What is the type of line pipe tempering?

What is the type of line pipe tempering? According to the performance requirements of pipeline steel pipes, depending on the tempering temperature, tempering can be divided into the following types:
1. Low temperature tempering (150-250 degrees)
The structure obtained by low temperature tempering is tempered martensite. The purpose is to reduce the internal stress and brittleness of the quenched steel under the premise of maintaining the high hardness and high wear resistance of the quenched steel, so as to avoid cracking or premature failure during use. It is mainly used for all kinds of high carbon cutting tools, measuring tools, GB/T9711.1 pipeline steel pipe, rolling bearings and carburizing parts, etc., the hardness after tempering is generally HRC58-64.
2. Medium temperature tempering (250-500 degrees)
The tissue obtained by medium temperature tempering is tempered troostite. Its purpose is to achieve high yield strength, elastic limit and high toughness. Therefore, it is mainly used for the treatment of various GB/T9711.1 pipeline steel pipes and hot work dies. The hardness after tempering is generally HRC35-50.
3. High temperature tempering (500-650 degrees)
The structure obtained by high temperature tempering is tempered sorbite. Conventionally, the heat treatment combined with quenching and high temperature tempering is called quenching and tempering treatment, and the purpose is to obtain comprehensive mechanical properties with good strength, hardness, plasticity and toughness. Therefore, it is widely used in important structural parts such as automobiles, GB/T9711.1 pipeline steel pipes, machine tools, etc., such as connecting rods, bolts, gears and shafts. After tempering, the hardness is generally HB200-330.