The influence of Al on the mechanical properties of hot rolled steel plates

The influence of Al on the impact behaviour and strength of hot rolled steels has been examined. The steels had a nominal composition of 0.1%C,1.4%Mn with Al contents of 0.02,0.2, 1 and 2% at two levels of Si, 0.02 and 0.3%. The steels were hot-rolled, finish rolling at similar to950degreesC. The 0.3% Si addition was generally beneficial increasing the yield strength by similar to30MPa without any detrimental influence on the impact behaviour. Exceptionally low impact transition temperatures(-90-100degreesC) were obtained in the very coarse grained ferrite/pearlite steel containing 0.2%Al. Measurement of the grain boundary carbide thickness in this steel found it to be very fine suggesting this is the reason for its excellent toughness. Increasing the Al level to 2% encouraged martensite formation resulting in a marked deterioration of impact behaviour. It appears that Al is very effective in slowing down the diffusion of carbon as well as preventing the growth of carbides. The yield strength of these steels, in accord with their coarse grain size, was low and adding Al produced very little strengthening.