Effect of Interrupted Quenching on the Microstructure, Mechanical Properties and Dislocation Density of Steel AISI 4340

The effect of interrupted quenching on the microstructure, mechanical properties and dislocation density of steel AISI 4340 is studied. Metallographic and x-ray diffraction analyses are performed. Tensile tests are conducted. The Vickers hardness is measured. The dislocation density is calculated. The effect of the duration of the hold at 300 degrees C during the interrupted quenching on the structure and properties of the steel is considered. It is shown that a duplex structure represented chiefly by martensite and bainite forms after interrupted quenching by all the variants studied. The duplex structure affects positively the properties of steel AISI 4340. The dislocation density, the ultimate strength and the hardness are the highest in the steel containing 34.7% bainite, 55% martensite and 10.3% retained austenite after the interrupted quenching at 300 degrees C with a 5-min hold.