Case hardening steel

Patent metadata

Field	Value
Publication number	US-10287668-B2
Application number	US-201414311594-A
Country	US
Kind code	B2
Filing date	Jun 23, 2014
Priority date	Jun 26, 2013
Publication date	May 14, 2019
Grant date	May 14, 2019

Abstract

Provided is a case hardening steel which allows effective inhibition of abnormal grain growth during carburizing treatment or the like and makes it possible to solve the problem of abnormal grain growth-induced reduction in characteristics. In the case hardening steel, a total amount of TiC, ZrC and AlN which are precipitate particles contained in 100 g of a steel material after subjecting the case hardening steel to hot rolling is 3.5×10−4 mole or less.

First claim

What is claimed is:

1. A steel comprising, in terms of % by mass:
C: 0.10% to 0.30%,
Si: 0.01% to 1.50%,
Mn: 0.40% to 1.50%,
S: 0.01% to 0.10%,
P: 0.03% or less,
Cu: 0.05% to 1.00%,
Ni: 0.05% to 1.00%,
Cr: 1.12% to 2.00%,
Mo: 0.01% to 0.50%,
Nb: 0.001% or less,
s-Al: 0.005% to 0.050%,
N: 0.005% to 0.030%, and
at least one element selected from Ti: 0.001% to 0.150% and Zr: 0.001% to 0.300%,
with the balance being Fe and unavoidable impurities, wherein the case-hardening steel satisfies the following expression (1);
|[Ti]/47.9+[Zr]/91.2−[N]/14|/100≤3.5×10 −6   (1)

where [Ti], [Zr], and [N] represent the content, in terms of % by mass, of each of these elements in the case-hardening steel,
wherein
a total amount of TiC, ZrC, and AlN, which are precipitate particles contained in 100 g of hot rolled steel after subjecting the case-hardening steel to the hot rolling step and before subjecting the hot rolled steel to the carburizing step, is 3.5×10 −4 mole or less,
a difference between the highest and the lowest of grain size indexes in accordance with JIS G 0551 (1998) of crystal grains in the case-hardened steel is 6 or less, and
the steel is subjected to surface hardening treatment by carburization.

2. The case-hardened steel according to claim 1 , exhibiting a coarsening temperature beyond 1100° C. and an absence of coarsening.

3. The case-hardened steel according to claim 1 , further comprising, in terms of % by mass:
B: 0.001% to 0.010%.

4. The case-hardened steel according to claim 3 , exhibiting a coarsening temperature beyond 1100° C. and an absence of coarsening.

5. A case-hardening steel comprising, in terms of % by mass:
C: 0.10% to 0.30%,
Si: 0.01% to 1.50%,
Mn: 0.40% to 1.50%,
S: 0.01% to 0.10%,
P: 0.03% or less,
Cu: 0.05% to 1.00%,
Ni: 0.05% to 1.00%,
Cr: 1.12% to 2.00%,
Mo: 0.01% to 0.50%,
Nb: 0.001% or less,
s-Al: 0.005% to 0.050%,
N: 0.005% to 0.030%, and
at least one element selected from Ti: 0.001% to 0.150% and Zr: 0.001% to 0.300%,
with the balance being Fe and unavoidable impurities, wherein
the case-hardening steel satisfies the following expression (1);
|[Ti]/47.9+[Zr]/91.2−[N]/14|/100≤3.5×10 −6   (1)

where [Ti], [Zr], and [N] represent the content, in terms of % by mass, of each of these elements in the case-hardening steel, wherein
a total amount of TiC, ZrC, and AlN, which are precipitate particles contained in 100 g of hot-rolled steel after subjecting the case-hardening steel to a hot rolling step and before subjecting the hot-rolled steel to a carburizing step to form a case-hardened steel, is 3.5×10 4 mole or less, and
a difference between the highest and the lowest of grain size indexes in accordance with JIS G 0551 (1998) of crystal grains in the case-hardened steel is 6 or less, and the case-hardening steel is to be treated with surface hardening treatment by carburization.

6. The case-hardening steel according to claim 5 , further comprising, in terms of % by mass:
B: 0.001% to 0.010%.

7. The case-hardening steel according to claim 6 , wherein the case-hardened steel exhibits a coarsening temperature beyond 1100° C. and an absence of coarsening.

8. The case-hardening steel according to claim 5 , wherein the case-hardened steel exhibits a coarsening temperature beyond 1100° C. and an absence of coarsening.

9. A steel comprising, in terms of % by mass:
C: 0.10% to 0.30%,
Si: 0.01% to 1.50%,
Mn: 0.40% to 1.50%,
S: 0.01% to 0.10%,
P: 0.03% or less,
Cu: 0.05% to 1.00%,
Ni: 0.05% to 1.00%,
Cr: 1.12% to 2.00%,
Mo: 0.01% to 0.50%,
Nb: 0.001% or less,
s-Al: 0.001 to 0.008%,
N: 0.005% to 0.030%,
Ti: less than 0.001%,
Zr: less than 0.001%, and
with the balance being Fe and unavoidable impurities,
the difference in crystal grain sizes of crystal grains in the case-hardened steel and crystal grains in the case-hardening steel is 6 or less when measured using the JIS G-0551 standard, and
the steel is subjected to surface hardening treatment by carburization.

10. The case-hardened steel according to claim 9 , further comprising, in terms of % by mass:
B: 0.001% to 0.010%.

11. The case-hardened steel according to claim 10 , exhibiting a coarsening temperature beyond 1100° C. and an absence of coarsening.

12. The case-hardened steel according to claim 9 , exhibiting a coarsening temperature beyond 1100° C. and an absence of coarsening.

13. A case-hardening steel comprising, in terms of % by mass:
C: 0.10% to 0.30%,
Si: 0.01% to 1.50%,
Mn: 0.40% to 1.50%,
S: 0.01% to 0.10%,
P: 0.03% or less,
Cu: 0.05% to 1.00%,
Ni: 0.05% to 1.00%,
Cr: 1.12% to 2.00%,
Mo: 0.01% to 0.50%,
Nb: 0.001% or less,
s-Al: 0.001% to 0.008%,
N: 0.005% to 0.030%,
Ti: less than 0.001%,
Zr: less than 0.001%, and
with the balance being Fe and unavoidable impurities,
the difference in crystal grain sizes of crystal grains in the case-hardened steel and crystal grains in the case-hardening steel is 6 or less when measured using the JIS G-0551 standard, and the case hardening steels is to be treated with surface hardening treatment by carburization.

14. The case-hardening steel according to claim 13 , further comprising, in terms of % by mass:
B: 0.001% to 0.010%.

15. The case-hardening steel according to claim 14 , wherein the case-hardened steel exhibits a coarsening temperature beyond 1100° C. and an absence of coarsening.

16. The case-hardening steel according to claim 13 , wherein the case-hardened steel exhibits a coarsening temperature beyond 1100° C. and an absence of coarsening.

17. A method of making a steel comprising:
hot-rolling case-hardening steel to obtain hot-rolled steel and then carburizing the hot-rolled steel to obtain case-hardened steel;
wherein the case-hardening steel comprises in terms of % by mass:
C: 0.10% to 0.30%,
Si: 0.01% to 1.50%,
Mn: 0.40% to 1.50%,
S: 0.01% to 0.10%,
P: 0.03% or less,
Cu: 0.05% to 1.00%,
Ni: 0.05% to 1.00%,
Cr: 1.12% to 2.00%,
Mo: 0.01% to 0.50%,
Nb: 0.001% or less,
s-Al: 0.005 to 0.050%,
N: 0.005% to 0.030%, and
at least one element selected from Ti: 0.001% to 0.150% and Zr: 0.001% to 0.300%, with the balance being Fe and unavoidable impurities,

wherein
a total amount of TiC, ZrC, and AlN, which are precipitate particles contained in 100 g of the hot-rolled steel is 3.5×10 −4 mole or less, and
a difference between the highest and the lowest of grain size indexes in accordance with JIS G 0551 (1998) of crystal grains in the case-hardened steel is 6 or less, and the steel is subjected to surface hardening treatment by carburization.

18. The method according to claim 17 , wherein the case-hardening steel further comprises in terms of % by mass:
B: 0.001% to 0.010%.

19. The method of making the case-hardened steel according to claim 18 , wherein the case-hardened steel exhibits a coarsening temperature beyond 1100° C. and an absence of coarsening.

20. The method of making the case-hardened steel according to claim 17 , wherein the wherein the case-hardened steel exhibits a coarsening temperature beyond 1100° C. and an absence of coarsening.

21. A method of making a steel comprising:
hot-rolling case-hardening steel to obtain hot-rolled steel and then
carburizing the hot-rolled steel to obtain case-hardened steel;
wherein the case-hardening steel comprises in terms of % by mass:
C: 0.10% to 0.30%,
Si: 0.01% to 1.50%,
Mn: 0.40% to 1.50%,
S: 0.01% to 0.10%,
P: 0.03% or less,
Cu: 0.05

Assignees

• NAKAYAMA Kyohei
• Sakai Yasuaki
• Morita Toshiyuki
• Inoue Keisuke
• Daido Steel Co Ltd

Inventors

• NAKAYAMA Kyohei
• Sakai Yasuaki
• Morita Toshiyuki
• Inoue Keisuke

Classifications

• C22C38/04

  containing manganese · CPC title

• C22C38/48

  with niobium or tantalum · CPC title

• C23C8/80 Primary

  After-treatment · CPC title

• C22C38/60

  containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur · CPC title

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title