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