Abstract: The microstructure of normalized & tempered 9Cr-2W-3Co martensitic heat-resistant steel and its tensile strength and fracture mechanism at different strain rates （5×10⁰， 5×10^-1， 5×10^-2， 5×10^-3， 5×10^-4 s^-1） at 625 ℃ was researched. The results showed that the tempered lath martensitic structure of 9Cr-2W-3Co martensitic heat-resistant steel was mainly structure obtained after normalizing and tempering， and there were a large number of chromium-containing carbide precipitation phase at the interface between the original austenite grain boundary and the lath bundle， and a certain density of dislocations in the matrix. The test steel was stretched at 625 ℃， with the increasing of strain rate， the yield strength of steel increased from 237 MPa to 430 MPa， the tensile strength was increased from 268 MPa to 480 MPa， and the reduction of area was between 28% and 15.5%. The test steel was stretched at 625 ℃， with the strain rate， the yield strength increased from 237 MPa to 430 MPa， the tensile strength increased from 268 MPa to 480 MPa， and the sectional shrinkage was 28% to 15.5%. There were a large number of dimples of different sizes in the fracture， and there were high density dislocation in the test steel matrix at different strain rates. The dislocation interacts with the interface of inclusions or lath or precipitates， leading to the initiation and expansion of micropores， and eventually the fracture of the material.

Key words: Martensitic Heat-resistant Steel, Strain Rate, Precipitated Phase, Inclusion, Dislocation

摘要： 研究了正火回火9Cr-2W-3Co马氏体耐热钢的组织及其在625 ℃不同应变速率（5×10⁰、5×10^-1、5×10^-2、5×10^-3、5×10^-4 s^-1）条件下的拉伸强度与断裂机理。结果表明，9Cr-2W-3Co 马氏体耐热钢正火与回火后组织主要是回火板条马氏体组织，原奥氏体晶界与板条束界面有大量含铬的碳化物析出相，基体中含有一定密度的位错。试验钢在625 ℃拉伸，随着应变速率的增加，钢的屈服强度从237 MPa增加到430 MPa，抗拉强度从268 MPa增加到480 MPa，断面收缩率为28%~15.5%。断口中有大量不同尺寸的韧窝，不同应变速率试验钢基体中均存在高密度位错，位错与夹杂物或碳化物析出相交互作用，导致微孔的萌生与扩展，最终导致材料断裂。

关键词: 马氏体耐热钢, 应变速率, 析出相, 夹杂物, 位错