A cold rolled martensitic steel and a method of martensitic steel thereof
OwnerDongwei FAN, Ranga Nikhil Vinayak YELLAKARAinventors
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Abstract
A martensitic steel sheet including the following elements 0.07%≤C≤0.12%; 1.9%≤Mn≤2.5%; 0.2%≤Si≤0.6%; 0.01%≤Al≤0.1%; 0.1%≤Cr≤0.5%; 0.2%≤Mo≤0.6%; 0%≤S≤0.09%; 0%≤P≤0.09%; 0%≤N≤0.09%; 0.001%≤Ti≤0.1%; 0.0005%≤B≤0.005%; 0%≤Nb≤0.1%; 0%≤V≤0.1%; 0%≤Ni≤1%; 0%≤Cu≤1%; 0%≤Sn≤0.1%; 0%≤Pb≤0.1%; 0%≤Sb≤0.1%; 0.001%≤Ca≤0.01%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel consisting of, by area percentage, tempered martensite from 80% to 94% and fresh martensite from 6% to 20%.
Claims18
1-15. (canceled)
A martensitic steel sheet having a composition comprising the following elements, expressed in percentage by weight:
- 0.07
- %
- ≦
- C
- ≦
- 0.12
- %
- ;
-
- 1.9
- %
- ≦
- Mn
- ≦
- 2.5
- %
- ;
-
- 0.2
- %
- ≦
- Si
- ≦
- 0.6
- %
- ;
-
- 0.01
- %
- ≦
- Al
- ≦
- 0.1
- %
- ;
-
- 0.1
- %
- ≦
- Cr
- ≦
- 0.5
- %
- ;
-
- 0.2
- %
- ≦
- Mo
- ≦
- 0.6
- %
- ;
-
- 0.001
- %
- ≦
- Nb
- ≦
- 0.1
- %
- ;
-
- 0
-
- %
- ≦
- S
- ≦
- 0.09
- %
- ;
-
- 0
-
- %
- ≦
- P
- ≦
- 0.09
- ;
-
- 0
-
- %
- ≦
- N
- ≦
- 0.09
- %
- ;
- and optionally one or more of the following elements:
- 0.001
- %
- ≦
- Ti
- ≦
- 0.1
- %
- ;
-
- 0.0005
- %
- ≦
- B
- ≦
- 0.005
- %
- ;
-
- 0
-
- %
- ≦
- V
- ≦
- 0.1
- %
- ;
-
- 0
-
- %
- ≦
- Ni
- ≦
- 1
-
- %
- ;
-
- 0
-
- %
- ≦
- Cu
- ≦
- 1
-
- %
- ;
-
- 0
-
- %
- ≦
- Sn
- ≦
- 0.1
- %
- ;
-
- 0
-
- %
- ≦
- Pb
- ≦
- 0.1
- %
- ;
-
- 0
-
- %
- ≦
- Sb
- ≦
- 0.1
- %
- ;
-
- 0.001
- %
- ≦
- Ca
- ≦
- 0.01
- %
- ;
- a remainder of the composition being composed of iron and unavoidable impurities caused by processing;
- a microstructure of the steel consisting of, by area percentage, tempered martensite from 80% to 94% and fresh martensite from 6% to 20%.
A method of production of a martensitic steel sheet comprising the following successive steps:
- providing a semi-finished product with a composition, expressed in percentage by weight:
- 0.07
- %
- ≦
- C
- ≦
- 0.12
- %
- ;
-
- 1.9
- %
- ≦
- Mn
- ≦
- 2.5
- %
- ;
-
- 0.2
- %
- ≦
- Si
- ≦
- 0.6
- %
- ;
-
- 0.01
- %
- ≦
- Al
- ≦
- 0.1
- %
- ;
-
- 0.1
- %
- ≦
- Cr
- ≦
- 0.5
- %
- ;
-
- 0.2
- %
- ≦
- Mo
- ≦
- 0.6
- %
- ;
-
- 0.001
- %
- ≦
- Nb
- ≦
- 0.1
- %
- ;
-
- 0
-
- %
- ≦
- S
- ≦
- 0.09
- %
- ;
-
- 0
-
- %
- ≦
- P
- ≦
- 0.09
- ;
-
- 0
-
- %
- ≦
- N
- ≦
- 0.09
- %
- ;
- and optionally one or more of the following elements:
- 0.001
- %
- ≦
- Ti
- ≦
- 0.1
- %
- ;
-
- 0.0005
- %
- ≦
- B
- ≦
- 0.005
- %
- ;
-
- 0
-
- %
- ≦
- V
- ≦
- 0.1
- %
- ;
-
- 0
-
- %
- ≦
- Ni
- ≦
- 1
-
- %
- ;
-
- 0
-
- %
- ≦
- Cu
- ≦
- 1
-
- %
- ;
-
- 0
-
- %
- ≦
- Sn
- ≦
- 0.1
- %
- ;
-
- 0
-
- %
- ≦
- Pb
- ≦
- 0.1
- %
- ;
-
- 0
-
- %
- ≦
- Sb
- ≦
- 0.1
- %
- ;
-
- 0.001
- %
- ≦
- Ca
- ≦
- 0.01
- %
- ;
- 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 1280° C.;
- rolling the semi-finished product in the austenitic range wherein the hot rolling finishing temperature is from Ac3 to Ac3+100° C. to obtain a hot rolled steel sheet;
- cooling the sheet at a cooling rate of at least 10° C./s to a coiling temperature, the cooling temperature being below 675° C., and coiling the hot rolled sheet;
- cooling the hot rolled sheet to room temperature;
- optionally performing a scale removal process on the hot rolled steel sheet;
- optionally annealing the hot rolled steel sheet;
- optionally performing a further scale removal process on the hot rolled steel sheet;
- cold rolling the hot rolled steel sheet with a reduction rate CR from 35 to 90% to obtain a cold rolled steel sheet;
- then heating the cold rolled steel sheet from room temperature to temperature Tsoak from Ac3 to Ac3+100° C., with a heating rate HR1 of at least 1° C./s, and holding for 10 to 500 seconds;
- then cooling the cold rolled steel sheet from Tsoak to a temperature T1 from Ms to Ms-100° C., with a cooling rate CR1 from 1° C./s to 150° C./s;
- then holding the cold rolled steel sheet at a T1 temperature for 5 to 100 seconds;
- then reheating the cold rolled steel sheet at a rate of at least 1° C./s to a tempering temperature Ttemper from 400° C. to 550° C. and holding for 10 to 600 seconds.
- then cooling to room temperature with a cooling rate of at least 1° C./s to obtain the martensitic steel sheet.
Dependencies are inferred from the claim text.