Analysis of Cracking Reasons in the Cold Heading Process of Q195 Steel

The surface quality,crack morphologies,microstructures,oxygen and nitrogen content and non-metallic inclusions of Q195 cold heading steel were studied by a set of analysis techniques,such as acid washing,optical microscopy,scanning electronic microscope （SEM）,and energy dispersive X-ray spectroscopy （EDS）.The results showed that the total oxygen content in steel was 154 × 10^-6,which indicated that non-metallic inclusions content was higher. Large size inclusions were found at the cracks of the rolled material,and a large number of large-sized inclusions were found near 1/4 width to the edge of rolled material,the composition of the inclusions was similar to that of the continuous casting mold powder. Large inclusions cause stress concentration during cold heading,which leads to and aggravates cold heading cracking. At the same time,improper control of rolling process causing the folding defects on the product surface and further 180 ° symmetrical longitudinal cracks,is the main reason for cold heading cracking.