(1) Reasonably adjust the hardness and strength of steel, improve the toughness of steel and make the workpiece meet the performance requirements. For example, the hardness and wear resistance of cutting tools, measuring tools, and molds can be improved by tempering, and the strength and toughness of various machine parts can be improved.
(2) Both quenched martensite and residual austenite are unstable structures, which will decompose during work, resulting in changes in the size of parts, which is not allowed for precision parts. Tempering can stabilize the structure so that the workpiece will not undergo structural changes during long-term use, thereby stabilizing the shape and size of the workpiece.
(3) Reduce or eliminate the workpiece's quenching internal stress to reduce the workpiece's deformation and prevent cracking.

Generally, quenching is performed to achieve the following purposes:
(1) Increase the hardness and wear resistance of the workpiece. For example, various tools, carburized parts, and parts that require surface wear resistance (gears, rollers, etc.) must be quenched and then tempered at low temperatures to improve their hardness and wear resistance.
(2) Quenching is performed to obtain certain mechanical properties for subsequent tempering, such as various springs and quenched and tempered workpieces. Their quenching is not to increase hardness, but to obtain a certain hardness, elasticity, toughness, and other comprehensive mechanical properties in the subsequent tempering.
(3) In order to change certain physical and chemical properties of steel, such as quenching of magnetic steel (to increase magnetic permeability) and stainless steel (to obtain a uniform single-phase solid solution).

Mold steel quenching is heating the mold steel to a certain temperature and keep it warm for a certain period of time, and then quickly cooling it. This process is called quenching. The main purpose of quenching is to make all or most of the structure of the mold steel change to austenite, obtain high toughness, and then quench at an appropriate temperature so that the product workpiece has the expected properties. Quenching is an extremely critical task in the heat treatment method to achieve the required comprehensive physical properties and wear resistance. Whether it is successful depends mainly on the heating rate, quenching temperature, holding time, and subsequent cooling method. For the heating rate, the temperature rise is too slow during heating, the product workpiece is easy to oxidize and carburize, the service life of the workpiece is low, and the cost is increased. However, if the temperature is raised too high, the surface and the center of the mold will cause a temperature difference. The greater the temperature difference, the greater the internal stress, and therefore, the greater the probability of deformation cracking.

The bending coefficient of stainless steel refers to the ratio of the minimum bending force required to the strength of the material itself under different material, thickness, and bending radius conditions. It is one of the important indicators to measure the bending performance of stainless steel. In the bending process of stainless steel, it is the ratio of the increase in the bend length after bending to the original length. Generally speaking, the bending coefficient of stainless steel is about 0.33.

1. Identify by checking the appearance. The surface of inferior seamless steel pipes is prone to scarring, which is mainly due to more impurities and uneven materials.
2. Dimensional accuracy. The inner and outer diameters of inferior small-diameter seamless steel pipes fluctuate too much. Some may also have a wall deviation phenomenon, and the wall deviation phenomenon is serious.
3. Folding. Fake steel pipes are prone to folding. Folding is a variety of fold lines formed on the surface of seamless steel pipes due to the manufacturer's pursuit of high efficiency. This defect usually runs through the entire product. The surface is pockmarked, prone to scarring and cracks, and it is even easy to scratch. There is no metallic luster and the cross-section is elliptical.
4. Material. The composition of the steel is uneven, and the end face of the cut head is not smooth and neat.

1. Inferior thick-walled seamless stainless steel pipes are more likely to fold. Folding refers to various fold lines on the surface of thick-walled seamless stainless steel pipes. This generally runs through the entire longitudinal direction of the product. The reason for the folding is that inferior manufacturers, in pursuit of efficiency, press down too much, produce ears, and fold during the next rolling. The folded product will crack after bending, and the strength of the thick-walled seamless steel pipe will drop significantly.

2. Inferior thick-walled seamless stainless steel pipes are more likely to be scratched, because the equipment and facilities of inferior manufacturers are relatively simple, which is easy to produce burrs and scratch the surface of thick-walled seamless stainless steel pipes. Deep scratches may reduce the strength of thick-walled seamless stainless steel pipes.

3. The surface of inferior seamless stainless steel pipes is more likely to crack. The reason is that the quality of the blanks is poor. Most of them are adobes, which have many pores. The adobes are cracked due to the effect of thermal stress during the cooling process, and cracks appear after rolling.

4. Scarring is easy to occur on the surface of inferior seamless stainless steel pipes because the material of inferior thick-walled seamless stainless steel pipes is uneven, there are many impurities, and generally the equipment and facilities of inferior thick-walled seamless stainless steel pipe manufacturers are relatively backward, which is easy to stick to the steel. These impurities bite the rollers and easily cause scarring.