| Heat-resistant austenitic stainless steel tube is widely used in large pressure vessel, power station boiler, petrochemical industry and other fields. In recent years, higher capacities and demands for heat-resistant stainless steel tube have been put forward in various application fields. It is greatly promoted the development of new heat-resistant austenitic steels, particularly demand for its large diameter seamless tube urgent. However, heat-resistant austenitic steel large diameter thick wall tube contents a high degree of alloying and its thermal processing window is narrow. Because the tube has a large size, coarse grain, mixed grain and other tissue defects often appear in the Thermal processing and affect its performance. Therefore, a reasonable choice of the organizational control process to obtain a uniform and fine grain structure is the key to ensure product performance.A new type of lean austenitic heat resistant steel as the main research object in this paper. Which contents a low degree of Ni and still better than 310（25Cr-21Ni） in high performance. It is a kind of high added value resource saving heat resistant stainless steel. The material obtains its heat-resistant properties by precise control of micro alloy additions, especially the rare earths combined with nitrogen is on the nominal composition basis of 21Cr-11 Ni. At present, many researches of the 21Cr-11Ni-N-Ce steel which focused on the reliability assessment for the service properties. However, there is still a lack of knowledge concerning the microstructural evolution and mechanical behavior in thermal process.The metadynamic recrystallization behavior of a novel 21Cr-11Ni-N-Ce austenite heat-resistant steel had been studied by Gleeble-3 800 thermal simulation testing machine, using double hit compression experiments, at temperature of 950℃1150℃, strain rate of 0.1s-110s-1 and inter-pass times of 0.5s30s. According to the present experimental results, the kinetic equation and the grain size model for the metadynamic recrystallization of 21Cr-11Ni-N-Ce austenite heat resistant stainless steel was proposed. Through the heating experiments in heat treatment furnace, the influence of heating temperature and holding time on grain size was studied, at temperature of 1000℃1200℃ and inter-pass times of 3min120min. The initial forging temperature range was determined and the mathematical model for describing grain growth behavior was developed. These results provide data support and reference for the actual hot working process.On the other hand, the large diameter thick wall tube extrusion process of 21Cr-11Ni-N-Ce heat-resistant steel on perspective of the grain structure control has studied on DEFORM-2D finite element simulation platform by using Fortran languages for secondary development. The organization evolution model was incorporated into the user-defined subroutines to numerical simulation of hot extrusion of thick wall tube. To discuss the different processes parameters on the final austenite grain structure and get a reasonable hot extrusion molding process. |
PDF Full Text Request