The influence of thermomechanical treatment on the microstructure and mechanical properties of aisi 4130 steel

Ultra high strength AISI 4130 Steel samples were submitted to various rolling schedules in order to find the rolling conditions leading to the optimum combination of strength and toughness. Reheating temperatures between 900 to 1230°C and reductions between 15 to 90% were employed. Rolling temperatures above Ar3 and also between 620 and 700°C were used and in some experiments annealing was applied to the samples. The influence of the above parameters on the microstructure and mechanical properties of the samples was studied by measuring the variation of their hardness, tensile and impact properties as well as using optical and scanning electron microscopy. The results show that by a judicious control of reheat temperature, percent deformation, interpass time, finish rolling and annealing temperatures it is possible to obtain fine ferrite and nodular colonies of pearlite with small interlammelar spacing. The results are discussed in the frame work of classical nucleation theory and the possible mechanisms which may be responsible for the observed behavior are proposed.