Cause Analysis of Cold Heading Cracking of Alloy Cold Heading Steel SCM435

A certain auto parts manufacturer uses alloy cold heading steel SCM435 hot-rolled wire rod with a specification of 24 mm to develop a mid-shaft product with a deformation rate approaching 90%. After the raw materials were drawn through a "2-draw-2-ball" process， a batch of cracks appeared during cold heading processing， with a cracking ratio of about 60%. Physical and chemical testing and analysis were conducted on the cracked products. The analysis results indicated that the cold heading cracking issue originated from insufficient material plasticity leading to stress cracking. Further inspection revealed that the user's spheroidizing annealing heat treatment process was poor， with a spheroidization structure only at grade 4.0， which was the fundamental cause of the insufficient material plasticity and toughness. By optimizing the spheroidizing heat treatment process， the spheroidizing annealing heating section temperature was reduced from 765°C to 745°C， bringing the material spheroidization structure grade to 5.0-6.0， effectively improving the material's plasticity and toughness， and successfully solving the quality issue of cracking during the cold heading process of the product.