Simulated Strains-Based Approach for Explaining Distortion and Residual Stress in Quenched Pure Iron Cylinder

Abstract

Distortion and residual stress in steel parts because of heat treatment affect assembled products’ performance and life. A trial-and-error method has been used traditionally to solve problems, which requires a lot of time and cost. In the 1970s, heat treatment simulation was realized based on theoretical studies for predicting temperature, volume fraction of metallic phase, stress, strains, and so on, during the processes. In the early 2000s, an approach was established to explain the origin of distortion and residual stress based on the simulated results, especially various kinds of strains, which is called the simulated strains-based approach by the author. This approach has been made possible by simulation, which has provided results such as the time history of strain distribution. The subject of the residual stress generation mechanism in a quenched pure iron cylinder is taken here to illustrate the advantages of this approach. The classic study of this problem is Rose's illustration using a conceptual diagram of the variation of temperature and stress at the surface and center of the cylinder. In connection with this diagram, thermal shrinkage and elastic deformation, and the relationship between them and stress, are qualitatively explained. However, it is difficult to understand this diagram logically because the meaning of the correction applied to the stresses after the onset of plasticity was not clearly explained. On the other hand, the simulated strains-based approach using changes in distributions of thermal, elastic, plastic, and total strains provided a clear explanation of how the final distribution of the elastic strain, which is corresponded to the residual stress, is generated. Because quenching of steel parts produces additional transformation strain and transformation plastic strain, the quenching of pure iron is an excellent introduction to the application of a simulated strains-based approach.

Elucidation of Blade Curving Mechanism in Japanese Sword Quenching Using the Simulated Strains-Based Approach

“…Thermocouples were inserted at three locations on one end face. 7) Quenching of the specimens was performed by the swordsmith. Prior to quenching, surfaces of all three specimens were coated with clay 9) in a traditional method.…”

“…The simulated-strains based approach 7) has been devised to explain why distortion and stress occur based on the strain distribution state obtained from the simulation. This method uses the equation for the total strain t ¾ ij and various strains, obtained from the simulation at time t:…”