Under the effect of thermal stress due to the beginning of the surface temperature is lower than central portion, leaving the central portion is larger than the contraction central portion in tension when the end of the cooling, the cooling due to the volume shrinkage of the final core section can be freely leaving the center portion of the pressure receiving surface tension. Under the premise of guarantee mold hardness, try p20 steel Factory to use pre-cooling, grading quenching or cooling temperature quenching process. When repair mold blisters, porosity, wear and other shortcomings, such as a small selection of cold welding heat affected repair equipment repair process to avoid distortion occurs. Some fine mess of mold can be used pre-heat treatment, aging heat treatment, quenching and nitriding heat treatment to control the accuracy of the mold.
Fine messy mold pre-heat treatment to eliminate residual stress occurs machining process. This phenomenon by cooling rate, the impact of material composition and heat treatment process and other factors. Fine mess of raw materials should be selected for good micro mold deformation of steel, carbide segregation grim casting mold steel should be reasonable and transfer of heat treatment, solution heat treatment on a large double refining and casting mold steel can not be carried out. On the other hand due to the heat treatment of lsaw steel pipe in the tissue changes during the austenite to martensite transformation that is, the specific volume is increased due to the volume expansion accompanied by the workpiece, the various parts of the workpiece has a phase change, causing the volume of tissue grown produce inconsistencies stress.
Reasonable selection of the heating temperature, heating rate manipulation, fine mess on the admissibility slowly heated mold, preheating and other balanced approach to reduce mold heating heat deformation.Uneven volume expansion and contraction stress, that is, the thermal stress.When the cooling speed is faster the higher the carbon content and alloy composition, plastic deformation unevenness in the cooling process, the greater thermal stress produced, the final form of the greater residual stress.First technical mold layout design should be reasonable, thickness should not be too poor, to be symmetrical shape, mold on large deformation deformation to grasp the rules, set aside allowance, on large-scale, fine molds can be used in combination messy layout. Fine mess of mold, in the case of the condition promised, try to use cryogenic vacuum heat treatment and quenching after quenching. That is the role of thermal stress eventually workpiece surface tension pressure and heart department..Rational use of materials