A test kit can be made up of steel samples of the steels that you generally deal with within the heat-treatment facility. Steels such as: D2/D3, A2, HSS, AISI 4140, H11, H13, AISI 8620, AISI 440, Nitralloy, O1, S6/S7 and so on.
Spark testing is an old craft that can be used to give you an indication of what the unknown steel might be. This is based on the analogy that “steel is gray, therefore everything gray is steel.” You cannot taste the steel analysis, you cannot see the steel analysis nor can you smell the steel analysis.
The spark-test method of steel identification can be used to give you a guide as to what the steel might be.
How do we spark test?
The first item to address will be the grinding wheel on a bench grinder or a portable grinder. The wheel speed should be approximately 4,000-5000 RPM, and the wheel should be fine-grained and well-dressed. The reason for this is that the wheel is often loaded with steel fines from previous grinding operations. This means that the steel sample will be ground with stone and steel onto steel and could give a somewhat distorted result.
The steel sample to be tested should be of a convenient size and should be clean from scale and decarburization. Checking the spark on a decarburized and oxidized sample will produce an incorrect spark and distort the final spark observation.
What sort of room light should we have?
The test should not be done in full sunlight. The room light should be a little on the dim side. Spark testing is an acquired skill. If you have made up a sample set of known steel test blocks, however, it will not take you too long to become reasonably skilled in your observation of the resulting sparks.
Take care to wear eye-safety protection goggles and light industrial gloves. Do not have any loose clothing that can be snagged by the grind wheel. Take the utmost of safety care when conducting the test.
The next blog will discuss the effect of alloying elements on the result of the spark burst (or lack of it) and show illustrations of the resulting sparks.