Evaluation of post weld heat treatments and susceptibility to sulfide stress corrosion cracking of simulated HAZ in forged supermartensitic stainless steel UNS S41427

Abstract

Supermartensitic stainless steels (SSMSs) with 12–13%Cr, 5%Ni, 2%Mo and microadditions were developed to casings, tubullars and mandrels used in the oil and gas off-shore production. These materials have great resistance to aqueous medium containing large amounts of CO2 and can withstand high temperatures and large amounts of chloride as well. However, SMSSs have a limited resistance to H2S containing solutions, and may fail due to sulfide stress cracking (SSC). This limit is even lower for forged and welded components that used in mandrels. Recent studies have been developed to find an operational envelope for safe use of SMSSs in sour production systems. The present study shows the results of slow strain rate testing (SSRT) of a forged V-alloyed SMSS submited to thermal simulation in Gleeble machine to produce a coarse grain heat affected zone (HAZ). The microstructure of the HAZ is characterized by fresh martensite, intergranular delta ferrite and fine precipitates which increase the hardness to a level above the maximum limit for sulfide stress corrosion cracking. The effects of two post weld heat treatments (PWHT) on the mechanical properties and susceptibility SSC were evaluated. Single and double tempering treatments provoked the decrease of hardness and the increase of ductility parameters. However, specimens representative of the HAZ, base metal, and HAZ with single and double tempering presented high SSC susceptibility parameters in SSRT in saline solution (200,000 ppm NaCl) with 1.0 psia of H2S partial pressure, and pH 4.5.