Control Of Microstructure And Mechanical Properties Of Copper-containing Cold-rolled High-strength Deep-drawing Automobile Steel

A copper-containing cold-rolled high-strength deep-drawing automobile steel is based on the ultra-low-carbon steel and some alloying elements,such as Ti?Nb?Mn?Si?Cu are added in order to improve the integrated properties of the steel.For a copper-containing cold-rolled high-strength deep-drawing automobile steel,this research mainly studied the effect of coiling temperature during hot rolling processing,cold-rolling reduction and different parameters during continuous annealing processing on microstructure,properties,orientation and texture of the steel,obtained the following conclusions:(1)The continuous cooling transformation behavior were studied and the CCT curve of the experimental steel was carried out.The results show that the austenite transformation product is ferrite and deformation before austenite transformation accelerates the austenite to ferrite progress,deformation and a higher cooling rate can refining ferrite grains.(2)The hot-rolling experiments about researching coiling temperature and the content of copper on microstructure and properties were carried out and the results show that ferrite grain size is enlarged and the texture of hot-rolling steel is transformed from alpha fiber texture to gamma fiber texture with the increasing of coiling temperature.The strength and elongation of hot-rolled steel are good under a coiling temperature of 650?,with a yield strength of 470MPa and a tensile strength of 580MPa and a elongation of 30%.There is no obvious effect on strength of hot-rolled steel with the increasing of copper content.(3)The continuous annealing experiments under different initial hot-rolling conditions,different cold-rolling reductions and different annealing parameters were studied and the results show that the ferrite grain is enlarged with the increasing of coiling temperature and the strength and elongation of the steel decrease after cold rolling and annealing;the properties are dropped with the increasing of cold-rolling reduction between 75%to 85%;the strength decreases and the elongation increases with the increasing of annealing temperature.The properties hardly changed with the increasing of heating rate and holding time The ferrite grain of continuous annealing steel refining and the yield strength and tensile strength increase as well as the work hardening index decrease with the increasing of copper content.There is a kind of copper-containing transient phase in ferrite grain with a size between 10nm to 20nm.(4)The orientation and texture of the steel under different continuous annealing parameters have been studied.The results show that the y-fiber texture increases and the?-fiber texture decreases and the formability of the steel enhances with the increasing of annealing heating rate,annealing temperature,holding time and cold-rolling reduction and coiling temperature of hot-rolling plate.(5)The integrated properties of the continuous annealing sheet are good under the copper content of 1.0wt.%,and a coiling temperature of 650? during hot-rolling progress,and the cold-rolling reduction of 80%and the continuous annealing temperature between 780? to 820? in the laboratory.The integrated properties of the experimental steel are equivalent to the super fine high strength IF steel and the high-strength IF steel containing P.