Transition from Type IV to Type I cracking in heat-treated grade 91 steel weldments

Yiyu Wang; Leijun Li; Rangasayee Kannan

doi:10.1016/j.msea.2017.12.088

Transition from Type IV to Type I cracking in heat-treated grade 91 steel weldments

Yiyu Wang, Leijun Li, Rangasayee Kannan

Research output: Contribution to journal › Article › peer-review

26 Scopus citations

Abstract

Increasing the post-weld heat-treating temperature from 600 °C to 840 °C causes a transition of creep rupture locations from the Type IV cracking in the intercritical heat-affected zone to the Type I cracking in the fusion zone in the Grade 91 steel weldments. The specimens following a heat-treatment at temperatures below the A₁ temperature of the base metal failed in the Type IV cracking mode after high-temperature creep tests at 650 °C. The creep-damaged region associated with the Type IV cracking mode is consistently located in a softened zone, which is identified as the intercritical heat-affected zone. In the specimens heat-treated at temperatures close to or above the A₁ temperature of the base metal, the fusion zone enters the intercritical temperature between its A₁ and A₃ temperatures. The fusion zone experienced a partial austenitization to become a mixture of retained ferrite and new martensite, which is believed the most creep-susceptible. The same microstructure, a mixture of retained soft ferrite and new hard martensite, caused nucleation and growth of cavities in the both Type IV and Type I damaged regions. Therefore, it is suggested that the same creep mechanism may have contributed to both cracking modes in Grade 91 steel.

Original language	English
Pages (from-to)	1-13
Number of pages	13
Journal	Materials Science and Engineering: A
Volume	714
DOIs	https://doi.org/10.1016/j.msea.2017.12.088
State	Published - Jan 31 2018
Externally published	Yes

Funding

The authors would like to thank Dr. Andrew Deceuster, Dr. Bishal Silwal, and Benjamin Griffiths, who helped in welding experiments, and Kecheng Jerry Xu who helped with hardness measurements, and the financial support by the Discovery Program of the Natural Sciences and Engineering Research Council (NSERC) of Canada.

Funders	Funder number
Natural Sciences and Engineering Research Council of Canada

Keywords

Grade 91 Steel
Heat-affected zone
Post Weld Heat Treatment
Type I Cracking
Type IV Cracking

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10.1016/j.msea.2017.12.088

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title = "Transition from Type IV to Type I cracking in heat-treated grade 91 steel weldments",

abstract = "Increasing the post-weld heat-treating temperature from 600 °C to 840 °C causes a transition of creep rupture locations from the Type IV cracking in the intercritical heat-affected zone to the Type I cracking in the fusion zone in the Grade 91 steel weldments. The specimens following a heat-treatment at temperatures below the A1 temperature of the base metal failed in the Type IV cracking mode after high-temperature creep tests at 650 °C. The creep-damaged region associated with the Type IV cracking mode is consistently located in a softened zone, which is identified as the intercritical heat-affected zone. In the specimens heat-treated at temperatures close to or above the A1 temperature of the base metal, the fusion zone enters the intercritical temperature between its A1 and A3 temperatures. The fusion zone experienced a partial austenitization to become a mixture of retained ferrite and new martensite, which is believed the most creep-susceptible. The same microstructure, a mixture of retained soft ferrite and new hard martensite, caused nucleation and growth of cavities in the both Type IV and Type I damaged regions. Therefore, it is suggested that the same creep mechanism may have contributed to both cracking modes in Grade 91 steel.",

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AB - Increasing the post-weld heat-treating temperature from 600 °C to 840 °C causes a transition of creep rupture locations from the Type IV cracking in the intercritical heat-affected zone to the Type I cracking in the fusion zone in the Grade 91 steel weldments. The specimens following a heat-treatment at temperatures below the A1 temperature of the base metal failed in the Type IV cracking mode after high-temperature creep tests at 650 °C. The creep-damaged region associated with the Type IV cracking mode is consistently located in a softened zone, which is identified as the intercritical heat-affected zone. In the specimens heat-treated at temperatures close to or above the A1 temperature of the base metal, the fusion zone enters the intercritical temperature between its A1 and A3 temperatures. The fusion zone experienced a partial austenitization to become a mixture of retained ferrite and new martensite, which is believed the most creep-susceptible. The same microstructure, a mixture of retained soft ferrite and new hard martensite, caused nucleation and growth of cavities in the both Type IV and Type I damaged regions. Therefore, it is suggested that the same creep mechanism may have contributed to both cracking modes in Grade 91 steel.

KW - Grade 91 Steel

KW - Heat-affected zone

KW - Post Weld Heat Treatment

KW - Type I Cracking

KW - Type IV Cracking

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Transition from Type IV to Type I cracking in heat-treated grade 91 steel weldments

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