Heat treatment methods for carbon and alloy steel pipe contain four primary types: normalizing, annealing, quenching and tempering. It’ll improve steel material mechanical properties, uniform chemical composition, and machinability.
Heat treatment for steel metal materials is divided into integral heat treatment, surface heat treatment and chemical heat treatment. Steel pipe usually adopts the integral heat treatment.
The performance of steel material primarily refers on mechanical properties, physical properties, and method performance. Heat treatment can bring totally different metallurgic structure and corresponding performance for the steel pipe, thus may be better applied in several industrial or the oil gas services.
There are 2 ways to enhance the properties of steel material. One technique is to adjust the chemical composition, named alloying technique. the alternative technique is heat treatment. Within the field of modern industrial technology, heat treatment improve steel pipe performance at dominate position.
Heat treatment procedures.
The steel material could be heated below the critical point or above critical point. The former heating way can stabilize structure and eliminated the residual stress. The latter way can make material austenitizing.
Austenitizing is to heat steel metal over its critical temperature long time enough, so it could be transformed. If a quenching followed after Austeniting, then the material will be hardened. Once reached austenitizing temperature, suitable microstructure and full hardness, the steel pipe material will be attained in further heat treatment processes.
2. Heat preservation
The purpose of heat preservation is to uniform the heating temperature of steel material, then it will get a reasonable heating organization.
The cooling process is the key process in heat treatment; it determines mechanical properties of steel pipe after cooling process.
Four main heat treatment methods in carbon and alloy steel pipe industry
The heat treatment processes for steel pipe includes normalizing, annealing, tempering, quenching and other process.
Heating the steel pipe above the critical temperature, and cooled in the air.
Through normalizing, the steel material stress could be relieved, improves ductility and toughness for the cold working process. Normalizing usually applied for the carbon and low alloy steel pipe material. It will produce different metal structure, pearlite, bainite, some martensite. This brings harder and stronger steel material, and less ductility than full annealing material.
Heating the material to above its critical temperature long enough until microstructure transform to austenite. Then slow cooled in the furnace, get maximum transformation of ferrite and pearlite.
Annealing will eliminate defects, uniform the chemical composition and fine grains. This process usually applied for the high carbon, low alloy and alloy steel pipe need to reduce their hardness and strength, refine the crystal structure, and improve the plasticity, ductility, toughness and machinability.
Heating the steel pipe material to critical temperature until microstructure transformation is done, cooling it in a rapid rate.
Quenching purpose is to produce the thermal stress and tissue stress. It can eliminate and improve through the tempering. The combination of quenching and tempering can make the comprehensive performance improved.
Heating the steel material to a precise temperature below the critical point, and often done in the air, vacuum or the inert atmospheres. There are low temperature tempering 205 to 595°F (400 to 1105°F), medium temperature and high temperature tempering (to 700℃ 1300℉).
The purpose of tempering is to increase the toughness of steel and alloy steel pipe. Before tempering, these steel is very hard but too brittle for the most application. After process can improve the plasticity and toughness of steel pipe, reduce or eliminate the residual stress and stabilize the steel pipe’s size. Brings good comprehensive mechanical properties, so that it does not change in service.
Heating an alloy to a right temperature, preserve it at this temperature long enough to cause or additional constituents to alter into a solid solution, then cooling it at speed rate to carry these constituents in solution.
There are many of cast and shaped nickel-based alloys that may achieve totally different needed performances through solution treatment or by precipitation age hardening. Characteristics as room temperature and elevated temperature mechanical strength, corrosion resistance and oxidization resistance are going to be considerably increased by this heat treatment. Several nickel-based alloys develop their desired properties alone through the solution treatment, like Hastelloy and nickel alloy steel pipe.
During solution treatment, the carbide and numerous alloying components are dissolved uniformly within the solid solution. Cooling quickly can create carbon and alloy components too late to precipitate, and acquire the heat treatment method of single solid solution tissue. The solution treatment will uniform internal structure and chemical composition. It also can restore the corrosion resistance for Hastelloy and nickel alloy steel pipe.
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