| Ethylene spherical tanks become increasingly huge along with the rapid advancement of the petrifaction industry and the unceasing enhancement of ethylene's yield. This trend of advancement induce the more strict requirement of the steel plate used in the manufacture of the ethylene spherical tanks.This paper takes the 07MnNiCrMoVDR steel which is used in low temperature pressure vessel to manufacture the ethylene spherical as the research object. Simulated the welding temperature field transformation of 07MnNiCrMoVDR steel utilizing the welding finite element analysis software, obtained the heat circulation curve of the heat-affected zone under the different weld condition, and established the relational model between the craft parameter and t8/5 and the tH. The method of thermal simulation has been used to study the performance of the HAZ of the 07MnNiCrMoVDR steel. The microstructure and the performance will be different under the various weld condition, the coarse grain zone of HAZ is the worst region of low temperature toughness. Under the small linear energy (10KJ/cm) and a higher preheating temperature (180℃) can attain better performance. In addition, linear regression method was used to establish the forecast formula of performance, and also utilize the MATLAB to optimize the welding procedure by the low temperature toughness optimal solution as the objective function. The small linear energy and the high preheating temperature is the best craft parameter.Finally, the change of microstructure and performance after the heat treatment also was inspected in this paper. From this we find the 07MnNiCrMoVDR steel has reheat brittleness in coarse grain zone, this phenomenon maybe relative with the alloying elements separated out in the crystal boundary. The reheat brittleness indicates this steel possibly has reheat crack tendency when through heat treatment. So, the heat treatment still needs improvement and consummation.
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