Vol.2, No1&2, 2002, pp. 5-10
UDC 620.1:669.14

A part of results of complex experimental analysis (hardness measurement, tensile test of smooth and notched specimens, impact toughness, microstructure and fractography) of two weldable high strength low alloyed, quenched and tempered steels, with ultimate tensile strength (UTS) of 900 MPa and yield strength about 0.95UTS, produced by different procedures, is presented. Instrumented Charpy tests results in testing temperature range +20 to -100°C, dealing with crack initiation and propagation energy are also included.

To understand better the microstructure and mechanical properties of heat-affected-zone of these steels, the specimens are produced of samples heat treated by two quenching and four tempering temperatures with corresponding microstructure, that can simulate different regions of the heat-affected-zone. The effect of different test temperatures applied in impact testing of Charpy V specimens on the behaviour of different microstructures which can be obtained during welding is analyzed in the paper.

The analysis revealed significant differences in impact energy required for fracture in dependence of microstructure and testing temperature, followed by different crack initiation to crack propagation energy ratio and differences in fractured surface appearance.

Keywords: high-strength low-alloyed steels, quenching and tempering, Charpy V specimen, instrumented impact test, crack initiation to crack propagation energy ratio, fracture surface appearance