DATE: February 11, 2009
TO: Josh Smith, CEO, Manly Products Intl.
FROM: Ben Felix, Consultant, Mighty Metallurgy
RE: Materials for knife and nail
CC: Bridget Smyser, Professor, Northeastern University
This memo regards my recommendations for the best materials to be used in your developing knife and nail products. The optimal material for both a knife and a nail is hot rolled steel; it has optimal hardness and toughness. Other materials tested did not have sufficient hardness or toughness for these applications.
Equipment and Sample Information
I applied two different tests to determine which of the four selected materials, brass, aluminum, hot rolled steel and cold rolled steel, was best suited to your purpose. I used the Rockwell B Hardness test and the Charpy Impact test. 4 materials were tested for hardness and toughness, or resistance to sudden impact, using the Rockwell B Hardness test and the Charpy Impact test, respectively.
The Rockwell B Harness test was run using a Rockwell Hardness Tester Series 500 with a 1/16” needle. 6 hardness tests were run for each metal. The Charpy Impact test used a 31” hammer weighing 42lbs attached at a hinge to be released from a height and create an impact. The Charpy Impact test was run with the samples at -220˚C, 25˚C and 125˚C.
The samples of each material were cut to a specification of 55mm X 10mm X 10mm. A triangular shaped piece of 2mm was cut out of the centers of the samples to give a definite breaking point for the Charpy Impact test.
Data and Precision
The data from the Rockwell Hardness test showed that cold rolled steel was the hardest metal. After cold rolled steel, the hardness decreased from hot rolled steel to brass to aluminum. This data can be seen in Table 1. Figure 1 gives a graphic comparison of the hardness of the materials. The standard deviation of the data can be seen in the error bars on the graph.
The Charpy Impact test showed hot rolled steel to be the toughest material. After hot rolled steel the toughness decreased from cold rolled steel to aluminum to brass. This data can be seen in table 2. Figure 2 compares the toughness at different temperatures graphically.
The data for the Rockwell Hardness test was precise. This can be seen in the standard deviation for each data set. The largest standard deviation, for brass, was 3.5 HRB. The standard deviation for each data set can be seen in Table 1. The Charpy Impact test produced data precise enough to be reliable. Two tests were run for each material and the average of the two tests was taken as the value for that material. Some data was omitted in this calculation due to clear errors in running the test. The lower level of precision of this test does not affect the legitimacy of the results because the result for each material was significantly different.
In the Charpy Impact test, none of the materials failed to break. The triangular notch cut into the samples likely played a large role in having no failed breaks. The notch acts like a large crack in material that makes failure inevitable. The most ductile material was hot rolled steel. The ductility of each material can be seen in the way that the material breaks. Brass showed a very brittle break at all temperatures. In aluminum, a cup and cone fracture could be seen at liquid nitrogen and room temperature but at furnace temperature it broke in a more ductile manner. The sample of cold rolled steel behaved in a brittle manner when cooled and at room temperature but became more ductile when heated. Hot rolled steel was brittle when cooled, like most samples, but showed ductility at room temperature and furnace temperature.
Heating the samples generally increased the energy required to break them, brass being the exception. Cooling hot and cold rolled steel affected them heavily. Cooling brass and aluminum had lesser effects as brass stayed brittle and aluminum continued to show its cup and cone breakage. Hot rolled steel was ductile at room temperature.
At room temperature, cold rolled steel was the hardest followed closely by hot rolled steel. The atoms that these materials are made of, carbon and iron, explain why the steels are relatively hard. Brass is the next hardest material. This is not explained as well by its composition of copper and zinc but by its body centered crystal structure. Aluminum’s being a non-alloy makes it the least hard of all the materials tested.
The Rockwell Hardness test and the Charpy Impact test are standardized tests that are accepted by the ASTM as consensus standards for testing. This means that if you wish to consult another firm about the best materials for your new products, their results will be comparable to the ones I have provided for you.
I know hot rolled steel will help you create some outstanding knife and nail products. I hope that your search for the right material is short and successful. My firm always appreciates your business and strives to keep you satisfied with our consultation. Direct any questions regarding my data or my recommended material to firstname.lastname@example.org.