Die Casting Sand Blasting Aluminium Parts

When the temperature of the forging part is through the heat, the temperature of the core part increases and expands. At this time, the forging part shows volume expansion; when the workpiece is cooled, the surface cooling rate is faster than that of the core part, and the surface layer shrinks. The high temperature of the core part prevents the contraction and generates tensile stress on the surface layer , The core produces compressive stress. When cooled to a certain temperature, the surface layer will no longer shrink by cold hardening, and the core will shrink due to continued cooling. At this time, the surface layer is subjected to compressive stress, while the core is subjected to tensile stress. After cooling, this stress still exists inside the forging, which is called residual stress.

The phase transformation stress is when the structure changes during the heat treatment of the forging, because the mass and volume of different structures are different, the mass and volume of the forging must change. Due to the temperature difference between the surface and the core of the forging, the surface and core structure are not changed in time, so that the internal and external mass and volume changes will cause internal stress. This kind of internal stress caused by the non-timeliness of the tissue transformation is called phase transformation stress.

The mass volume of each basic structure in steel increases in the order of austenite, pearlite, sorbite, troostite, lower bainite, tempered martensite and martensite.

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