①Heat treatment:
a. Heating: Heating below Ac1 is mainly to stabilize the structure of the steel and eliminate internal stress. Heating above Ac3 is mainly to austenitize the steel.
b. Insulation: The purpose is to uniform the heating temperature of the steel pipe to obtain a reasonable heating structure.
c. Cooling: The cooling process is a key process in the heat treatment of steel pipes. It determines the metallographic structure and mechanical properties of the steel pipe after cooling.
Commonly used cooling methods include furnace cooling, air cooling, oil cooling, water cooling, etc.
② Steel pipe normalizing: refers to the process of heating the steel pipe to a temperature above austenitization, holding it for a period, and then cooling it gently and evenly in the air to obtain a stable structure. The main purpose is to refine the steel grains, Uniform the internal structure, change the residual force state, and improve the overall performance of the steel pipe. Main functions: Reduce or eliminate the banded structure and mixed products formed during the deformation process of steel pipes; eliminate network carbides in hypereutectoid steel to facilitate spheroidizing annealing; used as a pre-quenching agent for medium C steel and alloy structural steel. Pretreatment to refine the grains to make the structure uniform and reduce steel pipe defects caused by the quenching process. For dry C steel and low alloy steel, it is used instead of annealing to improve the pre-cutting properties of the steel pipe. It can be used as the final heat treatment of general structural steel pipes with low requirements.
③Steel pipe annealing: The process of heating the steel pipe to a temperature higher or lower than the critical point (Ac3 or Ac1), holding it for some time, and then slowly cooling it to obtain an approximate equilibrium structure, which is divided into further Finish annealing, complete annealing, isothermal degradation, spheroidizing annealing, and stress relief annealing, etc. Generally, high C, low alloy, and alloy steel pipes need to be annealed to reduce their hardness and strength, improve plasticity, eliminate internal stress and structural unevenness, and refine the final structure to facilitate the machining of the steel pipe and lay the foundation for the final heat treatment of the steel pipe. Organizational basis.
④ Steel pipe tempering: A process in which the steel is heated to a certain temperature below Ac, kept warm for some time, and then cooled in a certain way to obtain a relatively stable state structure. The main purpose is to improve the plasticity and toughness of the steel pipe so that the steel pipe can obtain good comprehensive mechanical properties, reduce or eliminate the residual internal stress generated during quenching of the steel pipe, and stabilize the size of the steel pipe so that the structure of the steel pipe does not change during use. Air cooling is generally used after tempering steel pipes. To prevent the steel pipe from regenerating internal stress, it should be cooled slowly. For dry steel pipes with high-temperature tempering brittleness, rapid cooling should be used after tempering, such as oil cooling. Steel pipe tempering is generally divided into low-temperature tempering 150~250℃, medium-temperature tempering 350~500℃, high-temperature tempering 500~650℃
⑤Steel pipe quenching: The process of heating the steel pipe to 30~50℃ above Ac3, and then cooling the steel pipe quickly after being kept warm for some time to obtain the M and B structures. M generally has high hardness and brittleness and is the product of A-speed cooling. In addition to MB, the structure of the steel pipe after quenching also contains a small amount of A, which are all unstable structures. After the steel pipe is quenched, thermal stress and structural stress will be generated inside it, which can generally be eliminated and improved through tempering. Quenching and tempering (Q+T) can greatly improve the comprehensive performance of the steel.
⑥Solution treatment: The essence is the quenching process of steel pipes, but the temperature of solution treatment is higher. Solution treatment is mainly used for stainless steel pipes. Its purpose is to reduce the hardness and strength of the steel pipes, improve the plasticity and toughness of the steel pipes, and improve the corrosion resistance and comprehensive performance of the finished steel pipes to meet standard regulations or user requirements.
Post time: Mar-27-2024