局部感应加热对高强钢方管二次辊压成形的影响

本文通过对高强钢方管角部进行局部感应加热,提高其弯角区域的成形性能,降低其变形抗力,由此在不影响非变形区域组织性能的前提下,获得所需方管的截面尺寸和组织性能。在热辊压过程中,坯料在没有模具限制的方管角部外侧邻近区域发生堆积,且随着加热温度上升,角部外侧金属堆积更明显。同时,在方管内角表层出现显微裂纹恶化,裂纹以树枝状生长。热辊压成形后的残余温度会产生一个自回火过程,能够明显降低残余应力,且随着温度的升高,残余应力降低的幅度变大。当加热温度在650℃以上时,自回火对残余应力的影响大于宏观裂纹的扩展能力,起主导作用,且压扁过程中压下量超过方管对角线长度2/3时也不会产生裂纹。

Effect of local induction heating on secondary roll-forming of high strength square tubes

The formability of corners was improved by heating the corner area of high strength square tubes with induction coils. Under the premise of not impacting the undeformed zone, we obtained the ideal sectional dimension, microstructure and properties of products. In the hot roll forming process, the billet accumulated at the outside area of square corners without mold restrictions. With rising temperature, the accumulation became more serious. At the same time, microcracks deteriorated on the surface of the inner tube, while the cracks grew up in a form of arborization. A self-tempering process would be produced by residual temperature after hot roll forming, which could significantly reduce the residual stress. The residual stress sharply decreased as the temperature increased. When the heating temperature was above 650℃, the influence of self-tempering on the residual stress was greater than the extended capability of macrocracks and played a leading role; there was no crack when the distance was larger than 2/3 of diagonal length at flattening test.