Steel with high hardness and excellent toughness

Patent metadata

Field	Value
Publication number	US-11203803-B2
Application number	US-201615757968-A
Country	US
Kind code	B2
Filing date	Sep 16, 2016
Priority date	Sep 18, 2015
Publication date	Dec 21, 2021
Grant date	Dec 21, 2021

Abstract

A steel with high hardness and excellent toughness contains, in mass %, 0.55-1.10% C, 0.10-2.00% Si, 0.10-2.00% Mn, 0.030% or less P, 0.030% or less S, 1.10-2.50% Cr, and 0.010-0.10% Al, with the balance consisting of Fe and unavoidable impurities. The structure of the steel after quenching is a dual phase structure of martensitic structure and spheroidized carbide. Spheroidized cementite particles with an aspect ratio of 1.5 or less constitute at least 90% of all cementite particles. The proportion of the number of spheroidized cementite particles on the prior austenite grain boundaries to a total number of cementite particles is 20% or less.

First claim

The invention claimed is:

1. A steel comprising, in mass %, 0.55-0.92% C, 0.10-2.00% Si, 0.10-2.00% Mn, 0.030% or less P, 0.030% or less S, 1.10-2.50% Cr, and 0.010-0.10% Al, with the balance consisting of Fe and unavoidable impurities; a structure of the steel after quenching being a dual phase structure of martensitic structure and spheroidized carbide; spheroidized cementite particles with an aspect ratio of 1.5 or less constituting at least 90% of all cementite particles; regarding cementite on prior austenite grain boundaries, a proportion of the number of spheroidized cementite particles on the prior austenite grain boundaries to a total number of cementite particles being 20% or less,
wherein at least 90% of the spheroidized cementite particles on the prior austenite grain boundaries have a particle size of 1 μm or less.

2. The steel according to claim 1 , further comprising, in mass %, one or two or more selected from among 0.10-1.50% Ni, 0.05-2.50% Mo, and 0.01-0.50% V.

3. The steel according to claim 1 , wherein prior austenite grains have a grain size of 1-5 μm.

4. The steel according to claim 2 , wherein prior austenite grains have a grain size of 1-5 μm.

5. The steel according to claim 1 , wherein the steel has a HRC hardness of 58 HRC or more.

6. The steel according to claim 1 , further comprising, in mass %, 0.01-0.50% V.

7. The steel according to claim 1 , further comprising, in mass %, 0.01-0.08% Ni.

8. The steel according to claim 1 , further comprising, in mass %, 0.30-2.50% Mo.

9. The steel according to claim 1 , wherein prior austenite grains have a grain size of 1-2 μm.

10. The steel according to claim 1 , wherein the proportion of the number of spheroidized cementite particles on the prior austenite grain boundaries to the total number of cementite particles being 20% or less and 8% or more.

11. The steel according to claim 1 , wherein the steel has a Charpy impact value of 51 J/cm 2 or more.

Assignees

• Univ Osaka
• Komatsu Mfg Co Ltd

Inventors

• Minamino Yoritoshi
• Takayama Takemori
• Yamamoto Koji
• Hiratsuka Yusuke

Classifications

• C22C38/38

  with more than 1.5% by weight of manganese · CPC title

• C21D6/005

  containing Mn · CPC title

• C21D2211/004

  Dispersions; Precipitations · CPC title

• C22C38/34

  with more than 1.5% by weight of silicon · CPC title

• C21D2211/008

  Martensite · CPC title