1.What does the steel heat treatment process include?
Annealing,Normalizing,Quenching,Tempering
2.Annealing
Annealing is a heat treatment process in which steel is heated to an appropriate temperature, kept warm for a period of time, and then slowly cooled. It is to heat the steel to a temperature where phase change or partial phase change occurs, and then slowly cool it after keeping warm. Its purpose is to eliminate structural defects, improve the structure to make the composition uniform and refine the grains, improve the mechanical properties of steel, and reduce residual stress; at the same time, it can reduce hardness, improve plasticity and toughness, and improve cutting performance. Annealing is not only to eliminate and improve the structural defects and internal stress left over from the previous process, but also to prepare for subsequent processes. It belongs to the heat treatment of semi-finished products, also known as pre-heat treatment. For example, heating steel to an appropriate temperature, keeping warm for a period of time and then slowly cooling it can reduce hardness, improve plasticity and toughness
3.Normalizing
Normalizing is a heat treatment method that heats steel above the critical temperature, transforms all the steel into uniform austenite, and then cools it naturally in the air. After heating the workpiece to 30-50 degrees Celsius above the Ac3 temperature, keep it warm for a period of time, and cool it in air after it is taken out of the furnace. This is a heat treatment method that improves the toughness of steel. Normalizing can refine the grains and improve the strength of the material. It is widely used in various types of steel, such as structural steel, tool steel, stainless steel, etc. In the automotive manufacturing industry, it is often used to manufacture key components such as automobile engine cylinder blocks and crankshafts. Through normalizing treatment, the grains of these components can be refined, their strength and toughness can be improved, and the normal operation and safety of the engine can be ensured.
4.Quenching
Quenching is a heat treatment method in which steel is heated to above the critical temperature, kept warm for a period of time, and then quickly placed in a quenchant to reduce its temperature suddenly, and rapidly cooled at a rate greater than the critical cooling rate to obtain an unbalanced structure dominated by martensite. Quenching can increase the strength and hardness of steel, but will reduce its plasticity. Commonly used quenching agents include: water, oil, alkaline water and salt solutions, etc. The quenching agent for high-speed steel can be wind, so high-speed steel is also called wind steel. According to factors such as heating temperature, cooling medium and cooling rate, the quenching process can be divided into many types. For example, single-liquid quenching is easy to operate and suitable for mass production; double-liquid quenching can obtain higher hardness and wear resistance, and is suitable for parts that require high strength and wear resistance; graded quenching can reduce quenching deformation and cracking tendency, and is suitable for parts with complex shapes or high dimensional accuracy requirements. Quenching technology is widely used in various fields such as automobiles, machinery, petrochemicals, aerospace, etc. Key parts such as automotive gears, bearings, drill bits, blades in the petrochemical and aerospace fields need to be quenched to improve their hardness and strength, ensure their wear resistance and life.
5.Tempering
Heat the quenched steel to a temperature below Ac1, keep it warm for a certain period of time, and then cool it to room temperature. It is the last important process for the workpiece to obtain the required performance. It can eliminate the residual stress generated during the quenching of the workpiece, adjust the hardness, strength, plasticity and toughness of the workpiece, stabilize the structure and size, and improve and enhance the processing performance. For example, common mechanical parts can obtain good comprehensive performance after quenching and tempering.
