Steel, carburized steel component, and method for manufacturing carburized steel component

Patent metadata

Field	Value
Publication number	US-10597765-B2
Application number	US-201615777746-A
Country	US
Kind code	B2
Filing date	Nov 25, 2016
Priority date	Nov 27, 2015
Publication date	Mar 24, 2020
Grant date	Mar 24, 2020

Abstract

A steel according to an aspect of the present invention has a chemical composition within a predetermined range, in which a hardenability index Ceq ranges from greater than 7.5 to smaller than 44.0, a metallographic structure includes ferrite ranging from 85 to 100 area %, an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the steel and have an equivalent circle diameter ranging from 1 μm or greater to smaller than 2 μm, is shorter than 30.0 μm, and a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the steel and have an equivalent circle diameter ranging from 1 μm or greater to smaller than 2 μm, is 300 pieces/mm2 or more.

First claim

What is claimed is:

1. A steel, wherein
a chemical composition comprises, by mass %,
C: 0.07% to 0.13%,
Si: 0.0001% to 0.50%,
Mn: 0.0001% to 0.80%,
S: 0.0050% to 0.0800%,
Cr: more than 1.30% to 5.00% or less,
B: 0.0005% to 0.0100%,
Ti: 0.020% or more to less than 0.100%,
Al: 0.010% to 0.100%,
Bi: more than 0.0001% to 0.0100% or less,
N: 0.0080% or less,
P: 0.050% or less,
O: 0.0030% or less,
Nb: 0% to 0.100%,
V: 0% to 0.20%,
Mo: 0% to 0.500%,
Ni: 0% to 1.000%,
Cu: 0% to 0.500%,
Ca: 0% to 0.0030%,
Mg: 0% to 0.0030%,
Te: 0% to 0.0030%,
Zr: 0% to 0.0050%,
a rare earth metal: 0% to 0.0050%,
Sb: 0% to 0.0500%, and
a remainder including Fe and impurities,
wherein a hardenability index Ceq obtained by substituting the amount of each element in the chemical composition indicated by mass % in Expression 1 ranges from greater than 7.5 to smaller than 44.0,
wherein a metallographic structure includes ferrite ranging from 85 to 100 area %,
wherein an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the steel and have an equivalent circle diameter ranging from 1 μm or greater to smaller than 2 μm, is shorter than 30.0 μm, and
wherein a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the steel and have an equivalent circle diameter ranging from 1 μm or greater to smaller than 2 μm, is 300 pieces/mm 2 or more,
Ceq=(0.7×Si+1)×(5.1×Mn+1)×(2.16×Cr+1)×(3×Mo+1)×(0.3633×Ni+1)  (Expression 1).

2. The steel according to claim 1 ,
wherein the chemical composition includes, by mass %, one or more selected from the group consisting of
Nb: 0.002% to 0.100%,
V: 0.002% to 0.20%,
Mo: 0.005% to 0.500%,
Ni: 0.005% to 1.000%,
Cu: 0.005% to 0.500%,
Ca: 0.0002% to 0.0030%,
Mg: 0.0002% to 0.0030%,
Te: 0.0002% to 0.0030%,
Zr: 0.0002% to 0.0050%,
a rare earth metal: 0.0002% to 0.0050%, and
Sb: 0.0020% to 0.0500%.

3. A carburized steel component comprising:
a steel portion; and
a carburized layer, which is a region on an outer surface of the steel portion and which has Vickers hardness of HV 550 or higher,
wherein a thickness of the carburized layer ranges from greater than 0.40 mm to smaller than 2.00 mm,
wherein an average Vickers hardness at a position in a depth of 50 μm from a surface of the carburized steel component ranges from HV 650 or higher to HV 1,000 or lower,
wherein an average Vickers hardness at a position in a depth of 2.0 mm from the surface of the carburized steel component ranges from HV 250 or higher to HV 500 or lower,
wherein a chemical composition of the steel portion includes, by mass %,
C: 0.07% to 0.13%,
Si: 0.0001% to 0.50%,
Mn: 0.0001% to 0.80%,
S: 0.0050% to 0.0800%,
Cr: more than 1.30% to 5.00% or less,
B: 0.0005% to 0.0100%,
Ti: 0.020% or more to less than 0.100%,
Al: 0.010% to 0.100%,
Bi: more than 0.0001% to 0.0100% or less,
N: 0.0080% or less,
P: 0.050% or less,
O: 0.0030% or less,
Nb: 0% to 0.100%,
V: 0% to 0.20%,
Mo: 0% to 0.500%,
Ni: 0% to 1.000%,
Cu: 0% to 0.500%,
Ca: 0% to 0.0030%,
Mg: 0% to 0.0030%,
Te: 0% to 0.0030%,
Zr: 0% to 0.0050%,
a rare earth metal: 0% to 0.0050%,
Sb: 0% to 0.0500%, and
a remainder including Fe and impurities,

wherein a hardenability index Ceq obtained by substituting the amount of each element in the chemical composition of the steel portion indicated by mass % in Expression 2 ranges from greater than 7.5 to smaller than 44.0,
wherein an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the carburized steel component and have an equivalent circle diameter in the steel portion ranging from 1 μm or greater to smaller than 2 μm, is shorter than 30.0 μm, and
wherein a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the carburized steel component and have an equivalent circle diameter in the steel portion ranging from 1 μm or greater to smaller than 2 μm, is 300 pieces/mm 2 or more,
Ceq=(0.7×Si+1)×(5.1×Mn+1)×(2.16×Cr+1)×(3×Mo+1)×(0.3633×Ni+1)  (Expression 2).

4. The carburized steel component according to claim 3 ,
wherein the chemical composition of the steel portion includes, by mass %, one or more selected from the group consisting of
Nb: 0.002% to 0.100%,
V: 0.002% to 0.20%,
Mo: 0.005% to 0.500%,
Ni: 0.005% to 1.000%,
Cu: 0.005% to 0.500%,
Ca: 0.0002% to 0.0030%,
Mg: 0.0002% to 0.0030%,
Te: 0.0002% to 0.0030%,
Zr: 0.0002% to 0.0050%,
a rare earth metal: 0.0002% to 0.0050%, and
Sb: 0.0020% to 0.0500%.

5. A method for manufacturing the carburized steel component according to claim 3 , the method comprising:
cold plastic working a steel, wherein
a chemical composition comprises, by mass %,
C: 0.07% to 0.13%,
Si: 0.0001% to 0.50%,
Mn: 0.0001% to 0.80%,
S: 0.0050% to 0.0800%,
Cr: more than 1.30% to 5.00% or less,
B: 0.0005% to 0.0100%,
Ti: 0.020% or more to less than 0.100%,
Al: 0.010% to 0.100%,
Bi: more than 0.0001% to 0.0100% or less,
N: 0.0080% or less,
P: 0.050% or less,
O: 0.0030% or less,
Nb: 0% to 0.100%,
V: 0% to 0.20%,
Mo: 0% to 0.500%,
Ni: 0% to 1.000%,
Cu: 0% to 0.500%,
Ca: 0% to 0.0030%,
Mg: 0% to 0.0030%,
Te: 0% to 0.0030%,
Zr: 0% to 0.0050%,
a rare earth metal: 0% to 0.0050%,
Sb: 0% to 0.0500%, and
a remainder including Fe and impurities,
wherein a hardenability index Ceq obtained by substituting the amount of each element in the chemical composition indicated by mass % in Expression 1 ranges from greater than 7.5 to smaller than 44.0,
wherein a metallographic structure includes ferrite ranging from 85 to 100 area %,
wherein an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the steel and have an equivalent circle diameter ranging from 1 μm or greater to smaller than 2 μm, is shorter than 30.0 μm, and
wherein a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the steel and have an equivalent circle diameter ranging from 1 μm or greater to smaller than 2 μm, is 300 pieces/mm2 or more,
Ceq=(0.7×Si+1)×(5.1×Mn+1)×(2.16×Cr+1)×(3×Mo+1)×(0.3633×Ni+1)  (Expression 1);

cutting the steel after the cold plastic working; and
carburizing or carbonitriding the steel after the cutting.

6. The method for manufacturing the carburized steel component, according to claim 5 , further comprising:
quenching, or quenching and tempering after the carburizing or the carbonitriding.

7. The method for manufacturing the carburized steel component, according to claim 5 , wherein
the chemical composition includes, by mass %, one or more selected from the group consisting of
Nb: 0.002% to 0.100%,
V: 0.002% to 0.20%,
Mo: 0.005% to 0.500%,
Ni: 0.005% to 1.000%,
Cu: 0.005% to 0.500%,
Ca: 0.0002% to 0.0030%,
Mg: 0.0002% to 0.0030%,
Te: 0.0002% to 0.0030%,
Zr: 0.0002% to 0.0050%,
a rare earth metal: 0.0002% to 0.0050%, and
Sb: 0.0020% to 0.0500%.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Shiga Akira
• Kubota Manabu
• Hasegawa Hajime
• Mizukami Hideo

Classifications

• C23C8/02

  Pretreatment of the material to be coated (C23C8/04 takes precedence) · CPC title

• C22C38/60

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

• C21D2211/005

  Ferrite · CPC title

• C23C8/80

  After-treatment · CPC title

• C21D9/32

  for gear wheels, worm wheels, or the like · CPC title