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- Feb 1, 2015
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Not much useful information here. One part that I found of of use was the homemade sclerometer. The advice to mark any known alloys well was also good.
The other tests were too vague or misleading to be of use. His spark tests didn't show enough of the spark stream to be of use. He also didn't differentiate between the spark colors or of branching sparks of various steels. Much better visualization of spark test characteristics can be found in charts online. I have noticed that spark streams from hardened steel are shorter, more highly branched, and more intense than the same steel in an unhardened state.
Regarding, visual appearance, it has more to do with the surface prep than the type of steel. I have a length of hot rolled W1 that by all appearances, looks like hot rolled mild steel. I have some HSS tool steels and stainless steel that have black oxide coating. I also have highly polished stainless steel.
I certainly wouldn't recommend sniffing the spark stream while grinding steels, especially tool or stainless steels that contain chromium. While the scratch test is a valid test for hardness, the results depend to a large degree on the amount of pressure exerted, the hardness of the file, and the sharpness on the file. I expect that the reasoning for coarse tooth vs. fine tooth files is because more pressure is exerted with the fine tooth file. Files are sold in varying hardness's specifically for test for hardness.
Hardening a piece of steel by heating and quenching is a lot more involved than the presenter has described. Different steels have different hardening temperatures. If one were to heat a piece of HSS steel to a bright red and quench it, it would fail the test miserably. The effectiveness of the quench medium, whether brine, water, oil, or air, depends greatly on the amount of agitation of the quenched piece in the medium.
Identifying steel is a difficult task with home tests. I have an extensive collection of various steels ranging from wrought iron to some exotic alloy steels that to a large extent, I don't use because of the lack of definitive identification. The task isw a little easier with steels of known antiquity as varying the carbon content was the primary means of modifying mechanical properties. For instance, I know that spring steel used for a nineteenth century dump rake tooth is pretty much a straight carbon steel and makes fairly good tools. Modern spring steel is alloy steel as ultimate hardness is not a defining trait.