Variation of cavity hydrogen pressure in the forming process of heavy forging

Flake is an irreparable crack type defect in many huge steel products, especially in heavy forging. Lots of previous studies have revealed that flake is usually originated at cavities within heavy forging. In addition, whether it is generated and what size after it is formed both largely depend on the hydrogen pressure within the cavity. However, the most part of previous studies only related cavity hydrogen pressure to steel hydrogen concentration, and few studies considered the metal forming effect. In this paper, the relationship between cavity hydrogen pressure and metal forming process of heavy forging is addressed from a simulation perspective. Different from previous research, this paper wants to emphasize the importance of metal forming process in the flake formation. There are four parts in this paper. We start with a brief introduction to the flake and the importance of cavity hydrogen pressure in its formation. Then, we propose a cavity hydrogen pressure calculation model. After that, the simulation results and discussions are provided. We end the study with the conclusion. We find in our research that metal forming has a great influence on cavity hydrogen pressure, especially with large deformation. Based on these findings, we may conclude that flake formation not only depends on the steel hydrogen content, but also very depends on the way of forming. Admittedly, what we have discussed in this study is far from complete. And some improvements we want to make in our further research include (1) studying the influence of metal forming on flake formation in micro-scale, such as in grain scale; (2) verifying the simulation results with experiment; and (3) considering the hydrogen diffusion process in metal forming process.