This paper describes the welding of two dissimilar metals of grade A335 P22 and P91 Chromium-Molybdenum low alloy steels by Gas Metal Arc Welding (GMAW) by using pure argon as shielding gas.

To obtain the good welded joint several practical trails were taken on by changing various welding parameters. During the trails it was felt that preheating (above 210 0C) was required before welding to obtain a good welded joint.

After optimization of welding parameters practically several numbers of plates of size 300 mm × 110 mm × 6 mm were welded in butt welding position and the welded workpieces were taken for investigation.

Tensile strength, percentage elongation, impact toughness and micro hardness of the weldments were measured to investigate the mechanical properties of the weldments. The ultimate tensile strength (UTS) of both the base metals were tested.

The UTS of P91 was found higher than P22. The longitudinal ultimate tensile strength of weldments was found higher than both the base metals. During transverse tensile testing of weldments all the specimens were broken from P22 base metal side. Therefore, it may be concluded that the welded joints were stronger than the base metal. Whereas the percentage elongation of the longitudinal tensile specimens was found much less than both the base metals due to increase in hardness in the welded joint.

Micro hardness test results show that the hardness was increased in HAZ and weld metal zone. Impact toughness of weldments were found higher than both the base metals. Microstructure of the weldments was investigated by an optical microscope. Formation of martensite in the heat affected zone (HAZ) towards P22 steel side was identified whereas mixture of martensite and bainite was found in the weld metal zone.

This martensite and bainite were responsible for the increase in the hardness of HAZ and weld metal zone as compared to the base metal. Defect free good welded joints were obtained between P22 and P91 steel with GMAW.

This article is shared by Pradip Mandal and A. K. Pathak of Mechanical and Manufacturing Engineering Department, NIAMT