1. Introduction: Heat treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the product shape. Heat treatment is sometimes done inadvertently due to manufacturing processes that either heat or cool the metal such as welding or forming. Heat Treatment process is a series of operations involving the heating and cooling of metals in the solid state. By heat treating, a metal can be made harder, stronger, and more resistant to impact, heat treatment can also make a metal softer and more ductile. No one heat-treating operation can produce all of these characteristics. In fact, some properties are often improved at the expense of others. In being hardened, for example, a metal may become brittle.
1.1 Types of Heat Treatment: a. Softening: It used to reduce strength or hardness, remove residual stresses, improve toughness, restore ductility and refine grain size or change the electromagnetic properties of the steel. Restoring ductility or removing residual stresses is a necessary operation after a large amount of cold working have been performed, such as in a cold-rolling operation or wiredrawing. And there is three ways to soft a material listed below: 1. Annealing: A technique used to recover cold work and relax stresses within a metal. Annealing involves recovery, recrystallization and grain growth. When an annealed part is allowed to cool in the furnace, it is called a "full anneal" heat treatment. Sometimes, an annealed parts is allowed to cool in oil, fresh water or salt water to give various value of stiffness. And sometimes the annealed parts is allowed to cool in air. That leads to Normalizing. 2. Normalizing: It is a type of heat treatment applicable to ferrous metals only. It differs from annealing in that the metal is heated to a higher temperature and then removed from the furnace for air cooling. The purpose of normalizing is to remove the internal stresses induced by heat treating, welding, casting, forging, forming, or machining. 3. Tempering.
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b. Hardening: Hardening of steels is done to increase the strength and wear properties. One of the pre-requisites for hardening is sufficient carbon and alloy content. If there is sufficient Carbon content then the steel can be directly hardened. Otherwise the surface of the part has to be Carbon enriched using some diffusion treatment hardening techniques. And there is some ways to Hard a material listed below: 1. Quenching: Quench hardening is a mechanical process in which steel and cast iron alloys are strengthened and hardened. These metals consist of ferrous metals and alloys. This is done by heating the material to a certain temperature. This produces a harder material by either surface hardening or through-hardening varying on the rate at which the material is cooled. Items that may be quenched include gears, shafts, and wear blocks. 2. Case Hardening: is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy.
1.2 Thermal conductivity, (often denoted k, λ, or κ) is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction. Heat transfer across materials of high thermal conductivity occurs at a higher rate than across materials of low thermal conductivity. Correspondingly materials of high thermal conductivity are widely used in heat sink applications and materials of low thermal conductivity are used as thermal insulation. Thermal conductivity of materials is temperature dependent. The reciprocal of thermal conductivity is thermal resistivity.
2. Objective:
To be familiar with furnace which used to heat inspection parts.
To be familiar with ways to soft materials.
To be familiar with ways to hard materials.
To show the different between annealing and normalizing and other ways to hard or soft materials.
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3. Apparatus: a. Furnace: which used to heat inspection parts. b. Combined Digital Hardness Tester.
4. Procedure: 1. 2. 3. 4.
At first, prepare four identical parts of same material. Take the parts to hardness tester and calculate its hardness values. Put these parts in the Furnace, to heat up until specific temperature. Then, take three parts out of the Furnace, and let the fourth part to cool in the Furnace slowly (Annealing), and let one of three parts to cool in air, and one in fresh water, and the last part in oil. 5. After the part cooled, take it to hardness tester, and calculate its hardness values. 6. Record the results in a table. 7. Use the engineering sense to compare between the different values g hardness.
5. Results: Table (1): Hardness after heat treatment ( HRB )
part Annealing Normalizing (air) 1 49.6 77.3 2 55.2 80.7 3 52.9 82.4 4 53.2 80.5 Average 52.725 80.225
Oil Water 97.5 98 99.6 104.2 88.9 109 93.9 103.5 94.975 103.675
Table (2): Reduction in hardness after annealing hardness before after annealing Reduction % 82.7 49.6 0.400241838 84.3 55.2 0.34519573 83.2 52.9 0.364182692 87.3 53.2 0.390607102 84.375 52.725 0.375111111
Table (3): Reduction in hardness after normalizing 3
hardness before 82.7 84.3 83.2 87.3 84.375
afher normalizing 77.3 80.7 82.4 80.5 80.225
Reduction % 0.065296252 0.042704626 0.009615385 0.077892325 0.049185185
Table (4): Increase in hardness after oil quenching hardness before after quenching increase % 82.7 97.5 0.178960097 84.3 99.6 0.181494662 83.2 88.9 0.068509615 87.3 93.9 0.075601375 84.375 94.975 0.12562963
Table (5): Increase in hardness after water quenching hardness before after quenching increase % 82.7 98 0.185006046 104.2 0.236061684 84.3 83.2 109 0.310096154 87.3 103.5 0.18556701 103.675 84.375 0.228740741
6. Conclusion: In table one, the hardness strength arranged regarding to the more strength as 103.675MPa (water), 94.975MPa (oil), 80.225MPa (normalizing) and last 52.725MPa (annealing process). This forms as a results of thermal conductivity which defined previously. The thermal conductivity of water is higher than of thermal conductivity of the oil and air that mean the part which cooled in water will lose its temperature faster than the part cooled in oil and air and annealing process. 4
In other ward, the water cools the part faster than oil, and oil cools the part faster than air, and the air cools the part faster than annealing process. Then, the part which cooled by water is the hardest part, and the part which cooled by oil is harder than part which cooled by air, and the part which cooled by air is harder than part which cooled by annealing process. And we see the same results in other tables.
7. References: a. Websits:
http://en.wikipedia.org/wiki/Quenching http://en.wikipedia.org/wiki/Heat_Treatment http://en.wikipedia.org/wiki/Heat_Treatment http://www.efunda.com/processes/heat_treat/introduction/heat_treatments.cfm http://en.wikipedia.org/wiki/Thermal_conductivity
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