CLASSIFICATION

ísol-78 is intended for both single-pass and multiple-pass welding. They are characterized by a stable globular arc, low spatter, and good resistance to porosity, and smooth bead shape when using high current with CO2 shielding gas. These electrodes can be used either with CO2 shielding gas or with mixtures of argon and CO2. Typical specifications for these steels are ASTM A36, A285- C, A515-70, and A516-70, which have UNS numbers K02600, K02801, K03101, and K02700, respectively.

CHEMICAL COMPOSITION OF SOLID ELECTRODES AND RODS

Single values are maxima, except where specified otherwise.

 

ALL-WELD-METAL MECHANICAL PROPERTIES

Single values are minima, except where specified otherwise.

Diffusible Hydrogen Content Average, Maximum, mL (H2)/100 g Deposited Metal: 4.00

Welding Considerations

Gas metal arc welding (GMAW) can be divided into three categories based on the mode of metal transfer. These modes are…

1. spray (conventional or pulsed),
2. globular, and
3. short circuiting transfer.

In the spray, pulsed spray, and globular modes, transfer occurs as distinct droplets that are detached from the electrode, transferring along the arc column into the weld pool. In the short-circuiting mode, the metal is deposited during frequent short circuiting of the electrode in the molten pool.

Spray Transfer: The spray transfer mode, for carbon steel, is most commonly obtained with argon shielding gas mixtures with up to 5% of oxygen or up to 15% carbon dioxide. A characteristic of this transfer mode is the smooth arc plasma through which hundreds of very fine droplets are transferred to the weld pool each second.

Spray transfer with argon-oxygen shielding gas is, primarily, a function of current density, polarity, and resistance heating of the electrode. The high droplet rate (approximately 250 droplets per second) develops suddenly above a critical current level, commonly referred to as the transition current (for each size of electrode).

Below this current, the metal is transferred in drops generally larger in diameter than the electrode and at a rate of from 10 to 20 per second (globular transfer). The transition current is also dependent, to some extent, on the chemical composition of the electrode. For 1.6 mm diameter carbon steel electrodes, a transition current of 270 amperes (dcep) is common. Alternating current is not recommended for this type of welding because it does not produce a stable arc.

Pulsed Spray: Metal transfer in pulsed spray welding is like that of the spray transfer described above, but it occurs at a lower average current. The lower average current is made possible by rapid pulsing of the welding current between a high level, where metal will transfer rapidly in the spray mode, and a low level, where no transfer will take place. At a typical rate of 60 to 120 pulses per second, a melted drop is formed by the low current arc, which is then “squeezed off” by the high current pulse. This permits all-position welding.

Globular Transfer: The mode of transfer that characterizes 100% CO2 as a shielding gas is globular. Common practice with globular transfer is to use low arc voltage to minimize spatter. This shortens the arc length causing the arc to be “buried” and results in deeper penetration and better containment of spatter within the weld pool. Electrodes of 1.2 mm through 1.6 mm diameter normally are used at welding currents in the range of 275 to 400 amperes (dcep), for this type of transfer. The rate at which droplets (globules) are transferred ranges from 20 to 70 per second, depending on the size of the electrode, the amperage, polarity, and arc voltage.

Short Circuiting Transfer: This mode of transfer is obtained with small diameter electrodes 0.8 to 1.2 mm using low arc voltages and amperages, and a power source designed for short circuiting transfer. The electrode short-circuits to the weld metal, usually at a rate of from 50 to 200 times per second.

Metal is transferred with each short circuit, but not across the arc. Short circuiting gas metal arc welding of carbon steel is done most commonly with mixtures of argon and CO2 as the shielding gas or with CO2 alone. The penetration of such welds is greater with CO2 than it is with argon-CO2 mixtures.

Mixtures of 50 to 80% argon with CO2 remainder can be advantageous for thin material. They provide low penetration, higher short-circuiting rates, and lower minimum currents and voltages than CO2 alone does.

Gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) are generally considered to be low hydrogen welding processes. However, as the weld metal or heat-affected zone strength or hardness increases, the concentration of diffusible hydrogen that will cause cracking under given conditions of restraint and heat input becomes lower.

It may be appropriate to evaluate the diffusible hydrogen produced during welding with these processes. This cracking (or its detection) is usually delayed some hours after cooling. It may appear as transverse weld cracks, longitudinal cracks (especially in root beads), and toe or under-bead cracks in the heat-affected zone.

Since the available diffusible hydrogen level strongly influences the tendency towards hydrogen-induced cracking, it may be desirable to select proper consumable and measure the diffusible hydrogen content resulting from welding with the same.

ELECTRODE SIZE & WELDING CURRENT (GMAW)

SHIELDING-GAS: CO2 | Argon+CO2

• If sizes other than 1.2 mm and 1.6 mm are used, wire feed speed (and resulting current), arc voltage, and tip-to-work distance shall be changed as needed.
• If shielding gases other than CO2 are used, the wire feed speed (and resulting current), arc voltage, and travel speed shall be as agreed to between purchaser and METAFIL. Use of gases with lower oxidizing potential (e.g., argon plus 10% CO2) will result in greater Mn and Si recovery in the weld metal and correspondingly higher strength.
• The required combination of electrode feed rate, arc voltage, and tip-to-work distance should produce welding currents in the ranges shown.
• Currents substantially outside these ranges suggest errors in feed rate, tip-to-work distance, voltage settings, or in instrumentation.
• Distance from the contact tip to the work, not from the shielding gas cup to the work.

 

ELECTRODE SIZE & WELDING CURRENT (GTAW)

SHIELDING-GAS: Argon

• Arc voltage shall be reported for information only. The voltage range is only a suggested range and may change based on power source characteristics. Typically, the voltage cannot be set independent of the current.

WARNING: Safety and health information is available from many sources, including, but not limited to Safety and Health Fact Sheets listed in A11.3, ANSI Z49.1 Safety in Welding, Cutting, and Allied Processes published by the American Welding Society, 8669 Doral Blvd., Suite 130, Doral, FL 33166., and applicable federal and state regulations. The Safety and Health Fact Sheets are revised, and additional sheets added periodically.