Heat Treatment and Metallurgy Lab

Jominy end-quench test :- Jominy end-quench test is quite simple and easy test, and is thus, almost universally employed for the determination of hardenability. For this test, a slightly oversized bar of steel is normalisad at about 66°C (≈ 150°F) above Ac 3 , and then machined to the final dimensions of 4″ (102 mm) long and 1″ (25.4 mm) diameter. Machining removes any decarburised layer formed in the normalising treatment. The machined bar is put inside a closed box, half-filled with cast iron chips to prevent decarburisation, and then austenitised for 30 minutes at about 22-23°C above Ac 3 . Standard Jominy-test specimen and fixture :- Meanwhile, the special water-quenching device is kept ready. In this device, the diameter of the pipe opening is 1/2 inch. Specimen holder is such that the bottom of the specimen remains at 1/2 inch above the nozzle. The constant pressure of the water is such that the height of the impinged jet is 2 inch. The water temperature is 75 ± 5°F.

Case depth  is the thickness of the hardened layer on a specimen. Case hardening improves both the wear resistance and the fatigue strength of parts under dynamic and/or thermal stresses. Hardened steel parts are typically used in rotating applications where high wear resistance and strength is required. The characteristics of case hardening are primarily determined by surface hardness, the effective hardness depth and the depth profile of the residual stress. Gears and engine parts are examples where hardening is used. Effective case depth is the depth up to a further point for which a specified level of hardness is maintained . Total case depth is the depth to a point where there is no difference in the chemical or physical properties. Case depth testing often involves performing a series of hardness impressions from the edge of the specimen towards the center. The hardness progression is plotted on a graph and the distance from the surface to the hardness limit (HL) is c