Contents lists available at ScienceDirect International Journal of Pressure Vessels and Piping journal homepage: www.elsevier.com/locate/ijpvp Infuence of tempering treatments on mechanical properties and hydrogen embrittlement of 13wt% Cr martensitic stainless steel Sunil Kumar Bonagani a,c, ⁎ , Vishwanadh B. b , Sharma Tenneti d ,NaveenKumarN. b , Vivekanand Kain a,c a Materials Processing & Corrosion Engineering Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India b Materials Science Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India c Homi Bhabha National Institute, Anushaktinagar, Mumbai, 400094, India d Indian Navy, India ARTICLEINFO Keywords: Martensitic stainless steel Tempering Hydrogen embrittlement Slow strain rate tensile testing ABSTRACT Theinfuenceoftemperingtreatmentsonmechanicalpropertiesandhydrogenembrittlement(HE)of13wt%Cr martensitic stainless steel (MSS) have been investigated by Charpy impact tests and slow strain rate tensile (SSRT)testsfollowedbyfracturesurfaceexamination.Theaustenitizedandquenchedspecimensweretempered at 300, 550 and 700°C for 2.5h. The MSS tempered at 550°C showed brittle intergranular (IG) fracture after impact tests indicating its susceptibility to temper embrittlement. The experimental results showed that the 13wt% Cr MSS is sensitive to HE. The as-quenched condition showed cracking during hydrogen pre-charging itself. Hydrogen pre-charging duration increased the susceptibility to HE of tempered MSS. The maximum HE susceptibility was observed for specimen tempered at 550°C with a drastic reduction in strength and strain to failure. Tempering at 300 and 550°C showed brittle IG fracture with hydrogen pre-charging in SSRT tests whereasincreasedIGregionwithductiledimpleswasobservedforspecimentemperedat700°Cwithincreaseof pre-charging duration. The reason for maximum susceptibility to HE of specimen tempered at 550°C is due to synergistic interaction of hydrogen and impurities segregated at prior austenitic grain boundaries. 1. Introduction Martensiticstainlesssteels(MSSs)suchasType403,410&420are used as parts of pumps, valve seats, stem rods, nut and blots in light water reactors (LWRs) and also in other industries. MSSs are used be- cause of their good mechanical properties and moderate corrosion re- sistance [1,2]. MSSs, as the name implies, derive strength from the transformation of austenite to martensite on fast cooling from an aus- tenitization temperature. The hardened (martensitic microstructure) condition is highly brittle and tempering is done to improve the duc- tilityandtoughness,reducetheresidualstress&dislocationdensityand to increase the machinability of MSS in the hardened condition [3–5]. The efect of tempering treatments on mechanical properties of steels hasbeenatopicofinterestoverthepastfewdecadesastheproperties ofthesesteelscouldbetailoredbytheheattreatments[6,7].Thefnal microstructure obtained after heat treatments plays an important role in controlling the mechanical properties. MSSs, often did not show decrease in hardness with increase of tempering temperature at fxed tempering duration [4]. The phenomenon of secondary hardening as- sociated with fne carbide precipitation was also observed for some of the MSSs with tempering [4]. MSSsaresusceptibletotemperembrittlement(i.e.decreaseinnotch impact toughness of the material) in the tempering temperature range of450–600°C.Thereasonfortemperembrittlementhasbeenshownto bethesegregationofimpurityelementsi.e.phosphorous(P)alongthe prior austenitic grain boundaries (PAGBs) [3,8–10]. The phenomenon oftemperembrittlementhasbeenknownforalongtimeinthecaseof lowalloysteelswhensubjectedtotemperingbelow600°Cbutmainly inthetemperaturerangeof350–550°C[11,12]. The yield strength of the temper embrittled steels is not particularly high and is less than 1000MPa[13]. The cracking associated with impurity segregation in temperedMSSsandinquenched&temperedsteelsarecharacterizedby brittle intergranular (IG) fracture with low impact toughness value as observed in impact toughness tests [3,4,8–13]. Itiswellknownthatthehighstrengthsteelsarehighlysusceptible to hydrogen embrittlement (HE) than the low strength steels. The https://doi.org/10.1016/j.ijpvp.2019.103969 Received 5 June 2018; Received in revised form 9 May 2019; Accepted 13 August 2019 ⁎ Corresponding author. E-mail addresses: bsunil@barc.gov.in (S.K. Bonagani), bvisu@barc.gov.in (B. Vishwanadh), tenneti.sharma@gmail.com (S. Tenneti), naveenm@barc.gov.in (N. Naveen Kumar), vivkain@barc.gov.in (V. Kain). International Journal of Pressure Vessels and Piping 176 (2019) 103969 Available online 16 August 2019 0308-0161/ © 2019 Elsevier Ltd. All rights reserved. T