Cr-Ni Alloy Dislocation Density Control for Geothermal Corrosion
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Solution Overview
Problem
Conventional Cr-Ni alloys fail to achieve high yield strength and resistance to sulfuric acid general corrosion at high temperatures, particularly in harsh geothermal environments with high sulfuric acid concentrations.
Innovation Solution
A Cr-Ni alloy with a specific chemical composition and dislocation density range, including Si, Mn, Cr, Ni, Mo, W, Cu, Co, and controlled impurities, that satisfies the formula 8.00 × 10^14 ≤ ρ ≤ 2.50 × 10^15 + 1.40 × 10^14 × (Cu + Co), where ρ is the dislocation density, enhancing both yield strength and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional Cr-Ni alloys are used for deep geothermal wells, then the alloy structure provides basic mechanical properties, but the yield strength is insufficient to withstand high earth pressure and corrosion resistance against sulfuric acid at 250°C is inadequate
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (Cr: 20-30%, Ni: 40-50%, Mo: 4-10%, Cu: 2-6%, Co: 0.01-2%, W: 2-6%) and the dislocation density parameter (8.00×10^14 ≤ ρ ≤ 2.50×10^15 + 1.40×10^14×(Cu+Co)) to simultaneously achieve high yield strength and corrosion resistance. This quantitative parameter optimization resolves the contradiction between mechanical strength and corrosion reliability
Solution Approach 2:
The patent creates a composite alloy system by combining multiple alloying elements (Cr, Ni, Mo, Cu, Co, W) in specific proportions, forming a complex multi-element alloy that exhibits synergistic effects. This composite material approach enables the alloy to possess both high strength and excellent corrosion resistance in the harsh geothermal environment
2Reliability
If alloy composition is optimized for sulfuric acid corrosion resistance, then corrosion protection improves, but yield strength decreases and cannot withstand deep well pressure
Solution Approach 1:
The patent resolves this contradiction through parameter changes by establishing a multi-dimensional parameter space that includes chemical composition (Cr: 20-30%, Ni: 40-50%, Mo: 4-10%, Cu: 2-6%, Co: 0.01-2%, W: 2-6%) and microstructural parameters (dislocation density: 8.00×10^14 ≤ ρ ≤ 2.50×10^15 + 1.40×10^14×(Cu+Co)). By optimizing all parameters simultaneously rather than prioritizing one, the patent achieves both high corrosion resistance and high yield strength
Solution Approach 2:
The patent applies dynamics by controlling the dislocation density, which is a dynamic microstructural parameter that can be adjusted through processing conditions. The dislocation density formula ρ ≤ 2.50×10^15 + 1.40×10^14×(Cu+Co) dynamically relates the microstructure to the chemical composition, enabling the material to adapt its mechanical properties while maintaining corrosion resistance
3Reliability
If Ni-base alloy with high Mo content (such as Hastelloy C22 and C276) is used, then corrosion resistance is excellent, but cost increases significantly and machinability deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the Mo content to a moderate range (4-10%) rather than using high Mo content alloys, and by introducing additional alloying elements (Cu: 2-6%, Co: 0.01-2%, W: 2-6%) that provide synergistic corrosion resistance. This parameter optimization achieves corrosion resistance equivalent to high-Mo alloys while improving machinability and reducing cost
Solution Approach 2:
The patent replaces expensive high-Mo content alloys (Hastelloy C22, C276) with a more cost-effective alloy composition that uses moderate Mo content combined with other affordable alloying elements. This substitution achieves comparable corrosion resistance at lower material cost and with better manufacturability
Data Source
AI summary
A Cr-Ni alloy having high yield strength and high resistance to sulfuric acid general corrosion at a high temperature of 250°C is provided. The Cr-Ni alloy has a chemical composition consisting of, in mass%, Si: 0.01 to 0.50%, Mn: 0.01 to 1.00%, Cr: 21.0 to 27.0%, Ni: 40.0 to less than 50.0%, Mo: 4.5 to less than 9.0%, W: 2.0 to 6.0%, Cu: more than 2.0% and not more than 6.0%, Co: 0.01 to 2.00%, one or two kinds selected from the group consisting of Ca and Mg: 0.001 to 0.010% in total, sol. Al: 0.005 to 0.200%, N: 0.01 to 0.20%, and the balance being Fe and impurities. The dislocation density in the Cr-Ni alloy satisfies the following Formula (1): 8.00×1014≤ρ≤2.50×1015+1.40×1014×Cu+Co