Microstructure and Precipitation Studies of Gas Tungsten Arc Welded Haynes 282 Superalloy

Improvement in efficiency of energy conversion requires the use of high temperature materials in thermal power plants. This has led to the development of new γ' strengthened nickel based superalloy (Haynes 282). This alloy is used for advanced ultra-supercritical (AUSC) plants which are operated under the service conditions of 760 oC temperature and 35 MPa pressure. Bead on plate gas tungsten arc welding experiments were done with optimized process parameters. Thermal cycle in heat affected zone was measured by K-type thermocouple attached to a data acquisition system. Welding simulations were carried out in simufact welding® by using experimental parameters and thermal field was established. Base metal is characterized with γ solid solution and randomly distributed MC carbides. SEM results showed that the carbides are of MC type. The carbide precipitate distribution correlates with the segregation pattern during solidification of the weld.

Precipitation Versus Partitioning Kinetics during the Quenching of Low-Carbon Martensitic Steels

Low-carbon, low-alloy steels undergo auto-tempering and carbon partitioning to austenite during quenching to martensite. The microstructures of two such steels quenched at two cooling rates have been evaluated using electron microscopy to characterise lath and carbide precipitate morphologies, and the results have been compared with theoretical predictions based on the Thermo-Calc modules DICTRA and TC-Prisma. The modelling tools predicted the carbon depletion rates due to diffusion from the bcc martensite laths into austenite and the precipitation of cementite in the ferrite matrix. The predictions showed a satisfactory agreement with the metallographic results, indicating that the Thermo-Calc based software can aid in the design of new low-carbon martensitic steels.

Application of design of experiment to a FCAW process

This work presents the results of research on the anti-abrasion surfacing welds designated to operate under wear conditions. The main purpose of the work was to produce single-layer surface welds by means of semi-automatic hard-facing/surface welding with the use of filler material containing carbide precipitate and with the use of 10 mmand 20 mmwide beads. The samples were subject to visual and penetrant testing and to destructive testing in the form of macro and micro metallographic testing, hardness testing and bend testing with a view to determine the effect which thebeads of various widths have on the analyzed factors.

Evaluation of Repair Welding Influence on GH3535 Superalloy Microstructure and Mechanical Properties

GH3535 supperalloy, whose grade of ASME is UNS N10003, is currently considered as a candidate material for solid-fuel and fluid-fuel molten salt reactor in china. During the development of procedures for welding GH3535 superalloy, consideration should always be given to the possibility that repair welding may be necessary. This paper presents weld repairs of GH3535 alloy rolled plates using gas tungsten arc welding with filler metal. The purpose of this work is to evaluate the low heat input process for weld repair of GH3535 alloy plates about the microstructure features and mechanical properties. The results demonstrated that sound joints without defects could be obtained after weld repairs. Due to repair thermal cycles on the original weld seam, the size of carbide precipitate became large, but repair welding is found to cause no decrease in short-term time-independent strength.

Effects of Carbide Precipitate Formation on the Change in Ultrasonic Velocity in Austenitic Stainless Steels

Ultrasonic tests were conducted for 304 type austenitic stainless steels with different annealing conditions and effects of carbide precipitate formation on the velocity changes were evaluated. The velocity increased with higher annealing temperature and/or longer annealing time. SEM observations indicated that carbide precipitates were formed mainly on grain boundaries. Results show that it is not the precipitation itself but the removal of carbon from the matrix that determines the velocity change.