Effect of multi-pass friction stir processing on microstructure and mechanical properties of cast ASTM A۲۱۶-WCB alloy

One of the main problems in oil and gas pipelines is abrasion corrosion on the edges of the flowchannel in the plug and ball valves. Under normal conditions, the gas is moving at a pressure of about۱۴۵ bar and an approximate speed of ۷۰ feet per second; The suspended particles in the gas collidewith the edges of the flow channel and cause severe erosion on them. Abrasion resistance of steelsdepends mainly on their surface properties and can be increased by increasing the surface hardness byfriction stir processing (FSP). In this study, A۲۱۶-WCB steel, which is used in the manufacturing ofcasting parts for valves, flanges and fittings, was processed using a friction stir process for one andthree passes. The microstructure, hardness and wear properties of the processed area wereinvestigated. Due to the friction stir process, the ferrite grain size in the stirred zone decreased from ۲۵microns to about ۳ microns. The hardness of the stir zone increased from ۱۶۵ Vickers (HV) to about۷۸۰ HV. Also, the abrasion resistance of the stirring area increased up to ۲.۵ times.