Slag Metal Reactions during Submerged Arc Welding of Alloy Steels
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I.
INTRODUCTION
D U R I N G the past two 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. Recently much work has been done on slag-metal reactions of submerged arc welds involving manganese, silicon, and oxygen transfer. ~-4 This work has resulted in a better understanding of the basic and semi-basic fluxes which are capable of achieving excellent properties in carbon and low alloy steels. Much less work has been done on the reactions during submerged arc welding involving chromium, molybdenum, and nickel steels, although low and high alloy steels with these elements are finding increased use in energy conversion technologies. Also, research on slag-metal reactions of alloy steels has generally been confined to either the austenitic stainless steels 5'6 or to steels containing less than 2.5 pct chromium. 7'8 The objective of the present investigation 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 reaction temperature between the slag and the metal. In addition, the spatial distribution of chroTable I.
mium, silicon, and manganese in the weld metal has also been investigated.
II.
EXPERIMENTAL PROCEDURE
The experiment consisted of producing undiluted weld beads by using electrodes and baseplates of the same composition. Other researchers 2'3 have used multiple bead pad techniques to study slag-metal equilibrium, but this method gives only a steady state weld metal chemistry. Since it is difficult to procure alloy steel baseplates and electrodes of identical chemical composition, artificial baseplates were made from the wire electrodes. Fifteen to eighteen pieces approximately 0.6 m long were cut from each electrode spool, straightened, and tied together to produce the artificial baseplate. This was then placed on a water cooled copper trough and welded using an identical electrode. During the experiment the welding parameters were kept constant with the voltage at 30 V DCEP, welding current at 350 A, and travel speed at 6.16 mm per second. Throughout the experiment it was necessary to maintain these constant welding conditions since varying welding parameters can appreciably change weld metal chemical composition unless one is operating precisely at the neutral point. ~'9 Seven alloy steel electrodes with chromium content varying from 1.37 to 26.31 pct were used. The chemical composition of these electrodes is shown in Table I. Four fluxes were used, the chemical composition of which is shown
Chemical Composition of Electrodes Used
Electrode
Pct Cr
Pct C
Pct Mn
Pct Mo
Pct Ni
Pct O
Pct S
Pct Si
5151 5212 50
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