汽车用高强度钢CR1030/1300MS连铸板坯的热塑性

Thermoplasticity of Continuous Casting Slab of High Strength Steel CR1030/1300MS for Auto

试验用CR1030/1300MS钢236 mm×1 350 mm连铸板坯(/%:0.13C,0.26Si,1.53Mn,0.011P,0.002S,0.31Cr,0.047Als,0.029Nb,0.032Ti,0.002 5B,0.003 2N)的工艺流程为260 t BOF-LF-RH-CC。采用Gleeble3500热模拟试验机测试了试验板坯650～1 300℃的热塑性曲线,并分析了高温拉伸试样断口组织。试验结果得出,试验钢两个脆性区为熔点～1 120℃和800～650℃在1 120-800℃呈现良好的塑性,断面收缩率均在85%以上。900℃断口属于穿晶韧性断裂,700℃为韧性和沿晶断裂。1 250℃和900℃近断口组织均为马氏体,温度升高马氏体板条更粗大。750℃原奥氏体晶界出现先共析铁素体是产生裂纹的根本原因。1 120～800℃进行矫直可防止铸坯产生裂纹。

Abstract The flowsheet of 236 mm × 1 350 mm casting slab of tested steel CRIO30/13OOMS （/% ： 0. 13C, 0. 26Si, 1.53Mn, 0. 011P, 0. 002S, 0. 31Cr, 0. 047Als, 0. 029Nb, 0. 032Ti, 0. 002 5B, 0. 003 2N） is 260 t BOF-LF-RH-CC process. With using Gleeble3500 thermal simulation test machine the thermoplastieity curves of test slab at 650 - 1 300 ℃ has been measured and the structure of high temperature tensile specimen fracture is analyzed. The test results obtain that the two brittle zones in test steel are melting point - 1 120 ℃ and 800 - 650 ℃, and the better plasticity occurs at 1 120 ～ 800 ℃, in this zone the reduction of area of steel is more than 85%. The fracture of tensile of steel at 900 ℃ is transgranular toughness fracture and at 700 ℃ it is toughness and along crystal fracture. The structure near fracture of tensile of steel at 1 250 ℃ and 900 ℃ is martensite and with increasing temperature the martensite lath is coarser. The basic reason to form crack is that the proeutectoid ferrite occurs in original austenite grain boundary at 750 ℃. Straightening at 1 120 ～ 800 ℃ is available to avoid the casting bloom forming crack.