| In many industrial corrosive environment, nickel based corrosion resistant alloy not only has the unique corrosion resistant, high strength and good toughness, but also has excellent smelting, castability, machine-shaping and welding performance. Accordingly, this alloy is widely used in the fields of petrochemical, energy, marine, aerospace and so on. Alloy800H is the most typical of a nickel base corrosion resistant alloy. Since its introduction to the market in the1950s,800H has been broadly utilized in furnace components of metallurgical industry, petrochemical industrial tube and heat exchanger in nuclear reactor, which is based on its advantages such as high strength and corrosion resistance at high temperatures. However, there are lots of difficulties in the hot working of alloy800H. For example, the flow stress and deformation temperature of alloy800H is high and the processing temperature range is too narrow. Moreover, the cost of smelting of alloy800H is too high. Accordingly, the research of hot working processing of alloy800H with the method of thermal simulation test has important academic and engineering significance.This paper can be devided into seven sections. The main work and conclusions in this paper can be drawn as follows:(1) The effect of hot working processing parameters on flow stress of alloy800H has been studied through the single-pass compression test. During the process of hot deformation, the flow stress of alloy800H increases with decreasing deformation temperature and increasing strain rate. The change of above two factors can lead to dynamic recovery (DRV) and dynamic recrystallization (DRX). As a result, the effects of strain on flow stress will have a complex change. A mathematical model of flow stress for800H has been established, which has a good fitting accuracy.(2) The law of occurence of DRX has been revealed through the micro structure observation of single-pass compression samples with different deformation conditions combined with analysis technology of EBSD. DRX is more likely to happen when deformation temperature is high and strain rate is low. It can’t be neglected that the solubility of precipitate such as carbide will change with the variation of temperature. The change of substructure in alloy800H during hot deformation has been analyzed using TEM analysis techlology. It’s found that the substructure of alloy800H consists of high density dislocation walls, microbands and subgrains by TEM. It is also seen that initial grain boundaries are the preferential nucleation sites for DRX. Besides, the change of microband in the interior of the grain will provide additional nucleation sites. The mechanism of nucleation forming includes the bulging of grain boundary and the growth of substructure.(3) A high temperature consistive equation has been established on the basis of Zener-Hollomon equation. The method to predict critical stress of DRX for alloy800H has been studied through the three polynomial fitting methods. The DRX kinetics equation has been determined based on JMA equation, which realize the accurate prediction of DRX volume fraction. The volume fraction of static recrystallization for alloy800H (SRX) has been calculated through0.2%off-set method. The law of effect of hot working processing parameters on the rate of SRX has been analyzed. However, due to the occurrence of strain induced precipitate at low temperature, there is a platform in the SRX curve. The SRX kinetics equation has been established based on Avrami equation.(4) The basic theory of dynamic material model (DMM) has been studied. The hot processing maps for alloy800H with different strains have been established by the data from single-pass compression. To optimize hot working processing, the distribution of safe regions and instable regions of processing maps has been analyzed combined with the obversation of microstructure. At the true strain of0.6, the best hot working temperatures range from990℃to1030℃and the strain rates range from0.01s-1to0.05s-1. |
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