14MnNb钢管外折叠原因分析

Analysis on 14MnNb Steel Pipe Forming Outer Fold

采用电弧炉、炉外精炼和连铸工艺生产了直径330 mm的14MnNb钢连铸管坯,并轧制成外径323.8 mm、壁厚23.83 mm的管线用管。然而,沿钢管全长进行磁粉探伤时发现表面有外折叠。对本批次钢管和连铸坯进行了金相检验、酸浸及能谱分析,以揭示产生外折叠的原因。结果表明:钢管外折叠是连铸坯表面的网状裂纹所致,而铸坯表面产生网状裂纹的原因是高温析出的Nb、Al元素的碳、氮化物引起晶界脆化。

Continuous casting billets for pipe-making of 14MnNb steel 330 mm in diameter were produced by electric arc furnace,ladle refinery furnace and continuous casting,and rolled into pipeline pipes 323.8 mm in OD by 23.83 mm wall thickness.Outer folds,however,were found at the surface of steel pipe when subjected to magnetic particle inspection along their hull length.This batch of steel pipes and continuously cast billets were subjected to metallographic testing,acid leaching,and energy spectrum analysis,to reveal the cause of occurrence of the outer fold.The results showed that the outer folds on the steel pipe was caused by resillage at continuously cast billet surface,whereas the reason why there was the resillage at the billet surface proved to be the intergranular embrittlement stemming from the precipitation of carbides and nitrides of niobium and aluminum at high temperature.