What is the function and significance of homogenization annealing in metal heat treatment process?


Release time:

2022-06-17

Metal heat treatment process, the workpiece is heated to a predetermined temperature and kept for a certain period of time and then slowly cooled.

What is the function and significance of homogenization annealing in metal heat treatment process?

  Metal heat treatment process, the workpiece is heated to a predetermined temperature and kept for a certain period of time and then slowly cooled. Its main purpose is:
  1. In the process of casting, forging, rolling, welding, etc., to improve or eliminate various structural defects and residual stresses produced in the production, forging, rolling, and welding of steel.
  2. Only soft workpieces can be cut.
  3. Refine the grain, improve the structure and improve the mechanical properties of the workpiece.
  4. Prepare for the final heat treatment (tempering, tempering). Common annealing methods are:
  ①Complete annealing. During the refining process, low carbon steel produces a coarse superheated structure with poor mechanical properties after casting, forging and welding. Heat the workpiece until ferrite is completely transformed into austenite, maintain 30~50°C, keep 30~50°C, and then cool slowly with the furnace, after cooling, austenite transformation occurs again, which can make the structure of steel thinner .
  ② Spheroidizing annealing. Tool steel and bearing steel reduce the high hardness after forging. Heating until the temperature at which the steel begins to form austenite is higher than 20~40°C, and then cooling slowly after keeping warm. On cooling, the flaky carbides in pearlite transform into spherical shapes, reducing hardness.
  ③Isothermal annealing. Used to reduce the hardness of some high-nickel-chromium alloy structural steels for cutting. Usually, the austenite is rapidly cooled to the most unstable temperature of the austenite, and after holding for an appropriate time, the austenite will change into troostite or sorbite, and the hardness can decrease.
  ④Recrystallization annealing. It is used to remove metal wire, and the thin plate is hardened (increase in hardness and decrease in plasticity) during cold drawing and cold rolling. The heating temperature is usually lower than the temperature at which the steel begins to form austenite at 50~150°C. Only in this way can the work hardening effect be eliminated and the metal softened.
  ⑤Graphitization annealing. It is used to transform cast iron into malleable cast iron with good cementite. During the production process, the casting temperature is about 950°C, and after holding for a certain period of time, it is properly cooled to decompose the cementite into flocculent graphite.
  ⑥ Diffusion annealing. It is to homogenize the chemical composition of alloy castings and improve their performance. This method uses the premise of no melting, as high a temperature as possible and a long time of heat preservation, so that the diffusion of each element in the alloy tends to be uniform, and then slowly cools.
  ⑦Stress relief annealing. It is used to eliminate the internal stress of steel parts and welded parts. When the product is heated, austenite begins to form at 100~200°C, and after heat preservation, it is cooled in the air to eliminate internal stress.