Duplex stainless steel material
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Solution Overview
Problem
Existing duplex stainless steel materials do not adequately balance high strength and excellent low-temperature toughness, particularly for deep wells below sea level, necessitating a novel approach beyond previous techniques.
Innovation Solution
A duplex stainless steel material with a specific chemical composition and microstructure, comprising 35-55% ferrite, 40-55% primary austenite, and 5-20% secondary austenite, along with controlled amounts of elements like C, Si, Mn, Cr, Mo, and Ni, to achieve a yield strength of 80 ksi (552 MPa) and excellent low-temperature toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of chromium (Cr) is increased to enhance corrosion resistance, then corrosion resistance is improved, but strength and low-temperature toughness deteriorate
Solution Approach 1:
The patent applies composite material principles by creating a duplex microstructure consisting of both ferrite and austenite phases. The ferrite phase provides corrosion resistance through chromium oxide passive film formation, while the austenite phase contributes to high strength and low-temperature toughness. This composite microstructure allows the material to simultaneously achieve excellent corrosion resistance (ferrite: 60-90% area fraction) and high mechanical strength (yield strength: 80 ksi or more) without sacrificing either property.
2Strength
If high strength is achieved through conventional methods, then strength is improved, but low-temperature toughness deteriorates
Solution Approach 1:
The patent applies local quality by creating different phases with distinct properties within the same material. The ferrite phase is optimized for corrosion resistance with high chromium content (20-30%), while the austenite phase is optimized for mechanical strength and toughness. The controlled distribution of these phases (ferrite: 60-90%, austenite: 10-40%) allows each phase to contribute its specific properties to the overall material performance, achieving both high yield strength (80 ksi or more) and excellent low-temperature toughness.
3Reliability
If ferrite content is increased to improve corrosion resistance, then corrosion resistance is improved, but low-temperature toughness deteriorates
Solution Approach 1:
The patent resolves this contradiction by creating a composite microstructure where ferrite (60-90% area fraction) provides corrosion resistance through chromium oxide passive film formation, while the accompanying austenite phase (10-40% area fraction) provides high strength and low-temperature toughness. The synergistic combination of these two phases allows the material to achieve excellent corrosion resistance while maintaining high mechanical properties at low temperatures.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the chemical composition parameters (Cr: 20-30%, Ni: 4-9%, Mn: 0.5-7%, Mo: 0.5-2%, N: 0.1-0.35%) and microstructural parameters (ferrite area fraction: 60-90%, austenite area fraction: 10-40%) to optimize the balance between corrosion resistance and low-temperature toughness. This parameter optimization enables the material to achieve both excellent corrosion resistance and high mechanical strength simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed material achieves both high yield strength and excellent low-temperature toughness, enhancing its performance in corrosive and low-temperature environments.
Implementation Method 1
increases the content of chromium (Cr) and forms a passive film mainly composed of Cr oxides on the surface of the steel material
Implementation Method 2
a duplex stainless steel material which contains ferrite in an amount of 60 to 90% in area fraction
Data Source
AI summary
A duplex stainless steel material that has high strength and excellent low-temperature toughness is provided. A duplex stainless steel material according to the present disclosure consists of, by mass %, C: 0.030% or less, Si: 0.20 to 1.00%, Mn: 0.50 to 7.00%, P: 0.040% or less, S: 0.0200% or less, Al: 0.100% or less, Ni: 4.20 to 9.00%, Cr: 20.00 to 30.00%, Mo: 0.50 to 2.00%, Cu: 0.50 to 3.00%, N: 0.150 to 0.350%, and V: 0.01 to 1.50%, with the balance being Fe and impurities. The duplex stainless steel material has a yield strength of 552 MPa or more, and when an austenite grain with a minor axis of 20 μm or more is defined as primary austenite and the balance of austenite is defined as secondary austenite, the microstructure is composed of, in volume ratio, ferrite in an amount of 35 to 55%, primary austenite in an amount of 40 to 55%, and secondary austenite in an amount of 5 to 20%.