Method for the production of martensitic steel having a very high yield point and sheet or part thus obtained
By carrying out specific heating, rolling and cooling steps in the manufacture of steel sheets, combined with appropriate carbon and manganese contents, the problems of insufficient mechanical strength and elongation of steel sheets in the existing technology are solved, and high mechanical properties and good welding are achieved combination of properties and maintains excellent performance without the need for tempering.
Active Publication Date: 2014-01-15
ARCELORMITTAL INVENSTIGACION Y DESARROLLO S L
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Problems solved by technology
However, this higher carbon content reduces the weldability of the sheets or components manufactured from these sheets and increases the risk of crack formation associated with the presence of hydrogen
Method used
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Experimental program
Comparison scheme
Effect test
Embodiment Construction
[0039] As a non-limiting example, the following results will reveal the advantageous properties conferred by the present invention.
[0040] Example:
[0041] Provide steel semi-finished products whose composition expressed in weight content (%) is as follows:
[0042]
C
mn
Si
Cr
Mo
Al
S
P
Nb
Ti
B
Ca
A
0.27
1.91
0.01
0.01
0.01
0.03
0.003
0.020
0.042
0.010
0.0016
0.001
B
0.198
1.94
0.01
1.909
0.01
0.03
0.003
0.020
0.003
0.012
0.0014
0.0004
[0043] Underlined value does not comply with the invention
[0044] The 31mm thick semi-finished product is heated and at a temperature T of 1250°C 1 under for 30 minutes, then at a temperature of 1100°C T 2 Under the cumulative reduction rate ε of 164% 1 (ie up to a thickness of 6mm) undergoing 4 passes of rolling. At this stage, at high temperature after rou...
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Abstract
The invention relates to a method for the production of a martensitic steel sheet having a yield point greater than 1300 MPa. The method comprises the following steps consisting in: supplying a semi-finished steel product having a composition containing, expressed as weight percent, 0.15% <= C <= 0.40%, 1.5% <= Mn <= 3%, 0.005% <= Si <= 2%, 0.005% <= Al <= 0.1%, S <= 0.05%, P <= 0.1%, 0.025% <= Nb <=0.1% and, optionally, 0.01% <= Ti <= 0.1%, 0% <= Cr <= 4%, 0% <= Mo <= 2%, 0.0005% <= B <= 0.005%, 0.0005% <= Ca <= 0.005%, the remainder of the composition being formed by iron and the inevitable impurities resulting from production; heating the semi-finished product to a temperature T1 between 1050 DEG C and 1250 DEG C and, subsequently, subjecting the heated semi-finished product to rough rolling at a temperature T2 between 1050 and 1150 DEG C, with a cumulative reduction rate ea greater than 100%, such as to obtain a sheet having an austenitic structure that is not totally recrystallised, with an average grain size of less than 40 micrometres and preferably less than 5 micrometres; and cooling the sheet, such as to prevent the transformation of the austenite, at a rate VR1 greater than 2 DEG C / s to a temperature T3 between 970 DEG C and Ar3+30 DEG C, and, subsequently, subjecting the cooled sheet to final hot rolling at temperature T3, with a cumulative reduction rate eb greater than 50%, such as to obtain a sheet that is then cooled at a rate VR2 above the critical cooling rate.
Description
technical field [0001] The present invention relates to a method for producing a steel sheet having a martensitic structure, which has a mechanical strength greater than that obtainable by a simple rapid cooling treatment using martensitic quenching, and whose mechanical strength and elongation properties are such that They are useful in the manufacture of energy absorbing components in motor vehicles. Background technique [0002] In certain applications it is sought to obtain components from steel sheets with extremely high mechanical strength. Combinations of this type are particularly desirable in the automotive industry where significant weight reduction of vehicles is sought. This can be achieved in particular by using steel components whose microstructure is martensitic with extremely high mechanical properties. Such properties are required, for example, for intrusion-resistant, structural or motor vehicle safety components such as bumpers, door or B-pillar reinforc...
Claims
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IPC IPC(8): C21D6/00C21D8/02C21D9/46C22C38/02C22C38/04C22C38/38B62D29/00
CPCC21D6/005C21D8/0205C21D8/0226C21D8/0263C21D9/46C21D2211/008C22C38/002C22C38/02C22C38/04C22C38/06C22C38/12C22C38/14C22C38/22C22C38/26C22C38/28C22C38/32C22C38/38C21D6/00
Owner ARCELORMITTAL INVENSTIGACION Y DESARROLLO S L