Reason Analysis of Cracks Formed on 42CrMo Steel Rollers

To analyze reason of cracks formed on 42CrMo steel rollers after heat treatment, the material composition, heat treatment techniques, metallographical structure, crack morphologies were investigated. It was found that there are foreign matters in the cracks by using metallographic microscopes and scanning electron microscopes. Furthermore, there were a lot of pinholes and punctate foreign matters. The result from energy spectrum analysis showed that the oxygen content of foreign matters in cracks was remarkably higher than that of non-crack area. Combining the observation and analysis of polarizing microscope, it was concluded that the foreign matters are the mixture of FeO, Fe₃O₄ and Fe₂O₃, and the reason of cracks resulted form the foreign matters of ferriferous oxides formed the forging pucker during the forging process. After the mould cavity of the forging die had been improved, the cracks of the rollers disappeared.