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What is the difference between the various Carbon Equivalent Formulae used in

relation to hydrogen cracking?

Frequently Asked Questions

Carbon equivalent formulae were originally developed to give a numerical

value for a steel composition which would give an indication of a carbon

content which would contribute to an equivalent level of hardenability for that

steel !hese formulae were later e"tended to represent the contribution of the

composition to the hydrogen cracking susceptibility of steel !hey are also used

as compositional characterising parameters for other properties that may be

linked to hardness# such as toughness and strength

!hese kind of relationships originate from about $%&' when (earden and

)*+eill proposed a carbon equivalent formula to predict steel strength#

hardenability and ,A- hardness .$/ 0n $%12# the 0nternational 0nstitute forWelding 300W4 adopted a somewhat simplified form of (earden and )*+eill*s

formula for hardenability which became a generally accepted measure of steel

weldability 5 CE00W 

6ince its adoption by 00W# the equation has been incorporated into a number of

material standards and codes# including E+ $'$$5787''$ .7/  3replaces 96 :$;:5

$%<& .;/  4 and in a modified form in AW6 ($$ .&/  # with a =>6i1= term added tothe equation

Further development of Carbon equivalent formulae has taken place and several

can be found in technical literature today !hree of the more common ones are

@cm# CEq and CE+ 0to and 9essyo .:/  developed @cm in apan based on a wider

range of steels than the 00W formula8

!he CEq formula devised by (Bren .1/  has a similar appearance8

9oth the @cm and the CEq formulae were developed for low carbon steels for

which the CE00W is less suitable @cm is generally used for modern steels typically

used for pipeline manufacture# where carbon contents are no more than '$$ wt

D .2/ 

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,owever# it should be noted that the @cm formula was derived largely from lower 

C low alloy steels

!he CE+ formula was proposed to evaluate the weldability of a wide variety of

steels For the higher C range# the values of CE+ correlate well with carbon

equivalents such as CE00W# whereas for lower carbon steels the values are close

to those of the CEq formula CE+ is given by8

urioka .</ illustrated a good correlation between @cm and CE+ for structural

steels# low5alloy steels 3+i5Cr5o type4 and carbon steels# provided the carbon

content was less than '$2 wtD From this comparison the followingrelationship was derived8

CE+ G 7@ cm 5 ''%7 3C H '$2D4

For carbon steels# the values deviate from this relationship as the

@cm overestimates the cold cracking susceptibility Where the carbon content

e"ceeds '$2 wtD# there is a better correlation between CE+ and CE00W 8

CE+ G CE00W > ''$7 3C I '$2D4

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urioka .</  grouped a number of carbon equivalents for the assessment of

weldability# as follows8

Group Formula

A  

B 

C  

Jroup A are characterised by $1 as the coefficient of anganeseK Jroup 9 has

Carbon as more important than the other alloying elements and is more

applicable to modern steelsK Jroup C includes interactions between Carbon and

other elements

)ther e"isting formulae that could be classified as Jroup 9 are the CEw

developed by Cottrell .%/  # and the CE! included in the standard E+ $'$$5

787''$ .;/  Cottrell claimed that the CEw formula could improve the predictions

of cracking by a factor of three# compared to CE00W !he data on which the

formula was based was collected from results published in open literature# and

covered a wide range of composition and welding conditions !he resulting

formula is as follows8

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!he CE! formula is based on similar elements to the CE00W formula with the

e"ception of Lanadium# although carbon is considered to have moresignificance than the other elements8

Meferences

N° Author Title

$

(earden

and )*+eill

,8

*A guide to the selection and welding of low alloy structural

steel* !ransactions of the 0nstitute of Welding# Lol;# $%&'#

 pp7';57$&

7  

E+ $'$$57# *Welding 5 Mecommendations for welding of

metallic materials 5 @art 78 Arc welding of ferritic steels*#

9ritish 6tandards 0nstitution# arch 7''$ A( A$ (ec 7'';

;  

96:$;:5$%<&# *@rocess or arc welding of carbon and carbon

manganese steels*# 9ritish 6tandards 0nstitution# $%<&

6uperseded by 374

&  AW6 ($$57'$' Anne" 0# *Juideline on alternative methods

for determining preheat*# American Welding 6ociety 0nc# 7'$'

:0to and

9essyo N8

*Weldability formula of high strength steels related to heat

affected Oone cracking*# @ublished by the 0nternational 0nstitute

of Welding# $%1<# (oc 0P5:2151<

1 (Bren C F8

*@rediction of the hardness in the ,A- of ,6A steels by

means of the C5equivalent*# 6elect Conference on

,ardenability of 6teels# (erby# RN# $2 ay $%%'# @aper &

2 9ailey +8

*Factors 0nfluencing Weldability*# 0n 9ook *Weldability of

Ferritic 6teels*# Abington @ublishing $%%&# 069+ $ <::2; '%7

<

< urioka +8

*Carbon equivalents for hardenability and cold cracking

susceptibility of steels*# 6elect Conference on ,ardenability of

6teels# (erby# RN# $2 ay $%%'# @aper ;

%Cottrell C

8

*An improved prediction method for avoiding ,A- hydrogen

cracking*# Welding and etal Fabrication# Lol :<# +o ;# April

$%%'# pp $2<5$<;