INVESTIGATION OF THE TRANSFER OF SMALL AMOUNTS OF BORON INTO DEPOSITED METAL DURING MMA WELDING

Small amounts of boron were transferred from the electrode to weld metal by adding boron oxide or ferroboron powder to the electrode covering. Various factors affecting this transfer and its stability were studied. It was found that the process of transferring boron into weld metal became more stable by adding boron oxide instead of ferroboron into the covering. The kinetic process of boronization was investigated by measuring the transient boron content in the droplet, molten pool, deposited metal. It was revealed that in the process of boronization by boron oxide, the content of boron was increased continuously by the reduction of the oxide from the beginning of the formation of droplet,and the boron content was controlled by the kinetic process. However, in the process of boronization by ferroboron, the content of boron was at first increased excessively to a high value in the droplet and then decreased by oxidation to a pseudo-equilibrium level in the molten pool, and the boron content was controlled by the thermodynamic factors.