Methods for preheating deformation of straight seam steel pipes:
1. Reasonable material selection. For precision complex molds, micro-deformation mold steel with good quality should be selected. Mold steel with serious carbide segregation should be reasonably cast and subjected to quenching and tempering heat treatment. Solid solution double-refining heat treatment can be performed on larger and uncastable mold steel. Reasonably select the heating temperature and control the heating speed. For precision and messy molds, slow heating, preheating, and other balanced heating methods can be used to reduce mold heat treatment deformation.
2. Correct heat treatment process operation and reasonable tempering heat treatment process are also effective ways to reduce the deformation of precision and messy molds. The causes of deformation of precision complex molds are often complicated, but as long as the deformation rules are mastered, the causes of their occurrence, and special methods are used to prevent the deformation of the mold, the deformation of the mold can be reduced and controlled.
3. Precision and complex molds must be preheated to eliminate residual stress generated during machining. For precision and complex molds, if conditions permit, vacuum heating quenching and cryogenic treatment after quenching should be used as much as possible. On the premise of ensuring the hardness of the mold, try to use pre-cooling, graded cooling quenching, or warm quenching processes.
4. The design and design of the mold should be reasonable, the thickness should not be too different, and the shape should be symmetrical. For molds with large deformation, the deformation rules should be controlled and machining allowance should be reserved. For large, precise, and complex molds, a combined design can be used. For some precision and complex molds, pre-heat treatment, aging heat treatment, and quenching and tempering nitriding heat treatment can be used to control the accuracy of the mold. When repairing mold defects such as blisters, pores, and wear, use equipment with low thermal impact such as cold welding machines to avoid the occurrence of deformation during the repair process.
Straight seam steel pipe annealing steps: Straight seam steel pipe annealing is to heat the steel pipe to a certain temperature keep it warm at this temperature, and then slowly cool it to room temperature. Annealing includes annealing, spheroidizing annealing, stress relief annealing, etc.
1. Heating the steel pipe to a predetermined temperature, keeping it warm for a period of time, and then slowly cooling it in the furnace is called annealing. The purpose is to reduce the hardness of steel and eliminate uneven structure and internal stress in steel.
2. Heat the steel pipe to 750 degrees, keep it warm for a period of time, slowly cool it to 500 degrees, and then cool it in the air, which is called spheroidizing annealing. The purpose is to reduce the hardness and cutting performance of steel and is mainly used for high-carbon steel.
3. Steel pipe stress annealing is also called low-temperature annealing. The steel is heated to 500-600 degrees, kept warm for a period of time, slowly cooled in the furnace to below 300 degrees, and then cooled to room temperature. The structure does not change during the annealing process, and the internal stress of the metal is mainly eliminated.
4. Normalizing: The heat treatment process of heating the steel pipe to 30-50°C above the critical temperature, holding it for a suitable period of time, and then cooling it in still air is called normalizing. The main purpose of normalizing is to refine the structure and properties of steel and obtain a structure close to equilibrium. Compared with the annealing process, the main difference between normalizing and annealing is that the cooling rate of normalizing is slightly faster, so the production cycle of normalizing heat treatment is shorter. Therefore, when annealing and normalizing can both meet the performance requirements of the parts, normalizing should be used as much as possible.
5. Quenching: Heat the steel pipe to a certain temperature above the critical point (the quenching temperature of No. 45 steel is 840-860°C, and the quenching temperature of carbon tool steel is 760-780°C), hold for a certain time, and then immerse it in water at an appropriate speed ( The heat treatment process of cooling in oil to obtain martensite or bainite structure is called quenching. The main process difference between quenching, annealing, and normalizing is the fast cooling rate, which is intended to obtain a martensitic structure. The martensite structure is an unbalanced structure obtained after quenching steel. It has high hardness but poor plasticity and toughness. The hardness of martensite increases with the carbon content of steel.
6. Tempering: After the steel pipe is hardened, it is heated to a certain temperature below the critical temperature, held for a period of time, and then cooled to room temperature. The heat treatment process is called tempering. Generally, quenched steel parts cannot be used directly and must be tempered before use. Because quenched steel has high hardness and brittleness, brittle fracture often occurs when used directly. Tempering can eliminate or reduce internal stress, reduce brittleness, and improve toughness; on the other hand, the mechanical properties of quenched steel can be adjusted to achieve the performance of the steel. According to the different tempering temperatures, tempering can be divided into three types: low-temperature tempering, medium-temperature tempering, and high-temperature tempering.
1) Low-temperature tempering 150~250; reduce internal stress and brittleness, and maintain high hardness and wear resistance after quenching.
2) Medium temperature tempering 350~500; improve elasticity and strength.
3) High temperature tempering 500~650; tempering of quenched steel parts at temperatures above 500°C is called high-temperature tempering. After quenching at high temperatures, quenched steel parts have comprehensive mechanical properties (both strength and hardness, plasticity and toughness). Therefore, generally medium carbon steel and medium carbon alloy steel are often treated with high-temperature tempering after quenching. Shaft parts have many applications. Quenching + high-temperature tempering is called quenching and tempering treatment.
Post time: Sep-13-2023