Interpass temperature used was a 50˚C higher than the selected preheat temperature. Approximately 28 passes were made to completely fill the slot. The rail section was then allowed to cool after the welding and any ex-cessive material was ground off from the surface. The welded rail head was then sliced into thin sections of. For ASTM A709 Grade HPS 70W and ASTM A852, the maximum preheat and interpass temperatures shall not exceed 400°F 200°C for thicknesses up to 1-1/2 in 40 mm, inclusive, and 450°F 230°C for greater thicknesses. The use of high heat input welding processes such as submerged arc welding (SAW) may allow for lower preheat temperatures.

One of the best tips I have heard of I think actually came from some
Lincoln literature I read somewhere.
Take the unknown material and weld a small plate to the base material
forming a tee joint. The fillet should be about one to two inches long on
one side. Snap the piece off and inspect the weld fracture. If there is
material torn out of the base piece then the material needs some preheat.
The experiment can be repeated with increasing preheat until the fracture
does not show any tear out.
Even mild steel requires some preheat once you are welding items over
one inch thick. In a structural shop where I worked we started using a bit
of preheat on any plate over 3/4 inch just to be safe.
Randy

Josh wrote in message <36C42C04...@bellsouth.net>...
snip

>Has anyone out there got any rules of thumb that might come in handy
>for guestimating preheat on unknown metal?
>
>Interesting tidbit from the gizmo - It says on it that preheat and
>interpass temp should be increased 300 degrees F when non-low hydrogen
>processes are used.
>

Lincoln Electric Welding Preheat And Interpass Temperature Calculator

Carbon Equivalents

Welding Parameters / Preheating

Effective 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.

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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
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 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

• Effective Heat Input: The effective heat input Q, which is given by the product of the heat input E multiplied with an efficiency factor h , Q = h *E, is given here in kJ/mm. There are two ways to take the influence of the effective 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 effective heat input Q in kJ/mm or the heat input E in kJ/mm and the efficiency factor h , 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 heat input applied, the preheating temperature as well as the weld layer details. Normally the temperature-time cycle during welding is expressed by the time t_8/5 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 t_8/5 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 t_8/5 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*	0.69
One-pass fillet weld (T-joint)	0.45 - 0.67*	0.67

The welding geometry factor F₂ depends on the relation effective 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.

Lincoln Electric Welding Preheat And Interpass Temperature Calculator Is Still Available Today

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.

• Effective Heat Input: The effective heat input Q, which is given by the product of the heat input E multiplied with an efficiency factor h , Q = h *E, is given here in kJ/mm. The influence of the effective heat input in dependence of the preheating/interpass temperature and the minimum and maximum cooling time t_8/5 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 t_8/5 can be calculated if a three-dimensional heat flux is assumed:
  t_8/5 = (6700-5*T_P)*Q* (1/(500-TP)-1/(800-T_P))*F₃
  If the heat flux is two-dimensional the cooling time depends on the plate thickness and the following formula is used:
  t_8/5 = (4300-4.3*T_P)*10⁵*Q²/d²* (1/(500-T_P)²-1/(800-T_P)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:
  d_t = SQR(((4300-4.3*T_p)*10⁵/(6700-5*T_p)*Q*(1/(500-T_P)²-1/(800-T_P)²)/ (1/(500-T_P) -1/(800-T_P)))
  The maximum and minimum cooling times depend on the steel grade which is to be welded. The cooling times recommended by Dillinger 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.

Welding parameter box

Form the above parameters a welding parameter box is created giving the possible combinations of effective heat input Q and preheating/interpass temperature T_p fulfilling 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 effective heat input Q or the heat input E and the efficiency factor h is enabled.

______________________________________________________________________________________________________________

EFFECTIVE HEAT INPUT/ COOLING TIME

One determining parameter during the calculation of welding parameters is the effective heat input. By the input data

• Electric Tension U [V]
• Electric Current I [A]
• Welding Speed v [mm/min]

first the heat input E [kJ/mm] is calculated by the formula

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

The effective heat input Q results form the heat input by the multiplication with an energy efficiency factor h which depends on the welding process applied.

Q = h * E

with the efficiency factor

Energy efficiency factor for various welding processes

Welding process	Efficiency factor h
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 t_8/5 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:

• Effective Heat Input Q [in kJ/mm]
• Preheating temperature T_p [°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:

t_8/5 = (6700-5*T_P)*Q* (1/(500-T_P)-1/(800-T_P))*F₃

If the heat flux is two-dimensional the cooling time depends on the plate thickness an the following formula is used:

t_8/5 = (4300-4.3*T_P)*10⁵*Q²/d²* (1/(500-T_P)²-1/(800-T_P)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:

d_t = SQR(((4300-4.3*T_p)*10⁵/(6700-5*T_p)*Q*(1/(500-T_P)²-1/(800-T_P)²)/ (1/(500-T_P) -1/(800-T_P))*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 %.

______________________________________________________________________________________________________________

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 DIN EN ISO 15614-1.
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 t_8/5 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 t_8/5-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 HV_M
HV_M = 802 x C + 305

Bainite hardness HV_B
HV_B = 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- 0,5 * log t_8/5) + 0,3(CE*-C)] + 66x[1 - 0,8 x log t_8/5 ]

If HV < HV_M and HV > HV_B, the Yurioka-hardness is calculated according to the formulas

HV = 0,5 (HV_M + HV_B) - 0,455 (HV_M - HV_B) 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 + ΔH
CE2	:=	C+Si/24+Mn/5+Cu/10+Ni/18+Cr/5+Mo/2,5+Nb/3+V/5
CE3	:=	C + Mn/3,6 + 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)

Note that ΔH is a term introduced to account for the strong hardening effect of boron, such that;

ΔH	=	0	when B ≤ 1ppm,
ΔH	=	1.5 (0.02-N)	when B ≤ 2ppm,
ΔH	=	3.0 (0.02-N)	when B ≤ 3ppm, and
ΔH	=	4.5 (0.02-N)	when B ≤ 4ppm,

Moreover the maximum hardness values admissible by DIN EN ISO 15614-1 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 DIN EN ISO 15614-1.

Steel group CR ISO 15608	without heat treatment	with heat treatment
1a, 2	380	320
3b	450	380
4, 5	380	320
6	—	350
9.1 9.2 9.3	350 450 450	300 350 350

^a If hardness tests are demanded
^b For steels with R_eH, min > 890 MPa special agreements are required.

1) Steels with mind. ReH ≤ 460 MPa
2) Thermomechanically rolled steels with min. ReH > 360 MPa
3) Quenched and tempered steels with min. ReH > 360 MPa

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 :

DHV =	[884C+177-197CE2+16,5(HP-21,5)]xMM-7CE2+26
+[ 18 ( HP-18)2 - 138 ] V1/2
+[ 20 ( HP-18)2 - 268 ] Nb1/2
+[ 25 ( HP-17,3)2 - 55 ] Mo1/2
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.

INDEX

Carbon Equivalents
CET-equivalents
Cooling time
Düren-hardness
Efficiency factor
Hardness in the HAZ
Heat Affected Zone
Effective Heat Input
Hollomon-parameter
Hydrogen
Heat Input
Okumura-hardness
Preheating
Preheating temperature
Transition thickness
Weld geometry
Yurioka-Hardness