Application reason analysis of low temperature steel
The importance of low-temperature technology is becoming increasingly important. In recent years, China's low-temperature technology has made great progress, and high-tech enterprises such as Zhongke Fuhai have emerged, filling multiple gaps in China's low-temperature technology space. It can be used in aerospace, energy, high-end extreme testing environments, and special equipment construction to ensure the safety and economy of national defense and people's livelihood. He has also led a group of small-scale low-temperature technology penetration and application in various industries, breaking the inherent technological bottleneck for thousands of years.
1. The core application motivation of low-temperature steel
In extremely cold environments (-40 ℃ to -269 ℃), ordinary steel undergoes a sharp drop in toughness due to low-temperature brittle transformation. However, low-temperature steel has achieved the following key breakthroughs through material design and process optimization:
1.1. Breaking through the bottleneck of material brittleness
By adding alloying elements such as nickel (Ni), manganese (Mn), molybdenum (Mo), etc., the austenite or ferrite structure is stabilized, and grain boundary slip and dislocation pinning effects are suppressed. For example, the nickel content of 9% Ni steel maintains the austenite phase at -196 ℃ and has an impact toughness of over 200J.
1.2. Meet the requirements of extreme working conditions
Scenarios such as liquefied natural gas (LNG) storage tanks (-162 ℃), Arctic oil and gas platforms (-50 ℃), and aerospace fuel pipelines (-253 ℃) require materials with high strength and resistance to brittle fracture. Low temperature steel enhances strength and toughness synergistically through phase transformation induced plasticity (TRIP effect) and twinning induced plasticity (TWIP effect).
1.3. Balance between economy and safety
Compared to traditional stainless steel, low-temperature steel reduces costs through nickel saving designs (such as Fe Mn Al steel) while maintaining performance at -196 ℃, promoting large-scale applications in deep-sea equipment, superconducting magnets, and other fields.
2. Typical low-temperature steel grades and performance analysis
The following are representative steel grades and their mechanical properties in different temperature ranges:
Performance analysis:
| Steel classification | Grade example | Key alloying element | Mechanical properties (room temperature) | Low temperature performance (impact toughness) | Typical application scenario |
| Ferritic low temperature steel | 09Mn2V | Mn 2.0%, V 0.1% | σs=390MPa | -70℃时Akv≥27J | liquefied petroleum gas storage tank（-60℃） |
| low alloy steel | 06AlNbCuN | Al 0.02%, Nb 0.05% | σs=450MPa | -110℃时Akv≥40J | Ethylene low temperature separation device（-100℃） |
| medium alloy steel | 9%Ni钢 | Ni 9.0% | σs=690MPa | -196℃时Akv≥150J | LNG carrier storage tank（-162℃） |
| austenitic nonmagnetic steel | 0Cr21Ni6Mn9N | Cr 21%, Ni 6% | σs=550MPa | -269℃时Akv≥80J | Nuclear magnetic resonance equipment（Non-magnetic requirement） |
| Ultra-low temperature steel | 15Mn26Al4 | Mn 26%, Al 4% | σs=420MPa | -253℃时Akv≥50J | Liquid hydrogen storage tank（-253℃） |
9% Ni steel
Through nickel element solid solution strengthening and grain boundary stabilization, the face centered cubic structure is maintained at -196 ℃, with a fracture toughness of over 150J, widely used in the LNG industry chain.
Fe Mn Al steel
Replacing some nickel with manganese and refining the grain with aluminum reduces the cost by 40% compared to traditional nickel steel, but the corrosion resistance problem needs to be solved through surface coating.
austenitic stainless steel
18-8 steel (such as 304) forms stable austenite due to chromium nickel solid solution, and maintains an impact toughness of over 100J at -150 ℃, making it suitable for low-temperature chemical equipment.
3. Technical logic for selecting low-temperature steel
3.1. Thermodynamic stability
The CCT curve of austenitic steel is shifted to the right to avoid brittle fracture caused by low-temperature martensitic transformation. For example, 9% Ni steel maintains the austenite phase during rapid cooling without the precipitation of brittle phases.
3.2. Fracture toughness design
By controlling the grain size (ASTM grade 7 or above) and inclusion content (≤ grade 1.5), the resistance to crack initiation can be improved. ASTM A333 Gr.6 steel pipes require an impact energy of ≥ 20J at -45 ℃.
3.3. Process adaptability
Adopting narrow window heat treatment (such as normalizing+tempering) to ensure the uniformity of microstructure. For example, 09Mn2V steel needs to be normalized at 900 ℃ and tempered at 650 ℃ to refine the bainite structure.
4. Challenges and cutting-edge directions
Multi field coupling effect
The mechanism of corrosion fatigue coupling damage in extremely cold environments is not fully understood, and an environment sensitive fracture model needs to be developed.
Low cost alternative materials
Nano precipitation strengthened steel (such as Cu Ti system) achieves a 50% increase in strength while maintaining toughness at -100 ℃, with a cost reduction of 25% compared to traditional steel.
Intelligent monitoring technology
Embedded fiber optic sensors for real-time monitoring of strain distribution in low-temperature steel components to prevent brittle fracture.
Low temperature steel has broken through the low-temperature brittleness limitations of traditional steel through alloy design and process innovation, becoming a core material in fields such as deep space exploration and polar energy development. In the future, with the expansion of ultra-low temperature service scenarios (such as the construction of lunar polar bases), low-temperature steel will evolve towards high toughness integration and environmental adaptability, promoting human exploration and development of extreme environments.
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