o There are various types of martensite depending on the carbon content for C

O there are various types of martensite depending on

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o There are various types of martensite depending on the carbon content: for C <0.2% the martensite is in the form of well defined thin strips (laths), for C <= 0.6% plates of martensite are formed, for C <= 1.2% the martensite is in the form of arrays of well defined plates. o The martensite phase initiates at a temperature M s and is complete at a temperature M f . M s varies from 500 °C for C <= 0.1% to 200 °C for C <= 1.2%. Relevant Steel Links 1. Steels and Iron ...MetalworkMedia.com... A neat comprehensive article covering the whole range of Ferrous metal production 2. Casting Handbook European Standards ...Includes standards -data for European designated Ferrous Metals 3.Fundamentals Of Metal Alloys Equilibrium Diagrams...A very informative PowerPoint presentation 4. Steel for many purposes ...School Science back to basics for clear understanding of the principles 5. The Metallurgy of Carbon Steel ...GoWelding. A very clear concise set of notes on Carbon Steel
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~ Page 27 of 73 ~ EXERCISE 1. State briefly what is meant by the terms: (a) Ferrite(b) Pearlite(c) Cementite(d) Austenite 2. Describe the composition at room temperature of the following, and explain how their properties are influenced by their composition: (a) A low carbon steel; and (b) A high carbon steel. 3. Sketch a cooling curve for a 0.5% carbon steel. Identify and label the change points on the curve and explain what happens at each point. 4. Describe the effect of the following elements when included, by accident or by design, in plain carbon steels. 5. Explain how a plain carbon steel differs from wrought iron and cast iron in respect of their compositions and properties. 6. Show by means of a diagram the effect of carbon content on the hardness, tensile strength and ductility of annealed plain carbon steels. 7. Sketch the ‘steel section’ of the iron-carbon equilibrium diagram for plain carbon steels and describe the cooling from the austenitic condition to room temperature for a: (a) Hyper-eutectoid steel; (b) Hypo-eutectoid steel; and (c) Steel of eutectoid composition. 8.Since iron is allotropic:
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~ Page 28 of 73 ~ CRITICAL CHANGE POINTS Just like all phase equilibrium diagrams, the iron-carbon phase equilibrium is also constructed from a family of cooling curves by connecting its critical change points. The change points, in this case, are often simplistically referred to as the upper critical temperature (UCT) and the lower critical temperature (LCT). The critical change points, where changes to composition and structure occur, are also called arrest points since the time-temperature heating or cooling curve stops at these points as the latent heat energy associated with change is taken in during heating or given out during cooling as shown in Fig. 1 below.
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