Welding Heat Treatment Stress and Its Influence Analysis

Welding heat treatment residual stress refers to the residual stress of the workpiece after heat treatment, which has a very important impact on the shape, size and performance of the workpiece. When the material yield strength exceeds, it will cause deformation. When the strength limit of welding material exceeds, it will produce cracks, which should be reduced and eliminated.

1.Heat treatment stress of steel

In the process of heating and cooling, the difference of cooling time and speed leads to volume expansion and contraction, resulting in thermal stress. Under the effect of thermal stress, the surface layer of the workpiece is compressed while the core part is pulled. This phenomenon is affected by heat treatment process, cooling speed and material composition, resulting in fast cooling speed, high alloy composition and carbon content, The larger the plastic deformation is, the larger the residual stress is.

Practice has proved that as long as there is phase change in the heat treatment process of any workpiece, it will produce thermal stress and structural stress, but the thermal stress is generated before the structural transformation, and the structural stress is generated in the transformation process. The combined effect of structural stress and thermal stress is the actual stress in the workpiece.

2. Effect of heat treatment stress on quenching crack

The factors that can cause stress concentration in different parts of quenched parts can promote the formation of quenching cracks, but only in the tensile stress field, especially in the maximum tensile stress.

The cooling rate is an important factor that affects the quenching quality and determines the residual stress. In order to achieve the purpose of quenching, it is necessary to speed up the cooling rate of the parts in the high temperature section to make it exceed the critical quenching cooling rate of the steel. As far as the residual stress is concerned, it can increase the thermal stress value that counteracts the effect of the structural stress, so it can reduce the tensile stress on the surface of the workpiece, To achieve the purpose of restraining longitudinal cracks, its effect will increase with the acceleration of high temperature cooling rate. In the case of hardenability, the larger the section size is, the greater the risk of cracking is.

The stress in the process of heat treatment is inevitable. By controlling the heat treatment process and distributing the stress reasonably, the harmful degree can be reduced to the minimum, or even become beneficial.

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