低碳中板断后伸长率不合原因分析

CAUSE ANALYSIS OF UNQUALIFIED ELONGATION OF LOW CARBON MEDIUM PLATE AFTER BREAKING

对Q235B中板断后伸长率不合格试样进行了详细的物理化学分析,并与合格试样进行了对比,发现不合格试样中存在与板面呈约30℃夹角的裂纹,裂纹内有硫化物类夹杂,级别大于5级;带状组织为B系列3.5级;拉伸断口分层,断裂位呈脆性准解理形态,而周围呈韧窝型塑性断裂形态。此外,连铸坯中存在严重的中间裂纹,认为连铸坯中存在的中间裂纹易造成硫等杂质元素集中分布,而导致Q235B中板断后伸长率不合格。通过对生产工艺进行追溯,改进相应措施,断后伸长率合格率大幅提升。

A detailed physicochemical analysis was carried out on the unqualified elongation after plate break in Q235B.After comparing with the qualified sample, it was found that there were cracks in the unqualified specimen at an angle of about 30 ℃ to the plate surface, and there were sulfide inclusions in the cracks, and the grade was greater than 5. The band structure is grade 3.5 of the B series, and the tensile fracture is layered, and the fracture site is brittle quasi-cleavage form, while the surrounding is ligament-shaped plastic fracture form. In addition, there are serious intermediate cracks in the continuous casting billet, and it is believed that the intermediate cracks in the continuous casting billet are easy to cause the concentrated distribution of impurity elements such as sulfur, resulting in unqualified elongation after the plate break in Q235B. By tracing the production process and improving the corresponding measures, the elongation after breaking qualification rate has been greatly improved.