Steel Temperature Color Chart: A Complete Comparison

The color temperature of steel is closely related to the heating process. At room temperature, steel does not emit light. However, when heated to a certain temperature, it begins to glow, initially emitting a red light. As the temperature rises further, the color of the steel gradually changes from red to orange, and then to yellow.

This process aligns with the concept of black-body radiation, where color temperature is defined based on black-body radiation, with orange-yellow having a lower color temperature and blue having a higher one.

Specifically for steel, when its color temperature reaches 3200K, the color of the light is relatively close to red, which is the color of iron when heated to over a thousand degrees.

If the heating continues, the glow will become brighter and the color will get closer to white.

This indicates that by controlling the heating process, a color change from red to near white can be achieved.

  • Around 600 degrees Celsius, a slight red color begins to appear
  • At 700 degrees Celsius, it turns into a light orange color
  • At 800 degrees Celsius, it becomes red
  • At 900 degrees Celsius, it turns yellowish-red
  • At 1000 degrees Celsius, it turns a whitish-red color

This is not an accurate method and it may vary depending on the type of steel being used. These colors are only applicable for certain types of steels (probably carbon steel). The color of the flame can be different for different types of metals at the same temperature.

The relationship between the heating temperature of steel and its color:

In 1893, Wien studied the relationship between the maximum wavelength λmax and temperature T, which is λmaxT=2898μm•K.

Therefore, the temperature can be judged based on the color of the flame (i.e., the wavelength of light).

Empirical observation shows that dark red indicates 600°C, red indicates 900°C, orange-yellow indicates 1100°C, yellow indicates 1300°C, light yellow indicates 1400°C, yellow-white indicates 1500°C, and bright white (with a hint of yellow) indicates 1600°C.

There is a type of temperature-sensitive paper developed by Nichiyu Giken Kogyo Co., Ltd. that can be placed on the heated metal to show its temperature changes through different colors.

By observing the color changes of the paper on different parts of the metal, one can determine their respective temperatures and record them accordingly to make a color chart for further use.

The Relationship Between the Color of Steel Heating and Temperature

Fire colorTemperature ℃
Dark brown520——580
Dark red580——650
Dark cherry650——750
Cherry blossom750——780
Light cherry blossom780——800
Light red800——830
Orange-yellow with a hint of red830——850
Light withered880——1050
Yellow1050——1150
Light yellow1150——1250
Yellow-white1250——1300
Bright white1300——1350

The relationship between the tempering color and temperature of carbon steel.

Tempered colorTemperature ℃
Light yellow200
Yellow-white220
Golden yellow240
Yellow-purple260
Dark purple280
Blue300
Dark blue320
Blue-gray340
Blue-gray light white370
Black-red400
Black460
Dark black500

This seems to require a lot of experience, as the temperatures can be different during the day and night. The thermometer is not always easy to use and may not be very accurate.

There can also be differences between the temperature of the flame and the temperature of the object being measured.

How to accurately measure the color temperature of steel?

There are several methods to accurately measure the color temperature of steel:

1. Color Temperature Meter:

A color temperature meter is a tool specifically used for measuring the color temperature of a light source. Its usage is similar to a light meter, mainly by placing the measuring probe on the object to be measured. This method is suitable for directly measuring the intensity of all wavelength light emitted by the light source, thus obtaining the color temperature value.

2. Spectral Analysis:

Spectral analysis measures the color temperature by directly measuring the intensity of all wavelength light emitted by the light source. This method can provide more detailed spectral information, helping to accurately assess the color temperature of steel.

3. Colorimeter:

A colorimeter is another tool specifically used for measuring the color temperature of a light source, including filter-type and crystal-type. The filter-type colorimeter measures the color temperature by filtering specific wavelength light, while the crystal-type colorimeter determines the color temperature by measuring the crystal’s response to different wavelength light.

Accurate measurement of the color temperature of steel can be achieved by using a color temperature meter, spectral analysis, or a colorimeter. The choice of method depends on the specific measurement requirements and available resources. For example, if you need to get results quickly and the accuracy requirement is not very high, you can choose a color temperature meter; if more detailed spectral information is needed for in-depth analysis, spectral analysis may be more suitable; and if you have very high requirements for the accuracy of the measurement results, consider using a colorimeter for precise measurement.

What are the detailed changes in the luminescent properties of steel at different temperatures?

The detailed changes in the luminescent properties of steel at different temperatures can be understood from several aspects. Firstly, when the metal reaches a certain temperature, the movement of its internal particles becomes violent, which may cause photons to reach the minimum frequency of visible light, thus producing red luminescence. This indicates that at lower temperatures, steel may not glow or the light intensity may be weak, as the change in electron energy levels is not enough to produce visible light.

As the temperature rises, the luminescence intensity of the phosphor will decrease due to the thermal quenching phenomenon. This phenomenon is mainly due to the increase in temperature causing the matrix lattice vibration to intensify, enhancing the electro-acoustic interaction and the probability of non-radiative transition, thus reducing the light intensity. Although phosphors are mentioned here, this principle also applies to metal materials such as steel, and a decrease in luminescence intensity may be observed at high temperatures.

In addition, from the perspective of luminescence studies, changes in temperature have a significant impact on refrigeration efficiency, and this impact has a cubic relationship with temperature. This means that as the temperature decreases, the difference between the optimal excitation light frequency and the center frequency of the non-uniform line shape will increase, reaching a maximum at lower temperatures. This indicates that under low-temperature conditions, the luminescent properties of steel may vary due to excitation at specific frequencies, especially at low temperatures, where it may be easier to observe the luminescence at specific wavelengths.

The luminescent properties of steel will change at different temperatures as follows: at lower temperatures, due to the insufficient change in electron energy levels to produce visible light, steel may not glow or the light intensity may be weak; as the temperature rises, due to the intensification of lattice vibrations and the increase in electro-acoustic interaction, the luminescence intensity of steel may decrease; and under low-temperature conditions, excitation at specific frequencies may cause steel to exhibit different luminescent properties, especially at low temperatures, where it may be easier to observe the luminescence at specific wavelengths.

What is the relationship between color temperature and blackbody radiation theory during the heating process of steel?

The relationship between color temperature and blackbody radiation theory during the heating process of steel can be explained from the following aspects:

Definition of color temperature: Color temperature is a scale that measures the color of a light source, and its unit is Kelvin. It is determined by comparing the color of the light source with a theoretical thermally radiating blackbody. The Kelvin temperature at which the thermal radiating blackbody matches the color of the light source is the color temperature of that source.

Blackbody radiation theory: A blackbody is an idealized object that can absorb all radiation energy falling on it without loss and can radiate energy in the form of electromagnetic waves. Planck’s law describes the theoretical distribution of wavelengths in blackbody radiation, that is, as the temperature changes, the color of light will also change.

Color temperature changes during the heating process of steel: During the heating process of iron, the black iron gradually turns red. This is because as the temperature rises, the blackbody can emit all visible light waves in the spectrum, leading to color change. This process is an example of blackbody theory, illustrating the relationship between color temperature and temperature changes during the heating process of an object.

In practical applications, how do we select the appropriate steel material based on color temperature?

In practical applications, the selection of suitable steel materials based on color temperature requires the consideration of multiple factors. For instance, in the design of streetlights, choosing steel materials with an appropriate color temperature can enhance the effectiveness of road illumination, making the roads safer and easier to navigate. If the steel used in the streetlights has a high color temperature (cool tones), it might provide a clearer field of vision, but at the same time, it could reduce the warmth of the nighttime environment. On the contrary, steel with a low color temperature (warm tones) might increase the warmth of the environment, but it could affect visibility.

Furthermore, the choice of thermoforming temperature is crucial to ensure the quality of the formed parts. Different steel materials have different temperature-mechanical property curves, meaning that the physical state of the steel changes during the heating process, affecting its final shape and quality. Therefore, when choosing steel materials, it’s also necessary to consider the heat treatment requirements during its processing to ensure the material can meet specific application demands without sacrificing performance.

When selecting suitable steel materials based on color temperature, it’s important to consider the visual effects of the material, its physical and chemical properties, and the heat treatment requirements during its processing. By carefully evaluating these factors, one can choose the steel material that best suits the specific application requirements.

What are some specific examples of the impact of steel color temperature on product performance?

The impact of steel color temperature on product performance is mainly reflected in the following aspects:

1. Heat treatment process of mold steel:

The color of mold steel does not change at low temperatures, but when heated to about 600℃ and above, a slight dark red color appears. As the temperature rises, the color of the mold steel gradually changes. This shows that the color temperature change of the steel is related to the performance change during the heat treatment process, and the color change indirectly reflects the changes in the internal structure and performance of the material.

2. Changes in the strength and plasticity of steel:

An increase in temperature leads to a reduction in the strength of steel, and an increase in deformation. Especially near 250℃, the tensile strength of steel increases, but plasticity and toughness decrease, while a blue brittleness phenomenon occurs, that is, the oxide film turns blue. This phenomenon shows that the color temperature change of steel at a specific temperature (such as the color change of the oxide film) is closely related to its mechanical performance changes, especially the changes in tensile strength, plasticity, and toughness.

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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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