Welded pipe is a steel pipe made of steel plate or strip steel after being crimped and welded. Generally, the length is 6 meters. The production process of welded steel pipe is simple, the production efficiency is high, there are many varieties and specifications, and the investment in equipment is small, but the general strength is lower than that of seamless pipe. Heat treatment is a very important step in the production process of steel pipes. It is characterized by improving the internal quality of steel pipes. The defects in heat treatment of welded steel pipes include:
(1) Defects generated during heating. For the heating process, heat treatment heating equipment and heating medium must be selected. What appears or is easy to happen here is that the surface of the part will be affected by the oxidizing heating medium, and the heating temperature exceeds the process requirements. If the austenite grains are too thick, even the grain boundaries will melt, which will seriously affect the appearance and internal quality of the parts. Therefore, in the actual process, feasible measures should be taken for such defect analysis.
(2) Defective parts produced during quenching of small-diameter spiral tubes are cooled after heating and austenite homogenization to obtain the required structural and mechanical properties. At this time, based on the material and specific hardness of the steel pipe, it is necessary to select an ideal cooling medium. The ideal cooling medium is rapid cooling at high temperature and slow cooling at low temperature (3o0°C). If there is a problem the cooling medium will degrade (age) and if not caught in time it will be a significant source of defects. Insufficient hardness, soft spots, quenching cracks and poor deformation of quenched steel pipes are common heat treatment defects.
(3) Quenching the defective steel pipe produced during the tempering process to obtain a quenched martensite structure with high hardness or a lower bainite structure with a slightly lower hardness, but the structure at this time is unstable and its brittleness is very high. When used in production, it must be tempered to obtain the desired texture and properties. Therefore, the tempering process parameters will have an important impact on the heat treatment quality of the parts, such as hardness, tempering brittleness, tempering cracks and other defects, and effective measures must be taken to avoid the above defects during the tempering process.
(4) The surface quenching defect mentioned above is the overall heat treatment of the steel pipe, so that the inside and outside of the steel pipe can obtain the required hardness and requirements. The surface quenching treatment is only used to harden the surface of the steel pipe, and the core is still in the structural state before the treatment. Therefore, the surface quenching temperature, heating time, hardened layer depth, etc. will affect the heat treatment deformation and cracking, hardness level and service life of the steel pipe.
(5) Chemical heat treatment defects of small diameter spiral tubes. The chemical heat treatment of the spiral tube is a heat treatment process that infiltrates the metal or non-metal atoms on the surface of the part to obtain the required surface properties (such as high wear). This process endows the steel tube with dual functions and roles. However, if the process formula and process parameters are changed improperly, it will lead to deformation and cracking of the steel pipe, unqualified structure, unqualified hardness, etc. Therefore, full attention should be paid to the chemical heat treatment of steel pipes, otherwise the parts will completely lose the meaning of chemical heat treatment. The heat treatment of steel pipes should be safe, economical and practical, and at the same time create a cool, clean and quiet working environment.
The correct heat treatment process is the premise and foundation to ensure the qualified heat treatment quality of steel pipes. Once the above quality problems are found, they can be solved from people, machines, materials, methods, links and inspections. Through analysis and judgment, the root cause of the defect can be found.
(1) Defects generated during heating. For the heating process, heat treatment heating equipment and heating medium must be selected. What appears or is easy to happen here is that the surface of the part will be affected by the oxidizing heating medium, and the heating temperature exceeds the process requirements. If the austenite grains are too thick, even the grain boundaries will melt, which will seriously affect the appearance and internal quality of the parts. Therefore, in the actual process, feasible measures should be taken for such defect analysis.
(2) Defective parts produced during quenching of small-diameter spiral tubes are cooled after heating and austenite homogenization to obtain the required structural and mechanical properties. At this time, based on the material and specific hardness of the steel pipe, it is necessary to select an ideal cooling medium. The ideal cooling medium is rapid cooling at high temperature and slow cooling at low temperature (3o0°C). If there is a problem the cooling medium will degrade (age) and if not caught in time it will be a significant source of defects. Insufficient hardness, soft spots, quenching cracks and poor deformation of quenched steel pipes are common heat treatment defects.
(3) Quenching the defective steel pipe produced during the tempering process to obtain a quenched martensite structure with high hardness or a lower bainite structure with a slightly lower hardness, but the structure at this time is unstable and its brittleness is very high. When used in production, it must be tempered to obtain the desired texture and properties. Therefore, the tempering process parameters will have an important impact on the heat treatment quality of the parts, such as hardness, tempering brittleness, tempering cracks and other defects, and effective measures must be taken to avoid the above defects during the tempering process.
(4) The surface quenching defect mentioned above is the overall heat treatment of the steel pipe, so that the inside and outside of the steel pipe can obtain the required hardness and requirements. The surface quenching treatment is only used to harden the surface of the steel pipe, and the core is still in the structural state before the treatment. Therefore, the surface quenching temperature, heating time, hardened layer depth, etc. will affect the heat treatment deformation and cracking, hardness level and service life of the steel pipe.
(5) Chemical heat treatment defects of small diameter spiral tubes. The chemical heat treatment of the spiral tube is a heat treatment process that infiltrates the metal or non-metal atoms on the surface of the part to obtain the required surface properties (such as high wear). This process endows the steel tube with dual functions and roles. However, if the process formula and process parameters are changed improperly, it will lead to deformation and cracking of the steel pipe, unqualified structure, unqualified hardness, etc. Therefore, full attention should be paid to the chemical heat treatment of steel pipes, otherwise the parts will completely lose the meaning of chemical heat treatment. The heat treatment of steel pipes should be safe, economical and practical, and at the same time create a cool, clean and quiet working environment.
The correct heat treatment process is the premise and foundation to ensure the qualified heat treatment quality of steel pipes. Once the above quality problems are found, they can be solved from people, machines, materials, methods, links and inspections. Through analysis and judgment, the root cause of the defect can be found.
