High-strength steel material having outstanding ultra-low-temperature toughness and a production method therefor

Patent metadata

Field	Value
Publication number	US-9394579-B2
Application number	US-201113824647-A
Country	US
Kind code	B2
Filing date	Nov 21, 2011
Priority date	Nov 19, 2010
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

The present invention provides steel containing manganese and nickel that is used as a structural material for a cryogenic storage container for liquefied natural gas (LNG) or the like, and a manufacturing method thereof; and more particularly, to steel having good cryogenic temperature toughness and also high strength by adding low-cost Mn instead of relatively expensive Ni at an optimized ratio, refining a microstructure through controlled rolling and cooling, and precipitating retained austenite through tempering, and a manufacturing method of the steel. To achieve the object, the technical feature of the present invention is a method of manufacturing high-strength steel with cryogenic temperature toughness. In the method, a steel slab is heated to a temperature within a range of 1,000 to 1,250° C., wherein the steel slab includes, by weight: 0.01-0.06% of carbon (C), 2.0-8.0% of manganese (Mn), 0.01-6.0% of nickel (Ni), 0.02-0.6% of molybdenum (Mo), 0.03-0.5% of silicon (Si), 0.003-0.05% of aluminum (Al), 0.0015-0.01% of nitrogen (N), 0.02% or less of phosphorous (P), 0.01% or less of sulfur (S), with a remainder of iron (Fe) and other unavoidable impurities. Then, the heated slab is finish-rolled at a temperature of 950° C. or less at a rolling reduction rate of 40% or more. The rolled steel is cooled to a temperature of 400° C. or less at a cooling rate of 2° C./s or more. Thereafter, the steel is tempered for 0.5-4 hours to a temperature within a range of 550 to 650° C. after the cooling.

First claim

The invention claimed is:

1. High-strength steel with good cryogenic temperature toughness, comprising, by weight: 0.01-0.06% of carbon (C), 2.4-8.0% of manganese (Mn), 0.01-6.0% of nickel (Ni), 0.02-0.6% of molybdenum (Mo), 0.03-0.5% of silicon (Si), 0.003-0.05% of aluminum (Al), 0.0015-0.01% of nitrogen (N), 0.02% or less of phosphorous (P), 0.01% or less of sulfur (S), with a remainder of iron (Fe) and other unavoidable impurities,
wherein the Mn and Ni satisfy the condition of 8≦1.5×Mn+Ni≦12, and
wherein the steel has a yield strength of 500 MPa or more and a cryogenic impact energy of 70 J or more at −196° C. or less.

2. The high-strength steel with good cryogenic temperature toughness of claim 1 , further comprising, by weight, at least one selected from the group consisting of 0.003-0.055 of titanium (Ti), 0.1-5.0% of chromium (Cr) and 0.1-3.0% of copper (Cu).

3. The high-strength steel with good cryogenic temperature toughness of claim 2 , wherein said Mn, Ni, Cr and Cu satisfy the condition of 8≦1.5×(Mn+Cr+Cu)+Ni≦12.

4. The high-strength steel with good cryogenic temperature toughness of claim 1 , wherein the steel has a main phase of martensite and 3-15 vol % of retained austenite.

5. The high-strength steel with good cryogenic temperature toughness of claim 1 , wherein the steel has a main phase of martensite with a lath structure and 3-15 vol % of retained austenite.

6. The high-strength steel with good cryogenic temperature toughness of claim 1 , wherein the steel has a main phase of martensite with a lath structure, 10 vol % or less of bainite and 3-15 vol % of retained austenite.

7. A method of manufacturing high-strength steel with cryogenic temperature toughness, comprising:
heating a steel slab to a temperature within a range of 1,000 to 1,250° C., the steel slab comprising, by weight: 0.01-0.06% of carbon (C), 2.4-8.0% of manganese (Mn), 0.01-6.0% of nickel (Ni), 0.02-0.6% of molybdenum (Mo), 0.03-0.5% of silicon (Si), 0.003-0.05% of aluminum (Al), 0.0015-0.01% of nitrogen (N), 0.02% or less of phosphorous (P), 0.01% or less of sulfur (S), with a remainder of iron (Fe) and other unavoidable impurities, wherein the Mn and Ni satisfy the condition of 8≦1.5×Mn+Ni≦12;
finish-rolling the heated slab at a temperature of 950° C. or less at a rolling reduction rate of 40% or more;
cooling the rolled steel to a temperature of 400° C. or less at a cooling rate of 2° C./s or more; and
tempering the steel for 0.5-4 hours to a temperature within a range of 550 to 650° C. after the cooling.

8. The method of claim 7 , wherein the steel slab further comprises, by weight, at least one selected from the group consisting of 0.003-0.055 of titanium (Ti), 0.1-5.0% of chromium (Cr) and 0.1-3.0% of copper (Cu).

9. The method of claim 8 , wherein said Mn, Ni, Cr and Cu satisfy the condition of 8≦1.5×(Mn+Cr+Cu)+Ni≦12.

10. The method of claim 7 , wherein the steel has a main phase of martensite and 3-15 vol % of retained austenite.

11. The method of claim 7 , wherein the steel has a main phase of martensite with a lath structure and 3-15 vol % of retained austenite.

12. The method of claim 7 , wherein the steel has a main phase of martensite with a lath structure, 10 vol % or less of bainite, and 3-15 vol % of retained austenite.

Assignees

• Um Kyung-Keun
• Choi Jong-Kyo
• Jang Woo-Kil
• Noh Hee-Goon
• Cho Hyun-Kwan
• Posco

Inventors

• Um Kyung-Keun
• Choi Jong-Kyo
• Jang Woo-Kil
• Noh Hee-Goon
• Cho Hyun-Kwan

Classifications

• C21D8/00 Primary

  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

• C22C38/58

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

• C22C38/08

  containing nickel {(C22C38/105 takes precedence)} · CPC title

• C22C38/001

  containing N · CPC title

• C21D6/005 Primary

  containing Mn · CPC title