Steel for nitrocarburizing and nitrocarburized component, and methods for producing said steel for nitrocarburizing and said nitrocarburized component

Patent metadata

Field	Value
Publication number	US-10125416-B2
Application number	US-201314413549-A
Country	US
Kind code	B2
Filing date	Jul 22, 2013
Priority date	Jul 26, 2012
Publication date	Nov 13, 2018
Grant date	Nov 13, 2018

Abstract

The present invention provides a steel for nitrocarburizing having excellent mechanical workability before nitrocarburizing, and showing excellent fatigue properties after nitrocarburizing, which is suitable for applying in mechanical structural components for automobiles etc. prepared by adjusting the composition so that it contains in mass %, C: 0.01% or more and less than 0.10%, Si: 1.0% or less, Mn: 0.5% to 3.0%, P: 0.02% or less, S: 0.06% or less, Cr: 0.3% to 3.0%, Mo: 0.005% to 0.4%, V: 0.02% to 0.5%, Nb: 0.003% to 0.15%, Al: 0.005% to 0.2%, and Sb: 0.0005% to 0.02%, and the balance including Fe and incidental impurities, and setting the area ratio of bainite phase to the whole microstructure to more than 50%.

First claim

The invention claimed is:

1. A steel for nitrocarburizing, the steel consisting of, by mass %:
C: 0.01% or more and less than 0.10%;
Si: 1.0% or less;
Mn: 0.5% to 3.0%;
P: 0.02% or less;
S: 0.06% or less;
Cr: 0.3% to 3.0%;
Mo: 0.005% to 0.4%;
V: 0.02% to 0.5%;
Nb: 0.003% to 0.15%;
Al: 0.005% to 0.2%;
Sb: 0.0005% to 0.02%;
Ti: less than 0.010%; and
the balance being Fe and incidental impurities,
wherein an area ratio of bainite phase to a whole microstructure is more than 50%.

2. The steel for nitrocarburizing according to claim 1 , wherein a content of Ti is less than 0.005 mass %.

3. The steel for nitrocarburizing according to claim 1 , wherein a content of Sb is 0.0005 to 0.01 mass %.

4. A nitrocarburized component obtained by forming the steel for nitrocarburizing according to claim 1 into a desired shape, and then subjecting it to nitrocarburizing.

5. The nitrocarburized component according to claim 4 , wherein after the nitrocarburizing, precipitates including V and Nb are dispersed in a bainite phase.

6. A method for manufacturing a steel for nitrocarburizing, the method comprising:
hot working a steel at a heating temperature in a range of 950° C. to 1250° C. and finishing temperature of 800° C. or higher, the steel having a chemical composition consisting of, by mass %:
C: 0.01% or more and less than 0.10%;
Si: 1.0% or less;
Mn: 0.5% to 3.0%;
P: 0.02% or less;
S: 0.06% or less;
Cr: 0.3% to 3.0%;
Mo: 0.005% to 0.4%;
V: 0.02% to 0.5%;
Nb: 0.003% to 0.15%;
Al: 0.005% to 0.2%;
Sb: 0.0005% to 0.02%;
Ti: less than 0.010%; and
the balance being Fe and incidental impurities; and

then cooling the worked steel at a cooling rate of more than 0.5° C./s at least at a temperature in a range of 700° C. to 550° C.

7. A method for manufacturing a nitrocarburized component, wherein the steel for nitrocarburizing obtained by the manufacturing method according to claim 6 is formed into a desired shape and then subjected to nitrocarburizing at a nitrocarburizing temperature in a range of 550° C. to 700° C. for a nitrocarburizing time of 10 minutes or longer.

Assignees

• Jfe Steel Corp
• Jfe Bars & Shapes Corp
• Jfe Bars And Shapes

Inventors

• Omori Yasuhiro
• Uwai Kiyoshi
• Mitao Shinji
• Iwamoto Takashi
• Ando Keisuke
• Tomita Kunikazu

Classifications

• C21D8/00

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C21D8/06

  during manufacturing of rods or wires · CPC title

• C23C8/04

  Treatment of selected surface areas, e.g. using masks · CPC title

• C21D6/008

  containing Si · CPC title

• C21D6/005

  containing Mn · CPC title