Research On Service Lives Of Piercing Die In High Temperature

Since the utilization of the process tooling and dies, particularly the extremely large-sized ones act as a critical factor for steel-rolling operation and the product quality, enhancement of their service lives is an important approach to reducing their operation costs and ensuring product quality.The paper focuses on the hydraulic piercing die. As a large-sized ductile iron casting, 1750 mm long, maximum 638 mm in O.D and minimum 367 mm in ID and weighing up to 5 metric tons, the piercing die is operated at a temperature up to 600 ℃ and under a rather strong composite stress, which causes cracking or fracture thereof, thus, reducing its service life and increasing the operation cost.The study offered by the paper is aimed at developing a new economic approach based on the analysis of the working conditions ( i.e., operation temperature, loading conditions and working schedule ) and failure form of the said piercing die to further enhance its mechanical properties and wearability for a longer life span, lower operation costs and desired production capacity and product quality.The analysis shows that during casting the said piercing die which is extremely large, it is very frequent to occur such defects as gray spot, shrinkage porosity, pinhole and segregation due to the negative influence on the spheroidization and inoculation of the ductile iron by the rather long time for casting and crystallization of the material so as to eventually weaken strength and toughness of the piercing die considerably.The study identifies that spheroidization of the cast iron will be significantly improved by means of proper addition of relevant alloy elements, inoculant and spheroidizing agent and appropriate casting process. In addition, desirable high toughness and high wear-resistance will also be materialized owing to proper heat treatment schedule for development of the austenite-bainite ductile iron structure.On the basis of the research on the casting process and relevant heat treatment schedule, the metallographic structure examination, the results of mechanical tests of the austenite-bainite ductile iron as well the actual operation result, it is concluded that the large piercing die manufactured with the said austenite-bainite ductile iron process has fully satisfied the relevant technological requirements.The paper involves how to develop high comprehensive properties of the large-sized work piece with hi-tech material and improvement on the casting and heat treatment processes for development of the desirable austenite-bainite ductile iron structure on the basis of actual operation circumstances. It is a representative case concerning how to apply the material science to the industrial activities, being pretty valuable as a reference to be used by metallurgical enterprises for improving product quality, reducing operation costs and sharpening their competitive edges with relevant the state-of-art technologies...