ABRASION RESISTANT STEEL PLATE HAVING EXCELLENT LOW-TEMPERATURE TOUGHNESS AND HYDROGEN EMBRITTLEMENT RESISTANCE AND METHOD FOR MANUFACTURING THE SAME

• US 20160060721A1
• Filed: 03/19/2014
• Published: 03/03/2016
• Est. Priority Date: 03/28/2013
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: S Corporation (4i Ltd.)
• Inventors: NAGAO, Akihide, MIURA, Shinichi, ISHIKAWA, Nobuyuki
• Granted Patent: US 10,253,385 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B22D 7/00 Casting ingots, e.g. from ferrous metalsequipment for conveying molten metal B22D35/00
• CPC Class Codes: C21D 1/60 Aqueous agents
• CPC Class Codes: C21D 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 6/004 containing Cr and Ni
• CPC Class Codes: C21D 6/005 containing Mn
• CPC Class Codes: C21D 6/008 containing Si
• CPC Class Codes: C21D 8/0205 of ferrous alloys
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C22C 38/00 Ferrous alloys, e.g. steel alloys cast-iron alloys C22C37/00
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/005 containing rare earths, i.e. Sc, Y, Lanthanides
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/20 with copper
• CPC Class Codes: C22C 38/22 with molybdenum or tungsten
• CPC Class Codes: C22C 38/24 with vanadium
• CPC Class Codes: C22C 38/26 : with niobium or tantalum
• CPC Class Codes: C22C 38/28 : with titanium or zirconium
• CPC Class Codes: C22C 38/32 : with boron
• CPC Class Codes: C22C 38/42 : with copper
• CPC Class Codes: C22C 38/44 : with molybdenum or tungsten
• CPC Class Codes: C22C 38/46 : with vanadium
• CPC Class Codes: C22C 38/48 : with niobium or tantalum
• CPC Class Codes: C22C 38/50 : with titanium or zirconium
• CPC Class Codes: C22C 38/54 : with boron

Abstract

Abrasion resistant steel plates with excellent low-temperature toughness and hydrogen embrittlement resistance having a Brinell hardness of 401 or more, and methods for manufacturing such steel plates. The steel plates have a lath martensitic structure with an average grain size of not more than 20 μm, and the steel plates include fine precipitates that are 50 nm or less in diameter and that have a density of 50 or more particles per 100 μm². Additionally, the steel plates include, by mass %, C: 0.20 to 0.30%, Si: 0.05 to 0.5%, Mn: 0.5 to 1.5%, Cr: 0.05 to 1.20%, Nb: 0.01 to 0.08%, B: 0.0005 to 0.003%, Al: 0.01 to 0.08%, N: 0.0005 to 0.008%, P: not more than 0.05%, S: not more than 0.005%, and O: not more than 0.008%, the balance being Fe and inevitable impurities.

Claims

1. An abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance comprising:

C;

0.20 to 0.30%, by mass %;

Si;

0.05 to 0.5%, by mass %;

Mn;

0.5 to 1.5%, by mass %;

Cr;

0.05 to 1.20%, by mass %;

Nb;

0.01 to 0.08%, by mass %;

B;

0.0005 to 0.003%, by mass %;

Al;

0.01 to 0.08%, by mass %;

N;

0.0005 to 0.008%, by mass %;

P;

not more than 0.05%, by mass %;

S;

not more than 0.005%, by mass %;

O;

not more than 0.008%, by mass %; and

remaining Fe and unavoidable inevitable impurities as a balance,

wherein;

the steel plate includes fine precipitates that are 50 nm or less in diameter and that have a density of 50 or more particles per 100 μ

m²,

the steel plate has a lath martensitic structure from the surface of the steel plate to at least a depth of ¼

of the plate thickness, the lath martensitic structure having an average grain size of not more than 20 μ

m such that the average grain size is the average grain size of crystal grains surrounded by high-angle grain boundaries having an orientation difference of 15°

or more, and

the steel plate has a Brinell hardness (HBW10/3000) of 401 or more.

2. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the steel plate further comprises at least one of Mo:

not more than 0.8%, by mass %, V;

not more than 0.2%, by mass %, and Ti;

not more than 0.05%, by mass %.

3. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the steel plate further comprises at least one of Nd:

not more than 1%, by mass %, Cu;

not more than 1%, by mass %, Ni;

not more than 1%, by mass %, W;

not more than 1%, by mass %, Ca;

not more than 0.005%, by mass %, Mg;

not more than 0.005%, by mass %, and rare earth metal;

not more than 0.02%, by mass %.

4. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the contents of Nb, Ti, Al and V satisfy 0.03≦

Nb+Ti+Al+V≦

0.14 such that Nb, Ti, Al and V indicate the contents (mass %) of the respective elements and are 0 when Nb, Ti, Al and V are not added.

5. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the plate thickness is 6 to 125 mm.

6. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the Charpy absorbed energy at −

40°

C. is not less than 27 J and the safety index (%) of delayed fracture resistance is not less than 50%, the safety index being defined as a ratio (%) of the reduction of area exhibited when the steel plate contains 0.5 ppm by mass of diffusible hydrogen to the reduction of area obtained when the steel plate contains no diffusible hydrogen.

13. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the lath martensitic structure of the steel plate has an average grain size of not more than 10 μ

m.

14. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the lath martensitic structure of the steel plate has an average grain size of not more than 5 μ

m.

15. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the C content is from 0.20% to 0.25%, by mass %.

16. The abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 1, wherein the Al content is from 0.03% to 0.08%, by mass %.

7. A method for manufacturing an abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance, the method comprising:

casting a steel slab,

hot rolling the steel slab into a steel plate having a prescribed plate thickness; and

reheating the steel plate to a temperature of Ac₃ transformation point or above and subsequently quenching the steel plate by water cooling at a temperature of not less than Ar₃ transformation point to a temperature of not more than 250°

C.,

wherein the steel slab has a chemical composition comprising;

C;

0.20 to 0.30%, by mass %;

Si;

0.05 to 0.5%, by mass %;

Mn;

0.5 to 1.5%, by mass %;

Cr;

0.05 to 1.20%, by mass %;

Nb;

0.01 to 0.08%, by mass %;

B;

0.0005 to 0.003%, by mass %;

Al;

0.01 to 0.08%, by mass %;

N;

0.0005 to 0.008%, by mass %;

P;

not more than 0.05%, by mass %;

S;

not more than 0.005%, by mass %;

O;

not more than 0.008%, by mass %; and

remaining Fe and unavoidable inevitable impurities as a balance.

8. The method for manufacturing an abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 7, further comprising reheating the cast steel slab to 1100°

C. or above.

9. The method for manufacturing an abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 7, wherein during the hot rolling step, rolling reduction in an unrecrystallized region is not less than 30%.

10. The method for manufacturing an abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 7, wherein the water cooling cools the steel plate to a temperature of not more than 250°

C.

11. The method for manufacturing an abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 7, wherein the reheating of the steel plate is performed at a rate of not less than 1°

C./s.

12. The method for manufacturing an abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 7, wherein the abrasion resistant steel plate:

includes fine precipitates that are 50 nm or less in diameter and that have a density of 50 or more particles per 100 μ

m²,

has a lath martensitic structure from the surface of the steel plate to at least a depth of ¼

of the plate thickness, the lath martensitic structure having an average grain size of not more than 20 μ

m such that the average grain size is the average grain size of crystal grains surrounded by high-angle grain boundaries having an orientation difference of 15°

or more, and

has a Brinell hardness (HBW10/3000) of 401 or more.

17. The method for manufacturing an abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 7, further comprising reheating the cast steel slab to a temperature of 1200°

C. or above.

18. The method for manufacturing an abrasion resistant steel plate with excellent low-temperature toughness and hydrogen embrittlement resistance according to claim 7, wherein during the hot rolling step, rolling reduction in an unrecrystallized region is not less than 40%.