# US 8,465,601 B2 · High carbon steel sheet superior in tensile strength and elongation and method for manufacturing the same

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 8,465,601 B2
- Document ID: US8465601B2
- Status: Granted
- Kind: B2
- Application number: 12/745,621
- Filed: 2008-12-05
- Published: 2010-12-09
- Granted: 2013-06-18
- Earliest claimed: 2007-12-06
- Assignees: Posco
- Applicants: Young-Roc Im; Jae-Kon Lee; Kyoo-Young Lee; Yeong-Woo Jeon; Jae-Hwa Ryu; Kyong-Su Park
- Inventors: Young-Roc Im; Jae-Kon Lee; Kyoo-Young Lee; Yeong-Woo Jeon; Jae-Hwa Ryu; Kyong-Su Park
- Web page: https://patentgrep.com/patent/US8465601B2

## CPC

- C22C 38/02: containing silicon
- C21D 1/20: Isothermal quenching, e.g. bainitic hardening
- C21D 8/0226: {Hot rolling}
- C21D 8/0263: {following hot rolling}
- C21D 9/46: for sheet metals
- C22C 38/06: containing aluminium
- C22C 38/44: with molybdenum or tungsten
- C22C 38/50: with titanium or zirconium
- C22C 38/54: with boron
- C22C 38/56: with more than 1.7% by weight of carbon
- C22C 38/58: with more than 1.5% by weight of manganese
- C21D 2211/001: Austenite
- C21D 2211/002: Bainite
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- 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)

## Abstract

A high carbon steel sheet having superior strength and ductility and a method for manufacturing the same comprising: 0.2 to 1.0 wt % carbon (C), 0 to 3.0 wt % silicon (Si), 0 to 3.0 wt % manganese (Mn), 0 to 3.0 wt % chromium (Cr), 0 to 3.0 wt % nickel (Ni), 0 to 0.5 wt % molybdenum (Mo), 0 to 3.0 wt % aluminum (Al), 0 to 0.01 wt % boron (B), 0 to 0.5 wt % titanium (Ti), and the remainder substantially being iron (Fe) and inevitable impurities. The contents of carbon, manganese, chromium, and nickel satisfy the following Equation 1, and the contents of silicon and aluminum satisfy the following Equation 2: (3.0−2.5×C)wt %≦(Mn+Cr+Ni/2)≦8.5 wt %—(Equation 1) Si+Al>1.0 wt % (Equation 2).

## Claims

### Claim 1

A high carbon steel sheet comprises 0.2 to 1.0 wt % carbon (C), greater than about 1 wt % and less than or equal to 3.0 wt % silicon (Si), greater than 0 wt % and less than or equal to 3.0 wt % manganese (Mn), greater than 0 wt % and less than or equal to 3.0 wt % chromium (Cr), greater than 0 wt % and less than or equal to 3.0 wt % nickel (Ni), greater than 0 wt % and less than or equal to 0.5 wt % molybdenum (Mo), greater than about 1 wt % and less than or equal to 3.0 wt % aluminum (Al), greater than 0 wt % and less than or equal to 0.01 wt % boron (B), greater than 0 wt % and less than or equal to 0.5 wt % titanium (Ti), and the remainder substantially being iron (Fe) and inevitable impurities,
the contents of carbon, manganese, chromium, and nickel satisfy the following Equation 1, and the contents of silicon and aluminum satisfy the following Equation 2, and the carbon (C), manganese (Mn), chromium (Cr), nickel (Ni), and aluminum (Al) satisfy the following equation 3:
(3.0−2.5×C)wt %≦(Mn+Cr+Ni/2)8.5 wt % (Equation 1)
Si+Al> about 2.0 wt % (Equation 2),
Log 10 [50% transformation time (sec)]=−2.742+3.561×C+0.820×Mn+0.416×Cr+0.402×Ni−0.332×Al+1330/(T+273)≦Log10[3×3600] (Equation 3),
wherein T is a temperature in degrees Celsius and represents a transformation temperature, and 50% transformation time is a minimum time required for 50% transformation into bainite.

### Claim 2 (depends on 1)

The high carbon steel sheet of claim 1, wherein
the high carbon steel sheet comprises a fine microstructure, the fine microstructure comprises residual austenite, and the volume percentage of the residual austenite in the fine microstructure ranges from 15 vol % to 50 vol %.

### Claim 3 (depends on 2)

The high carbon steel sheet of claim 2, wherein
the fine microstructure further comprises bainite, and the bainite ranges from 50 vol % to 85 vol %.

### Claim 4 (depends on 3)

The high carbon steel sheet of claim 3, wherein
the tensile strength of the high carbon steel sheet is greater than 1000 MPa, and the elongation thereof is greater than 10%.

### Claim 5 (depends on 4)

The high carbon steel sheet of claim 4, wherein
the titanium (Ti) and nitrogen (N) satisfy the following Equation 6:
Ti(wt %)>N(wt %)×3.42 (Equation 6).

### Claim 6 (depends on 4)

The high carbon steel sheet of claim 4, wherein
the carbon (C) in the composition of the high carbon steel sheet ranges from 0.4 wt % to 1.0 wt %, and
the contents of the manganese (Mn), chromium (Cr), and nickel (Ni), satisfy the following equation:
1.5 wt %≦(Mn+Cr+Ni/2)≦8.5 wt %.

### Claim 7 (depends on 4)

The high carbon steel sheet of claim 4, wherein
the carbon (C) in the composition of the high carbon steel sheet ranges from 0.2 wt % to 0.7 wt %, and
the contents of the manganese (Mn), chromium (Cr), and nickel (Ni) satisfy the following equation:
3.0 wt %≦(Mn+Cr+Ni/2)≦8.5 wt %.

### Claim 8

A method for manufacturing a high carbon steel sheet, comprising:
i) preparing a high carbon steel sheet comprising 0.2 to 1.0 wt % carbon (C), greater than about 1 wt % and less than or equal to 3.0 wt % silicon (Si), greater than 0 wt % and less than or equal to 3.0 wt % manganese (Mn), greater than 0 wt % and less than or equal to 3.0 wt % chromium (Cr), greater than 0 wt % and less than or equal to 3.0 wt % nickel (Ni), greater than 0 wt % and less than or equal to 0.5 wt % molybdenum (Mo), greater than about 1 wt % and less than or equal to 3.0 wt % aluminum (Al), greater than 0 wt % and less than or equal to 0.01 wt % boron (B), greater than 0 wt % and less than or equal to 0.5 wt % titanium (Ti), and the remainder substantially being iron (Fe) and inevitable impurities;
ii) austenitizing the high carbon steel sheet;
iii) cooling the high carbon steel sheet while maintaining the austenite structure; and
iv) isothermally transforming the austenitized high carbon steel sheet in a temperature range from 150° C. below the bainite transformation starting temperature to the bainite transformation starting temperature,
wherein the contents of carbon, manganese, chromium, and nickel satisfy the following Equation 1, and the silicon and the aluminum satisfy the following Equation 2, and the carbon (C), manganese (Mn), chromium (Cr), nickel (Ni), and aluminum (Al) satisfy the following Equation 3:
(3.0−2.5×C)wt %≦(Mn+Cr+Ni/2)≦8.5 wt % (Equation 1)
Si+Al> about 2.0 wt % (Equation 2),
Log 10 [50% transformation time (sec)]=−2.742+3.561×C+0.820×Mn+0.416×Cr+0.402×Ni−0.332×Al+1330/(T+273)≦Log10[3×3600] (Equation 3),
wherein T is a temperature in degrees Celsius and represents a transformation temperature, and 50% transformation time is a minimum time required for 50% transformation into bainite.

### Claim 9 (depends on 8)

The method of claim 8, wherein, in the isothermal transformation, the isothermal transformation is carried out for one minute to 48 hours.

### Claim 10 (depends on 9)

The method of claim 9, wherein, during the isothermal transformation, the bainite transformation of the high carbon steel sheet is finished at greater than 50 vol % and less than 100 vol %.

### Claim 11 (depends on 10)

The method of claim 10, wherein the time taken to complete 50 vol % bainite transformation of the high carbon steel sheet is more than one minute and less than three hours.

### Claim 12 (depends on 9)

The method of claim 9, wherein the bainite transformation starting temperature satisfies the following equation:
bainite transformation starting temperature (Bs) (° C.)=830−270×C(wt %) 90×Mn(wt %)−37×Ni(wt %)−70×Cr(wt %)−83×Mo(wt %).

### Claim 13 (depends on 8)

The method of claim 8, wherein the cooling is performed on a run-out table at a cooling speed of 10-50°/sec.

### Claim 14 (depends on 13)

The method of claim 13, wherein the isothermal transformation is performed by coiling the high carbon steel sheet.

### Claim 15 (depends on 14)

The method of claim 14, wherein
the bainite transformation starting temperature satisfies the following equation:
bainite transformation starting temperature (Bs) (° C.)=830−270×C(wt %)−90×Mn(wt %)−37×Ni(wt %)−70×Cr(wt %)−83×Mo(wt %).

### Claim 16 (depends on 1)

The high carbon steel sheet of claim 1, wherein the content of at least one of silicon and aluminum is greater than 1.0 wt % and less than or equal to 3.0 wt %.

### Claim 17 (depends on 8)

The method of claim 8, wherein the content of at least one of silicon and aluminum is greater than 1.0 wt % and less than or equal to 3.0 wt %.