Though I have not done actual overlay, what I could gather from the available literature is that, F6NM Stainless Steel weld overlay is
commonly done in hydro turbine parts, valve internals, and pump sleeves . The success of overlay depends much more on dilution control,
hydrogen control, and post-weld hardness management than on the actual deposition process itself.
F6NM / CA6NM is a P6, air hardening low carbon martensitic stainless steel with approx. 13% Cr + 4% Ni + 1% Mo. Its UTS is 750-950 MPa, Yield 550-750 MPa, 15-22% EL and hardness 259-320 HB. Major issues observed during overlay are: Underbead cracking; delayed hydrogen
cracking; toe cracking after 24–72 hrs; hard martensitic HAZ overlay disbonding during service.This happens because F6NM transforms to
untempered martensite very easily during cooling.Typical HAZ hardness without proper control would be 420–550 HV and highly crack-sensitive.
To avoid them, a mandatory preheat at 150–250°C and an inter pass temperature of 180–250°C to be maintained. Low heat input should be
avoided as it causes fast cooling and forms martensite structure. Typical heat input range could be 1.5-2.0 kJ/mm. Excessive high heat input
may create Ferrite in-balance. Final overlay (Stellite, Ni alloy 625 or SS) should be done after buttering with ER 309L to avoid martensitic cracking;
PWHT at 580–620°C (furnace cooled up to 300 Deg C) for 2–4 hrs or controlled welding with preheat + slow cooling is recommended to improve
toughness. Usually a 2- layer minimum deposit is done; First layer may have high dilution and the second or third layer will have required chemistry.
Low hydrogen consumables, dry shielding gas, and clean surface are required to avoid Hydrogen (due to moisture/contamination) are mandatory.
Preferred furnace cooling or insulation blanket cover to avoid fast cooling. Recommended hardness targets are HAZ < 350 HV; Overlay transition
< 380 HV; Higher values usually indicate cracking risk.
For restrained and heavy F6NM components, no direct deposit on the cold base metal should be done. Never stop welding midway and leave partially
heated components overnight. Maintain minimum holding temperature until welding completion. A large number of failures originate from thermal
cycling interruptions.
Trust above info. may be of help to you.
C Sridhar.
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Hi respected group members,--
Pl share some experience on weld overlay on F6Nm material?Regards,
On Friday, May 8, 2026, 7:15 PM, sridhar cn <sridharcn305@gmail.com> wrote:
From the available Technical literatures.CS.
--On Fri, 8 May 2026 at 09:58, Kannayeram Gnanapandithan <kgpandithan@gmail.com> wrote:
could pl share the reference where it is givenTHANKS & BEST REGARDS,KG.PANDITHAN, BE, IWE,ISO 9712 Level 2 in VT,ASNT-Level II in PT,MT,RT & UT,LA ISO 9001-2015, ISO 3834, EN 1090 & EN 15085,International Welding Engineer.CONSULTANT-WELDING & QUALITYMobile no: +919940739349
--On Mon, May 4, 2026 at 3:18 PM Ashishranjan - Domech Fabricators Pvt.Ltd. <planningdfplril@gmail.com> wrote:
Yes, you can use multiple PQRs to support a single WPS under AWS as well but it’s handled a bit differently than in ASME Section IX, and you need to be careful about how you justify it.Regards,
Ashish Ranjan
+91 9555864374
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--On Mon, Mar 2, 2026 at 2:56 PM praba karan <prabakaran776@gmail.com> wrote:
Dear experts,
For procedure qualification as per ASME SEC IX- "Multiple PQRs may support one WPS",
Likewise can we follow the same practice in AWS also? Because which is not mentioned directly on the code that we can use multiple PQRs to support one WPS.(And I'm not using prequalified WPS)
Thanks & regardsPrabaharan--
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