Influence of Precipitation of China Low Activation Martensitic Steel on Its Mechanical Properties After Groove Pressing
XUE Kemin, SHENG Jie, YAN Siliang, TIAN Wenchun, LI Ping()
School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China
Cite this article:
XUE Kemin, SHENG Jie, YAN Siliang, TIAN Wenchun, LI Ping. Influence of Precipitation of China Low Activation Martensitic Steel on Its Mechanical Properties After Groove Pressing. Acta Metall Sin, 2021, 57(7): 903-912.
In this work, a constrained groove pressing experiment was carried out to investigate the influence of constrained groove pressing on precipitated phase dissolution and mechanical properties of China low activation martensitic (CLAM) steels. The aim of this study is to improve the comprehensive service performances of CLAM steels used in the first wall of fusion reactor cladding. The influence of the dissolution and precipitation of precipitates on the mechanical properties of CLAM steel subjected to multi-pass groove pressing was investigated via tensile tests at room temperature and 500oC, microhardness tests, SEM, and TEM. The results show that the grains and precipitated phases are effectively refined after three passes of groove pressing, the volume fraction of grains above 5 μm is reduced to 0.49%, and the average size of M23C6 and MX phases is reduced from 107.32 and 17.12 nm to 93.97 and 13.59 nm, respectively. When the cumulative strain of the billets reaches a value of 2.32 (pass two), the tensile strength and microhardness are found to be 720 MPa and 2.46 GPa, respectively. When the cumulative strain increases to 3.48 (pass three), the strength of the CLAM steel decreases by 4.31%, whereas the microhardness and elongation increase by 2.03% and 6.27%, respectively. These trends are related to the evident dissolution of the precipitates during the deformation process.
Fig.1 OM (a, c) and SEM (b, d) images of China low activation martensitic (CLAM) steel before (a, b) and after (c, d) heat treatment
Fig.2 TEM analyses of the precipitated phase of CLAM steel subjected to one pass constrained groove pressing at the grain boundary (a-c) and intergranular MX (d)
Fig.3 TEM images of CLAM steel before deformation (a) and after constrained groove pressing for pass one (b), pass two (c), and pass three (d) (DTs—dislocation tangles, DDWs—dense dislocation walls)
Fig.4 TEM images of precipitated phase of CLAM steel before deformation (a) and after constrained groove pressing for pass one (b), passe two (c), and pass three (d)
Fig.5 Size distributions of grains and precipitates in CLAM steel processed before and after deformation (ls—equivalent center to center distance of precipitates, f(d > 5 μm)—volume fraction of grain size greater than 5 μm, d—grain size, fv—volume fraction of precipitated phase, D—density of the precipitated phase, davg—average diameter of precipitated phase)
Fig.6 Tensile strength and elongation curves of CLAM steel with different groove pressing passes (a) and SEM image showing the fracture merphology of tensile specimen after three-passes groove pressing (b)
Fig.7 Hardness and average grain size of CLAM steel satisfy the Hall-Petch model
Fig.8 TEM image showing the pinning dislocation of MX phase
Processing
M23C6
MX
condition
σp
H
σp
H
MPa
MPa
MPa
MPa
As-tempered
47.1
141.3
127
381
One pass
57.4
172.2
167
501
Two passes
50.6
151.8
249
747
Three passes
42.1
126.3
169
507
Table 1 Results of precipitation strengthening
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