Welcome to Preheat Calculation Program In this help file you will find information and background of this program. The program itself is self explanatory. Nevertheless if you have some questions, problems or suggestions, you can send me an e-mail, so I can improve this program c.brak@it.fnt.hvu.nl The subjects discussed in this file are:

Avoidance of hydrogen cracking in ferritic steels

Method to determine preheat temperature

Weld temperature cycle

Heat input

Carbon equivalent

Combined Thickness

Diffusible H Content

Transition thickness

Calculating preheating temperature according AWS D1.1

Weld shape factor

Grouping system for steels (groups 1-4) Disclaimer All information obtained from this program shall be considered as a guideline. Under

no circumstances, the author can be hold liable for any situation resulting from using this program.

All rights reserved, including the right of reproduction in whole or in part in any form.

Avoidance of cracking in ferritic steels The scope of this program is to give guidance for avoiding hydrogen cracking (cold cracking) in unalloyed and low-alloyed ferritic steels. Cold cracking in ferritic steels can occur when there are three combined factors: Hydrogen generated by the welding process A microstructure, susceptible to cracking Residual stresses in the welded joint

In unalloyed en low alloyed steels, most of the hydrogen cracks are in the HAZ, however cracks can also occur in the weld metal, especially in low alloyed steel. To avoid this cracking you can minimize the combined contribution of the factors. Weld metal hydrogen content The principal source of hydrogen is the moisture in the consumables. Basic stick electrodes normally generated less hydrogen than rutile or cellulosic types. For cored wires, basic0, rutile- and metal cored wires, all can deposit weld metal with low hydrogen. In sub arc welding, basic fluxes typically give a low hydrogen weld metal. Parent metal composition The hardenability of a material is usually expressed in terms of its carbon content or, when other elements are taken into account its carbon equivalent (like CE). The higher the carbon equivalent the greater the risk of hydrogen cracking. Generally, steels with a CE < 0,4 are not susceptible to hydrogen cracking, as long as low hydrogen welding consumables are used. Parent material thickness The parent material thickness influences the cooling rate, and therefore the hardness of the HAZ, but also the amount of hydrogen retained in the weld and the residual stresses. Stresses acting on the weld The stresses generated across the welded joint will be greatly influenced by external restraint, material thickness, joint geometry and fit up. Areas of stress concentration are more likely to initiate a crack at the toe and root of the weld. Heat input The heat input, together with the material thickness and the preheat temperature will determine the thermal cycle and the resulting microstructure, the hardness and the remaining hydrogen content. A high heat input will reduce the hardness and hydrogen content, but increases the width of the heat affected zone and decreases the Charpy toughness. Preheating When it is not possible to avoid cold cracks by lowering the hydrogen content, preheat is a necessity. In EN 1011-2 (2001) recommendations for the preheating temperature of ferritic steels are given.

typical cold crack, due to high stresses in the root

(misalignment), as well as high hardness in the HAZ (from: Bailey, Welding of ferritic steels)

Method to determine preheat temperature of ferritic steels The methods, described in EN 1011-2:2001, are recommendations to avoid hydrogen cracking (also known as cold cracking) in ferritic steels. Many methods have been proposed for predicting preheat temperature to avoid hydrogen cracking in non-alloyed, fine grained and low alloy steel weldments. Examples are given in IIW documents. Two of those methods are described in this standard: Method A is based on extensive experience and data which is mainly, but not exclusively, for carbon-manganese type steels. Method B is based on experience and data which is mainly, but not exclusively for low alloy high strength steels. Beside these two methods there are tables which shall be used for creep resisting and low temperature steels. (method C). The recommendations apply only to normal fabrication restraint condition. Higher restraint situations may need higher preheat temperature or other precautions to prevent hydrogen cracking. The methods A and B refer to welding of parent metal at temperatures above 0 C. When welding is carried out below this temperature it is possible that special requirements will be needed. Otherwise lower preheat temperatures are possible, if this is supported by procedures. To calculate the preheat temperature for method A or B you have to know The hydrogen content of the consumable (HD) The composition of the parent metal (CE of CET); The plate thickness and joint geometry The heat input

In this program, a method D is added, based on the standard AWS D1.1 To calculate the preheat temperature for this method you have to know The hydrogen content of the consumable (HD) The composition of the parent metal (Pcm); The plate thickness The restraint level

Weld temperature cycle The calculation of the welding temperature cycle is based upon the simplified formulas of Rykalin. The formulas used here for respectively 3- and 2-dimensional cooling of a bead on plate are the following. 3-Dimensional: The temperature as a function of time and place is given by

.Tat4

Rexp

t2Q

)R,t(T 02

++

--

p lp l==

The cooling time from 800C to 500C then is

.T800

1T500

12Q

t00

5/8

--

----

p lp l

==DD

2-Dimensional: The temperature as a function of time and place is given by

.Tat4

Rexp

tc4d

Q)R,t(T 0

2

++

--

plrplr==

The cooling time from 800C to 500C then is

.)T800(

1

)T500(

1

cd4

Qt 2

02

02

2

5/8

--

----

plrplr

==DD

Here R represents the distance to the center of a point (3D) or line (2D) shaped heat source, ll, c en rr are the physical constants, d is the plate thickness and T0 the preheat and interpass temperature. The relations for the cooling time t8/5 have been empirically adapted to steel by Uwer et. al. (IIW doc. IX 1631-91), obtaining the formulas below. Here there is no need for the values of l, r en c, which are often difficult to obtain. Furthermore the weld shape factor for three- or two-dimensional heat flow (F3 respectively F2) has been introduced. This enables one to calculate more situations than a bead on plate. These new formulas for Dt8/5 are described in EN 1011-2.

3-Dimensional:

.FT800

1T500

1Q)T56700(t 3

0005/8

--

----

--==

2-Dimensional:

.F)T800(

1

)T500(

1

d

Q10)T3,44300(t 22

02

02

25

05/8

--

----

--==

The transition thickness dt is the plate thickness at which the transition from three-dimensional to two-dimensional heat flow takes place. In that case F2 = F3 and both values of t8/5 are equal, also:

--

++--

--

--==

000

50

t T8001

T5001

QT56700

10)T3,44300(d

Some values of the transition thickness are below:

Preheating temperature Q.

20C. 100C. 200C.

0,5 10.4 11.1 12.3

1 14.7 15.7 17.4

1,5 18 19.2 21.3

2 20.7 22.2 24.6

2,5 23.2 24.8 27.5

3 25.4 27.1 30.1

Heat Input The heat input is defined as

v

IUkQ

== (kJ/mm)

where k = relative thermal efficiency for the applicable process (see table); U = arc voltage in V I = welding current in mm/s v = welding speed in mm/s; Often the welding speed is given in cm/min. In case of shielded metal arc welding; it may be difficult to use the above formula, so you can use the data of the tables listed in EN 1011-2, in which the run out length is expressed in terms of electrode diameter and heat input, by different efficiencies and a consumed electrode length of 410 mm (when the electrode length is 450 mm). Otherwise you can use the following formula:

rol

FLDQ

2 == (kJ/mm)

where D = electrode diameter L = the consumed length of the electrode (mm). Normally this is the originally length

less 40 mm for the stub end rol = run out length F = factor in kJ/mm3 depending on the electrode efficiency

Efficiency approx. 95% F = 0,0368 95% < efficiency 110% F = 0,0408 110%< efficiency 130% F = 0.0472 efficiency > 130% F = 0,0608

This formula is normally used when the electrode length differs from 450 mm, but is also used in this program

Carbon equivalent Hardness and hardness penetration of steel (the hardenability) depends on the carbon content, the alloying elements, the cooling rate and the grain size. The effect of the alloying elements on the hardenability, and thus on the weldability of steel is usually expressed in a carbon equivalent. In a carbon equivalent formula the hardening effect of each alloying element is compared to that of carbon. Because it is an empirical formula, there are a number of carbon equivalents. In this program there are three formulas used (CE, CET and Pcm).

1. 15

CuNi5

VMoCr6

MnCCE

++++++++++++== in %

This carbon equivalent is applicable in the range of 0,30 to 0,70 and may be used for unalloyed, fine grained and low alloy steels within the following range of composition (weight %) Carbon 0,05 to 0,25 % Silicium 0,8% max. Manganese 1,7% max. Chromium 0,9% max. Copper 1,0% max. Nickel 2,5% max. Molybdenum 0,75% max. Vanadium 0.20% max.

The formula is not suitable for boron-containing steels When, of the elements in this formula, only carbon and manganese are stated on the mill sheet, then 0,03 should be added to the calculated value. (This is corrected in the program)

2. 40Ni

20CuCr

10MoMn

CCET ++++++++++== in %

This carbon equivalent is applicable in the range of 0,30 to 0,70 and may be used for unalloyed, fine grained and low alloy steels within the following range of composition (weight %). Carbon 0,05 to 0,32% Silicium 0,8% max. Manganese 0,5 to 1,9% Chromium 1,5% max. Copper 0.7% max. Nickel 2,5% max. Molybdenum 0,75% max. Vanadium 0.18% max. Niobium 0,06% max. Titanium 0,12% max Boron 0,005% max

The relationship is valid for structural steels with Rp02 < 1000 N/mm2 , and

CET = 0,2 to 0,5% The CET of the parent material exceeds that of the weld metal by at least 0,03% Otherwise the calculation of the preheat temperature has to be based on a CET of the weld metal, increased by 0,03% (This can not be corrected by the program)

3. B510V

15Mo

60Ni

20CuCrMn

30Si

CPcm ++++++++++++++++==

This carbon equivalent, according Ito and Bessyo, for low alloyed steels is valid within the following composition(weight %): C 0,07 to 0,22% Mn 0,4 to 1,40 % Si 0,6% max. Ni 1,2% max Cr 1,2% max Mo 0,7% max V 0,12% max Cu 0,5% max. B 0,005% max. This formula is used, together with the hydrogen content, plate thickness and restraint condition to calculate a preheating temperature from a table. (method D in this program)

Combined thickness The combined thickness (tg) is the sum of the parent metal thickness averaged over a distance of 75 mm from the weld line. Combined thickness is used to assess the heat sink of a joint for the purpose of determining the cooling rate In a fillet weld, the heat sink is greater than in a butt weld with the same thickness. The preheating temperature is higher because of the greater combined thickness.

Tg = d1 + d2 + d3

Tg = D1 + D2

Diffusible H Content In fusion welding the hydrogen content, immediately after solidification, is very high, but most of it diffuses out of the weld This diffusible hydrogen moves not only into the air, but also into the HAZ. The remaining diffusible hydrogen can be high resulting embrittlement. It is necessary to know the amount of diffusible hydrogen. Sources are not only the consumables, but also the plate surface and the atmosphere. The hydrogen content is usually expressed in ml/100 g deposited weld metal, known as HD. In setting up welding procedures, the hydrogen content in the weld metal as a result of supported by the consumable used, is divided in classes: hydrogen scales for A to E

Diffusible hydrogen content ml/100g of deposited metal Hydrogen scale > 15 A 10 15 B 5 10 C 3 5 D 3 E

Transition thickness The transition thickness dt is the plate thickness at which the transition from three-dimensional to two-dimensional heat flow takes place. In that case F2 = F3 and both values of t8/5 are equal, also:

--

++--

--

--==

000

50

t T8001

T5001

QT56700

10)T3,44300(d

Some values of the transition thickness (in mm) are below:

Preheating temperature

Q. 20 C. 100 C. 200 C.

0,5 10.4 11.1 12.3

1 14.7 15.7 17.4

1,5 18 19.2 21.3

2 20.7 22.2 24.6

2,5 23.2 24.8 27.5

3 25.4 27.1 30.1

Weld shape factor The influence of the weld shape on the cooling time has been investigated by Uwer et al. and is used in the calculations given in EN 1011-2. The shape factor for two dimensional is F2, for three dimensional F3

F2 F3 Form of weld

Two dimensional heat flow Three dimensional heat flow

1

1

0.9

0.9

0.9-0.67

0.67

0.45-0.67

0.67

Calculating preheating temperature according to AWS D1.1 Here the calculation of the preheating temperature from Pcm (method D) according to awsD1.1 is explained First calculate the Pcm value and determine the hydrogen content. A Susceptibility Index Grouping A-G is then derived from a table, or by calculation. Then a restraint condition and plate thickness is chosen. In the second table the advised minimum preheating temperature derived at the crossing of the Susceptibility Index and the plate thickness by the given restraint factor To calculate the susceptibility index grouping there are two methods 1. AWS formula method

The formula susceptibility index = 12*Pcm +10log HD Pcm is the calculated value and the following value of HD, given in ml/100 g of weld metal: H1 = 5, H2 = 10, H3 =30 This gives values for the SI, which are converted to a susceptibility index grouping: For greater convenience , the Susceptibility Index Groupings have been expressed in the table by means of letters A through G, to cover the following range:

susceptibility index susceptibility index grouping

H2 Low Hydrogen The consumables give a diffusible hydrogen content of less than 10 ml/100 g

deposited weld metal H3 Hydrogen not controlled Restraint Low restraint

This level describes common fillet and groove welded joints in which a reasonable freedom of movement of members exists.

Medium restraint This level describes common fillet and groove welded joints in which, because of

members being already attached to structural work, a reduced freedom of movement exists.

High restraint This level describes welds in which there is almost no freedom of movement for

members joined (such as repair welds, especially in thick material). Example, using the table. Suppose PCM = 0,24 and HD = 7 ml, Then the susceptibility index is D (Pcm 75 20 20 40 95 120 140 150

Medium restraint < 10 < 20 < 20 < 20 < 20 70 140 160

10-20 < 20 < 20 20 80 115 145 160

20-38 < 20 20 75 110 140 150 160

38-75 20 80 110 130 150 150 160

>75 95 120 140 150 160 160 160

High restraint < 10 < 20 < 20 < 20 40 110 160 160

10-20 < 20 20 70 105 140 160 160

20-38 20 85 115 140 150 160 160

38-75 115 130 150 150 160 160 160

>75 115 130 150 150 160 160 160

Table 2 Advised minimum preheating temperature as a function of restraint, plate thickness and Susceptibility Index (Pcm, HD).

Grouping system for steels (groups 1-4) Method B is valid for steel of groups 1-4 according to CR ISO/ TR 15608 (Welding Guidelines for a metallic material grouping system , 1999) Groups 1-4 are listed below Group Subgroup Type of steel

1 Steels with a specified minimum yield strength ReH 460 N/mm

2 and with analysis in %:

C 0.25 * A higher value is accepted provided that Cr + Mo + Ni+ Cu + V 0,75 %

Si 0.60 Mn 1.70 Mo* 0.70 S 0.045 P 0.045 Cu* 0.40 Ni* 0.5 Cr* 0.3** ** for castings 0,4 Nb 0.05 V* 0.12 Ti 0.05 1.1 Steels with a specified minimum yield strength ReH 275 N/mm

2

1.2 Steels with a specified minimum yield strength 275 N/mm2 460 N/mm

2

3 Quenched and tempered steels and precipitation hardened steels except stainless steels with a specified minimum yield strength ReH >360 N/mm

2

3.1 Quenched and tempered steels and precipitation hardened steels except stainless steels with a specified minimum yield strength 360 N/mm2 < ReH 690 N/mm2

3.2 Quenched and tempered steels and precipitation hardened steels except stainless steels with a specified minimum yield strength ReH >690 N/mm

2

3.3 Precipitation hardened steels except stainless steels

4 Low vanadium alloyed Cr-Mo-(Ni) steels with Mo 0,7 % and V 0,1% 4.1 Steels with Cr 0,3 % and Ni 0,7 % 4.2 Steels with Cr 0,7 % and Ni 1,5 %

Welcome to Preheat Calculation Program Avoidance of htydrogen cracking in ferritic steelsMethod to determine preheat temperature Weld temperature cycle Heat Input Carbon equivalent Combined thickness Diffusible H Content Transition thickness Weld shape factor Calculating preheating temperature according AWS D1.1Grouping system for steels (groups 1-4)