Features of deoxidation of electrode metal by carbon bonded to a Fe-C alloy

Abstract

The aim of the study is the choice of a rational system for deoxidation of the weld metal of
ilmenite electrodes, which in terms of strength, ductility and impact strength would not be inferior
to welds made with rutile-coated electrodes. Deoxidation of the weld metal by ferromanganese, as
well as partially by ferrosilicon and ferrotitanium, has practically exhausted its capabilities.
It is necessary to more intensively develop rational systems for deoxidation of weld metal,
among which, due to a number of advantages, a new direction should be singled out, which is
deoxidation with carbon bound in a Fe-C alloy.
For research, metal electrodes were used for manual arc welding of low alloy steels. Coatings of electrodes of ilmenite type were used. Ferromanganese of the FMN grade 1 was used as a
deoxidant. Gray iron of the SCh18 grade was used as a powder in the form of a Fe-C alloy. The
carbon content of cast iron was 3.5%. Crystalline graphite GSM-2 was used as carbon in the free
state. The weight coefficient of the coating of the electrodes was 0.45 ... 0.47. For comparison, electrodes without carbon components were made.
Melting electrodes with cast iron powder in the coating is characterized by the formation of
a fusible slag layer with a thickness of 0.1 ... 0.2 mm. The microhardness of the metal of the drop in its upper part is H20 = 1800 MPa. At the end of the electrode, the formation of a layer of carbon
melt with a thickness of about 0.1 mm is observed, the accumulation of gas bubbles and slag inclusions indicates an intensive process of boiling metal in the lower part of the drop. The microhardness of the metal in the lower part of the drop is H20 = 3400 MPa.
In the electrodes with graphite in the coating, intense boiling of the metal occurs over the entire volume of the drop due to the presence of solid inclusions of graphite. Graphite enters an oxidation reaction in a solid state. Therefore, it is impossible to fully use graphite as a deoxidizer in welding electrodes of this type.
When using cast iron powder, in an amount not exceeding critical, carburization of the deposited metal does not occur, which allows it to be used as a deoxidizing agent.