1. Internal defects and performance impact
During the production process of hot-rolled seamless steel pipes, due to the high-temperature rolling process, the internal non-metallic inclusions (such as sulfides, oxides and silicates) will be pressed into thin sheets, forming a stratification phenomenon. This stratification not only leads to a significant reduction in the tensile properties of the steel in the thickness direction, but is also likely to cause interlayer tearing when the weld shrinks. The local strain induced by the weld shrinkage often far exceeds the strain caused by the load.
2. Residual stress problem
During the hot rolling process, residual stress will be generated inside the steel due to the uneven cooling rate. These stresses can maintain internal balance without external forces, but they have an adverse effect on the deformation, stability and fatigue resistance of steel components under external forces. In particular, for large hot-rolled steel sections, the larger the cross-sectional size, the more significant the residual stress.
3. Difficulty in size control
There are certain challenges in size control for hot-rolled seamless steel pipes. Due to the principle of thermal expansion and contraction, even if the length and thickness meet the standards in the initial stage of hot rolling, there will still be deviations after cooling, and this deviation is particularly obvious in steel with wider side width and thicker thickness. Therefore, for large-size steel, it is difficult to accurately control the edge width, thickness, length, angle and edge line.
4. Uneven surface quality and organizational properties
The surface quality of hot-rolled seamless steel pipes is rougher than that of cold-rolled products, and its surface roughness Ra is generally between 0.5 and 1.5 μm. In addition, the organization and performance of hot-rolled products are not uniform enough, and its strength index is lower than that of cold-worked hardened products, but higher than that of fully annealed products; the plasticity index is higher than that of cold-worked hardened products, and lower than that of fully annealed products. This uneven organization and performance limits the application of hot-rolled seamless steel pipes in certain high-precision and high-performance occasions.
5. Production cost and environmental sensitivity
The production cost of seamless steel pipes is high, and hot-rolled seamless steel pipes are no exception. This is mainly due to its special production process and high material loss. At the same time, the production cycle of hot-rolled seamless steel pipes is long, and it needs to go through multiple processes, which further increases its cost. In addition, the cracks that are easy to appear inside the seamless steel pipe make its corrosion resistance poor, especially in harsh environments, it is more prone to corrosion and cracks, thereby limiting its service life and application range.
