H型钢表面裂纹成因分析

H型钢由异型坯轧制生产，异型坯形状独特，连铸生产中横向表面温度极不均匀，应力、应变状况复杂，对冶炼和连铸工艺均有较高要求。SS400异型坯生产中钢水未经精炼处理，部分炉次钢水碳含量处于包晶反应严重的碳含量范围，硫、磷含量较高，w（Mn）／w（S）较低，总氧和大型夹杂物含量较高；浸入式水口为直孔型，结晶器中上升流股较弱，坯壳生长不均匀；拉速较慢，并采用双水口浇铸，结晶器中上升流股更弱，弯月面处钢水供热不足，处于低温状态，保护渣也因温度低而熔融欠佳；二冷强度偏高，矫直辊前异型坯腹板表面温度处于低温脆性区，因此轧制成品H型钢的表面裂纹较多。

Genetic Analysis of Surface Cracks in H Beam

H beam is produced from beam blank at Masteel.Owing to the special shape,uneven distribution of lateral surface temperature,complicate distribution of strain and stress,high quality molten steel and high level continuous casting operation are required for continuous casting of beam blanks.The reasons of surface cracking are: in production,SS400 molten steel is not refined,C content of some heats locates in the range of peritectic reaction,S and P contents are high,Mn/S is low;and TO] and content of macro-inclusions are high;thickness of the shell is uneven and up stream of the liquid steel is weak in the mold by use of submerged nozzles with straight outlets and at low casting speed,which makes heat supply to molten steel insufficient and full melt of mould powder;the surface temperature of the web is in the brittleness range due to high cooling intensity in the secondary cooling zone.