Cold rolled and heat treated steel sheet and a method of manufacturing thereof
OwnerDamon PANAHI, Hyojin SONG +2inventors
InventorsDamon PANAHI, Hyojin SONG, Venkata Sai Ananth CHALLA, Brian LIN
Life of this patent
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Abstract
A cold rolled and heat treated steel sheet including in weight percent: 0.2%≤C≤0.35%; 0.5%≤Mn≤1.5%; 0.1%≤Si≤0.6%; 0%≤Al≤0.1%; 0.01%≤Ti≤0.1%; 0.0001%≤B≤0.010%; 0%≤P≤0.02%; 0%≤S≤0.03%; 0%≤N≤0.09% and can contain optional elements, the microstructure of the steel including, by area percentage, at least 80% of tempered martensite, 3 to 15% Bainite, 1% to 7% Martensite, 0 to 12% of Ferrite and 0 to 2% Residual Austenite.
Claims16
1-14. (canceled)
A cold rolled and heat treated steel sheet having a composition comprising the following elements, expressed in percentage by weight:
- 0.2
- %
- ≦
- C
- ≦
- 0.35
- %
- ;
- 0.5
- %
- ≦
- Mn
- ≦
- 1.5
- %
- ;
- 0.1
- %
- ≦
- Si
- ≦
- 0.6
- %
- ;
- 0
-
- %
- ≦
- Al
- ≦
- 0.1
- %
- ;
- 0.01
- %
- ≦
- Ti
- ≦
- 0.1
- %
- ;
- 0.0001
- %
- ≦
- B
- ≦
- 0.01
- %
- ;
- 0
-
- %
- ≦
- P
- ≦
- 0.02
- %
- ;
- 0
-
- %
- ≦
- S
- ≦
- 0.03
- %
- ;
- 0
-
- %
- ≦
- N
- ≦
- 0.09
- %
- ;
- and optionally one or more of the following elements
- 0
-
- %
- ≦
- Cr
- ≦
- 0.06
- %
- ;
- 0
-
- %
- ≦
- Nb
- ≦
- 0.09
- %
- ;
- 0
-
- %
- ≦
- Mo
- ≦
- 0.09
- %
- ;
- 0
-
- %
- ≦
- V
- ≦
- 0.1
- %
- ;
- 0
-
- %
- ≦
- Ni
- ≦
- 2
-
- %
- ;
- 0
-
- %
- ≦
- Cu
- ≦
- 2
-
- %
- ;
- 0
-
- %
- ≦
- Ca
- ≦
- 0.005
- %
- ;
- 0
-
- %
- ≦
- Ce
- ≦
- 0.1
- %
- ;
- 0
-
- %
- ≦
- Mg
- ≦
- 0.05
- %
- ;
- 0
-
- %
- ≦
- Zr
- ≦
- 0.05
- %
- ;
- a remainder of the composition being composed of iron and unavoidable impurities caused by processing;
- a microstructure of the steel comprising, by area percentage, at least 80% of tempered martensite, 3 to 15% Bainite, 1% to 7% Martensite, 0 to 12% of Ferrite and 0 to 2% Residual Austenite.
A method of production of a cold rolled and heat treated steel sheet comprising the following successive steps:
- providing a semi-finished product with a composition having a composition comprising the following elements, expressed in percentage by weight:
- 0.2
- %
- ≦
- C
- ≦
- 0.35
- %
- ;
- 0.5
- %
- ≦
- Mn
- ≦
- 1.5
- %
- ;
- 0.1
- %
- ≦
- Si
- ≦
- 0.6
- %
- ;
- 0
-
- %
- ≦
- Al
- ≦
- 0.1
- %
- ;
- 0.01
- %
- ≦
- Ti
- ≦
- 0.1
- %
- ;
- 0.0001
- %
- ≦
- B
- ≦
- 0.01
- %
- ;
- 0
-
- %
- ≦
- P
- ≦
- 0.02
- %
- ;
- 0
-
- %
- ≦
- S
- ≦
- 0.03
- %
- ;
- 0
-
- %
- ≦
- N
- ≦
- 0.09
- %
- ;
- and optionally one or more of the following elements
- 0
-
- %
- ≦
- Cr
- ≦
- 0.06
- %
- ;
- 0
-
- %
- ≦
- Nb
- ≦
- 0.09
- %
- ;
- 0
-
- %
- ≦
- Mo
- ≦
- 0.09
- %
- ;
- 0
-
- %
- ≦
- V
- ≦
- 0.1
- %
- ;
- 0
-
- %
- ≦
- Ni
- ≦
- 2
-
- %
- ;
- 0
-
- %
- ≦
- Cu
- ≦
- 2
-
- %
- ;
- 0
-
- %
- ≦
- Ca
- ≦
- 0.005
- %
- ;
- 0
-
- %
- ≦
- Ce
- ≦
- 0.1
- %
- ;
- 0
-
- %
- ≦
- Mg
- ≦
- 0.05
- %
- ;
- 0
-
- %
- ≦
- Zr
- ≦
- 0.05
- %
- ;
- a remainder of the composition being composed of iron and unavoidable impurities caused by processing;
- reheating the semi-finished product to a temperature from 1000° C. to 1300° C.;
- rolling the semi-finished product in the austenitic range wherein the hot rolling finishing temperature is above 850° C. to obtain a hot rolled steel sheet;
- cooling the sheet at a cooling rate of at least 5° C./s to a coiling temperature which is less than or equal to 680° C.;
- and coiling the hot rolled sheet;
- cooling the hot rolled sheet to room temperature;
- optionally performing scale removal process on the hot rolled steel sheet;
- optionally annealing the hot rolled steel sheet;
- optionally performing scale removal process on the hot rolled steel sheet;
- cold rolling the hot rolled steel sheet with a reduction rate from 35 to 90% to obtain a cold rolled steel sheet;
- then heating the cold rolled steel sheet starts from room temperature to a temperature TA from Ac3+10° C. to Ac3+150° C., with a heating rate HR1 from 1° C./s to 30° C./s, and holding for 100 to 1000 seconds;
- then cooling the scold rolled steel sheet starting from TA down to a temperature CS1 from Ms to Ms−150° C., with a cooling rate CR1 from 5° C./s and 200° C./s;
- then the cold rolled steel sheet is held at CS1 temperature for 1 to 500 seconds;
- and
- then cooling to room temperature with a cooling rate of at least 1° C./s to obtain a cold rolled and heat treated steel sheet.
Dependencies are inferred from the claim text.