rumus welding.pdf

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Help Welding calculation

WELDING

Carbon Equivalents

Welding Parameters/ Preheating

Heat Input/ Cooling Time

Hardness in the HAZ

Index

The data calculated by this program are for information only and do not cover all details

of a welding procedure. Therefore, this program does not give an assurance in respect to

the properties of the welded joints. In any case the underlying welding and construction

standards have to be obeyed. Furthermore the description of fabrication properties of

our material data sheets should be taken into account and all necessary levels of a

careful quality control be respected.

WELDING

CARBON EQUIVALENTS

The carbon equivalents are simplified parameters which try to estimate the

influence of the alloying content of a steel by summarising the content of the

various alloying elements by a particular averaging procedure. Plenty of carbon

equivalents have been developed until now with different suitability for a

special welding situation and steel grade. The four carbon equivalents the most

common are calculated here (in weight-%):

CET := C + (Mn + Mo)/10 + (Cr + Cu)/20 + Ni/40

CE := C + Mn/6 + (Cr + Mo + V)/5 + (Ni+ Cu)/15

CEN := C + [ 0.75 + 0.25*tanh(20*(C - 0.12))] *

[Si/24 + Mn/6 + Cu/15 + Ni/20 + (Cr + Mo + V + Nb)/5 + 5*B]

Pcm := C + Si/30 + (Mn + Cu + Cr)/20 + Mo/15 + Ni/60 + V/10 + 5*B

Fill in the alloying contents given in your inspection certificate. The program

will calculate the various carbon equivalents.

For the CET-equivalent, which is a prerequisite for the following welding

parameter calculation, the range of validity is as follows (in weight %):

C: 0.05 - 0.32

Si: �� 0.80

Mn: 0.50 - 1.90

Cr: �� 1.50

Page 1 of 8Help Welding calculation

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Ni: �� 2.50

Mo: �� 0.75

Cu: �� 0.70

V: �� 0.18

Nb �� 0.06

Ti: �� 0.12

B: �� 0.005

If an alloying content hurts this range of validity, this element as well as the

CET-parameter is marked in red.

WELDING

WELDING PARAMETERS/ PREHEATING

The calculation of welding parameters is based on the method B in EN 1011-2

(Welding - Recommendation for welding metallic materials - Part 2 Arc welding

of ferritic steels) described in annex C and D of this code.

This method describes how welding parameters should be selected in order to

avoid especially cold-cracking in the heat-affected zone (HAZ). In any case the

fabrication properties recommendations in our material data sheets should be

taken into account for a particular steel. Furthermore, the user has to ensure

that the relevant standards, such as EN 10 11, are fulfilled.

Preheating:

Preheating is very useful in order to avoid the phenomena of cold cracking as it

decelerates the cooling of the HAZ and enables the hydrogen induced during

welding to escape. Furthermore preheating improves the welding-induced

constraints. Multi-layer welds can be begun without preheating if a suitable

welding sequence is chosen and the interpass temperature is sufficient.

The preheating temperature is the lowest temperature before the first welding

pass which has not to be fallen below in order to avoid cold-cracking. For multi-

layer welds this term refers to the temperature of the second and the

subsequent weld passes and is also called interpass temperature. In general

the two temperatures are identical.

The preheating temperature depends on the following input data:

Carbon equivalent CET (see above): The CET can be explicitly filled in here

or be calculated by the contents of the alloying elements in the menu carbon

equivalent. The CET is inserted in weight-%

•

Plate thickness d: The plate thickness is inserted in mm. It should be

considered that the influence of the plate thickness is of minor importance

for plate thicknesses above 60 mm due to the three-dimensional heat flux.

•

Hydrogen content HD: The hydrogen content H2 is inserted in ml/100g. Here

either a value between 1 and 20 ml/100g can be inserted directly or a

typical value depending on the weld process used can be selected:

•

Typical hydrogen content for welding consumables

Method Common hydrogen content [ml/100

g]

Manual Metal Arc MMA 5

Gas Shielded Metal Arc MIG/MAG 3

Flux Cored Arc Basic FCAW 5

Submerged Arc Basic SAW 5

Heat Input: The heat input Q, which is given by the product of the line

energy E multiplied with an efficiency factor �� , Q = �� *E, is given here in

•



kJ/mm. There are two ways to take the influence of the heat input.

- The dependence between the preheating temperature and the weld energy

is shown in the weld parameter box which is shown after filling in all

necessary data.

- Moreover, the preheating temperature can be explicitly calculated by

inserting either the heat input Q in kJ/mm or the line energy E in kJ/mm

and the efficiency factor �� , which depends on the welding process used. The

efficiency factor the explicitly explained in the next section

From the data above the minimum preheating temperature is calculated as

follows:

Tp = 697*CET+ 160*tanh(d/35)+62*HD0,35

+ (53*CET-32)*Q-328

The range of validity for this formula is:

CET: 0:2 % - 0.5 %

d: 10 mm - 90 mm

HD: 1 ml/100g - 20 ml/100 g

Q: 0.5 kJ/mm - 4.0 KJ/mm

Influence of the cooling time:

The temperature-time cycle is of major importance for the mechanical

properties of the welded joint after welding. It is influenced in particular by the

welding geometry, the line energy applied, the preheating temperature as well

as the weld layer details. Normally the temperature-time cycle during welding

is expressed by the time t8/5 which is the time in which a cooling of the

welding layer from 800°C to 500°C occurs.

The maximum hardness in the HAZ normally decreases with growing cooling

time t8/5. If a given maximum hardness value is not to be exceeded for a

particular steel, the welding parameters have to the chosen in such a way that

the cooling time t8/5 does not fall under a particular value.

On the other hand, increasing cooling times cause a decrease of the toughness

of the HAZ, that means a decrease of the impact values measured in the Charpy

-V-test or an increase of the transition temperature of the Charpy-V-impact

energy. Therefore the welding parameters have to be selected in such a way,

that the cooling time does not exceed a particular value.

In general, for weldable fine -grain structural steel grades the cooling time for

filling and covering weld layers should be in the time 10 s and 25 s dependant

on the steel grade given here. After corresponding verification, there is no

problem to apply also other values of the cooling time t8/5 under the condition

that the quality demands on the structure to be welded are completely fulfilled

and suitable welding procedure qualification have been performed.

Furthermore you can calculate a welding parameter diagram which shows you

the possible heat-input - preheating temperatures for given maximum and

minimum cooling times. If you want to calculate explicit cooling times please

use the next section (Cooling time).

The following parameters have got an influence on the cooling time, either on

its calculation or on its selection and can be inserted here in order to obtain

optimised welding parameters:

Plate thickness d: The plate thickness is inserted in mm. It should be

considered that the influence of the plate thickness is of minor importance

for plate thicknesses above 60 mm due to the three-dimensional heat flux.

•

Welding geometry: The influence of the welding geometry is taken into

consideration by weld geometry factors F2 and F3 for two- and three-

dimensional heat flux. The values of the weld geometry factor for typical

weld geometries are:

•

Weld geometry F2 (two-

dimensional)

F3 (three-

dimensional)

Building-up weld 1.0 1.0



Filling passes of butt welds 0.9 0.9

Covering passes of butt

welds

1.0 0.9 - 1.0

One-pass fillet weld (Corner

joint)0.9 - 0.67

* 0.67

One-pass fillet weld (T-

joint)0.45 - 0.67

* 0.67

The welding geometry factor F2 depends on the relation heat input to plate

thickness. Approaching the three-dimensional heat flux F2 decreases for the

case of a one-pass fillet weld on a corner joint and increases for the one-

pass fillet weld on a T-joint. Therefore an adaptive calculation may be

necessary here.

The factors given above can be selected here. Moreover a free input of the

data in the range between 0 and 1 is also possible.

Heat Input: The heat input Q, which is given by the product of the line

energy E multiplied with an efficiency factor �� , Q = �� *E, is given here in

kJ/mm. The influence of the heat input in dependence of the

preheating/interpass temperature and the minimum and maximum cooling

time t8/5 is shown in the welding parameter diagram which is built up after

completion of the values needed.

•

Preheating/Interpass-temperature: The influence of the preheating time is

also expressed in the welding parameter diagram.

•

Maximum and minimum cooling time:

From the data given above the cooling time t8/5 can be calculated if a three-

dimensional heat flux is assumed:

t8/5 = (6700-5*TP)*Q* (1/(500-TP)-1/(800-TP))*F3

If the heat flux is two-dimensional the cooling time depends on the plate

thickness and the following formula is used:

t8/5 = (4300-4.3*TP)*105*Q

2/d

2* (1/(500-TP)

2-1/(800-TP)

2)*F2

Only the greater value obtained from the two formulas above is physically

valid. Often, a transition plate thickness dt is calculated, at which the

transition between the two-dimensional and the three-dimensional heat flux

occurs. This transition plate thickness is:

dt = SQR(((4300-4.3*Tp)*105/(6700-5*Tp)*Q*(1/(500-TP)

2-1/(800-TP)

2)/

(1/(500-TP) -1/(800-TP)))

The maximum and minimum cooling times depend on the steel grade which

is to be welded. The cooling times recommended by Dillinger Hütte GTS

brand products can be selected here. As described above, other cooling

times can be chosen under the condition that the quality demands on the

structure to be welded are completely fulfilled and suitable welding

procedure qualification have been performed. Therefore also a free input of

the cooling time is possible. In any case the recommendations given in our

material data sheets have to be taken into account too.

•

Recommended cooling times for Dillinger Hütte GTS steels

Steel grades Minimal cooling time t8/5 [s] Maximum cooling time t8/5

[s]

DI-MC 355 8 40



DI-MC 420 8 40

DI-MC 460 8 40

DILLIMAX

460

8 35

DILLIMAX

500

10 30

DILLIMAX

550

10 25

DILLIMAX

620

10 22

DILLIMAX

690

5 20

DILLIMAX

890

5 12

DILLIMAX

965

5 10

Welding parameter box

Form the above parameters a welding parameter box is created giving the

possible combinations of heat input Q and preheating/interpass temperature Tpfulfilling the following conditions:

sufficient preheating,•

Cooling time smaller than a maximum value defined above,•

Cooling time bigger than a minimum value defined above.•

Moreover a direct calculation of the preheating temperature by specifying

either the heat input Q or the line energy E and the efficiency factor �� is

enabled.

WELDING

HEAT INPUT/ COOLING TIME

One determining parameter during the calculation of welding parameters is the

heat input. By the input data

Electric Tension U [V]•

Electric Current I [A]•

Welding Speed v [cm/min]•

first the line energy E [kJ/mm] is calculated by the formula

E = U*I/v * (60/1000) in KJ/mm.

The heat input Q results form the line energy by the multiplication with an

energy efficiency factor �� which depends on the welding process applied.

Q = �� * E

with the efficiency factor

Energy efficiency factor for various welding processes

Welding process Efficiency factor ��

Manual Metal Arc 0.8

Submerged Arc 1.0

Metal Active Gas (MAG) 0.8



Metal Inert Gas (MIG) 0.7

Flux Cored Ard (FCAW) 0.9

Tungsten Inert Gas (TIG) 0.7

Cooling time

The cooling time between 800°C and 500°C t8/5 is the most important

parameter in order to determine the welding parameters applied during

welding of fine-grain structural steels. The underlying reasons are explicitly

described above.

In this menu you can easily calculate this cooling time by specifying the

following values:

Heat Input Q [in kJ/mm]•

Preheating temperature Tp [°C]•

Plate thickness d [mm]•

Welding geometry factors F2/F3: For the welding geometry factors the

suitable welding geometry has to be selected from a table, Moreover also a

free input in the range 0 to 1.0 is possible.

•

From the data given above the cooling time t8/5 can be calculated if a three-

dimensional heat flux is assumed:

t8/5 = (6700-5*TP)*Q* (1/(500-TP)-1/(800-TP))*F3

If the heat flux is two-dimensional the cooling time depends on the plate

thickness an the following formula is used:

t8/5= (4300-4.3*TP)*105*Q

2/d

2* (1/(500-TP)

2-1/(800-TP)

2)*F2

Only the greater values obtained from the two formulas above is physically

valid. Often, a transition plate thickness dt is calculated, at which the transition

between the two-dimensional and the three-dimensional heat flux occurs. This

transition plate thickness is determined as follows:

dt = SQR(((4300-4.3*Tp)*105/(6700-5*Tp)*Q*(1/(500-TP)

2-1/(800-TP)

2)/

(1/(500-TP) -1/(800-TP))*F2/F3)

Moreover it is signed whether a two- or three-dimensional heat flux occurs.

It should be considered that the assumptions underlying the formulas for the

cooling time are often not perfectly fulfilled. Therefore the values calculated

can deviate form the real values by up to 10 %.

WELDING

PEAK HARDNESS IN THE HEAT-AFFECTED ZONE

The peak hardness in the heat affected zone (HAZ) is often to be considered to

be a sign of the fabrication quality of the weld joint and is therefore often

measured during welding procedure approvals and welding test. Upper limits

for the HAZ hardness are determined in the welding standards such as EN 288.

Physically the maximum hardness depends on the cooling speed in the coarse-

grain zone of the HAZ. The faster the cooling speed the higher is the resulting

hardness in the HAZ. A slower cooling speed results in a smoother grain

structure such as bainite and ferrite. Therefore also the cooling time t8/5 is

often used to evaluate the maximum hardness in the HAZ zone.

The second important influencing factor is the chemical composition of the

steel because it determines the quantity of the various grain structures which

are formed during cooling. Normally alloying elements such as carbon,

molybdenum, manganese and chromium increase the hardability and shift the

hardness drop to longer cooling times. But also the hardness of the various

grain structures is influenced by the alloying composition.

Calculation of hardness values

The program offers two routines to evaluate the peak hardness in the HAZ, the

formula of Düren and the formula of Yurioka. Both formulas have been



developed by systematically performed investigations together with a

regression analysis of the HAZ-hardness in dependence of the chemical

composition and the t8/5-cooling time.

Here the chemical composition can be entered and then the theoretical

hardness according to the Düren- respectively Yurioka-formula is calculated in

dependence of the cooling time.

Moreover the value of the peak hardness for a special cooling time can be

calculated by inserting a cooling time.

The Düren-hardness is calculated according to the following formulas:

Martensite hardness HVMHVM = 802 x C + 305

Bainite hardness HVBHVB = 350 x CE* + 101

CE* = C +Si/11 +Mn/8 +Cu/9 +Cr/5 +Ni/17 +Mo/6 +V/3

Resulting hardness:

HV = 2019x[ C(1-log t8/5) + 0,3(CE*-C)] + 66x[1 - 0,8 x log t8/5 ]

If HV < HVM and HV > HVB, the Yurioka-hardness is calculated according to the

formulas

HV = 0,5 (HVM + HVB) - 0,455 (HVM - HVB) arctan t*

with HVM := 884 x C (1 - 0,3 C²) + 294

HVB := 145 + 130 x tanh (2,65 CE2 - 0,69)

CE1 := C + Si/24 + Mn/6 + Cu/15 + Ni/12 + Cr/8 + Mo/4

CE2 := C+Si/24+Mn/5+Cu/10+Ni/18+Cr/5+Mo/2,5+Nb/3+V/5

CE3 := C + Mn/3,5 + Cu/20 + Cr/5 + Ni/9 + Mo/4

t* := 4 (ln t8/5 - ln tnb)/(ln tnm - ln tnb) -2

tnb := exp (10,6 x CE1 - 4,8

tnm := exp (6,2 x CE3+ 0,74)

Moreover the maximum hardness values admissible by EN 288-3 can be called

by the button "Max. Hardness" and a maximum hardness value can be selected

and inserted in the hardness diagrams

Maximum admissible hardness values, HV 10 according to EN 288-3.

Steel group Single pass Multi-passes

After

welding

after post

weld heat

treatment

After

welding

after post

weld heat

treatment

1 - Steels with Reh �� 355

MPa

380 320 350 320

2 - Fine grain steel (N

or TM) with Reh > 355

MPa

380 320 350 320

3 - Quenchend and

tempered fine grain

steel with Reh > 500

MPa

450 to be

agreed

420 to be

agreed

4 - Steels with Cr �� 0,6

%, Mo �� 0,5 %, V �� 0,25

%,

to be

agreed

320 to be

agreed

320

5 - Steels with Cr �� 9 %,

Mo �� 1,2

to be

agreed

320 to be

agreed

320

Post-weld heat treatment (PWHT)

For welded joint which are treated by a post-weld heat treatment also the

hardness decrease due to this heat treatment can be calculated using the

formula of Okumura :



��HV = [884C+177-197CE2+16,5(HP-21,5)]xMM-7CE2+26

+[ 18 ( HP-18)2- 138 ] V

1/2

+[ 20 ( HP-18)2- 268 ] Nb

1/2

+[ 25 ( HP-17,3)2- 55 ] Mo

1/2

with MM

= martensite share = 0,5 - 0,455 arctan t*

CE2 and t* from the Yurioka formula

Herein HP is the so-called Hollomon-parameter HP = (T+273)/1000 x (20 + log

t) with the heat treatment temperature in °C and the annealing time t in hour.

For the calculation this parameter has to be entered or the annealing time and

temperature can be input.

After entering the input data a diagram shows the dependence of the PWHT-

induced hardness drop from the cooling time as well as the difference function

between Yurioka hardness and Okumura hardness decrease. A special value

can be evaluated by entering a cooling time.

WELDING

INDEX

Carbon Equivalents

CET-equivalents

Cooling time

Düren-hardness

Efficiency factor

Hardness in the HAZ

Heat Affected Zone

Heat Input

Hollomon-parameter

Hydrogen

Line Energy

Okumura-hardness

Preheating

Preheating temperature

Transition thickness

Weld geometry

Yurioka-Hardness



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rumus welding.pdf