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The effect of nickel on the beginning of transformation of austenite in a 0.55 carbon, 0.35 molydenum steel Scott, Donald Alexander


This study is carried out to find the effect of nickel on the beginning of isothermal transformation of austenite in an iron-carbon-molybdenum alloy containing 0.55 carbon and 0.35 molybdenum. An introduction describes the iron-carbon equilibrium system, the products of slow cooling of austenite, the relation between slow cooling and isothermal transformation at temperatures below equilibrium, and a full discussion of terminology used. A literature review discusses theories of transformation and previous work on the effect of nickel on austenite transformation. Development of experimental technique in isothermal transformation and melting of pure alloys is discussed. The isothermal transformation diagrams are shown for beginning of transformation of austenite of base composition 0.55 carbon and 0.35 molybdenum, relatively free from impurities (silicon, manganese, etc.), showing the effect of nickel on the beginning of transformation. Nickel additions used are 0, 2.13, 3.69, and 5.31 percent. Isothermal transformation is shown by photomicrographs which are discussed fully. The effect of increasing nickel on the isothermal transformation of an alloy containing 0.55 carbon and 0.35 molybdenum is as follows: (1) the pearlite reaction is delayed appreciably: (2) ferrite formed at intermediate temperatures (880 to 1000 deg. F.) becomes more prominently acicular, the acicular ferrite reaction taking the place of the upper bainite reaction of low nickel alloys: (3) the acicular ferrite reaction is followed first by rejection of carbide particles, and later by agglomeration and growth of the carbide phase: (4) the acicular ferrite and feathery bainite reactions as represented on the isothermal transformation diagram become separated by the appearance of a bay in the isothermal transformation curve.

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