Microstructure and Mechanical Properties of Ah-36 Steel Weldment Welded using Magnesium Modified E6013 Electrode

The base metal used in this study was high strength low alloy (HSLA) AH-36 steel. The welding process used the E6013 as a rutile electrode. Four rutile electrodes were produced by adding Mg metal powder, ranging from 0 to 5 wt.%, to the initial electrode layer in such a way as to obtain Mn and Si deposits according to ANSI/AWS standard A5.1-91. The shielded metal arc welding (SMAW) method was used with heat inputs of 1.5 kJ/mm and 2.5 kJ/mm. The tensile property, Charpy-V impact, and microhardness tests were performed to measure the mechanical properties of the weld metal. The observation of the metallographic structure was performed using an optical microscope. The results showed that with the increase of Mg layer content, the metal-oxygen level decreased, and the content of Mn and Si increased. The toughness and tensile strength of AH-36 steel improved, and the optimal Mg content is determined.

E6013 electrodes; Magnesium; Mechanical properties; Microstructure; SMAW

Rutile base electrodes constitute the largest percentage of the total manual electrodes that have been produced for many years (Surian and de Rissone, 1999). The E6013, E7014 and E7024 rutile base electrodes are the types widely used for welding in atmospheric conditions, especially in shielded metal arc welding (SMAW), because they are suitable for all welding positions and exhibit perfect arc stability, ease of handling, and excellent weld bead appearance (Brziak et al., 2011). E7014 and E7024 are mostly used in high strength steel welding, but they are costly, and their availability in the market is limited (Winarto et al., 2018). Another type of electrode that is easily found in the market and costs less than other rutile-based electrodes is the E6013 electrode. However, this type of electrode is rarely used for high strength structural applications because the mechanical properties of the weldment resulting from this type of electrode are poor (De Rissone et al., 2002).

Many efforts have been made by investigators to increase the mechanical properties of the resulting weldment of this electrode. The minimum tensile strength of the E6013 wire is around 410 MPa, much lower than that of the E7024 electrode, and based on previous research (Winarto et al., 2018), the performance of the E6013 electrode can be improved in toughness. It has been found that the E6013 electrode can increase the toughness of all incorporation of a strong deoxidant such as Mg powder and Ti as a coating to produce lower oxygen levels (Surian, 1997; De Rissone et al., 2001). Other investigators (Boniszewski and Evans, 1995a) found that adding elements of Mg and Ti cause a change in the microstructure evolution and an increase in the toughness properties in the HAZ and weld metal regions. Further, they found that the addition of Mg elements required that that Si content in the weld metal should be kept below a specific value to ensure proper weld toughness (Boniszewski and Evans, 1995a, 1995b). The development of research on the addition of Mg to the rutile-based electrode E7024 has been carried out by Surian (1997), who has found that increasing MgO content in the slag resulted in increasing impact resistance and reduced diffusible hydrogen content in the weld metal.

Manufacturers of consumable welding produce more coated rutile electrodes than the usual basic rutile electrodes because the former technically better (Surian, 1997). Besides, rutile electrodes are employed when joining using the SMAW. Because of that, and due to its low cost and straightforward operation, this electrode is in high demand (Ibarra et al., 1989).

As such, the aim of this investigation is to determine the operating characteristics of diffused electrodes and hydrogen from deposited metals. The reason for choosing Mg powder is that it can reduce the oxygen content in the weld deposits (Evans, 1980; Kotecki, 2000) that is transferred to slag and increases its basicity, and thus will improve its weldment mechanical properties. Chi et al. (Feng et al., 2009) reported that the Mg addition would refine the microstructure of the coarse grain in the heat-affected zone (CG-HAZ) and increase the impact toughness of low carbon steel through the mechanism of MgO formation. Furthermore, they also explained that the Ti-Mg-O oxide compound has a strong potential to initiate nucleation of an acicular ferrite (AF). Zhu and Yang (2011) likewise found that Mg could increase the ratio of AF crystals appearing at large angle boundaries to each other in the HAZ of low carbon steels. Additionally, MgO-MnS and MgO-Al₂O₃-MnS are the most effective complex inclusions to start the nucleation of AFs (Lin et al., 2018).

The addition of Mg content from 1 to 3 wt.% into the E6013 modified electrodes increased the elemental content of Mn and Si and reduced the oxygen levels in the weld metal. The presence of AF was increased in the weld metal. The tensile properties and toughness of AH-36 welds improved by the additional Mg up to 3 wt.% into the E6013 modified electrodes using the SMAW process. The addition of Mg also improved the tensile properties and toughness of AH-36 when the weld HI was increased. However, the hardness value in the weld metal was reduced when the HI increased.

The authors would like to acknowledge the Directorate of Research and Public Services, Universitas Indonesia (DRPM-UI), for the financial support for this study through the TADOK Research Grant in 2018.

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