Investigation on Precipitation Hardening High Strength IF Steel Sheet for Automotive Application
High strength IF steel sheets with sufficient formability had been extensively used in automotive industry. In this paper, a new type of high strength cold-rolled IF steel with higher carbon and niobium contents was studied. Thermal plastic and continuous annealing were performed on thermo-mechanical simulator. The transformation points were tested by thermal expansion apparatus. Optical microscopy and transmission election microscope (TEM) were used to analyze the microstructure and the secondary precipitates of the steel. The results showed, the ductibility temperature range was from 950℃ to 1250℃ and the transformation points were 887℃ and 913℃ respectively. The grain size of this steel was smaller than that of conventional high strength IF steel. At the mean time, there were many fine Nb(C, N) precipitates distributed in the intra-granular regions and the PFZ (precipitate free zone) were formed in the neighborhood of grain boundaries. Due to the unique micro-structural feature, the yield strength and the yield ratio of the steel were decreased while the tensile strength was increased. With the increasing of the annealing temperature, the strength decreased, the total elongation A50, r-value at 15％ strain and n-value were all increased. In order to obtain the favorable mechanical properties, the skin-pass rolling rate should be chosen at 0.6-0.8％.
high strength IF steel precipitation hardening grain refinement precipitate free zone (PFZ)
WANG Xu LIU Ren-dong WANG Ke-qiang GUO Jin-yu LIN Li XU Rong-jie
Automobile&Home Appliance Steel Institute of Ansteel Company Limited Technology Centre, Anshan 114009,Liaoning, China
国际会议
The 6th International Conference on High Strength Low Alloy Steels(第六届高强度低合金钢国际会议HSLA Steels2011)
北京
英文
574-578
2011-05-31（万方平台首次上网日期，不代表论文的发表时间）