Weldability pc

Metals & Their Weldability

Pallav Chattopadhyay

Weldability

• No universally accepted meaning

• AWS Definition :“The capacity of a metal to be welded under the fabrication conditions imposed, into a specific, suitably designed structure, and to perform satisfactorily in the intended service”

Weldability

• C-Mn Steel

• Low Alloy Steel (Cr-Mo / Cr-Mo-V steel)

• Quenched & tempered Steel

• Stainless Steel

• Ni Alloys

• Al Alloys

• Ti Alloys

Weldability of C-Mn Steel

• C – 0.15% max, Mn- 1.65%max, Cu & Si- 0.60% max• SA516 Gr60 / 70, SA537 Cl.1, SA 106 Gr.B, SA 105• CE (IIW) = C + (Mn/6) + [(Cr+Mo+V)/5]+ [(Ni+Cu)/15]

• Excellent weldability upto CE = 0.45• Comparatively less susceptible to Hydrogen cracking• Preheat / PWHT called for only higher thk (>30mm)• Suitable for all type of Arc & other Welding processes• Weld soundness is not problem with Killed steels



Typical CCT Diagram


• SMAW– Matching electrodes available for chemistry / strength level– Low Hydrogen electrodes (E7018) reduce chance of

Hydrogen cracking– Baking & Storage of electrode – Moisture free

• GTAW / GMAW– Suitable bare electrodes available like SMAW– Electrodes with de-oxidizer preferred to reduce chance of

porosity (e.g. ER 70S-2)– Argon based gas mixtures for GTAW – CO2 / Argon-CO2 Mixture for GMAW– Proper cleaning / packing / storage of Filler metal & good

quality Shielding gas required


• FCAW– Self Shielded / Gas Shielded consumables available

– Shielding Gas – CO2 / CO2-Argon mixture (e.g. E71T-1)

– Normally low in Hydrogen level – baking not required

• SAW– Solid (even Metal Cored wires) wire + Suitable Flux

– Fused / Agglomerated Flux (Mostly Neutral)

– Solid wire – Cu coated / Flux – requires Redrying

– Desired properties – As welded / With PWHT


• Other Welding Processes– Electro Slag / Electro Gas Welding:

• Suitable Consumable available

• May require additional Heat Treatment as per Code

– Oxy Acetylene Welding:• Suitable consumable available

• Slower than Arc Welding – Extensive heating of steel / slow cooling

• Chance of imperfection more


• Other Welding Processes– Resistance Welding:

• Spot/ Seam/ Flash / Upset welding possible

• Heating / Cooling rates higher

– Electron / Laser Beam Welding:• Readily weldable

• Rapid Heating & Cooling rates – Smaller grains in Weld / HAZ

• Fully Killed steel preferred

Weldability of Cr-Mo / Cr-Mo-V Steel

• Cr : 0.5 ~ 9%, Mo : 0.5 ~ 1%, V : ~0.25% & C 0.20%

• Cr provides improved oxidation & corrosion resistance

• Mo provides better elevated temp properties

• Good weldability

• High hardenability (Most of them Air-hardenable)

• Rapid cooling from above Ac3 temperature (~900°C) strength , hardness , ductility & toughness

• Requires Tempering (~650°C) to restore the properties

• PWHT at >680°C (Typical: 680-705°C) mandatory for all thickness


SA 387 Gr - 11 CL - 2

SA 336 Gr - F11 CL - 2

SA 336 Gr - F11 CL - 3

SA 387 Gr - 22 CL - 2

SA 336 Gr- F22 CL- 3

SA 335 Gr - P5

SA 387 Gr - 5 CL - 2

SA 542 Type D CL.4a

Product From. Plate Forgings Forgings Plate Forgings Smls.pipe Plate PlateC, Max. 0.04 - 0.17 0.10 - 0.20 0.10 - 0.20 0.04 - 0.15 0.05 - 0.15 0.15 0.15 0.09 - 0.18Mn, Max 0.35 - 0.73 0.30 - 0.80 0.30 - 0.80 0.25 - 0.66 0.30 - 0.60 0.30 - 0.60 0.25 - 0.66 0.25 - 0.66Cr, Max. 0.94 - 1.56 1.00 - 1.50 1.00 - 1.50 1.88 - 2.62 2.00 - 2.50 4.00 - 6.00 3.90 - 6.10 1.08 - 2.62Mo, Max. 0.40 - 0.70 0.45 - 0.65 0.45 - 0.65 0.85 - 1.15 0.90 - 1.10 0.45 - 0.65 0.40 - 0.70 0.85 - 1.15V, Max. - - - - - - - 0.23 - 0.37

-SA 387 Gr - 11 CL - 2

SA 336 Gr - F11 CL - 2

SA 336 Gr - F11 CL - 3

SA 387 Gr - 22 CL - 2

SA 336 Gr- F22 CL- 3

SA 335 Gr - P5

SA 387 Gr - 5 CL - 2

SA 542 Type D CL.4a

Tensile strength (Min)Ksi 75 - 100 70 - 95 75 - 100 75 - 100 75 - 100 60 75 - 100 85 - 110Mpa 515 - 690 485 - 660 515 - 690 515 - 690 515 - 690 415 525 - 610 585 - 760

Yield strength (Min)Ksi 45 40,000 45,000 45 45 30 45 60Mpa 310 275 310 310 310 205 310 415

Elongation in 8 inch (200mm) min,%

18.00 - - - - - - -


22.00 20.00 18.00 18.00 19.00 - 18.00 18.00

Reduction of area, min %

- 40 40 45.00 40.00 - 45.00 -

Chemical properties

Mechanical properties


• Highly susceptible to Hydrogen Induced Cracking / Cold Cracking

• Use of Low Hydrogen consumables is must

• Control on welding Heat Input

• Appropriate Preheat (~125-200°C), De Hydrogenation Treatment (300-400°C) and Intermediate Stress relieving (640-660°C) mandatory to prevent cracking

• In between cooling to room temperature not allowed – followed by DHT /ISR

• High Cr(>5%)-Mo/ Cr-MoV steel calls for Direct PWHT after welding


• Susceptible to Temper Embrittlement while operating between 375-575°C

– Control tramp elements (P, Sn, Sb, As etc) in Base metal & Weld metal (‘J’ factor & ‘X’ factor respectively)

– “J” Factor : (P+Sn) x (Mn+Si) x 104 100

“X” Factor : (10P+5Sb+4Sn+As) / 100 15 ppm

– Perform Step cooling treatment and measure shift in DBTT

. STEP COOLING HEAT TREATMENT

1hr (1) 15hr (1) 24hr (1) 60 hr (2) 100 hr (3)

STEP COOLING HEAT TREATMENT

COOLING RATE ( °C / Hr. )Sr.No.

REQUIRED ACTUAL(1) 5.6 (MAX.) 5.0(2) 2.8 (MAX.) 2.5(3) 27.8 (MAX.) 25

538°C524°C 496°C

468°C315°C air/furnacecooling

593°C

50 °C/hr

TEMPER EMBRITTLEMENT TEST

0306090

120150

180210240270300

-50 -40 -30 -20 -10 0 10 20 30 40TEMPERATURE(°C)

AB

SO

RB

ED E

NER

GY

(J)

MIN.PWHT AVG.TW1 MIN.PWHT+ SC AVG.TW2

54J

TT54= -27°C TT54SC= -22 °C

TEMPER EMBRITTLEMENT PARAMETER : TT54 + 3TT54 <10 °C

Where, TT54 = TT54SC - TT54


• Arc Welding Processes– Suitable weld consumables available for all types of Arc

Welding processes

Consumable Table

SMAW GTAW SAW1.25Cr-0.5Mo E 8018 B2 ER 80S B2 EB2 + Suitable Flux2.25Cr-1Mo E 9015 B3 ER 90S B3 EB3 + Suitable Flux2.25Cr-1Mo-0.25V E 9018 G ER 90S G Union S1CrMo 2V (Brand name)5Cr-0.5Mo E 8018 B6 ER 80S B6 EB6 + Suitable Flux9Cr-1Mo E 8018 B8 ER 80S B8 EB8 + Suitable Flux9Cr-1Mo-0.25V E 9018 B9 ER 90S B9 EB9 + Suitable Flux

Weld Consumable Steel


• Other Welding Processes– Resistance Upset Welding:

• Sometimes used for Longitudinal seam welding of Cr-Mo pipes & tubes

• Strip roll formed to shape – continuously welded to make Tubes using high frequency AC and forging by pressure rolls

• High localized heat inputs and fast cooling rates – low ductility• Sometimes PWHT performed in welding machine only

– Electro Slag Welding:• Primarily used for 3” thickness• Filler wire same as SAW is used• Large build-up of heat – automatic preheating + Stress relief• Subsequent Annealing / Normalizing is mandatory

Weldability of Quenched & Tempered Steel

• Heat Treatment Condition: Quenched & Tempered• High YS, UTS with good toughness, ductility &

weldability• Alloy addition to achieve desired mechanical

properties – mainly Ni, Cr, Mo, Mn, V• Welded structures normally don’t need PWHT except

Stress Relieving


Typical Chemistry & Properties

CHEMICAL COMPOSITION

SA 533 Gr - B CL-3

SA 517 Gr. - F

SA 533 Gr - B CL-1

SA 533 Gr - B CL-2

HY-80

Product From. Plate Plate PlateC, Max. 0.25 0.08-0.22 0.25 0.25Mn, Max 1.07-1.62 0.55-1.10 1.07 - 1.621.07 - 1.62Si, Max. 0.13-0.45 0.13-0.37 0.13 - 0.450.13 - 0.45 0.15-0.35Cu, Max. - 0.12-0.53 - - 0.25Ni, Max. 0.37-0.73 0.67-1.03 0.37 - 0.730.37 - 0.73 2.00-3.25Cr, Max. - 0.36-0.69 - - 1.00-1.80Mo, Max. 0.41-0.64 0.36-0.64 0.41 - 0.640.41 - 0.64 0.20-0.60V, Max. - 0.02-0.09 - - 0.03Cb, Max. - - - -Boron, Max. - 0.005-0.006N - -

SA 533 Gr - B CL-3

SA 517 Gr. - F

SA 533 Gr - B CL-1

SA 533 Gr - B CL-2 HY-80

Tensile strength (Min)Ksi 100-125 105-135 80 - 100 90 - 115 Mpa 690-860 725-930 550 - 690 620 - 795

Yield strength (Min)Ksi 83 90 50 70 80Mpa 570 620 345 485


- - - -


16.00 14.00 18.00 16.00

Mechanical properties


• Appropriate joint design (No Stress-raisers), good workmanship & adequate Inspection checks are MUST

• Preheat extremely critical – to be chosen carefully• Excess preheat / Interpass temp– Slower coling rate –

re-austenitized zone near weld metal transform to Ferrite + High C Martensite /Bainite

• Heat input needs to be controlled on lower side • Excess heat input – Reduction in Strength, Toughness


• All Arc Welding processes available • Electro Slag / Electro Gas/ Multiple wire SAW requires

re-heat treatment due to high heat input• EBW / LBW preferred• Small stringer weld beads – good toughness• Selection of weld consumable – based on mechanical

property requirement (many times non-matching chemistry)

• Very sensitive to Hydrogen cracking – allows extremely low level of moisture / Hydrogen in weld metal (target: 2ml/100gm)


• Manual / Mechanized oxy fuel cutting allowed – remove 2-3mm hardened zone by grinding

• Machine cutting preferred• Arc gouging allowed – with less heat input• Gas gouging not allowed• Brazing allowed – but may require Q&T since brazing

temp is high

Weldability of Stainless Steel

• Major types:– Chromium Martensitic SS– Chromium Ferritic SS– Austenitic SS– Precipitation hardenable SS– Duplex / Super Duplex SS

• Relatively high coefficient of thermal expansion / low thermal conductivity

• Protection of molten arc mandatory – prevent chromium oxide formation

• Pre-weld & Post-weld cleaning crucial – prevent C contamination / Surface oxidation

• All welding processes other than Oxy-acetylene welding recommended

Weldability of Martensitic Stainless Steel

• Essentially Fe-Cr-C alloys with 11.5-18% Cr• Rapid cooling – hardened structure• E410NiMo, E410 are commonly used consumables• Weldability improved if welded by Austenitic SS cons.• Weld joints require PWHT to get optimum property• Susceptible to Hydrogen cracking• Preheat & Interpass control required• Suitable for all Arc welding processes• Resistance welding (Spot & Flash) possible• EBW, FSW possible

Weldability of Ferritic Stainless Steel

• Fe-Cr-C alloys with>11.5% Cr+ other Ferrite stabilizer (Mo, Al, Ti, Cb etc) – Low C content

• Non Air-hardenable

• Few Matching filler metal available – however Austenitic SS / Ni based alloys used as weld metal

• Susceptible to cracking under high restraint / surfacing

• Preheat (~150°C) may be required

• Mostly used in ‘As-welded’ condition – No PWHT

• All types of Arc welding possible

• Resistance welding / Other welding processes available

Weldability of Austenitic Stainless Steel

• Typical 18%Cr-8%Ni steel

• Cr- Oxidation / Corrosion resistance, Ni & Mn- Stabilize Austenite

• Better Ductility & Toughness (FCC structure)

• Intentionally little Delta Ferrite (3~8%) added in Weld metal– to reduce hot cracking sensitivity

• Excessive Delta Ferrite also not allowed – compromise in corrosion resistance / sigma phase at high temp exposure


Delong Diagram


• Improper welding condition (long arc, lack of proper shielding etc) change Delta Ferrite content

• Sensitization: Slow cooling between 750-375°C – Cr carbide precipitation at Grain boundaries – Corrosion attack

• Preheat not required

• Interpass temp control extremely important

• Stress corrosion cracking – Presence of stress + Halogen atmosphere

• PWHT not required

• Suitable for all types of Arc welding / Plasma welding, Resistance and other welding processes (EBW, FSW)

Weldability of PH Stainless Steel

• Precipitation Hardenable (PH) SS possess high strength with reasonably simple heat treatment – Martensite formation / Precipitation hardening

• Three types – Martensitic, Semi-Austenitic & Austenitic

• Martensitic: Martensitic structure + Ageing

• Semi-Austenitic: Initially Austenite after Cooling – Reheat and cool to convert to Martensite + Ageing

• Austenitic: Austenite + Ageing

• Mostly require PWHT after Welding to restore properties

• All Arc welding / Resistance Welding is possible

• Stringent control on weld parameters / heat input

Weldability of Duplex Stainless Steel

• Typical 40-50% Ferrite + Balance Austenite

• Corrosion (mainly Pitting) resistance + High strength / toughness

• Low coefficient of Thermal expansion – like CS

• Less prone to hot cracking

• High heat input / interpass: HAZ loses Ductility/ toughness, Phase balance disturbs

• Clean joint, good fit-up very important

• Preheating not required

• PWHT must be avoided (Sigma/ Chi/ Alpha Prime embrittlement)

• Arc Welding processes / High energy beam welding done

Weldability of Duplex Stainless Steel

Micro Of Standard Duplex Dark Areas:- Ferrite Light Areas:- Austenite

Weldability of Ni Alloys

• Ni – FCC structure upto Melting point

• Pure Ni & Solid solution of Ni-Cu, Ni-Cr-Fe, Ni-Cr-Mo widely used

CHEMICAL COMPOSITION

Nickel 200

Monel 400 Incoloy

825Inconel

625

C, Max. 0.08 0.2 0.03 0.05Mn, 0.2 1.00 0.5 0.2Si, 0.2 0.20 0.25 0.2Cu, . 0.1 31.5 2.25 0.2Ni 99.5 66.5 42 61Cr, 21.5 21.5Mo, 3 9Fe 0.1 1.2 30 2.5

Weldability of Ni Alloys

• Extremely sensitive to surface cleaning / preparation

• Suitable filler metal available for most arc welding process

• Resistance Welding, Oxyacetylene Welding, High Energy Beam welding possible

• Preheat not required

• Heat input and Interpass temp must be restricted

• Viscous weld metal – prone to solidification / end cracker cracking – suitable technique required

• PWHT usually not required – however not detrimental

Weldability of Al Alloys

• Thermal & electrical conductivity – 4 times of Steel

• Higher heat input required

• Highly prone to oxidation - Refractory oxide formed – removed / broken during welding

• Most fusion / solid state welding possible

• Suitable filler wires available for arc / oxy-fuel welding

• Weld prone to cracking – hot shortness, HAZ inter-granular crack, lesser strength + shrinkage stress

Weldability of Al Alloys

• Prevented by using higher alloyed filler wire

• Surface / Joint cleaning very important

• Preheat – normally not required except high thickness

• AC / DC welding suitable

• Special technique required to prevent crater cracking

• GTAW / GMAW / Solid state welding - most preferred

• Usually PWHT not required

Weldability of Ti Alloys

• Highly reactive – requires protection from atmosphere

• Extremely sensitive to cleaning – special reagents used

• GTAW, GMAW, Plasma & Solid state welding popular

• Gas shielded welding: Use of Trailing gas in addition to High purity Shielding & Purging gases

• Highly susceptible to porosity

• Colour of weld bead confirms protection from oxidation

• PWHT normally not required

• No Preheat

• Very stringent Interpass temp & Heat input control

• Solid state welding preferred for dissimilar welding

Weldability of Ti Alloys

Weld Colour Probable Cause and Treatment

Light Straw, Dark Straw, Light Blue Surface oxide. Remove by wire brushing with new stainless steel wire brush.

Dark Blue, Grey Blue, Grey Metal contamination. Welds should be removed and done over after corrections in shielding are made.

White (loose deposit) Metal contamination. Welds should be removed and done over after corrections in shielding are made

Engineering

Weldability pc