Nickel to Stainless Dissimilar Metal Welding

Kristopher Doll

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.