Reasons for deformation in steel part heat treatment

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The last edit to this post was made by huanghong on 2023-3-18 at 17:04. There are many factors that cause deformation during heat treatment; generally speaking, there are three main ones: 1. During solid-state phase transformation, changes in the mass and volume of various phases inevitably lead to volume changes, resulting in dimensional expansions and contractions of the parts； 2 Thermal stress, including rapid heating stress and rapid cooling stress, will cause plastic deformation in a part when it exceeds the yield limit of that part at that temperature, resulting in a change in the part’s shape – that is, warping or distortion ； 3 Tensile stress can also cause changes in shape, that is, distortion. Generally speaking, the deformation of quenched workpieces is always the result of the combined effect of the two or three factors mentioned above, but which factor has the greatest impact on the deformation requires a specific analysis based on the particular circumstances. In general, the change in volume is caused by the change in specific volume during phase transition. The mass-volume ratio of martensite is greater than that of the other phase compositions in steel; when steel is transformed from these other phase compositions into martensite during heat treatment, an increase in volume is inevitable. The mass volume of austenite is smaller than that of other microstructures in steel; when it transforms from other phase compositions into austenite during heat treatment, this results in a decrease in volume. Regarding changes in shape, warping or distortion is mainly caused by internal stresses or external stresses. During heating and cooling, due to differences in temperature across various parts of the workpiece, phase changes occur at different times, and the structural transformations that take place may also vary, which leads to internal stresses. Once this internal stress exceeds the yield limit of the material at that temperature, plastic deformation occurs, leading to a change in shape. Furthermore, the relaxation of the cold-worked residual stresses within the workpiece during heating, as well as the application of large external stresses during heating, can also cause changes in shape. The reasons that may cause volume and shape changes during heat treatment are listed in the table below. The column \"Reasons for volume change\" in the table does not include the volume changes that occur in steel due to thermal expansion and contraction. When steel is subjected to cold treatment by cooling it from its quenching temperature to sub-zero levels, its volume changes accordingly as the temperature changes. The uneven volume changes caused by thermal expansion and contraction are the source of thermal stress, and they have a significant impact on deformation.