Toughness study of Borided, Borided and induction modified AISI 4340 steel

Abstract

Abstract In this study, pack boriding is done on AISI 4340 steel in steel containers for 3 hours at 950°C. Boriding results in the formation of FeB or Fe2B columnar microstructure at the case. Such microstructure brings about a high brittleness of the boride layer. Induction surface modification is done on Borided samples to bring down the surface hardness. We put an effort to enhance the toughness of boride layer using 30 kW power high frequency induction heat source. The toughness of borided, borided and induction surface modified specimens are evaluated by shear punch test. Cylindrical punch of 4 mm diameter is used in this test. The toughness is calculated from the load-displacement curve. Induction modified specimens exhibit 38% improvement in toughness as compared with borided specimens. This improvement in toughness may be due to blunting of acicular boride structure in to a globular structure at the interface, smooth hardness gradient and formation of single phase Fe2B microstructure as a result of induction surface modification.