Effect of Finish Cooling Temperature on Properties of High Strength Engineering Machinery Steel

High strength steel which meets the requirement of Q690 and Q620 in GB/T 16270-1996 was obtained through grain refinement strengthening,transformation strengthening and precipitation strengthening by two stage controlled rolling followed by accelerated cooling.It was found that the mechanical properties were especially sensitive to the finish cooling temperature.Yield strength,tensile strength and yield ratio increased while elongation decreased with the decrease of the finish cooling temperature.Good low temperature toughness was obtained for the experimental steel.The formation of acicular ferrite was helpful to the improvement of low temperature impact toughness and uniformly distributed equiaxed M-A islands were less detrimental to low temperature impact toughness.