Weldability evaluation of high tensile plates using GMAW process

High tensile plates, SAILMA-450 high impact (HI) (yield strength, 45 kg/mm( 2) minimum; ultimate tensile strength, 57 kg/mm(2) minimum; elongation, 19% minimum; Charpy impact energy 2.0 kg.m at -20 degrees C minimum) were succ essfully developed at the Steel Authority of India Ltd., up to 32 mm plate thickness. Since then the steel has been extensively used for the fabricati on of impellers, bridges, excavators, and mining machineries, where welding is an important processing step. The present study deals with the weldability properties of SAILMA-450 HI pl ates employing the gas metal are welding process and carbon dioxide gas. Im plant and elastic restraint cracking tests were conducted to assess the col d cracking resistance of the weld joint under different welding conditions. The static fatigue limit values were found to be in excess of minimum spec ified yield strength at higher heat input levels (9.4 and 13.0 kJ/cm), indi cating adequate cold cracking resistance. The critical restraint intensitie s, K-cr, were found to vary between 720 and 1280 kg/mm(2), indicating that the process can be utilized for fabrication of structures involving moderat e to low restraint intensities (200 to 1000 kg/mm(2)). Lamellar tear tests conducted using full thickness plates at heat input levels ranging from 10 to 27 kJ/cm showed no incidence of lamellar tear upon visual, ultrasonic, a nd four-section macroexamination. These tests were repeated using machined plates, such that the midthickness of the plates (segregated zone) correspo nded to the heat affected zone of the weld. No cracks were observed, indica ting good lamellar tear resistance of the weld joint. Optimized welding con ditions were formulated based on these tests. The weld joint was subjected to extensive tests to assess the physical properties and soundness of the w eld joint. The weld joint exhibited good strength (64.7 kg/mm(2)) and impac t toughness (5.7 and 3.5 kg.m at -20 degrees C for weld metal and heat affe cted zone properties. Crack tip opening displacement (CTOD) tests carried o ut for parent metal, heat-affected zone, and weld metal resulted in delta m values of 0.41, 0.40, and 0.34 mm, respectively, which indicates adequate resistance to cleavage fracture. It was concluded that the weld joint confo rms to the requirements of SAILMA-450 HI specification and ensures a high i ntegrity of the fabricated products.