Stress generated during quenching and cooling in t

Stress generated during quenching and cooling of annealing furnace

thermal stress and structural stress will be generated during quenching and cooling of annealing furnace. Generation process of thermal stress: during quenching and cooling of annealing furnace, the cooling speed of each part is inconsistent, resulting in temperature difference, so that the expansion and contraction of each part are uneven and the production internal stress. This internal stress is called thermal stress. The faster the cooling speed is, the greater the thermal stress is. The higher the quenching temperature is, the greater the thermal stress is. The parts have shortcomings such as environmental pollution, high production cost, easy paint removal of parts. At the initial stage of quenching and cooling, the surface shrinkage is greater than that of the heart, and the heart resists surface shrinkage, Make the surface produce tensile stress and the center produce compressive stress. With the increase of cooling time, the heart cools and shrinks. The surface that no longer cools and shrinks resists the heart contraction, so that the external and internal stresses offset each other and the stress sum is zero. With the extension of time, the heart stress becomes tensile stress. Thermal stress changes with time

production process of structural stress: the order of volume increase of various structures in steel is: austenite → pearlite → bainite → martensite. When quenching and cooling, the cooling rate of each part of the annealing furnace is different, so that the time of phase transformation is different. When the surface temperature is lower than MS, the surface volume increases, resulting in compressive stress, and the center generates tensile stress. With the extension of time, martensitic transformation takes place in the inner layer, which intensifies the volume effect. At a certain moment, the sum of the external and internal organization stress is equal to fragmentary, the temperature continues to decrease, the inner layer volume increases, the stress distribution changes in the opposite direction, and when it is cooled to normal temperature, the surface is under tensile stress, and the center is under compressive stress. The size of the organization stress is related to the carbon content of steel, cooling rate, heating temperature, holding time and other factors, and the volume effect is larger than that of the inner layer, Therefore, the standard gb/t50123 (1) 999 stress for surface compressive stress geotechnical test method, the tensile stress in the inner layer, the tissue stress during quenching, and how to operate the testing machine at any time? Many domestic steel mills are running close to full capacity. (end)