How to judge the heating temperature of steel with the naked eye?

One way to determine the heating temperature of steel with the naked eye is to observe the changes in color on the surface of the steel as it is heated. The temperature of steel can be estimated based on the color that it takes on as it is heated.

When steel is heated, it gradually changes color from red to yellow and then to white. At a temperature below 600°C (1000°F), steel will glow a dull red, orange or yellow color. This is known as “cherry red” or “annealing” due to the softening of the steel at those temperatures. As the steel continues to be heated, the color will become brighter and move from yellow to white. At around 750°C (1390°F) the steel begins to turn white with a bluish tint. This is known as “white-hot” and indicates that the steel has reached its critical temperature. Beyond this, the steel will continue to emit sparks and an intense red and yellow color.

Once the steel is heated, the color of the steel provides an indication of how hot it is. This makes it possible to judge the temperature of the steel with the naked eye. A steel bar heated to a red-orange color is likely to be at 600°C (1000°F), while a steel bar heated to a bluish-white color is likely at 750°C (1390°F).

The color of steel can also be used as an indicator of how much heat has been applied to it. Steel that has been heated for a long period of time, such as for welding, will turn brown due to the oxidation of the surface. This is an indication that the steel has been exposed to too much heat and should be cooled quickly.

In general, the heating temperature of steel can be judged based on the color changes that occur as it is heated. Steel will gradually move from red to yellow and then to white as it is heated. The temperature of steel is estimated by the color it takes on as it is heated. Steel that has been heated to a red-orange color is likely to be at 600°C (1000°F), while steel heated to a bluish-white color is likely at 750°C (1390°F). Additionally, if the steel has turned brown due to oxidation it is an indication that the steel has been exposed to too much heat and should be cooled quickly. With a little practice, it is possible to estimate the temperature of steel with the naked eye.

It is possible for an untrained individual to judge the temperature of steel by just looking at it. With enough experience, heated steel objects can be identified through observation of the objects color and surface condition. Steel is a good conductor of heat, which means that it heats up quickly and cools off relatively quickly when heat is removed.

The most common way to identify steel’s heating temperature is by using the temper color chart. Steel has a range of colors that indicate the temperature of the steel in (degrees Celsius). For example, steel heated up to a temperature of approximately 150 degrees Celsius will have a faint red hue, while a bright yellow hue indicates a temperature of approximately 700 degrees Celsius. The chart generally provides a shorthand way to judge approximate temperatures without having to measure the surface temperature of the steel itself.

In addition to relying on the temper color chart, another way to determine the heating temperature of steel is by its surface condition. As steel is heated, its surface begins to oxidize, forming a thin coating of iron oxide that appears as a dark black color. If the oxides are still in their dark black state, it is generally a good indicator that the steel has been heated to a high temperature.

While these methods can provide an approximate idea of the temperature at which steel has been heated, it is still best to use a thermometer. Surface thermometers are easy to use and provide a more accurate temperature reading compared to looking for visual cues. In addition, surface temperature readings allow for a more precise temperature judgement when determining whether a certain temperature is sufficient to harden or temper the steel. Therefore, relying on a thermometer is the best way to accurately judge the heating temperature of steel.