Abstract: SPCC steel met the technical requirements in trial production, but the surface hardness was extremely low after mass production. After analyzing the incoming materials, manufacturing processes, and testing various process elements, the reasons were determined, and the problem of ultra-low surface hardness was resolved through consultation with customers. According to the verification and detection of the possible reasons, it is finally determined that the low hardness is caused by the mismatch between the product surface structure and the hardness testing method, that is, the turning tool cutting pattern on the product surface affects the accuracy of the inspection equipment. The correspondingly improved hardness testing is carried out by direct polishing without cutting and inlaying, and the detection position is only selected at the “wave peak” position.

Key words: SPCC steel, gas nitrocarburizing, extra-low hardness, cause analysis