Microstructures Of Cutting Chips Of Sus430 And Sus304 Steels, And Ncf 750 And 6061-T6 Alloys

Microstructures of chip specimens of high-strength materials produced by machining were examined by FE-SEM/EBSP method (an orientation imaging microscopy, OIM). In the ferritic SUS430 (16Cr) steel, the chip specimen with shear strain (gamma) of similar to 7.5 was principally composed of equiaxed submicron grains which were for the most part surrounded by large angle grain boundaries (misorientation, theta >= 15 degrees). A similar microstructure was observed in the chip specimen with gamma approximate to 22 of the Inconel X-750 (NCF 750) nickel-base alloy. However, the chip specimen of the austenitic SUS304 (18Cr-8Ni) steel (gamma approximate to 14) and that of the 6061-T6 (aluminum) alloy (gamma approximate to 10) exhibited principally a deformed microstructure with elongated grains and sub grains separated by small angle (2 degrees <=theta<5 degrees) or medium angle grain boundaries (5 degrees <=theta<15 degrees), although equiaxed submicron grains were partly observed. The chip specimens exhibited very high hardness compared to the original materials except 6061-T6 alloy. The maximum hardness value (609 Hv) was observed in the chip specimen with gamma approximate to 22 of the Inconel X-750 alloy. Strong particles with equiaxed submicron grain structure, which can be easily produced by milling of cutting chips of commercial alloys, will be potential strengthener for metal matrix composites.