Citation: Sun, Q.; Li, X.; Li, K.; Cai,
Z.; Han, C.; Li, S.; Gao, D.; Pan, J.
Effects of Long-Term Service on
Microstructure and Impact
Toughness of the Weld Metal and
Heat-Affected Zone in CrMoV Steel
Joints. Metals 2022, 12, 278. https://
doi.org/10.3390/met12020278
Academic Editor: Alberto
Campagnolo
Received: 10 January 2022
Accepted: 31 January 2022
Published: 3 February 2022
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Article
Effects of Long-Term Service on Microstructure and Impact
Toughness of the Weld Metal and Heat-Affected Zone in
CrMoV Steel Joints
Qixing Sun
1,2
, Xiaogang Li
1,2
, Kejian Li
1,2,
*, Zhipeng Cai
1,2,3,4
, Chaoyu Han
1,2
, Shanlin Li
1,2
, Dangxun Gao
5
and Jiluan Pan
1,2
1
Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China;
sqxtsinghua@163.com (Q.S.); lxg18@mails.tsinghua.edu.cn (X.L.); czpdme@mail.tsinghua.edu.cn (Z.C.);
hancy19@mails.tsinghua.edu.cn (C.H.); shanlinli2015@163.com (S.L.); pjl-dme@mail.tsinghua.edu.cn (J.P.)
2
Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Beijing 100084, China
3
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
4
Collaborative Innovation Center of Advanced Nuclear Energy Technology, Tsinghua University,
Beijing 100084, China
5
Fundamental Industry Training Center, Tsinghua University, Beijing 100084, China;
gaodx@mail.tsinghua.edu.cn
* Correspondence: kejianli@mail.tsinghua.edu.cn
Abstract:
The microstructure and impact toughness of weld metals (WMs) and heat-affected zones
(HAZs) of a low-alloy CrMoV steel gas turbine rotor which had served for 14 years were investigated.
The ex-service joints in the turbine part (serving at 500–540
◦
C) and the compressor part (serving
below 300
◦
C) of the rotor were selected for comparative research. The microstructure of the WMs
and HAZs between the turbine part and the compressor part was similar, indicating that there was
no significant deterioration in microstructure of the turbine part during service. However, compared
with the compressor part WM, the impact energy of the turbine part WM decreased significantly, and
FATT
50
increased greatly. The degraded toughness of turbine part WM was related to more serious
intergranular cracking caused by higher segregation level of phosphorus (P) at prior austenite grain
(PAG) boundaries. Welding and post-weld heat treatment led to obvious segregation of P at PAG
boundaries in WMs, and the segregation of P in turbine part WM was further aggravated during
serving at 500–540
◦
C. Additionally, the inhomogeneous microstructure of the WMs also aggravated
the segregation of P. The toughness of the HAZs in both turbine part and compressor part was high,
which was because of fine grains. Furthermore, due to there being more grain boundaries and low
P content, the segregation of P in HAZs was slight and its adverse effect on the toughness could
be ignored.
Keywords: weld metal; heat-affected zone; long-term service; phosphorus segregation; toughness
1. Introduction
Due to the excellent elevated temperature strength, the good oxidation resistance, and
the high hydrogen embrittlement resistance, low-alloy CrMoV steels are widely used for
high-temperature applications in the power, chemical, and oil industries [
1
–
3
]. In the power
industry, these steels are extensively used to manufacture critical components operated
under the circumstances of high temperature, high pressure, and dynamic loads [
1
–
3
]. At
present, thousands of thermal power generating units in China have been in service for
more than ten to twenty years. The microstructure and mechanical properties of these
steels might deteriorate during service, leading to threats to the service safety of critical
components [
1
–
5
]. Thus, investigating the effects of service on the microstructure and the
mechanical properties of low-alloy CrMoV steels is meaningful for ensuring service safety
and assessing the remaining service life of critical components in generating units.
Metals 2022, 12, 278. https://doi.org/10.3390/met12020278 https://www.mdpi.com/journal/metals
