Metallography and Heat Treatment

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MAEN100 Engineering Materials

LABORATORY REPORT: METALLOGRAPHY AND HEAT TREATMENT

Helen Marie 17777045

                        Lab Time: Friday 4-6pm

                        Group:

Abstract

Heat treatment involves heating metals such as iron and steel to very high temperatures and then cooling them down to specific temperatures at rates that disseminate the properties of iron and steel. Heat treatment will change the hardness, resistance to wear, tensile strength, shock and malleability of steel and iron. Engineers require these controlled properties to make important decisions. It this experiment a macrographic study was done on cast, wrought and multi-phase structures.  The effects of solid solution strengthening, precipitation hardening were studied using non-ferous metal system.  Data collected was used to measure the hardness value of Alluminium Alloy 2011 4.0% Cu at different times up to 240 minutes.   The effect of rate of cooling on the hardness of plain carbon and alloy was studied,

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Introduction

The purpose of this investigation was;

1. To perform macrographic study on cast, wrought and multiphase structure.
2. To observe the effect of solid solution strengthening and precipitation hardening of a non-ferrous system
3. To observe the demonstration of Jominy Bar test and to investigate the incremental hardness value of different ferrous samples

1. Theory

1.1 Metallography

Metallography is the study of the microstructure and constitution of metallic alloys ( Cerri & Evangelist, 1999). Processing and the influence on the alloys properties and behaviour are controlled. At melting point the metal crystallized structure breaks down. As the molten metal cool, it aligns in unit cells. The rate at which it has been cooled determines the size of the grain as well as its characteristics. Metals that have been cooled slowly have a larger grain size as they have been allowed to expand as shown in Figure 1b.

On the other hand metals that are cooled rapidly have a smaller grain structure, as there is not as much time for the grains to expand. The slow cooled alloys will have fewer grains in comparisons to the rapid cooled as shown in Figure 1c. Slow cooled alloys will also be more ductile where as rapidly cooled alloys will have greater strength.

Copper metal solidifies to form crystals that grow in preferred directions and form open tree like structures called dendrites (CDA, 2011) as shown in Figure 1d. At low melting points, a eutectic forms in the open spaces between the dendrites, which are normally dark ‘bodies’ in a copper background. Other pores, seen as dark spots, are also present in the material.  Structures that are multiphase microstructures can be determine through their transformation temperature and length of time that the process is performed.