CRITERION OF WARPING DURING THE HEAT TREATMENT OF SYMMETRIC PRODUCTS

During the heat treatment process, the temperature change always occurs unevenly over the volume of the product. At the same time, thermal (stretching in colder zones, and compressive in more heated ones) and phase stresses arise. The theory of heat treatment of materials states that with symmetrical heating or cooling of homogeneous products of simple shape, thermal stresses are distributed symmetrically, the bending moment is zero, shape changes (warping, leashes) should not occur. Under certain conditions, warping is possible with symmetrical heating or cooling of a homogeneous symmetrical object. During temperature changes inside the product, areas with macro stresses of stretching and compression arise. The resulting normal stresses create two compensated forces (stretching and compression). As is known from the theory of resistance of materials, if the compressive force exceeds the critical one, then even with a symmetrical distribution of stresses, there is a loss of compression stability (warping of the object). Consequently, we obtain a dimensionless criterion, if the critical value of which is exceeded (for the plate – 2.6, for the rod – 2.2), there is a danger of uncontrolled shape change (warping) even with absolutely symmetrical heating or cooling during heat treatment. The experiment confirmed the theoretical estimates. The danger of such warping should be taken into account when assigning heat treatment modes for symmetrical products (sheets, strips, disks, rods).

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