Hardfacing of metal-cutting tools by arc welding in vacuum

Abstract

Purpose: To present a technology for hardfacing of metal-cutting tools by arc welding in vacuum. Design/methodology/approach: The experiments were carried out using an installation for arc welding in vacuum. Objects of research were metal cutting tools (lathe knives), made of high-speed steel HS6-5-2 on a base metal of structural steel C45. The structure, hardness and wear resistance after hardfacing and after a triple tempering at 560°C have been determined. The heat resistance of the obtained instruments has been examined. Findings: The microstructural analysis showed that the structure of the built-up layer consisted of martensite, retained austenite and carbides. This was confirmed by the values of measured hardness after welding which were about 63-64 HRC. The triple tempering led to an increase in hardness by 3-4 HRC. It was found that the built-up layers (cutting edges of tools) retain their hardness (HRC=63-65) up to a temperature of 615-620°C, which shows that the heat resistance of the build-up layers was similar to that of the hardened and tempered tools of the same steel. The built-up work-pieces (excluding heat treated) and the reference knife showed the same cutting qualities at cutting speeds in the range of 55 to 120 m/min. It has been found that triple tempering after hardfacing led to increased wear resistance and consequently the durability of the tool also increased due to the higher hardness. Practical implications: The practical application is related to the production of metalcutting tools. Originality/value: The proposed technological method allows to produce defects free built-up layers. The cutting properties of the built-up in vacuum layers are comparable to or better than those of new tools made of steel HS 6-5-2.