This document provides information on predicting the minimum necessary preheat temperature for steel welding to prevent hydrogen-assisted cold cracking. It discusses factors that influence cold cracking such as chemical composition, plate thickness, welding heat input, residual stresses, and preheating method. The document describes methods for predicting weld metal hardness and tensile strength based on chemical composition and cooling time. It also provides carbon equivalent formulas used to evaluate steel weldability and references papers on determining preheat temperatures under various conditions.

1. .4 Minimum Necessary Preheat Temperature
The minimum necessary preheat temperature is predicted based on
a method described in the following paper:
N. Yurioka and T. Kasuya: "A chart method to determine necessary preheat in steel welding"
Welding in the World, vol. 35 (1995), p. 327-334
The validity of this method is compared with the British Standard and American Welding Society
method:
N. Yurioka: "Comparison of preheat predictive methods"
Welding in the World, vol. 48 (2004), p. 21-27
The objective of preheating is to effuse diffusible hydrogen out of welds to prevent hydrogen-
assisted cold cracking. The occurrence of cold cracking is influenced by the following factors:
1.Chemical composition of steel;
2.Plate thickness or wall thickness;
3.Weld metal diffusible hydrogen content
4.Welding heat input
5.Welding residual stresses or weld metal yield strength
6.Weld joint restraint
7.Notch concentration factor at weld toe and weld root or groove shape
8.Weld pass number
9.Preheating method (Heating rate, heating width)
10. Ambient temperature
11. Immediate postheating
The present predictive method considers most of the factors above mentioned.
1. Chemical composition of steel
The following carbon equivalent has been long used as an index representing the susceptibility to
cold cracking. or weldability.
CE(IIW) = C + Mn/6 + (Cu + Ni)/15 + (Cr + Mo + V)/5 [wt%]
This carbon equivalent satisfactorilly evaluates weldability whose carbon content is higher than
0.12%. Modern low alloy steel is mostly of a carbon reduced type (C <= 0.12%). Weldability of this
type of steel is more adequetly evaluated by the following carbon equivalent.
Pcm = C + Si/30 + Mn/20 + Cu/20 + Ni/60 + Cr/20 + Mo/15 +V/10 + 5B [wt%]
Susceptibility to cold cracking is determined by hardness of welds (HAZ and weld metal). The weld
hardness is determined by an interactive effect of weld hardenability and carbon content. The
following carbon equivalent considers this effect and can evaluates weldability of steel with a wide
range of carbon.
CEn = C + f(C) {Si/24 + Mn/6 + Cu/15 + Ni/20 + (Cr + Mo + Nb + V)/5} [wt%]
Where, f(C) = 0.5 + 0.25 tanh {20 (C - 0.12)} [wt%]
With decreasing carbon content, f(C) decreases from 1.0 to 0.5. Therefore, CEn is close to CE
(IIW) when C is higher than 0.15% and CEn approaches to as carbon content decreases. The
present preheat predictive method uses CEn carbon equivalent. CEn is stipulated in ASTM
A1005/A-00 and ASME B16.49-2000.

2. 2. Plate thickness and wall thickness
With increasing plate thickness, 1) the welding cooling rate increases (welding cooling time, t8/5
decreases) and thus, weld hardenability is raised; 2) the welding cooling time to 100°C, t100
decrease and thus, an oppotunity of effusion of diffusible hydrogen from weld metal decreases; 3)
the welding pass (layer) increases and thus the amount of hydrogen accumulated in weld metal is
raised. These effects raise a risk of the occurrence of cold cracking.
3. Weld metal diffusible hydrogen Weld metal diffusible hydrogen
Weld metal hydrogen is one of the important factors in hydrogen-assisted cold cracking. It is
desired to use welding materials of low hydrogen types. A care must be taken to prevent welding
materials from being moistened and to clean weld grooves before welding.
The following is an example of the diffusible hydrogen content, H(IIW) for various welding
materials:
Rutile electrode: 30ml/100g
Cellulosic electrode: 60ml/100g
Low hydrogen electrode: 5 - 8ml/100g
Ultra low hydrogen electrode: 2 - 5ml/100g
TIG, Solid wire GMAW: 2ml/100g
Flux cored wire GMAW: 6 - 10ml/100g
SMAW: 2 - 8ml/100g
4. Welding heat input
With increasing heat input, the cooling rate decreases (the welding cooling time between 800 and
500°C, t8/5 and welding cooling time to 100°C, t100 increases) and thus, a risk of the occurrence
of cold cracking is reduced. Roughly speaking, cold cracking is a matter of concern only when heat
input is not higher than 3kJ/mm.
5. Welding residual stresses or weld metal yield strength
Welding residual stresses are one of the important factors in cold cracking. The welding residual
stresses often attain the yield strength of weld metal. Hydrogen-assisted cold cracking is more
likely occur in welding of high strength steel with using high strength welding materials.
6. Weld joint restraint
The weld joint restraint affects the cold cracking occurrence in one-pass welding. In multi-pass
welding, the joint restraint influences cold cracking to much lesser extent because a joint has been
restrained after root-pass welding. Very low restraint may cause bending distortion leading to high
bending stresses in weld root. As a result, root cracking may be caused. The present predictive
method does not consider the effect of joint restraint.
7. Notch concentration factor at weld toe and weld root or groove shape
Cold cracking is more likely to occur at the root pass in the first side of double bevel groove (K
groove, X groove) because of a high notch concentration factor at the root. However, the root weld

3. of the first side is generally gouged before the start of second side welding. In welding with V
groove and single-bevel groove, a notch concentration factor at the root is far less than that in
double bevel groove welding. Therefore, the present predictive method does not consider the
effect of a notch concentration factor.
In practical penetration welding with Y groove or single bevel groove, it is difficult to detect root
cracking. Therefore, it is desired to employ the preheat temperature for repair welding.
8. The number of weld passes
In muti-pass welding, a root pass is reheated by subsequent passes so that residual stresses as
well as hydrogen in the root bead are reduced. As a result, root cracking is less likely to occur in
multi-pass welding than in one-pass welding.
This predictive method firstly gives the preheat temperature necessary to avoid root cracking in y-
groove restraint testing in which a one-pass short bead is deposited with high restraint as well as
high notch concentrations. This testing is so sever that much higher preheat is required than in
normal welding practices. For normal welding, this predictive method gives preheating
temperatures much lower than that for y-groove testing. For instance, the necessary preheating
temperature for normal welding is 75°C less than that for y-groove testing when YP380MPa class
steel is welded.
9. Welding residual stress
This predictive method considers the effect of welding residual stresses. The maximum welding
residual stress is considered to be close to the yield strength of the weld metal. For higher strength
steel, HAZ toe cracking, HAZ under bead cracking and weld metal transverse cracking are more
likely other than root cracking. As mentioned above, the necessary preheat can be decreased from
that obtained by y-groove testing. However, the amount of this temperature reduction decreases as
the steel strength increases (the weld metal strength also increases and welding residual stress
increases as well). For instance, the temperature reduction is 75°C for YP360 steel and 0°C for
YP700 steel.
In this predictive method, the yield strength of weld metal has to be input. When it is unknown, the
specified minimum yield strength of the steel may be input.
10. Preheating method
The objective of preheating is to enhance the hydrogen evolution from a weld. The effect of
preheating increases as the width of preheating increases and the heating rate of preheating
decrease. The preheating width over 200mm each side of the groove is desired. The necessary
preheating temperature has to be increased in the case of rapid preheating and narrow local
preheating.
11. Ambient temperature
The occurrence of cold cracking is significantly affected by the ambient temperature; The cracking
is more likely at the lower temperatures. As for the determination of preheat at lower ambient
temperatures, the following paper should be referred to.
T. Kasuya and N. Yuiroka: "Determination of necessary preheat temperature to avoid cold cracking under
various ambient temperatrues", ISIJ International, vol. 35 (1995), No.10, p.1183-1189

4. 12. Immediate post heating
Post heating immediately after welding is very effective for the hydrogen evolution. When the
predicted necessary preheating temperature is excessively high, immediate post heating should be
employed so that the necessary preheating temperature could be reduced.
150 °C for 95 hrs, or 200 °C for 29 hrs, or 250 °C for 12 hrs, or 300 °C for 2 hrs.
Copyright The Japan Welding Engineering Society,2002-2013 All Right Reserved,
1.5 Prediction of weld metal tensile strength
This predictive method is base on the following paper.
N. Yurioka: Perdition of weld metal strength, IIW Doc. IX-2058-03
This method first predicts the weld metal hardness, Hv from weld metal
chemical composition (C, Si, Mn, Cu, Ni, Cr, Mo, V, Nb, Ti[wt%]) and the
welding cooling time (t85[s]).
Hv = (HM + HB)/2 - (HM-HB) arctan(x)/2.2
x = 4log(t85/tM) / log(tB/tM) - 2
HM = 884C + 294
tM(s) = exp(10.6CEI - 4.8)
CEI(wt%) = C + Si/24 + Mn/(2.88(1 +Mn)) + Ni/30 + Cr/16 + Mo/8
HB = 145 + 130 tanh(2.65CEII - 0.69)
CEII(wt%) = C + Si/24 + Mn/(2.16(1 + Mn)) + Cu/10 + Ni/45 + Cr/10 + Mo/5
+2V + 2.2Nb/(1 + 5Nb) + Ti/10
tB(s) = exp(6.2CEIII + 0.74)
CEIII(wt%) = C + Mn/(1.68(1 + Mn)) + Ni/15 + Cr/10 + Mo/8
Then, Hv thus obtained is converted to the weld metal tensile strength,
TS.

5. TS(MPa) = 3.0Hv + 22.3