March_2022_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 | M A R C H 2 0 2 2 3 7 for the coupons are shown in Fig. 2 and confirm that the slow transformation rate did not alter the microstructure of the DCGQ processed coupons, compared to coupons processed using a standard 2-bar HPGQ process. MECHANICAL TESTING Tensile testing and Charpy V-notch impact testing were conducted at room temperature to compare the me- chanical properties of DCGQ processed C64 and HPGQ processed C64. Table 1 shows the results from these tests and reveals equiva- lent tensile and yield strengths, elongation and reduction of area, and impact energy for Ferrium C64 processed using HPGQ and DCGQ. These tests are promising, as they in- dicate that a slow martensitic transformation can be used for Ferrium C64 without degrad- ing the microstructure or mechanical prop- erties. Materials with similar MS and temper- ing temperatures should also be suitable for DCGQ, though further testing is required. RESIDUAL STRESS AND DISTORTION Residual stress profiles for a carburized coupon were compared between the two processes, at two locations, and are shown in Fig. 3. There is no significant difference be- 8 TABLE 1 — TENSION AND CHARPY IMPACT RESULTS FOR FERRIUM C64 COUPONS Tensile strength, MPa Yield strength, MPa Elongation, % RA, % CVN energy, J DCGQ 1627 1405 17.75 71.2 25.35 HPGQ 1625 1401 16.75 71.0 24.00 Fig. 2 — Hardness profile comparison of carburized coupons processed using DCGQ and HPGQ. Fig. 3 — Residual stress profile comparison of carburized coupons processed using DCGQ and HPGQ. 5