ARC WELDING

GAS WELDING, BRAZING & SOLDERING

TIG WELDING ALLOYS

WELDING AID PRODUCTS

 

How Magna alloys are designed for maintenance

It happens frequently that electrode users analyze the core wire of an electrode to predict or consider the weld metal composition.  This procedure falls down completely.  The analysis of the core wire of an electrode is by no means the same as the deposit chemistry.

Many people presume that if they are welding a specific base metal, they will have an identical and satisfactory weld if they use an electrode having a core wire of the same composition as the base metal.  As an example, they presume that by welding a base metal of Type SAE 4130 (chrome moly steel) with an electrode with a Type SAE 4130 steel core wire, the weld deposit will match exactly the base metal and the weld will perform identically to the base metal.

This is an understandable, but completely illogical conclusion for many reasons. Following are a few examples:

(1) The base metal is usually a hot or cold worked material, having had grain refinement from the working (such as rolling).  The weld metal is a cast material and thus cannot exactly resemble the base metal if the analysis is the same, unless the electrode has additional properties to compensate for this vast difference.

(2) Weld metals are prone to pore-formation, which will also make a weld deposit differ from a base metal even if the analysis of the core wire is identical.

(3) Some ingredients of the core wire, such as chromium, are invariably lost in gaseous form into the atmosphere during the arc transfer.

(4) Ordinary welds are prone to contamination from many sources including:

(a) Carbon, phosphorous, and sulphur content of the electrode or the base metal fused into the weld deposit, which often cause interdentric cracking in the weld deposit. These contaminants, and many others, segregate following solidification of the weld metal and follow the primary grain boundaries causing hot-cracks.  Phosphorous also causes welds to be brittle at low temperature.

(b) Ordinary weld deposits are quite susceptible to oxygen contamination.  Oxygen in solid solution reduces the impact toughness and tensile strength of steel.  Welds made with other electrodes than Magna generally contain more oxygen than do ordinary steel base metals.

(c) Nitrogen absorption of welds made with ordinary electrodes is a matter of serious concern.  Nitrogen in solid solution absorbed from the atmosphere during welding lowers the impact toughness of welds, lowers the elongation, and is generally responsible for "ageing", which is a precipitate process in welds which causes impact toughness and ductility to deteriorate to very low values.  When one considers that 78% of the air is nitrogen and that nitrogen causes welds to be brittle, the need for prevention of nitrogen contamination becomes obvious.

Magna has recognized that a series of problems result from the old idea of presuming that the same type core wire as base metal is adequate and will supply good results for maintenance applications.

Magna research has proven that in virtually any maintenance weldment, the electrodes must have much higher alloy content and much higher physical properties than the base metal.

Magna solutions

An electrode consists of two parts: a core wire and a coating.  Magna uses high-purity core wire having generally a much higher content of noble or semi-noble metals (such as nickel, molybdenum, columbium, cobalt, silicon, manganese, vanadium, chromium, and other "super-metals") than ordinary electrodes.

The highly researched super high alloy Magna core wires with extra high alloy content, stabilizing agents, highly deoxidized metals, and high purity metals and other improvements completely change the character of the arc.  The core wires of Magna Maintenance Welding Electrodes are carefully controlled so that metals or elements that - in excess - can cause difficulty or possible weld failure, such as carbon, sulphur, or phosphorous, are either refined out or held in exceedingly low amounts.  This enables them to be stabilized by special additives which Magna incorporates in the formulation of the electrode.  Nothing has been left to chance.

Magna conducts continuous extensive research in electrode coating chemistry and electrode coating technology.  Magna employs leading scientists and many highly qualified chemists and technicians who perform studies in electrode coating technology. Among the reasons for Magna Maintenance Welding superiority is the advanced state of Magna' s Maintenance Electrode coating technology.  It is believed that the coatings of Magna electrodes are the most advanced in the world with respect to maintenance applications.  Magna electrode coatings contribute to maintenance weld quality in many special ways, including:

  • Magna's unique coatings deoxidize the weld metal.  Oxygen contamination is a major cause of weld failure.  Magna electrodes contain special deoxidizers which completely remove most oxygen and reduce the balance to exceedingly finely dispersed inclusions.  The deoxidizer system is of a proprietary and special nature not universally available.
  • Magna coatings actually produce a super shielding gas to protect the molten weld metal.  This gas envelope produced by the melting of the coatings is especially designed to prevent the weld from being contaminated by nitrogen, oxygen, hydrogen and other harmful elements that often cause failure in ordinary electrode deposits.
  • Pore-resistant coatings.  Magna electrode coatings contain scavengers, cleansers, degreasers, and have an ability to absorb foreign matter, dirt, contamination, and impurities, float them away, and hold them in the slag for easy removal.  This special feature enables Magna maintenance welds to be made without the porosity that is common with ordinary electrodes.
  • Magna Maintenance Electrodes provide a slag layer around the molten metal globules during transfer, and then form a protective chemical slag blanket over the complete weld deposit.  With most electrodes, the slag is usually little more than a residue of the electric welding process.  Magna Maintenance Electrodes have a completely different type coating which forms a protective blanket that not only provides a resistance to oxidation and other contamination but emphatically retards the cooling rate.  A "Widmanstatten" structure occurs when ordinary electrodes are used which allow the weld to cool too rapidly.  The Widmanstatten structure caused by rapid cooling with ordinary production electrodes is harmful. Rapid cooling causes the ferrite to form needle-like plates which are transverse to the pearlite.

The Magna slag blanket holds the heat and retards the cooling to permit the complete precipitation of the ferrite in the grain boundaries in such a way that the ferrite surrounds the pearlite grains.  The Magna protective slag blanket effectively retards the cooling rate and promotes a more refined and more desirable grain structure.

  • Hydrogen gas inclusion (commonly referred to as "fish-eyes") is a major problem in maintenance welding.  Hydrogen's main threat to welding comes from the chemically combined water which is present in the coatings of many production welding electrodes.  This water decomposes into hydrogen and oxygen in the arc transfer process.  Iron has a high solubility for hydrogen even at moderate temperatures, so considerable amounts of hydrogen enter weld deposits.  The hydrogen which enters the weld when production welding electrodes are used can be completely removed by heating the weld to 482 oF (250 oC) and holding the part at this heat for 15 hours.

This procedure can be carried out in production factories as another step in manufacture. However, it is totally impractical in maintenance welding.  This is why the Magna Research Department has given consideration to the problem of hydrogen inclusion in maintenance welds.

It has repeatedly been demonstrated that hydrogen contamination of welds cause cracking and underbead cracking (this is a type of cracking in the heat affected zone adjacent to or under the weld, caused by the hydrogen contamination during welding). Hydrogenous welds cause a pronounced reduction in ductility and elongation and are crack sensitive.

Magna has built into the special coatings a resistance to hydrogen transfer across the arc.  Electrodes such as Magna 305, Magna 303 and many others are based on all mineral coatings with special additives that tend to repel hydrogen.  These coatings, in manufacture, are baked at high temperatures to remove even the last traces of hydrogen. These special coatings are another reason Magna electrodes result in more reliable maintenance welds.

Magna coatings are not mere simple cellulose or rutile formulations.  They contain many supplements and special features. Some of these are:

(1) Higher purity, higher quality binders.

(2) Higher purity, higher quality chemicals.  There are many grades of chemicals available to electrode manufacturers including the lower quality technical grades, U.S. pure, Pharmaceutical grades, etc.  Magna quality requires unusually high grades of chemicals.

(3) Magna coatings are produced with special mixing equipment, using a variety of mixers to attain different results with different chemicals.  The particle size of chemicals is carefully studied.  The mixing of the coatings is carefully monitored so that every batch is identical.

(4) Magna introduces many additional metals such as strontium, sodium, aluminum, graphite, as well as stabilizing compounds and various other additives such as fluorides, carbonates and calcium, through the unique coatings to improve both maintenance weld quality and weld ability.

(5) Magna upgrades the quality of the deposit by adding finely ground metal to the coating.  Such metals as molybdenum, chromium, cobalt, nickel and many others enrich the weld deposit.

(6) The concentricity of all Magna Maintenance Welding Electrodes is controlled with such surgical preciseness that the maximum core-plus-one-covering dimension by more than 5 per cent of the minimum core-plus-one-covering dimension.  This precise concentricity control prevents "finger-nailing", uneven burn-off, erratic performance and spatter which occurs with so many welding electrodes because of poor concentricity.

(7) Magna employs carefully controlled amounts of ferrite formers in the coatings in order to enable the Magna deposits to resist hot-cracking.  Magna electrode coatings are highly sophisticated coatings, many containing more than 20 ingredients.  They are the result of specific research to design coatings especially engineered for the special problems of maintenance welding.  It is believed that they represent the highest state of the art today for the purpose for which they have been designed.  They supply weld deposit additions that provide increased physical properties and increased resistance to cracking or costly weld failures.  The coatings are so rich in extra metals and supplements that the final alloying process is actually only completely finished at the tip of the electrode.