时间：2013-11-20 10:00　作者：admin　点击： 次

XNUMX. Annealing is a heat treatment process in which steel parts are heated to a certain temperature, and then slowly cooled after heat preservation.Annealing is often used as a preliminary heat treatment, which is carried out in the part manufacturing process to prepare for the next processing procedure.
The main purpose of annealing is:
1) Reduce the hardness of steel, improve its cutting performance, and restore plastic deformation ability.
2) Uniform the structure and chemical composition of the steel, and refine the grains.
3) Eliminate the residual stress in the steel, stabilize the structure and prevent deformation.
4) Drive out the hydrogen in the steel, prevent white spots, and eliminate hydrogen embrittlement.
XNUMX. Normalizing is a heat treatment process in which the workpiece is heated and austenitized and then cooled in the air.
The effect of normalizing is similar to annealing, but normalizing is cooled outside the furnace, does not occupy equipment, and has high productivity. Therefore, low-carbon steel is often normalized instead of annealing.However, as the carbon content in steel increases, the difference in strength and hardness between these two methods becomes greater.The strength and hardness after normalizing are higher than those after annealing.
Common defects of annealing and normalizing are:
1) The hardness of the stone is too high, the cooling rate is too fast, or the waiting temperature is not enough to cause the hardness of the stone to be too high.The steel parts with high hardness can be re-annealed.
2) Poor spheroidization, too high heating temperature, too long holding time, and too slow cooling speed may cause poor spheroidization, and the generated ones can be reprocessed.
3) Fracture of fine grain.If the heating temperature is too low or the holding time is insufficient, the crystal grains damaged by the cold working cannot be recrystallized, resulting in the fracture of fine crystal grains.This structure has low plasticity and cannot continue cold deformation processing.
4) Fracture of coarse grains.If the heating temperature is too high or the high temperature holding time is too long, it will cause the coarse grains to fracture.The mechanical properties of this organization are very poor, especially the impact toughness is very low.The generated parts can be reprocessed.
XNUMX. After the quenched workpiece is heated and austenitized, it is cooled in an appropriate manner to obtain the heat treatment process of martensite or (and) bainite structure.The most common ones are water-cooled quenching, oil-cooled quenching, and air-cooled quenching.
The main purpose of quenching is:
1) Improve the hardness and wear resistance of parts.
2) Cooperate with the tempering process to obtain the required comprehensive mechanical properties of the parts.
3) Improve some physical and chemical properties of special performance steel.
XNUMX. Tempering, the workpiece is heated to A after hardening_C1A heat treatment process in which one of the following temperatures is maintained for a certain period of time, and then cooled to room temperature.
The purpose of tempering is to: ① reduce or eliminate stress and improve the toughness of the parts; ② obtain the comprehensive mechanical properties required by the parts; ③ stabilize the structure to transform or stabilize the residual austenite.