Gas metal reaction and slag metal reaction
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Slag-Metal Reactions During Welding: Part Two
Abstract:
As the steel technologies have increased the possibilities to make new and improved materials with excellent mechanical and corrosion properties the need for matching advancements in weld properties has become increasingly apparent.
Slag-melt reactions particularly relating to Cr and Si hold some key information for driving these improvements.
During the past three decades there has been tremendous progress in steel technology leading to many alloys possessing excellent mechanical and corrosion resistant properties. In many cases it is necessary to join these materials by welding techniques which are capable of achieving similar properties.
The aim of an investigation presented in the paper of Mitra U. et al. (1984) was to determine the extent of the interaction between slags and weld metals containing chromium, molybdenum, and nickel in addition to carbon, silicon, manganese, sulfur and phosphorus. This study utilizes the concept of an equilibrium or neutral point as developed by Chai and provides an estimate of the effective reactions temperature between the slag and the metal.
The transfer of Cr, Si, Mn, P, S, Ni, and Mo between slag and the weld pool has been studied for submerged arc welds made with different fluxes. The results show a strong interaction between Cr and Si transfer but no interaction with Mn.
The effect of slag-metal reactions on the transfer of various elements present in low alloy and stainless steels has resulted in the following conclusions:
The transfer of chromium is strongly dependent on the type of flux used. Lime silicate fluxes produced weld metal with much higher chromium content than manganese silicate fluxes, although both fluxes contained the same amount of chromium (III) oxide.The transfer of silicon is greatly influenced by the basicity index of the flux used by the initial chromium content of the electrode, the greater will be the amount of silicon in the weld metal.The manganese content of the weld metal depends mainly on the amount of manganese oxide in the flux and the initial manganese content of the electrode. The amount of the other alloying elements present does not appear to have significant influence on the transfer of manganese.The desulfurizing capability of a flux should be judged by the flux type, the basicity index, and the initial amount of sulfur present in the flux. The MnO-Cr2O3-SiO2 flux (Basicity index=0.35) gave slightly better desulfurization than CaO-Cr2O3-SiO2 type fluxes (Basicity index = 0.8-1.0).
On the other hand in the paper of Lau T and al., a detailed study is presented of the interactions of Mn, Al and O at the different stages of the welding operation. These interactions have been studied by analyzing the total Mn, Al and O contents, as well as the composition of inclusions formed at the different stages. At the electrode tip and in the arc column, changes in oxygen, aluminum and manganese were dominated by flux decomposition, while at the weld metal stage, slag-metal reactions occurred.
These reactions were most extensive in MnO containing fluxes, and resulted in a significant loss of oxygen, as well as metallic species such as aluminum, by the separation of oxidized products into the slag phase. In the CaF2-Al2O3 containing flux studied, reactions involving CaF2, AI2O3 and dissolved Al and Si led to enhanced Al pickup at the electrode tip. The applicability of equilibrium thermodynamic arguments to welding was assessed by determining the effective temperatures for the pertinent equilibrium reactions. These temperatures were found to be in reasonable agreement with other values in the literature. However, it is the efficiency of inclusion separation to the slag that determines the effective temperature.
Abstract:
As the steel technologies have increased the possibilities to make new and improved materials with excellent mechanical and corrosion properties the need for matching advancements in weld properties has become increasingly apparent.
Slag-melt reactions particularly relating to Cr and Si hold some key information for driving these improvements.
During the past three decades there has been tremendous progress in steel technology leading to many alloys possessing excellent mechanical and corrosion resistant properties. In many cases it is necessary to join these materials by welding techniques which are capable of achieving similar properties.
The aim of an investigation presented in the paper of Mitra U. et al. (1984) was to determine the extent of the interaction between slags and weld metals containing chromium, molybdenum, and nickel in addition to carbon, silicon, manganese, sulfur and phosphorus. This study utilizes the concept of an equilibrium or neutral point as developed by Chai and provides an estimate of the effective reactions temperature between the slag and the metal.
The transfer of Cr, Si, Mn, P, S, Ni, and Mo between slag and the weld pool has been studied for submerged arc welds made with different fluxes. The results show a strong interaction between Cr and Si transfer but no interaction with Mn.
The effect of slag-metal reactions on the transfer of various elements present in low alloy and stainless steels has resulted in the following conclusions:
The transfer of chromium is strongly dependent on the type of flux used. Lime silicate fluxes produced weld metal with much higher chromium content than manganese silicate fluxes, although both fluxes contained the same amount of chromium (III) oxide.The transfer of silicon is greatly influenced by the basicity index of the flux used by the initial chromium content of the electrode, the greater will be the amount of silicon in the weld metal.The manganese content of the weld metal depends mainly on the amount of manganese oxide in the flux and the initial manganese content of the electrode. The amount of the other alloying elements present does not appear to have significant influence on the transfer of manganese.The desulfurizing capability of a flux should be judged by the flux type, the basicity index, and the initial amount of sulfur present in the flux. The MnO-Cr2O3-SiO2 flux (Basicity index=0.35) gave slightly better desulfurization than CaO-Cr2O3-SiO2 type fluxes (Basicity index = 0.8-1.0).
On the other hand in the paper of Lau T and al., a detailed study is presented of the interactions of Mn, Al and O at the different stages of the welding operation. These interactions have been studied by analyzing the total Mn, Al and O contents, as well as the composition of inclusions formed at the different stages. At the electrode tip and in the arc column, changes in oxygen, aluminum and manganese were dominated by flux decomposition, while at the weld metal stage, slag-metal reactions occurred.
These reactions were most extensive in MnO containing fluxes, and resulted in a significant loss of oxygen, as well as metallic species such as aluminum, by the separation of oxidized products into the slag phase. In the CaF2-Al2O3 containing flux studied, reactions involving CaF2, AI2O3 and dissolved Al and Si led to enhanced Al pickup at the electrode tip. The applicability of equilibrium thermodynamic arguments to welding was assessed by determining the effective temperatures for the pertinent equilibrium reactions. These temperatures were found to be in reasonable agreement with other values in the literature. However, it is the efficiency of inclusion separation to the slag that determines the effective temperature.
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