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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
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
Base and Weld Metal PropertiesStainless 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 80 58
Elongation 60% 17% 45%
Service Temperature (F) 800 1500 1200
Composition Ni 10-14%Cr 16-18%Mo 2-3%Fe 62-72%C .03-.08%
Ni 58%Cr 20-23%Mo 8-10%Nb 3-4%
Ni 50-55%Cr 17-21%Mo 2.8-3.3%Nb 4.8-5.5%Fe BalanceTi 0.7-1.2% Al 0.2-0.3%
* www.matweb.com** Special Metals Corporation, INCONEL alloy 625 and INCONEL alloy 718
316 to 718 Welding Concerns
• Base Metal Dilution– Typically 20-50% for GTAW– Determined chemically or
by cross sectional area– Reduces mechanical properties
and corrosion resistance
Image: Avery, R. Pay Attention to Dissimilar Metal Welds. Chem. Eng. Prog. (1991)
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
Estimated Fusion Zone Composition with 625 filler
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
718 Welding Concerns
• Microfissuring– Low heat input
Grain boundaries melt and crack
• Laves Phase– High heat input
intermetallic precipitates
Gordine, J. Some Problems in Welding Inconel 718. Welding Research Supplement. 1971
Groove Design for 718
Groove Shape Root Opening
Gordine, J. Some Problems in Welding Inconel 718. Welding Research Supplement. 1971
Welding ApproachProcess GTAW
Electrode 3/32”
Nominal Amperage 150 DCEN
Shielding Gas Argon
Filler Diameter 3/32”
Travel Speed (ipm) 1-6
Welding Parameters
Recommended Welding Parameters(For 1/2” plate with GTAW)
Base Metal 316 718
Nominal Amperage 200-300 120
Travel Speed (ipm) 10-12 3
Preliminary Experiments
60° Vno root gap
60° V.03” root gap
90° V.03” root gap
Weld did not reach root Incomplete Fusion Un-fused weld metalin root gap
Weld and HAZ Hardness Survey
0.0 0.2 0.4 0.6 0.8 1.0 1.245
50
55
60
65
70
Distance (inches)
Har
dnes
s Roc
kwel
l A
Nickel 718 Stainless 316Nickel625
177
138
108
88
75
Approximate U
TS (ksi)
Nickel 718 62.0
Stainless 316 62.6
HRA Before Welding
Weld
Nickel 718(solutionized)
130
Nickel 625(weld metal)
120
Stainless 316(annealed)
80
Reported UTS (ksi)from Technical Literature
Transverse Weld Tensile Test
Tensile (ksi) 91.6
Area Reduction 31%
316 718 316Properties Derived from Test
625 to 718 (ksi) 107
625 to 304 (ksi) 92
Reported Dissimilar MetalWeld Tensile Strength *
*Reference: Special Metals Corporation, INCONEL alloy 625
Root Penetration Experiment
0 0.01 0.02 0.03 0.040
0.020.040.060.08
0.10.120.14
90° Chamfer U GrooveRoot Gap (in)
Root
Pen
etra
tion
(in)
90° Chamfer
U Groove
Increasing Root Gap
718 718
718 718
316
316
316
316
Summary of Results
• HAZ and Dilution– 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.