During fabrication of modified 9Cr–1Mo steels, δ-ferrite formed in the weld metal and heat-affected zone may not transform completely to austenite during subsequent cooling. The influence of changes in weld metal composition on δ-ferrite content was investigated using weld pads produced using basic coated P91 electrodes from four different manufacturers. The weld pads were designated Electrodes 1, 2, 3, and 4 according to the different manufacturers. Electrodes 1 and 3 fully complied with the EN ISO 3580-A CrMo91 specification. Electrode 2 had very low nickel and high niobium contents, and Electrode 4 had carbon content above the maximum allowable limit. Thermo-Calc results showed that the temperature range over which a mixture of δ-ferrite and austenite is stable (the Ae4 − Ae3 temperature range) was smaller by more than 100 °C for Electrode 2 when compared with those of the other three electrodes. The limited (Ae4 − Ae3) temperature range, high ferrite factor, and chromium − nickel balance value of Electrode 2 were associated with an increase in the δ-ferrite content of the weld metal. Metallography results confirmed a significant amount of δ-ferrite in the as-welded microstructure of Electrode 2. Thermo-Calc estimates for the amount of δ-ferrite at high temperatures were supplemented by experimental anneal heat treatment on the weld metal. High-temperature anneal heat treatments were carried out at 1320 °C and 1420 °C. The amount of δ-ferrite in the high-temperature annealed and quenched samples was significantly lesser than predicted by Thermo-Calc property diagrams.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Price excludes VAT (USA)
Tax calculation will be finalised during checkout.
Pandey C, Mahapatra MM, Kumar P, Saini N (2018) Some studies on P91 steel and their weldments. J Alloy Compd 743:332–364
Arivazhagan B, Kamaraj M (2013) "A study on influence of D-ferrite phase on toughness of P91 steel welds." White Paper, Steel-Grips. Com: 19–24
Liu XY, Fujita T (1989) Effect of chromium content on creep rupture properties of a high chromium ferritic heat resisting steel. ISIJ Int 29(8):680–686
Swindeman RW, Santella ML, Maziasz PJ, Roberts BW, Coleman K (2004) Issues in replacing Cr–Mo steels and stainless steels with 9Cr–1Mo–V steel. Int J Press Vessels Pip 81(6):507–512
Pandey C, Giri A, Mahapatra MM (2016) Evolution of phases in P91 steel in various heat treatment conditions and their effect on microstructure stability and mechanical properties. Mater Sci Eng, A 664:58–74
Arivazhagan B, Srinivasan G, Albert SK, Bhaduri AK (2011) A study on influence of heat input variation on microstructure of reduced activation ferritic martensitic steel weld metal produced by GTAW process. Fusion Eng Des 86(2–3):192–197
Onoro J (2006) Martensite microstructure of 9–12% Cr steels weld metals. J Mater Process Technol 180(1–3):137–142
Honda T, Kusano T, Osada T, Hirano K, Takemoto K (1998) Development of 9Cr-2W cast steel for the valves in elevated temperature fossil power plants. In Advanced heat resistant steels for power generation (San Sebastian, 27–29 April 1998, preprints)
Roberts BW, Swindeman RW, Maziasz PJ, Wright IG (2001) TVA experience in the application of 9Cr–1Mo–0.2V–Cb (Grade 91) steel. Paper Presented at the EPRI Conference on 9Cr Materials Fabrication and Joining Technologies, July 10–11, Myrtle Beach, South Carolina, USA.
Wang Y, Mayer KH, Scholz A, Berger C, Chilukuru H, Durst K, Blum W (2009) Development of new 11% Cr heat resistant ferritic steels with enhanced creep resistance for steam power plants with operating steam temperatures up to 650 C. Mater Sci Eng, A 510:180–184
I received financial support from the Southern African Institute of Welding.
Conflict of interest
The authors declare that they have no conflict of interest.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Recommended for publication by Commission IX—Behaviour of Metals Subjected to Welding
About this article
Cite this article
Mahlalela, S.S., Pistorius, P.G.H. Investigation of ẟ-ferrite content in weld metal of modified 9Cr–1Mo electrodes using thermodynamic modelling and quenching experiments. Weld World 66, 1191–1198 (2022). https://doi.org/10.1007/s40194-022-01272-x