JPH0364429A - Tool steel excellent in machinability - Google Patents

Abstract

PURPOSE:To obtain a tool steel excellent in machinability by incorporating specific amounts of B and N to various carbon tool steels and also controlling the total content of Ti, Zr, and REM and O2 content <= specific values, respectively. CONSTITUTION:A high carbon tool steel or high carbon low alloy-type tool steel which has a composition consisting of, by weight, 0.70-1.20% C, 0.10-1.50% Si, 0.10-1.50% Nn, 0.004-0.020% B, 0.005-0.020% N, <0.01% (Ti+Zr+REM), <0.002% O, and the balance Fe or further containing 0.20-1.50% or 4.0-15.0% Cr or W, Mo, Ni, V, Co, etc., independently or, if necessary, containing C by 0.25-0.69% and also containing the above various metallic elements and can be widely used for various purposes and, further, has superior machinability can be produced.

Description

[Detailed description of the invention] [Purpose of the invention]

(Field of Industrial Application) The present invention relates to a tool steel that is used as a material for various tools such as cutting tools, impact-resistant stamp tools, cold-work molds, and hot-work molds, and has particularly excellent machinability. . (Prior art) Conventionally, as carbon tool steel, for example, JISSKI~7
For example, JIS 5KSI~8 is an alloy tool steel mainly suitable for cutting tools.
For example, JIS 5K34~ is an alloy tool steel mainly suitable for impact-resistant tools.
For example, JIS 5KS3 is an alloy tool steel mainly suitable for cold-work molds.
-95.5KDI~2, and alloy tool steels mainly suitable for hot molds include, for example, J
There are those established in IS 5KD4-62.5KT2-6. In tools made from these various tool steels,
When the hardness is HRC55 or higher, the machinability is extremely poor and it is difficult to perform cutting with carbide tools or high-speed steel tools.
Grinding was being carried out. (Problems to be Solved by the Invention) However, grinding has a problem in that the processing efficiency is significantly lower than that of cutting, and the cost is high due to inferior productivity. (Object of the Invention) The present invention has been made in view of such conventional problems, and has the ability to extend the life of high speed steel and cemented carbide tools in an annealed state. 5
It is possible to extend the life of carbide tools and cermet tools in the HRC 0 condition and improve the finished surface roughness, and furthermore, it is possible to extend the life of ceramic tools and CBN tools in the HRC 50 to 65 condition. It is possible to extend the length and improve the roughness of the finished surface, increasing the efficiency of rough machining. The purpose of the present invention is to provide a tool steel with excellent machinability that enables shortening or omission of process time.

[Structure of the invention]

(Means for Solving the Problems) The tool steel with excellent machinability according to the first claim of the present invention has the following features:
Razor, file, hide, drill, punch, gauge,
Carbon tool steel used for chisels, mainsprings, press dies, etc., C: 0.70 to 1.20 in weight%
%, Si: 0.10-1.50%, Mn: 0.10-1
．． 50%, B: 0.004-0.020%, N: 0.
005-0.020%, T i + Z r
+REM: 0.01% or less, O:: 0.02% or less, and the remainder consists of Fe and impurities. Moreover, the second aspect of the present invention. The tool steel with excellent machinability according to the third claim is a pie l-, tie, and tap. Alloy tool steel (e.g. 5KS
) series, in weight%, C: 0.70-1.20
%, Si: 0.10-1.50%, Mn: 0.10-1
．． 50%, Cr+0.20-1.50%, B:0.
004-0.020%, N: 0.005-0.020%
Contains W: 0, 50-1, 5 as necessary.
0%, Mo: 0.50-2.00%, Nj: 0.50
-2.00%, V: 0.20-2.00%, Co: 0.
Contains one or more selected from 20-2.00%, T i + Z r + REM: 0.01
% or less, O: 0.002% or less, and the remainder consists of Fe and impurities. Furthermore, the fourth aspect of the present invention. The tool steel with excellent machinability according to the fifth claim is of the alloy tool #4 (for example, 5KD) series, which is mainly suitable for cold-work molds such as dies, cutting dies, gauges, etc., and has a weight percentage of C: 0.70-2.50%, S
i: 0.10-1.50%, M n + 0, 10-
1, 50%, Cr:4. O~15.0%, B: 0.0
04-0, 029%, N: O, 005-0.
020%, and if necessary, Ni: 0.10 to 1
．． 00%, Mo: 0.10-3.00% 9w: 0.1.
O~4.00%, 'V: 0.10~2.00%, C
o: 0.10 to 1.00% Contains one or more selected from the group consisting of Ti+Zr+REM: 0.01%
Hereinafter, the O content is regulated to 0.002% or less, and the remainder is Fe and impurities. Furthermore, the tool steel with excellent rigidity according to the sixth aspect of the present invention is an alloy tool steel (for example, 5KD) that is suitable mainly for hot molds such as presses and die casting, and has a weight percentage of So, C: 0.25-0.69%, Si: 0
．． 10-1.50%, Mn: 0, 10-1,
50%, Cr: 1.50-6.00%, ■=: 20-3
．． 00%, B: 0.004-0.020%, N:
0.005-0.020%, and Ni: 0.10-1
．． 00%, Mo: 0.10-4.00%, W: 0.50
~12.00%, Co:, 0.10~1.00%, containing one or more types selected from T i +
Z r + RE M: 0.01% or less, O: 0.
0.002% or less, with the remainder consisting of Fe and impurities. Furthermore, the tool steel with excellent machinability according to the seventh aspect of the present invention is an alloy tool steel (for example, 5KT) that is mainly suitable for hot molds such as press molds and type locks. C: 0.35-0.69%, Si: 1% by weight
0.10-1.50%, Mn: 0.10-1.50%,
Ni: 0.20-2.00%, Cr: 0.50-N, 5
0%, Mo: 0, 20-1, 00%, B: 0.
004-0.020%, N: 0.005-0.020%
, and W: 0.10-4.00%, V: 0.02-0
．． 19%, Co: one or more selected from 0.10 to 1.00%.
M: 0.01% or less, O: 0.002% or less,
It is characterized in that the remainder consists of Fe and impurities. The tool steel with excellent rigidity according to the first claim of the present invention is:
As mentioned above, it is a carbon tool steel based material such as JIS SK, and has a weight percentage of C: 0.70 to 1.20% and Si.
:0.10-1.50%, Mn:0.10-1.50%
, B: 0.004-0.020%, N: 0.005-0
．． 020%, Ti + Z r + REM: 0.
0.01% or less, 0:0.002% or less, and the balance Fe
and impurities. Among the basic components, C is an effective element for ensuring the hardness and wear resistance required for carbon tool steel, so it is desirable to have a content of 0.70% or more, but if it is too large, the toughness Since Si is an element that acts as a deoxidizing agent and is effective in increasing tempering hardness and improving toughness, it is best to keep it at 1.20% or less since it reduces processability and 0.10%. It is better to contain more than 1.5%, but too much will deteriorate hot workability and toughness, so it is better to keep it below 1.50%. Mn acts as a deoxidizing and desulfurizing agent, improves the cleanliness of the steel, and Since it is an effective element for improving hardenability, it is preferable to contain it in an amount of 0.10% or more, or it is preferable to contain it in an amount of 1.50% or less since too much content lowers hot workability. Moreover, the second aspect of the present invention. As mentioned above, the tool steel with excellent machinability according to the third claim is an alloy tool type steel such as JISSKS, and has a C: 0.70 to 1.20 in weight%.
%, Si: 0. 10-1.50%, Mn
: 0, 10-1, 50%, Cr
:0.20~1.50%, B:0.004-0;02
0%, N: 0.005~O; 020%, if necessary, W: 0.50~], 50%, Mo: 0
, 50~2, 00%, Ni::5o~2. oo゛%
, V: 0.20-2; 00%, Co: 0.20-2.0
Contains one or more selected from 0%,
Ti+Zr+REM: 0.01% or less, O: 0.002
% or less, with the remainder consisting of Fe and impurities. Here, among the basic components, C is an element effective in ensuring the hardness and wear resistance required for cutting and impact-resistant tool steel, so it should be at least 0.70%. However, if it is too large, the toughness and workability will decrease, so it is best to keep it at 1.20% or less.Si acts as a deoxidizer and is effective in increasing tempering hardness and improving toughness. Mn is a strong element, so it is better to contain it at 0.10% or more, but too much will deteriorate hot workability and toughness, so it is better to keep it at 1.50% or less. Mn is used as a deoxidizer and desulfurizer. Because it is an effective element in increasing the cleanliness of steel and improving its hardenability:
io% or more, but if it is too high it will reduce hot workability, so it is better to keep it below 1.50%. Cr improves the hardenability of alloy tool steel, increases its strength, and increases its resistance 0.20% as it is an effective element to improve impact resistance.
It is better to contain W in an amount above 1.50% or less, since too much W will reduce toughness and workability. M: Ni, V, and Co are elements that improve the strength, wear resistance, and impact resistance of alloy tool steel, so W is 0.5.
0 N1.50%, Mo 0.50-2.
00%, 0.50 to 2.00% for Ni, 0.20 to 2.00% for ■, 0.20 for Co
It is preferable to add one or more selected from 2.00% to 2.00% as necessary. Furthermore, the fourth aspect of the present invention. As mentioned above, the tool steel with excellent machinability according to the fifth claim is an alloy tool type JISSKDI, 2, etc., and has a C: 0.70 to 2 in weight%.
．． 50%, Si: 0.10-1.50%, Mn: 0.1
0-1.50%, Cr:4. (1-15,0%, B:0
．． 004-0.020%, N: 0.005-0.020
%, and if necessary, Ni: 0.10 to 1.00
%, Mo: 0, 10-3.00%, W: 0.
10-4.00%, v2 0.10-2.00%, Co:
One or two selected from 0.10 to 1.00%
M! Contains the above, Ti + Z r + REM: 0.0
The content is regulated to 1% or less, ○: 0.002% or less, and the remainder consists of Fe and impurities. Here, among the basic components, C is an effective element to ensure the hardness and wear resistance necessary for alloy tool steel suitable for cold-work molds, and in order to obtain such effects, C is ．．
It is better to contain 70% or more, but if it is too much, the toughness and workability will deteriorate, so it is better to keep the content to 2.50% or less.Si acts as a deoxidizer, improves tempering hardness, and improves toughness. It is an effective element for improving corrosion resistance and corrosion resistance.
In order to obtain such effects, it is better to contain Mn at 0.10% or more, but adding too much will impair hot workability, so it is better to limit it to 1.50% or less.Mn is used as a deoxidizing and desulfurizing agent. It is an element that increases the cleanliness of steel and also contributes to improving hardenability.To obtain these effects, it is recommended to add 0.10% or more, but if it is too large, hot workability will deteriorate. It is best to keep it below 1.50% as C
r is an effective element for increasing the strength of alloy tool steel, especially high-temperature strength, as well as thermal shock resistance, and in order to obtain such effects, it is recommended to add 4.0% or more. However, if it is too large, the toughness and workability will deteriorate, so 15.
Mo, W, and V are effective elements for forming carbides and increasing heat treatment hardness to improve wear resistance, and Mo is preferably 0.10 to 0%. 3.
00%, W is 0.10-4.00%, ■ is 0.10-2
．． It is also good to add one or more selected from 00% as necessary, and both Ni and Co strengthen the matrix and increase the strength, impact resistance, and heat check resistance of the tool steel. Therefore, one or two types selected from 0.10 to 1.00% of Ni and io to 1.00% of CO may be added as necessary. Furthermore, the tool steel with excellent machinability according to the sixth aspect of the present invention is, as described above, an alloy tool type such as JISSKD6, and has a C: 0.25 to 0. 6
9%, Si: 0.10-1.50%, Mn: 0.10~
1.50%, Cr: 1.50-6.00%, V: 0.2
0-3.00%, B: 0.004-0.020%, N:
0.005-0.020%, and Ni: 560, 10-1,00%, Mo:
0, 10 to 4.00%, W: 0.50
~12.00%, Co: 0.10~1.00%, and contains one or more types selected from Co:0.10~1.00%, Ti +
Z r + RE M: 0.01% or less, O: 0.0
The content is regulated to 0.02% or less, and the remainder consists of Fe and impurities. Here, among the basic components, C is an effective element to ensure the hardness and wear resistance necessary for alloy tool steel suitable for hot molds, and in order to obtain such effects, C is ．．
It is better to contain 25% or more, but if it is too much, the toughness and workability will decrease, so it is better to keep it at 0.69% or less.Si acts as a deoxidizer, improves tempering hardness, and improves toughness. It is an effective element for improving corrosion resistance and corrosion resistance.
In order to obtain such an effect, it is better to add 0.10% or more, but adding too much will impair hot workability and deteriorate toughness, so it is better to keep it at 1.50% or less. It is an element that acts as an acid and a desulfurizing agent, increasing the cleanliness of steel and also contributing to improving hardenability.
In order to obtain such effects, it is better to add 0.10% or more, but too much will impair hot workability, so 1.50% or more is added.
% or less, and Cr is an effective element for increasing the strength of tool steel, especially high-temperature strength, as well as thermal shock resistance.
% or more, but too much will deteriorate toughness and workability, so it is best to keep it below 6.00%. ■ and M added as necessary: W forms carbide and heat treatment Since it is an effective element for increasing hardness and improving wear resistance, 0.20 to 3.00% of ■ is essential.
Also, MO is 0.10-4.00%, W is 0.50-12
．． It is also good to selectively add one or two types selected from 00%.Ni and Co strengthen the matrix and increase the strength, impact resistance, and heat check resistance of tool steel, so Ni is 0.10-1.00%, Co is 0.1%
One or two selected from 0 to 1.00% may be added as necessary. Furthermore, the tool steel with excellent machinability according to the seventh aspect of the present invention is, as described above, an alloy tool steel such as JISSKT4, and has a C: 0.35 to 0 in weight%. ．．
69%, Si: 0.10-1.50%, Mn: 0.10
~1.50%, Ni:0.20~2.00%, Cr:
0.50-1.50%, Mo: 0.20-1.00
%, B: 0.004~0.020%, N: 00OO5~
0.020%, and W+0.10-4.00%, V:
: 02 to 0.19%, Co: 0.10 to 1,00%, and contains one or more selected from Ti +
Zr+REM: 0.01% or less, O: 0.002% or less, and the remainder consists of Fe and impurities. Here, among the basic components, C is an effective element to ensure the hardness and wear resistance necessary for alloy tool steel suitable for hot molds, and in order to obtain such effects, C is ，
It is better to contain 35% or more, but if it is too high, toughness and workability will deteriorate, so it is better to keep it below 0.69%.Si acts as a deoxidizer, improves tempering hardness, and improves toughness and processability. An element effective in improving corrosion resistance,
In order to obtain such an effect, Mn should be contained in an amount of 0.10% or more, but adding a large amount impairs hot workability and deteriorates toughness, so it is better to limit it to 1.50% or less. It is an element that acts as a deoxidizing and desulfurizing agent, increasing the cleanliness of steel and contributing to improving the hardenability of the tool.It is recommended to add 0.10% or more to obtain such effects. 1.50% as too much will impair hot workability.
The value is preferably 0.0 or less since Ni is an effective element for improving strength, impact resistance, and heat check resistance.
It is better to set the content to 20% or more, but if it is too large, the toughness will decrease, so it is better to keep the content to 2.00% or less. It is an effective element, and in order to obtain such effects, it is best to add 0.50% or more, but too much may deteriorate workability, so it is 1.50% or more.
90% or less, and since Mo is an effective element for improving wear resistance, it is better to set it to 0.20% or more.
If it is too large, the toughness and fatigue properties will deteriorate, so it is best to keep it below 1.00%. W and ■ form carbides, increase heat treatment hardness, and improve wear resistance. Since W is an effective element for
, ■ may be added as needed with one or two selected from 0.02 to 0.19%, and CO strengthens the base and increases the strength and impact resistance of tool steel. Since it improves heat check resistance, it may be added as necessary in the range of 0.10 to i,00%. The tool steel with excellent machinability according to the present invention includes the various carbon tool steels (SK series, etc.) and alloy tool steels (SKS, etc.) mentioned above.
SKD, SKT series, etc.), B:O,,004~
0.020%, N: 0.005 to 0.020%, Ti + Zr + REM: 0.01% or less, O
: It is characterized by being regulated to 0.002% or less. In this case, B combines with N to produce a BN compound, which improves machinability, especially with HSS and carbide tools in the annealed state, without reducing the strength and toughness of the tool steel. , machinability and finished surface roughness with carbide tools and cermet tools in HRC40-50 conditions,
Ceramic tools and C in the state of HRC50-65
Since it is an effective element for improving machinability and finished surface roughness with BN tools, it is set at 0.004% or more, but if it is too large, hot workability decreases, so it is set at 0.02%.
As mentioned above, N combines with B to form a BN compound, which improves the machinability of the tool steel without reducing its strength and toughness. Since it is an effective element, it is set at 0.005% or more, but if it is too large, it reduces castability, so it is 0.020%.
It is as follows. In this way, from the perspective of improving machinability, the N/B ratio is 0.5.
It is desirable that the N content be in the range of ~4.0, and from the viewpoint of maintaining greater strength, the N amount should be in the range of 1.
It is desirable that the /B ratio is in the range of 1.3 to 4.0. Furthermore, 0 combines with B added to the steel to produce B2O3, making it difficult to obtain the effect of increasing machinability due to the formation of BN compounds, so it is necessary to set the double yang to 0.002%. Yes, Ti, Zr. REM combines with N in steel to form nitrides, making it difficult to obtain the effect of improving machinability through the formation of BN compounds.
The total must be 0.01% or less. (Action of the invention) The tool steel with excellent machinability according to the present invention has the above-mentioned composition, and by regulating the O content, the formation of B oxide (B203) is suppressed, Also T
By controlling the content of elements that have a strong tendency to form nitrides, such as i, Zr, and REM, the formation of nitrides can be suppressed and the precipitation of nitride BN (hexagonal boron nitride) can be sufficiently prevented. As a result, the life of HSS and carbide tools in the annealed state is extended, the life of carbide tools and cermet tools in the HRC40-50 state is extended, and the finished surface roughness is improved. Furthermore, the life of ceramic tools and CBN tools with HRC 50 to 65 is extended, and the finished surface roughness is improved. In this case, the roughness of the finished surface of the tool steel increases as the tool wears, but since the tool wear decreases due to the precipitation of BN compounds, it is possible to obtain a good finished surface roughness. Become. (Example) Each tool steel with the chemical composition shown in Table 1 was melted and then each steel ingot (cast). 3 4 Next, the steel ingot with the chemical composition shown in Table 1 above was hot A round bar with a diameter of 25 mmφ was forged and then annealed.The Brinell hardness (HB) of each annealed material was examined, and the results are shown in the hardness (HB) column of Table 5. In addition, a drilling test using a high-speed steel tool was conducted under the conditions shown in Table 2, and the machining efficiency was calculated as the ratio of the cutting speed at which the life of the high-speed steel drill for each annealed material was 50.00 rn m to that of each comparative steel. The results are also shown in the machining efficiency ratio column of Table 5. When the Rockwell hardness (HRC) of each quenched and tempered material was investigated, the results were also shown in the hardness (HRC) column of Table 5. Each of the quenched and tempered materials Nos. 1 to 5 was grooved using a ceramic chip end mill under the conditions shown in Table 3, and the ratio of the ceramic chip end mill life to each comparison steel was determined as the tool life. The roughness of the finished surface (gmRmax) after cutting for IO minutes was investigated.These results were also calculated using the tool life ratio and the finished surface roughness of the invention steels 1 to 5 and comparative steels 1 to 5 in Table 5. It is shown in each column. 6 7 Table 3 - It is shown in each column of roughness. Carbide tip face milling was carried out under the conditions shown in the table, and the ratio of the carbide tip face milling cutter life to each comparative steel was determined as the tool life. Also, the finished surface roughness after 10 minutes of cutting ( gm
Rmax) was investigated. As is clear from the results shown in Table 5, the tool life ratios and specifications of Invention Steels 6 to 8 and Comparative Steels 6 to 8 in Table 5, both of the invention steels have a It was recognized that the machining efficiency of high-speed steel tools is high, and the life of high-speed steel tools is longer. In addition, it was observed that the life of the ceramic chip end mill in the quenched and tempered state of the steels of the present invention No. 5 to No. 5 was significantly longer than that of the comparative steels Nos. 1 to 5, and the finished surface roughness was also significantly improved. Ta. Furthermore, the life of the carbide tip face milling cutter in the quenched and tempered state is considerably longer, and the finished surface roughness is also significantly improved compared to the comparative steels 6 to 8. [Effect of the invention] The tool steel with excellent machinability according to the present invention is carbon tool steel (
SK, etc.), cutting tools (SKS, etc.), shock-resistant tools (SKS, etc.), cold molds (SKS, SKD, etc.),
In alloy tool steel suitable for hot molds (SKD, SKT, etc.), B: 0.00
4 to 0.020%, N: 0.005 to 0.020%, and Ti + Zr + REM: 0.01% or less,
Since O: is regulated to 0.002% or less, it is possible to extend the life of HSS and σ carbide tools in the annealed state, and it is also possible to extend the life of HSS and σ carbide tools in the HRC40-50 state. It is possible to extend the tool life and improve the finished surface roughness, and it is also possible to extend the life of ceramic tools and CBN tools in HRC50-65 conditions. That is]
(It is possible to improve the finished surface roughness, increase the efficiency of rough machining, and improve the accuracy of fine machining.)
By significantly reducing the roughness of the exposed surface, it is possible to shorten or omit the polishing process after cutting, which significantly reduces the process and time required to manufacture various tools and molds, resulting in a significant cost reduction. This has the great effect of making it possible.

Claims (1)

[Claims] (1) In weight%, C: 0.70 to 1.20%, Si: 0
．． 10-1.50%, Mn: 0.10-1.50%, B
:0.004~0.020%, N:0.005~0.0
A tool steel with excellent machinability characterized by containing 20% Ti+Zr+REM, regulated to 0.01% or less, O: 0.002% or less, and the remainder consisting of Fe and impurities. (2) In weight%, C: 0.70-1.20%, Si: 0
．． 10-1.50%, Mn: 0.10-1.50%, C
r: 0.20-1.50%, B: 0.004-0.02
0%, N: 0.005-0.020%, Ti+
A tool steel with excellent machinability, characterized in that Zr+REM: 0.01% or less, 0: 0.002% or less, and the remainder consists of Fe and impurities. (3) In weight%, C: 0.70-1.20%, Si: 0
．． 10-1.50%, Mn: 0.10-1.50%, C
r: 0.20-1.50%, B: 0.004-0.02
0%, N: 0.005-0.020%, and W: 0.
50-1.50%, Mo: 0.50-2.00%, Ni
: 0.50-2.00%, V: 0.20-2.00%, C
o: Contains one or more selected from 0.20 to 2.00%, Ti + Zr + REM: 0.01%
Hereinafter, a tool steel with excellent machinability, characterized in that O: is regulated to 0.002% or less, and the remainder consists of Fe and impurities. (4) In weight%, C: 0.70-2.50%, Si: 0
．． 10-1.50%, Mn: 0.10-1.50%, C
r: 4.0-15.0%, B: 0.004-0.020
%, N: 0.005-0.020%, Ti+Z
A tool steel with excellent machinability, characterized in that r+REM: 0.01% or less, 0: 0.002% or less, and the remainder consists of Fe and impurities. (5) In weight%, C: 0.70-2.50%, Si: 0
．． 10-1.50%, Mn: 0.10-1.50%, C
r: 4.0-15.0%, B: 0.004-0,020
%, N: 0.005-0.020%, and Ni: 0.
10-1.00%, Mo: 0.10-3.00%, W:
0.10-4.00%, V: 0.10-2.00%, C
o: Contains one or more selected from 0.10 to 1.00%, Ti+Zr+REM: 0.01%
Hereinafter, a tool steel with excellent machinability, characterized in that O: is regulated to 0.002% or less, and the remainder consists of Fe and impurities. (6) In weight%, C: 0.25-0.69%, Si: 0
．． 10-1.50%, Mn: 0.10-1.50%, C
r: 1.50-6.00%, V: 0.20-3.00%
, B: 0.004-0.020%, N: 0.005-0.020%, Ni: 0.10-1.00%, Mo: 0.10-4.00%, W: 0. 50-12.0
0%, Co: 0.10 to 1.00%, containing one or more selected from among Ti + Zr + REM: 0
．． 0.01% or less, O: regulated to 0.002% or less, and the remainder F
A tool steel with excellent machinability characterized by consisting of E and impurities. (7) In weight%, C: 0.35-0.69%, Si: 0
．． 10-1.50%, Mn: 0.10-1.50%, N
i: 0.20-2.00%, Cr: 0.50-1.50
%, Mo: 0.20-1.00%, B: 0.004-0
．． 020%, N: 0.005-0.020%, and W
:0.10~4.00%, V:0.02~0.19%,
Co: Contains one or more selected from 0.10 to 1.00%, Ti + Zr + REM: 0.01
% or less, O: 0.002% or less, and the remainder consists of Fe and impurities.A tool steel with excellent machinability.