Austenitic Stainless Steel

FN ranges for austenitic (2)

1. 0-3 FN -> A, AF 2. 3-20 FN -> FA

Suutala Diagram for austenitic (2)

1. 1.5 magic cr/ni, cracking susceptibilty 2. curve with vertical line at 1.5, left is cracking, right is safe

Original Base Composition Name for austenitic

1. 18-8

stabilized grades of austenitic (3)

1. 321 (Ti) 2. 347 (Nb Ta) 3. 348 (Nb Ta)

intermediate temp embrittlement (sigma) for austenitic (6)

1. 600-800C 2. increases with higher Cr, Mo, Si 3. decreases with Ni, N, C 4. reduces toughness and ductility 5. most damaging when continuous 6. minimize with full austenitic FM

Alloy variations for austenitic (5)

1. H - high carbon 2. L - low carbon 3. N - nitrogen 4. F - free machining 5. S - sensitization

Precipitation rx for austenitic (4)

1. M23C6 carbides 2. MC carbides 3. nitrides and carbonitrides 4. sigma and alpha' for high Cr

PHIC for austenitic ss

1. PH not required 2. IC at 350F max

type FA solidification behavior austenitic (4)

1. Skeletal or lathy ferrite (at higher cr/ni) 2. diffusion controlled transform of ferrite to austenite

type F solidification behavior austenitic (3)

1. acicular ferrite or widmanstatten austenite in ferrite matrix 2. diffusion controlled transform of ferrite to austenite 3. widmanstatten austenite precipitates at grain boundary

type AF solidification behavior austenitic (3)

1. austenite with eutectic ferrite 2. ferrite forms at end of solidification 3. some dissolution possible during cooling

Cryogenic issues with austenitic ss (3)

1. austenitic ss has high toughness at cryogenic temps 2. ferrite reduces cryogenic toughness 3. ferrite control is critical for cryogenic

prevent corrosion with austenitic (2)

1. composition (high cr, L, stabilized) 2. welding procedures (low heat input, min time in range, solution HT)

DDC in austenitic (4)

1. dramatic drop in ductility in solid state 2. fully austenitic weld metal and HAZ, large grain size and low impurity 3. intergranular failure 4. 310, 316, high purity-high nickel

factors that control WM liquation cracking in austenitic (4)

1. ferrite number 2. grain size 3. heat input 4. impurity content

factors that control HAZ liquation cracking in austenitic (4)

1. heat input 2. grain size 3. impurity levels 4. ferrite potential of base metal

Benefits of ferrite solidification for austenitic (7)

1. high solubility of impurity elements 2. better high temp ductility 3. lower CoTE 4. smaller solidification range 5. less partitioning during solidification 6. FA,F GB are not easily wetted 7. tortuous crack path

effect of restraint on sol. cracking in austenitic ss (2)

1. large contraction stresses with A, AF 2. effect of thick sections

Filler metals for austenitic ss (3)

1. matching 2. 308, 309 for solidification cracking 3. Ni base - corrosion or transition

weld metal liquation cracking in austenitic (3)

1. multipass welds 2. fully austenitic deposits are more susceptible 3. liquation at GB in PMZ

PWHT for austenitic ss (3)

1. not required for thin sections 2. stress relief @ 650C, watch for embrit phases 3. solution anneal (expensive)

reheat cracking in austenitic (3)

1. occurs during PW stress relief 2. WM and HAZ 3. associated with 347

How does ferrite solidification reduce cracking susceptibility in austenitic ss (2)

1. peritectic/eutectic rx at the end of solidification GB 2. austenite/ferrite boundaries have poor wetting and tortuous path

importance of solidification control for austenitic (2)

1. primary ferrite solidification reduces cracking susceptibility 2. weld metal ferrite content indicates solidification behavior

Corrosion issues with austenitic (2)

1. sensitization 2. SCC

Weldability issues for austenitic (8)

1. solidifcation cracking 2. liquation 3. reheat 4. DDC 5. Cu contamination 6. Corrosion 7. intermediate temp (sigma) embrittlement 8. lack of penetration

effect of impurity content on sol. cracking in austenitic ss (2)

1. strong partitioning during solidification 2. eutectic films and boundary wetting

Uses for austenitic ss (4)

1. structural 2. corrosion protection 3. decorative 4. kitchen

300 series austenitic general service temp

1700F

Free machining grade austenitic ss

303, high sulfur

workhorse grade austenitic

304

High temp austenitic alloy

310, high Cr and Ni

3 examples of HAZ segregation liquation cracking for austenitic ss

316, 310, 304

2 examples of HAZ penetration liquation cracking for austenitic ss

321, 347, b and Ti carbides

influence of solidification mode on sol cracking in austenitic ss

A is most susceptible, F is most resistant

austenite solidification mode that are resistant to sol. cracking

FA

effect of rapid solidification in austenitic ss

HED welding shifts solidification mode to A

A weld metal transformation for austenitic

L -> L + A -> A

AF austenite weld metal transformation for austenitic

L -> L + A -> L + A + (A + F)e -> A + F_e

F austenite weld metal transformation for austenitic

L -> L + F -> F + A_ss

FA austenite weld metal transformation for austenitic

L -> L + F -> L + F + (F + A)e/p -> F + A_e/p

plot of weld sol. cracking based on sol. mode for austenitic

Sharp decrease thru FA

eutectic triangle for austenitic ss

a, af, fa, f

Copson curve for SCC in austenitc

based on wt % Ni, parabola

Cu contamination cracking in austenitic

copper penetrates the austenite GB

Plot of sigma phase on toughness for austenitic

exponential decreasing based on % of sigma

modified suutala diagram

for HED austenitic welding, 1.7 is magic number

type A solidification behavior austenitic

fully austenitic

pitting resistance in austenitic

function of Mo content

reheat c curve plot for austenitic

nose of plot if in stress relief range

low temp sensitization in austenitic

service temp below 300C for extended period of time