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

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.

Evaluation of Creep Strength Reduction Factors for Welded Joints of Modified 9Cr-1Mo Steel (P91)

2006 ◽  
Author(s):  
Masaaki Tabuchi ◽  
Yukio Takahashi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Rupture Strength ◽  
Reduction Factor ◽  
Creep Rupture ◽  
Type Iv ◽  
Rupture Data ◽  
Term Creep

In order to review the allowable creep strength of high Cr ferritic steels, creep rupture data of base metal and welded joints have been collected and long-term creep strength have been analyzed in the SHC committee in Japan since 2004. In the present paper, the creep rupture data of 370 points for welded joint specimens of modified 9Cr-1Mo steel (ASME Grade 91) offered from seven Japanese companies and institutes were analyzed. These data clearly indicated that the creep strength of welded joints was lower than that of base metal due to Type IV fracture in HAZ at or above 600°C. From the activities of this committee, the master curve for life evaluation of welded joints of Gr.91 steel could be represented as follows: LMP==34154+3494(logσ)−2574(logσ)2,C=31.4 The reduction factor of 100,000 hours creep rupture strength of welded joint to base metal was concluded to be 0.75 at 600°C and 0.70 at 650°C for the Gr.91 steel.

Microstructure and mechanical performance of welded joint between a novel heat-resistant steel and Inconel 617 weld metal

2018 ◽  
Vol 139 ◽  
pp. 279-292 ◽  
Author(s):  
Yu Zhang ◽  
Hongyang Jing ◽  
Lianyong Xu ◽  
Yongdian Han ◽  
Lei Zhao ◽  
...  
Keyword(s):  
Weld Metal ◽  
Mechanical Performance ◽  
Welded Joint ◽  
Resistant Steel ◽  
Heat Resistant Steel ◽  
Heat Resistant ◽  
Inconel 617

A Study for Proposal of Welded Joint Strength Reduction Factors of Modified 9Cr-1Mo Steel for Japan Sodium Cooled Fast Reactor (JSFR)

2013 ◽  
Author(s):  
Takashi Wakai ◽  
Takashi Onizawa ◽  
Takehiko Kato ◽  
Shingo Date ◽  
Koichi Kikuchi ◽  
...  
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Polynomial Equation ◽  
Creep Rupture ◽  
Short Term ◽  
Type Iv ◽  
Rupture Data

This paper proposes provisional welded joint strength reduction factors (WJSRF) of modified 9Cr-1Mo steel (ASME Gr.91) applicable to the structural designing of “Japan sodium cooled fast reactor (JSFR)”. In the welded joints of creep strength enhanced ferritic steels including modified 9Cr-1Mo steel, creep strength may obviously degrade especially in long-term region. This phenomenon is known as “Type-IV” damage. The authors had proposed provisional allowable stress for the welded joints made of the steel in PVP 2010 conference, taking creep strength degradation due to “Type-IV” damage into account. Available creep rupture data of the welded joints made of the steel provided by Japanese steel venders were collected. The temperature range was from 500 to 650°C. The database was analyzed by stress range partitioning method. The creep rupture data were divided into two regions of short-term and long-term and those were individually evaluated by regression analyses with Larson Miller Parameter (LMP). The difference in the creep failure mechanisms between short-term and long-term regions is taken into account in this method. Boundary between these regions was half of 0.2% proof stress of the base metal at corresponding temperature. First order polynomial equation of logarithm stress was applied. For conservativeness, allowable stress was proposed provisionally considering design factor for each region. JSME (Japan Society of Mechanical Engineers) published a revised version of the elevated temperature design code in last year. Modified 9Cr-1Mo steel was officially registered in the code as a new structural material for sodium cooled fast reactors. The creep rupture curve for the base metal of the steel was standardized by employing stress range partitioning method, same as for the welded joint. However, second order polynomial equation of logarithm stress was applied in the analysis for the base metal. In addition, the creep rupture data obtained at 700°C were included in the database and data ruptured in very short term, i.e. smaller than 100 hours, were excluded from the analysis. Thus, there are some differences between the procedures to determine the creep rupture curves for base metal and welded joint made of modified 9Cr-1Mo steel. This paper discusses the most feasible procedure to determine the creep rupture curve of the welded joint of the steel by performing some case studies to focus on physical adequacy and harmonization with the determination procedure of the creep rupture curve for the base metal. Then, the WJSRF are provisionally proposed based on the design creep rupture stress intensities. In addition, the design of JSFR pipes was reviewed taking WJSRF into account.

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

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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