The combination of the chemistry of UNS R30035 (33-37% Nickel, 19-21% Chrome, and 9-10.5% Molybdenum, small additions of Titanium and Iron (1% max each), Carbon, Manganese, Silicon, Phosphorous and Sulphur (all less than 0.15% each), and with Cobalt as the balancing element (around 33%) together with the strength and toughness imparted by cold working and ageing of the material make this an expensive material relative to nickel alloys and stainless gardes. No one wants to make a mistake and end up scrapping material.
So, while we are not welders ourselves, we have gone out to seek the best advice we can, and are indebted to Thomas C. Williams, Applications Engineer – Energy of Carpenter Technology Corporation for the advice below.
The good news is that UNS R30035 can be welded and can be likened to 304 stainless. The same preparations and precautions must be used for any ASM Ni Co Alloys.
The following parameters are recommended for gas-tungsten-arc welding (GTAW) based on work with 1.5 mm to 6.5 mm pieces:
- Argon gas flow rate: 9.4 to 11.8 L/minute (20-25 feet3/hour)
- Weld speed: 140 mm/minute (5.5 in / minute)
- Voltage: 10V
- UNS R30035 filler wire feed: 355 to 560 mm / minute (14-27 in/minute).
The heat input per pass should be kept low (approximately 50-65% of that used for 304 stainless)
We would also caution machinists and fabricators that exposure to temperatures above the recommended aging levels may result in a significant (and non-reversible) loss of strength caused by the reversion of the cold worked metallurgical structure to a much softer annealed structure. Of course, the recommended ageing levels also depend on the specification the material is aimed at and the properties aimed for – for further information on this point see article 2 and article 3 in this series.
This does mean that the weld’s heat affected zone (HAZ) will have been weakened by the elevated temperatures in the near-weld region. It is not possible to recover strength lost in the HAZ by re-ageing. The weld can be solution annealed to relieve residual stresses from the welding process but strengthening would require a subsequent cold work process.
As we mentioned in article 4, we recommend that the material contains 33-37% Nickel, 19-21% Chrome, 9-10.5% Molybdenum, Titanium and Iron (1% max each), Carbon, Manganese, Silicon, Phosphorous and Sulphur (less than 0.15% each). Cobalt is the balancing element (around 33%), and all precautions must be taken to avoid dust inhalation or dust coming into contact with bare skin.
This is the last in this series of articles – Broder Metals Group hope that these articles have been useful and would welcome enquiries for our stock range and any questions not covered.
Acknowledgement: all values quoted are courtesy of Carpenter Technology Corporation: “MP35N: A Superalloy for Critical OIL and Gas Applications”