| ? ? ? ? The conventional normalizing process of 20Cr precision seamless steel pipe can completely eliminate the widmanstatten structure of Wuxi precision steel pipe, which makes the matching of yield strength and tensile strength more reasonable and yield strength ratio more reasonable ¦Ò S/b ¦Ò 78, elongation 5 ¦Ä When the temperature is more than 30%, the cold forming performance is greatly improved and the cold bending cracking phenomenon is avoided. The coefficient of expansion can be expressed in volume or length, usually in length.
? ? ? ? The density of the material is the mass per unit volume of the material, the unit is kg / m3 or 1B / in3. The residual tensile stress mainly comes from the residual tensile stress produced in the welding process. At present, annealing treatment after welding cooling is widely used in engineering to eliminate residual stress, and post welding cooling is an important process of residual stress generation, which not only wastes energy, but also easily produces large welding residual stress. Post weld heat treatment is a new technique to eliminate residual stress.
? ? ? ? Before welding, the Wuxi precision steel pipe was preheated to the post heat treatment temperature, and the weldment was continuously heated to maintain this temperature during the welding process. After the welding was completed, the insulation cotton was used to keep it cool slowly. Quenching can increase the strength and hardness of steel pipe, but reduce its plasticity. The quenchants commonly used in quenching are water, oil, alkali water and salt solution.
? ? ? ? The tempering of 20Cr precision seamless steel pipe is called tempering when the quenched Wuxi precision steel pipe is reheated to a certain temperature and then cooled by a certain method. The purpose is to eliminate the internal stress produced by quenching, reduce the hardness and brittleness, and obtain the expected mechanical properties. Tempering can be divided into high temperature tempering, medium temperature tempering and low temperature tempering. Tempering is usually used with quenching and normalizing. Quenching and tempering treatment the heat treatment method of high temperature tempering after quenching is called quenching and tempering treatment.