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12Cr1MoV alloy steel pipe offers better oxidation resistance and thermal strength compared to 12CrMoV steel. This material is widely used in high-pressure, ultra-high-pressure, and subcritical power plant boilers for superheaters, headers, and main steam pipelines. At temperatures up to 580°C, it maintains high thermal strength and oxidation resistance, along with excellent permanent plasticity.
One of the key features of 12Cr1MoV is its close relationship between creep limit and permanent strength, making it highly ductile under sustained loads. It also has good formability and weldability, though preheating to 300°C before welding is recommended, followed by stress relief after welding.
The production process is relatively straightforward, and the steel exhibits good welding performance. However, it is sensitive to the normalizing cooling rate. Prolonged exposure at 580°C may lead to pearlite spheroidization, which can affect long-term performance. A major advantage of this steel is that it can be recycled 100%, aligning with national environmental protection and resource conservation strategies. Domestic policies are encouraging the expansion of its application in various industries.
Currently, the consumption of 12Cr1MoV alloy steel pipes in China is only about half of that in developed countries. Expanding its usage fields provides significant growth opportunities for the industry. According to research from the China Special Steel Association, the demand for high-pressure 12Cr1MoV alloy steel pipes is expected to grow by an average of 10–12% in the coming years.
There are two main manufacturing processes: hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes. Cold-drawn tubes can be either round or special-shaped. The hot-rolling process includes steps such as heating, piercing, rolling, sizing, cooling, straightening, testing, and marking. Meanwhile, the cold-drawing process involves heating, piercing, heading, annealing, pickling, oiling, multiple passes of cold drawing, heat treatment, and final inspection.
Microstructure strengthening plays a vital role in determining the properties of 12Cr1MoV alloy steel pipes. The parent phase must be present for effective microstructure strengthening. The process includes both deformation and diffusion mechanisms, depending on the cooling environment. In low-temperature conditions, non-diffusion dominates, while in high-temperature settings, diffusion becomes more important.
Two key factors influence microstructure strengthening: strain and cooling environment. Temperature changes affect the structure and energy state of the steel. Additionally, the presence of fine precipitates within the alloy influences its overall properties. Therefore, careful attention must be given to the microstructure when adjusting the performance of the steel.
Hardenability of 12Cr1MoV alloy steel is primarily determined by the critical cooling rate, which is influenced by the stability of the supercooled austenite. Several factors impact this stability:
1. **Chemical Composition**: Carbon content significantly affects hardenability. When carbon content is below 1.2%, increasing carbon improves hardenability by shifting the C curve to the right. However, above 1.2%, the opposite occurs. Most alloying elements, except cobalt, enhance hardenability by shifting the C curve to the right.
2. **Austenite Grain Size**: Larger grain sizes increase hardenability but may also raise the risk of deformation and cracking, reducing toughness.
3. **Uniformity of Austenite**: A more uniform composition leads to slower transformation and improved hardenability.
4. **Original Structure**: The distribution and thickness of the original structure affect the final properties of the steel.
5. **Alloying Elements**: Elements like Mn and Si improve hardenability but may introduce other drawbacks.
Overall, 12Cr1MoV alloy steel is a versatile and valuable material in high-temperature applications, with strong potential for future development and broader use.