JP2014031575A - Steel for high hardness cold die and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel for a cold die providing high hardness of 58 HRC or more, further 60 HRC or more and excellent in machinability and to provide its manufacturing method.SOLUTION: A steel for a high hardness cold die contains, by mass%, C:0.6 to 1.2%, Si:2.5% or less, Mn:2.0% or less, P:0.10% or less, S:0.02 to 0.1%, Cr:3.0 to 9.0%, Mo and W independently or in combination by (Mo+1/2W):1.2% or less, Nb and V independently or in combination by (Nb+1/2V):0.1 to 1.0%, Al:0.04 to less than 0.3% and the balance Fe with inevitable impurities, and has an area ratio of a primary carbide in a sectional structure of 3 to 6% and a hardness of 58 HRC or more. A method of manufacturing the steel for the high hardness cold die includes conducting a temper treatment at 450°C or higher after a quenching treatment of the steel containing a component composition described above to adjust hardness to 58 HRC or more.

Description

  The present invention relates to a steel with high hardness for cold molds suitable for cold mold materials for molding home appliances, mobile phones and automobile-related parts, and a method for producing the same.

  In cold molds used for press forming such as bending, drawing, and punching of plate materials at room temperature, cold metal that can achieve a hardness of 58 HRC or higher, or even 60 HRC or higher in order to improve its wear resistance. A technique of forming a hard film on the surface of mold steel by PVD (physical vapor deposition) is widely used. In PVD, the mold surface is polished as a pretreatment to improve the adhesion of the hard coating. When primary carbide is present in the mold steel, the polishing depth depends on the hardness of the matrix and the primary carbide. A difference arises, and the adhesiveness of a film | membrane falls (patent document 1). For this reason, many so-called matrix-type cold mold steels have been proposed in which the amount of primary carbides is reduced and the surface treatment due to the above-mentioned film adhesion is improved (Patent Documents 2 to 4). Reduction of primary carbide is also effective in improving machinability when cold-working die steel is cut into a die shape.

JP 2009-132990 A JP 2001-107181 A JP 2008-189982 A JP 2009-167435 A

  Matrix-based cold mold steel is advantageous in terms of PVD surface treatability and machinability in that the amount of primary carbide is reduced, but the hardness after quenching and tempering is reduced. Therefore, in order to ensure a high hardness of 58 HRC or higher, or even 60 HRC or higher, a large amount of alloy elements such as Mo and W that exhibit secondary hardening during tempering are added. However, since Mo and W are expensive alloy elements, the cost of the steel for cold mold itself increases. In addition, Mo and W stabilize residual austenite. Therefore, residual austenite tends to remain even after tempering, and austenite decomposes into martensite during surface treatment or during use as a cold mold, Dimensional changes occur.

  The object of the present invention is to provide a cold mold steel that can obtain a high hardness of 58 HRC or more, further 60 HRC or more, and can maintain and further improve machinability, surface treatment property, and dimensional stability. It is to provide with suppressed.

  The present inventor is a component composition of cold mold steel that suppresses the addition amount of expensive alloy elements such as Mo and W, and achieves both high hardness and machinability in the high hardness region, We have intensively studied methods that consider the maintenance of processability and dimensional stability. As a result, in order to maintain many of these characteristics comprehensively, it was found that not only the review of the component composition but also the optimization of the carbide form was necessary. And it came to this invention by having specified these conditions.

That is, the present invention is mass%,
C: 0.6-1.2%
Si: 2.5% or less,
Mn: 2.0% or less,
P: 0.10% or less,
S: 0.02-0.1%,
Cr: 3.0-9.0%,
Mo and W are single or composite (Mo + 1 / 2W): 1.2% or less,
Nb and V are single or composite (Nb + 1 / 2V): 0.1 to 1.0%,
Al: 0.04 to less than 0.3%,
The balance Fe and inevitable impurities,
The area ratio of the primary carbide in the cross-sectional structure is 3 to 6%,
A high hardness cold mold steel characterized by having a hardness of 58 HRC or more.

  The steel for cold mold of the present invention may further contain 1.0% or less of Ni. Moreover, the steel for cold mold of the present invention may further contain 1.0% or less of Cu.

And this invention is the mass%,
C: 0.6-1.2%
Si: 2.5% or less,
Mn: 2.0% or less,
P: 0.10% or less,
S: 0.02-0.1%,
Cr: 3.0-9.0%,
Mo and W are single or composite (Mo + 1 / 2W): 1.2% or less,
Nb and V are single or composite (Nb + 1 / 2V): 0.1 to 1.0%,
Al: 0.04 to less than 0.3%,
A steel for high-hardness cold mold, wherein the steel comprising the balance Fe and inevitable impurities is quenched and then tempered at a temperature of 450 ° C. or higher to adjust the hardness to 58 HRC or higher. It is a manufacturing method. The steel before being quenched may further contain 1.0% or less of Ni. Further, the steel before being quenched may further contain 1.0% or less of Cu.

  According to the present invention, it is possible to obtain a cold mold steel that can obtain high hardness of 58 HRC or more, further 60 HRC or more, and can maintain and further improve machinability, surface treatment property, and dimensional stability. It is possible to provide with reduced.

It is an image obtained by binarizing the cross-sectional structure of the cold mold steel of the present invention analyzed by EPMA (electron beam microanalyzer), and is a drawing-substituting photograph showing the distribution of primary carbides in the cross-sectional structure. . It is a drawing substitute photograph which shows the element distribution which analyzed the deposit | attachment formed on the surface of a cutting tool by EPMA when cutting the steel for cold molds of the example of this invention. It is a drawing substitute photograph which shows the element distribution which analyzed the deposit | attachment formed on the surface of the cutting tool by EPMA when cutting the steel for cold molds of a comparative example. It is the drawing substitute photograph which image | photographed the form of the flank and rake face of the cutting tool after cutting the steel for cold molds of the example of this invention with the digital microscope. It is a drawing substitute photograph which image | photographed the form of the flank and rake face of the cutting tool after cutting the steel for cold molds of a comparative example with the digital microscope. The maximum wear width of the tool base material on the flank of the cutting tool and the area ratio of the primary carbide in the cold mold steel after cutting the cold mold steel of the present invention example and the comparative example. It is the figure which showed the relationship. It is a micro structure photograph when the cross-sectional structure of the steel for cold molds of the example of the present invention is observed with an optical microscope. It is a micro structure photograph when the cross-sectional structure of the steel for cold molds of a comparative example is observed with an optical microscope. It is the drawing substitute photograph which image | photographed the form of the flank and rake face of the cutting tool after cutting the steel for cold molds of the example of this invention with the digital microscope. It is a drawing substitute photograph which image | photographed the form of the flank and rake face of the cutting tool after cutting the steel for cold molds of a comparative example with the digital microscope. The maximum wear width of the tool base material on the flank of the cutting tool and the area ratio of the primary carbide in the cold mold steel after cutting the cold mold steel of the present invention example and the comparative example. It is the figure which showed the relationship.

The feature of the present invention is that even when there are few expensive alloy elements such as Mo and W, a high hardness of 58 HRC or more, and further 60 HRC or more can be obtained. Furthermore, since this high hardness can be achieved at a high tempering temperature of 450 ° C. or higher, which is close to the surface treatment temperature, the deformation during the surface treatment can be suppressed. And despite the high hardness, it has just realized the steel for cold mold that has good machinability and secured the above-mentioned surface treatment property related to film adhesion and the above-mentioned dimensional stability of the mold. . Specifically, first, primary carbide was imparted to the structure as a means for maintaining hardness. Next, in order to compensate for the deterioration of machinability due to the application of the primary carbide, an alloy component is added so that a composite lubricating protective film of Al ₂ O ₃ and MnS is formed on the surface of the cutting tool by heat during cutting. Designed. On the other hand, the microstructure is designed so that the amount of primary carbide can ensure the adhesion of the hard coating. Hereinafter, the cold mold steel of the present invention will be described.

C: 0.6 to 1.2% by mass (hereinafter simply expressed as%)
C is an important element that forms carbides in the steel and imparts hardness to the cold mold steel. In the present invention, an element for achieving a hardness of 58 HRC or higher, even 60 HRC or higher even at high temperature tempering of 450 ° C. or higher by vigorous addition of V and Nb described below and application of an optimal amount of primary carbide. is there. If the amount of C is too small, the amount of carbide formed is insufficient, and it is difficult to impart the high hardness in tempering at 450 ° C. or higher. On the other hand, if the content is excessive, the amount of primary carbide that becomes insoluble when quenched is increased, so that not only the machinability is lowered but also the PVD surface treatment property is lowered. Therefore, the content of C is set to 0.6 to 1.2%. Preferably it is 0.7% or more. Further, it is preferably 1.0% or less.

-Si: 2.5% or less Si is an important element which dissolves in steel and imparts hardness to the steel for cold mold. In addition to being more oxidative than Fe and Cr, it is an element that easily forms a corundum-based oxide with Al ₂ O ₃ , so during cold cutting steel cutting, There is an important effect of promoting the formation of the Al ₂ O ₃ protective film and improving the machinability. However, if it is too much, hardenability and toughness are significantly reduced. Therefore, Si is set to 2.5% or less. Preferably it is 0.5% or more. Moreover, it is preferably 2.0% or less.

-Mn: 2.0% or less Mn is an important element of this invention with S and Al mentioned later. First, during cutting, Al in steel forms a protective film of Al ₂ O _{3 on} the cutting tool surface. Then, Mn in steel, on the Al ₂ O ₃ protective film formed on the cutting tool surface, also forming a S and MnS in the steel, which acts as a good lubricating film. And Mn is an austenite forming element, and it dissolves in steel and improves hardenability. However, if the amount added is too large, a large amount of retained austenite remains after quenching and tempering, which causes a dimensional change during surface treatment or when using a mold. Further, since the easily form a Fe and Cr and a low melting oxide, is a factor that inhibits the formation of the Al ₂ O ₃ protective coating. Therefore, in the present invention, it was made 2.0% or less. Preferably it is 0.3% or more. Further, it is preferably 1.5% or less.

-P: 0.10% or less P is contained in the steel for cold molds as an inevitable impurity, and accelerates precipitation of carbides. For this reason, when the mold size is large and the cooling rate when cooling from the quenching temperature to room temperature is slow, a fine eutectoid structure (hereinafter referred to as troostite) composed of ferrite and carbide is formed. Since troustite has a lower hardness than martensite, the quenching hardness decreases as a result, and it is difficult to obtain the high hardness even when tempering at 450 ° C. or higher. Therefore, in this invention, it restricted to 0.10% or less. Preferably it is 0.05% or less.

・ S: 0.02-0.1%
S is an important element of the present invention, and forms Mn and MnS in the steel on the Al ₂ O ₃ protective film formed on the cutting tool surface, and acts as a good lubricating film. Addition of 0.02% or more is necessary in order to sufficiently exhibit such a lubricating action, but since S deteriorates the toughness of steel, the upper limit is made 0.1%. Preferably it is 0.03% or more. Moreover, Preferably it is 0.08% or less.

・ Cr: 3.0-9.0%
Cr is an important element in the present invention, and imparts hardness to the steel for cold mold by forming M ₇ C ₃ carbide which is a primary carbide. Moreover, it exists as an insoluble carbide during quenching, and has the effect of suppressing heat treatment deformation by suppressing the growth of crystal grains. However, if Cr is less than 3.0%, even if Nb or V of the present invention amount described later is added, the amount of primary carbide formed is small, and the above-mentioned high hardness is achieved in tempering at 450 ° C. or higher. Is difficult. On the other hand, when it exceeds 9.0%, as will be described later, since the carbide exceeding the amount of primary carbide on which the composite lubricating protective film acts effectively is formed, the machinability is lowered. For this reason, it is important for Cr to be 3.0 to 9.0%. Preferably it is 3.5% or more. Moreover, Preferably it is 8.0% or less.

Mo and W are single or composite (Mo + 1 / 2W): 1.2% or less Mo and W are elements that improve the hardness by precipitating fine secondary carbides in the matrix during tempering after quenching. . However, since Mo and W are expensive elements, adding a large amount to obtain the above high hardness leads to an increase in the cost of the steel for cold mold. Moreover, in order to stabilize a retained austenite, a retained austenite remains even after tempering, and a dimensional change is easy to occur at the time of surface treatment or use of a mold. W shows the same effect as Mo, but when the effect is compared with the same addition amount, it is half of Mo. Therefore, the content of these elements may be non-added (including 0%) or, if added, is 1.2% or less in the relational expression (Mo + 1 / 2W). When added, 0.1% or more is preferable in the relational expression. More preferably, it is 0.5% or more.

Nb or V is single or composite (Nb + 1 / 2V): 0.1 to 1.0%
Nb and V are important elements in the present invention. That is, it is an element that forms MC carbide, which is a primary carbide, instead of Mo and W that form fine secondary carbide, and increases the hardness of the steel for cold mold. Furthermore, this primary carbide has the effect of suppressing the coarsening of crystal grains during quenching and reducing heat treatment deformation. However, since MC carbide has a very high hardness, if it is added excessively, the machinability is lowered. V shows the same effect as Nb, but is half of Nb when the effect is compared with the same content. In the case of the present invention, when evaluated by the relational expression (Nb + 1 / 2V) according to the above, if it is 1.0% or less, the wear of the tool is caused by the formation of a composite lubricating protective film of Al ₂ O ₃ and MnS. It is suppressed and machinability can be maintained. On the other hand, if the relational expression is less than 0.1%, the amount of MC carbide formed is small, and the effect of suppressing the increase in hardness and coarsening of crystal grains cannot be obtained. Therefore, the addition amount of these elements is 0.1 to 1.0% in the relational expression of (Nb + 1 / 2V). Preferably it is 0.8% or less.

Al: 0.04 to less than 0.3% Al is an important element of the present invention, and Al ₂ O ₃ which is a high melting point oxide is formed on the cutting tool surface during cutting and functions as a protective film. . And by containing 0.04% or more, the protective film of sufficient thickness is formed and a tool life improves. However, when a large amount of Al is added, since a large amount of Al ₂ O ₃ is formed as inclusions in the mold steel, the machinability of the cold mold steel is lowered. For this reason, the upper limit of the amount of Al added is less than 0.3%. Preferably it is 0.05% or more. Moreover, it is preferably 0.15% or less.

-Preferably, Ni: 1.0% or less Ni is an element which improves the toughness and weldability of steel for cold mold. On the other hand, Ni is an expensive metal, and it is an element that it is desirable to reduce the addition amount as much as possible for practical use. Therefore, the content of Ni may be 1.0% or less even when it is added except that it may be additive-free (including 0%).

-Preferably, Cu: 1.0% or less Cu precipitates as (epsilon) -Cu in the tempering after hardening, and has the effect of raising the hardness of steel for cold molds. However, Cu is an element that causes hot brittleness of a steel material. Therefore, the content of Cu in the present invention may be 1.0% or less except that it may be 0%. In order to suppress hot brittleness due to Cu, it is also preferable to contain Ni at the same time. And it is further more preferable that Cu and Ni at this time shall be substantially the same amount.

  In the steel for cold mold of the present invention, Ca, Ti, Zr, and a rare earth metal may be further contained for fine dispersion of primary carbide and MnS.

・ The area ratio of primary carbide in the cross-sectional structure is 3 to 6%.
For the present invention that utilizes primary carbides to maintain the hardness of the cold mold steel, the amount is an important factor of the present invention. That is, in addition to the above-described addition of V and Nb, by imparting an appropriate amount of primary carbide in the structure, it is possible to achieve a hardness of 58 HRC or higher, further 60 HRC or higher, and improve wear resistance. At the same time, it is possible to reduce heat treatment deformation during quenching and tempering. In order to obtain such an effect, the primary carbide needs to be present in an area ratio of 3% or more in the matrix. On the other hand, primary carbide is a factor that deteriorates machinability. However, in the present invention, excellent machinability can be obtained by forming the above-described composite lubricating protective film on the surface of the cutting tool. And the machinability at this time is equivalent to or more than the case where there is no primary carbide when the area ratio of the primary carbide is 6% or less. Moreover, if the amount of primary carbides is within this range, it is possible to maintain the adhesion of the hard film in the surface treatment by PVD. The area ratio of the primary carbide is preferably 5% or less, more preferably 4% or less. The adjustment to the area ratio of the primary carbide in the present invention is possible by adjusting the solidification rate at the time of producing an ingot made of the component composition in addition to the adjustment of the component composition of the steel for molds, for example.

-Hardness is 58HRC or more (preferably 60HRC or more).
The steel for cold mold of the present invention can achieve a hardness of 58 HRC or more, and further 60 HRC or more in the quenching and tempering step. And excellent machinability can be secured even in a high hardness state after quenching and tempering. For this reason, the problem of the heat treatment deformation resulting from the quenching and tempering treatment is solved by using the pre-hardened steel. Therefore, the finish cutting process can be omitted as compared with the mold manufacturing process in which the rough cutting process and the finishing cutting process are performed with the quenching and tempering process interposed therebetween.

-The manufacturing method of the steel for cold molds of this invention adjusts hardness to 58 HRC or more by performing a tempering process at the temperature of 450 degreeC or more after performing a quenching process.
In the steel for cold mold of the present invention, the high hardness of 58 HRC or higher can be achieved even at a high tempering temperature of 450 ° C. or higher close to the surface treatment temperature. Preferably, the high hardness can be achieved even at a tempering temperature of 500 ° C. or higher. Therefore, deformation due to temperature rise during the previous surface treatment can be suppressed, and the mold shape after cutting can be maintained well.

  The material was dissolved to prepare an ingot composed of the components shown in Table 1. Next, hot forging was performed on these ingots so that the forging ratio was about 10, and after cooling, annealing was performed at 860 ° C. And after performing the quenching process by air cooling from 1030 degreeC to these annealing materials, the maximum hardness of each hardness which can be achieved by performing a tempering process at various temperatures of 450 degreeC or more was measured. And on the other hand, after performing said hardening process, aiming at the hardness of 60HRC, the tempering process was performed twice at 500-540 degreeC, and the cut material for evaluating machinability was produced. Table 1 shows the maximum tempering hardness obtained by tempering treatment at 450 ° C. or higher and the hardness of the work material subjected to the machinability evaluation. With respect to the maximum tempering hardness, the present invention example 1 and comparative examples 1, 2, and 3 obtain a hardness of 58 HRC or more in any sample by the tempering temperature of 500 ° C. and the present invention example 2 by the tempering temperature of 480 ° C. I was able to.

  The primary carbide measurement method in the work material was performed in the following procedure. First, after the annealed material was cut so that the plane parallel to the forging direction was 15 mm × 15 mm, quenching and tempering were performed under the same conditions as the work material used for machinability evaluation. Next, the parallel surfaces were mirror-polished using diamond slurry and colloidal silica. Next, three fields of view of a 180 μm × 180 μm region of the parallel surface were taken with an EPMA at a magnification of 100 times. Next, Cr, Nb, and V forming the primary carbide were binarized by the content in the primary carbide to obtain a binarized image showing the primary carbide distributed in the matrix cross section. FIG. 1 is a binarized image of the work material of Example 1 of the present invention (primary carbides are shown by the distribution of white points). Then, only primary carbides having an equivalent circle diameter of 0.2 μm or more were extracted from the binarized image, and the area ratio of the primary carbides occupying these regions was obtained as an average value for three fields of view. Table 2 shows the area ratio of primary carbides in the samples of Table 1. Comparative Example 2 is a steel that has a lower C content and Cr content than Comparative Example 1 and a smaller amount of primary carbide, but has secured tempering hardness by adding Cu.

  The machinability test on the work material was performed by plane cutting using an insert PICOmini manufactured by Hitachi Tool Co., Ltd. as a cutting edge exchangeable tool corresponding to the cutting of a hard material. The insert is made of a cemented carbide as a base material and a TiAlN coating on the surface. Cutting conditions were a cutting speed of 70 m / min, a rotation speed of 1857 / min, a feed speed of 743 mm / min, a feed amount per blade of 0.4 mm / blade, a cutting depth of 0.15 mm, a cutting width of 6 mm, and a blade count of 1. . The cutting test was performed by a dry method without using cutting oil.

The machinability was evaluated based on the following two points. First, the presence or absence of the formation of a composite lubricating protective film composed of Al ₂ O ₃ and MnS on the cutting tool surface was evaluated. This is because the insert is analyzed from the rake face side using EPMA at the stage of the cutting distance 0.25 m immediately after the start of cutting, and the presence of Al, O, Mn, and S at this time is confirmed. Can be determined. Next, the cutting distance was extended to 50 m, and the tool surface at this time was photographed using a digital microscope. Then, on the flank face, the exposed width of the cemented carbide base material where the TiAlN coating was peeled was measured.

  2 and 3 are the results of analyzing the deposits formed on the surface of the cutting tool at the stage of cutting 0.25 m for each of Invention Examples 1 and 2 and Comparative Examples 1 and 2 using EPMA. Yes (high concentrations of each element are shown in light color). As shown in FIG. 2, in Example 1 of the present invention, it was confirmed that Al, O, Mn, and S were adhered over a wide range. In Example 2 of the present invention, although the range was narrower than Example 1 of the present invention, the above-mentioned elements adhered to cover the tool tip. Compared to these, as shown in FIG. 3, in the case of Comparative Examples 1 and 2, all of Al, O, Mn, and S were slightly attached to the tool tip. In addition, O detected from Comparative Example 2 having a low Al and S content in the steel originally coincided with the detection positions of Fe, Cr, and Si, and was an oxide composed of these elements.

  4 and 5 are digital microscope photographs showing the flank and rake face of the cutting tool after extending the cutting distance to 50 m for each of the inventive examples 1 and 2 and comparative examples 1 to 3. FIG. . Inventive Example 1 in which Al, O, Mn, and S were adhered over a wide range contained a large amount of primary carbide, but as shown in FIG. 4, the tool was hardly worn even after cutting 50 m. As shown in Tables 1 and 2, Invention Example 2 has the highest amount of primary carbide and the highest hardness among the mold steels evaluated in Example 1, but wears both the rake face and the flank face. Was slow and maintained sufficient machinability. On the other hand, in Comparative Examples 1, 2, and 3, the tool was worn out as compared with Invention Examples 1 and 2, as shown in FIG.

  FIG. 6 shows the relationship between the area ratio of the primary carbide of the work material and the maximum exposed width (wear width) of the tool base material on the tool flank surface for Invention Examples 1 and 2 and Comparative Examples 1 to 3. Is. In the case of Invention Examples 1 and 2, the composite lubricant protective film is formed on the surface of the cutting tool, so that even if a large amount of Nb or V that forms primary carbides is added to the work material, coating peeling is small. Good machinability is maintained.

  The material was dissolved to prepare an ingot composed of the components shown in Table 3. Next, hot forging was performed on these ingots so that the forging ratio was about 5, and after cooling, annealing was performed at 860 ° C. And after performing the quenching process by air cooling from 1030 degreeC to these annealing materials, the maximum hardness of each hardness which can be achieved by performing a tempering process at various temperatures of 450 degreeC or more was measured. And on the other hand, after performing said hardening process, aiming at the hardness of 60HRC, the tempering process was performed twice at 500-540 degreeC, and the cut material for evaluating machinability was produced. Table 3 shows the maximum tempering hardness obtained by tempering treatment at 450 ° C. or higher and the hardness of the work material subjected to machinability evaluation. With regard to the maximum tempering hardness, each of the inventive examples 3, 4, 5 and comparative example 4 has a tempering temperature of 500 ° C., and the inventive example 6 has a tempering temperature of 480 ° C., and any sample has a hardness of 58 HRC or more. I was able to.

  Table 4 shows the area ratio of primary carbide in the work material of the sample of Table 3. At this time, the measurement method of the primary carbide conformed to the procedure of Example 1. 7 and 8 are optical micrographs (100 times) showing the microstructure at the time of the above binarized image on the work material of each sample. In FIG. 7, primary carbides are found exclusively in linear aggregates. Of the primary carbides forming this set, the primary carbide having an equivalent circle diameter of 0.2 μm or more is the area ratio measurement target in the present invention.

  The machinability test on the work material was performed by plane cutting using the insert PICOmini manufactured by Hitachi Tool Co., Ltd. The insert is made of cemented carbide as a base material and TiN coating is applied to the surface. The cutting conditions are the same as in Example 1 with respect to the cutting speed, the number of rotations, the feed speed, the feed amount per blade, the depth of cut, the width of cut, and the number of blades. The cutting test was performed by a dry method without using cutting oil. And machinability was evaluated by measuring the amount of wear of the cutting tool when the cutting distance reached 8 m. The measurement procedure was in accordance with Example 1. First, the tool surface after cutting was photographed using a digital microscope. Then, on the flank face, the exposed width of the cemented carbide base material where the TiN coating was peeled was measured.

  9 and 10 are digital microscope photographs showing the flank and rake face of the cutting tool for each of Invention Examples 3 to 6 and Comparative Example 4. FIG. In Invention Example 3, the tool was hardly worn. And the example 4 of this invention containing many amounts of primary carbides also hardly worn out the tool. In Invention Examples 5 and 6, the area ratio of primary carbide is the same as that in Invention Example 3, but the amount of V and Nb is large and hard MC carbide is included. Nevertheless, the progress of wear was suppressed as compared with Comparative Example 4, and sufficient machinability was maintained.

  FIG. 11 shows the relationship between the area ratio of the primary carbide of the work material and the maximum exposed width (wear width) of the tool base material on the tool flank for Invention Examples 3 to 6 and Comparative Example 4. It is. In Invention Examples 3 to 6, even if a large amount of Nb or V forming primary carbides is added to the work material, the coating is less peeled than Comparative Example 4, and good machinability is maintained. Yes. In the case of Example 2, although the cutting distance is shorter than that of Example 1 (FIG. 6), the absolute amount of the wear width of the tool base material is larger than that of TiAlN on the coating of the cutting tool. This is due to the application of TiN having a low thickness.

Claims (6)

% By mass
C: 0.6-1.2%
Si: 2.5% or less,
Mn: 2.0% or less,
P: 0.10% or less,
S: 0.02-0.1%,
Cr: 3.0-9.0%,
Mo and W are single or composite (Mo + 1 / 2W): 1.2% or less,
Nb and V are single or composite (Nb + 1 / 2V): 0.1 to 1.0%,
Al: 0.04 to less than 0.3%,
The balance Fe and inevitable impurities,
The area ratio of the primary carbide in the cross-sectional structure is 3 to 6%,
High hardness cold mold steel characterized by having a hardness of 58 HRC or more. The high-hardness cold mold steel according to claim 1, further comprising Ni: 1.0% or less in terms of mass%. The steel for high-hardness cold mold according to claim 1 or 2, further comprising Cu: 1.0% or less in terms of mass%. % By mass
C: 0.6-1.2%
Si: 2.5% or less,
Mn: 2.0% or less,
P: 0.10% or less,
S: 0.02-0.1%,
Cr: 3.0-9.0%,
Mo and W are single or composite (Mo + 1 / 2W): 1.2% or less,
Nb and V are single or composite (Nb + 1 / 2V): 0.1 to 1.0%,
Al: 0.04 to less than 0.3%,
A steel for high-hardness cold mold, wherein the steel comprising the balance Fe and inevitable impurities is quenched and then tempered at a temperature of 450 ° C. or higher to adjust the hardness to 58 HRC or higher. Manufacturing method. The method for producing steel for high-hardness cold mold according to claim 4, wherein the steel further contains, by mass%, Ni: 1.0% or less. The method for producing a steel for high-hardness cold mold according to claim 4 or 5, wherein the steel further contains, by mass%, Cu: 1.0% or less.