Hardfacing overlay of AISI 4130

[Beth22]

Hi,
I am creating a new WPS for hardfacing overlay of AISI 4130 Q&T using the parameters below:
Base metal Tensile: 655 MPa; Hardness: 235 HBW
Filler: Stellite 6 (SFA-5.21; ERCoCr-A)
Process: GTAW
Preheat temp: 225ºC
Current: 90-94 A
Voltage: 10-13 V
Travel Speed: 50-90 mm/min
Heat Input: 0.921 to 1.156 kJ/mm
PWHT Temp: 635 ºC Holding Time: 5 hrs
Test coupon size: 10” x 10” x 1” (extracted from 15” dia. shafting
But after using the parameters above I still can't meet our HAZ hardness requirements of 250HV (0.039" from fusion line).
Thanks if someone could help

 

[EdStainless]

That close to the weld your C levels will higher because the overlay is 1% C.
What is the hardness as deposited? Is it tempering at all?

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P.E. Metallurgy, Plymouth Tube

 

[Beth22]

HAZ hardness: 293HV, 344HV and 438HV
WM hardness: 311HV - 432HV
Base metal hardness: 188HV - 210HV

 

[metengr]

I would use an Inconel butter layer over the 4130, PWHT and overlay with Stellite.

 

[Beth22]

metengr, but our client requires us to use Stellite 6 without a butter layer. Actually we already have a newly qualified WPS also hardfacing using stellite but different base material (A36 and A487) and this is the last WPS we need to qualify but I am a little bit stuck up on what else I can do or change on my parameters to lower the hardness on HAZ.

 

[metengr]

Your PWHT is too low to reduce the hardness of this material. If you cannot use a butter layer, then increase the PWHT temperature to 660 deg C. Also, using a temper bead technique may help to temper the previous weld passes in addition to the elevated PWHT. 4130 is a different material in comparison to what you previously qualified using A36 or even some grades of A487.