A few days ago, Shougang made a breakthrough in the development and high-efficiency manufacturing technology of precision welded steel pipes with a bimetallic coating, thereby solving a series of longstanding “bottleneck” problems in precision welded automotive steel pipes in China, significantly improving quality and efficiency, and accelerating the localization process of important materials.

Precision welded automotive pipes have such advantages as high dimensional accuracy, stable performance, strong impact resistance and good processing performance. They are widely used in the manufacture of core pipes such as brake oil pipes, fuel pipes and lubricating oil pipes. Due to automotive safety requirements, precision welded pipe manufacturing demands extremely high material performance. Since the introduction of pipe making equipment in the 1980s, despite many years of efforts, some Chinese welded pipe enterprises still rely on imports for certain materials. To this end, the Research Institute of Technology, Jingtang Company and Shougang Marketing Center jointly established a cross-departmental and cross-professional R&D team covering scientific research, on-site production and user services in a bid to tackle this “tough nut”.

The pipe-making rate is influenced by multiple factors. Even for the same batch of materials, there are significant differences in pipe making performance, which is concerning for technicians. The team accumulated a wealth of first-hand data during a long-term on-site tracking process, and the “mystery” was gradually uncovered through many simulation calculations and experimental verification. After mastering the key factors hindering the improvement of the pipe-making rate, the team carried out collaborative control in multiple aspects such as microstructure, mechanical properties and surface morphology, and successfully developed a complete set of precision welded pipe preparation technology, with the pipe making rate increased by more than 20% compared to the highest value of imported materials.

The manufacturing process of precision welded pipes is long and affected by multiple processes such as electroplating, pipe making and brazing. The solid solution elements in steel are extremely difficult to stably control, resulting in “orange peel” defects during pipe making which can even affect the plasticity of the pipes and pose hidden dangers to automotive safety. In order to eliminate this “roadblock”, the team members insisted on a meticulous and quantitative analysis of more than ten processes from steel coil production to pipe forming, determined the most critical process parameters, developed unique annealing technology and jointly optimized the pipe making process with users, ultimately solving the problem thoroughly.

The traditional precision welded pipe steel strip generally uses the double-sided copper plating process, while the brake pipes of high-end cars such as those of Mercedes-Benz and BMW use a bimetallic dissimilar coating process of inner wall copper plating and outer wall nickel plating. Due to the difficulty of copper-nickel co-plating technology, only a foreign enterprise could produce it at that time. In order to resolve this predicament, the Shougang team conducted deep cooperation with downstream users. On the basis of optimizing and integrating the existing production lines, they jointly developed key technologies such as single-sided electroplating to realize copper-nickel co-plating, as a result of which the quality of the coating reached the level of imported steel strips.

At present, Shougang Automobile’s market share of steel for precision welded pipes ranks first in the country. Copper-nickel coated steel strips are exclusively supplied in China, and the precision welded pipes made from them are widely used by high-end automotive enterprises at home and abroad. Shougang’s development and application of steel for automotive precision welded pipes with a bimetallic coating has played an important role in promoting the comprehensive localization of key materials for automobiles in China.