JP6635890B2 - Martensitic stainless steel sheet for cutting tools with excellent manufacturability and corrosion resistance - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a martensitic stainless steel plate for a cutting tool having excellent corrosion resistance after quenching or quenching and tempering, and excellent in productivity.

  The general applications of martensitic stainless steel and the types of steel used in each application are summarized. SUS420J1 and SUS420J2 are generally used for tools such as tableware knives (table knives), scissors, loom parts, and calipers. SUS440A steel is used for Western knives, fruit knives and the like which are used and require higher hardness. In addition, SUS410 steel is used for a brake disk, a reinforcing bar, and the like of a motorcycle. This is because in such applications, plating and painting for rust prevention and the use of rust-preventive oil are difficult, and high hardness that is strong against abrasion is required. The specifications of these martensitic stainless steels are defined by the amount of C. SUS410 is C: 0.15% or less and Cr is 11.5 to 13.5%. SUS420J1 is C: 0.16 to 0.25%. SUS420J2 is classified as C: 0.26 to 0.40%, Cr is 12 to 14%, and SUS440A is classified as C: 0.60 to 0.75% and Cr is 16 to 18%. Have been. The higher the C content, the higher the quenched hardness, but the lower the productivity and the toughness after quenching. Therefore, SUS410 is generally used in a quenched state, and SUS420 is generally tempered to improve toughness. It is a target.

  The corrosion resistance of these stainless steels is generally classified by components, and it is known that the corrosion resistance is improved by adding Cr, Mo, and N. Many studies have been made on the effect of each element, and even in martensitic stainless steel, the pitting corrosion resistance index PRE = Cr + 3.3Mo + 16N can be arranged, and it is said that the larger this value is, the higher the corrosion resistance is. In addition, since the steel may be used after being quenched and then polished, it is also necessary to reduce the amount of Al or the like to avoid large inclusions and improve the polishing properties.

  These findings are explained in the patent literature. First, in Patent Document 1, high hardness martensitic stainless steel containing C: less than 0.15%, Cr: 12.0 to 18.5%, and N: 0.40 to 0.80% and having excellent corrosion resistance. Is described.

Nitrogen is effective in improving corrosion resistance and is an inexpensive element that expands the austenite range. However, nitrogen that exceeds the solid solubility limit at the time of melting and casting forms bubbles, and the problem is that a sound steel ingot cannot be made. The solid solubility limit of nitrogen varies depending on the components and the atmospheric pressure of the atmosphere. As a component, the influence of the amounts of Cr and C is large. When a martensitic stainless steel such as SUS420J1 or SUS420J2 is cast under atmospheric pressure, the amount of dissolved nitrogen is generally reported to be about 0.1%. I have.
Therefore, in Patent Literature 1, 0.40% or more of nitrogen is dissolved by pressure casting. However, the pressure casting method is difficult to continuously cast, has low productivity, and is not suitable for mass production. Also, there is a problem that nitrogen blow occurs even in pressure casting.

  Therefore, in Patent Document 2, in a method of dissolving nitrogen by using a pressure casting method, C: 0.15% or less, Cu: 0.05% or more and 3.0% or less, Ni: 0.05% Mo, Ni, Cr: 13.0% to 20.0%, Mo: 0.2% to 4.0%, N: 0.30% to 0.80%. It is said that by positively adding N and the like, the amount of dissolved N is increased and nitrogen blow is suppressed. Although it is thought that the blow hole is improved by this method, continuous casting is difficult because pressure casting is essential, and the problem of low productivity has not been solved. Further, there is a problem that the raw material cost is increased by adding Ni, Mo, or the like.

On the other hand, Patent Literature 3 discloses a pressure casting method and a technique for improving the corrosion resistance of martensitic stainless steel without adding a large amount of Mo or Ni. In Patent Document 3, C: 0.03% or more and 0.25% or less, Sn: 0.03% or more and 0.15% or less, N: 0.01% or more and 0.08% or less, and a quenching and tempering hardness of 300 HV. By setting it to 600 HV or less, the effect of improving the corrosion resistance by Sn is obtained. However, in this technique, since the amount of C is in the range of SUS420J1 steel, the increase in quenching hardness due to C is small. Therefore, there is a problem that the toughness after quenching is reduced. Further, even when C and N are added to the maximum and solid solution is obtained, the obtained hardness does not exceed 550 HV, which is not suitable for applications requiring higher hardness.
Patent Literature 4 discloses a steel in which the corrosion resistance is improved by adding a small amount of Sn and an optimum amount of N. However, its corrosion resistance evaluation was only SST24hr, which was somewhat insufficient.

  As techniques for obtaining high hardness, there are EN1.4403 steel and EN1.411 steel disclosed in Non-Patent Document 1. EN1.4034 steel has C: 0.43% to 0.50%, Cr: 12.5% to 14.5%, Si: 1% or less, Mn: 1% or less, P: 0.04%. Hereinafter, S: 0.015% or less. In EN1.411 steel, C: 0.48% to 0.60%, Cr: 13.0% to 15.0%, Mo: 0.50% to 0.80%, V: 0. 15% or less, Si: 1% or less, Mn: 1% or less, P: 0.04% or less, S: 0.015% or less. However, even if the amount of C is simply increased, the solution of the carbide requires heating at a high temperature for a long time to reduce the productivity of the quenching step. In addition, when the cooling rate at the time of quenching is low, the precipitation of Cr carbide causes There is a problem that sensitization occurs to reduce corrosion resistance.

  As described above, various techniques for improving the corrosion resistance of martensitic stainless steel have been proposed. However, in Patent Documents 1 and 2, the addition of N for improving the rust resistance requires a pressure casting method, and the production of the steel is difficult. The problem was that there was difficulty in productivity and productivity. In addition, nitrogen blow tends to occur even in pressure casting, and it is necessary to increase the solid solubility limit of nitrogen by adding Mo, Ni, or the like, so that an increase in alloy cost has been a problem.

  Patent Literature 3 has a problem that it is difficult to obtain a quenching and tempering hardness exceeding 550 HV. In addition, when heating at a high temperature for a long time to form a solution of carbonitride, γ grains are coarsened and quenching and tempering toughness is reduced.

  In the high-C martensitic stainless steel described in Non-Patent Document 1, it is difficult to completely turn the carbide into a solution, and even if heated at a high temperature for a long time, the undissolved carbonitride is present, so that the gamma grains are coarse. It is difficult to reduce the quenching and tempering toughness, but the carbonitride coarsened during hot-rolled sheet annealing is slow in solution during quenching, and it is difficult to obtain quenching hardness corresponding to the C content. In addition, there is also a problem that sensitization is apt to occur during the quenching and cooling process, and the corrosion resistance is reduced.

JP-A-2002-25697 JP 2005-344184 A JP 2010-215995 A WO2015 / 022932A1

Stainless steel European standard EN10088-2

  Generally, the corrosion resistance of stainless steel is greatly affected by its components, and is classified by a pitting resistance index PRE = Cr + 3.3Mo + 16N. The higher the value, the higher the corrosion resistance. The corrosion resistance at this time refers to a neutral chloride aqueous solution environment. Examples of the evaluation method include a pitting potential measurement of stainless steel specified in JIS G0577 and a salt spray test specified in JIS Z2371. Are used. However, except for applications used in water tanks such as chemical and food plants and water heaters, and in beach environments, that is, in everyday indoor environments, the possibility of exposure to high-concentration chloride environments is extremely low. As in the case of SUS420J1 steel, sufficient corrosion resistance can be obtained with about 13% Cr.

  However, in some cases, the corrosion resistance (rust resistance) expected from the base metal component may not be obtained, and a solution has been desired for high-C martensitic stainless steel.

  The present inventors have conducted detailed studies on the corrosion resistance (rust resistance) of high-C martensitic stainless steel in order to achieve the above object. As a result, it has been found that although the corrosion resistance may be reduced due to the sensitization of the carbonitride, the corrosion resistance may still be inferior even if the sensitization is avoided by setting conditions during quenching. As a result of further detailed investigation, it has been found that steelmaking inclusions having a maximum diameter of 10 μm or more are likely to become rusting points, and that if there are many such inclusions, rust resistance will be low.

  Furthermore, it has been found that this kind of inclusions contains a large amount of Al, Ca, and O. In order to suppress these inclusions, it can be achieved by controlling Al, Ca, and O to a certain value or less. It was also found that the rust resistance was improved. Further, since the Cr content of the steel of the present invention may be relatively low, it has been found that the corrosion resistance in a neutral chloride aqueous solution environment is greatly improved by adding a trace amount of a corrosion resistance improving element such as Ni, Cu, or Mo.

  The present invention has been achieved based on these findings, and means for solving the problems of the present invention, that is, the manufacturability of the present invention, a martensitic stainless steel sheet for cutting tools excellent in corrosion resistance are as follows. is there.

(1) In mass%,
C: 0.40 to 0.50%,
Si: 0.05 to 0.60%,
Mn: 0.5-1.5%,
P: 0.035% or less,
S: 0.010% or less,
Cr: 11.0 to 15.5%,
Ni: 0.01 to 0.30%,
Cu: 0.01 to 0.30%,
Mo: 0.01 to 0.30%,
V: 0.01 to 0.10%,
Al: 0.02% or less,
Sn: 0.002 to 0.10%,
N: 0.010-0.035%,
Ca: 0.0001 to 0.0010%,
O: 0.001 to 0.01% or less, the balance being Fe and unavoidable impurities,
And satisfy Cu + Ni + Mo = 0.05 to 0.30%,
Further, the number of inclusions having a size of 10 μm or more is 0.2 / cm ² or less.
(2) Further, one or more of Nb: 0.05% or less, Ti: 0.05% or less, Bi: 0.1% or less, and B: 0.0050% or less are contained by mass%. The martensitic stainless steel for cutting tools according to (1), which is characterized in that:

  The high-C martensitic stainless steel of the present invention enables the production of a martensitic stainless steel sheet for cutting tools excellent in corrosion resistance, and the present steel is excellent in productivity and can be provided at a lower cost.

  Hereinafter, embodiments of the present invention will be described. First, the reason for limiting the steel composition of the stainless steel sheet of the present embodiment will be described. The notation of% for the composition means mass% unless otherwise specified.

C: 0.40 to 0.50%
C is an element essential for obtaining a predetermined hardness after quenching. To stably obtain a Vickers hardness of 550 HV or more required as a high C martensitic stainless steel, 0.40% or more is required. On the other hand, if added excessively, sensitization at the time of quenching is promoted and corrosion resistance is impaired, and the toughness after quenching is also reduced due to undissolved carbonitrides. In consideration of a decrease in hardness and toughness due to a change in quenching heating conditions, the content is preferably 0.42% or more and 0.48% or less.

Si: 0.05 to 0.60%
Si is necessary for deoxidation at the time of refining and refining, and is also useful for suppressing the formation of oxide scale at the time of quenching heat treatment. % Or more. On the other hand, if the content of Si is low, deoxidation tends to be insufficient, the number of inclusions increases, and there may be a case where rust occurs as a starting point, resulting in poor corrosion resistance. However, the upper limit of Si was set to 0.60% in order to narrow the austenite single-phase temperature range and impair quenching stability. If it is less than 0.05%, flaws due to oxide-based inclusions occur. In order to reduce the rate of occurrence of flaws due to the oxide-based inclusions, the content is desirably 0.30% or more.

Mn: 0.5-1.5%
Mn is an element added as a deoxidizing agent, and also expands the austenite single phase region and contributes to the improvement of hardenability. If Mn is not added sufficiently, the two-phase region expands and the α-phase increases. As a result, the amount of Cr carbonitride increases, and a Cr deficient layer is formed around the carbon nitride, so that it easily becomes a rusting point and the corrosion resistance decreases. Since the effect of the addition of Mn clearly appears at 0.5% or more, the content is set to 0.5% or more. In order to stably secure hardenability, it is desirable that the content be 1.1% or more. However, excessive Mn lowers the corrosion resistance, promotes the formation of oxide scale during quenching and heating, and increases the subsequent polishing load, so the upper limit is made 1.5% or less. 1.3% or less is desirable in consideration of a decrease in corrosion resistance due to granulated matter such as MnS.

P: 0.035% or less P is an element contained as an impurity in the main material such as hot metal or ferrochrome as the material. Since it is a harmful element to the hot-rolled annealed sheet and toughness and corrosion resistance after quenching, the content is set to 0.035% or less. In addition, it is preferably 0.030% or less. An excessive reduction leads to an increase in cost such as indispensable use of a high-purity raw material, so that the lower limit of P is preferably 0.010%.

S: 0.010% or less S forms sulfide-based inclusions, deteriorating the general corrosion resistance (corrosion and pitting) of steel materials, and deteriorating hot workability to reduce the edge of hot-rolled steel sheets. In order to enhance cracking sensitivity, the upper limit of the content is preferably as small as possible, and is set to 0.010% or less. The lower the S content, the better the corrosion resistance. However, the lower the S content, the greater the desulfurization load and the higher the production cost. Therefore, the lower limit is preferably made 0.001%. In addition, it is preferably 0.001 to 0.008%.

Cr: 11.0 to 15.5%
Cr must be at least 11.0% in order to maintain the corrosion resistance required in the main applications of martensitic stainless steel. On the other hand, the upper limit was set to 15.5% in order to prevent generation of residual austenite after quenching. In order to exhibit these effects more effectively, 12.0 to 14.0% is preferable.

Ni: 0.01 to 0.30%
Ni is an austenite stabilizing element like Mn. It also has the effect of improving the toughness after quenching. On the other hand, if a large amount is added, there is a possibility that the press formability of the hot-rolled annealed steel sheet may be reduced due to solid solution strengthening, and it is an expensive element, so its upper limit is set to 0.30%. On the other hand, it is an element effective in suppressing the progress of pitting corrosion, and its effect is stably exhibited by adding 0.01% or more, so the lower limit is preferably made 0.01%. In addition, since it is an expensive element, 0.01 to 0.15% is desirable in consideration of alloy cost.

Cu: 0.01 to 0.30%
Cu is effective in improving the corrosion resistance of a martensitic structure containing δ ferrite, and the effect is exhibited at 0.01% or more. In some cases, aggressive addition is performed as an austenite stabilizing element to improve hardenability. However, excessive addition leads to a reduction in hot workability and an increase in raw material costs, so the upper limit is 0.30%.

Mo: 0.01 to 0.30%
Mo is effective in improving the corrosion resistance of a martensite structure containing δ ferrite, and the effect is manifested at 0.01% or more, so the lower limit is made 0.01%. Mo is a stabilizing element for the ferrite phase, and excessive addition impairs the quenching characteristics by narrowing the austenite single-phase temperature range, so the upper limit is made 0.30%.

V: 0.01 to 0.10%
V is generally contained in the range of 0.01 to 0.10% because V is mixed as an inevitable impurity into the alloy raw material of the ferritic stainless steel and is difficult to remove in the refining process. In addition to forming fine carbonitrides to improve the wear resistance of the brake disc and improving the corrosion resistance, it is an element that is intentionally added as necessary. Since the effect is stably exhibited by adding 0.02% or more, the lower limit is preferably set to 0.02%. On the other hand, if added excessively, the precipitates may be coarsened, and as a result, the toughness after quenching is reduced. Therefore, the upper limit is set to 0.10%. In consideration of manufacturing cost and manufacturability, it is preferable to set the content to 0.03 to 0.08%.

Al: 0.02% or less Al is an element that improves oxidation resistance in addition to being added as a deoxidizing element. Since the effect is obtained at 0.001% or more, it is preferable to set the lower limit to 0.001% or more. On the other hand, excessive addition tends to form large oxide-based inclusions. In the present invention, since the rust resistance of the mother phase is reduced to the last minute for cost reduction, the presence of inclusions is large, and in order to reduce and reduce the inclusions, the upper limit of Al is set to 0.02%. The present invention is susceptible to inclusions. Therefore, the lower the Al content is, the more preferable it is. From the viewpoint of deoxidation and cost, the content is desirably 0.01% or less. Of course, Al may not be contained. Here, Al is T. Al.

Sn: 0.002 to 0.10% or less Sn is an element effective for improving corrosion resistance after quenching, and is preferably 0.002% or more, and preferably 0.05% or more if necessary. However, excessive addition promotes edge cracking during hot rolling, so that the content is preferably 0.10% or less.

N: 0.010-0.035%
N has an effect of being excellent in rust resistance when it is dissolved. The lower limit is 0.010% at which the effect is clearly exhibited. However, when a Cr-based nitride is formed, a Cr-deficient layer may occur, in which case the rust resistance is reduced. Further, if it is added excessively, it is difficult to control in the steel making stage, and it is easy to form a bubble-type defect. When a bubble-based defect is formed, it is likely to become a rusting point, which not only lowers rust resistance but also lowers the yield, so the upper limit is 0.035%. More preferably, it is 0.020% or less.

Ca: 0.0001-0.0010%
Ca is added for the purpose of adjusting the composition at the steelmaking stage, but is added because it acts as a strong deoxidizer and has the effect of accelerating deoxidation. However, since they are powerful deoxidizing elements, most of them float in molten steel as inclusions and hardly remain in steel. However, when the content exceeds 0.0010%, CaO is contained in the steelmaking inclusions, which is highly likely to be a rusting point and lowers rust resistance. Therefore, the upper limit is set. Further, since it is impossible to remove even fine inclusions, it is difficult to make Ca less than 0.0001% in the manufacturing process, so the lower limit is made 0.0001%.

O: 0.001 to 0.01%
In order to reduce inclusions, O is an important element together with Al and Ca. If the content exceeds 0.01%, the number of large inclusions remaining in the steel increases, which adversely affects rust resistance. Therefore, the upper limit is set to 0.01%. Although it is preferable to reduce as much as possible, an excessive reduction increases the cost, so the lower limit is 0.001% or more. From the balance between cost and rust resistance, 0.001% or more and 0.005% or less are most preferable. Where O is T. O.

Cu + Ni + Mo = 0.05-0.30%
In the present invention, since the Cr content is relatively low from 11.0% to 15.5%, it has been found that the effects of Cu, Ni, Mo, N, etc. on the rust resistance are remarkable. In particular, the case where the amount of Cr is 14% or less is effective. Among them, in M-based SUS, N has a low solid solubility and is difficult to increase in the steel making stage, so that it cannot be fully utilized, and the addition of other Cu, Ni, and Mo ensures rust resistance. If the total amount is less than 0.05%, the effect is not exhibited, and if it exceeds 0.30%, remarkable improvement in rust resistance is not seen and only the cost is increased. 0.05 to 0.30%. In order to stabilize rust resistance, it is preferable to add 0.10% or more, and considering cost, it is preferable to add 0.10 to 0.20%.

  In addition, in the present invention, in addition to the essential elements described above, Nb, Ti, Bi, and B elements can be added to improve rust resistance, heat resistance, hot workability, and the like.

Nb: 0.05% or less Nb is an element that suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. However, an excessive addition destabilizes the martensite phase and lowers the hardness, so the upper limit is 0.05%.

Ti: 0.05% or less Ti is an element that suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. 0.001% or more is preferable. However, since the formation of large TiN leads to the occurrence of hot rolling defects and a decrease in toughness, the upper limit is made 0.05% or less.

Bi: 0.1% or less Bi is an element which improves corrosion resistance. Although the mechanism is not clear, it is considered that MnS, which easily becomes a rusting point, has an effect of miniaturizing MnS by adding Bi, so that the probability of becoming a rusting point is reduced. Effective when added at 0.01% or more. The effect is only saturated even if added over 0.1%, so the upper limit is made 0.1%.

B: 0.0050% or less B is an element effective for improving hot workability, and its effect is manifested at 0.0002% or more. Therefore, B may be added at 0.0002% or more. In order to improve the hot workability in a wider temperature range, the content is desirably 0.0010% or more. On the other hand, excessive addition impairs hardenability due to complex precipitation of boride and carbide, so the upper limit is 0.0050%. In consideration of corrosion resistance, 0.0025% or less is desirable.

  In addition to the above-described elements, they may be contained in a range that does not impair the effects of the present invention. It is preferable to reduce P, S, Zn, Pb, Se, Sb, H, Ga, Ta, Mg, Zr, and the like, which are general impurity elements, as much as possible. On the other hand, these elements are, as long as they solve the problems of the present invention, as necessary, Zn ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, Sb ≦ 500 ppm, H ≦ 100 ppm, Ga ≦ 500 ppm, Ta ≦ 500 ppm, One or more of Mg ≦ 120 ppm and Zr ≦ 120 ppm may be contained.

Further, the number of inclusions having a size of 10 μm or more present in the martensitic stainless steel of the present invention is set to 0.2 / cm ² or less in terms of areal density. In the steel sheet of the present invention, since the amount of alloy addition is reduced, inclusions which have not been a problem so far tend to become rusting points. In particular, it was also revealed that inclusions containing CaO tended to be a starting point of rust in the composite inclusions. As a result of a detailed investigation, it was found that when the inclusions had a size of less than 10 μm, the progress of the rust was stopped even when the rust started, and it was substantially harmless. Therefore, only the inclusions having a size of 10 μm or more are targeted, and if the number exceeds 0.2 / cm ² , rusting becomes severe and it is not satisfactory for blades. The size of the inclusion is defined as the maximum diameter of the inclusion (including the aggregate).

  The steel sheet of the present invention is generally a hot-rolled steel sheet or a cold-rolled steel sheet manufactured using a method for manufacturing a martensitic stainless steel sheet. That is, in the case of a hot-rolled steel sheet, it is manufactured in the steps of melting, casting, hot-rolling, hot-rolled sheet annealing, and pickling, and the cold-rolled steel sheet is subsequently manufactured by cold-rolling, cold-rolled sheet annealing and pickling. .

  In order to make inclusions as small and small as possible, a melting and casting process is important. In the present invention, the presence of large inclusions is suppressed by reducing Al, Ca and O as much as possible. For this reason, in the dissolving step, although not particularly specified, it is preferable to reduce the stirring as much as possible to within 1 hour, and then to allow a standing time of 3 minutes or more to float the inclusions. Inclusions are more likely to float and be removed as the standing time is longer. However, if the time is longer, the temperature of the molten steel is too low. Furthermore, in the continuous casting process, the time required for the inclusions to float can be ensured by casting as slowly as possible. The drawing speed in the continuous casting is preferably 2 m / min or less.

  The hot-rolling and hot-rolled sheet annealing steps are not particularly limited, but a conventional method for producing martensitic stainless steel can be applied. In the hot rolling step, the slab is heated at 1100 to 1300 ° C., and then finished to a sheet thickness of 2 to 8 mm by rough rolling and finish rolling. In the hot-rolled sheet annealing step, annealing is performed at 750 to 900 ° C. using ordinary box annealing. After pickling, the scale on the surface is removed to obtain a hot-rolled steel sheet. In the case of a cold-rolled steel sheet, cold rolling, final annealing, and pickling are continuously performed to obtain a product.

  When this material is used for a blade, it is preferable to perform quenching at a heating temperature of 1000 to 1100 ° C. Thereby, the hardness becomes 550 HV or more.

  Hereinafter, the effects of the present invention will be described with reference to examples, but the present invention is not limited to the conditions used in the following examples.

  In this example, first, steels having the component compositions of Invention Examples A1 to 29 shown in Table 1 and Comparative Examples B1 to 29 shown in Table 2 were melted and cast into slabs having a thickness of 200 mm. This slab was heated to 1150 to 1250 ° C., then subjected to rough hot rolling and finish hot rolling to obtain a hot-rolled steel sheet having a thickness of 3 mm. Subsequently, the hot-rolled steel sheet was annealed in a box-type annealing furnace. The maximum heating temperature was set to a temperature range from 800 ° C. to 900 ° C. Then, after pickling and removing a scale, it was made into a steel sheet having a thickness of 1 mm by cold rolling. Final annealing and pickling were performed to obtain a cold-rolled steel sheet of a product sheet. In some cases, the steps after cold rolling were not performed and the hot rolled steel sheets were left as they were. Further, both the cold-rolled steel sheet and the hot-rolled steel sheet were heated to 1000 to 1100 ° C., then quenched, and evaluated.

  First, after the surface was polished and finished with # 80, the JIS surface hardness (hardened hardness) was evaluated by Vickers hardness.

For the evaluation of corrosion resistance, after polishing with # 600, a salt spray test was performed for 24 hours or 96 hours (JIS Z2371 “Salt spray test method”), the rust area ratio was measured, and a rust area ratio of 10% or more was rejected. , And less than that were considered acceptable (合格). In particular, those having a rust area ratio of zero were judged as acceptable (合格). Even if the salt spray test was carried out for 96 hours or more, rust did not develop much more, and the rust resistance was judged based on the result of 96 hours.
The number of inclusions was calculated as an average number of each sample by visually observing a region of 50 mm × 50 mm at 20 places by an optical microscope of × 50 magnification.

  The results are shown in Tables 3 and 4. As is clear from Tables 3 and 4, it is clear that the examples of the present invention show excellent rust resistance, have no problem in hardenability, and show excellent properties as steel for cutting tools. On the other hand, in the comparative example, either the rust resistance or the hardenability is inadequate and the steel is not satisfactory as a steel for cutting tools, or the steel is satisfactory in performance but has an excessive amount of alloy added and is expensive. It is shown.

As is clear from the above description, the martensitic stainless steel sheet for cutting tools of the present invention exhibits excellent properties.
By applying the material to which the present invention is applied to a blade, a blade having practically sufficient performance can be used at low cost. That is, the present invention has sufficient industrial applicability.

Claims (2)

In mass%,
C: 0.40 to 0.50%,
Si: 0.05 to 0.60%,
Mn: 0.5-1.5%,
P: 0.035% or less,
S: 0.010% or less,
Cr: 11.0 to 15.5%,
Ni: 0.01 to 0.30%,
Cu: 0.01 to 0.30%,
Mo: 0.01 to 0.30%,
V: 0.01 to 0.10%,
Al: 0.02% or less,
Sn: 0.002 to 0.10%,
N: 0.010-0.035%,
Ca: 0.0001 to 0.0010%,
O: 0.001 to 0.01%
And the balance consists of Fe and unavoidable impurities,
And satisfy Cu + Ni + Mo = 0.05 to 0.30%,
Further, the number of inclusions having a size of 10 μm or more is 0.2 / cm ² or less.   Further, it is characterized by containing one or more of Nb: 0.05% or less, Ti: 0.05% or less, Bi: 0.1% or less, and B: 0.0050% or less by mass%. The martensitic stainless steel for cutting tools according to claim 1.