Understanding Steel Temperature Range: A Guide for Optimal Use

Steel, a versatile and widely used material in various industries, exhibits different properties and behaviors across different temperature ranges. Understanding these temperature-dependent characteristics is crucial for engineers, manufacturers, and designers to optimize steel’s performance in diverse applications. This comprehensive guide explores the key temperature ranges that affect steel’s properties and provides insights into how to leverage this knowledge for optimal use.

1. Room Temperature (20°C to 100°C)

At room temperature, steel displays its standard mechanical properties as specified in material data sheets. This range is ideal for most everyday applications, where steel’s strength, ductility, and toughness are well-balanced. However, it’s important to note that even within this range, slight temperature fluctuations can affect precision in high-accuracy applications.

Key considerations:

• Ideal for most structural and mechanical applications
• Provides a baseline for comparing property changes at other temperatures
• Suitable for standard fabrication and joining processes

2. Low Temperature Range (-50°C to 20°C)

As temperatures drop below room temperature, steel generally becomes stronger but less ductile. This phenomenon, known as low-temperature embrittlement, can significantly impact steel’s performance in cold environments.

Key considerations:

• Increased yield and tensile strength
• Reduced ductility and impact toughness
• Higher risk of brittle fracture, especially in high-stress areas
• Selection of appropriate steel grades (e.g., low-temperature steels) for cryogenic applications

Best practices:

• Conduct thorough material testing at intended service temperatures
• Implement more stringent safety factors in design calculations
• Consider using nickel-alloyed steels for enhanced low-temperature toughness

3. Moderate Heat Range (100°C to 450°C)

In this range, steel begins to experience noticeable changes in its mechanical properties. While strength may initially increase slightly due to strain aging, prolonged exposure can lead to tempering effects and a gradual decrease in yield strength.

Key considerations:

• Potential for blue brittleness (temper embrittlement) around 300°C
• Gradual decrease in yield strength and elastic modulus
• Increased importance of creep resistance for long-term applications

Best practices:

• Account for reduced yield strength in design calculations
• Consider using heat-resistant steel grades for prolonged exposure
• Implement appropriate heat treatment processes to optimize properties

4. High Temperature Range (450°C to 900°C)

At these elevated temperatures, steel undergoes significant microstructural changes, leading to substantial alterations in its mechanical properties. This range is critical for heat treatment processes but can be detrimental to steel’s strength in service conditions.

Key considerations:

• Dramatic decrease in yield and tensile strength
• Increased ductility and formability
• Accelerated oxidation and scaling
• Potential for phase transformations (e.g., austenite formation)

Best practices:

• Utilize high-temperature resistant steel grades (e.g., stainless steels)
• Implement protective coatings or controlled atmospheres to minimize oxidation
• Design for reduced load-bearing capacity at elevated temperatures
• Leverage increased formability for hot-forming processes

5. Extreme Heat Range (Above 900°C)

Temperatures above 900°C are typically encountered in steelmaking, heat treatment, and welding processes. At these extreme temperatures, steel becomes highly malleable and undergoes significant microstructural changes.

Key considerations:

• Steel becomes austenitic, highly ductile, and easily formable
• Rapid grain growth can occur, potentially weakening the material
• Risk of incipient melting at grain boundaries
• Crucial range for heat treatment processes (e.g., austenitizing, normalizing)

Best practices:

• Carefully control time and temperature to achieve desired microstructures
• Implement rapid cooling techniques when necessary to refine grain structure
• Use appropriate flux and shielding methods in welding to prevent oxidation
• Consider the effects of thermal cycling on the final properties of the steel

Steel usage temperature range

Note:

1. The usage restrictions for A3F steel plate are as follows:

(1) it shall not be used for pressurized components with extremely hazardous, highly hazardous or explosive media;

(2) the usage temperature is 0~250℃;

(3) design pressure ≤0.6MPa;

(4) vessel volume ≤10m3;

(5) for main pressurized components (shell, formed head), plate thickness ≤12mm; for flanges, flange covers, etc., plate thickness ≤16mm.

2. The usage restrictions for A3 steel plate are as follows:

(1) it shall not be used for pressurized components with extremely hazardous, highly hazardous or liquefied petroleum gas media;

(2) vessel volume ≤10m3;

(3) for main pressurized components (shell, formed head): usage temperature 0~350℃; design pressure ≤1.0MPa; plate thickness ≤16mm;

(4) for flanges, flange covers, tube sheets and similar pressurized components: usage temperature >-20~350℃; design pressure ≤4.0MPa; P×Di≤2000 (D is the nominal diameter in mm; P is the design pressure in MPa).

When the usage temperature is <0℃ (but >-20℃) and the plate thickness is ≥30mm, the room temperature impact toughness of the steel plate (longitudinal, V-shaped Charpy specimens, average value of three specimens per group) shall not be less than 27J.

3. The usage restrictions for 16Mn steel plate are as follows:

(1) steel plates without additional inspection or assurance of room temperature impact toughness requirements shall not be used for main pressurized components of pressure vessels;

(2) when used for flanges, flange covers, tube sheets and similar pressurized components, the usage restrictions are the same as those for A3 steel;

(3) after inspection or re-inspection, if the room temperature impact toughness is guaranteed (longitudinal, V-shaped Charpy specimens, average value of three specimens per group) not less than 27J, it can be used as the main pressurized component of pressure vessel, and the usage restrictions are as follows: a. design temperature 0~350℃; b. design pressure ≤2.5MPa; c. plate thickness ≤30mm.

4. There is currently no steel plate or steel pipe standard for 16Mo and INCOLOY 800, and there is no steel plate standard for 12CrMo, 15CrMo, 12Cr2Mo1, and 1Cr5Mo. The design can refer to the corresponding foreign steel standards.

5. When the long-term usage temperature of 16Mo exceeds 475℃, the influence of graphitization tendency should be considered. Therefore, pressurized components with cumulative usage time exceeding 4 years should be checked for graphitization.

6. The long-term usage temperature of ultra-low carbon austenitic stainless steel exceeding 425℃ will result in the precipitation of carbide chromium at grain boundaries, leading to the loss of intergranular corrosion resistance.

7. Ferritic stainless steel steel plates (excluding composite plates) with a nominal chromium content of ≥13% shall not be used as main pressurized components of pressure vessels with a design pressure ≥0.25MPa and wall thickness >6mm.

8. The minimum temperature indicated in the table is the applicable lower limit temperature value of this standard (> -20℃).

9. The “maximum oxidation temperature” in the table is only applicable to non-stressed components with low stress.

Source: HGJ15-89 Design Code for Steel Chemical Vessel Materials Selection of the Ministry of Chemical Industry of the People’s Republic of China.

Stainless heat-resistant steel usage temperature