A Novel Method of Pack Nitriding of AISI 1018 and 1045 Steels Using Melamine Derived from Urea

Abstract

Steels are one of the most broadly used ferrous metallic engineering materials used in many application. Example medium carbon steels are used in gears, railway wheels and tracks, crankshafts, axles, and other structural components. Having all these applications medium carbon steels often face the problem of corrosion and fatigue resulting less strength, less hardness, wear, and other mechanical failures. Surface Engineering is used as a method to overcome all of these problems. Surface engineering is applied for purpose of: increasing wear resistance, strength, hardness, corrosion resistance and impact resistance. Nitriding is a thermochemical surface treatments process in which nitrogen diffuses to the surface of the metal. The surface of the metal changes chemical composition and mechanical properties but the inner core of the metal remains unaffected. In this research pack nitriding was used for surface treatment of AISI 1018 mild carbon steel (low carbon steel) and AISI 1045 medium carbon steels. The effect of temperature, time, concentration of nitrogen, furnace cooling and air cooling was studied. Samples with a dimension of 0.1cm×1cm×1cm were taken and heated at 500oC, 530oC, 550oC, 580oC at the rate of 10oC/min for 2, 3,4,5 and 6 hours. The prepared samples were buried in a dry melamine-urea powder as a source of nitrogen. This was done in a silica crucible kept in a container made of stainless steel sealed tightly using fire clay to prevent leaking of gases. The nitrided surface of the metal formed two layers. These are compound layer and diffusion zone. The microstructural, mechanical and corrosion properties of the samples before and after nitriding were investigated. Thickness of the samples before and after nitriding were measured using micrometer screw gauge. Phases present in the surface of samples were investigated using XRD. ̍ and ε phases were identified in the compound zone of the metal and metal nitride precipitates in the diffusion zone. All nitrided samples were characterized using powder XRD, hardness testing and further characterized for corrosion resistance using cyclic voltammetry.