Surface modification method of duplex type stainless steels by the pack boriding process

Abstract

This work presents the investigation of a boriding process on two grades of stainless steel namely UNS32750 super duplex stainless steel and UNSS31803 duplex stainless steel in order to improve material properties and possibly to reduce catastrophic failure of industrial components. Usage of duplex stainless steels has become customary in the fields of oil and refinery, marine and pipeline applications due to increased corrosion resistance; however, these materials exhibit low wear characteristics. To overcome this problem, in this work the pack boriding process was employed. Evaluation of effects of the boriding process on the microstructure and mechanical properties was performed using scanning electron and optical microscopy, Vickers hardness tests and wear tests. It was shown that the 4 h process resulted in the greatest boriding layer thickness yielding the maximum surface hardness of 1407 HV in the super duplex stainless steel UNS32750 while this value was 1201 HV in the duplex stainless steel UNSS31803. Wear resistance of borided materials were up to 6-fold greater than those of non - treated materials. Also, the borided duplex materials were shown to be more suitable for industrial applications for valve and shaft components as compared to the boronized super duplex stainless steel.