IMPROVEMENT OF THE CAVITATION EROSION RESISTANCE OF UNS 31803 STAINLESS STEEL BY DUPLEX TREATMENT

• Published in: Tecnologia em Metalurgia, Materiais e Mineracao Vol. 20101124; pp. 700 - 708
• Main Authors: Mesa, D H, Eduardo Pinedo, Carlos, Paulo Tschiptschin, Andre
• Format: Journal Article
• Language: English
• Published: 01.01.2010
• Subjects: Austenite; Austenitic stainless steels; Cavitation; Crystallography; Duplex stainless steels; Ion nitriding; Steels; Tribology
• ISSN: 2176-1515

A Duplex surface treatment consisting of High Temperature Gas Nitriding (HTGN) followed by Low Temperature Plasma Nitriding (LTPN) was carried out in an UNS S31803 duplex stainless steel. The HTGN treatment was intended to produce a relatively thick and hard fully austenitic layer giving mechanical support to the thinner and much harder expanded austenite layer. HTGN was performed at 1200 degree C for 3 hours, in a 1 atm N(2) atmosphere while LTPN was carried out in a 75%N(2)+25%H(2) atmosphere, at 400 degree C for 12 hours. An expanded austenite YN layer, 2.3 urn thick, 1500 HV0.025 hard, was formed on top of a 100 urn thick, 330 HV 0.1 hard, fully austenitic layer, containing 0.9 wt% N. For comparison purposes Low Temperature Plasma Nitriding (LTPN) was carried out with UNS S30403 stainless steel specimens obtaining a 4.0<m thick, 1500 HV 0.025 hard, expanded austenite layer formed on top of a fully austenitic matrix having 190 HV 0.1. The nitrided specimens were tested in a 20 kHz vibratory cavitation erosion testing equipment. Comparison between the duplex treated UNS S31803 steel and the low temperature plasma nitrided UNS S30403 steel, resulted in incubation times almost 9 times greater. The maximum cavitation wear rate of the LTPN UNS S31403 was 5.5 g/m(2)h, 180 times greater than the one measured for the duplex treated UNS S31803 steel. The greater cavitation wear resistance of the duplex treated UNS S31803 steel, compared to the LTPN treated UNS S30403 steel was explained by the greater mechanical support the fully austenitic, 330 HV 0.1 hard, 100<m layer gives to the expanded austenite layer formed on top of the specimen after LTPN. A strong crystallographic textured surface, inherited from the fully austenitic layer formed during HTGN, with the expanded austenite layer showing {101} crystallographic planes//surface contributed also to improve the cavitation resistance o f the duplex treated steel.