PM-08Microstructure analysis of MX precipitates in weld metal for heat resistant steel

The effect of the post-weld heat treatment on the microstructures and mechanical properties of the dissimilar joint of G115, a novel developed martensite heat resistant steel, and CB2 steel, currently used in an ultra-super-critical power unit, was investigated. The results indicate that the quenched martensite underwent decomposition and transformation, and the amount of dislocations were sharply decreased in the weld metal after post-weld heat treatment (PWHT). Many nano-scale M23C6 precipitates present in the weldment were distributed on the grain and grain boundary in a dispersed manner with PWHT. The average microhardness of the weldment decreased from about 400 HV to 265–290 HV after PWHT and only a slight decrease in the microhardness of CB2 steel was detected after PWHT at 760 °C. In contrast to the case of the as-received joint, the tensile strength of the joint was improved from 630 MPa to 694 MPa and the fracture location moved from the weld metal to the base metal after PWHT. The fracture surface consisted of a cleavage fracture mode without PWHT, whereas many dimples were observed on the fracture surface with PWHT.

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Precipitates in W Alloyed 9Cr Weld Metal for Heat Resistant Steel.

QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY ◽

10.2207/qjjws.16.512 ◽

1998 ◽

Vol 16 (4) ◽

pp. 512-521 ◽

Cited By ~ 6

Author(s):

Hiroshi MORIMOTO ◽

Takashi TANAKA ◽

Shigeru OHKITA ◽

Masao FUJI

Keyword(s):

Weld Metal ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant

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Microstructure and properties of Co3W2 heat-resistant steel by vacuum electron beam welding

International Journal of Modern Physics B ◽

10.1142/s0217979220400585 ◽

2019 ◽

Vol 34 (01n03) ◽

pp. 2040058

Author(s):

Youyi Zhang ◽

Guoqing Gou

Keyword(s):

Tensile Strength ◽

Electron Beam ◽

High Temperature ◽

Weld Metal ◽

Base Metal ◽

Electron Beam Welding ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant ◽

The Impact

12Cr10Co3W2MoNiVNbNB (Co3W2) is a new type of martensitic heat-resistant steel, which is mainly used in high-temperature dynamic, static blades, high-temperature bolts and other components of ultra-supercritical steam turbines. The Co3W2 steel was joined by vacuum electron beam welding, and the microstructures of the joints were analyzed. The hardness, tensile strength and impact toughness of the joints were investigated. The results show that the joints mainly consist of weld metal, fusion-line, heat-affected zone (HAZ) and base metal, the microstructure of the weld metal is a coarse martensite. The hardness of the weld metal is about 326 HV higher than that of the base metal, and the tensile strength of the joints is 939 MPa, which can reach 98.63% of base metal. The impact absorbed energy of weld metal is such that the weakest part of the welded joints during the impact process is about 18.5 J.

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Rupture Behavior of Multi-Pass Welded Joints of Heat Resistant Steel Subjected to Creep Loading

Volume 6: Materials and Fabrication ◽

10.1115/pvp2007-26536 ◽

2007 ◽

Author(s):

Masayoshi Yamazaki ◽

Hiromichi Hongo ◽

Takashi Watanabe

Keyword(s):

Weld Metal ◽

Base Metal ◽

Welded Joints ◽

Stress Condition ◽

Welded Joint ◽

Creep Rupture ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant ◽

Type Iv

By Conducting long-term creep rupture tests for ferritic (2.25Cr-1Mo and 9Cr-1Mo-VNb) and austenitic (18Cr-8Ni and 16Cr-12Ni-2Mo-0.01C-0.07N) heat resistant steel multi-pass welded joints, creep rupture behavior and microstructures were examined. Constant-load creep rupture tests were conducted at 550 and 600 °C up to about 30,000h. Viewpoint in this study was centered on the influence of microstructure on the fracture location of welded joints in heat resistant steels. The results obtained are as follows; 1. The rupture location of the welded joint in austenitic heat resistant steel was found to shift from the base metal at the higher stress condition to the weld metal at lower stress condition at 550 and 600 °C. 2. In the welded joint of austenitic heat resistant steels, the last layer of weld metal showed considerably lager creep strain than the central layers of weld metal. 3. The rupture location of the welded joint in ferritic heat resistant steel was found to shift from the base metal or weld metal at the higher stress condition to the fine-grained HAZ adjacent to the base metal at lower stress condition at 550 and 600 °C. 4. Type IV creep crack initiation occurred in the fine grained HAZ region adjacent to the base metal for the weld metal pass overlap regions of multi-pass large welded joints specimen in 2.25Cr-1Mo steel. 5. Type IV creep crack of the 9Cr-1Mo-V-Nb welded joint nucleated in the curved part of the groove angle and propagated to the top part of the V-groove. It was found that the voids and cracks were initiated inside the plate thickness.

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