Investigation on the microstructure and machinability of ASTM A131 steel manufactured by directed energy deposition

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 31.53% higher than that of the HR samples. As a major post-processing method for AM, milling operation was conducted at varying cutting speeds. Cutting forces, 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