Rolled steel bar for machine structural use and method of producing the same

Patent metadata

Field	Value
Publication number	US-10266908-B2
Application number	US-201515322251-A
Country	US
Kind code	B2
Filing date	Jul 3, 2015
Priority date	Jul 3, 2014
Publication date	Apr 23, 2019
Grant date	Apr 23, 2019

Abstract

A rolled steel bar for machine structural use includes a predetermined chemical composition comprising, by mass %, C: 0.45% to 0.65%, Si: higher than 1.00% to 1.50%, Mn: higher than 0.40% to 1.00%, P: 0.005% to 0.050%, S: 0.020% to 0.100%, V: 0.08% to 0.20%, Ti: 0% to 0.050%; Ca: 0% to 0.0030%, Zr: 0% to 0.0030%, Te: 0% to 0.0030%, and a remainder including Fe and impurities, wherein the impurities include: Cr: 0.10% or lower, Al: lower than 0.01%, and N: 0.0060% or lower. In the rolled steel bar for machine structural use, K1 obtained from “K1=C+Si/7+Mn/5+1.54×V” is 0.95 to 1.05, K2 obtained from “K2=139−28.6×Si+105×Mn−833×S−13420×N” is more than 35, a Mn content and a S content satisfy Mn/S≥8.0, and a total decarburized depth of a surface layer is 500 μm or less.

First claim

The invention claimed is:

1. A rolled steel bar for machine structural use having a chemical composition comprising, by mass %,
C: 0.45% to 0.65%,
Si: higher than 1.00% to 1.50%,
Mn: higher than 0.40% to 1.00%,
P: 0.005% to 0.050%,
S: 0.020% to 0.100%,
V: 0.08% to 0.20%,
Ti: 0% to 0.050%;
Ca: 0% to 0.0030%,
Zr: 0% to 0.0030%,
Te: 0% to 0.0030%, and
a remainder including Fe and impurities,
wherein the impurities include:

Cr: 0.10% or lower,
Al: lower than 0.01%, and
N: 0.0060% or lower,
K1 obtained from the following Expression 1 is 0.95 to 1.05,
K2 obtained from the following Expression 2 is more than 35,
a Mn content and a S content satisfy the following Expression 3,
a total decarburized depth of a surface layer is 500 μm or less,
K 1= C+Si/ 7+ Mn/ 5+1.54× V   (Expression 1),

K 2=139−28.6× Si+ 105× Mn− 833× S− 13420× N   (Expression 2),

Mn/S≥ 8.0  (Expression 3), and

C, Si, Mn, V, S, and N in the Expressions 1 to 3 represent the amounts of the respective elements in mass %.

2. The rolled steel bar for machine structural use according to claim 1 , wherein the chemical composition further comprising, by mass %,
one or more selected from the group consisting of
Ti: 0.010% to 0.050%,
Ca: 0.0005% to 0.0030%,
Zr: 0.0005% to 0.0030%, and
Te: 0.0005% to 0.0030%.

3. A method of producing the rolled steel bar for machine structural use according to claim 2 , the method comprising:
making molten steel having the chemical composition with said one or more of Ti, Ca, Zr and Te;
continuously casting the molten steel to obtain a cast piece;
blooming the cast piece to obtain a steel piece;
scarfing all faces of the steel piece after the blooming at 2 mm or more from a surface; and
performing a steel bar rolling after holding the steel piece after the scarfing at a heating temperature of 1000° C. to 1150° C. for 7000 seconds or shorter.

4. A method of producing the rolled steel bar for machine structural use according to claim 1 , the method comprising:
making molten steel having the chemical composition;
continuously casting the molten steel to obtain a cast piece;
blooming the cast piece to obtain a steel piece;
scarfing all faces of the steel piece after the blooming at 2 mm or more from a surface; and
performing a steel bar rolling after holding the steel piece after the scarfing at a heating temperature of 1000° C. to 1150° C. for 7000 seconds or shorter.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Takada Hiromasa
• Teramoto Shinya
• Ohyama Osamu

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

• C22C38/28

  with titanium or zirconium · CPC title

• C22C38/24

  with vanadium · CPC title

• C22C38/06

  containing aluminium · CPC title