Study On Low-temperature Rapid Phosphating Process And Mechanics Used For Drawing

As high-grade structure material, 1860MPa prestressed concrete (PC) steel strand is widely used in modern construction, such as skyscrapers, large span bridges, and so on. It was made of high-carbon steel wires after drawing deformation. The bar to bar are connected by butt resistance welding in order to keep continuous drawing. Fracture often occurrs in the weld joint of the wire during drawing and twisting.According to fracture analysis , it is found that the fractures of the stands are mainly caused by the surface deficiency in weld joints where is badly lubricated. Phosphate treatment can improve surface lubricating property. This is also an effective way to reduce surface flaws.This paper studies the influence of accelerators(HAS&La(NO3)3) onφ-t diagram and growth laws of phosphate film. The results show that HAS has a dramatic effect on accelerating the corrosion reaction of parkerizing. It makes deposition rate faster, film forming time shorter and grain finer and denser. La(NO3)3 is involved in nucleation process of phosphate film, and reduces the potential barrier for grain nucleation. Furthermore, it accelerates the grain to form and makes grain fine and dense. When both are added, they can promote each other and have better result.The influence of phosphating process on the morphology of phosphate film is also studied. Besides, the tribological property is also studied. The results indicate that the phosphate film which is heavier and composed of finer and denser grains has better antifriction effect. The friction coefficient is approximately 0.2 while on the same condition the sample is 0.7 which is unphospharized. After soap treatment, phosphate film shows better antifriction property, and friction coefficient is below 0.2.When the above phosphating process is used in weld joints during the production process of strands, it turns out to be an effective way to reduce the appearence of surface cracks.