Effect of post weld heat treatment on the interplay of microstructure, precipitates and properties of creep-resistant 2.25Cr-1Mo-0.25V weld metal

Hannah Schönmaier*, Michael Musi, Mihaela Albu, Ronny Krein, Ronald Schnitzer

*Korrespondierende/r Autor/-in für diese Arbeit

Publikation: Beitrag in einer FachzeitschriftArtikelBegutachtung

Abstract

For the application in heavy wall pressure vessels such as hydrocracking reactors in the petrochemical industry,creep-resistant 2.25Cr–1Mo-0.25V steel is usually joined via submerged-arc welding. To ensure a long servicelifetime at elevated temperatures and high pressures, the steel plates and weldments must maintain a beneficialcombination of toughness and creep strength for several years. One approach to adjust the weldments’ mechanicalproperties is to perform a post-weld heat treatment (PWHT).This study is dedicated to the impact of the PWHT-temperature and -time on the complex interplay ofmicrostructure, precipitates and mechanical properties of 2.25Cr–1Mo-0.25V weld metal. The mechanical testingshowed that a higher PWHT-temperature increases the weld metal’s impact toughness and ductility whilesimultaneously decreasing its strength and creep resistance. The high-resolution investigation with transmissionelectron microscopy and high-energy X-ray diffraction demonstrated that this is linked to accelerated recoveryprocesses and severe coarsening of fine MX carbonitrides. At lower PHWT-temperatures, the absolute increase ofthe MX phase fraction during PWHT and the MX coarsening is less pronounced, allowing the MX carbonitrides toeffectively contribute to precipitation hardening by maintaining their fine size. Besides MX carbonitrides, theweld metal consists of Cr-rich M7C3 and M23C6 as well as a substantial amount of Mo- and V-rich M2C carbides.The precipitate transformation sequence during PWHT was found to be M3C→M3C + MX + M7C3→M3C + MX +M7C3+M23C6+M2C→MX + M7C3+M23C6+M2C, whereas prolonged annealing times at higher PWHTtemperaturesagain lead to the dissolution of M7C3 in favor of MX.
Originalspracheenglisch
Aufsatznummer143550
Seitenumfang11
FachzeitschriftMaterials Science and Engineering A
Jahrgang850
DOIs
PublikationsstatusVeröffentlicht - 2022

ASJC Scopus subject areas

  • Allgemeine Materialwissenschaften
  • Physik der kondensierten Materie
  • Werkstoffmechanik
  • Maschinenbau
  • Werkstoffwissenschaften (insg.)

Fields of Expertise

  • Advanced Materials Science

Treatment code (Nähere Zuordnung)

  • Basic - Fundamental (Grundlagenforschung)

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