THERMOCHEMICAL HEAT TREATMENT OF MEDIUM CARBON STEEL (Nst 60-2) IN THE ATMOSPHERE OF NATURAL NITROGENOUS MATERIALS

Publication Date : 01/08/2014


Author(s) :

Yekeen, N.A., Abdullahi, A.T..


Volume/Issue :
Volume 9
,
Issue 2
(08 - 2014)



Abstract :

Thermo-chemical heat treatment behaviour of medium carbon steel grade (Nst 60-2) is investigated using nitrogenous materials. In this study the effect of carbonitriding and nitriding on the formation and decomposition of martensite and other phases of steel are investigated. Tensile specimen with and without notch were produced and subjected to Nitriding with Bean Leaves (NIBL), Nitriding with Cow Dung (NIBL), Carbonitriding with Charcoal and Bean Leaves (CNCBL) and Carbonitriding with Charcoal and Cow Dung (CNCCD). Microstructural examinations and chemical analyses of the samples were conducted. The ductility, ultimate tensile strength and yield strength of the heat treated samples were determined from their stress- strain curves. The Ultimate Tensile Strength (UTS) was observed to be 42% higher for NICD specimen as a result of the grain re-arrangement, followed by that of CNCCD specimen with 36% then CNCBL with 27% and NIBL with 24% increase compared with the control specimen which had UTS of 1248.56 N/mm2. Experimental results were analyzed graphically to reveal the variations that complemented the microstructures. The case of the steel became hardened with soft core, thereby making the steel component to be tough and wear resistant. The average UTS for thermo-chemically heat treated specimens are the same with or without a notch, but the average Yield Stresses (YS) are 2.3-4.2% lower for specimens without notch.


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