Mr. Hamid,
The cracking and other issues during overlay could be due to metallurgical incompatibility, thermal stress
and dilution problems.
Cracks could be due to differential thermal expansion and solidification behaviour. Brittle intermetallic
formation from Zr-Fe or Zr-Ni interaction.
Buffer layer with ER Ni-1 is not absorbing thermal/mechanical or metallurgical mismatch between Ni-1 and
Zr alloy. It could also be due to improper preheat/interpass temp or weld pool control.
Recommendations:
1. Try with a multi-layer buffer overlay or use the first layer with ERNiCr-3 (inconel 82) or ERNiCrMo-3 (inconel 625)
which has a better metallurgical compatibility and ductility.
2. Second layer with ERNi-1, keeping it thin and to control dilution.
3. Then apply ERZr-2.
4. Use stringer beads and keep low heat input.
5. Though Pre heat for SS is not recommended, pre heat to 100-150 deg. C will help to reduce the thermal shocks.
6. Keep interpass temp within 150 deg. C.
7. Even though PWHT is not applicable to Zr. alloys, controlled cooling will help to avoid cracking.
8. SR with 300-350 deg. C for 1 to 2 hrs. hold time and Argon purged or vacuum furnace may help.
This will help to reduce sharp transitions and thermal expansion and composition.
If ERZr-2 is not suitable, consider ERZr-1 or other Zr based alloys with improved weldability.
You can also try with proprietary Zr filler wires with better GTAW compatibility from other leading
manufacturers.
rgds,
C Sridhar.
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