In Situ Measurement of Thermal Strain Development in 420 Stainless Steel Additive Manufactured Metals

Metal components fabricated through additive manufacturing processes generally require post-processing in the form of thermal treatments in order to relieve residual stresses or facilitate development of a desired microstructure. In this work, the thermal strain response of multiple variations of 420 stainless steel made using a laser-powder bed fusion were probed during a low temperature (315 °C) heat treatment. Surface strains in both the build plane and build direction were measured in situ during the thermal cycle using a three-dimensional digital image correlation method. The effect of specimen build parameters on the thermal expansion coefficients and relief of residual strains are presented. Results show that specimens with lower layer build heights produced both slightly higher thermal expansion coefficients and higher degrees of strain relief after the thermal cycle. The addition of niobium and molybdenum content was also found to reduce the coefficient of thermal expansion and lower the strain relief found after the low temperature cycle.