Lab8SteelsS07-4

Lab8SteelsS07-4 - Laboratory 8 Steels: Tailoring Properties...

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Laboratory 8 Steels: Tailoring Properties Through Heat Treatment Goal: To tailor the mechanical properties of plain carbon steels through proper thermal processing (i.e., “heat treatment”) such as slow cooling in air, water quenching, and tempering. Learning Objectives: 1. Use the numerical classification system of steels (e.g., 1018). 2. Describe the range of mechanical properties such as hardness (strength) that can be exhibited by steels. 3. List the different phases that occur in steels using the Fe-C phase diagram and describe each phase. 4. List the eutectoid reaction that takes place in the Fe-C system. 5. Use isothermal transformation (IT) diagrams and phase diagrams to predict the microstructures that result from the transformation of austenite by quenching or slow cooling steels. 6. Discuss how martensite and tempered martensite are formed. 7. Measure the relative strengths of plain carbon steels based on the carbon content and cooling rate. This is a challenging lab. What follows in the write-up will make the most sense if you read it slowly . Taking a few notes would be a good idea. If you simply “breeze” through the write-up, it has the possibility of making virtually no sense. Taking your time will pay off in a meaningful lab i Caution! MatE 215 Lab 8: Heat Treatment of Steels (Spring 07) Page 1 of 18
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What Is The Big Deal About Steel? For many engineering applications steel is the number one material for the job. Steel is so popular because the properties can vary so widely depending on alloy content and heat treatment. Heat treatment is simply controlled heating and cooling – an example of processing . Steel can be hard and brittle, soft and ductile, or anywhere in between. The name “steel” implies a mixture of iron (majority element) with other elements (minority elements, or alloying elements). The major alloying element in steel is carbon. Most steels contain small amounts of carbon, usually less than 1 weight percent (wt.%). Steel = Fe + C (usually < 1 wt.%C) The mechanical properties of steel are directly attributable to how the phases are distributed within the steel. In addition, how different phases are arranged makes up the microstructure , which also plays a role in properties. As with everything in materials engineering: structure controls properties, and the structure we refer to here is going to be the microstructure of the steel. Steels have their own special classification system that is used widely in industry. Using this classification system for steels is important. The American Iron and Steel Institute (AISI) designation usually has four digits: the first two represent the major alloying elements in the steel, and the last two digits indicate the carbon content in hundredths of a percent. For example, plain carbon steels have the label of 10xx, while 43xx represent nickel-chromium-molybdenum alloy steels. A 1018 steel would be iron with 0.18 wt.% carbon. Our lab only deals with plain carbon steels: 1018, 1050, and 1095. These steels contain only Fe + C.
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Lab8SteelsS07-4 - Laboratory 8 Steels: Tailoring Properties...

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