Effect of Cryogenic Treatments on Mechanical Properties of AISI 420 Stainless Steel

DARJA JENKO; J. PEREZ IPIÑA; W. R. TUCKART; G. PRIETO

Portoroz

Congreso; 20th Conference on Materials and Technology; 2012

Institute of Metals And Technology, Slovenia

The objetive of this study was to determinate the effect of cryogenic treatment on hardness and impact toughness on martensitic AISI 420 stainless steel. Research made over the last three decades has indicated that wear resistance of steel alloys can be improved substancially by deep cryogenic treatment. In order to establish its influence on the microstructure before and after its application, optical and high resolution transmission electron microscopy with X-Ray microanalysis were used. While hardness was evaluated with the Vickers technique, impact toughness by mean of Charpy V tests, and the micromechanisms of fracture surfaces were analyzed by scanning electron microscopy images. All the specimens were heated up to 1030 °C in an argon atmosphere and oil quenched. Liquid nitrogen was used as cooling medium to achieve cryogenic temperature (-196,4 °C). Two cooling methods were employed, one by direct immersion of specimens in the nitrogen, and the other one, a controlled cooling of 27 °C/min. Soaking time varied between 1 and 2 hours at cryogenic temperature. After that, all samples were tempered at 410 °C during 25 minutes in a furnace cooling. Microstructural changes, hardness and absorbed energy during impact were studied. From the analysis of the obtained results, it was found that the best properties were achieved with one hour of soaking time with controlled cooling. This treatment developed a hardness increase in the order of 10%, compared to the quenched and tempered condition. Although the absorbed energy decreased in the same order of magnitude, in all cases, SEM analysis of fracture surfaces showed the presence of dimples.