Steel for carburizing, carburized steel component, and method of producing the same

Patent metadata

Field	Value
Publication number	US-9796158-B2
Application number	US-201213818056-A
Country	US
Kind code	B2
Filing date	Feb 8, 2012
Priority date	Feb 10, 2011
Publication date	Oct 24, 2017
Grant date	Oct 24, 2017

Abstract

A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and an AlN precipitation parameter.

First claim

The invention claimed is:

1. A steel for a carburizing comprising as a chemical composition, by mass %,
C: 0.07% to 0.13%,
Si: 0.0001% to 0.50%,
Mn: 0.0001% to 0.80%,
S: 0.0001% to 0.100%,
Cr: more than 1.30% to 5.00%,
B: 0.0005% to 0.0100%,
Al : 0.105% to 0.200%,
N: 0.0030% to 0.0100%,
Ti: limited to 0.020% or less,
P: limited to 0.050% or less,
O: limited to 0.0030% or less, and
a balance consisting of iron and unavoidable impurities,
wherein amounts expressed in mass % of each element in the chemical composition satisfy simultaneously,
a following Equation 1 as a hardness parameter,
a following Equation 2 as a hardenability parameter, and
a following Equation 3 as an AlN precipitation parameter,
0.10<C+0.194×Si+0.065×Mn+0.012×Cr+0.078×Al<0.235  (Equation 1),

7.5<(0.7×Si+1)×(5.1×Mn+1)×(2.16×Cr+1)<44  (Equation 2), and

0.0003<Al×(N−Ti×(14/48))<0.0011  (Equation 3), and

wherein a metallographic structure includes, by area %, a ferrite and a pearlite of 85% to 100% in total, and the hardness of the steel is HV 125 or less.

2. The steel for the carburizing according to claim 1 , further comprising as the chemical composition, by mass %, at least one of
Nb: 0.002% to 0.100%,
V: 0.002% to 0.20%,
Mo: 0.005% to 0.50%,
Ni: 0.005% to 1.00%,
Cu: 0.005% to 0.50,
Ca: 0.0002% to 0.0030%,
Mg: 0.0002% to 0.0030%,
Te: 0.0002% to 0.0030%,
Zr: 0.0002% to 0.0050%,
Rare Earth Metal: 0.0002% to 0.0050%, and
Sb: 0.002% to 0.050%,
wherein the hardness parameter is defined as a following Equation 4 on behalf of the Equation 1 and the hardenability parameter is defined as a following Equation 5 on behalf of the Equation 2,
0.10<C+0.194×Si+0.065×Mn+0.012×Cr+0.033×Mo+0.067×Ni+0.097×Cu+0.078×Al<0.235  (Equation 4), and

7.5<(0.7×Si+1)×(5.1×Mn+1)×(2.16×Cr+1)×(3×Mo+1)×(0.3633×Ni+1)<44  (Equation 5).

3. A method of producing the steel for the carburizing according to claim 1 , the method comprising,
a casting process to obtain a bloom,
a hot working process of hot-working the bloom to obtain a hot worked steel material, and
a slow cooling process of slow-cooling by a cooling rate of more than 0° C./s to 1° C./s in a temperature range where a surface temperature of the hot worked steel material is 800° C. to 500° C. after the hot working process.

4. The method of producing the steel for the carburizing according to claim 3 , the method further comprising,
a spheroidizing annealing process of spheroidizing-annealing the hot-worked steel material after the slow cooling process.

5. A method of producing the steel for the carburizing according to claim 1 , the method comprising,
a casting process to obtain a bloom,
a hot controlled rolling process of hot-rolling the bloom by controlling conditions so that a surface temperature at an exit side of a final finish rolling becomes 700° C. to 1000° C. to obtain a hot-controlled-rolled steel material,
a rapid cooling process of rapid-cooling so that the surface temperature of the hot-controlled-rolled steel material is more than 0° C. to 500° C. after the hot controlled rolling process, and
a heating process of heating the hot-controlled-rolled steel material after the rapid cooling process at least one time or more.

6. The method of producing the steel for the carburizing according to claim 5 , the method further comprising,
a spheroidizing annealing process of spheroidizing-annealing the hot-controlled-rolled steel material after the heating process.

7. A method of producing the steel for the carburizing according to claim 2 , the method comprising,
a casting process to obtain a bloom,
a hot working process of hot-working the bloom to obtain a hot worked steel material, and
a slow cooling process of slow-cooling by a cooling rate of more than 0° C./s to 1° C./s in a temperature range where a surface temperature of the hot worked steel material is 800° C. to 500° C. after the hot working process.

8. A method of producing the steel for the carburizing according to claim 2 , the method comprising,
a casting process to obtain a bloom,
a hot controlled rolling process of hot-rolling the bloom by controlling conditions so that a surface temperature at an exit side of a final finish rolling becomes 700° C. to 1000° C. to obtain a hot-controlled-rolled steel material,
a rapid cooling process of rapid-cooling so that the surface temperature of the hot-controlled-rolled steel material is more than 0° C. to 500° C. after the hot controlled rolling process, and
a heating process of heating the hot-controlled-rolled steel material after the rapid cooling process at least one time or more.

9. The method of producing the steel for the carburizing according to claim 7 , the method further comprising,
a spheroidizing annealing process of spheroidizing-annealing the hot-worked steel material after the slow cooling process.

10. The method of producing the steel for the carburizing according to claim 8 , the method further comprising,
a spheroidizing annealing process of spheroidizing-annealing the hot-controlled-rolled steel material after the heating process.

Assignees

• Kubota Manabu
• Nippon Steel & Sumitomo Metal Corp

Inventors

• Kubota Manabu

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

• C22C38/26

  with niobium or tantalum · CPC title

• C21D1/32

  Soft annealing, e.g. spheroidising · CPC title

• C22C38/04

  containing manganese · CPC title