The Fifteen Cr2ni3mow Seamless Steel Pipe And Piercing Plug Failure Analysis And Process Improvement

Based on the work theory of rotary piercing and stress analyse of piercing plug, a general analyse the stick mechanism during piercing 27SiMn tubes with the internal water cooling cone type piercing plug (hereafter call "plug") which produced by the material 15Cr2Ni3MoW has been proposed and give the improvement measure. The process flow for produce plugs is:ingot—annealing—forging—annealing—machining—heat treatment and surface oxidation treatment. Ingot, forging, heat treatment and surface oxidation treatment are the key process to influence and decide the plug structure and performance. Observement and analyse of the key process shows that: high working temperature, high stress of the plug, plug's surface oxidation film porosity and the big viscosity of the high Silicon content in materail 27SiMn are the main reasons for stick. Focus on the plug structure, surface oxidation film and its performance , the rare earth has been added to improve the plug's high temperature performance. The result shows that: addition of 0.25% rare earth can get the largest improvement of the plug's structure . A typical fine, homogeneous Bainite structure can be obtained, with this addition quantity, the plug's surface oxidation film is compact and has the fasten integrate with plug body. The sorength increases 23%, the impact value increases 45%, the hardness increase 2HRC.The material's fracture mode changes from mainly brittle fracture to mainly toughness fracture. Industry trial (piercing 27SiMn ) result is consistent to laboratorial result, and the service life improve 3 times. The mechanism why rare earth can improve the plug's structure, performance and surface oxidation film is: rare earth can improve the cleanness of the molten steel, decontaminate the grain boundary, refined grain, reinforce grain boundary, and change the diffusion pattern of Fe, O atomic. However the other hand, during the surface oxidation treatment, rare earth speed the decarbonization of plug surface, Which deserve to be concerned and investigated.