How to deal with the problem of uneven wall thickness of precision seamless steel pipes in the production process? The uneven wall thickness of the steel pipe is mainly reflected in the uneven wall thickness of the spiral, the uneven wall thickness of the linear wall, and the uneven wall thickness of the head and tail. The influence of continuous rolling process adjustment is an important factor leading to the uneven wall thickness of the finished pipe.

The reasons for the uneven wall thickness of the spiral are as follows: due to adjustment reasons such as irregular rolling centerlines of the piercing machine, unequal inclination angles of the two rolls, or too small front pressure at the head, the wall thickness is uneven, and generally spiral along the entire length of the steel pipe. spread. During stress annealing, the small-diameter precision seamless steel pipe undergoes internal partial plastic deformation (when the stress exceeds the yield strength of the material at this temperature) or a partial relaxation process (when the stress is less than the yield strength of the material at this temperature) Relax the residual stress at a certain temperature to achieve the purpose. During the stress annealing process, the workpiece is generally slowly heated to a lower temperature (500-550°C for gray cast iron, 500-650°C for precision seamless steel pipe, and non-ferrous metal alloy stamping parts are all lower than the recrystallization initiation temperature). After holding for a period of time, the workpiece is cooled slowly to avoid new residual stresses.

Precision seamless steel pipes are widely used, and different types have different applications. Various problems will be encountered during use. What are the reasons for the grinding cracks on the surface of precision seamless steel pipes?

1. Large block and coarse mesh carbides increase the brittleness of the appearance and reduce the strength of the matrix, especially the low strength and poor resistance along the grain boundary, and the thermal conductivity of the carbide is only half of the remaining austenite , so the heat dissipation is worse, which increases the tendency of grinding cracks. Generally speaking, grinding cracks tend to expand along the grain boundaries, so they appear as cracks.

2. During the grinding process of carburized parts after heat treatment, the surface of the part will generate a lot of heat, which will increase the surface temperature, and the residual austenite structure will be transformed into a martensite structure, and the specific volume will increase, so it will increase The tensile stress of the outer layer causes the cracking of the part. In addition, the thermal conductivity of residual austenite is worse than that of martensite. Excessive residual austenite slows down the heat dissipation of grinding heat, so the surface temperature rises faster, the thermal stress increases, and the cracking tendency is promoted. intensification.

3. After quenching, the internal stress of the coarse needle-shaped martensite structure is large, and the strength is low. The microcracks in the martensite structure may also become the source of grinding cracks, so the tendency of grinding cracks is increased. Coarse-grained martensite must be accompanied by a lot of residual austenite, so grinding cracks are more likely to occur.

Cherry
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Email: Cherry@jinyoumetal.com
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