1. Nickel to Stainless Dissimilar Metal Welding
Kristopher Doll

2. Nickel to Stainless Dissimilar Metal Welding Project Objectives
Assess mechanical properties of a 316 to 718 weld
Determine relationship of groove design to root penetration

3. Nickel to Stainless Dissimilar Metal Welding Presentation Overview
Base and Filler Metal Properties
Welding Concerns
Experimental Results
Hardness Survey
Transverse Weld Tensile Test
Groove Geometry

4. Base and Weld Metal Properties
Stainless 316L* (Annealed)
Nickel 625 ** (All-Weld-Metal)
Nickel 718 ** (Solutionized)
Primary means of Strengthening
Cold Work
Solid Solution Strengthening
Precipitation Hardening
UTS (ksi) 80
120
130
Yield (ksi) 35 58
Elongation
60%
17%
45%
Service Temperature (F)
800
1500
1200
Composition
Ni %
Cr % Mo 2-3%
Fe %
C %
Ni 58% Cr % Mo 8-10% Nb 3-4%
Ni % Cr %
Mo % Nb %
Fe Balance Ti % Al % *
** Special Metals Corporation, INCONEL alloy 625 and INCONEL alloy 718

5. 316 to 718 Welding Concerns Base Metal Dilution
Estimated Fusion Zone
Composition with 625 filler
Base Metal Dilution
Typically 20-50% for GTAW
Determined chemically or by cross sectional area
Reduces mechanical properties and corrosion resistance
20%
50%
Nickel 53 45
Chromium 21 20
Iron 9 22
Molybdenum
8.5
6.5
Niobium
3.9
2.7
Titanium
0.1
0.3
Dilution is very sensitive to welding technique. Dilution increases with root penetration.
Image: Avery, R. Pay Attention to Dissimilar Metal Welds. Chem. Eng. Prog. (1991)

6. Nickel Alloy Welding Concerns
Root Penetration
Nickel has high viscosity and low thermal conductivity
Weld pool is “Sluggish”
Solidification Shrinkage
Weld Craters
Must gradually decrease heat input
Dilution is very sensitive to welding technique. Dilution increases with root penetration.

7. 718 Welding Concerns Microfissuring Laves Phase
Low heat input  Grain boundaries melt and crack
Laves Phase
High heat input  intermetallic precipitates
Gordine, J. Some Problems in Welding Inconel Welding Research Supplement

8. Groove Design for 718 Groove Shape Root Opening
Gordine, J. Some Problems in Welding Inconel Welding Research Supplement

9. Welding Approach Welding Parameters Process GTAW Electrode 3/32”
Nominal Amperage
150 DCEN
Shielding Gas
Argon
Filler Diameter
Travel Speed (ipm)
1-6
Recommended Welding Parameters (For 1/2” plate with GTAW)
Base Metal
316
718
Nominal Amperage
120
Travel Speed (ipm)
10-12 3

10. Preliminary Experiments
60° V
no root gap
60° V
.03” root gap
90° V
.03” root gap
Weld did not reach root
Incomplete Fusion
Un-fused weld metal
in root gap

11. Weld and HAZ Hardness Survey
HRA Before Welding
Nickel 718
62.0
Stainless 316
62.6
Nickel 718
Stainless 316
Nickel 625
177
138
108 88 75
Approximate UTS (ksi)
Reported UTS (ksi) from Technical Literature
Nickel 718 (solutionized)
130
Nickel 625 (weld metal)
120
Stainless 316 (annealed) 80
718 – aging and solutionizing/overaging – annealing. It was originally cold worked. Weld zone – dilution with On par with properties in the literature of dissimilar metal weld
Good – weld is stronger than annealed 316.

12. Transverse Weld Tensile Test
Properties Derived from Test
Tensile (ksi)
91.6
Area Reduction
31%
Reported Dissimilar Metal Weld Tensile Strength *
625 to 718 (ksi)
107
625 to 304 (ksi) 92
Tensile strength – exactly as reported in technical literature. Broke at 45 degrees right in the weld zone. The 718 midsection did not even yield. Effective yield strength and ductility cannot be determined because non-uniform stress distribution.
It wasn’t supposed to fail in the weld, however…
*Reference: Special Metals Corporation, INCONEL alloy 625

13. Root Penetration Experiment
U Groove
718
316
718
316
CNC Machined U groove and 90 degree chamfers. Used shim to get root gap. Tacked together and welded; then EDM’d down the middle and sanded down. Nickel and steel oxides have different colors, so you can tell how large the weld zone is.
Lack of fusion when V groove and no gap – difficulty focusing arc at the root. Did not have this problem with U groove.
General increasing trend, but lots of variance – very sensitive to welder technique. Interpass temperature as well – the bead becomes wide and shallow when it’s red hot. However, it would have taken me much longer if I had to quench and dry the sample after each pass.
U grooves take more metal to fill and are difficult to make, so if the design allows for a root gap >.03”, use 90 degree V.
90° Chamfer
718
316
718
316
Increasing Root Gap

14. Summary of Results HAZ and Dilution Transverse weld tensile strength
Solutionized 718 gets stronger in HAZ
Dilution reduces strength of fusion zone
316 approaches annealed properties in HAZ
Transverse weld tensile strength
92 ksi with ductile failure in weld zone
Root penetration
Very sensitive to welding technique
U-grooves superior for small root gaps.
No significant difference for large root gaps.