Method for manufacturing steel for high-strength hollow spring

Patent metadata

Field	Value
Publication number	US-10526675-B2
Application number	US-201515520616-A
Country	US
Kind code	B2
Filing date	Oct 26, 2015
Priority date	Oct 31, 2014
Publication date	Jan 7, 2020
Grant date	Jan 7, 2020

Abstract

A method for manufacturing steel, by quenching and tempering a seamless pipe for use as a material of a hollow spring, where the seamless pipe including predetermined components is subjected to a heat treatment which is performed to satisfy quenching conditions (1) and tempering conditions (2),
(1) quenching conditions:

26,000≤( T 1+273)×(log( t 1)+20)≤29,000

900° C.≤ T 1≤1,050° C.,

10 seconds≤ t 1≤1,800 seconds,  formula (1)
where T1 is a quenching temperature (° C.), and t1 is a holding time (seconds) in a temperature range of 900° C. or higher, and (2) tempering conditions:

13,000≤( T 2+273)×(log( t 2)+20)≤15,500

T 2≤550° C., and

t 2≤3,600 seconds,  formula (2)
where T2 is a tempering temperature (° C.), and t2 is a total time (seconds) from start of heating to completion of cooling.

First claim

The invention claimed is:

1. A method for manufacturing steel, the method comprising:
quenching and tempering a seamless pipe comprising a steel composition comprising, in percent by mass:
C: 0.35 to 0.5%,
Si: 1.5 to 2.2%,
Mn: 0.1 to 1%,
Cr: 0.1 to 1.2%,
Al: more than 0% and 0.1% or less,
P: more than 0% and 0.02% or less,
S: more than 0% and 0.02% or less,
N: more than 0% and 0.02% or less,
at least one element selected from the group consisting of V: more than 0% and 0.2% or less, Ti: more than 0% and 0.2% or less, and Nb: more than 0% and 0.2% or less, and
at least one element selected from the group consisting of Ni: more than 0% and 1% or less, and Cu: more than 0% and 1% or less,
wherein
the quenching is performed to satisfy quenching conditions (1), and the tempering is performed to satisfy tempering conditions (2),
(1) quenching conditions:
26,000≤( T 1+273)×(log( t 1)+20)≤29,000

900° C.≤ T 1≤1,050° C., and

10 seconds≤ t 1≤1,800 seconds,  formula (1)

wherein
T1 is a quenching temperature by ° C.,
t1 is a duration time in quenching by seconds, which is timed starting at a moment when the pipe reaches 900° C. and ending at a moment when the pipe reaches 900° C. after the pipe is held at the quenching temperature T1 for a quenching holding time,
when the quenching temperature T1 is 900° C., the duration time t1 equals to the quenching holding time, and
when the quenching temperature T1 is higher than 900° C., the duration time t1 is greater than the quenching holding time; and
(2) tempering conditions:
13,000≤( T 2+273)×(log( t 2)+20)≤15,500  formula (2)

T 2≤550° C., and

t 2≤3,600 seconds,

wherein
T2 is a tempering temperature by ° C., and
t2 is a total time in tempering by seconds, which is timed starting at a moment when the pipe reaches a heating start temperature and ending at a moment when the pipe reaches a cooling completion temperature after the pipe is held at the tempering temperature T2 for a tempering holding time.

2. The method according to claim 1 , wherein the hydrogen content in the steel is controlled to be 0 ppm or more by mass and 0.16 ppm by mass or less.

3. The method according to claim 1 , wherein the tempering conditions (2) are:
13,000≤( T 2+273)×(log( t 2)+20)≤15,200

T 2≤550° C., and

t 2≤3,600 seconds.

4. The method according to claim 1 , wherein in the tempering,
the tempering temperature T2 satisfies 300° C.≤T2≤550° C.,
the heating start temperature ranges from room temperature to 200° C., and
the cooling completion temperature ranges from 200° C. to room temperature.

Assignees

• Kobe Steel Ltd
• Nhk Spring Co Ltd

Inventors

• Kochi Takuya
• Hatano Hitoshi
• Tange Akira
• Kurimoto Kiyoshi
• Goto Yurika

Classifications

• C22C38/40

  with nickel · CPC title

• C22C38/48

  with niobium or tantalum · CPC title

• C22C38/46

  with vanadium · CPC title

• C22C38/42

  with copper · CPC title

• C22C38/50

  with titanium or zirconium · CPC title