What is the four fire process of steel?

In the process of steel processing, the four processes of annealing, normalizing, quenching and tempering are required. Here is a brief introduction.
1. Annealing
Annealing is the process of heating a steel to a certain temperature and holding it for a period of time, then cooling it slowly. The annealing of steel is a heat treatment method that the steel is heated to the temperature of phase transformation or partial phase transformation and cooled slowly after heat preservation. The purpose of annealing is to eliminate the structure defects, improve the structure, homogenize the composition, refine the grains, improve the mechanical properties of the steel, reduce the residual stress, reduce the hardness, improve the plasticity and toughness, and improve the cutting performance. Therefore, annealing is not only to eliminate and improve the structural defects and internal stress left by the previous process, but also to prepare for the subsequent process, so annealing belongs to semi-finished heat treatment, also known as pre heat treatment.
2. Normalizing
Normalizing is a kind of heat treatment method that the steel is heated above the critical temperature to make the steel change into uniform austenite and then cooled naturally in air. It can eliminate the net cementite of hypereutectoid steel, refine the lattice for normalizing hypoeutectoid steel, improve the comprehensive mechanical properties, and replace the annealing process with normalizing for parts with low requirements is more economical.
3. Quenching
Quenching is to heat the steel above the critical temperature, keep it warm for a period of time, and then put it into the quenching agent quickly, so that its temperature suddenly decreases, and rapidly cools at a speed greater than the critical cooling speed, and then obtain the heat treatment method of unbalanced structure dominated by martensite. Quenching can increase the strength and hardness of steel, but reduce its plasticity. The commonly used quenchants in quenching are: water, oil, alkali water and salt solution, etc.
4. Tempering
It is called tempering to reheat the quenched steel to a certain temperature and then cool it in a certain way. Its purpose is to eliminate the internal stress produced by quenching, reduce the hardness and brittleness, and achieve the expected mechanical properties. Tempering includes high temperature tempering, medium temperature tempering and low temperature tempering. Tempering is often used in combination with quenching and normalizing.
Quenching and tempering treatment: the heat treatment method of high temperature tempering after quenching is called quenching and tempering treatment. High temperature tempering refers to tempering between 500 ℃ - 650 ℃. Quenching and tempering can adjust the properties and materials of steel to a great extent, with good strength, plasticity and toughness, and good comprehensive mechanical properties.