Did you ever wonder if the test coupon run with the load is truly representative of the results obtained on the parts themselves? The answer we tell ourselves is yes, it is. However, at least a shadow of doubt creeps in as the part size becomes larger and the test coupon size remains the same. Conducting tests on actual parts, while often both time-consuming and expensive, is extremely rewarding. Let’s learn more.
The cooling transformation characteristics of large SAE/AISI 4320 mill pinions were investigated by instrumenting the teeth of the pinion with thermocouples (Fig. 1) so that the quench rate and resultant metallurgical properties could be investigated and compared to that of the standard 2.5-inch (63-mm) test coupon run with every load. The pinion weighed approximately 18.5 tons (37,000 pounds) and was some 18 feet (5.5 meters) long. The largest diameter was 35 inches (890 mm) with a 4-inch (100-mm) gun-drilled hole through to the core.