低温用无缝钢管管坯表面裂纹分析与控制

Analysis and Control of Surface Flaw of Billet for Making of Cryogenic Service Seamless Steel Pipe

介绍了低温用无缝钢管Gr6管坯表面微裂纹的形貌,分析了管坯表面裂纹的形成原因,并提出有效的防止措施。分析认为:凝固时结晶器弯月面初生凝固坯壳随温度下降发生δ-Fe→γ-Fe转变,伴随着较大的体积收缩和线收缩,坯壳与铜管壁过早脱离形成气隙,导致坯壳生长不均匀,在坯壳的最薄弱处形成裂纹。通过提高钢水洁净度、控制钢水过热度、降低拉坯速度、控制结晶器液面波动和选取合适的结晶器锥度等工艺措施,可有效地控制低温用无缝钢管管坯表面微裂纹的产生。

Described in the assay is the morphology of the surface flaws of the Gr6 billet for making of the cryogenic service seamless steel pipe. Moreover,the causes for formation of the said flaws are investigated,and then relevant preventative actions are put forward. The investigation leads to the following conclusion. During the solidification process,δ-Fe →γ-Fe transformation occurs with the initially-solidified shell of the mould meniscus region along with dropping of the temperature. Meanwhile,with considerable volume and linear shrinkages,the shell breaks away from the mould copper surface so early that air gas is formed,and this leads to uneven growth of the shell,and flaws in turn develop in the weakest area of the shell. Accordingly,occurrence of flaws of the billet for making the cryogenic service seamless steel pipe could be properly controlled by means of such actions as enhancing steel cleanness,well controlling overheat of the hot metal, reducing withdrawing velocity, appropriately controlling fluctuation of the mould level,and selecting suitable mould tamper,etc.