Steel Grade Identification Black Technology - Spark Identification Method

What Is Spark Identification Method:The method of contacting steel with a high-speed rotating grinding wheel and determining the chemical composition of the steel approximately according to the shape and color of the spark produced by grinding is called the spark identification method.

When the steel sample is ground on the grinding wheel, the high-temperature fine metal particles are projected along the tangential direction of the grinding wheel rotation, and then rubbed with the air, the temperature continues to rise, and the particles oxidize and melt violently, so they appear as stripes during operation. Bright streamlines.

The abrasive particles are in a high temperature state, and the surface is strongly oxidized to form a layer of FeO film. The carbon in steel easily reacts with oxygen at high temperature, FeO+C→Fe+CO, to reduce FeO; the reduced Fe will be oxidized again, and then reduced again; this oxidation-reduction reaction cycle will continue, CO gas is produced. When the iron oxide film on the surface of the particles cannot control the CO gas produced, a burst phenomenon occurs and sparks are formed.

If the broken particles still have FeO and C that have not participated in the reaction, the reaction will continue, and there will be two, three or more burst sparks.

Carbon in steel is the basic element that forms sparks. When steel contains elements such as manganese, silicon, tungsten, chromium, molybdenum, their oxides will affect the line, color and state of sparks. According to the characteristics of sparks, the carbon content of steel and the content of other elements can be roughly judged.

Spark form: The sparks generated when steel is ground on the grinding wheel are composed of root sparks, middle sparks and tail sparks. The linear trajectory formed by high-temperature grinding particles is called streamline. The bright and thicker points on the streamline are called nodes. When the spark bursts, the short lines produced are called awn lines. The spark formed by the awn line is called the knot flower. With the increase of carbon content, the bursts continue to produce secondary flowers and tertiary flowers on the awn line. The bright dots near the awn line are called pollen. Due to the different chemical compositions of steel materials, sparks with different shapes at the tail of the streamline are called tail flowers. The tail flower has bud-shaped tail flower, foxtail-shaped tail flower, chrysanthemum-shaped tail flower and pinnate tail flower.

1. Spark characteristics of carbon steel

Carbon is the basic element of sparks in steel materials and the main component measured by spark identification method. Due to the difference in carbon content, the spark shape is different.

• The streamline of mild steel is thick and thin, with few popping flowers and more one-shot flowers, and the awning line is thick and long with bright nodes. The sparkle is yellowish with dark red.
• The streamline of medium carbon steel is slender and many. There are nodes at the tail and middle of the streamline. There are more popcorns than low-carbon steel. The pattern is larger. There are primary flowers and secondary flowers with a small amount of pollen. The sparkle is yellow in color.
• The streamlines of high carbon steel are thin, short, straight, multiple and dense. There are many popcorn flowers, small flower types, mostly secondary flowers, tertiary flowers or multiple flowers, with thin and sparse awn lines, many pollen, and bright yellow sparkles.

2. Spark characteristics of cast iron

The cast iron fire bouquets are very thick and have many streamlines. They are generally secondary flowers with many pollen and pop flowers. The tail gradually thickens and droops into an arc, and the color is mostly orange-red. During the spark test, the hand feels softer.

3. Spark characteristics of alloy steel

The spark characteristics of alloy steel are related to the alloying elements it contains. In general, elements such as nickel, silicon, molybdenum, and tungsten inhibit spark burst, while elements such as manganese, vanadium and chromium can promote spark burst. Therefore, the identification of alloy steel is difficult to grasp.

In general, chrome steel fire bouquets are white and bright, with a slightly thicker and longer streamline. The bursting is mostly a one-time flower, with a larger flower shape, a large star shape, multiple and thin branches, with broken pollen, and a brighter burst of sparks.

The fire bouquets of nickel-chromium stainless steel are thin, with darker luminescence, bursting into a single flower, with five or six branches, star-shaped, and slightly bursting at the tip.

The high-speed steel fire bouquets are long and slender, with few streamlines, no spark burst, dark red color, intermittent streamlines at the root and middle, and arc-shaped tail flowers.

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