C36船板钢铸坯角部横裂和高温热塑性分析及改进工艺

Analysis on Corner Transverse Crack and High Temperature Thermoplastic of C36 Ship Plate Steel Cast Slab and Process Improvement

利用Gleeble-3500热模拟试验和Factsage7.0软件、扫描电子显微镜、红外热像仪等方法对微合金化0.125%C C36船板钢250 mm×2070 mm连铸板坯高温热塑性及其角部横裂纹的形成机理进行了系统分析。结果表明,800~1 200℃为C36船板钢的高温塑性区间,其中800~1 000℃的断面收缩率为75.5%~80.9%,1 050~1 200℃的断面收缩率达到87.8%~95.0%。第二相粒子NbC在950~1 100℃的大量析出是阻碍该变形温度下C36船板钢中再结晶晶粒长大的主要原因。C36船板钢铸坯角部横裂纹形成于外弧且为沿晶脆性开裂,其裂纹的形成可能与其连铸二冷9段铸坯外弧角部温度(706℃)接近脆性温度区间且进行了静态压下有关。通过将C36钢连铸拉速从0.90 m/min提高至0.95 m/min,铸坯外弧角温度由706℃提高至731℃,铸坯外弧角裂纹发生率由5.67%降至3.68%。

Gleeble-3500 thermal simulation test,Factsage7.0 software,scanning electron microscope and infrared thermal imager are used to analyze the mechanism of high temperature thermoplastic and corner transverse crack formation of 0.125% C micro-alloying C36 ship plate steel 250 mm×2 070 mm slab.The results show that the high temperature plasticity range of C36 ship plate steel is from 800℃ to 1200 ℃,and the reduction of area of slab rate is 75.5% to 80.9% at 800℃to 1 000 ℃,and 87.8% to 95.0% at 1 050 ℃ to 1 200 ℃.The large precipitation of the second phase NbC at 950~1 100℃ is the main reason to block the growth of recrystallized grains in C36 steel at this deformation tenperature.The transverse crack at the corner of the cast slab of C36 ship plate steel is formed in the outer arc and in the intercrystalline brittle cracking.The formation of the crack may be related to the fact that the temperature(706℃) of the corner of the outer arc of the cast slab at the ninth stage of continuous casting of secondary cooling zone is close to the brittle temperature range and the static pressure is carried out.By increasing cast speed of C36 steel from 0.90 m/min to 0.95 m/min,cast slab out arc temperature be enhanced from 706 ℃to 731 ℃,the out arc corner crack yield rate decreases from 5.67% to 3.68%.