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MIME 1650 Laboratory 6 Heat Treatment of Metal Alloys Objective The Student should learn the principles involved in the treatment of metal alloys, in particular ferrous alloys. Practical application of hardness testing is also a key to this experience. Agenda - Safety - Review of TTT Diagrams (can be found on page 130 of text) - Laboratory 5 performance Instructional Materials The fundamentals of heat treatment are based on phase transformations of the structure of steel. The beginning point in understanding the heat treatment process is the phase diagram shown below. Fig. 1 Iron-iron carbide equilibrium phase diagram (iron-rich portion). (adapted from Metal Progress Data Sheets, No. 38, American Society for Metals, Metals Park, Ohio, 1952.) Note that steel changes phases at several critical temperatures depending on the alloy. The austenite region defines steel at elevated temperatures. As the austenite cools, it will form an alloy of ferrite and cementite. The exact temperature that this occurs is determined by where the vertical line drawn for the alloy crosses the curves marked A1, A3 and/or A1, 3 marked on the diagram above. Below these temperatures, the austenite is unstable and will transform to martensite, bainite or perlite depending upon how the austenite is cooled. Each of these alloys is a form of the combination of ferrite and cementite but with different microstructure and physical properties. The Time and rate of cooling to form these alloys depends on the carbon content as well as any other alloying elements in the steel. The objective of heat-treating is to create in the material the set of material properties desirable for the purpose the metal is used for. These phase transformations alter the grain structure of an alloy, which directly affects the alloy’s mechanical properties. The degree of treatment depends on a material’s current condition, microstructure, and chemical composition. Mechanical properties affected by heat treatment include strength, toughness and hardness. Common treatment methods include annealing, quenching, tempering, and normalizing. These methods work in conjunction with a material’s composition to yield reasonably predictable results. Charts, which are useful while studying the effects of treatments, are known as time-temperature-transformation (TTT) diagrams as shown below. Fig 2 Isothermal transformation diagram for eutectoid steel. This is a graph with temperature along the ordinate and time along the abscissa. This TTT diagram applies to only one alloy of steel, in this case eutectoid of 0.8\% carbon steel (AISI 1080). Each different alloy of steel will have a separate TTT diagram. The critical temperature line is taken from the A1, A3, Acm and/or A1, 3 curves of the phase diagram. For this chart, the critical temperature is A1 at the eutectoid temperature, 727°C or 1340°F. In standard heati1 MIME 1650 MATERIALS SCIENCE & ENGINEERING Spring 2020 Introduction to Materials Science & Engineering – Laboratory The laboratory portion of MIME 1650 Materials Science & Engineering seeks to give the engineering student a hands-on appreciation of what Material Science is all about. In this portion of the course the student should gain an understanding of material properties and these properties are affected by different processes. The knowledge of these effects is valuable when selecting a material for a part or design. For example, certain applications require a material that will not buckle under stress; others require more strength while others require more ductility. In addition to selecting the right material, engineers must make their design cost effective. There will be seven (7) laboratory exercises spread over the course of the semester. Each student will be required to submit a lab report which will be due one week after the completion of the lab unless otherwise specified. ALL reports must be typed. Failure to do so will result in a rejected report. Details on what is expected from your report are in the Report Requirements section. If there are any questions about a particular lab, please talk to your Teaching Assistant (TA) about your concerns and they will provide the needed help. They can often critique your report upon request. Do not hesitate in asking questions if something is confusing to you as asking questions is an excellent way to learn. 2 Laboratory Report Requirements Introduction All engineers and scientists are required to write reports documenting their work. Each organization establishes its own required format. Reports are used for a variety of purposes. First and foremost, it is a historical document of what, when, why and how something was done. A reader of the report should, by the report alone, be able to replicate the experiment. A report is often used by management to determine whether or not a project is meeting expectations. Decisions of where to allocate available resources (such as labor and capitol) are often made based on the written report. Engineers and scientists that communicate well through the written report are in demand by industry. Report Style The report must be clear, concise and complete. A well written report avoids engineering jargon and specialized language. The writer must remember that the reader often does not have the knowledge or background that the writer has. Ideas must be expressed in a logical flow and in complete sentences. Furthermore, the report must be concise. What this means is that the writer should favor simple sentences where possible. Long, flowery sentences with many subordinate clauses and qualifications are not appropriate in an engineering report. On many organizations, the pertinent ideas being reported on must be stated in one page, often called “The Executive Summa