Thermal Simulation Analysis of Microstructure and Hardness for CrMoV with PWHT in Type IV Region
- PDF / 2,476,957 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 41 Downloads / 144 Views
Thermal Simulation Analysis of Microstructure and Hardness for CrMoV with PWHT in Type IV Region BIN XU, SONG XUE, YONG CAI, JITAI NIU, and LIANGCHAO LI Welded components of CrMoV steam pipe exhibit a pernicious form of type IV cracking after long-term service at elevated temperature. To investigate the cracking mechanism, the type IV microstructure and hardness were characterized after thermal simulation of post-weld heat treatment. Below 1098 K (825 °C), loss of carbon from the pearlite region was apparent, and the work zone exhibited a slightly lower hardness than the parent material because of a minor amount of austenite transformation. In addition, for peak temperatures above 1133 K (860 °C), additional transformation into austenite occurred and was followed by retransformation into ferrite upon further increasing the temperature. The pearlite formed at 1173 K to 1223 K (900 °C to 950 °C) resulted in an increase of the volume fraction of pearlite and microstructural refinement, which yielded a remarkable increase of hardness in the work zone. For the peak temperature of 1573 K (1300 °C), previous austenite grains were coarsened and alloy carbides were dissolved in the austenite, which significantly hardened the work zone. DOI: 10.1007/s11663-017-1084-8 Ó The Minerals, Metals & Materials Society and ASM International 2017
I.
INTRODUCTION
FERRITIC Cr-Mo steels with Cr contents ranging from 0.5 to 12 wt pct are applied as structural materials for steam generators because of their excellent creep resistance.[1] The welded components of CrMoV steam pipes often operate at high temperatures in thermal power plants and experience creep deformation and rupture in the type IV region at the outer edge of the heat-affected zone (HAZ) of the weld due to aging under long-term service.[2–7] Type IV cracking is an especially pernicious form of cracking because of the enhanced rate of creep void formation, which often causes serious failure of welded components. Weld repair procedures are generally necessary to extend the life of failed parts. There is thus active interest in type IV cracking, and numerous efforts have been made to investigate the failure mechanism of P91 and P92 steels, which are typically used in power plants.[8–12] BIN XU, SONG XUE, YONG CAI, and LIANGCHAO LI are with the Key Laboratory of Testing Technology for Manufacturing Process, Ministry of Education, Southwest University of Science and Technology, Mianyang 621010, China. Contact e-mail: [email protected] JITAI NIU is with the Key Laboratory of Testing Technology for Manufacturing Process, Ministry of Education, Southwest University of Science and Technology, and also with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China, and also with the School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China. Manuscript submitted November 14, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Currently, the type IV failure mechanism is understood as being strongly linked to
Data Loading...
