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Welding consumables - Part 3

   

Job Knowledge 84

Part 1
Part 2
Part 4
Part 5

jk84f1.jpgThe last two articles covered the various types of manual metal arc consumables that are available.

In order to be able to specify the type of flux coating, welding characteristics and chemical composition of an electrode for a particular application, there needs to be some standardised method of unique identification that is universally recognised.

This requirement has led to the writing of a series of consumable specifications that enable an electrode to be easily and uniquely identified by assigning a consumable a 'classification'. The two MMA electrode classification schemes that will be dealt with in this month's article are the EN (Euronorm) and the AWS (American Welding Society) specifications. There is insufficient space to cover in detail the whole range of compositions for MMA electrodes so the emphasis here will be on the carbon steel filler metals.

The European specification for non-alloy and fine grained steel MMA electrodes is EN 499. This divides the classification or designation number into two parts. Part 1 is a compulsory section that requires symbols for the process, strength and elongation, impact strength, the chemical composition and the type of flux coating. The second part is optional and includes that includes symbols for the type of current and metal recovery, the welding position(s) that the electrode can be used in and for the maximum hydrogen content of the deposited weld metal (NOT the electrode).

The designation of a covered electrode begins with the letter 'E'. This tells us that this is a covered electrode intended for MMA welding. The next two numbers give the minimum yield strength that may be expected as shown in Table 1.

Table 1 Strength and elongation symbols

SymbolMin Yield Strength
N/mm
Tensile Strength
N/mm
Minimum
Elongation %
35 355 440 - 570 22
38 380 470 - 600 20
42 420 500 - 640 20
46 460 530 - 680 20
50 500 560 - 720 18

The next symbol indicates the temperature at which an average impact value of 47J can be achieved, as shown in Table 2.

Table 2 Impact value symbol

SymbolTemperature for
average of 47J °C
Z No requirement
A +20
0 0
2 -20
3 -30
4 -40
5 -50
6 -60

The third mandatory symbol is for the composition. Although the specification title (non-alloy and fine grained steels) suggests that the electrodes have no alloying elements present, up to 3% Ni and NiMo electrodes are included, see Table 3. (This symbol is only applied where the electrode contains ≥0.3Mo or ≥0.6Ni).

Table 3 Chemical composition symbols

SymbolChemical composition % max or range
 MnMoNi
No symbol 2.0 - -
Mo 1.4 0.3 - 0.6 -
MnMo >1.4 - 2.0 0.3 - 0.6 -
1Ni 1.4 - 0.6 - 1.2
2Ni 1.4 - 1.8 - 2.6
3Ni 1.4 - >2.6 - 3.8
Mn1Ni >1.4 - 2.0 - 0.6 - 1.2
1NiMo 1.4 0.3 - 0.6 0.6 - 1.2
Z Any other agreed composition

The fourth symbol indicates the type of flux coating - basic, rutile etc as shown in Table 4.

Table 4 Symbol for flux coating

SymbolCoating
A acid
C cellulosic
R rutile
RR thick rutile
RC rutile-cellulosic
RA rutile-acid
RB rutile-basic
B basic

The next three symbols are not compulsory and give additional information on the percentage weld metal recovery and the type of welding current on which the electrode can be operated (Table 5); the welding position (Table 6) and the maximum hydrogen content of the deposited weld metal if the electrodes are dried or baked as recommended by the manufacturer (Table 7).

Table 5 Symbol for weld metal recovery and current type

SymbolWeld metal recovery %Current type
1 <= 105 AC or DC+
2 <= 105 DC+ or DC-
3 >105<=125 AC or DC+
4 >105<=125 DC+ or DC-
5 >125<=160 AC or DC+
6 >125<=160 DC+ or DC-
7 >160 AC or DC+
8 >160 DC+ or DC-

 

Table 6 Symbols for welding position

SymbolWelding position
1 All positions
2 All positions except V-down
3 Flat butt and fillet welds, HV fillet weld
4 Flat
5 V-down, flat butt, flat and HV fillet welds

Table 7 Symbol for hydrogen content in weld metal

SymbolMax Hydrogen
ml/100gms weld metal
H5 5
H10 10
H15 15

A full designation may therefore read E42 2 B32H5. This describes a basic carbon manganese steel electrode; weld metal yield strength of 420N/mm2, better than 47J at -20°C, a weld metal recovery of over 105%, capable of being used on AC or DC+ current in all positions except vertical down and providing less than 5mls hydrogen in the weld metal.

jk84f2.jpg

The AWS specification equivalent to EN 499 is AWS A5.1 - Carbon Steel Electrodes for Shielded Metal Arc Welding. The classification comprises five characters but in the 2004 edition of the specification there are two separate schemes. A5.1, based on the US units of tensile strength in pounds per square inch, Charpy -V values in foot-pounds and A5.1M, based on the SI system, with strength in MPa, Charpy-V values in Joules.

It is thus possible to have virtually identical electrodes with different classifications, one using US units, the other SI units. There is insufficient space within this brief article to describe fully all of the 18 types covered by the specification except perhaps for the most commonly used electrodes. For full details of the AWS scheme it is necessary to consult the specification.

To illustrate briefly how the electrodes are classified, the following gives a summary of the key features.

The first character 'E' is common to both classifications and indicates that the electrode is a flux coated manual metal arc electrode. The next two digits indicate the tensile strength. In the A5.1 designation this is either '60',indicating a UTS of 60ksi and a yield strength of 48ksi, or '70', indicating a UTS of 70ksi and a yield strength of 58ksi. In the A5.1M designation these are 43 or 49, indicating a UTS of 430MPa, yield strength of 330MPa or 490MPa UTS,400MPa yield respectively.

The last two digits give information on flux coating type, welding position, current type and polarity and Charpy-V impact strength, if required. Those electrodes suffixed XX10 or XX11 have cellulosic coatings; those suffixed XX12,XX13, XX14, XX19 or XX24 have rutile coatings and those suffixed XX15, XX16, XX18, XX28 and XX48 are basic low hydrogen. XX18, XX28 and XX48 all have iron powder additions and are therefore high recovery electrodes.

Listed below are those EN and AWS specifications that prescribe the requirements for ferrous electrodes.

BS EN 499 Non-alloyed and fine grained steel electrodes
BS EN 757 High strength steels
BS EN 1599 Creep resisting steels
BS EN 1600 Stainless and heat resisting steels
AWS A5.1/A5.1M Carbon Steel Electrodes for SMAW
AWS A5.4 Stainless Steel Electrodes for SMAW
AWS A5.5 Low Alloy Steel Electrodes for SMAW

This article was written by Gene Mathers.