MechEracing
Mechanical
- Sep 17, 2004
- 3
I'm working on qualifying a weld procedure for hard surfacing of a valve and running into some hardness concerns.
Base Material for weld procedure: Q&T 4340
Process: PTAW Auto
Filler Material: Cobalt-Chrome based powder
C: 1.58, Mn: .42, Si: 1.50, Cr: 26.79, Ni: 2.26, W: 4.40, Fe: .50, Co: Bal
Overlay machined/ground to .040" layer (Applied in one layer)
Hardness should be a minimum of 43 HRc. We are obtaining hardness values of 38-41 HRc with an alloy Q&T base material, 4340 or 9310 6" diameter bar stock and 3" diameter bar stock.
Previous testing was completed on a 1" thick 304SS block, hardness values came in at 43-45 HRc. Also conducted testing on low carbon steel tubing 1" wall, hardness values came in at 48-51 HRc.
Parameters were the same between all weld test, except the 304SS block was welded with a weave/oscillation. 304SS had two layers applied. Carbon steel tubing was one layer and two layer samples. Allow steel bar were one and two layers.
I have not been able to draw any conclusions as to why the hardness values are lower on the alloy steel material. At .040" thickness, dilution is playing a factor, but it seems odd the alloy steel would have the lowest hardness value. With the low carbon steel tubing the hardness changed very little at surface clean-up of the hard surfacing layer, approximately .125" thick, versus the final .040" thickness. At first glance the low carbon from the 304 and low carbon steel might be a factor, but the 9310 has carbon values in the .07-.13 range (Mn .4-.7, Si .15-.35, Cr 1.0-1.4, Ni 3.0-3.5, Mn .08-.15)
Any ideas as to why the change in hardness would be greatly appreciated. Thank you!
Base Material for weld procedure: Q&T 4340
Process: PTAW Auto
Filler Material: Cobalt-Chrome based powder
C: 1.58, Mn: .42, Si: 1.50, Cr: 26.79, Ni: 2.26, W: 4.40, Fe: .50, Co: Bal
Overlay machined/ground to .040" layer (Applied in one layer)
Hardness should be a minimum of 43 HRc. We are obtaining hardness values of 38-41 HRc with an alloy Q&T base material, 4340 or 9310 6" diameter bar stock and 3" diameter bar stock.
Previous testing was completed on a 1" thick 304SS block, hardness values came in at 43-45 HRc. Also conducted testing on low carbon steel tubing 1" wall, hardness values came in at 48-51 HRc.
Parameters were the same between all weld test, except the 304SS block was welded with a weave/oscillation. 304SS had two layers applied. Carbon steel tubing was one layer and two layer samples. Allow steel bar were one and two layers.
I have not been able to draw any conclusions as to why the hardness values are lower on the alloy steel material. At .040" thickness, dilution is playing a factor, but it seems odd the alloy steel would have the lowest hardness value. With the low carbon steel tubing the hardness changed very little at surface clean-up of the hard surfacing layer, approximately .125" thick, versus the final .040" thickness. At first glance the low carbon from the 304 and low carbon steel might be a factor, but the 9310 has carbon values in the .07-.13 range (Mn .4-.7, Si .15-.35, Cr 1.0-1.4, Ni 3.0-3.5, Mn .08-.15)
Any ideas as to why the change in hardness would be greatly appreciated. Thank you!
