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 9 5 8 even for a properly designed boost/diffuse LPC schedule. Excessive carbides should be avoided initially, or their location should be known well enough so finish machining can remove them without degrading mechanical properties. An LPC process was designed to achieve a surface carbon value of 1.0% and an ECD of 1.0 mm in an axisymmetric ring made of X-2M steel with a 100-mm OD and 13-mm wall thick- ness. The first geometry investigated used sharp corners on the ID and OD surfaces. Figure 3 is a graph at the corner of the part for carbon with- in the austenite matrix, carbon in carbide form, and the total amount of carbon, plotted over the entire LPC process. The predictions show the carbon level is well above the aim level of 1%, and there is reason to be concerned about car- bide formation at this location. A post-heat treatment machining operation would be needed to remove unwanted carbides. Besides the added costs, the carburized case would be altered, and the reduc- tion of the carburized case would have serious implications on hardness andmechanical properties of themartensite. In addition, beneficial compressive stresses placed in the sur- face layer would be significantly reduced. With the ability to thoroughly interrogate modeling results, an area can be found where the amount of carbide formation is acceptable. The area corresponding to this cri- terion occurs at 0.5 mm from the sharp corner on the OD surface. Figure 4 shows this location for the full cross section (left) and a close-up of the top right corner (right). 10 Fig. 4 — Full cross section of sharp corner ring model (left) and a close-up of the top right corner (right) to better show the relation- ship between the locations used to generate plots of the carbon. Fig. 6 — Full cross section of 0.5 x 0.5 mm cham- fer ring model (left) and a close-up of the top right chamfer (right) to better show the location used to generate plots of the carbon. Fig. 5 — Plot of carbon as carbon in the austenite matrix (free carbon), carbon in carbides (carbide) and the total amount of carbon (free carbon + carbide) at 0.5 mm from the corner of the OD on the surface of the sharp corner ring model. Fig. 3 — Plot of carbon as carbon in the austenite matrix (free carbon), carbon in carbide form (carbide), and the total amount of carbon (free carbon + carbide) at the corner of the OD on the surface of the ring with sharp corners. (continued from page 9) (continued on page 12)