HARDFACING COMPOSITIONS AND HARDFACING COATINGS FORMED BY PULSED PLASMA-TRANSFERRED ARC

摘要

A new hardfacing composition is disclosed. In addition, a pulsed plasma transferred arc method for depositing hardfacing material with a higher content of carbide and lower dilution by a substrate metal is disclosed. The disclosed method produces a hardfacing coating which has a strong metallurgical bond to the substrate metal. The method includes the following steps: (1) establishing a transferred plasma arc between an electrode and an area of a work piece, (2) optionally preheating the work piece to at least 250°F, (3) forming a plasma column of inert gas in the arc by passing an electrical current between the electrode and the work piece, (4) feeding a stream of hardfacing material in powder form into the plasma column, and (5) pulsing the current between a pre-selected high pulse current value and low pulse current value while feeding the powdered hardfacing material. In this method, the low pulse current is selected to be sufficiently high to melt at least one component of the hardfacing material. The pulse rate and the high pulse current are selected to minimize the formation of a weld pool on the metal substrate during the hardfacing process. This method has applications in hardfacing any metallic work piece which requires wear resistance or erosion resistance. This method is especially effective in hardfacing roller cone surfaces and the milled teeth of a rock bit for erosion and wear protection.