Although cold-formed steel has been used in Chinese railway wagons for over a decade, its application still lags behind countries like Russia and the United States in terms of variety, quantity, and overall performance. There are several challenges in the manufacturing process and loading of cold-formed steel products. First, cold-formed steel often contains significant internal stress after production. During the initial processing stages—such as unwinding, rolling, rewinding, and flat bending—the material undergoes mechanical deformation that increases internal stress. Even after cold bending, the material retains high internal stress due to the forced shaping method.
Although a correction process is applied afterward, it mainly targets the outer dimensions rather than effectively reducing internal stress. After being stored for some time, aging deformation becomes apparent, confirming the presence of residual stress. Second, the pre-loading treatment causes deformation. Since cold-formed steel is not primed upon delivery, it must go through shot blasting before loading. While this process removes rust and improves surface passivation, it also relieves internal stress, leading to bending or torsional deformation. This issue is especially pronounced in asymmetrical structures.
Third, although China's weathering steel has good mechanical properties, corrosion resistance, and weldability, its stamping performance is not as favorable as that of ordinary carbon steel. The parts tend to rebound significantly after bending, so careful optimization of process parameters during cold forming is necessary to ensure product quality. Fourth, the technical standards for new cold-formed steel need urgent improvement. When applying cold-formed steel in railway wagons, specific technical guidelines should be developed for processing, manufacturing, working conditions, and deformation characteristics to support production, usage, and inspection. Currently, there is no clear specification for cold-formed steel in existing railway wagon inspection standards, which hinders its broader adoption.
The use of cold-formed steel in Chinese railway wagons is still in its early stages. Looking at global trends in truck development, the application of cold-formed steel in Chinese rail freight cars is expected to grow significantly. Although current challenges remain—such as improving production techniques, finalizing application methods, and establishing industry standards—it is essential for manufacturers and railway companies to collaborate closely. By enhancing communication and cooperation, they can promote the wider use of cold-formed steel in trucks, optimize railway wagon designs, and elevate the overall performance of rail freight products to a new level.
Several types of reactive filler such as Silica Fume or microsilica, metakaolin, work very well in mortar or concrete applications. Owes to secondary reaction with hydrated lime, reactive fillers can improve the long-term strength development and early strength at water immersion condition for various mortars which strength development are hindered by additives such as Redispersible Polymer Powder or Cellulose Ether. Some lightweight fillers like exfoliated vermiculite are also key ingredients for lightweight mortar, thermal insulation mortar or fireproof mortar based on cement or gypsum.
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