STP1321

    Fracture Initiation by Local Brittle Zones in Weldments of Quenched and Tempered Structural Alloy Steel Plate

    Published: Jan 1997


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    Abstract

    The heat-affected zone (HAZ) embrittlement of an API 2Y Grade 50T quenched and tempered offshore structural steel plate, welded by the submerged-arc process at a heat input of 4.5 kJ/mm, was investigated from the viewpoint of identifying the local brittle zone (LBZ) microstructure and the metallurgical factors associated with its formation. Microstructural and fractographic analysis showed the LBZ microstructure to be dual phase martensite-austenite (M-A) constituent. The formation of M-A constituent was found to be related to microstructural banding of the hot-rolled base plate. When the banded base plate was welded, M-A constituent formed only within the band microstructure which penetrated the intercritically-reheated coarse-grain HAZ (IRCGHAZ). The chemistry of the band microstructure in conjunction with the thermal cycle of the IRCGHAZ provided the critical conditions for the formation of M-A constituent in the API 2Y Grade 50T steel investigated. The influence of local brittle zones (i.e., M-A constituent) on the HAZ fracture toughness was evaluated by means of Crack-Tip Opening Displacement (CTOD) tests. These tests showed the steel to suffer embrittlement when the fatigue precrack sampled an intercritically-reheated coarse-grain HAZ which contained M-A constituent, confirming that M-A constituent is the major microstructural factor controlling the HAZ toughness of this particular steel.

    Keywords:

    Local Brittle Zone (LBZ), Heat-Affected Zone (HAZ), Unaltered Coarse-Grain Heat-Affected Zone (UACGHAZ), Fine-Grain Heat-Affected Zone (FGHAZ), Intercritically-Reheated Coarse-Grain Heat-Affected Zone (IRCGHAZ), Subcritically-Reheated Coarse-Grain Heat-Affected Zone (SRCGHAZ), Crack-Tip Opening Displacement (CTOD)


    Author Information:

    Kenney, KL
    Idaho National Engineering Laboratory, Idaho Falls, ID

    Reuter, WG
    Idaho National Engineering Laboratory, Idaho Falls, ID

    Reemsnyder, HS
    Bethlehem Steel Corporation, Bethlehem, PA

    Matlock, DK
    Colorado School of Mines, Golden, CO


    Paper ID: STP12323S

    Committee/Subcommittee: E08.04

    DOI: 10.1520/STP12323S


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