CTU in Prague

Faculty of Mechanical Engineering

Ing. Petr Vondrouš, PhD., IWE

Weldability

1st semester 2015/2016

ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování

Hodnocení svařitelnosti

Welding and weldability

Welding is heating locally material to a high temperature, and is

possibly accompanied by this detrimental phenomena. Then is

stress in the weld, stress concentration… Welding have influence on

structure safety, on prize…

AREA Causes Change of properties Defects, where

Heated Phase changes Annealing, recrystalization,

precipitation, grain coarsening,

segragation

Change of mech.

Properties in HAZ

Molten Fast segregation Non homogeneous properties in WM,

HAZ

Soliidification cracks

in WM , HAZ

Fast

cooled

Metastable phases Change of mechanical properties -

martenzite, retained austenite.

Loss of ductility,

Cold cracks

Knowledge of Material weldability

Change of material properties due to weld thermal cycle.

Influence of

Chemical compostion.

Material production method

Heat treatment

If materials have different properties, then their weldability will differ.

Imagine welding such semiproducts

Shrinkage

Segragation

Weldability (joinability) -definition

Technologist view Weldability is technological property of

material, an ability of material to be welded.

Explanation from ISO/TR 581

Component is weldable by a process if metallic continuity can

be obtained by suitable procedure. Weld shall also comply

requirments in regard of metallurgical and mechanical

properties.

Explanation of AWS

Capacity of metal to be welded under fabrication conditions

into suitably designed structure to perform inteded service.

Often is used to determine welding process and to compare

materials. Weldability is not easy to be quantified. Weldability

is similar to quality in broad meaning.

Weldability by process[1]

Material Arc welding

Oxy-

acetylene

welding

Electron

beam

welding

Resistance

weldingBrazing Soldering

Adhesive

bonding

Cast iron C R N S D N C

Carbon steel

and low-alloy

steel

R R C R R D C

Stainless

steelR C C R R C C

Aluminum

and

magnesium

C C C C C S R

Copper and

copper alloysC C C C R R C

Nickel and

nickel alloysR C C R R C C

Titanium C N C C D S C

Lead and

zincC C N D N R R

Thermoplasti

c† N N N N N N C

Thermosets N N N N N N C

Elastomers N N N N N N R

Ceramics N S C N N N R

Dissimilar

metalsD D C D D/C R R

TABLE 1. Metallurgical compatibility of metal pairs:

Metals: Al: aluminum; Ag: silver; Au: gold; Cu: copper; Pt: platinum; Ni: nickel;

Fe: iron; Ti: titanium; and W: tungsten.

Key: C: Complex structures may exist; X: Intermetallics compounds formed—

undesirable combination; S: Solid solubility exists in all alloy

combination; D: Insufficient data for proper evaluation; and N: No data available

from http://www.industrial-lasers.com/articles/2012/03/fiber-laser-welding-of-

dissimilar-materials.html

Weldability according to ISO/TR 581

Weldability is governed by 3 factors, each of them can be

decisive.

From - Weldability Of Thermo-Mechanically Rolled Steels Used In Oil And Gas Offshore Structures Joshua

Omajene, Jukka Martikainen, Paul Kah

Weldability evaluation

What can be the customer demand on „weld product quality“?

strength safety

production volume

precision assembly

price lead time

What is your demand on these welded structures?

balcony flower pot holder

IKEA clothes holder

weekend bugy

student formula

production car

ship

bridge

Weldability evaluation

Weldability is very complex property, all is interrelated.

The best to evaluate weldability, i.e. fulfillment

of all demands on welded structure, is to create the structure and test it.

Yet is it possible and meaningful?

Testing of balcony flower pot holder - evaluation not needed

IKEA clothes holder – rigid testing done, needed

weekend bugy- evaluation not needed

student formula-needed

production car– rigid testing done, pre-production series

ship – testing needed, yet not full scale

bridge– testing needed, yet not full scale

Testing of weldability must be simplified, yet with good results, secure.

Different levels of quality requirements are to be fulfilled acc. to product.

Weldability evaluation

Testing of weldability must be simplified, yet with good results, secure.

How to do it?

not needed – easy, highest risk

when needed

1. Theoreticaly from past experience, books in library- past experience,

calculation of material composition, CCT, CET

2. Practically by welding

On simplified piece- normalized weldability tests – weld ductility,

tensile test

On representative piece - normalized weldability tests

On piece to be welded- welding process qualification

Ad. 1. Much experience summarized into simply to apply calculations –

summarized in norms, material composition,CCT, CET

e.g. C-Mn steels have excellent weldability upto C=0,2 %, CE=0,45 %,

preheat only for thick sheets (30 mm), suitable for all welding methods

Serves for TECHNOLOGY PREPARATION, For very simple tasks

Practical weldability evaluation

normalized weldability tests – weld ductility, tensile test

For new materials, complicated ones where research must be done as

data do not exist. Serves for RESEARCH and process qualifications

On piece to be welded- welding process qualification of DEMANDING

PRODUCTS

Scientific approach

Knowledge of CCT, cooling speeds enables knowing phases, properties

It needs precise measurement and know how

Experience of many experiments summarized into simply to apply

general calculations – summarized in norms

Material weldability

Steels

C-Mn

HSLA – Cr-Mo, Cr-Mo-V

Quenched and tempered steels

Thermomechanically treated steel

High alloy steel

Stainless

…

Al alloys

Ni alloys

Ti alloys

…

If materials have different chemical, mechanical, physical properties,

then their weldability will differ.

Weldability of steels

C-Mn – excellent weldability upto C=0,2 %, CE=0,45 %,

preheat only for thick sheets (30 mm),

suitable for all welding methods

HSLA – Cr-Mo, Cr-Mo-V low alloy,

oxidation, corrosion resistence, good weldability, but high hardenability (in

air), preheat or PWHT needed, control of q, temper embittlement

Quenched and tempered steels – already in heat treated state, structures

will be effected, stress relieve, critical preheating , excess heat input,

stringer beads, low hydrogen, HAZ can transform to martensite, bainite,

oxy fuel cutting problematic, grinding, gouging

Thermomechanically treated steel

High alloy steel

Stainless – martensitic, austenitic, feritic, duplex

Tool steels

Influence of Chemical composition

over time summarized into Practical recommendations and

calculations:

Norm ISO 15608 - places materials into weldability groups

Steels have 11 groups, every group has different weldability issues

Norm 1011 – Recommendations for fusion welding

CET – carbon equivalent – combined influence of elements on

cold cracking

Preheat temperature

Hot cracking factor – sensitivity to segregation and solidification

cracking

Lamellar tearing factor

…

Weldability is often judged by susceptibility to certain detrimental

phenemona, i.e. cold cracking, hot cracking…

http

://w

ww

.iiw

india

.com

/pdf/

Sum

mary

%20IS

O%

20T

R%

20156

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Meta

llic_M

ate

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_G

roupin

g_S

yste

m.p

df

Carbon equivalent for ferittic steels

• In ČSN EN 1011-2 is presented CET for method B:

wt.%

Suitable for steels 1-4 acc. to ISO/TR 15608

C (0,05-0,25 wt. %), Si (max. 0,8 wt. %), Mn (0,5-1,9 wt. %), Cr (max. 1,5

%), Cu (max. 0,7 %), Mo (max. 0,75 %), Nb (max. 0,06 %), Ni (max.

2,5 %), Ti (max. 0,12 %), V (max. 0,18 %) a B (max. 0,005 %).

Limiting thickness

402010

NiCuCrMoMnCCET

Carbon equivalent

• In ČSN EN 1011 is presented CET for method B,

recommended manily for HSLA steels:

wm.%

Tp = TpCET + Tpd + TpHD + TpQ. [ ͦC]

Tp = 697*CET + 160 tanh (d/35) + 62*HD^0.35 +(53*CET-32)*Q-330

402010

NiCuCrMoMnCCET

Carbon equivalent

IIW/IIS and EN 1011-2 (method A) recommend for ferittic C-

Mn steels:

C (0,05-0,25 wt. %), Si (max. 0,8 wt. %), Mn (max 1,7 wt. %),

Cr (max. 0,9 %), Cu (max. 1 %), Mo (max. 0,75 %), Ni

(max. 2,5 %), V (max. 0,2 %).

Usable for CE=0,3-0,7, not suitable for B steels

If it is till 0,45 % thickness 4 mm, 0,4 % thickness 6,5 mm

0,35 % thickness 25 mm, 0,3 thickness 50 mm

Steel can be welded without preheat.

1556)(

CuNiVMoCrMnCIIWCe

wt.%

Preheat calculation – Seferian calculation

Seferian :

[°C]

s = thickness

Suitable for carbon and low alloy steels with C > 0,1 %

25,0.350 pp CT scp CCC

360

2820)(40360 MoNiCrMnCCc

cs CsC ..005,0

Preheat calculation – Ito + Bessya

H = diffusible H [ml ⁄ 100 g]

K = weld stiffness = 69.s butt weld (66.s fillet weld)

s = thickness [mm]

392.1440 PwTp[°C] Kde :

4000060

KHPcmPw

BVMoNiCrCuMnSi

CPcm 510156020202030

Hot cracking sensitivity

EN 1011 – recommends using UCS-unit of crack susceptibility

Usable for steels with composition max. C = 0,23 wt.%, S = 0,05 %, P =

0,045 %, Si = 0,65 %, Mn = 1,6 %, Nb = 0,07 %

results: UCS < 10 … low risk of solidification crack

USC > 30 … high risk of solid. crack

Other sources show other parameters to show probability of solidification

cracking, e.g. HCS

VMoCrMn

NiSiPSC

SCH

3

10).10025

.(

...

3

14,512404575190230... MnSiNiNbPSCSCU

Other possible calculations

Lamelar tearing factor

Reheat cracking

Diagrams

….

Normalized tests of welds

ČSN EN ISO 17642 – Destructive tests on welds in metallic materials –

Cold cracking tests for weldments- Arc welding

ČSN EN ISO 17641 – Destructive tests on welds in metallic materials –

Hot cracking tests for weldments- Arc welding

ČSN EN ISO 9017 – Fracture test

ČSN EN ISO 17639 – Macroscopy

ČSN EN ISO 9015 – Hardness

ČSN EN ISO 9016 - Destructive tests on welds–Impact test

ČSN EN ISO 4136 – Destructive tests on welds – Bend test

ISO 18278,18595 – Resistance spot welding weldability

Welding procedure qualification

ČSN EN ISO 15607 Specification and qualification of welding procedures

for metallic materials - General rules

ISO 15609-1-6 - Specification and qualification of welding procedures for

metallic materials - Welding procedure specification – from arc, gas

welding upto laser hybrid welding

ISO 15610 Qualification based on tested welding consumables

ISO 15611 Qualification based on previous welding experience

ISO 15612 Qualification by adoption of a standard welding procedure

ISO 15613 Qualification based on pre-production welding test

ISO 15614-1-14 Specification and qualification of welding procedures for

metallic materials - Welding procedure test - from Arc and gas welding of

steels, Ni up to laser welding, resistence welding, cladding ….