Hong-chul Jung

Bio: Hong-chul Jung is an academic researcher from POSCO. The author has contributed to research in topics: Welding & Heat-affected zone. The author has an hindex of 2, co-authored 3 publications receiving 52 citations.

Effects of flux composition on the element transfer and mechanical properties of weld metal in submerged arc welding

Abstract: Submerged arc welding was performed using metal-cored wires and fluxes with different compositions. The effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the weld metal, i.e., Δ quantity. Both carbon and manganese show negative Δ quantity in most combinations, indicating the transfer of the elements from the weld metal to the slag during welding. The amount of transfer, however, is different depending on the flux composition. More basic fluxes yield less negative Δ C and Δ Mn through the reduction of oxygen content in the weld metal and presumably higher Mn activity in the slag, respectively. The transfer of silicon, however, is influenced by Al2O3, TiO2 and ZrO2 contents in the flux. Δ Si becomes less negative and reaches a positive value of 0.044 as the oxides contents increase. This is because Al, Ti, and Zr could replace Si in the SiO2 network, leaving more Si free to transfer from the slag to the weld metal. Accordingly, the Pcm index of weld metals calculated from chemical compositions varies from 0.153 to 0.196 depending on the wire/flux combination, and it almost has a linear relationship with the tensile strength of the weld metal.

Comparison of the effects of fluorides in rutile-type flux cored wire

Abstract: Various fluorides, CaF2, Na3AlF6, K2SiF6, MnF3, and MgF2, were added to rutile-type flux cored wires at concentrations of 1.8–2.3% and their effects on hydrogen reduction in weld metals were studied. All the fluorides reduced the hydrogen content but there were differences in the levels of reduction among the wires; CaF2 showed the greatest reduction and MnF3 showed the least. The hydrogen content in the weld metals was not influenced by the fluorine formed in the arc but by the slag basicity due to the small amount of fluorides added. The weld metal with higher slag basicities had a lower hydrogen content. The effects of fluorides on the arc stability, weld metal hardness, and microstructure were also examined. Because of the higher ionization potential of Mn, the wire containing MnF3 had the most unstable arc during welding. The wire containing MnF3 also produced a lower weld metal hardness than the other wires owing to its lower weld metal hardenability due to the greater oxidation loss of the C, Si, and Mn elements during welding.

Effects of Welding Consumables on the Solidification Cracking in SAW Weld Metal of Medium Carbon Steel

Abstract: s: The effects of submerged-arc welding consumables, wire and flux, on solidification cracking in the weld metal of medium-carbon steel were investigated. It showed that weld metal with a greater amount of C, S, and P had a wider brittleness temperature range, BTR, which resulted in longer total and maximum crack lengths in Varestraint tests. To determine the effect of flux on the amount of C, S, and P in the weld metal, transfers of the elements between the slag and the weld metal were evaluated. While C and S were removed from the weld metal to the slag, P was added from the slag to the weld metal. The amount of each element removed or added, however, was dependent on the basicity of the flux used. As the flux became more basic, more S was removed and less P was added, resulting in less S and P in the weld metal. In contrast, with increasing flux basicity, less C was removed, leaving a larger amount of C in the weld metal. Therefore, to minimize the amounts of these elements in the weld metal, in addition to the wire used, the flux basicity should also be carefully considered. (Received September 7, 2017; Accepted November 6, 2017)

Effects of acicular ferrite on charpy impact properties in heat affected zones of oxide-containing API X80 linepipe steels

Abstract: This study was concerned with effects of acicular ferrite on Charpy impact properties in heat affected zones (HAZs) of two API X80 linepipe steels containing oxides. In the one steel, Mg and O 2 were additionally added to form a larger amount of oxides than the other steel, which was a conventional X80 steel containing a considerable amount of Al and Ti. Various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs of 35 kJ cm −1 and 60 kJ cm −1 . Oxides present in the API X80 linepipe steels were complex oxides whose average size was 1–2 μm, and the number of oxides increased with increasing amount of Mg and O 2 . The volume fraction of acicular ferrite present in the steel HAZs increased with increasing number of oxides, and decreased with increasing heat input. When the volume fraction of acicular in the HAZ was higher than 20%, Charpy impact energy at −20 °C was higher than 100 J as the ductile fracture mode was dominant. Particularly in the steel HAZs having a larger amount of oxides, Charpy impact properties were excellent because oxides worked as nucleation sites of acicular ferrite during welding. Charpy impact properties of the HAZs could be well correlated with the volume fraction of acicular ferrite and number of oxides under different heat input conditions.

Inclusions Nucleating Intragranular Polygonal Ferrite and Acicular Ferrite in Low Alloyed Carbon Manganese Steel Welds

Abstract: The inclusion-assisted formation of two types of intragranular ferrite in low alloyed C-Mn steel welds, intragranular polygonal ferrite (IPF) and acicular ferrite (IAF), was investigated in relation to the inclusion characteristics (mainly size and chemistry) and the welding heat input For this analysis, inclusions engulfed by one ferrite grain and those shared by two ferrite grains were considered as the IPF nucleants, and the rest of them (in contact with more than three ferrite grains) were considered as the IAF nucleants All inclusions were multi-component oxides having Ti oxides as the nucleoid The inclusion size exhibited a log-normal distribution and the average size increased as the heat input increased Inclusions larger than ∼04 μm were found to be effective on IAF nucleation, and the effectiveness increased as the inclusion size increased Accordingly, the overall IAF nucleant fraction increased as the heat input increased due to the corresponding inclusion size increase However, the probability of the IAF nucleant in the same inclusion size range was insensitive to the heat input There was no difference in the elemental distribution between the IAF and IPF nucleants except for Si The Si distribution was uniform in the IPF nucleants while its content was relatively high at the inclusion periphery in the case of the IAF nucleants regardless of the heat input and the inclusion size

Element Transfer Behaviors of Fused CaF 2 -TiO 2 Fluxes in EH36 Shipbuilding Steel During High Heat Input Submerged Arc Welding

Abstract: Fused CaF2-TiO2 fluxes are developed and applied on EH36 shipbuilding plates under high heat input submerged arc welding. Transfer behaviors of O and major alloying elements are systematically investigated. TiO2 contributes to O gain in the weld pool, but leads to concurrent losses of Si, Mn, and C via deoxidation and decarburization reactions. Transfer of Ti to the weld metal is suppressed due to improved flux O potential and chemical interaction between CaF2 and TiO2.

The effect of flux chemistry on element transfer in Submerged Arc Welding: application of thermochemical modelling

Abstract: Post-weld slag and weld metal analyses were used to interpret the effects of different commercial flux compositions on element transfer between molten flux (slag) and weld metal in Submerged Arc Welding (SAW). Selected fluoride based flux compositions cover a wide range of basicity index (BI) values of 0.5–3.0. Thermochemical modelling in FactSage software is used to simulate the welding process in terms of gas-slag-metal equilibria. The importance of the gas phase in SAW element transfer is illustrated. The model provides improved accuracy in predicted weld metal oxygen values (ppm O) compared to the generally used empirical relationship of weld metal ppm O vs. flux BI. Model predicted oxygen values are within 150 ppm of the analysed values, compared to the empirical relationship values which are within 240 ppm from the analysed values. The model provides resolution in ppm O values at BI > 1.8. This information is lacking in the empirical relationship with constant ppm O of 250 ppm at BI > 1.8. The measured ppm O values follow the Fe–FeO equilibrium trend with a positive offset. The relative level of oxygen to deoxidation elements (Ti, Al, Mn, Si) in the weld metal is an important factor in oxide inclusion engineering. This model will aid in the specification of flux formulations to attain specific weld metal compositions for maximum acicular ferrite formation. In this way the weld metal mechanical properties can be improved. This model will reduce the number of welding tests required to develop new flux formulations.