700MW级水轮发电机镜板镜面均匀性控制研究

Research on surface uniformity control of runner plate for 700MW hydrogenerator

大型水轮发电机组镜板制造是制约我国水电装备国产化的瓶颈之一。某700 MW级国产化机组镜板采用25CrMo4材料锻造而成,保证镜板面的硬度均匀性是其主要技术难点之一。本文采用热模拟锻造及热处理实验,深入研究了锻造温度、应变量、应变速率、回火温度和淬火深度对25CrMo4的微观组织及硬度均匀性的影响。结果表明:锻造时,在高温下采用大变形速率有利于细化晶粒,而混晶可能导致镜板面硬度超差;热处理时,回火温度和淬火深度对硬度的影响明显,只有镜板面上各点回火温度波动小于40℃,淬火深度的差异小于30mm时,硬度差才可能满足小于30HB的要求。

The large runner plate is a bottleneck of complete localization of China-made hydrogenerator. 25CrMo4 is used for a China-designed runner plate of 700MW hydrogenerator. To ensure hardness uniformity of runner surface is one of the main technical difficulties. The effects of forging temperature, strain,strain rate, temper temprature and depth of quenching on microstructure and hardness uniformity of 25CrMo4 were investigated by simulation forging and heat-treating test. The result shows that high strain rate of forging at high temperature is favourable for grain refinement, and mixed crystal may be a reason for big hardness difference on runner surface. Temper temperature and depth of quenching affect hardness obviously in heat treatment.To achieve a hardness difference less than 30 HB, the range of temperature variation must be less than 40 ℃ and the difference of depth of quenching between any point of runner surface must be limited to 30 mm.