Vickers Hardness Testing Two

Three Pieces of different types of steel were tested.

1. Hexagonal 2. Oval 3. Circle

The aim of the experiment was to complete a Vickers hardness test on each sample in order to recognize some characteristics of the heat-treated pieces.

Firstly, the pieces of metal were polished in order to create a light, clear surface to test. This is because if the surface of the metal is dark and uneven then the indent might not be visible, or could be inaccurate.

The diamond test was then performed on the three pieces in of hardened steel using the same hardometer as previously. The same machine had to be used as when testing the pieced before treatment for consistency in results. For example, if there was an initial calibration error, this would be carried forwards to this set of readings, therefore making the error negligible.

1. Hexagonal 2. Oval 3. Circle

The results can be seen below. They have been tabulated against the previous results for easy comparison.Sample Normalized

Diagonal Measurement (divisions)

Normalized Vickers Hardness (V.H)

Heat Treated Diagonal Measurement (divisions)

Heat Treated Vickers Hardness (V.H)

1. Hexagonal 4.4 287 3.8 385

2. Oval 3.6 429 2.6 8233. Circle 5.0 223 5 223

From the test results, it can be concluded that the circular sample is not effected by heat treatment. This can be said, as the hardness is the same for both pre, and post hardening. This metal is probably used in manufacture that involved welding. As welding is a process that involved a great amount of hear, so the metal must be resistant to heat treatment. The circular piece is still the softest piece, meaning that it would be unsuitable for making one of the three tools, as they need to be both tough and surface hard. The oval is the opposite – having quite a small indent and therefore being the most resistive of the three samples to the force. It is also the sample that reacted the most to the heat treatment process, increasing its surface hardness from 429VH to 823VH. This could be problematic for creating one of the suggested tools, as with hardness comes brittleness, and as stated previously the metal needs to be both hard and tough. The hexagonal piece has an increased surface hardness after heat treatment – however is still a fairly soft metal considering the maximum value of the Vickers hardness scale. This means that it can be both hardened, and still be slightly ductile. This is ideal as it means that the point of the tool made will not grind down over long use, and the tool will not break/buckle under a great force.

The hardness test was also performed on the fourth normalized sample (the method for which can be found in week 6).

The hardness of this untreated metal was found to be 2.7 divisions, which is 763VH. This can now be heat-treated and the hardness retested post treatment.