The effect of cutting speed and wear land length on the phenomenon of microchip formation during machining of quenched and tempered AISI 4340 steel under dry orthogonal conditions is determined. Machined test pieces are examined using scanning electron and optical microscopy. Surface roughness is determined using a profilometer. A possible mechanism of microchip formation based on the interaction between the surfaces of the tool and freshly machined work piece is discussed. It is suggested that the grooves left by the generation of microchips may act as sources for the initiation of failures by creep, fatigue and stress corrosion cracking. It is also suggested that the results obtained using scanning electron microscopy may be more indicative of the true surface condition than surface roughness measurements.

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