Carburized component

Patent metadata

Field	Value
Publication number	US-10428414-B2
Application number	US-201414899878-A
Country	US
Kind code	B2
Filing date	Jun 24, 2014
Priority date	Jun 26, 2013
Publication date	Oct 1, 2019
Grant date	Oct 1, 2019

Abstract

The present invention provides a carburized part having a total amount of TiC, AlN and ZrC, which are precipitate particles, of 4.5×10 −10 mole or less per 1 mm 2 of grain boundary area of prior austenite grains after carburization. According to the present invention, it is possible to provide a carburized part which allows effective inhibition of abnormal grain growth in spite of a carburizing treatment and makes it possible to solve the problem of reduction in properties caused by abnormal grain growth.

First claim

The invention claimed is:

1. A carburized part having a total amount of TiC, AlN and ZrC, which are precipitate particles, of 4.5×10 −1 ° mole or less per 1 mm 2 of grain boundary area of prior austenite grains after carburization, which is formed by processing a steel material into a shape of a part and performing a carburizing treatment on the steel material, the steel material having a composition consisting of, in terms of % by mass:
0.10% to 0.30% of C;
0.01% to 0.49% of Si;
0.65% to 1.50% of Mn;
0.01% to 0.10% of S;
0.03% or less of P;
0.05% to 1.00% of Cu;
0.05% to 1.00% of Ni;
0.01% to 2.00% of Cr;
0.01% to 0.50% of Mo;
0.001% or less of Nb;
0.005% to 0.050% of s-Al;
0.005% to 0.030% of N; and
one or two elements selected from
0.001% to 0.150% of Ti and
0.001% to 0.300% of Zr,

and optionally:
0.001% to 0.010% of B,

with the remainder being Fe and inevitable impurities,
wherein
[Ti], [Zr] and [N] which respectively represent contents of Ti, Zr, and N, in mole/g, satisfy the following equation (1):
|[Ti]/47.9+[Zr]/91.2−[N]/14|/100≤3.5×10 −6 mole/g  Equation (1);

wherein at least one element selected from Ti and Zr combines with N included in the steel at the time of forging of the steel, and crystallizes in a form of at least one of TiN and ZrN having no contribution to a pinning of crystal grain boundaries to prevent AlN having a pinning action from being precipitated, and
a structure thereof after the carburization is a well-ordered grain structure having a uniform crystal grain size in which an average crystal grain size of the prior austenite grain is greater than 3 and 7.5 or less, and a crystal grain size difference of the prior austenite grains is 6 or less.

2. The carburized part according to claim 1 , wherein the content of B is 0.001% to 0.010%.

3. The carburized part according to claim 1 , wherein a driving force for crystal grain growth is greater than a pinning force of precipitate particles.

4. A carburized part having a total amount of TiC, AlN, and ZrC, which are precipitate particles, of 4.5×10 −10 mole or less per 1 mm 2 of grain boundary area of prior austenite grains after carburization, which is formed by processing a steel material into a shape of a part and performing a carburizing treatment on the steel material, the steel material having a composition consisting of, in terms of % by mass:
0.10% to 0.30% of C;
0.01% to 0.45% of Si;
0.40% to 1.50% of Mn;
0.01% to 0.10% of S;
0.03% or less of P;
0.05% to 1.00% of Cu;
0.05% to 1.00% of Ni;
0.01% to 2.00% of Cr;
0.01% to 0.50% of Mo;
0.001% or less of Nb;
0.001% to 0.008% of s-Al;
less than 0.001% of Ti;
less than 0.001% of Zr; and
0.005% to 0.030% of N,
and optionally:
0.001% to 0.010% of B,
with the remainder being Fe and inevitable impurities;
wherein the added amount of s-Al is sufficiently minute to prevent AlN having a pinning action from being precipitated, and
a structure thereof after the carburization is a well-ordered grain structure having a uniform crystal grain size in which an average crystal grain size of the prior austenite grain is greater than 3 and 7.5 or less, and a crystal grain size difference of the prior austenite grains is 6 or less.

5. The carburized part according to claim 4 , wherein the content of B is 0.001% to 0.010%.

6. The carburized part according to claim 4 , wherein a driving force for crystal grain growth is greater than a pinning force of precipitate particles.

Assignees

• Daido Steel Co Ltd

Inventors

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

Classifications

• C21D1/06

  Surface hardening · CPC title

• C22C38/44

  with molybdenum or tungsten · CPC title

• C21D9/28

  for plain shafts · CPC title

• C22C38/60

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

• C23C8/22 Primary

  of ferrous surfaces · CPC title