The reasons for the deformation of steel-plastic composite pipes are often complicated, but we only need to grasp the deformation rules, analyze the causes, and choose different methods to prevent the deformation of the mold, which can be reduced and controlled. Generally speaking, the following measures can be adopted to prevent the deformation of steel-plastic composite pipe by heat treatment.
(1) Reasonable selection of materials. For steel-plastic composite pipes, micro-deformed die steels with good raw materials (such as air-quenched steel) should be selected. For die steels with severe carbide segregation, reasonable casting and quenching and tempering heat treatment should be performed. Larger and uncastable die steels can be treated with solid solution double refinement heat treatment.
(2) The mold structure design should be reasonable, the thickness should not be too wide, the shape should be symmetrical, the deformation rules should be grasped for the larger deformation mold, and the processing allowance should be reserved. For the large, steel-plastic composite pipe, a combined structure can be selected.
(3) The S-P composite pipe should be pre-heated to eliminate the residual stress during the machining process.
(4) Reasonably select the heating temperature and control the heating speed. For the S-P composite pipe, slow heating, preheating and other balanced heating methods can be adopted to reduce the heat treatment deformation of the mold.
(5) On the premise of ensuring the hardness of the mold, try to use pre-cooling, staged cooling quenching or warm quenching process.
(6) For steel-plastic composite pipes, when conditions permit, try to use vacuum heating and quenching and cryogenic treatment after quenching.
(7) For some sophisticated molds, pre-heat treatment, aging heat treatment, and tempering and nitriding heat treatment can be used to control the accuracy of the mold.
(8) When repairing mold blisters, pores, wear and other shortcomings, use cold welders and other correction equipment with low thermal impact to avoid deformation during the repair process.
In addition, the correct heat treatment process operation of the spiral tube (such as hole plugging, tying hole, mechanical fixing, suitable heating method, correct selection of the cooling direction of the mold and the movement direction in the cooling medium) and the reasonable tempering heat treatment process are also the useful methods for steel-plastic composite pipe deformation.