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4.
Classification of Steels,
Welding of Mild Steels
4. Classification of Steels, Welding of Mild Steels 32
In the European Standard DIN EN
10020 (July 2000), the designations
(main symbols) for the classification of
steels are standardised. Figure 4.1
shows the definition of the term „steel“
and the classification of the steel
grades in accordance with their
chemical composition and the main
quality classes.
In accordance with the chemical com-
position the steel grades are classified
into unalloyed, stainless and other
alloyed steels. The mass fractions of
the individual elements in unalloyed
steels do not achieve the limit values
which are indicated in Figure 4.2.
Stainless steels are grades of steel
with a mass fraction of chromium of at
least 10,5 % and a maximum of 1,2 %
of carbon.
Other alloyed steels are steel grades
which do not comply with the definition
of stainless steels and where one
alloying element exceeds the limit
value indicated in Figure 4.2.
Figure 4.1
Definition for theclassification of steels
© ISF 2004br-er05-01.cdr
Classification in accordance with the chemical composition:
l
l
l
unalloyed steels
stainless steels
other, alloyed steels
Classification in accordance with the main quality class:
·
·
·
unalloyed steels - unalloyed quality steels- unalloyed special steels
stainless steels
other, alloyed steels - alloyed quality steels- alloyed special steels
Definition of the term “steel”
Steel is a material with a mass fraction if iron which is higherthan of every other element, ist carbon content is, in general,lower than 2% and steel contains, moreover, also otherelements. A limited number of chromium steels might contain acarbon content which is higher than 2%, but, however, 2% is thecommon boundary between steel and cast iron [DIN EN 10020(07.00)].
Figure 4.2
4. Classification of Steels, Welding of Mild Steels 33
As far as the main quality classes are concerned, the steels are classified in accor-
dance with their main characteristics and main application properties into unalloyed,
stainless and other alloyed steels.
As regards unalloyed steels a distinction is made between unalloyed quality steels
and unalloyed high-grade steels.
Regarding unalloyed quality steels, prevailing demands apply, for example, to the
toughness, the grain size and / or the forming properties.
Unalloyed high-grade steels are characterised by a higher degree of purity than
unalloyed quality steels, particularly with regard to non-metal inclusions. A more
precise setting of the chemical composition and special diligence during the manufac-
turing and monitoring process guarantee better properties. In most cases these
steels are intended for tempering and surface hardening.
Stainless steels have a chromium mass fraction of at least 10,5 % and maximally
1,2 % of carbon. They are further classified in accordance with the nickel content and
the main characteristics (corrosion resistance, heat resistance and creep resistance).
Other alloyed steels are classified into alloyed quality steels and alloyed high-grade
steels.
Special demands are put on the alloyed quality steels, as, for example, to toughness,
grain size and / or forming properties. Those steels are generally not intended for
tempering or surface hardening.
The alloyed high-grade steels comprise steel grades which have improved properties
through precise setting of their chemical composition and also through special manu-
facturing and control conditions.
4. Classification of Steels, Welding of Mild Steels 34
The European Standard DIN EN 10027-1 (September 1992) stipulates the rules for
the designation of the steels by means of code letters and identification numbers.
The code letters and identification numbers give information about the main applica-
tion field, about the mechanical or physical properties or about the composition.
The code designations of the steels are divided into two groups. The code designa-
tions of the first group refer to the application and to the mechanical or physical
properties of the steels. The code designations of the second group refer to the
chemical composition of the steels.
According to the utilization of the
steel and also to the mechanical or
physical properties, the steel grades
of the first group are designated with
different main symbols (Fig. 4.3).
Figure 4.3
Classification of steels in accordancewith their designated use
© ISF 2004br-er05-03.cdr
l
l
l
l
l
l
l
l
l
l
l
e.g. S235JR, S355J0
P =e.g. P265GH, P355M
L =e.g. L360A, L360QB
E =e.g. E295, E360
B =e.g. B500A, B500B
Y =e.g. Y1770C, Y1230H
R =e.g. R350GHT
H =
e.g. H400LA
D =e.g. DD14, DC04
T =
e.g. TH550, TS550
M =e.g. M400-50A, M660-50D
S = Steels for structural steel engineering
Steels for pressure vessel construction
Steels for pipeline construction
Engineering steels
Reinforcing steels
Prestressing steels
Steels for rails (or formed as rails)
Cold rolled flat-rolled steels with higher-strengthdrawing quality
Flat products made of soft steels for cold reforming
Black plate and tin plate and strips and also speciallychromium-plated plate and strip
Magnetic steel sheet and strip
4. Classification of Steels, Welding of Mild Steels 35
An example of the code designation structure with reference to the usage and the
mechanical or physical properties for “steels in structural steel engineering“ is ex-
plained in Figure 4.4.
Figure 4.4
4. Classification of Steels, Welding of Mild Steels 36
For designating special features of the steel or the steel product, additional symbols
are added to the code designation. A distinction is made between symbols for spe-
cial demands, symbols for the type of coating and symbols for the treatment con-
dition. These additional symbols are stipulated in the ECISS-note IC 10 and depicted
in Figures 4.5 and 4.6.
© ISF 2004br-er-05-06.cdr
1
2
))The symbols are separated from the preceding symbols by plus-signs (+)In order to avoid mix-ups with other symbols, the figure T may precede,for example +TA
Symbol ) )
+ A+ AC+ C
+ Cnnn+ CR+ HC+ LC+ Q+ S+ ST+ U
1 2 treatment condition
softenedannealed for the production of globular carbideswork-hardened (e.g., by rolling and drawing), also a distinguishingmark for cold-rolled narrow strips)cold-rolled to a minimum tensile strength of nnn MPa/mm²cold-rolledthermoformed/cold formedslightly cold-drawn or slightly rerolled (skin passed)quenched or hardenedtreatment for capacity for cold shearingsolution annealeduntreated
Symbols for the treatment condition
Figure 4.6
© ISF 2004br-er-05-05.cdr
Symbol ) )
+ A+ AR+ AS+ AZ+ CE+ Cu+ IC+ OC+ S+ SE+ T+ TE+ Z+ ZA+ ZE+ ZF+ ZN
1 2 Coating
hot dippedaluminium, cladded by rollingcoated with Al-Si alloycoated with Al-Tn alloy (>50% Al)electrolytically chromium-platedcopper-coatedinorganically coatedorganically coatedhot-galvanised
upgraded by hot dipping with a lead-tin alloyelectrolytically coated with a lead-tin alloyhot-galvisedcoated with Al-Zn alloy (>50% Zn)electrolytically galvaniseddiffusion-annealed zinc coatings (galvannealed, with diffused Fe)nickel-zinc coating (electrolytically)
electrolytically galvanised
1
2
))The symbols are separated from the preceding symbols by plus-signs (+)In order to avoid mix-ups with other symbols, the figure S may precede,for example +SA
Symbols for the coating type
Figure 4.5
4. Classification of Steels, Welding of Mild Steels 37
Figure 4.7 shows an example of the novel designation of a steel for structural steel
engineering which had formerly been labelled St37-2.
Figure 4.8 depicts the chemical composition and the mechanical parameters of dif-
ferent steel grades. The figure explains the influence of the chemical composition on
the mechanical properties.
Figure 4.7
© ISF 2002br-er-05-07.cdr
S = steels for structural steel engineeringP = steels for pressure vessel constructionL = steels for pipeline constructionE = engineering steelsB = reinforcing steels
The steel St37-2 (DIN 17100) is, according to the new standard (DIN EN 10027-1),designated as follows:
S235 J 2 G3
Steel for structural steel engineering
R 235 MPa/mmeH
2³
further property(RR = normalised)
test temperature 20°C
impact energy ³ 27 J
Steel designation in accordance with DIN EN 10027-1
Stahl C Si Mn P S Cr Al Cu N Mo Ni Nb VS355J0(St 52-3)S500N(StE500)P295NH(HIV)S355J2G1W(WTSt510-3)S355G3S(EH36)
Stahl
S355J2G3(St 52-3)S500N(StE500)P295NH(HIV)S355J2G1W(WTSt510-3)S355G3S(EH36)
Kerbschlagarbeit AV
[J]
Zugfestigkeit Rm
[N/mm²]BruchdehnungA
[%]
StreckgrenzeReH
[N/mm²]0°C -20°C
27
610-780 500 16 31-47
27355510-680 20-22
285
355
355
>18
22
>22
49(bei +20°C)
76(bei -10°C)
21-39
460-550
510-610
400-490
£0,18
£0,55
£0,35
£0,1-0,35
£0,50
0,1- 0,6
£0,26
£0,15
0,21
£0,20 £1,60 0,040
1- 1,7 0,035
³0,6 £0,05
0,5- 1,3 0,035
0,7- 1,5 £0,05
0,040 /
0,030 0,30
£0,05 /
0,0350,40-0,80
£0,05 /
/ /
0,020 0,20
/ /
/0,25-0,5
/ /
£0,009 /
0,020 0,1
/ /
/ £0,30
/
/ /
1 0,05
/ /
£0,65 /
/
0,22
/
0,02-0,12
// / /
Chemical composition and mechanicalparameters of different steel sorts
© ISF 2004br-er-05-08.cdr
impact energy AVelongation after fracture Ayield point ReHTensile strength RmSteel
Steel
Figure 4.8
4. Classification of Steels, Welding of Mild Steels 38
The steel S355J2G2 represents the basic type of structural steels which are nowa-
days commonly used. Apart from a slightly increased Si content for desoxidisation it
this an unalloyed steel.
S500N is a typical fine-grained structural steel. A very fine-grained microstructure
with improved tensile strength values is provided by the addition of carbide forming
elements like Cr and Mo as well as by grain-refining elements like Nb and V.
The boiler steel P295NH is a heat-resistant steel which is applied up to a temperature
of 400°C. This steel shows a relatively low strength but very good toughness values
which are caused by the increased Mn content of 0,6%.
S355J2G1W is a weather-resistant structural steel with mechanical properties similar
to S355J2G2. By adding Cr, Cu and Ni, formed oxide layers stick firmly to the work-
piece surface. This oxide layer prevents further corrosion of the steel.
S355G3S belongs to the group of shipbuilding steels with properties similar to those
of usual structural steels. Due to special quality requirements of the classification
companies (in this case: impact energy) these steels are summarised under a special
group.
4. Classification of Steels, Welding of Mild Steels 39
Figure 4.9
The steel grades are classified into four subgroups according to the chemical com-
position (Fig. 4.9):
● Unalloyed steels (except free-cutting steels) with a Mn content of < 1 %
● Unalloyed steels with a medium Mn content > 1 %, unalloyed free-cutting
steels and alloyed steels (except high-speed steels) with individual alloying
element contents of less than 5 percent in weight
● Alloyed steels (except high-speed steels), if, at least for one alloying element
the content is ≥ 5 percent in weight
● High-speed steels
The unalloyed steels with Mn con-
tents of < 1% are labelled with the
code letter C and a number which
complies with the hundredfold of the
mean value which is stipulated for the
carbon content.
Unalloyed steels with a medium Mn
content > 1 %, unalloyed free-
cutting steels and alloyed steels
(individual alloying element con-
tents < 5 %) are labelled with a num-
ber which also complies with a
hundredfold of the mean value which
is stipulated for the carbon content,
the chemical symbols for the alloying
elements, ordered according to the
decreasing contents of the alloying
elements and numbers, which in the
sequence of the designating alloying
elements give reference about their content. The individual numbers stand for the
medium content of the respective alloying element, the content had been multiplied
4. Classification of Steels, Welding of Mild Steels 40
by the factor as indicated in Fig. 4.9 / Table 4.1 and rounded up to the next whole
number.
The alloyed steels are labelled with the code letter X, a number which again com-
plies with the hundredfold of the mean value of the range stipulated for the carbon
content, the chemical symbols of the alloying elements, ordered according to de-
creasing contents of the elements and numbers which in sequence of the designating
alloying elements refer to their content.
High-speed steels are designated with the code letter HS and numbers which, in the
following sequence, indicate the contents of elements:: tungsten (W), molybdenum
(Mo), vanadium (V) and cobalt (Co).
The European Standard DIN EN 10027-2 (September 1992) specifies a numbering
system for the designation of steel grades, which is also called material number
system..
The structure of the material number is as follows:
1. XX XX (XX)
Sequential number The digits inside the brackets are intended for possible future demands.
Steel group number (see Fig. 4.10)
Material main group number (1=steel)
4. Classification of Steels, Welding of Mild Steels 41
Figure 4.10 specifies the material numbers for the material main group „steel“.
Figure 4.10
4. Classification of Steels, Welding of Mild Steels 42
The influence of the austenite grain size on the transformation behaviour has been
explained in Chapter 2. Figure 4.11 shows the dependence between grain size of the
austenite which develops during the welding cycle, the distance from the fusion line
and the energy-per-unit length from the welding method. The higher the energy-per-
until length, the
bigger the austen-
ite grains in the
HAZ and the width
of the HAZ in-
creases. Such
coarsened austen-
ite grain decreases
the critical cooling
time, thus increas-
ing the tendency of
the steel to harden.
With fine-grained structural steels it is tried to suppress the grain growth with alloying
elements. Favourable are nitride and carbide forming alloys. They develop precipita-
tions which suppress undesired grain growth. There is, however, a limitation due to
the solubility of these precipitations, starting with a certain temperature, as shown in
Figure 4.12. Steel 1 does not contain any precipitations and shows therefore a con-
tinuous grain growth related to temperature. Steel 2 contains AIN precipitations which
are stable up to a temperature of approx. 1100°C, thus preventing a growth of the
austenite grain.
Influence of the energy-per-unitlength on the austenite grain size
13
11
9
7
5
30 0,2 0,4 0,6 0,8 1,0
Aust
enite
gra
in s
ize in
dex
acc
ord
ing
to D
IN 5
0601
Distance of the fusion linemm
Energy-per-unit length in kJ/cm
9 12 18 36
© ISF 2004br-er-05-11.cdr
Figure 4.11
4. Classification of Steels, Welding of Mild Steels 43
With higher temperatures, these
precipitations dissolve and cannot
suppress a grain growth any more.
Steel 3 contains mainly titanium car-
bonitrides of a much lower grain-
refining effect than that of AIN. Steel 4
is a combination of the most effective
properties of steels nos. 2 and 3.
The importance of grain refinement
for the mechanical properties of a
steel is shown in Figure 4.13. Pro-
vided the temperature keeps con-
stant, the yield strength of a steel
increases with decreasing grain size.
This influence on the yield point Rel is
specified in the Hall-Petch-law:
dKR
iel
1⋅+= σ
According to the
above-mentioned
law, the increase of
the yield point is
inversely propor-
tional to the root of
the medium grain
diameter d. σi
stands for the inter-
nal friction stress of
the material. The
grain boundary
resistance K is a
measure for the
influence of the grain size on the forming mechanisms. Apart from this increase of the
yield point, grain refinement also results in improved toughness values. As far as
Austenite grain size as a functionof the austenitization temperature
Steel % C % Mn % Al % N % Ti
1 0,21 1,16 0,004 0,010 /
2 0,17 1,35 0,047 0,017 /
3 0,18 1,43 0,004 0,024 0,067
4 0,19 1,34 0,060 0,018 0,140
900 1000 1100 1200 1300 1400°C
Austenitization temperature
18
6
4
2
10-1
8
6
4
2
10-2
6 10-3
8
mm
Me
diu
m f
ibre
len
gth
Gra
in s
ize
ind
ex
acc
ord
ing
to
DIN
50
60
1
-4
-2
0
2
4
6
8
10
12
Steel 1Steel 2Steel 3Steel 4
© ISF 2004br-er05-12.cdr
Figure 4.12
Connection betweenyield point and grain size
900
800
700
600
500
400
300
200
N/mm²
10 2 3 4 5 6 7 8 10mm-1/2
Yie
ld p
oin
t o
r 0
,2 b
ou
nd
ary
Grain size d-1/2
Temperature in °C:
-193
-185
-180
-155
+20
-40
-100
-170
© ISF 2004br-er-05-13.cdr
Figure 4.13
4. Classification of Steels, Welding of Mild Steels 44
structural steels are concerned, this means the improvement of the mechanical prop-
erties without any further alloying. Modern fine-grained structural steels show im-
proved mechanical properties with, at the same time, decreased content of alloying
elements. As a consequence of this chemical composition the carbon equivalent
decreases, the weldability is improved and processing of the steel is easier.
The major advan-
tages of microal-
loyed fine-grained
structural steels in
comparison with
conventional struc-
tural steels are
shown in Figure
4.14. Due to the
considerably better
mechanical proper-
ties of the fine-
grained structural
steel in comparison
with unalloyed structural steel, substantial savings of material are possible. This
leads also to reduced joint cross-sections and, in total, to lower costs when making
welded steel constructions.
Based on the
classification of
Figure 4.2, Fig-
ure 4.15 divides the
steels with regard
to their problematic
processes during
welding. When it
comes to unalloyed
steels, only ingot
Figure 4.14
Influence of the steel selection on theproducing costs of welded structures
S235JR S355J2G3 S690Q S890Q S960Q Verhältnis
(St37-2) (St52-3) (StE690) (StE890) (StE960) S235JR - S960Q
Streckgrenze N/mm2215 345 690 890 960 1 : 5
Blechdicke mm 50 31 14,4 11 10 5 : 1
Nahtquerschnitt mm2870 370 100 60 50 17 : 1
Schweißdraht ø 1.2 mm SG2 SG3 NiMoCr X 90 X 96 -
Schweißdrahtkosten Verhältnis 1 1 2,4 3,2 3,3 1 : 3,3
Stahlkosten Verhältnis 1 1,2 1,9 2,3 2,4 1 : 2,4
Schweißgutkosten Verhältnis 5,3 2,3 1,5 1,16 1 5,3 : 1
Spez. Schweißnahtkosten Verhältnis 12 5,1 1,8 1,18 1 12 : 1
Kostenverhältnis inklusiveGrundwerkstoffe
5 : 1
Randbedingungen: Schweißverfahren = MAG
Abschmelzleistung = 3 kg Schweißdraht / h, Nahtform X - 60°
Lohn- und Maschinenkosten = 60 DM / h
Spez. Schweißnahtkosten = Schweißzusatzwerkstoffe + Schweißen
Berechnungsgrundlage =szul = Re / 1.5
Stahlsorte
© ISF 2004br-er-05-14.cdr
Yield point
Plate thickness
Weld cross-section
Welding wire Ø 1.2
Welding wire costs
Steel costs
Weld metal costs
Special weld costs
Costs ratio inclusive basematerials
Ratio
Ratio
Ratio
Ratio
Boundary condition: welding process = MAG
Deposition rate = 3 kg welding wire/h, weld shape X -60°
Costs of labour and equipment = 30€/h
Special weld costs = weld filler materials + welding
Calculation base = = Re/1.5szul
Steel type Ratio
Figure 4.15
Classification of steels withrespect to problems during welding
low-alloyed high-alloyed
hardeningspecial properties areachieved, for example:
heat resistance,tempering resistant,
high-pressure hydrogen resistance,toughness at low temperatures,
surface treeatment condition, etc.
corrosionresistant steels
tool steels
Hardening,special properties
are achieved
steels
unalloyed alloyed
mild steel higher-carbon steel
HardeningUnderbead cracking
rimmed steel killed steel duplex killed steel
cutting ofsegregation
zones
cold brittleness(coarse-grained recrystallization
after critical treatment)stress corrosion crackingsafety from brittle fracture
ferritic pearlitic-martensitic austenitic
grain desintegrationstress corrosion
cracking hot cracks(sigma phaseembrittlement)
hardeningembrittlement
formationof chromium
carbide
grain increase inthe weld interfaces
Post-weld treatment forhighest corrosion resistance
© ISF 2004br-er-05-15.cdr
4. Classification of Steels, Welding of Mild Steels 45
casts, rimmed and semi-killed steels are causing problems. “Killing” means the re-
moval of oxygen from the steel bath.
Figure 4.16 shows cross-sections of ingot blocks with different oxygen contents.
Rimming steels with increased oxygen content show, from the outside to the inside,
three different zones after solidification: 1.: a pronounced, very pure outer envelope,
2.: a typical blowhole formation (not critical, blowholes are forged together during
rolling), 3.: in the
centre a clearly
segregated zone
where unfavourable
elements like sul-
phur and phospho-
rus are enriched.
During rolling, such
zones are stretched
along the complete
length of the rolling
profile.
Figure 4.17 shows important points to be observed during welding such steels. Due
to their enrichment with alloy elements, the segregation zones are more transforma-
tion-inert than the
outer envelope
and are inclined to
hardening. In
addition, they are
sensitive to hot-
cracking, as, in
these zones, the
elements phospho-
rus and sulphur
are enriched.
Figure 4.16
Ingot cross-sectionsafter different casting methods
Figures: mass content of oxygen in %
fully killed steel semi-killed steel rimmed steel
0,003
0,012
0,025
© ISF 2004br-er-05-16.cdr
Figure 4.17
Example of unfavourable (a) andfavourable (b) welds
a b
B CD
E
© ISF 2004br-er-05-17.cdr
4. Classification of Steels, Welding of Mild Steels 46
Therefore, “ touching” such segregation zones during welding must be avoided by all
means.
In the case of low-
alloy steels, the
problem of HAZ
hardening during
welding must be
observed. Figure
4.18 shows hard-
ness values of
various microstruc-
tures. The highest
hardness values
can be found with
martensite and
cementite. Hardness values of cementite are of minor importance for unalloyed and
low-alloy steels because its proportion in these steels remains low due to the low C-
content.
However, hardening because of martensite formation is of greatest importance as the
martensite proportion in the microstructure depends mainly on the cooling time.
Figure 4.19 shows
the essential influ-
ence of the mart-
ensite content in
the HAZ on the
crack formation of
welded joints.
Hardening through
martensite forma-
tion is not to be
expected with pure
carbon steels up to
about 0,22%,
Hardness of Several Microstructures
Microstructures Average Brinell Hardness (Approximately)
Ferrite 80
Austenite 250
Perlite (granular) 200
Perlite (lamellar) 300
Sorbite 350
Troostite 400
Cementite 600 - 650
Martensite 400 - 900
© ISF 2004Br-er-05-18.cdr
Figure 4.18
Influence of Martensite Content
strength,calculated at
max. hardness
with maximummartensite
contentHV HRC N/mm2 %
root crackingpresumable
400 41 1290 70
root crackingpossible
400 - 350 41 - 36 1290 - 1125 70 - 60
no root cracking 350 36 1125 60
sufficient operational safetywithout heat treatment
280 28 900 30
maximum hardness
If too much martensite develops in the heat affected zone during welding (below or next to the weld),a very hard zone will be formed which shows often cracks.
© ISF 2004Br-er-05-19.cdr
Figure 4.19
4. Classification of Steels, Welding of Mild Steels 47
because the critical cooling rate with these low C-contents is so high that it normally
won’t be reached within the welding cycle. In general, such steels can be welded
without special problems (e.g., S. 235).
In addition to car-
bon, all other alloy
elements are im-
portant when it
comes to marten-
site formation in
the welding cycle,
as they have sub-
stantial influence
on the transforma-
tion behaviour of
steels (see
Fig. 2.12 ). It is not
appropriate just
to take the carbon content as a measure for the hardening tendency of such steels.
To estimate the weldability, several authors developed formulas for calculating the
so-called carbon equivalent, which include the contribution of the other alloy ele-
ments to hardening tendency, (Fig. 4.20). As these approximation formulas are em-
pirically determined
and as for the
hardening tendency
the general condi-
tions like plate
thickness, heat
input, etc., are also
of importance, the
carbon equivalent
cannot be a com-
mon limit value for
the weldability.
For the determina-
Figure 4.20
Definition of C - Equivalent
C-Äqu.= carbon equivalent (%) PLS = pipeline steels PCM = (%)cracking parameters
IIW
Stout
Ito and Bessyo
Mannesmann
Hoesch
Thyssen
15
NiCu
5
VMoCr
6
MnCÄqu.C
++
++++=-
40
Cu
20
Ni
10
MnCr
6
MnCÄqu.C ++
+++=-
5B10
V
15
Mo
60
Ni
20
CrCuMn
30
SiCPCM ++++
++++=
40
Ni
20
CuCr
10
MoMnCCET +
++
++=
20
VMoNiCrCuMnSiCÄqu.C
+++++++=-
15
V
40
Mo
60
Ni
20
Cr
16
CuMn
25
SiCÄqu.C PLS ++++
+++=-
© ISF 2002Br-er-05-20.cdr
Mo
Figure 4.21
Quelle: DIN EN 1011-2br-er05-21.cdr
Calculation of the preheating temperatures
Tp =697 CET + 160 tanh (d/35) + 62 HD + (53 CET - 32) Q - 3280,35
-100
-80
-60
-40
-20
0
20
40
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5
Wärmeeinbringen Q [kJ/mm]
delt
aT
p[°
C]
delta Tp = (53 CET - 32) Q - 53 CET + 32
d = 50 mmHD = 8
CET = 0,4 % CET = 0,2 % CET = 0,2 %
delta Tp = (53 CET - 32) Q - 53 CET + 32
CET = 0,4 % CET = 0,2 % CET = 0,2 %
d = 50 mmHD = 8
0
20
40
60
80
100
0 5 10 15 20 25
Wasserstoffgehalt HD des Schweißgutes [%]
de
lta
Tp
[°C
]
delta Tp = 62 HD 0,35 - 100
CET = 0,33 %d = 30 mmQ = 1 kJ/mm
delta Tp = 62 HD - 1000,35
CET = 0,33 %dQ = 1 kJ/mm
= 30 mm
0
50
100
150
200
250
0,2 0,3 0,4 0,5
Kohlenstoffäquivalent CET [%]
Tp
[°C
]
Tp = 750 CET - 150
d = 30 mmHD = 4Q = 1 kJ/mm
Tp = 750 CET - 150
d = 30 mmHD = 4Q = 1 kJ/mm
0
10
20
30
40
50
60
0 20 40 60 80 100
Blechdicke d [mm]
de
lta
Tp
[°C
]
delta Tp = 160 tanh (d/35) - 110
CET = 0,4 %HD 2Q = 1 kJ/mm
delta Tp = 160 tanh (d/35) - 110
CET = 0,4 %HD = 2Q = 1 kJ/mm
© ISF 2005
Heat input
Hydrogen content of the weld metalCarbon aquivalent
Plate thickness
Source:
4. Classification of Steels, Welding of Mild Steels 48
tion of the preheating temperature Tp, the formula as shown in Figure 4.21 is used.
The effects of the chemical composition which is marked by the carbon equivalent
CET, the plate thickness d, the hydrogen content of the weld metal HD and the heat
input Q are considered.
The essential factor
to martensite forma-
tion in the welding
cycle is the cooling
time. As a measure
of cooling time, the
time of cooling from
800 to 500°C (t8/5) is
defined (Fig. 4.22).
The temperature
range was selected
in such a way that it
covered the most
important structural transformations and that the time can be easily transferred to the
TTT diagrams.
Figure 4.23 shows
measured time-
temperature distri-
butions in the vicin-
ity of a weld. Peak
values and dwell
times depend obvi-
ously on the loca-
tion of the
measurement and
are clearly strongly
determined by the
heat conduction
conditions.
Figure 4.22
Definition of t8/5
Tem
pera
ture
T
Time t
Tmax
°C
800
500
t t s800 500
DT
t8/5
© ISF 2004br-er-05-22.cdr
Figure 4.23
Temperature-time curvesin the adjacence of a weld
2000
°C
1500
1000
500
00 50 100 150 200 250 s 300
Time t
Tem
pe
ratu
reT
A
B
C
10mm
A
B
C
© ISF 2004br-er-05-23.cdr
4. Classification of Steels, Welding of Mild Steels 49
With the use of thinner plates with complete heating of the cross-section during weld-
ing, the heat conductivity is only carried out in parallel to the plate surface, this is the
two-dimensional heat dissipation.
With thicker plates, e.g. during welding of a blind bead, heat dissipation can also be
carried out in direction of plate thickness, heat dissipation is three-dimensional.
These two cases
are covered by the
formulas given in
Figure 4.24, which
provide a method
of calculating the
cooling time t8/5 of
low-alloyed steels.
In the case of a
three-dimensional
heat dissipation,
t8/5 it independent
of plate thickness.
In the case of two-dimensional heat dissipation it is clear that t8/5 becomes the shorter
the thicker the plate thickness d is. Provided, the cooling times are equal, the plate
thickness can be calculated from these relations where a two-dimensional heat dissi-
pation changes to a three-dimensional heat dissipation.
Figure 4.25 shows
the influence of the
welding method on
the heat dissipa-
tion. With the same
heat input, the
energy which is
transferred to the
base material
depends on the
Figure 4.24
Calculation equation for two- andthree-dimensional heat dissipation
3 - dimensional:
2 - dimensional:
© ISF 2004br-er-05-24.cdr
÷÷ø
öççè
æ
--
-×
××
××=
00
5/8800
1
500
1
2 TTv
IUt
lph
( ) 3
00
04
5/8800
1
500
110567,0 N
TTv
IUTt ×¢×÷÷
ø
öççè
æ
--
-×
×××-= - h
úúû
ù
êêë
é÷÷ø
öççè
æ
--÷÷
ø
öççè
æ
-××÷
ø
öçè
æ ××
××××=
2
0
2
02
22
5/8800
1
500
11
4 TTdv
IU
ct
rlph
( ) 22
2
0
2
02
2
05
5/8800
1
500
11103,4043,0 N
TTdv
IUTt ×¢×
úúû
ù
êêë
é÷÷ø
öççè
æ
--÷÷
ø
öççè
æ
-××÷
ø
öçè
æ ×××-= - h
÷÷ø
öççè
æ
-+
-×
××¢×
×-×-
=-
-
0004
05
800
1
500
1
10567,0
103,4043,0
TTv
IU
T
Td
üh
K3
universal formula:
extended formulaFor low-alloyed steel:
universal formula:
extended formulaFor low-alloyed steel:
K2
formula for the transitionthickness of low-alloyed steel:
Figure 4.25
Relative thermal efficiency degreeof different welding methods
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
SA welding
Manual arc welding
MAG-(CO )-2 welding
MIG-(Ar)-welding
TIG-(Ar)-welding
TIG-(He)-welding
welding methods
Relative thermal efficiency degree ‘h
© ISF 2004Br-er-05-25.cdr
4. Classification of Steels, Welding of Mild Steels 50
welding method. This dependence is described by the relative thermal efficiency ŋ’.
The influence of
the groove ge-
ometry is covered
by seam factors
according to
Fig. 4.26. Empiri-
cally determined,
these factors were
introduced for an
easier calculation.
For other groove
geometries, tests
to measure the
cooling time are recommended.
Fig. 4.27 shows the transition of the two-dimensional to the three-dimensional heat
dissipation for two different preheating temperatures in form of a curve according to
the equation of Fig. 4.24. Above the curve, t8/5 depends only on the energy input, but
not on the plate thickness, heat dissipation is carried out three-dimensionally.
Figure 4.26
Weld factors for differentweld geometries
Type of weldweld factor
2-dimensionalheat dissipation
3-dimensionalheat dissipation
1
0,45 - 0,67
0,9
0,9
1
0,67
0,67
0,9
© ISF 2004br-er-05-26.cdr
Figure 4.27
Transition From Two to ThreeDimensional Heat Flow
Heat input E. .N [kJ/cm]h n
0 10 20 30 40 50
5
cm
3
2
1
0
Pla
te t
hic
kne
ss
cooling time t [s]10 15 20 25
8/5
3040
60100
2-dimensional
3-dimensional
T =20°CA
0 10 20 30 40 50
cooling time t [s]10 20 30 40 50
8/5
2-dimensional
3-dimensional
T =200°CA
60
80
100
150
© ISF 2004Br-er-05-27.cdr
4. Classification of Steels, Welding of Mild Steels 51
Fig. 4.28 shows the
possible range of
heat input depend-
ing on the elec-
trode diameter. It is
clear that a rela-
tively large working
range is available
for arc welding
procedures. A
variation of the
energy-per-unit
length can be
carried out by alteration of the welding current, the welding voltage and the welding
speed.
Fig. 4.29 depicts variations of the heat
input during manual metal arc weld-
ing. The shorter the fused electrode
distance, i.e., the shorter the ex-
tracted length, the higher the energy-
per-unit length.
Figure 4.28
br-er-05-28.cdr
Heat Inputs ofVarious Welding Methods
3,25 4 5 6 0,8 1,0 1,2 1,6 2,5 3,0 4,0 5,0
20
kJ/cm
12
8
4
Heat in
put
Manual metal arc welding MAGC-, MAGM-method
SA-welding
-short arc
-sprayarc
© ISF 2004
Figure 4.29
© ISF 2004br-er05-29.cdr
35
kJ/cm
25
20
15
10
5
0
En
erg
y-p
er-
un
it le
ng
th
0 50 100 150 200 250 300 350 400 450 500 mm 600
run-out length
Stick electrode(mm)
Current intensity (A)
Current intensity (A)
2,5
90
75
3,25
135
120
4,0
180
140
5,0
235
190
6,0
275
250
Æ6,0mm x 450mm
Æ5,0mm x 450mm
Æ4,0mm x 450mm
Æ3,25mm x 350mm
Æ2,5mm x 350mm
Energy-per-unit length as afunction of the run-out length
4. Classification of Steels, Welding of Mild Steels 52
In order to minimize calculation efforts in practice, the specified relations were
transferred into nomograms from which permissible welding parameters can be read
out, provided some additional data are available. Fig. 4.30 shows diagrams for two-
dimensional heat dissipation, where a dependence between energy-per-unit length,
cooling time and preheating temperature is given, depending on the plate thickness. .
If a fine-grained structural steel is to be welded, the steel manufacturer presets a
certain interval of cooling times, where the steel characteristics are not too negatively
affected. The user lays down the plate thickness and, through the selection of a
welding method, a specified range of heat input E. Based on the data E and t8/5 the
diagram provides the required preheating temperature for welding the respective
plate thickness.
Figure 4.30
br-er05-30.cdr
Dependence of E, t andd During SA - Welding
8/5
Heat input E5 6 7 8 9 10 15 20 30 kJ/cm 50
504030
20
10
7
504030
20
10
7
504030
20
10
7
504030
20
10
7
Coolin
g tim
e t
in s
8/5
d = 7,5 mm
d = 10 mm
d = 15 mm
d = 20 mm
transition to3-dimensional
heat flow
T 200°C150°C100°C
20°C
0
T 200°C150°C100°C
20°C
0
T 200°C150°C100°C
20°C
0
T 200°C150°C100°C
20°C
0
© ISF 2004
4. Classification of Steels, Welding of Mild Steels 53
With the transition to thicker plates,
the diagrams in Fig. 4.31 apply. The
upper part of the figure determines
whether a two-dimensional or a three-
dimensional heat dissipation is pre-
sent. For the three-dimensional heat
dissipation, the lower diagram applies
where the same information can be
determined, independent of plate
thickness, as with Fig. 4.30.
The relation be-
tween current and
voltage for MAG
welding is shown
in Fig. 4.32 and
the used shielding
gas is one of the
parameters. Weld-
ing voltage and
welding current, or
wire feed speed,
determine the type
of arc.
Figure 4.31
br-er05-31.cdr
Dependence ofE, T , t And d0 8/5 Ü
Heat input E
50s
40
30
20
15
109
87
Coolin
g tim
e t 8
/5
5 6 7 8 9 10 15 20 30 kJ/cm 50
T250
°C
200°C
150°C
100°C
20°C
0
Heat input E
50mm
40
30
20
15
109
87
Tra
nsi
tion thic
kness
dÜ
5 6 7 8 9 10 15 20 30 kJ/cm 50
aera of3-dimensional
heat flow
area of2-dimensional
heat flow
T250 °C 200 °C
150 °C 100 °C
20 °C
0
© ISF 2004
Figure 4.32
br-er-05-32.cdr
Dependence of Current And Voltage DuringMAG-Welding, Solid Wire, 1.2 mmÆ
35V
30
25
20
15
We
ldin
g v
olta
ge
Welding current
Wire feed
150 200 250 A 300
3,5 4,5 5,5 7,0 8,0 9,0 10,5 m/min
C1
M21
M23
gas composition:C1 100% COM21 82% Ar + 18% COM23 92% Ar + 8% O
2
2
2
short arc
contact tube distance ~15mm contact tube distance ~19mm
mixed arc spray arc
© ISF 2004
4. Classification of Steels, Welding of Mild Steels 54
The diagram in Fig. 4.33 demon-
strates the dependence of plate thick-
ness, heat input E and cooling time
t8/5 for fillet welds at a preheating
temperature of T0 = 150°C. If d and
t8/5 are given, the acceptable range of
heat input can be determined with the
help of this diagram. The kinks of the
curves mark the transition between
two-dimensional and three-
dimensional heat dissipation.
Fig. 4.34 shows the same depend-
ence for butt welds with V groove
preparation.
Figure 4.33
br-er05-33.cdr
Permissible E-RangeDuring SA - And MAG - Welding
hh
' = 1' = 0,85
d = 32 mmd = 15 mm
UP
MAG
U max
U min
F = 0,67F = 0,67
3
2
t = 30 st = 6 s8/5 max
8/5 min
E = 66 kJ/cmE = 14 kJ/cm
max
min
60
kJ/cm
50
45
40
35
30
25
20
15
10
5
0
70
kJ/cm
59
53
47
41
35
29
23
18
12
6
0
He
at
inp
ut
ES
A-
we
ldin
g
He
at
inp
ut
EM
AG
- w
eld
ind
Plate thickness
0 5 10 15 20 25 30 mm 40
cracking tendency
toughness affection
fillet weldsT = 150 °C0 30s
25s
20s
15s
10s
6s
© ISF 2004
Figure 4.34
br-er05-34.cdr
Permissible E-RangeDuring SA - And MAG - Welding
hh
' = 1' = 0,85
d = 34 mmd = 15 mm
UP
MAG
U max
U min
F = 0,9F = 0,9
3
2
t = 30 st = 6 s8/5 max
8/5 min
E = 49 kJ/cmE = 10 kJ/cm
max
min
60
kJ/cm
50
45
40
35
30
25
20
15
10
5
0
70
kJ/cm
59
53
47
41
35
29
23
18
12
6
0
Heat
inp
ut
ES
A-
weld
ing
Heat
inp
ut
EM
AG
- w
eld
ing
Plate thickness
0 5 10 15 20 25 30 mm 40
cracking tendency
toughness affection
butt weldsT = 150 °C0
30s
25s
20s
15s
10s
6s
© ISF 2004
4. Classification of Steels, Welding of Mild Steels 55
The curve family in Fig. 4.35 shows the dependence of the heat input from the weld-
ing speed as well as the acceptable working range. The parameters of the curves 1
to 8 in the table
have been taken
from Figures 4.32
and 4.34 and apply
only for related
conditions like wire
diameter, wire
feed, welding
voltage, etc.
Figure 4.36 shows
a reading example
for such diagrams
(according to DVS-
Reference Sheet
Nr. 0916).
In this example, a
plate thickness of
15 mm and a cool-
ing time t8/5 be-
tween 10 and 20 s
are given. In this
case, the maximum
cooling time for MAG welding is 15 s. A solid wire with a diameter of 1.2 mm at 29V
and 300A is used.
The left diagram provides heat input values between 13 and 16 kJ/cm, based on the
given data. Using these values, the acceptable range of welding speeds can be
taken from the diagram on the right.
Figure 4.35
br-er-05-35.cdr
E as a Function of Welding Speed,Solid Wire, 1.2mmÆ
MAG/ M21 (82% Ar, 18% CO)
25kJ/cm
20
15
10
5
010 15 20 25 30 35 40 45 50 cm/min 60
Welding speed vS
He
at
inp
ut
E
working range
12
34
56
7
8
curve
V
A
v (m/min)Z
29
300
10.5
27
275
9.0
24
250
8.0
22
225
7.0
20
200
5.5
19
175
4.5
18
150
3.5
17
125
3.0
1 2 3 4 5 6 7 8
© ISF 2004
Figure 4.36
br-er-05-36.cdr
Determination of Welding Speedfor MAG - Welding
curve
V
A
v (m/min)Z
29
300
10.5
27
275
9.0
24
250
8.0
22
225
7.0
20
200
5.5
19
175
4.5
18
150
3.5
17
125
3.0
1 2 3 4 5 6 7 860
kJ/cm
50
45
40
35
30
25
20
15
10
5
0
70
kJ/cm
59
53
47
41
35
29
23
18
12
6
0
He
at
inp
ut
E
SA
- w
eld
ing
He
at
inp
ut
E
MA
G -
we
ldin
g
Plate thickness0 5 10 15 20 25 30 mm 40
cracking tendency
toughness affection
butt weldsT = 150 °C0
30s
25s
20s
15s
10s
6s
30s
25s
20s
15s
10s
6s
1613
25kJ/cm
20
15
10
5
010 15 20 25 30 35 40 45 50 cm/min 60
Welding speed vS
he
at
inp
ut
E working range
12
34
56
7
8
16
13
33 41
© ISF 2004
4. Classification of Steels, Welding of Mild Steels 56
Fig. 4.37 presents a simplification of
the determination of the microstruc-
tural composition and cooling time
subject to peak temperatures which
occur in the welding cycle. In the
lower diagram, the point of the plate
thickness at the top line is linked with
the point of heat input at the lower
line. The point of intersection of the
linking line with the middle scale
represents the cooling time t8/5 .
If the peak temperature of the welding
cycle is known, one can read from the
middle diagram in which transition
field the final microstructures are
formed. The advantage of the deter-
mination of microstructures compared
with the upper TTT diagram is that
a TTT diagram applies only for exactly one peak temperature, other peak tempera-
tures are disregarded. The disadvantage of the PTCT diagram (peak temperature
cooling time diagram) is the very expensive determination, therefore, due to the
measurement efforts a systematic application of this concept to all common steel
types is subject to failure.
Figure 4.37
© ISF 2004
Peak temperature/cooling time– diagram for the determination
of t and the structure8/5
bie5-37.cdr
1400
°C
1200
1000
800
600
800
°C
700
600
500
400
300
200
1 10 100 1000Te
mpera
ture
Peak
tem
pera
ture
B
M
M
Arc3
Arc1
B+M F+B
300 200HV30=400
F+P
F
P
s t8/5
40 30 25 20 15 10 9 8 7 6 5 mm 4plate thickness
300 100200three-dimensional
1 2 3 5 10 20 50 100 200 400 s 1000two-dimensional
0 100 °C 200preheating temperature
6 8 10 20 30 40 50 kJ/cm 70energy-per-unit length
t8/5
1000°C1400°C
Peak temperature