WELDING OF ULTRAHIGH STRENGTH STEEL

Structural steels with very high strength levels capable of developing minimum yield strength of nearly 1400 MPa is called ultrahigh strength steels. In recent times, the ultrahigh strength steels are in a great demand for critical structural aircraft and aerospace application. In aircrafts, automobiles, power plants, chemical industries etc. for technical as well as economic reasons the dissimilar combination of steels are necessary. Maraging steel and medium alloy medium carbon steel are used in these situations. Maraging steels are a class of precipitation hard enable martensitic steels. It develop strength due to the precipitation of inter metallic compounds.

Fabrication process which is widely employed for ultrahigh strength steels is fusion welding. Gas tungsten arc welding and electron beam welding are the two fusion welding employed. Three types of filler materials are used which include maraging steels filler, austenitic stainless steel filler and medium alloy medium carbon steel filler. The austenite get transformed to martensite during cooling in the fusion zone in maraging steels welds. In medium alloy steel weld the columnar grain growth is prevalent at the center. After post weld aging no variation is observed in microstructure as compared to as welded condition in respect of austenite stainless steel and medium alloy medium carbon steel filler welds.

The hardness survey was done on different filler welds. Austenite stainless steel weld metal shows the lowest hardness. The region of weld of medium alloy medium carbon steel filler shows the highest hardness. The hardness of maraging steel filler weld is as likely as parent metal. The residual stress at the center of the weld metal zone is compressive in case of maraging steel and medium alloy medium carbon steel weld metals. When it comes to the case of austenite weld the residual stress at the center of the weld metal zone is tensile. welding inspection courses in Kochi.

The similar metal welds will show symmetrical fusion zone and heat affected zones, whereas the dissimilar metal welds shows un symmetrical fusion zone and heat affected zones. The difference in the thermal conductivity of materials is the reason for the unsymmetrical nature. In medium alloy medium carbon steel the width of heat affected zone is more when compared to maraging steel. The residual stress in similar metal weld of maraging steel is compressive and in similar metal weld of medium alloy medium carbon steel it is tensile. In case of dissimilar metal weld it is compressive in maraging steel and tensile in medium alloy medium carbon steel.