The difference between normalizing, tempering, annealing and quenching lies in different processes, different changes in material structure, and different results of changes in material properties.
1. The process is different:
Normalizing is to heat the workpiece to Ac3 (Ac refers to the final temperature at which all free ferrite transforms to austenite during heating, generally from 727 ° C to 912 ° C) or Acm (Acm is the critical temperature line for complete austenitizing of eutectoid steel during actual heating) 30 ~ 50 ℃, after holding for a period of time, take out the metal that is cooled in the air or sprayed with water, sprayed or blown from the furnace Heat treatment process.
Tempering treatment means that the steel after quenching hardening or normalization treatment is cooled down at a certain rate after being immersed for a period of time below the critical temperature.
Annealing is a metal heat treatment process that heats the metal to a certain temperature for a sufficient time and then cools at an appropriate rate (usually slow cooling, sometimes controlled cooling).
The steel is quenched by heating the steel to a temperature above the critical temperature Ac3 (hypoeutectic steel) or Ac1 (hypereutectic steel), holding it for a period of time to make it fully or partially austenitized, and then cooling at a temperature greater than the critical cooling rate Rapid cooling to below Ms (or isothermal near Ms) for martensite (or bainite) transformation heat treatment process.
2. The changes in material organization are different:
Structure after normalizing: hypoeutectoid steel is ferrite + pearlite, eutectoid steel is pearlite, hypereutectoid steel is pearlite + secondary cementite, and it is discontinuous.
The martensite structure is obtained by low temperature tempering; the structure obtained by tempering at medium temperature is tempered trophite; the structure obtained by high temperature tempering is tempered sorbite structure.
After annealing, the grains are refined, the structure is adjusted, and the structure defects are eliminated.
Quenching causes the supercooled austenite to undergo martensite or bainite transformation to obtain martensite or bainite structure, and finally to obtain an unbalanced structure dominated by martensite (sometimes obtaining bainite or maintaining Phase austenite).
3. The results of changes in material properties are different:
During normalizing, the crystal grains of the steel can be refined in a slightly faster cooling, which can not only obtain satisfactory strength, but also significantly improve the toughness (AKV value) and reduce the cracking tendency of the component. -After normalizing the low-alloy hot-rolled steel plates, low-alloy steel forgings and castings, the comprehensive mechanical properties of the material can be greatly improved, and the cutting performance is also improved.
After tempering, it will be quenched and normalized for a period of time and then immersed in the medium temperature for a period of time, which can promote the precipitation of some of the carbides, and at the same time can eliminate some of the residual stress caused by rapid cooling, thus improving the toughness and flexibility of the material.
Annealing can reduce the hardness and improve the machinability. Eliminate the residual stress, stabilize the size, reduce the tendency of deformation and cracks; refine the grain, adjust the structure, and eliminate the tissue defects. Uniform material structure and composition, improve material performance or prepare for tissue preparation for future heat treatment.
Quenching can greatly improve the rigidity, hardness, wear resistance, fatigue strength and toughness of steel, so as to meet the different requirements of various mechanical parts and tools. It can also meet special physical and chemical properties such as ferromagnetism and corrosion resistance of some special steels through quenching.
