Annealing method for transformation Induced Plasticity of bainite

摘要

The present invention is a low-cost, lightweight vehicle with the purpose around the automotive industry, reliability and eco-friendly elements providing excellent formability and high strength characteristics at the same time everything about 800MPa grade cold rolled steel sheet for automotive members with the transformation of organic plastic steel to meet chukeungryeok state of plane strain mode bainite transformation treatment method that can improve the formability in order to develop in the ; the configuration of the present invention for achieving the above object, a carbon weight% (C):. 0.2~0.25%, silicon (Si): 1.3~1.6%, manganese (Mn): 1.4 to 1.6%, sulfur (S): 0.01~0.02%, and charged to the first step of heating the slab in the composition of the balance of iron (Fe) and heated to 1200~1300 ; A second step of hot-rolling the slabs to take-off from the heating furnace, heated in the first step of the hot rolled strip to ronaeng 500~600 and charged to the cooling; A third step of cold rolling to a take-off from the strip cooled by cooling in a second step, and annealing the cold-rolled strip with the contents in a 750~850 annealing; Step 4 charged in a salt bath heat treated and heat-treated at a constant temperature for the bainite 300~450 strip charged to the heat treatment in the salt bath to withdraw the strip from the annealing in the third step to the annealing; Is to include a fifth step of air cooling of the heat-treated strip at room temperature for bainite constant temperature in the fourth step.