Stainless steel heat treatment processing technology and its evolution process

Generally speaking, there are four main heat treatment processes for stainless steel materials. One method is annealing, which involves heating the stainless steel workpiece to a suitable temperature, using different insulation times based on the material and workpiece size, and then slowly cooling it. This is done to achieve a balanced internal structure of the stainless steel, or to release the internal stress generated in the previous process, in order to obtain good process and usage performance, and even to prepare the structure for further quenching.

The second is normalizing, which means heating stainless steel workpieces to a suitable temperature and cooling them in air. The effect of normalizing is similar to annealing, but the resulting metallographic structure is finer, often used to improve the cutting performance of stainless steel materials, and also used as the final heat treatment for some stainless steel with lower requirements.

The third is quenching, which means heating and insulating stainless steel workpieces, and then rapidly cooling them in quenching media such as water, oil, or other inorganic salt solutions, organic aqueous solutions, etc. After quenching, stainless steel parts will become harder but also brittle. To reduce the brittleness of stainless steel parts, quenched stainless steel parts are kept at an appropriate temperature above room temperature but below 650 ° C for a longer period of time, and then cooled. This processing technique is called tempering. Annealing, normalizing, quenching, and tempering are the "four fires" in overall heat treatment, among which quenching and tempering are closely related and often used in conjunction.

The above stainless steel processing technology can also evolve into different heat treatment processes with different heating temperatures and cooling methods. The processing technology that combines quenching and high-temperature tempering to obtain a certain strength and toughness is called quenching and tempering. Some stainless steel alloys are quenched to form supersaturated solid solutions and then kept at room temperature or a slightly higher appropriate temperature for a longer period of time to enhance their hardness, strength, or electrical magnetism. This heat treatment process is called aging treatment.

Surface heat treatment is a metal heat treatment process that only heats the surface layer of stainless steel workpieces, thereby changing their surface mechanical properties. In order to heat only the surface of the workpiece without transferring too much heat to the interior of the workpiece, the heat source used should have a high energy density, which means that a unit area of the workpiece can provide a large amount of heat energy, so that the surface or local area of the stainless steel workpiece can reach high temperature in a short time or instantaneously. The main methods of surface heat treatment include flame quenching and induction heating heat treatment. Commonly used heat sources include flames such as oxyacetylene or oxypropane, induced currents, lasers, and electron beams.

Chemical heat treatment is a metal heat treatment process that involves changing the surface chemical composition, structure, and properties of a workpiece. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface layer of stainless steel workpieces. Chemical heat treatment is the process of heating a workpiece in a medium containing carbon, nitrogen, or other alloying elements for a prolonged period of time, resulting in the infiltration of elements such as carbon, nitrogen, boron, and chromium into the surface of the workpiece. After infiltration of elements, other heat treatment processes such as quenching and tempering are sometimes required. The main methods of chemical heat treatment include carburizing, nitriding, and metalizing.

The heat treatment process of stainless steel is one of the important processes in the manufacturing of mechanical parts and molds. Overall, it can ensure and enhance various properties of the workpiece, such as wear resistance, corrosion resistance, etc. It can also improve the microstructure and stress state of the blank, facilitating various cold and hot processing.