Carbon content in steel is one of the key parameters determining its mechanical properties and applications. There are several ways to determine the chemical composition of steels and alloys, and one of the fastest and simplest is the spark method. It was developed by American blacksmith John Francis Keller in 1921 and later described in the world’s first welding encyclopedia.
The spark method is based on observing luminous particles formed when a grinding wheel contacts the surface of various steel types. Heating causes ejection of particles exposed to atmospheric oxygen, leading to various visual effects.
When a grinding wheel contacts the metal surface, friction heats it. This causes the wheel to eject tiny particles. With up to 0.02% carbon in steel or alloy, particles move along expanding straight lines and become brighter until they disappear completely. This phenomenon is presumed to occur due to atmospheric oxygen acting on the red-hot particles.
To observe material behavior it is recommended only lightly to touch the grinding wheel with the test sample and to watch spark behavior against a black or other dark background.
Low-carbon steel with 0.02 to 0.25% carbon can be identified by splitting of luminous streaks. As carbon content decreases, the number of sparks decreases and the spatial distance between them increases.
Medium-carbon materials contain 0.3 to 0.65% carbon and are characterized by unique branching of luminous lines on contact with a grinding wheel. This is explained by elevated carbon that, under heat from iron sparks, forms flashes interrupting initially thick lines.
Steel containing more than 0.65% carbon is distinguished by abundant frequent star-shaped flashes. Iron and carbon in the material oxidize easily with oxygen, creating a risk of burning the steel. Note that as carbon content in the steel rises, flash frequency also rises and the distance between them shrinks significantly.
Steel chemical composition plays a decisive role in its mechanical and thermal properties. The spark method described in this article provides a quick estimate of carbon content, but it is approximate. For precision alloys, accuracy of chemical composition determination is critically important. In laboratories of modern metallurgical enterprises steel and alloy composition is assessed using spectral analysis methods to ensure high quality of finished products.
PZPS operates a spectral laboratory where modern equipment and precise analysis methods determine not only carbon quantity but also content of other chemical elements in steels and alloys. This ensures high quality of products manufactured and guarantees precise chemical composition of the precision alloys melted. The laboratory also studies customer materials and helps obtain all necessary information about experimental samples.
