In order to study the kinetics of bainite continuous transformation, AISI 4340 steel was austenitized in a temperature range of 950～1150℃ to obtain different austenite grain sizes(AGS) and then step-cooled to room temperature.
By means of thermal dilatation a AISI 4340 steel was austenitized at some different temperatures in a range from 900 to 1? 150? ℃ to obtain different austenite grain sizes(AGS),then rapidly cooled to room temperature to obtain martensitic structures.
Experimental results differentiated the effects of the various coatings on the AISI 4340 steel behavior when submitted to fatigue testing and the influence of coating thickness on the fatigue strength.
In the abrasive wear mode, the wear rate of ADI was comparable to that of alloyed hardened AISI 4340 steel, and approximately one-half that of hardened medium-carbon AISI 1050 steel and of white and alloyed cast irons.
The fracture of AISI 4340 steel at a yield strength of 200 ksi (1378 MN/mm2) occurs by nucleation and subsequent growth of voids formed by fracture of the interface between manganese sulfide inclusions and the matrix.