Fossil fuels continue to be the primary source of energy in the world. The worldwide demand for clean and affordable energy will continue to grow, and a strong emphasis has been placed on increasing the efficiency and reducing the carbon footprint of new and existing fossil fired power plants. Throughout Asia, Europe and the USA, this demand is being met with programmes to develop advanced materials that have enhanced high temperature creep and corrosion properties. A new class of ferritic alloys, known as creep strength enhanced ferritic steels, has been developed to meet these requirements. This article focuses on the weldability of the advanced ferritic alloys used in boilers and boiler components of ultrasupercritical coal fired power plants. This review focuses on alloy selection; welding and weldability issues, including in service weld failure such as type IV cracking; welding of dissimilar metals; and weld repair. Future articles will address the welding and weldability issues of two other...

https://www.tandfonline.com/doi/pdf/10.1179/1362171813Y.0000000152

Welding and weldability of candidate ferritic alloys for future advanced ultrasupercritical fossil power plants

The current work investigates activated flux TIG welding of dissimilar steel combination of 8 mm thick plates of Modified 9Cr-1Mo (P91) steel and 2.25Cr-1Mo (P22) steel. The effect of different fluxes namely- SiO2, TiO2, Cr2O3, MoO3 and CuO on the weld bead geometry was investigated. The possible mechanism for the increase in depth of penetration has been discussed. The integrity of the weld joint made with MoO3 flux was investigated by evaluating metallurgical and mechanical characteristics in as-welded and post weld heat treated (750 °C/2 h) conditions. The occurrence of carbon migration was confirmed by optical microscopy and elemental redistribution through EPMA analysis. The precipitation of carbides of M23C6 type in the carbon enriched zone was confirmed through TEM analysis. The beneficial effect of A-TIG welding in reducing the widths of carbon enriched/depleted regions at the P22 steel-weld interface after post weld heat treatment has been discussed with the help of DICTRA simulations. The weld joints failed from P22 steel base metal in both as-welded and post weld heat treated conditions during a tensile test. The impact toughness was found to be improved after post weld heat treatment.

Study of mechanism, microstructure and mechanical properties of activated flux TIG welded P91 Steel-P22 steel dissimilar metal joint

Dissimilar metal welding of P91 steel-AISI 316L SS with Incoloy 800 and Inconel 600 interlayers by using activated TIG welding process and its effect on the microstructure and mechanical properties

Studies on A-TIG welding of 2.25Cr-1Mo (P22) steel

In the present work, the influence of process parameters such as welding current (I), welding speed (S), and flux coating density (F) on different aspects of weld bead geometry for example depth of penetration (DOP), bead width (BW), depth to width ratio (D/W), and weld fusion zone area (WA) were investigated by using the central composite design (CCD). 9–12% Cr ferritic stainless steel (FSS) plates were welded using A-TIG welding. It was observed that all input variables have a direct influence on the DOP, BW, and D/W. However, flux coating density has no significant effect on WA. Mathematical models were generated from the obtained responses to predict the weld bead geometry. An optimized DOP, BW, D/W, and WA of 6.95 mm, 8.76 mm, 0.80, and 41.99 mm2, respectively, were predicted at the welding current of 213.78 A, the welding speed of 96.22 mm/min, and the flux coating density of 1.99 mg/cm2. Conformity test was done to check the practicability of the developed models. The conformity test result...

Optimization of A-TIG process parameters using response surface methodology

Tungsten inert gas (TIG) welding process is generally used to produce high quality weld joints of 9Cr-1Mo steel. However, there is limitation associated with the depth of penetration achievable in single pass autogenous welding. Specific activated flux has been developed in the present work to enhance the depth of penetration up to 6 mm in single pass by A-TIG welding. 9Cr-1Mo steel A-TIG weld joint using activated flux was made in single pass welding while the multipass TIG weld joint using modified 9Cr-1Mo filler wire was made in seven passes. The enhancement in depth of penetration during A-TIG welding process for this steel was attributed to arc constriction. The strength properties of the A-TIG weld joint was superior to that of the multipass TIG weld joint. The multipass TIG weld joint exhibited slightly improved impact toughness than the A-TIG weld joint in PWHT condition. Therefore, there was no degradation in the microstructure and mechanical properties of the weld joint produced by A-TIG welding...

Effect of Activated Flux on the Microstructure and Mechanical Properties of 9Cr-1Mo Steel Weld Joint

It is essential to set up the activated tungsten inert gas (A-TIG) welding process parameters to produce the desired weld bead geometry and heat affected zone (HAZ) width in modified 9Cr–1Mo steel weld joints. Therefore, it becomes necessary to develop a tool for optimisation of A-TIG welding process. Genetic algorithm (GA) based model has been developed to determine the optimum process parameters. In this methodology, first independent ANN models correlating depth of penetration, weld bead width and HAZ width with current, voltage and torch speed respectively were developed. Then, GA code was developed in which the objective function was evaluated using the ANN models. There was good agreement between the target and actual values of bead geometry and HAZ width obtained using the GA optimised process parameters. Thus, a methodology using GA has been developed for optimising the A-TIG process parameters for modified 9Cr–1Mo steel.

V. Arunkumar

Papers

Effect of Activated Flux on the Microstructure and Mechanical Properties of 9Cr-1Mo Steel Weld Joint

Genetic algorithm for optimisation of A-TIG welding process for modified 9Cr–1Mo steel