Hot forging use non-heat-treated steel and hot forged non-heat-treated steel part

Patent metadata

Field	Value
Publication number	US-9487848-B2
Application number	US-201615066730-A
Country	US
Kind code	B2
Filing date	Mar 10, 2016
Priority date	Oct 29, 2007
Publication date	Nov 8, 2016
Grant date	Nov 8, 2016

Abstract

The present invention provides hot forging use non heat-treated steel where controlled cooling after shaping by hot forging is used to make the main structure of the steel martensite even without subsequent reheating and heat treatment by quenching and tempering and thereby give a steel part with a high strength and high toughness and superior machineability and a hot forged non heat-treated steel part made of that steel, in particular provides a martensite type hot forging use non heat-treated steel characterized by containing, by mass %, C: 0.10 to 0.20%, Si: 0.10 to 0.50%, Mn: 1.0 to 3.0%, P: 0.001 to 0.1%, S: 0.005 to 0.8%, Cr: 0.10 to 1.50%, Al: over 0.1 to 0.20%, and N: 0.0020 to 0.0080% and having a balance of substantially Fe and unavoidable impurities and a hot forged non heat-treated steel part made of such steel and characterized in that the steel structure of the entire cross-section at part or all of that part is substantially a martensite structure with an effective crystal grain size of 15 μm or less.

First claim

The invention claimed is:

1. A hot forged non-heat-treated steel part made of a hot forging use non-heat-treated steel consisting of, by mass %,
C: 0.14 to 0.20%,
Si: 0.10 to 0.50%,
Mn: 1.0 to 3.0%,
P: 0.001 to 0.1%,
S: 0.005 to 0.8%,
Cr: 0.56 to 1.50%,
Al: over 0.1 to 0.20%,
N: 0.0020 to 0.006%,
optionally, B: 0.0005 to 0.0050% and Ti: 0.005 to 0.030%,
optionally, one or more of V: 0.05 to 0.30%, and Mo: 0.05 to 1.0%, and
a balance of Fe and unavoidable impurities, wherein

the steel structure of the entire cross-section at part or all of that part is substantially a martensite structure with an effective crystal grain size of 15 μm or less.

2. The hot forged non-heat-treated steel part as set forth in claim 1 , wherein an amount of solute Al is 0.05 to 0.18 mass % in the steel at a location where the steel structure of the entire cross-section at part or all of that part is substantially a martensite structure with an effective crystal grain size of 15 μm or less.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Teramoto Shinya
• Miyanishi Kei
• Hashimura Masayuki

Classifications

• C22C38/02 Primary

  containing silicon · CPC title

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title

• C21D7/13

  by hot working · CPC title

• C21D1/25

  Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten") · CPC title