September AMP_Digital

FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 1 8 5 2 20 CHTE UPDATE Table 3 shows that decarburization also occurred during SLM for the 20MnCr5 component. In the part, carbon concentration is 0.134 wt%, which is out of specification. Therefore, the carbon concentration in the powder should be higher to compensate for the decarburization that occurs during the SLM process. PRELIMINARY FINDINGS The following results are based on characterization of AISI 8620 and 20MnCr5 powder, SLM parts, and wrought parts. Decarburization was observed during the SLM pro- cess. The carbon concentration in the powder should be higher to ensure the carbon concentration in the SLM parts. Both SLM andwrought parts showmicrohardness variations that may be related to residual stress, microstructure, or compositional variation. The average microhardness of the wrought part (HV 231 for AISI 8620, HV 186 for 20MnCr5) is much lower than that of the SLM part (HV 328 for AISI 8620, HV 331 for 20MnCr5). The microstructure of the SLM part is tempered martensite and retained austenite, while the mi- crostructure of the wrought part is ferrite and pearlite. TABLE 3 — CHEMISTRY COMPARISON BETWEEN POWDER AND PART FOR 20MnCr5, WT% C Cr Mn Si P S Fe Powder 0.17 1.2 1.2 0.31 0.0015 0.007 Bal. Part 0.134 1.24 1.05 0.146 0.0036 0.0024 Bal. Based on these preliminary findings, normalizing must be conducted before the carburizing process for both SLM and wrought parts. Normalizing will help to reduce the ef- fects of the precarburizing condition. Different defects were found in the SLM and wrought parts. In SLM, part pores are the main defects, while in wrought parts inclusions are the main defects. Effects of different defects on the properties after carburizing need to be investigated. NEXT STEPS In the coming months, CHTE researchers will work to normalize and carburize AISI 8620 and 20MnCr5 SLM and wrought parts. The mechanical properties of carburized AISI 8620 and 20MnCr5 SLM parts will be compared with the car- burized wrought parts separately. Expected completion of this three-year project is scheduled for late 2020. ~HTPro For more information: Visit www.wpi.edu/+chte or email Rick Sisson at sisson@wpi.edu . TABLE 2 — CHEMISTRY COMPARISON BETWEEN POWDER AND PART FOR AISI 8620, WT% C Cr Mn Mo Ni Si P S Fe Powder 0.24 0.6 0.9 0.21 0.6 0.3 0.009 0.005 Bal. Part 0.192 0.59 0.86 0.21 0.66 0.276 0.0068 0.0032 Bal. ABOUT CHTE The CHTE collaborative is an alliance between the industrial sector and university researchers to address short-term and long-termneeds of the heat treating industry. Membership in CHTE is unique becausemembers have a voice in select- ing quality research projects that help them solve today’s business challenges. Research projects aremember driven. Each project has a focus group comprisingmembers who provide an industri- al perspective. Members submit and vote on proposed ideas and three to four projects are funded each year. Companies also have the option of funding a sole-sponsored project. In addition, members own royalty-free intellectual property rights to precompetitive research and are trained on all research technology and software updates. CHTE is located inWorcester, Mass., onWPI’s NewEngland campus. The university was foundedmore than 150 years ago. For more information about CHTE, visit wpi.edu/+chte , call 508.831.5592, or email Rick Sisson at sisson@wpi.edu .