A novel process to refine the grain size of NiCrMoV steel
Published:2014-09-22 Hits:1343

材料科学与工程  2011


摘 要:

NiCrMoV steel is a commonly used material for the low pressure (LP) rotor of steam turbine, and the corresponding large forging has a diameter of 1.8 m in a 600 MW generator. During high temperature forging, the coarse austenite grains are formed, influencing the microstructure and fracture behavior of the steel in subsequently quenched and tempered state.

The average grain sizes of the specimens normalized at 870, 900, 930 and 950 ℃ are ASTM No. 3.6, 3.4, 2.7, and 2.2, respectively. The conventional normalizing process has just a little effect on grain refining of the NiCrMoV steel, because the special requirements for heating rate and holding time in production are difficult to be satisfied, and the prior coarse grains still remain due to structural heredity.

The proposed “isothermal treatment” can effectively refine the grain size of NiCrMoV steel to ASTM No. 6.0 from the initial ASTM No. 1.8, indicating the structural heredity has been successfully eliminated by the pearlitic transformation. The size of isolated non-pearlite area after isothermal treatment is related to the largest grain size, and the more the pearlite transformed, the finer the grain size is.

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