The heat treatment of forging process of four fires, do you know?

In forging process, heat treatment is the most important link, heat treatment roughly has annealing, normalizing, quenching and tempering four basic processes, commonly known as metal heat treatment of the "four fire".

A, metal heat treatment of the fire - annealing:


2, the purpose of annealing: ① to improve or eliminate the steel in the casting, forging, rolling and welding process caused by various organizational defects and residual stress, prevent the workpiece deformation, cracking. ② Soften the workpiece for cutting. ③ Refine the grain and improve the structure to improve the mechanical properties of the workpiece. Prepare the organization for the final heat treatment (quenching, tempering).


Second, the second fire of metal heat treatment -- normalizing:


1, normalizing is the workpiece heated to the appropriate temperature after cooling in the air, normalizing effect is similar to annealing, but the organization is finer, often used to improve the cutting performance of materials, and sometimes used for some parts with low requirements as the final heat treatment.


2. Purpose of normalizing:


(1) It can eliminate the superheated coarse crystal structure and Weil's structure in casting, forging and welding parts, and the banded structure in rolling; Refining grain; And can be used as pre-heat treatment before quenching.


(2) The network of secondary cementite can be eliminated, and the pearlite refinement, not only improve the mechanical properties, but also conducive to the future spheroidization annealing.


③ The free cementite in grain boundary can be eliminated to improve its deep drawing performance.


Third, metal heat treatment of the third fire - quenching:


1. Quenching is the rapid cooling of the workpiece in the quenching medium such as water, oil or other inorganic salts and organic water solution after heating and holding heat. After quenching, the steel becomes hard but brittle at the same time.


2. Purpose of quenching:


(1) Improve the mechanical properties of metal materials or parts. For example, improve the hardness and wear resistance of tools and bearings, improve the elastic limit of springs, and improve the comprehensive mechanical properties of shaft parts.


(2) Improve the material properties or chemical properties of some special steels. Such as improve the corrosion resistance of stainless steel, increase the permanent magnetism of magnetic steel.


Four, the fourth fire of metal heat treatment -- tempering:


1, tempering in order to reduce the brittleness of steel parts, the quenchable steel parts at an appropriate temperature higher than room temperature and lower than 710℃ for a long time, and then cooling, this process is called tempering.


2. Purpose of tempering:


(1) Reduce internal stress and brittleness. There is a lot of stress and brittleness in quenched parts. If not tempered in time, deformation and even cracking will often occur.


(2) Adjust the mechanical properties of the workpiece. After quenching, the workpiece has high hardness and brittleness. In order to meet the different performance requirements of various workpieces, the hardness, strength, plasticity and toughness can be adjusted by tempering.

(3) Stabilize the workpiece size. The microstructure can be stabilized by tempering to ensure that no deformation will occur in the future use process.


(4) Improve the cutting performance of some alloy steels.