Judging from the cold weapons unearthed in modern China […]
Judging from the cold weapons unearthed in modern China, the early heat treatment process can be traced back to the sixth century BC. In order to improve the strength of iron and steel appliances, people used a quenching process to meet this requirement. This is not a joke. Historical relics can be used to prove it, and it can be confirmed from the martensite contained in the current unearthed cultural relics.
But people at that time may not know what kind of process they used, what kind of principle caused the change of material properties, they may only know the way of heating or cooling, and the use of different cooling media, can Achieve their desired purpose.
Heat treatment "four fires"
With the development of the times and the progress of science and technology, people now understand that steel has a variety of metallographic structures, and can use the "iron-carbon equilibrium phase diagram" or other phase diagrams to guide us to obtain the desired organizational structure, and the temperature As the ordinate of the phase diagram, it naturally needs to be given priority attention in the heat treatment process.
Although there are many forms of heat treatment, the main process is composed of three stages: heating, heat preservation, and cooling. According to different metal materials and different purposes, the heating temperature will be different, but in order to obtain the required structure, it is generally heated to above the phase transition temperature. At the same time, because of the difference in the temperature change rate on the surface and inside of the metal workpiece, Therefore, in order to transform the microstructure, a fixed holding time is required, and the length of the holding time has a great relationship with the heating method.
According to the different cooling rate and material, the process can be divided into quenching, normalizing, annealing, and tempering, which is known as the "four fires".