The American Welding Society (AWS) has published the A5 series of specifications for consumables used in the arc and electroslag welding processes.
Historical Background
Standards for arc welding electrodes did not exist until 1940, although by that time manufactures were recommending similar types of electrodes for various welding applications. In 1940, the AWS, in conjunction with the American Society for Testing and Materials (ASTM), developed tentative specifications for iron and steel arc welding electrodes used to weld mild steels.
AWS Classification System
The AWS has since developed specifications for filler metals to cover arc welding of carbon, alloy, stainless and corrosion-resistant steels; copper and copper-base alloys, and aluminum alloys. Through these specifications and classifications, an electrode can be selected which will produce a weld metal with specific mechanical properties. The electrode identification system is shown in Figure E-4.
This system also classifies electrodes for minimum tensile strength, various positions of welding, and for type of welding current (alternating or direct current).
See Table E-2.
The AWS classification system uses a four or five- digit number to identify the properties of the electrode, prefixed by the letter E. The letter E indicates that the filler material is an electrical conductor. The first two digits indicate minimum tensile strength in thousands of pounds per square inch (stress relieved); if it is a five digit number, the first three digits indicate minimum tensile strength. The second to last digit designates welding position. The last two digits taken together designate the type of current with which the electrode can be used and the type of covering on the electrode. Additional designators may be used to indicate special electrode classifications. These classifications are extremely important to help the welder to select the right electrode for each specification of the weld; for example, selecting a particular type of filler metal capable of depositing a high-strength, ductile weld.
Coated Electrodes
Prior to the development of coated electrodes, atmospheric gases in the high-temperature welding zone formed oxides and nitrides with the weld metal. In general, oxides are low in tensile strength and ductility, and tend to reduce the normal physical properties of the base metal. Coating materials were added to the electrode to provide an automatic cleansing and deoxidizing action on the molten weld puddle. As the coating bums in the arc, it releases a gaseous atmosphere that protects the molten end of the electrode, as well as the molten weld pool. This atmosphere excludes harmful oxygen and nitrogen from the molten weld area while the burning residue of coating forms a slag to cover the deposited weld metal. The slag also serves to exclude oxygen and nitrogen from the weld until it is cooled to a point where oxides and nitrides will no longer form; it slows the cooling of the deposit metal to produce welds with better ductility.
Through metal additives to the coating, electrodes can be used to add alloying agents to the weld metal or restore lost elements, and sometimes to enhance deposition rates. In addition, the slag from the coating not only protects the weld bead, but even helps shape it.
Iron Powder in Coatings
Some electrodes are made for use with direct current (dc) and some for alternating current (ac). Some d-c electrodes are for DCEN (electrode holder connected to the negative pole) and some are for DCEP (electrode holder attached to the positive pole). Still other d-c electrodes perform satisfactorily with either polarity.
Iron powders are added to the coating of many basic electrodes. In the intense arc heat, the iron powder is converted to steel, and this contributes additional metal to the weld deposit. When iron powder has been added to the electrode coating in relatively large amounts (up to 50% by weight), weld appearance and the speed of welding is appreciably increased. These electrode coatings have an insulating effect, help control the puddle for out-of-position welding, and also affect the arc length and welding voltage.
Obviously, to serve all these functions, the composition of an electrode must be a careful blend of specific ingredients so that performance characteristics are correctly balanced. There are other requirements of the electrode coating. It should have a melting point somewhat lower than that of the core wire or the base metal. The resulting slag must have a lower density in order to be expelled quickly and thoroughly from the rapidly solidifying weld metal. If the electrode is to be used in overhead or vertical welding positions, the slag formed from the melted coating must solidify quickly.
Alloy Steel Electrodes
The greatly expanded use of high alloy steel precipitated development of coated electrodes capable of producing weld deposits with tensile strengths exceeding 690 MPa (100 000 psi). Mechanical properties of this magnitude are achieved by using alloy steel in the core wire of the electrode.
In most electrode compositions, the coating is lime ferritic, typical of the low-hydrogen design and frequently containing iron powder. These high-tensile electrodes are usually classified as EXX15, EXX16 or EXXl8. The operational characteristics parallel those
of the typical E60XX low-h:ydrogen electrode.
In alloy steel electrodes, the basic four- or five-digit number designation for an electrode is usually followed by a letter symbol, such as Al, B2, B3. These AWS suffixes have been added to indicate specific additions of alloying elements as indicated in Table E-3.
General Coating Types
Coated or shielded metal-arc electrodes achieve performance characteristics through design or formulation of the coating. The coatings of electrodes for welding mild and low-alloy steels may be designed to include as many ingredients and performance characteristics as necessary from among the following:
(1) Cellulose to provide a gaseous shield on disintegration
(2) Metal carbonates to adjust slag basicity and provide a reducing atmosphere
(3) Titanium dioxide to improve slag fluidity and freezing, and to aid in ionization
(4)Ferromanganese and ferrosilicon to help with deoxidation of molten weld metal and supplement the Mn or Si content in the deposit
(5) Clays and gums to aid in coating extrusion
(6) Calcium fluoride to provide shielding, adjust slag basicity, and provide fluidity and solubility to metal oxides
(7) Mineral silicates to provide slag and give strength to the coating
(8) Alloying metals (Le., Ni, Mo, Cr and others) to provide alloy content to the deposit
(9) Iron or manganese oxide to adjust slag fluidity, and, for small amounts of iron oxide, help stabilize the arc
(10) Iron powder to enhance deposition rate.
By using different combinations and amounts of these and other ingredients, a tremendous diversity of coatings can be produced. Following are descriptions of electrodes used for mild and low-alloy steels.
E6010 Electrodes. Electrodes in this classification have a cellulose/sodium coating and are designed to produce the best possible mechanical properties consistent with good usability characteristics in all welding positions, using DCEP.
They are best suited for vertical and overhead welding and some sheet metal applications. The spray-type arc produced by the E6010 electrode has a digging characteristic to produce deep penetration. This calls for electrode manipulation by the welder to minimize spatter and the tendency to undercut.
Fillet welds made with 6010 electrodes are relatively flat in profile and have a rather coarse, unevenly spaced ripple. These electrodes are highly recommended when quality of deposit is of prime importance, particularly on multi-pass applications in
vertical and overhead positions, and when radiographic requirements must be met. Most applications for the E6010 electrode are on mild steel; however, they may be used to advantage on galvanized plate and some low-alloy steels.
E6011 Electrode. These electrodes are sometimes considered the a-c counterpart of the E6010. Performance characteristics of the two are similar; however, the E601 1 electrode performs equally well with either a-c or d-c power sources. These electrodes produce a
forceful digging arc resulting in deep penetration.
While the coating is slightly heavier on the E6011, the resulting slag and weld profiles are similar to those of the E6010. The coatings are high in cellulose and are designated as the high cellulose potassium type. In addition to the other ingredients usually found in the E6010 electrode coating, small quantities of calcium and potassium are usually present.
E6012 Electrodes. The E6012 electrodes are designed for all purpose welding in all positions, using either DCEN or an a-c power source. They are specifically recommended for horizontal and most downhill welding applications. They are especially recommended for single pass, high-speed, high-current horizontal fillet welds. Characteristics of the E6012 are ease of handling, medium penetration, no spatter, and good fillet weld profile. These electrodes can withstand high current and can bridge gaps caused by poor-fit-up conditions.
The 6012 electrodes are referred to as titania or rutile type, since the coating is high in titania, usually exceeding 35% by weight. In addition to titania, the coatings usually contain various silicious material such as feldspar and clay, small amounts of cellulose, and ferromanganese, with sodium silicate as the binder. Small amounts of calcium may be used to produce satisfactory arc characteristics on DCEN, and a
small amount of iron powder is added to improve arc characteristics. The slag coverage is complete and is easily removed.
When E6012 electrodes are used with a d-c power source, DCEN is preferred.
E6013 Electrodes. Although E6013 electrodes are very similar to the E6012s, there are some notable differences. They are designed for welding in all positions, ac or dc. They produce a minimum spatter and have a minimum tendency to undercut. The beads
have a fine ripple and are superior in appearance.
Slag removal is somewhat better and the arc can be established and maintained more readily, particularly with the small (1.6,2.0, and 2.4 mm [1/16,5/64, 3/32 in.]) electrodes, thus permitting satisfactory operation at a lower open-circuit voltage. These characteristics make the E6013 ideally suited to welding thin metals; the arc is soft and penetration very light. Mechanical and radiographic properties are slightly better than E60 12. These electrodes were originally designed specifically for sheet metal work.
While the E6012 electrode produces convex fillet weld contour characteristics, the E6013s produce a flat fillet weld similar to that of the E6020 electrode classification. The E6013 electrodes are also used for making groove welds because of the concave bead shape and easily removed slag. In addition, the weld metal contains fewer slag and oxide inclusions than E6012 weld metal, and quality verified by radiography is better.
The E6013 coating is very similar to that of the E6012, containing rutile, silicious materials, cellulose, ferromanganese and silicate binders. An important difference, however, is that easily ionized materials are incorporated in the coating, permitting establishment and maintenance of an arc with ac at lower welding currents and low open-circuit voltages. Some manufacturers have also introduced small quantities of iron
powder into the E6013 coating.
E701 4 Electrodes. This designation supersedes the E6014 designation. As the first two numbers of E7014 electrodes indicate, this is a 70,000 psi minimum tensile strength electrode. Although similar to E6013 electrodes, the coating of E7014 electrodes is considerably thicker, since it contains substantial amounts of iron powder (30% of coating weight). The amount of coating and the percentage of iron powder in it is usually less than that found in the E7020 electrodes.
The presence of iron powder in E7014 permits higher welding currents and means higher deposition rates and welding speeds. While the electrode is classified for all-position welding, the thicker coating is not ideally suited for out-of-position production welding on thin-gauge materials. Performance characteristics make it particularly suited for production welding of irregularly shaped products, where some out-of-position welding is required.
Mechanical properties of the E7014 weld metal are superior to those of E6012 or E6013. Slag removal is very easy, sometimes almost self-cleaning. General penetration and the rapid solidification characteristics make it well suited for handling poor fit-up conditions.
E7015 Electrodes. This electrode is commonly referred to as a low-hydrogen electrode. It was the first DCEP, all-position electrode designed for welding high-sulphur and high-carbon steels, materials which tend to develop porosity and sometimes crack under
the weld bead.
Underbead cracks usually occur just below the weld metal in the base metal, and are caused by hydrogen absorption from arc atmospheres. Elimination of hydrogen with its subsequent underbead cracking improves welding conditions, and permits welding of “difficult-to-weld” steels ,with less preheat than required for electrodes which are not classified as low hydrogen electrodes. Although underbead cracks do not occur in mild steel, they may occur when an electrode that is not low-hydrogen is used on high tensile steels.
The E7015 coating is high in limestone, sodium, and other ingredients with low-hydrogen content, which prevents the introduction of hydrogen in the weld. The arc is moderately penetrating; the slag is heavy, friable and easily removed, and the deposited
weld metal lies in a flat bead, or may even be slightly concave.
The E7015s, through 4nun (5/32 in.) diameter, can be used in all positions. The larger diameters are useful for fillet welds and horizontal and flat positions. Welding currents are somewhat higher than recommended for E6010s of compixable diameter. Also recommended: as short an arc as possible for all welding positions will produce best results. A short arc reduces the tendency for underbead cracking.
The E7015 electrode was originally developed for welding hardenable steels, in addition to alloy, high carbon and high-sulfur steels. They are useful in welding malleable irons, spring steel, and the mild steel sides of clad plates. These electrodes are commonly used for making small welds on heavy weldments, since they are less susceptible to cracking than non-low-hydrogen electrodes. They are also extensively used for welding steels which are subsequently enameled, and on all steels which contain selenium.
The successful performance of this electrode led to development of the E7016 and E7018 electrodes, which also have a coating with very low moisture content.
E7016 Electrodes. These electrodes have all the characteristics of the E7015. The core wire and coatings are very similar except that the coatings of the E7016 contain certain amounts of potassium silicate and other potassium salts, which makes this electrode suitable for use with ac as well as DCEP. All the characteristics attributed to the lE7015 also apply to the E70 16 electrodes.
E7018 Electrodes. Similar to the E7016 electrodes, E7018 electrodes are all-position, low-hydrogen, and have a coating of 25% to 40% iron powder. They operate with either a-c or DCEI?. The E7018 electrodes have all the desirable low-hydrogen characteristics of producing sound welds on troublesome steels, such as the high-sulfur, high-carbon, and low-alloy grades.
As is common with all low-hydrogen electrodes, a short arc should be maintained at all times. Fillet welds made in a horizontal or flat position are slightly convex in profile, with a smooth, finely rippled surface. Electrodes are characterized by a smooth, quiet arc, low penetration, very low spatter, and they can be used at high lineal speeds.
The minerals in the low-hydrogen electrode coatings are limited to inorganic compounds such as calcium fluoride, calcium carbonate, magnesium-aluminum-silicate, ferroalloys and such binding agents as sodium and potassium silicate. These electrodes are referred to as lime-ferritic electrodes because of the lime-type coatings (since this lime is a decomposed product of such compounds as calcium carbonate).
Since the coating of E7018 electrodes is heavier than most, vertical and overhead welding are usually limited to the smaller diameter electrodes. Currents used are somewhat higher than for the E6010 electrodes of corresponding size.
E6020 Electrodes. These electrodes are designed to produce high quality, horizontal fillet welds at high welding speeds, using either ac or DCEN. In the flat position, the E6020 can be used with ac or DCEN or DCEP.
The E6020 electrodes are characterized by a forceful spray-type arc and heavy slag, which completely covers the deposit and is easily removed. Penetration is medium at normal welding speeds, but high current and high travel speeds result in deep penetration. Deposits are usually flat or may be slightly concave in profile, and have a smooth, even ripple. Radiographic qualities are excellent, but the electrode produces
medium spatter and has a tendency to undercut.
The E6020 electrodes are essentially mineral-coated electrodes, with high percentages of iron oxide, with manganese compounds and silicates, and sufficient deoxidizers to give the deposit the desired composition. The slag coverage is so extensive and the slag-metal reaction of such a nature that the electrodes generally do not depend on gaseous protection.
The coatings of E6020 electrodes usually produce iron oxide, manganese oxide, and silica slag. Other materials such as aluminum, magnesium or sodium may be present in the coating to modify this slag. Ferromanganese is used as the main deoxidizer; sodium silicate is used as a binder. The quantity of basic oxide, acid silica and silicates and deoxidizers must be carefully controlled to assure satisfactory operation and to produce good weld metal. The heavy slag produced will be well honeycombed on the underside, while completely covering the deposit. It can be readily removed.
E7024 Electrodes. These electrodes, ideally suited for production fillet welding, are designed for horizon- tal fillet or flat positions using either an a-c or d-c power source.
The E7024, although generally used on mild steel, also produces satisfactory welds on many low-alloy, medium and high carbon steels. The welds are slightly
convex in profile, with a smooth surface and an extremely fine ripple. The electrodes are characterized by a smooth, quiet arc, very low spatter, low penetration, and can be used at high lineal speeds.
The coating contains 50%iron powder, which helps produce deposition rates and welding speeds considerably higher than those of the E6012, E6013 or E7014 types which have similar performance characteristics. Except for the high percentage of iron powder, the coating ingredients of the E7024 are similar to those used in the E6012 and E6013 electrodes.
E6027 Electrodes. With a 50% iron powder design, these electrodes have arc characteristics which closely duplicate the E6020. They are designed to produce satisfactory fillet or groove welds in the flat position with ac or dc, either polarity, and will produce flat or slightly concave horizontal fillet welds with either ac or DCEN.
The E6027 has a spray-type metal transfer and deposits metal at a high lineal speed. Penetration is medium and spatter loss is very low. The slag, though very heavy and honeycombed on the underside, crumbles for easy removal. The E6027 is particularly suited for multi-pass, deep groove welding.
Welds produced with the E6027 have a flat to slightly concave profile with a smooth, fine, even ripple, and with good metal wash up the joint sides. The weld metal might be somewhat inferior in soundness to that produced with E6020.
High current can be used; a considerable portion of the electrical energy passing through the electrode is needed to melt the coating and the iron powder contained in it. These electrodes are well suited to welding fairly heavy sections.
In many respects, the E6027 electrodes produce high quality weld metal with physical properties closely duplicating those of E6010.
E7028 Electrodes. The E7028 electrodes are the last of the mild steel series. They have a low-hydrogen coating containing 50%iron powder. These electrodes are very much like the E7018 electrodes, but have several different characteristics.
The E701 8s are all-position electrodes; but E7028s are suitable for horizontal fillet and flat position welding only. The coating of the E7028 electrode is much thicker than that of the E7018 because of its higher iron powder content, so it has a much higher deposition rate on horizontal fillet and flat welding than E7018 electrodes of comparable size. (The coating of E7028 represents about 50% of its weight).
The means of metal transfer of these two electrodes is also different. The E7028 has a spray transfer; the E7018 has a globular transfer. Both these electrodes are capable of producing the physical properties and weld quality typical of low-hydrogen electrodes.