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Metals 2016, 6(4), 75; doi:10.3390/met6040075

Influence of Post-Weld Heat Treatment on the Microstructure, Microhardness, and Toughness of a Weld Metal for Hot Bend

1
CNPC Bohai Petroleum Equipment Manufacture Co., Ltd., Qingxian 062658, China
2
Key Laboratory of Metastable Materials Science & Technology, College of Materials Science & Engineering, Yanshan University, Qinhuangdao 066004, China
*
Author to whom correspondence should be addressed.
Academic Editor: Hugo F. Lopez
Received: 31 December 2015 / Revised: 13 March 2016 / Accepted: 18 March 2016 / Published: 25 March 2016
View Full-Text   |   Download PDF [21514 KB, uploaded 25 March 2016]   |  

Abstract

In this work, a weld metal in K65 pipeline steel pipe has been processed through self-designed post-weld heat treatments including reheating and tempering associated with hot bending. The microstructures and the corresponding toughness and microhardness of the weld metal subjected to the post-weld heat treatments have been investigated. Results show that with the increase in reheating temperature, austenite grain size increases and the main microstructures transition from fine polygonal ferrite (PF) to granular bainitic ferrite (GB). The density of the high angle boundary decreases at higher reheating temperature, leading to a loss of impact toughness. Lots of martensite/austenite (M/A) constituents are observed after reheating, and to a large extent transform into cementite after further tempering. At high reheating temperatures, the increased hardenability promotes the formation of large quantities of M/A constituents. After tempering, the cementite particles become denser and coarser, which considerably deteriorates the impact toughness. Additionally, microhardness has a good linear relation with the mean equivalent diameter of ferrite grain with a low boundary tolerance angle (2°−8°), which shows that the hardness is controlled by low misorientation grain boundaries for the weld metal. View Full-Text
Keywords: M/A constituent; cementite; toughness; microhardness; EBSD M/A constituent; cementite; toughness; microhardness; EBSD
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Han, X.-L.; Wu, D.-Y.; Min, X.-L.; Wang, X.; Liao, B.; Xiao, F.-R. Influence of Post-Weld Heat Treatment on the Microstructure, Microhardness, and Toughness of a Weld Metal for Hot Bend. Metals 2016, 6, 75.

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