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US-12623306-B2 - MIG welding method

US12623306B2US 12623306 B2US12623306 B2US 12623306B2US-12623306-B2

Abstract

A MIG welding method for carbon steels using an Ar shielding gas. The method includes short-circuiting a welding wire and a base material. The average short-circuiting frequency in welding is 20 Hz to 300 Hz and the maximum short-circuiting period is 1.5 s or less.

Inventors

  • Kyohei KONISHI
  • Chikaumi SAWANISHI
  • Hiroshi Matsuda
  • Yoshiaki Murakami

Assignees

  • JFE STEEL CORPORATION

Dates

Publication Date
20260512
Application Date
20201029
Priority Date
20191031

Claims (4)

  1. 1 . A MIG welding method for carbon steels using an Ar shielding gas that includes a volume fraction of Ar of more than 99%, the method comprising: short-circuiting a welding wire and a base material, wherein: an average short-circuiting frequency in welding is in a range of 20 Hz to 300 Hz, and a maximum short-circuiting period is 1.5 s or less, and a welding current in the welding is a pulse current and a value X calculated by the following formula (1) satisfies 50≤X≤250: X=I p t p /L +( I p +I b )( t up +t down )/(2 L ) (1) where, I p is a peak current (A), I b is a base current (A), t p is a peak term (ms), t up is a rise term (ms), t down is a fall term (ms), and L is a distance (mm) between a contact tip and the base material.
  2. 2 . The MIG welding method according to claim 1 , wherein the welding wire is a solid wire.
  3. 3 . The MIG welding method according to claim 2 , wherein the solid wire has a wire chemical composition comprising, by mass %: C: 0.020% to 0.150%; Si: 0.20% to 1.00%; Mn: 0.50% to 2.50%; P: 0.020% or less; S: 0.03% or less, and the remainder being Fe and incidental impurities.
  4. 4 . The MIG welding method according to claim 3 , wherein the wire chemical composition further comprises at least one selected from the group consisting of, by mass %: Ni: 0.02% to 3.50%, Cr: 0.01% to 1.50%, Ti: 0.15% or less, and Mo: 0.8% or less.

Description

TECHNICAL FIELD This application relates to a MIG welding method in which carbon steels are welded together by the heat of an arc using an Ar gas as a shielding gas. Herein, the composition of the Ar gas is such that the volume fraction of Ar is more than 99.0%. A shielding gas made of the Ar gas is also referred to as an Ar shielding gas. BACKGROUND In MAG welding intended for carbon steels, O2 or CO2 contained in a shielding gas is decomposed by the heat of an arc as shown by Formula (2) or (3), respectively, and produced oxygen dissolves in molten metal. Oxygen dissolved as described above forms pores when a weld metal solidifies or causes an oxidation reaction with iron to deteriorate the mechanical performance of the weld metal. Therefore, in general, base material steel sheets and welding wires (hereinafter also simply referred to as wires) contain a nonferrous element such as Si, Mn, or Ti in the form of a deoxidizer. This allows oxygen in the weld metal to be discharged in the form of slug made of SiO2, MnO, TiO2, and the like. O2→2[O]  (2) CO2→CO+[O]  (3) On the other hand, in MIG welding in which the Ar shielding gas is used, the dissolution of oxygen in a weld metal is extremely low and therefore the addition of an element intended for deoxidation only is not necessary. This facilitates the design of a welded joint and allows the reduction in production cost of a welding material to be expected. In addition, slug which is made of oxides is not produced and therefore an improvement effect is expected on failures in coating properties due to the agglomeration or adhesion of slug on a surface of the weld metal. Furthermore, the usage of CO2, which is known as a greenhouse effect gas, can be significantly reduced, which is significantly advantageous for environmental protection. However, in MIG welding intended for carbon steels, there is a problem in that welding is extremely unstable. Since MAG welding or MIG welding is generally reverse-polarity welding in which an electrode is an anode, a cathode spot originating from a location which has a low work function like an oxide and in which electron emission is likely to occur is formed on a surface of a base material. In an aluminium alloy having a strong oxide film on a surface of a base material, a cathode spot originating from an oxide film on a weld line is stably formed and therefore good welding is possible. However, in a carbon steel having a relatively thin oxide film or no oxide film and in MIG welding in which no oxide derived from O2 or CO2 is produced unlike MAG welding, a cathode spot is not stationary but moves rapidly on a surface of a base material in pursuit of a location with a low work function. Therefore, welding is unstable and a weld bead has a meandering or wavy shape. For this problem, improving problems by techniques described in, for example, Patent Literatures 1 to 3 has been proposed. Patent Literature 1 describes a welding method in which a joint with improved fatigue properties as compared with conventional MAG welding is obtained by reducing the proportion of CO2 in a shielding gas to a limit at which the wandering of an arc does not occur. Patent Literature 2 describes a welding method in which a good joint with no bead meanders is obtained in such a manner that an arc in MIG welding is stabilized by combining TIG welding with MIG welding. Patent Literature 3 describes a welding method in which a flux-cored wire is used and is melted in two stages in such a manner that a steel hull is melted early and flux is melted late, so that a cross section of the wire is prevented from being uniformly melted and regular metal transfer is achieved in MIG welding. CITATION LIST Patent Literature PTL 1: Japanese Patent No. 6373549 PTL 2: Japanese Unexamined Patent Application Publication No. 53-034653 PTL 3: Japanese Patent No. 5205115 SUMMARY Technical Problem However, in the welding method disclosed in Patent Literature 1, a slight amount of slug is produced and the deterioration of joint characteristics that results from the slug is inevitable because an acidic gas or gases are contained in the shielding gas, that is, 3% or more CO2, 1% or more O2, or 3% or more CO2 and O2 are contained on a volume basis. Furthermore, it is concerned that the increase in amount of an added alloy element in association with the hyper-increase in tensile strength of steel sheets and wires facilitates the increase in formation of slug. In the welding method disclosed in Patent Literature 2, a welding equipment, particularly a welding torch is complicated and is large-sized and the number of control parameters such as welding conditions is large because TIG welding and MIG welding are performed at the same time. In addition, it is difficult to apply this welding method to a joint with a three-dimensional shape. Therefore, this welding method is of little practical use. In the welding method disclosed in Patent Literature 3, an iron powder which has