Dual-phase steel, flat product made of such dual-phase steel and method for manufacturing a flat product

摘要

#CMT# #/CMT# Dual-phase steel comprises 20-70% of martensite, up to 8% of residual austenite and balance of ferrite and/or bainite and which possess a tensile strength of at least 950 MPa, and composition of e.g. manganese (2.1-2.8 wt.%), chromium (0.2-0.8 wt.%), titanium (0.02-0.10 wt.%), boron (less than 0.002 wt.%), molybdenum (less than 0.25 wt.%), aluminum (less than 0.1 wt.%), copper (up to 0.2 wt.%), nickel (up to 0.1 wt.%), calcium (up to 0.005 wt.%), phosphorus (up to 0.2 wt.%), sulfur (up to 0.01 wt.%), nitrogen (up to 0.012 wt.%) and balance of iron and unavoidable contamination. #CMT# : #/CMT# Dual-phase steel comprises 20-70% of martensite, up to 8% of residual austenite and balance of ferrite and/or bainite and which possess a tensile strength of at least 950 MPa, and composition of carbon (0.050-0.105 wt.%), silicon (0.2-0.6 wt.%), manganese (2.1-2.8 wt.%), chromium (0.2-0.8 wt.%), titanium (0.02-0.10 wt.%), boron (less than 0.002 wt.%), molybdenum (less than 0.25 wt.%), aluminum (less than 0.1 wt.%), copper (up to 0.2 wt.%), nickel (up to 0.1 wt.%), calcium (up to 0.005 wt.%), phosphorus (up to 0.2 wt.%), sulfur (up to 0.01 wt.%), nitrogen (up to 0.012 wt.%) and balance of iron and unavoidable contamination. Independent claims are included for: (1) a flat product comprising the dual-phase steel; (2) production of a hot laminated strip with a tensile strength of at least 950 MPa and a dual phase structure, comprising melting the dual-phase steel, pouring the melt to a preproduct such as slab or thin slab, reheating or holding the preproduct at a hot rolling starting temperature of 1100-1300[deg] C, hot rolling the preproduct at a hot rolling temperature of 800-950[deg] C to the hot laminated strip and winding the hot laminated strip at a winder temperature of up to 650[deg] C, preferably 500-650[deg] C; and (3) production of a cold strip with a tensile strength of at least 950 MPa and a dual phase structure, comprising melting the composite dual-phase steel, pouring the melt to a preproduct such as slab or thin slab, reheating or holding the preproduct at a hot rolling starting temperature of 1100-1300[deg] C, hot rolling the preproduct at a hot rolling temperature of 800-950[deg] C to the hot laminated strip, winding the hot laminated strip at a winder temperature of up to 650[deg] C, preferably 500-650[deg] C, cold rolling the hot laminated strip to a cold strip, tempering the cold strip to a tempering temperature of 700-900[deg] C and controlled cooling of the tempered cold strip. #CMT#USE : #/CMT# The dual-phase steel is useful to produce a flat product, which is hot laminated strip and cold strip (all claimed). #CMT#ADVANTAGE : #/CMT# The dual-phase steel shows high strength of 1000 MPa and good deformability. #CMT#INORGANIC CHEMISTRY : #/CMT# Preferred Components: The amount of phosphorus, carbon, silicon, manganese, chromium, titanium, boron, molybdenum, aluminum, copper, sulfur and nitrogen is less than 0.1 (preferably less than 0.02) wt.%, 0.06-0.09 wt.%, 0.2-0.4 wt.%, 2.20-2.70 wt.%, 0.4-0.7 (less than 0.3) wt.%, 0.06-0.09 wt.%, 0.0005-0.0020 (preferably 0.0007-0.0015) wt.%, 0.05-0.20 (preferably 0.065-0.150) wt.%, 0.01-0.06 wt.%, 0.07-0.13 wt.%, less than 0.003 wt.% and less than 0.007 wt.%, respectively. In the presence of nitrogen, the titanium content (more than 5.1 times) is greater than the respective nitrogen content. The amount of residual austenite is less than 7%. The metallic protective coating is produced by hot-dip galvanizing or galvannealing. The winder temperature is greater than 500-580[deg] C. #CMT#INSTRUMENTATION AND TESTING : #/CMT# Preferred Components: The dual-phase steel exhibits: a yield strength of at least 580 MPa; and an elongation (A 8 0) of at least 10%. The flat product is only hot-rolled hot laminated strip. The flat product is a cold strip obtained by cold rolling. The flat product is provided with a metallic protective coating. The hot laminated strip with a cold-roll degree of 40-70% is cold-rolled to cold strip. #CMT#ORGANIC CHEMISTRY : #/CMT# Preferred Process: The controlled cooling takes place at 550-650[deg] C with a cooling rate of at least 10 K/s.