Abstract
Abstract This paper investigates the microstructure and machinability of ASTM A131 steel parts manufactured by directed energy deposition (DED). The surface finish of A131 steel parts is improved by a combination of additive manufacturing (AM) and subtractive manufacturing technologies. Microstructures of the DED and hot-rolled (HR) samples are studied. A large amount of acicular martensite appears on the top face (DED-top) and side face (DED-side) of the DED samples which are substantially different as compared to the ferrite + pearlite microstructure commonly observed in HR samples. The measured microhardness on the DED-top face is over 30% higher than that of the HR samples. As a major post-processing method for AM, milling operation was conducted at varying cutting speeds. Cutting force, tool wear, chip formation, surface roughness, and microhardness before/after milling were investigated to evaluate the machinability of additively manufactured parts. It is evident that the microhardness of both DED-top and DED-side samples change slightly after milling. The surface roughness (Ra) can be greatly modified from >20 μm to
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