Experiment Report: Metals Tensile Properties

Summary

The objective of this experiment is to assess the tensile properties of different metals by subjecting them to strain. The stress imposed on the metals is measured using two methods: the Monsanto tensiometer, which presses a bar against a mercury pressure chamber, and the MF40 techquipment, which is used to determine Young's modulus.

Introduction/Background

One of the key factors influencing the mechanical properties of steel is heat treatment. Adjusting the carbon content is a common method to alter the properties of steel.

Heating steel to around 400°C and holding it at that temperature results in decreased hardness and the formation of hard and tough steel.

Rapid cooling of steel, such as quenching, leads to the formation of martensite, which is the hardest and most brittle form of steel. Tempering martensitic steel by raising its temperature reduces hardness and brittleness, producing strong and tough steel. The specific heat treatment processes involve varying cooling rates, holding times, and temperatures.

Metals subjected to extreme heat undergo expansion, which affects their structure, electrical resistance, and magnetism.

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Heat treatment is commonly used to enhance strength, hardness, toughness, ductility, and corrosion resistance in metals.

When heat is applied to a material, its molecules and atoms vibrate faster, leading to increased spacing between atoms and expansion. A yield point is the stress at which a material begins to deform plastically. Beyond this point, some deformation becomes permanent and non-reversible. The expected strength of these metals is approximately 260 MPa.

Methodology

Various methodologies were employed for this report:

• Selection of an appropriate site and conducive environment
• Obtaining information through:
• Direct inquiry from the lecturer
• Personal observations and study
• Carrying out the experiment
• Reference to textbooks from the library
• Internet search engines

Results

The results of the experiment indicate that for tempering performed at 550°C, an increase in carbon content leads to higher yield and tensile strengths in the studied steels, consistent with hardness measurements.

However, this trend is not observed when tempering at 610°C, where the yield strength of the 0.033% carbon steel becomes higher than that of the 0.067% carbon steel. Ultimate strength remains of the same order as indicated by hardness measurements. This discrepancy may be attributed to strain-induced phase transformation, with the transformation of austenite into martensite responsible for the unexpected increase in yield strength of the 0.033% carbon steel.

Discussion

The findings of this experiment align with the effects of heat treatment on steel properties. The control of steel properties through heat treatment processes is vital for various engineering and construction applications. It allows for the optimization of steel's mechanical properties, making it suitable for specific use cases.

Conclusion

Based on the results of this experiment, it is recommended that the choice of metal for construction should consider factors such as the grade and properties of the metal, durability, corrosion resistance, life cycle costing, environmental impact, production and fabrication techniques, surface finishing, and maintenance. Additionally, non-metallic inclusions, while present in low fractions in high-oxygen weld deposits, play a significant role in various steel properties.