How should seamless steel pipes be heat treated?

Fujin Iron and Steel2021-09-29

In the heat treatment process, the repaired parts must be normalized, and the structural parts that require mechanical properties must be normalized and quenched and tempered to meet the mechanical performance requirements. After normalizing, medium and high alloy steels and large forgings must be tempered at high temperature to eliminate the internal stress generated during normalizing.

The annealing treatment of Shandong seamless steel pipe is a heat treatment process in which metals and alloys are heated to an appropriate temperature, kept for a certain period of time, and then slowly cooled. After annealing, the structure of hypoeutectoid steel is ferrite plus lamellar pearlite; eutectoid steel or hypereutectoid steel is granular pearlite. In short, the annealed structure is a structure close to equilibrium.

Shandong seamless steel pipe

Normalizing is a heat treatment process in which small-diameter thick-walled seamless steel pipes are heated to 45°C above Ac3, kept for an appropriate time, and then cooled in still air.

The hypereutectoid steel normalizing heating knife is above Acm, so that all the cementite that was originally networked is dissolved into the austenite, and then cooled at a faster rate to inhibit the precipitation of cementite at the austenite grain boundary. It can eliminate network carbides and improve the structure of hypereutectoid steel. Welding parts that require weld strength are normalized to improve the weld structure and ensure the weld strength.

Some small-diameter thick-walled seamless steel pipes undergo partial martensite transformation during forging to form a hard structure. In order to eliminate this kind of undesirable organization, when normalizing is adopted, the normalizing temperature is about 20℃ higher than the normal normalizing temperature by heating and keeping warm. The normalizing process is relatively simple, which is conducive to normalizing using forging waste heat, which can save energy and shorten the production cycle. Improper normalizing process and operation also produce structural defects, similar to annealing, and the remedies are basically the same.

Classification of seamless steel pipes: seamless steel pipes are divided into two types: hot-rolled and cold-rolled (dial) seamless steel pipes.

Executive standard of seamless steel pipe

Seamless steel pipe implementation standard

Seamless steel pipe standard

Structural steel pipe GB/T8162-99 Petroleum drilling steel pipe YB528-65 Fluid steel pipe GB/T8163-99

Ship steel pipe GB5312-85 medium pressure boiler steel pipe GB/T3087-99 petroleum sleeve steel pipe API5CT

Geological drilling steel pipe YB235-70 Automobile half shaft steel pipe GB3088-8 Fertilizer special steel pipe GB6479-86

Hydraulic prop steel pipe GB173-98 Petroleum cracking steel pipe GB9948-88 Pipeline steel ASTMA53B/106B/API 5L B High pressure boiler steel pipe DIN17175 ST45.8-Ⅲ GB5310-95 20G