Ansteel Co., Ltd. has achieved stable mass production of 6.0-millimetre-thick No. 50 high-strength carbon steel

Recently, the Cold Rolling Mill of Ansteel Co., Ltd. has achieved a breakthrough in the production of thick-gauge, high-strength pickled steel products. The company has successfully overcome technical bottlenecks in the production of 6.0-millimetre-thick Grade 50 high-strength carbon steel and has commenced stable mass production, with the product’s surface quality and mechanical properties both meeting customer requirements. Previously, the maximum thickness the plant had rolled for this steel grade was 4.0 millimetres; the extension of the maximum thickness to 6.0 millimetres marks a further step forward in the plant’s capacity to cover a wider range of high-end pickled steel grades.

Grade 50 steel is a medium-carbon, high-strength carbon structural steel with a carbon content of approximately 0.47 per cent to 0.55 per cent and a tensile strength of not less than 630 MPa. It possesses high strength and hardness, but its weldability is significantly lower than that of low-carbon steel. As thickness increases, the tendency for the heat-affected zone to become hard and brittle, as well as its susceptibility to cracking, rises further. Under conventional processes, weld cracking is likely to occur; in severe cases, this can lead to strip breakage and production stoppages, becoming a key obstacle to the continuous and stable production of thick-gauge steel. From an industry perspective, there is a clear demand for thick-gauge high-strength pickled sheets in load-bearing components such as commercial vehicles and construction machinery; however, the greater the thickness, the more stringent the requirements for welding and operational control become, and there are only a limited number of steel mills in China with the capacity for stable production.

To address the aforementioned bottlenecks, the technical research team at Ansteel Co., Ltd.’s Cold Rolling Mill undertook a systematic optimisation of technical parameters, focusing on three key aspects: the welding process, speed regulation and tension control. With regard to the welding process, the team made precise adjustments to core parameters—such as preheating temperature and duration before and after welding, wire feed speed and welding speed—taking into account the tendency of this steel grade to become brittle in the heat-affected zone, with the aim of improving the toughness and crack resistance of the weld. Consequently, the first-pass weld acceptance rate for 6.0 mm-thick Grade 50 high-strength carbon steel reached 100 per cent.

With regard to strip running control, the plant has established a dedicated tension-straightening model to precisely regulate loop tension and process section speed. This reduces equipment loads whilst preventing shutdowns caused by strip misalignment, thereby ensuring the continuity and stability of production for thick-gauge, high-strength steel. This breakthrough has not only expanded the range of deliverable thicknesses for Ansteel Co., Ltd.’s pickled products, but has also provided the necessary process capabilities for undertaking future orders for high-strength, thick-gauge cold-rolled and pickled steel, thereby further enhancing the company’s competitive edge in the high-end steel market.