# US 12,110,566 B2 · Steel material and method for producing same

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- Number: US 12,110,566 B2
- Document ID: US12110566B2
- Status: Granted
- Kind: B2
- Application number: 17/913,106
- Filed: 2021-03-10
- Published: 2023-04-27
- Granted: 2024-10-08
- Earliest claimed: 2020-03-27
- Applicants: Motp LLC
- Inventors: Michio Shimotomai
- Web page: https://patentgrep.com/patent/US12110566B2

## CPC

- C21D 9/0081: {for slabs; for billets}
- C21D 6/004: {containing Cr and Ni}
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C21D 8/00: 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)
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0263: {following hot rolling}
- C21D 9/46: for sheet metals
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/08: containing nickel {(C22C38/105 takes precedence)}
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/34: with more than 1.5% by weight of silicon
- C22C 38/38: with more than 1.5% by weight of manganese
- C22C 38/42: with copper
- C22C 38/46: with vanadium
- C22C 38/58: with more than 1.5% by weight of manganese
- C21D 2211/002: Bainite
- C21D 2211/004: Dispersions; Precipitations
- C21D 2211/008: Martensite
- C22C 2202/04: Hydrogen absorbing
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- C22C: ALLOYS (treatment of alloys C21D, C22F)

## Abstract

To provide a steel and a manufacturing method thereof that can contribute to achieving both high strength and hydrogen embrittlement resistance. The steel has a chemical composition represented by: C: 0.15% to 0.35%; Si: 0.8% to 2.5%; Mn: 0.8% to 2.5%; Al: 0.03% to 2.0%; N: 0.002% to 0.010%; P: 0.01% or less; S: 0.01% or less; O: 0.01% or less; B: 0.0001% to 0.005%; Nb: 0.0% to 0.05%; Ti: 0.0% to 0.2%; V 0.0% to 0.05%; Mo: 0.0% to 1.0%; Cr: 0.0% to 1.0%; Ni: 0.01% to 1.0%; Cu: 0.05% to 1.0%; at least one of Ca, Mg and REM: 0.0005% to 0.01%; and the balance: Fe and impurities, and has a martensite phase or/and a bainite phase in which ε-carbide is dispersedly precipitated.

## Claims

### Claim 1

A steel, having a chemical composition consisting of: in mass %,
C: 0.15% to 0.35%;
Si: 0.8% to 2.5%;
Mn: 0.8% to 2.5%;
Al: 0.03% to 2.0%;
N: 0.002% to 0.010%;
P: 0.01% or less;
S: 0.01% or less;
O: 0.01% or less;
B: 0.0001% to 0.005%;
Nb: 0.0% to 0.05%;
Ti: 0.0% to 0.2%;
V: 0.0% to 0.05%;
Mo: 0.0% to 1.0%;
Cr: 0.0% to 1.0%;
Ni: 0.01% to 1.0%;
Cu: 0.05% to 1.0%;
at least one of Ca, Mg and REM (rare earth metals): 0.0005% to 0.01%; and the balance being Fe and impurities,
wherein the steel has a martensite phase or/and a bainite phase in which ε-carbide having a size of 2 nm or more to 150 nm or less is dispersedly precipitated at a density of 1×106 or more per 1 mm2, and wherein the ε-carbide has a hexagonal crystal structure containing hydrogen trapping carbon vacancy sites inside a crystal grain thereof, the hydrogen trapping carbon vacancy sites being stable from 0° C. to about 300° C., and wherein the steel is substantially free of cementite.

### Claim 2 (depends on 1)

The steel according to claim 1, wherein at least one of the Nb, the Ti and the V has a mass % greater than 0%, and
wherein at least one of the Mo and the Cr has a mass % greater than 0%.

### Claim 3 (depends on 1)

The steel according to claim 1, wherein the chemical composition of the steel has a ratio of Al to N in mass % of more than 7 or at least 10.

### Claim 4 (depends on 1)

The steel according to claim 1, wherein, in volume fraction, the
martensite phase or/and the bainite phase exist(s) 70% or more and less than 90%.

### Claim 5 (depends on 4)

The steel according to claim 4, wherein, in volume fraction, a residual austenite phase exists 5% or more and less than 30%, and other phase(s) containing at least ferrite exists less than 20%.

### Claim 6 (depends on 1)

The steel according to claim 1, wherein the steel has a thermal desorption spectrum having a second peak in a temperature range of 300° C. to 400° C. as compared to a first peak appearing around 100° C., the second peak being caused by one or both of: desorption of hydrogen stably trapped by the hydrogen trapping carbon vacancy sites in the ε-carbide and transformation thereof over an entire thermal desorption spectrum ranging from 0° C. to 400° C.

### Claim 7 (depends on 1)

The steel according to claim 1, wherein the ε-carbide has substantially no hydrogen trapping after heating at 400° C. detectable with a thermal desorption spectrum.

### Claim 8 (depends on 1)

The steel according to claim 1, wherein the steel is substantially free of cementite in a temperature range of from 0° C. to about 300° C.