Microstructure, Toughness and Hardness of a Simulated HAZ in Steel S1100QL and of the HAZ of an Actual MAGWelded Joint Made Using a Metallic Flux-Cored Wire

Abstract

Simulation tests discussed in the article involved structural steel S1100QL having a yield point of more than 900 MPa. The simulations included single (Tmax = 1250°C) and double welding thermal cycle (Tmax = 1250°C + 600°C, Tmax = 1250°C + 760°C and Tmax = 1250°C + 900°C) as well as cooling times t8/5 = 3, 5 and 10 s. Specimens with the simulated heat affected zone (HAZ) were subjected to impact strength tests performed at a temperature of -40°C and +20°C, Vickers hardness tests (HV10) and microscopic metallographic tests (involving light microscopy). Test results were presented in diagrams and photographs. Related comparisons included results of the structural, hardness and toughness tests of simulated HAZs with analogous results obtained during the actual repair welding of a MAG-welded joint made of steel S1100QL. The final part of the article contains discussion concerning the test results and the statement concerning the obtainment of the significant conformity of the phase composition and the morphology of the microstructure as well as the average hardness values of the HAZ areas obtained in the simulations and those of the HAZ area obtained in the actual welded joint. In relation to all tested simulation variants, the impact energy of the simulated HAZ area of steel S1100QL satisfied the minimum criterion of KV = 27 J both in relation to a test temperature of -40°C and that of +20°C. The number of repeated (1 through 4) thermal cycles having preset parameters did not trigger explicitly noticeable changes in impact energy values as regards the simulated HAZ of steel S1100QL.