Steel article having improved contact fatigue resistance and a method of making

Patent metadata

Field	Value
Publication number	US-10087512-B2
Application number	US-201314421285-A
Country	US
Kind code	B2
Filing date	Mar 15, 2013
Priority date	Aug 15, 2012
Publication date	Oct 2, 2018
Grant date	Oct 2, 2018

Abstract

A steel article with resistance to contact fatigue having a martensitic stainless steel body with a hardened surface layer and a core. The hardened surface layer is tempered martensite and M7C3 carbides, has at least 1.6 wt. % carbon, and has a depth equal to or greater than the depth where the steel article experiences the maximum shear stress when placed in service. Also, a method of manufacturing such as a steel article having resistance to contact fatigue comprising: providing a martensitic stainless steel article having a prior austenite grain size of ASTM #6 or smaller; carburizing the surface of the steel article; solution treating the steel article; tempering the steel article for a first time; hardening the steel article; cooling the steel article at a temperature below 0° F.; and tempering the steel article for a second time.

First claim

The invention claimed is:

1. A method of manufacturing a martensitic stainless steel article having resistance to contact fatigue comprising:
a) providing a martensitic stainless steel article having a prior austenite grain size of ASTM #6 or smaller;
b) carburizing the surface of the steel article at a first temperature;
c) heating the steel article from the first temperature to a second temperature that is greater than the first temperature, wherein the steel article is heated directly from the first temperature to the second temperature;
d) solution treating the steel article at the second temperature;
e) rapidly quenching the steel article from the second temperature to a third temperature that is lower than the second temperature;
f) tempering the steel article for a first time;
g) hardening the steel article;
h) cooling the steel article at a temperature below 0° F.; and
i) tempering the steel article for a second time,
wherein the steel article after carburizing and heat treatment has a hardened surface layer comprising M 7 C 3 carbides in a tempered martensite matrix, and
wherein the hardened surface layer comprises at least 1.6 wt. % carbon.

2. The method of claim 1 , further comprising one or more of conducting the carburizing of the steel article at 1600° F. to 1700° F., the solution treating of the steel article at 1750° F. to 2000° F. for 20 to 120 minutes, the tempering of the steel article for the first time at 1000° F. to 1250° F. for 2 to 5 hours, the hardening of the steel article at 1900° F. to 2000° F. for 15 to 60 minutes, the cooling of the steel article at −100° F. to −320° F. for a minimum of 1 hour, and the tempering of the steel article for a second time at 925° F. to 975° F. for 2 to 3 hours.

3. The method of claim 1 further comprising rapidly quenching the steel article to a temperature below the martensite start (M s ) temperature after hardening the steel article and before cooling the steel article at a temperature below 0° F.

4. The method of claim 1 , further comprising repeating the last tempering step one or more times.

5. The method of claim 1 , wherein the hardened surface layer comprises 1.6-2.4 wt. % carbon.

6. The method of claim 1 , wherein the hardened surface layer has a depth equal to or greater than a depth where the steel article will experience a maximum shear stress when placed in service.

7. The method of claim 6 , wherein the hardened surface layer has a thickness of at least 0.001 inches.

8. The method of claim 1 , wherein the steel article comprises one or more of Cr, Ni, Mo, Co, Mn, and V.

9. The method of claim 8 , wherein the steel article comprises 11-15 wt. % Cr, 1.5-3.5 wt. % Ni, 1-3 wt. % Mo, 3-8 wt. % Co, up to 1.5 wt. % Mn, and 0.1-1 wt. % V.

10. The method of claim 1 , wherein the steel article is given a refinement treatment prior to carburizing comprising:
a) normalizing the steel article;
b) quenching the steel article rapidly; and
c) subcritically annealing the steel article.

11. The method of claim 10 , wherein the refinement treatment further comprises one or more of normalizing at 1600° F. to 1800° F. and soaking for 1-2 hours and subcritical annealing at 1050° F. to 1300° F. for 4 to 24 hours.

Assignees

• Timken Co

Inventors

• Imundo Jr John R
• Bedekar Vikram M
• Damm Edward F
• Hyde R Scott

Classifications

• C21D6/005

  containing Mn · CPC title

• B32B15/011

  all layers being formed of iron alloys or steels · CPC title

• C21D6/007

  containing Co · CPC title

• C22C38/02

  containing silicon · CPC title

• C22C38/52

  with cobalt · CPC title