Cold rolled and heat treated steel sheet and a method of manufacturing thereof
A cold rolled and heat treated steel sheet having a composition including the following elements: 0.1%≤Carbon≤0.5%, 1%≤Maganeses≤3.4%, 0.5%≤Silicon≤2.5%, 0.01%≤Aluminum≤1.5%, 0.05%≤Chromium≤1%, 0.001%≤Niobium≤0.1%, 0%≤Sulfur≤0.003%, 0.002%≤Phosphorus≤0.02%, 0%≤Nitrogen≤0.01%, 0%≤Molybdenum≤0.5%, 0.001%≤Titanium≤0.1%, 0.01%≤Coppers≤2%, 0.01%≤Nickel≤3%, 0.0001%≤Calcium≤0.005%, 0%≤Vanadium≤0.1%, 0%≤Boron≤0.003%, 0%≤Ceriurm≤0.1%, 0%≤Magnesium≤0.010%, 0%≤Zirconium≤0.010% the remainder composition being composed of iron and the unavoidable impurities, and a microstructure of the rolled steel sheet includes by area fraction, 10% to 60% Bainite, 5% to 50% Ferrite, 5% to 25% Residual Austenite, Martensite 2% to 20%, Tempered Martensite 0% to 25%, the balance being Annealed Martensite, which content shall be from 1% to 45%.
1 . A cold rolled and heat treated steel sheet having a composition comprising the following elements, expressed in percentage by weight:
0.1%≤Carbon≤0.5%
1%≤Manganese≤3.4%
0.5%≤Silicon≤2.5%
0.01%≤Aluminum≤1.5%
0.05%≤Chromium≤1%
0.001%≤Niobium≤0.1%
0%≤Sulfur≤0.003%
0.002%≤Phosphorus≤0.02%
0%≤Nitrogen≤0.01%
and optionally comprising the following elements:
0%≤Molybdenum≤0.5%
0.001%≤Titanium≤0.1%
0.01%≤Copper≤2%
0.01%≤Nickel≤3%
0.0001%≤Calcium≤0.005%
0%≤Vanadium≤0.1%
0%≤Boron≤0.003%
0%≤Cerium≤0.1%
0%≤Magnesium≤0.010%
0%≤Zirconium≤0.010%
a remainder of the composition being composed of iron and the unavoidable impurities, and a microstructure of the cold rolled and heat treated steel sheet including by area fraction, 10% to 60% Bainite, 5% to 50% Ferrite, 5% to 25% Residual Austenite, Martensite 2% to 20%, Tempered Martensite 0% to 25%, a balance of the microstructure being Annealed Martensite from 1% to 11%,
wherein the cold rolled and heat treated steel sheet has a tensile strength greater than 960 MPa, a total elongation of 20% or more and a yield strength from 479 MPa to 611 MPa.
2 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the composition includes, in percentage by weight, 0.8%≤Silicon≤2%.
3 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the composition includes, in percentage by weight, 1.2%≤Manganese≤2.8%.
4 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the composition includes, in percentage by weight, 0.01%≤Aluminum≤1%.
5 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the composition includes, in percentage by weight, 0.001%≤Niobium≤0.09%.
6 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the composition includes, in percentage by weight, 0.1%≤Chromium≤0.8%.
7 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the microstructure contains, by area fraction, 12% to 55% of bainite.
8 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the microstructure contains, by area fraction, 8% to 24% of Residual Austenite.
9 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the composition includes, in percentage by weight, 1.45%≤Manganese≤3.4%.
10 . The cold rolled and heat treated steel sheet as recited in claim 1 wherein the microstructure contains, by area fraction, 16% to 50% of Ferrite.
11 . The cold rolled and heat treated steel sheet as recited in claim 1 having a yield strength/tensile strength ratio is 0.45 or greater.