Difference between ER70S-2、ER70S-3、ER70S-4、ER70S-6、ER70S-7

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    AWS A5.18 is the specification for carbon steel electrodes and rods for gas shielded arc welding like gas metal arc (GMAW), gas tungsten arc (GTAW) and plasma arc (PAW) welding, we all know class ER70S-2、ER70S-3、ER70S-4、ER70S-6、ER70S-7welding electrodes can be used for welding the carbon steel and the low alloy carbon steel with a strength less than 500Mpa, do you know what’s the difference between them?

    Let’s see their chemical composition comparison firstly:

    AWSCMnSiPSNiCrMoVCuTiZrAl
    ER70S-20.070.9-1.40.4-0.70.0250.0350.150.150.150.030.50.05-0.150.02-0.120.05-0.15
    ER70S-30.06-0.150.9-1.40.45-0.750.0250.0350.150.150.150.030.5///
    ER70S-40.06-0.151.0-1.50.65-0.850.0250.0350.150.150.150.030.5///
    ER70S-60.06-0.151.4-1.850.8-1.150.0250.0350.150.150.150.030.5///
    ER70S-70.07-0.151.5-2.00.5-0.80.0250.0350.150.150.150.030.5///

    We can see that the main difference between them is the content of C, Mn and Si elements except for ER70S-2 welding wire. The content of Mn and Si will affect the welding metallurgical reaction and weld properties.

    Secondly, their impact test requirements(As welded) differ:

    AWS A5.18(A5.18M)Average impact strength(A5.18M), Min
    ER70S-2(ER48S-2)20 ft.lb.at -20F (27J at -30℃)
    ER70S-3(ER48S-3)20 ft.lb.at 0F (27J at -20℃)
    ER70S-4(ER48S-4)Not required
    ER70S-6(ER48S-6)20 ft.lb.at -20F (27J at -30℃)
    ER70S-7(ER48S-7)20 ft.lb.at -20F (27J at -30℃)

    As can be seen from the above table, ER70S-4 does not require impact toughness under welding state, and ER70S-3 has a weaker impact toughness requirement than ER70S-2, ER70S-6 and ER70S-7.

    Thirdly, AWS 5.18 specified their different application scenarios:

    ER70S-2 welding wire and filler wire are mainly used for single-pass welding of killed, semi-killed, and rimmed steels, as well as for some multi-pass welding applications. The addition of deoxidizer allows the filler metal to be used for welding steel with rust or dirt on the surface, but may damage the weld quality, depending on the surface conditions. It is widely used for high quality and high toughness GTAW welds, and is well suited for single-side welding without the need for root gas protection on the reverse side of the joint.

    ER70S-3 welding wires and filler wires are suitable for single-pass and multi-pass welds. Typical base metal standards are usually the same as those applicable to the ER70S-2. ER70S-3 is the most widely used GMAW wire.

    ER70S-4 wire and filler wire are suitable for the welding of steels whose conditions require that they provide more deoxidation capacity than ER70S-3 filler metal. Typical base metal standards are usually the same as ER70S-2. No impact test is required.

    ER70S-6 welding wire and filler wire are suitable for both single pass and multi-pass welding. They are particularly suitable for sheet metal where smooth weld passes are expected and for section and sheet steel with moderate amounts of rust or hot rolled scale. These wires allow for higher current ranges when welding with a CO2 shielded gas or a mixture of argon and oxygen or argon and carbon dioxide. Typically, the base material used is the same as ER70S-2.

    ER70S-7 welding wire and filler wire are suitable for single-pass and multi-pass welding. They can be welded at higher moving speeds compared to ER70S-3 filler metals. They also provide some better wetting and bead shaping than those of filler metals. These wires allow for a higher current range when welding with a CO2 shielded gas or a mixture of argon and oxygen or argon and carbon dioxide. Base metal standards are usually the same as ER70S-2.

    Currently, ER70S-6 is the most consumed electrode and filler metal, there was followed by ER70S-3, with less use of other wires. ER70S-3 is applied in the automotive, construction or machinery industry, and ER70S-4 is mainly used in places where low requirements are needed such as bicycle welding.

    Shielding gas for the MAG welding of carbon and low alloy steel

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      MAG welding is also known as “metal active gas welding”, is a gas shielded arc welding method by adding a certain amount of active gas such as O2 , CO₂, etc., in the inert gas argon. MAG is characterized by its good welding quality, high efficiency, easy automation and other advantages that can be used for welding in various positions, especially for carbon steel, alloy steel and stainless steel and other ferrous metal materials. It can be carried out by short circuit transition, jet transition and pulse jet transition, which can obtain stable welding process performance and good welding joints, The purpose of welding protective gas is to improve the quality of the welding seam, reduce the width of the heating band of welding seam, and avoid material oxidation. The shielding gas for MAG include:

      Pure gases: Pure argon or carbon dioxide(CO₂);

      The binary gas mixture: Argon and oxygen, argon and carbon dioxide, argon and helium, and argon and hydrogen.

      The ternary mixture: Helium argon and carbon dioxide.

      Different welding mixtures should be selected according to different welding materials and its base materials.

      Ar + CO₂

      This is the most commonly used typical mixed gas, suitable for short circuit transition, spray transfer and under the condition of the pulse transition welding of carbon steel, low alloy steel materials, has a stable arc, little splash, easy to obtain axial injection transition, and oxidation resistance, which overcome the surface tension, the liquid argon welding metal viscous, cathode spots easily slips and other issues, can be used for high speed welding of low carbon steel and low alloy steel.

      The commonly used mixing ratio (volume) is 70%Ar+30% CO₂ (C-30) and Ar80% + CO₂20% (C-20), which is suitable for all-position welding under short circuit transition, such as ASTM (America) A335 P11 pipe TIG backing welding +MAG filler cover welding process, and the qualified rate is 100%. During MAG welding, the shielding gas shields the atmosphere while protecting the high-temperature metal. Poor protection will cause pores and pits. In the Ar+CO₂ mixture, obvious pores can be seen in the welding of 2% CO₂, while the pores are greatly reduced in the welding of 10% CO₂. When pure CO₂ is used, pores are almost non-existent.

      Ar + O2 

      The arc stability can be improved by adding trace O2 in shielding gas, and the surface tension of droplet, pool and the defect of undercut can be significantly reduced. When welding high alloy steels such as stainless steel and high strength steels with higher strength grade, the content of O2 should be controlled in 1% ~ 5%, and when welding carbon steels and low alloy structural steels, the content of O2 can reach 20%. The mixture is suitable for jet transition and pulse transition of carbon steel and low alloy steel welding wire, suitable for flat welding and fillet welding, as well as steel melting very narrow gap welding.

      Ar+He

      The shape and color of the arc change with the change of the ratio of the gas in the welding process of Ar-He mixture gas. With the more content of Helium in mixed gases, the arc gradually shrink, arc column and concentration, and gradually turn into orange, this is mainly due to the pure helium line in the orange wavelength range, with the increasing of helium content, the number of helium atom ionization, a compound in arc gradually increased, the relative intensity of the spectral lines is also increasing, the visually changed from white to orange color.

      80%Ar + 15%CO₂+ 5%O2

      The ternary mixed gas concentrates the respective advantages of Ar, CO₂ and O2, and the arc is more stable, the welding depth and width are moderate, and can obtain a good forming. It can weld carbon steel, low alloy steel, stainless steel of various thickness, suitable for various transition forms, can be called the perfect gas mixture.

      Shielding gas for the stainless steel MIG welding

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        Due to the small thermal conductivity and large linear expansion coefficient, the welding of Austenitic stainless steel is easy to produce deformation, so the welding method with linear energy concentration should be selected as far as possible. MIG welding (Molten inert gas shielded welding) using a molten electrode, with external gas as arc medium, and protect metal droplet, welding pool and welding area of high-temperature metal, is the most commonly used welding method of stainless steel welding. How to choose shielding gas is a primary problem a welder needs to solve.

        Pure argon can only be used for the TIG welding of stainless steel, but not for MIG. Because the surface tension of the stainless steel droplet and the molten pool is large in pure argon gas welding, the liquid metal fluidity of the molten pool is poor, the weld surface cannot be spread and wetting, and the weld pass is poorly formed. Therefore, the following gas mixtures should be selected:

        Ar+1～2% O2 

        The addition of 1-2% O₂ makes the surface tension of the stainless steel droplet and the molten pool decrease, the liquid metal fluidity of the molten pool and the spread wettability of the weld surface is improved. Appropriate weld depth and width, beautiful weld bead forming.

        Ar+2～5% CO₂

        When the 2-5% CO₂ is added, there may be a tendency to carburize. The test shows that CO₂≤5%, weld carbon content ≤0.03%, below in the ultra-low carbon grades. The arc stability is good, the oxidation weakened, the alloying element burns less, has no carburization tendency, is suitable for the stainless steel welding wire short circuit transition, the jet transition and the pulse transition.

        Ar + 25% CO₂

        It is suitable for combination welding of TIG backing welding (pure argon protection, argon filling behind) +MAG filling cover welding, all-position welding, short circuit transition, smooth and beautiful welding seam.

        Ar+5%CO₂+2%O₂

        The arc concentration of ternary mixed gas, good single welding seam and double forming, suitable for stainless steel welding with higher technical requirements.

        Ar+He+CO₂

        The addition of helium gas can increase the welding depth, welding speed and reduce the deformation of weldment.

        Ar+CO₂+ N₂

        This is a new process developed in which the addition of nitrogen can increase the weld depth and weld width.

        Ar + He (25%)

        Suitable for welding nickel alloy solid wire (Nickel 625) MIG welding.