of hot rolling recrystallizes, so the accumulation of crystal orientation and the change in the thickness direction are relaxed. Also, when the hot rolling finish temperature is less than 900 °C, it is considered that the shear deformation region in the plate thickness increases, the change in crystal orientation in the plate thickness direction becomes small, and it becomes difficult to block the progress of fracture.

[0023] <Experiment 4> The hypothesis of the mechanism by which the toughness of the hot-rolled martensitic stainless steel plate changes with the finish temperature and coiling temperature of hot rolling was verified. A slab of 12.3% Cr - 0.3% Si - 1.2% Mn - 0.04% C - 0.02% N steel was heated to 1160 °C, hot rolled to a thickness of 3.7 mm with a finish rolling temperature of 950 °C, cooled at about 30 °C / s by ROT, and coiled at 100 - 800 °C while changing the coiling temperature. Then, the effect of the coiling temperature of the steel plate on the crystal orientation at the center of the plate thickness of the steel plate was investigated. The crystal orientation was comparatively evaluated in the (200)ND orientation at the center of the plate thickness. (200)ND and (100)ND are the same in terms of orientation, but (200)ND notation is usually used in the inverse pole figure measurement by X-ray diffraction, so it is denoted as (200)ND in the present invention. The results are shown in Fig. 4.

[0024] As shown in Fig. 4, the (200)ND orientation at the center of the plate thickness is greatly affected by the coiling temperature. In the temperature range of 100 to 550 °C for the coiling temperature, the surface strength in the (200)ND orientation showed stable and high values.

[0025] <Martensitic stainless steel plate> Based on the above findings, the present invention has found an ideal product structure form and its control method for a martensitic stainless steel plate suitable for use as a brake disk. Hereinafter, the martensitic stainless steel plate and its manufacturing method will be described.

[0026] Note that the martensitic stainless steel plate of the present embodiment includes a steel strip and a coil wound with the steel strip.

[0027] [Chemical composition] Hereinafter, the reasons for limiting each component of the martensitic stainless steel plate of the present embodiment will be described below. In the following description, "%" indicating the content of each element represents "mass%" unless otherwise specified.

[0028] C: 0.030 to 0.090% C is an essential element for obtaining hardness and is contained in combination with N so as to reach a predetermined hardness level. In order to avoid excessive content of C and make the most of the effect of N, in the present invention, C is set to 0.090% or less. If the content exceeds this, it will be too hard, causing problems such as brake noise and reduced toughness. From the viewpoints of hardness control and corrosion resistance improvement, the upper limit is desirably 0.060% or less. On the other hand, if it is less than 0.030%, it is necessary to contain N excessively to obtain hardness, which not only causes equipment load but also impairs productivity. Therefore, C is set to 0.030% or more. From the viewpoint of hardness stability, it is desirably 0.040% or more.

[0029] Si: 0.05% to 0.80% Si is necessary for deoxidation during melting refining, and its effect is manifested when it is 0.05% or more, so the lower limit is set at 0.05% or more. However, since Si is mixed in from raw materials such as hot metal, excessive reduction will lead to an increase in cost, so it is desirable to set it at 0.10% or more. Also, since Si narrows the austenite single-phase temperature range and impairs the hardness stability, the upper limit is set at 0.80% or less. In addition, in order to reduce the content of austenite stabilizing elements and lower the cost, it is desirable to set it at 0.60% or less.

[0030] Mn: 0.20 - 1.50% Mn is an element contained as a deoxidizer, and it expands the austenite single-phase region and contributes to an increase in hardness. Since its effect clearly appears when it is 0.20% or more, the lower limit is set at 0.20% or more. In order to stably ensure the hardness, it is desirable to set it at 0.50% or more. However, since Mn promotes the formation of oxide scale during heating before hot rolling, increases the polishing load during descaling, and increases the retained austenite, its upper limit is set at 1.50% or less. Considering the decrease in corrosion resistance caused by particulate matter such as MnS, it is desirable to set it at 1.30% or less.

[0031] P: 0.035% or less P is an element contained as an impurity in main raw materials such as hot metal and ferrochrome which are raw materials. It is a harmful element to the toughness of the steel plate and is also a stabilizing element of δ-ferrite, so the upper limit is set at 0.035% or less. Preferably, it is 0.030% or less. Since excessive reduction of P leads to an increase in cost such as the use of high-purity raw materials being essential, the lower limit of P may be 0.010% or more.

[0032] S: 0.015% or less S forms sulfide-based inclusions and deteriorates the general corrosion resistance (general corrosion and pitting corrosion) of the steel plate. Therefore, the upper limit of its content is preferably as low as possible, and is set at 0.015% or less. Also, the lower the content of S, the better the corrosion resistance. However, since desulfurization load increases for low-S and manufacturing cost increases, the lower limit may be set at 0.001% or more. Preferably, the content of S is 0.001 - 0.008%.

[0033] Cr: 11.00 - 13.50% In the present invention, Cr is an essential element for ensuring oxidation resistance and corrosion resistance. If it is less than 11.00%, these effects will not be manifested. On the other hand, if it exceeds 13.50%, the austenite single-phase region will shrink and the hardenability will be impaired. Therefore, the Cr content is set to 11.00 - 13.50%. Considering the stability of corrosion resistance and press formability, 12.00% - 13.00% is desirable.

[0034] Ni: 0.01 - 0.50% Ni may be mixed as an inevitable impurity in the alloy raw materials of stainless steel. Since it is an element effective in suppressing the progress of pitting corrosion, it is preferably contained at 0.01% or more. Also, Ni is an austenite stabilizing element and increases the hardness of the steel sheet. Since its effect is stably exhibited when contained at 0.05% or more, it is desirable to set the lower limit to 0.05% or more. On the other hand, a large amount of Ni may increase the retained austenite due to the decrease in the Ms point and lower the hardness of the steel sheet. Therefore, its upper limit is set to 0.50% or less. Considering the alloy cost, 0.03 - 0.15% is desirable.

[0035] Cu: 0.01 - 0.70% Cu is effective in improving the corrosion resistance of a martensite structure containing δ ferrite, and its effect is manifested when it is 0.01% or more. Also, Cu may be actively contained to improve the hardness of the steel sheet as an austenite stabilizing element. However, excessive inclusion of Cu leads to a decrease in hot workability and an increase in raw material cost. Therefore, Cu is set to 0.70% or less. On the other hand, considering rusting due to acid rain, etc., it is more desirable to set the lower limit to 0.02% or more. Also, considering the risk of Cu precipitation due to aging caused by the braking heat generation of the brake disc and impairing the corrosion resistance, 0.50% or less is more preferable.

[0036] Mo: 0.01 - 0.50% Mo is effective in improving the corrosion resistance of a martensite structure containing δ-ferrite, and its effect is manifested when the content is 0.01% or more. Therefore, the lower limit is set to 0.01% or more. Since Mo is also effective in improving the hardness of the steel sheet, it is preferably 0.02% or more. On the other hand, Mo is a stabilizing element of the ferrite phase, and excessive content will reduce the stability of the hardness of the steel sheet by narrowing the austenite single-phase temperature range. Therefore, the upper limit is set to 0.50% or less. Since the corrosion resistance required for the brake disc has already been ensured from the balance between Cr and N, Mo may be 0.20% or less.

[0037] V: 0.01 - 0.10% V may be intentionally contained because it has the effect of forming fine carbonitrides and suppressing the coarsening of austenite grains during hot rolling, thereby enhancing toughness. In the present invention, the V content is set to 0.01% or more. Since the toughness improvement effect due to the refinement of austenite grains is stably manifested when the content is 0.02% or more, it is preferably set to 0.02% or more as the lower limit. On the other hand, excessive V content may cause coarsening of precipitates, resulting in a decrease in the toughness and hardness of the steel sheet. Therefore, the upper limit is set to 0.10% or less. Considering the manufacturing cost and manufacturability, it is desirable to set it to 0.03% - 0.08%.

[0038] Al: 0.05% or less Al is an element that increases the ferrite phase, and excessive content will cause a decrease in hardness due to an increase in δ-ferrite. Therefore, the upper limit is set to 0.05% or less. Preferably, it is desirably 0.03% or less. Al may not be contained, and the lower limit may be set to 0%. On the other hand, Al is contained as a deoxidizing element and is also an element that improves oxidation resistance. Since its effect can be obtained when the content is 0.001% or more, the lower limit may be set to 0.001% or more.

[0039] N: 0.010 - 0.060% N is one of the very important elements in the present invention. It is an essential element for obtaining a predetermined hardness in hot-rolled sheets, similar to C, and is contained in combination with C to achieve a predetermined hardness level. Also, when quenching rapidly as a two-phase structure of austenite and δ-ferrite during ROT cooling, C may cause a sensitization phenomenon due to the precipitation of Cr carbides, resulting in a decrease in corrosion resistance. However, nitrogen may suppress the precipitation of Cr carbides and show an effect of improving corrosion resistance. Since the effect is manifested at 0.010% or more, N is set to 0.010% or more. On the other hand, the effect saturates at 0.060%, and there are concerns about a decrease in yield due to the formation of gas bubble defects and excessive hardness. Therefore, the upper limit is set to 0.060%. Considering the effect of improving corrosion resistance by strengthening the passive film, it is desirable to be in the range of 0.030% or more and 0.050% or less.

[0040] In the martensitic stainless steel sheet according to the present embodiment, the balance other than the above-described elements and the elements selectively contained hereinafter is Fe and impurities. However, other elements other than the above-described elements can also be contained within a range that does not impair the effects of the present embodiment. Here, the impurities referred to herein are components that are mixed in due to raw materials such as ores and scraps and various factors in the manufacturing process when industrially manufacturing the martensitic stainless steel according to the present invention, and are those that are allowed within a range that does not adversely affect the present invention.

[0041] β′ (beta prime): 0.60 - 2.40 β′ is a component formula for estimating the tendency of martensite transformation during ROT cooling of the target martensitic stainless steel. In order to surely obtain a martensite structure by ROT cooling in hot rolling, it is preferably 0.60 or more. On the other hand, if β′ becomes too high, minute cracks may occur due to martensite transformation when cooling the slab to room temperature, and surface defects may occur in the steel sheet. Therefore, the upper limit of β′ is preferably 2.40 or less. Since β′ also affects the temper softening resistance and the δ-ferrite phase fraction during heating before hot rolling, it is preferably 0.80 or more and 2.00 or less.

[0042] β′ = 2.7C + 2.5N + 0.4Si + Mn + 0.45Ni + 0.5Cu + 2.0Mo … Equation (1) In addition, each element in Equation (1) represents the content (mass %).

[0043] In addition, in the present invention, in addition to the above elements, one or more groups of elements from the following Group A, Group B, Group C, or Group D may be contained. (Group A) One or two elements of Sn: 0.001% or more and 0.1% or less, Co: 0.001% or more and 0.1% or less. (Group B) One or more elements of Nb: 0.005% or more and 0.2% or less, Ti: 0.005% or more and 0.05% or less, Zr: 0.005% or more and 0.1% or less. (Group C) B: 0.0003% or more and 0.003% or less. (Group D) One or more elements of Ca: 0.0001 to 0.0040%, Mg: 0.0001 to 0.0040%, REM: 0.001 to 0.020%.

[0044] Sn and Co, which are elements of Group A, are elements that contribute to the improvement of high-temperature strength and corrosion resistance.

[0045] Sn: 0.001 to 0.1% Sn, like Mo and Cu, is an element that enhances corrosion resistance by suppressing the progress of pitting corrosion. Therefore, it is preferably contained as necessary. In order to exhibit its effect, 0.001% or more is preferable. However, since Sn is known to reduce toughness due to grain boundary segregation, a content of 0.1% or less is preferable.

[0046] Co: 0.001 to 0.1% Co enhances the tendency of martensitic transformation but is a relatively expensive element. Therefore, it is preferably contained as necessary. In order to exhibit its effect, 0.001% or more is preferable. However, excessive content is feared to reduce hardness due to an increase in retained austenite, so a content of 0.1% or less is preferable.

[0047] The elements Nb, Ti, and Zr, which are elements of Group B, contribute to the improvement of tempering softening resistance.

[0048] Nb: 0.005 to 0.2% Nb is an element that precipitates finely during tempering to improve tempering softening resistance. The required content varies depending on the C and N amounts in the steel, but a content of 0.005% or more is preferable. Since there is also an effect of improving tempering softening resistance by solid-solution Nb, it is desirable to make it 0.010% or more. On the other hand, excessive content preferably makes it 0.2% or less in order to reduce the amount of solid-solution C and N in martensite and lower the hardness. In order to balance high-temperature ductility during continuous casting and hot rolling and tempering softening resistance, it is desirable to make it 0.05% or less.

[0049] Ti: 0.005 to 0.05% Ti, together with Nb and Zr, is an element that combines with C, N, and S and precipitates finely during tempering to improve tempering softening resistance. Therefore, the content of Ti preferably contains 0.005% or more. Also, since Ti has a high sulfide-forming ability and is effective in suppressing the occurrence of pitting corrosion, it is desirable to contain 0.010% or more. On the other hand, excessive content of Ti preferably makes the upper limit 0.05% or less in order to lower the hardness of martensite due to a decrease in the amount of solid-solution C and N. Considering the decrease in toughness and fatigue life due to TiN crystallized in the molten steel, it is desirable to make it 0.03% or less.

[0050] Zr: 0.005% to 0.1% Zr is an element that precipitates finely during tempering to improve tempering softening resistance, and it is desirable to contain it as needed. In order to exhibit its effect, it is preferably 0.005% or more. On the other hand, a large amount of content preferably makes it 0.1% or less because there is a concern that it may reduce the amount of solid-solution C and N in martensite and lower the hardness due to the formation of coarse carbides.

[0051] B, which is an element of Group C, is an element that contributes to the improvement of hot workability.

[0052] B: 0.0003% to 0.003% Since B has the effect of improving hot workability by increasing grain boundary strength due to grain boundary segregation, it may be contained as necessary. To exert this effect, it is preferable that the lower limit is 0.0003% or more. However, excessive inclusion may 23 reduce toughness and corrosion resistance due to the precipitation of Cr2B, (Cr, Fe)(C, B)6, so it is preferable that the upper limit is 0.003% or less.

[0053] Elements Ca, Mg, and REM in Group D contribute to the refinement of the solidification structure by oxide metallurgy and the improvement of corrosion resistance by reducing sulfides.

[0054] Ca: 0.0001 to 0.0040% Ca is an element contained for desulfurization and is also an element mixed in due to the melting loss of refractories and the entrainment of slag. To prevent defects caused by sulfides and deterioration of corrosion resistance, it is preferable that the content is 0.0001% or more. However, excessive inclusion may cause nozzle clogging due to an increase in Ca-containing oxides and the occurrence of defects, so it is preferable that the upper limit is 0.0040% or less.

[0055] Mg: 0.0001 to 0.0040% Mg is an element contained for desulfurization and is also an element mixed in due to the melting loss of refractories and the entrainment of slag. To prevent defects caused by sulfides and deterioration of corrosion resistance, it is preferable that the content is 0.0001% or more. However, excessive inclusion may cause nozzle clogging due to an increase in Mg-containing oxides and the occurrence of defects, so it is preferable that the upper limit is 0.0040% or less.

[0056] REM: 0.001 to 0.020% REM is an element contained to desulfurize and fix P in steel to prevent temper embrittlement. It may also be contained for the purpose of refining the solidification structure and improving oxidation resistance. In order to exert these effects in combination, it is preferable that REM be 0.001% or more. However, excessive inclusion may cause nozzle clogging and the occurrence of defects due to the formation of coarse oxides and sulfides, so it is preferable that the upper limit be 0.020% or less.

[0057] Here, REM (rare earth element) generally refers to the collective name of two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu) according to the general definition. These elements may be contained alone or as a mixture. The amount of REM is the total amount of these elements.

[0058] [Surface hardness of steel sheet: 31.0 HRC to 39.0 HRC] Wear resistance is required for sliding parts such as brake discs, and the higher the surface hardness, the better the wear resistance. Therefore, in order to ensure the braking life of the brake disc, the hardness of the steel sheet needs to be 31.0 HRC or more. Considering the prevention of defects when foreign matter adheres, 32.0 HRC or more is preferable. On the other hand, if the hardness becomes too high, brake noise (abnormal noise, squeaking sound) will occur during braking. In order to prevent this brake noise, it is necessary to make it 39.0 HRC or less. In order to prevent noise in cold weather, it is preferable to make it 38.0 HRC or less.

[0059] Moreover, it is preferable that most of the structure of the martensitic stainless steel sheet of this embodiment be a martensite structure.

[0060] [V-notch Charpy impact value at 0°C: 40 J / cm 2 or more] The martensitic stainless steel sheet of this embodiment is processed by punching or the like in order to be processed into a brake disc. In order to prevent sheet fracture at this time, the impact value in the V-notch Charpy impact test is 40 J / cm 2It is necessary to be as above. Also, in order to prevent the occurrence of scratches during surface grinding or partial cutting when processing the brake disk, 50 J / cm 2 or more is desirable. The higher the upper limit of the Charpy impact value, the better, but considering factors affecting productivity such as chip crushability during cutting, 250 J / cm 2 or less is preferable.

[0061] [Integrity of the (200)ND orientation at the center of the plate thickness: 1.2 or more] In order to ensure the toughness of the steel plate, control of the crystal orientation is important. When the (111)ND orientation becomes strong, the toughness decreases due to the homogenization of the structure, so it is necessary to strengthen the (200)ND orientation, and since the effect can be obtained at 1.2 or more, the (200)ND orientation integrity is set to 1.2 or more. Considering the influence of the remaining δ-ferrite and retained austenite, it is preferably 1.3 or more in order to stably obtain high toughness.

[0062] The brake disk of this embodiment is manufactured by performing a forming process such as cutting the steel plate into a predetermined shape without performing heat treatment such as a quenching process on the martensitic stainless steel plate of this embodiment. Therefore, the brake disk of this embodiment contains the above chemical components, has a hardness of 31.0 HRC to 39.0 HRC, the crystal orientation at the center of the plate thickness has an integrity of the (200)ND orientation of 1.2 or more with respect to the random orientation, and the Charpy impact value at 0 °C is 40 J / cm 2 or more. Such a brake disk can be suitably used as a component of a brake system for motorcycles or four-wheel vehicles.

[0063] <Manufacturing method> Hereinafter, the manufacturing method of the martensitic stainless steel plate of this embodiment will be described. The manufacturing method of this embodiment manufactures a slab having the chemical components described above by a continuous casting method, the thickness of the slab is in the range of 150 to 250 mm, this slab is heated to 1100 to 1250 °C, and hot rolling is performed on the heated slab so that the finish rolling temperature is 900 to 1000 °C to make the plate thickness 3 to 8 mm. Cooling is started immediately after the end of hot rolling, cooled at an average cooling rate of 20 °C / s or more, and coiled at 300 to 550 °C. Further, if necessary, mechanical descaling such as shot blasting and pickling are carried out. The manufacturing method will be described in detail below.

[0064] [Casting of Slab and Charging into Hot Rolling Heating Furnace] The thickness of the slab needs to be 150 mm or more in order to obtain the hot rolling ratio necessary for forming the structure by hot rolling. Considering the productivity during continuous casting, a slab thickness of 200 mm or more is preferable. On the other hand, if the slab thickness becomes too thick, especially the solidification structure in the 1 / 4 position to the center of the slab thickness becomes coarse, and it becomes impossible to form a hot rolled plate structure with less segregation even by increasing the heating temperature before hot rolling and lengthening the in-furnace time. Therefore, 250 mm or less is preferable.

[0065] Also, if necessary depending on the surface condition of the slab and the use of the final product, it is preferable to perform surface maintenance such as using a grinder. Further, since the target steel has a smaller grain size of the coarse solidification structure due to phase transformation, there is little risk of cracking even if the slab is not put into a heat preservation furnace while waiting for hot rolling. Therefore, in order to improve productivity, it is possible to store at room temperature. Also, it may be heat-preserved in a slab heat preservation furnace at 300 to 500 °C.

[0066] [Heating Temperature of Slab before Hot Rolling: 1100 °C or more, 1250 °C or less] When heating the slab, it is necessary to dissolve the solidification segregation and carbides in the slab into the melt, and at the same time, improve the hot workability to prevent ear cracking of the steel plate after hot rolling. For this reason, the slab is heated to 1100 °C or higher to reduce solidification segregation and dissolve carbides. On the other hand, if the heating temperature is too high, the δ-ferrite phase fraction increases and ear cracking is likely to occur, so it is set to 1250 °C or lower.

[0067] [Finish rolling temperature of hot-rolled steel strip: 900 °C or higher and 1000 °C or lower] The finish rolling temperature of the hot-rolled steel strip is measured before ROT cooling after exiting the final stand of the finish hot rolling mill. If the finish rolling temperature drops, the recrystallization of austenite is suppressed, the martensite structure unit becomes large, and toughness is impaired, so it is set to 900 °C or higher. On the other hand, if the finish rolling temperature is too high, the recrystallization of the austenite phase progresses too much, and the uniformity of the crystal orientation in the plate thickness direction progresses, which also causes a loss of toughness, so the hot rolling finish temperature is set to 1000 °C or lower.

[0068] [Thickness of the steel plate after hot rolling: 3.0 mm or more and 8.0 mm or less] The thickness of the martensitic stainless steel plate of this embodiment is 3.0 mm or more in order to suppress the recrystallization of austenite due to an increase in hot rolling strain and develop a collective structure of the martensite structure. Also, if the plate thickness becomes too thick, the ductile-brittle transition temperature of the steel plate increases due to the size effect, and the toughness decreases, so it is 8.0 mm or less.

[0069] [Average cooling rate: 20 °C / s or more] After hot rolling, in order to obtain a martensite structure, it is necessary to start cooling immediately after the finish rolling and cool down to a coiling temperature of 550°C or lower. Martensitic stainless steel has high hardenability and transforms into martensite even at a lower cooling rate compared to ordinary steel. However, when the cooling rate is slow, Cr carbides precipitate, forming a Cr-depleted layer called sensitization, which impairs the corrosion resistance. Therefore, the average cooling rate should be 20°C / s or higher. However, if the average cooling rate is increased too much, water may remain on the steel plate, resulting in shape defects due to uneven cooling. Therefore, it is desirable that the average cooling rate be 300°C / s or lower.

[0070] Cooling is performed by water cooling on a run-out table (ROT) attached to the hot rolling facility. Since the run-out table (ROT) is installed between the finish rolling roll and the coiler, water cooling can be started within 3 seconds after the finish rolling. Also, coiling can be started immediately after the water cooling ends. The average cooling rate is the value obtained by dividing the difference between the surface temperature of the steel plate at the start of water cooling and the surface temperature of the steel plate at the end of water cooling by the required time from the start of water cooling to the end of water cooling.

[0071] [Coiling temperature: 300°C or higher and 550°C or lower] The cooled steel plate is coiled at a temperature of 550°C or lower in order to obtain a martensite structure and prevent sensitization after coiling. On the other hand, if the coiling temperature is lowered too much, the strength of the steel strip increases, the sheet shape is disturbed, and surface scratches are likely to occur. Therefore, the coiling temperature should be 300°C or higher.

[0072] The steel plate obtained by the above manufacturing method has a main structure of martensite structure and the surface hardness is in the range of 35.0 ± 4.0 HRC. Since ear cracking hardly occurs at both end faces in the width direction of the hot rolled steel plate, the yield is good. Also, by preventing sensitization, the corrosion resistance on the polished surface is good, and almost no rust is observed even when a salt spray test is performed.

[0073] [Descaling] After coiling, the steel plate may be descaled by mechanical methods such as shot blasting, bending rolls, and grinding brushes, and then immersed in acid for descaling. For pickling, it is preferable to use a bath with sulfuric acid as the main component at 50 to 90 °C from the viewpoint of the resulting surface properties. Pickling after mechanical descaling may be omitted, or the descaling process itself may be omitted.

[0074] <Characteristic evaluation> The surface hardness is measured by the Rockwell hardness test method specified in JIS Z2245:2021. The corrosion resistance is evaluated by performing the salt spray test specified in JIS Z 2371:2015 for 24 hours after polishing the surface of the steel plate to #600 finish, and checking for the presence or absence of running rust on the surface of the steel plate after the test. The toughness is evaluated by taking a sub-size V-notch test piece with the thickness of the steel plate from the steel plate, performing the Charpy impact test specified in JIS Z2242:2018 at 0 °C, and measuring the Charpy impact value. The crystal orientation at the center of the plate thickness is evaluated, for example, by measuring the inverse pole figure using an X-ray diffractometer manufactured by Shimadzu Corporation and obtaining the (200)ND orientation integration degree.

Example

[0075] Next, the present invention will be described in more detail with reference to examples. Slabs with a thickness of 250 mm having the steel compositions shown in Table 1A and Table 1B were cast, heated to a predetermined temperature in a heating furnace, hot-rolled, cooled on a ROT, and coiled to obtain hot-rolled steel strips. Cooling on the ROT started water cooling within 3 seconds after the end of hot rolling. The slab heating temperature, finish rolling temperature, average cooling rate in the ROT, and coiling temperature were as shown in Table 2, in accordance with hot rolling conditions C01 to C11 and D01 to D11.

[0076] Among the manufacturing conditions shown in Table 2, in Conditions C01 - C11 and D01 - D09, hot - rolled plate annealing and induction hardening were omitted. After mechanical descaling by shot blasting, sulfuric acid pickling was performed to remove the scale. For the stainless - steel plates of Test Examples P01 - P40 and R01 - R30 thus obtained, various properties were evaluated. The results are shown in Table 3A and Table 3B.

[0077] Also, among the conditions shown in Table 2, in Condition D10, hot - rolled plate annealing was performed by heating the coiled steel plate at 800°C for 4 hours. After mechanical descaling by shot blasting, sulfuric acid pickling was performed to remove the scale. Induction hardening was omitted. For the stainless - steel plate of Test Example R31 thus obtained, various properties were evaluated. The results are shown in Table 3A and Table 3B.

[0078] Furthermore, in Condition D11, hot - rolled plate annealing was performed by heating the coiled steel plate at 800°C for 4 hours. After punching the steel plate into a disk shape with a diameter of 200 mm, the outer peripheral part with a width of 50 mm was heated to 1000°C by a high - frequency induction heating device, and then die quenching was performed. For the disk - shaped stainless - steel plate of Test Example R32 thus obtained, various properties were evaluated. The results are shown in Table 3A and Table 3B.

[0079]

Table 1A

[0080]

Table 1B

[0081]

Table 2

[0082] <Property Evaluation> [Rockwell Hardness Test] Based on the "Rockwell Hardness Test Method" of JIS Z 2245:2021, after smoothing the surface of the steel plate by wet grinding for smoothing, a hardness test was carried out on the surface of the steel plate using the C scale or B scale of Rockwell hardness. Those with a hardness in the range of 31.0 HRC to 39.0 HRC were considered qualified, and those that deviated were considered defective. The results are shown in Table 3A and Table 3B.

[0083] [Charpy Impact Test] Based on the "Charpy Impact Test Method for Metallic Materials" of JIS Z2242:2018, a sub-size V-notch test piece with the thickness of the steel plate as the thickness was cut out from the steel plate, and the test was carried out at 0 °C to measure the impact value. 40 J / cm 2 The above was considered qualified, and 40 J / cm 2 Less than that was considered defective. The results are shown in Table 3A and Table 3B.

[0084] [(200)ND Orientation Integration Degree] The cross-section in the thickness direction of the steel plate was exposed, the center part of the thickness of the cross-section was used as the evaluation surface, and an inverse pole figure was measured using a sample with the evaluation surface chemically polished. For the measurement of the inverse pole figure, an X-ray diffractometer (X-RAY DIFFRACTOMETER RINT2200) manufactured by Rigaku Corporation was used, and the measurement was carried out using Mo-Kα rays as the X-ray source. The X-ray output conditions were 40 kV and 30 mA. The (200)ND orientation integration degree was obtained from the inverse pole figure. The value obtained by dividing the integrated intensity in the (200) orientation by the integrated intensity of the random sample was defined as the (200)ND orientation integration degree. As the random sample, a sample prepared by sintering powders of extra-low carbon ferritic stainless steel with Fe-17 mass% Cr was used. Those with a (200)ND orientation integration degree of 1.2 or more were considered qualified, and those less than 1.2 were considered defective. The results are shown in Table 3A and Table 3B.

[0085] [Corrosion Resistance] Based on the "Salt Spray Test Method" of JIS Z 2371:2015, a 200-mm-diameter disc-shaped test piece with a surface finish of wet grinding to 600 grit was subjected to a neutral salt spray test for 24 hours, and the occurrence of running rust was confirmed in the entire area of the disc-shaped test piece. Those with no running rust in the entire area of the disc-shaped test piece were designated as "○○", those with running rust in the entire area were designated as "××", and those with running rust only in the inner peripheral part within a circle with a radius of 150 mm from the center on the surface of the disc-shaped test piece were designated as "○×". "○○" was regarded as qualified, and "××" and "〇×" were regarded as defective. The results are shown in Table 3A and Table 3B.

[0086]

Table 3A

[0087]

Table 3B

[0088] In Test Nos. P01 to P40 of the present invention examples, the surface hardness was in the range of 31.0 HRC to 39.0 HRC, no running rust occurred in the salt spray test, and the Charpy impact value at 0 °C was 40 J / cm 2 or more. Also, in Test Nos. P01 to P40, the (200)ND orientation in the center of the plate thickness was developed to 1.2 or more.

[0089] Despite Test Nos. P01 to P40 omitting the hot rolling plate annealing and quenching processes after hot rolling, they were excellent in wear resistance, toughness, and corrosion resistance. Therefore, they could contribute to the reduction of CO2 emissions.

[0090] On the other hand, in the case of R01, which is a comparative example, since C was less than 0.030% and Ti exceeded 0.05%, the hardness was poor. In the case of R02, since C exceeded 0.090%, the hardness was poor, and since B exceeded 0.003%, chromium boride precipitated and the corrosion resistance was also poor.

[0091] Since Si in R03 was less than 0.05%, deoxidation and desulfurization were insufficient, resulting in an increase in oxide-based inclusions and sulfide-based inclusions, and thus poor corrosion resistance and toughness. Since Si in R04 exceeded 0.80%, the amount of δ-ferrite increased and the hardness was poor.

[0092] Since Mn in R05 was less than 0.20%, the austenite stability decreased, the amount of δ-ferrite increased, the hardenability decreased, and the hardness was poor. Since Mn in R06 exceeded 1.50%, the formation of retained austenite led to poor hardness.

[0093] Since P in R07 exceeded 0.035%, the δ-ferrite was stabilized and remained in the structure even after hot rolling, resulting in poor hardness. Since S in R08 exceeded 0.015%, the amount of sulfide-based inclusions increased and the toughness was poor.

[0094] Since Cr in R09 was less than 11.00%, the corrosion resistance was poor. Since Cr in R10 exceeded 13.50% and Nb exceeded 0.20%, a large amount of δ-ferrite remained in the structure, and the amount of solid-solved C in martensite also decreased, resulting in poor hardness. Also, the corrosion resistance decreased.

[0095] Since Ni in R11 was less than 0.01%, the progress of pitting corrosion was not suppressed and the corrosion resistance was poor. Also, since Ti exceeded 0.05%, the hardness of martensite decreased and the hardness was poor. Since Ni in R12 exceeded 0.50%, retained austenite was formed and the hardness was poor.

[0096] Since Cu in R13 was less than 0.01%, the progress of pitting corrosion was not suppressed and the corrosion resistance was poor. Since Cu in R14 exceeded 0.60%, the formation of retained γ led to poor hardness. Also, the corrosion resistance decreased.

[0097] Since Mo in R15 was less than 0.01%, the corrosion resistance of martensite decreased. In addition, since Ca exceeded 0.0040%, water-soluble sulfides were generated, so the progress of pitting corrosion was not suppressed and the corrosion resistance was poor. Since Mo in R16 exceeded 0.50%, the hardness was poor due to the formation of residual γ.

[0098] Since V in R17 was less than 0.01%, the γ grain growth during hot rolling progressed too much and the toughness was poor. Since V in R18 exceeded 0.10%, the amount of solid-solved C in martensite decreased and the hardness was poor.

[0099] Since Al in R19 exceeded 0.05%, the amount of δ ferrite increased during heating before hot rolling, the amount of residual δ ferrite in the steel plate increased, and the amount of solid-solved N in martensite decreased, so the hardness was poor.

[0100] Since N in R20 was less than 0.010%, the amount of solid-solved N in martensite decreased and the hardness was poor. Furthermore, since REM exceeded 0.020%, the corrosion resistance was poor due to the formation of water-soluble sulfides. Since N in R21 exceeded 0.06%, the amount of solid-solved N in martensite increased too much and the hardness was poor.

[0101] Since the heating temperature before hot rolling of R22 was low, solidification segregation remained in the steel plate, so the toughness and corrosion resistance were poor. Since the heating temperature before hot rolling of R23 exceeded 1250°C, the amount of δ ferrite increased and remained in the steel plate, so the hardness was poor.

[0102] Since the thickness of the steel plate of R24 was less than 3.0 mm, the recrystallization of austenite was promoted due to the increase in hot rolling strain, and the randomization of crystal orientation was promoted, so the toughness was poor. Since the thickness of the steel plate of R25 exceeded 8.0 mm, the ductile-brittle transition temperature of the steel plate increased due to the plate thickness effect, and the toughness was poor.

[0103] In R26, since the finish rolling temperature exceeded 1000°C, the recrystallization of austenite was promoted and the randomization of crystal orientation was promoted, resulting in poor toughness. In R27, since the finish rolling temperature was less than 850°C, austenite recrystallization did not occur. Along with the coarsening of the austenite structure, the toughness of martensite decreased, resulting in poor toughness.

[0104] In R28, since the average cooling rate in ROT was less than 20°C / s, Cr carbides precipitated and the prior austenite grain boundaries in the martensite structure were sensitized, resulting in poor corrosion resistance and toughness.

[0105] In R29, since the coiling temperature exceeded 550°C, the precipitation of Cr carbides progressed and partial ferrite transformation occurred, resulting in poor hardness and poor corrosion resistance. In R30, since the coiling temperature was less than 300°C, the formation of hot rolling defects increased the initiation points of fracture, resulting in poor toughness.

[0106] In R31, since the coiling temperature exceeded 550°C and hot rolled plate annealing was performed, the hardness, corrosion resistance, and toughness were all poor. In R32, the coiling temperature exceeded 550°C and quenching by high-frequency heating was performed after hot rolled plate annealing, but due to insufficient quenching heating in the center of the disk, the corrosion resistance was poor.

Industrial Applicability

[0107] According to the present invention, it is possible to produce, with good productivity, a martensitic stainless steel sheet excellent in wear resistance, corrosion resistance, and toughness, which is suitable for brake disk applications and can reduce the CO2 emissions during the production of materials and the processing of parts, as required in a low-carbon society. Therefore, the present invention contributes to the development of the industrial world.

Claims

1. The chemical composition is by mass percentage: C: 0.030 to 0.090%, Si: 0.05 to 0.80%, Mn: 0.20 to 1.50%, P: 0.035% or less, S: 0.015% or less, Cr: 11.00 to 13.50%, Ni: 0.01 to 0.50%, Cu: 0.01 to 0.70%, Mo: 0.01 to 0.50%, Al: 0.05% or less, V: 0.01 to 0.10%, N: 0.010 to 0.060%, and the balance consists of Fe and impurities, the hardness is 31.0 HRC to 39.0 HRC, and the crystallographic orientation at the center of the plate thickness has an integration degree in the (200) ND orientation of 1.2 or more with respect to the random orientation. The Charpy impact value at 0 °C is 40 J / cm or more ２ A martensitic stainless steel sheet characterized by the above.

2. The martensitic stainless steel sheet according to claim 1, further comprising one or more groups of elements from the following Group A, Group B, Group C, or Group D. (Group A) One or two elements of Sn: 0.001% or more and 0.1% or less, Co: 0.001% or more and 0.1% or less. (Group B) One or more elements of Nb: 0.005% or more and 0.2% or less, Ti: 0.005% or more and 0.05% or less, Zr: 0.005% or more and 0.1% or less. (Group C) B: 0.0003% or more and 0.003% or less. (Group D) One or more elements of Ca: 0.0001 to 0.0040%, Mg: 0.0001 to 0.0040%, REM: 0.001 to 0.020%.

3. A step of heating a slab having the chemical composition according to claim 1 or claim 2 and having a thickness of 150 to 250 mm to 1100 to 1250°C, a hot rolling step of performing hot rolling on the heated slab such that the finish rolling temperature is 900 to 1000°C to make the plate thickness 3.0 to 8.0 mm, a step of starting cooling immediately after the end of hot rolling and cooling at an average cooling rate of 20°C / s or more, and a step of coiling at 300 to 550°C. A method for manufacturing a martensitic stainless steel sheet, characterized by comprising the above steps.

4. The chemical composition is by mass percentage: C: 0.030 to 0.090% or less, Si: 0.05 to 0.80%, Mn: 0.20 to 1.50%, P: 0.035% or less, S: 0.015% or less, Cr: 11.00 to 13.50%, Ni: 0.01 to 0.50%, Cu: 0.01 to 0.70%, Mo: 0.01 to 0.50%, Al: 0.05% or less, V: 0.01 to 0.10%, N: 0.010 to 0.060%, and the balance consists of Fe and impurities. The hardness is 31.0 HRC to 39.0 HRC, the crystal orientation at the center of the plate thickness has an integration degree in the (200) ND orientation of 1.2 or more with respect to the random orientation, Charpy impact value at 0°C is 40 J / cm ２ A brake disc made of a martensitic stainless steel with the above properties.

5. Furthermore, the brake disc according to claim 4, characterized by containing one group or two or more groups of elements of the following Group A, Group B, Group C or Group D. (Group A) One or two elements of Sn: 0.001% or more and 0.1% or less, Co: 0.001% or more and 0.1% or less. (Group B) One or more elements of Nb: 0.005% or more and 0.2% or less, Ti: 0.005% or more and 0.05% or less, Zr: 0.005% or more and 0.1% or less. (Group C) B: 0.0003% or more and 0.003% or less. (Group D) One or more elements of Ca: 0.0001 to 0.0040%, Mg: 0.0001 to 0.0040%, REM: 0.001 to 0.020%.

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