工业汽轮机转子用钢28CrMoNiV脆性转变温度的研究

Research on the fracture appearance transition temperature of industrial steam turbine rotor steel 28CrMoNiV

针对如何正确评定工业汽轮机转子用钢28CrMoNiV的脆性转变温度(fracture appearance transition temperature,FATT)的问题,通过系列温度冲击法测定了该转子钢的冲击吸收功、脆性断面率,利用扫描电镜(scanning electronic microscopy,SEM)对冲击试样断口形貌的变化进行了研究,结合Boltzmann函数对冲击试验结果的拟合分析,正确评定了该转子钢的FATT。并对影响FATT的因素进行了归纳,研究分析了化学成分、微观组织和晶粒尺寸对转子钢FATT的影响。研究结果表明,28CrMoNiV钢的断口形貌随着温度的降低由韧窝逐渐向解理断裂变化,该转子钢的FATT为-52℃,明显低于技术标准要求值(≤85℃);通过先进的冶炼技术和热加工工艺严格控制化学成分,获得晶粒细小均匀的回火索氏体组织以及针状铁素体内部的高密度位错和亚晶界结构,可以提高转子钢的冲击韧性及降低FATT。

Aiming at the problems of how to assess the FATI＂ of industrial steam turbine rotor steel 28CrMoNiV correctly, the impact absorbing energy and percentage of brittle fracture surface of rotor steel at different temperatures were measured by impact test, the change of fracture morphology were studied by using SEM, and these experimental results were fitted by using Boltzmann function, then the FATT of rotor steel were assessed correctly. Meanwhile, the factors affecting FATT were summarized; the effects of chemical component, microstrueture and grain size on the FATF of rotor steel were investigated. The results indicate that the fracture morphology of 28CrMoNiV steel is gradually changed from dimple to cleavage fracture with decreasing temperature, the FATT of rotor steel （ - 52 ℃ ） is less than technical standard requirements obviously （ ≤85 ℃ ）. The strictly controlled chemical component, small and homogeneous tempered sorbite grain, high density dislocation and sub-grain boundary in acicular ferrite which achieved by advanced smelting and hot-working technology, are the main reasons for the increase of impact toughness and decrease of FATT of rotor steel.