Duplex Stainless Steel Low-Temperature Toughness via Ni Distribution Control
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Solution Overview
Problem
Duplex stainless steel used in line pipes for transporting oil and natural gas lacks sufficient low-temperature toughness, and existing materials do not adequately evaluate or ensure toughness in sub-zero temperatures, compromising their performance in corrosive acid chloride environments.
Innovation Solution
A duplex stainless steel with a specific chemical composition and microstructure, including a balanced austenite and ferrite phase ratio, and a controlled Ni distribution, is manufactured using a solution treatment process at 960 to 1045°C to enhance low-temperature toughness and prevent precipitation phase formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the amount of austenite phase is increased to improve toughness, then low-temperature toughness is improved, but the phase balance is compromised and corrosion resistance may deteriorate
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (Ni: 3-7%, Cu: 2.0-4.0%, Cr: 20-28%, Mo: 0.5-2.0%, Co: 0.02-0.5%) and microstructure parameters (austenite phase ratio, ferrite phase ratio) to achieve optimal low-temperature toughness while maintaining phase balance. The solution treatment temperature parameter (960-1045°C) is also controlled to prevent σ-phase precipitation and maintain the desired phase distribution.
Solution Approach 2:
The patent utilizes composite materials by creating a duplex stainless steel with a controlled two-phase microstructure (austenite + ferrite) where each phase contributes different properties. The austenite phase provides toughness while the ferrite phase provides strength and corrosion resistance, and their balanced combination achieves both low-temperature toughness and phase stability.
2Reliability
If alloy element contents are increased to improve corrosion resistance, then corrosion resistance is improved, but phase balance becomes difficult to maintain
Solution Approach 1:
The patent applies parameter changes by establishing specific composition ranges for alloying elements (Ni: 3-7%, Cr: 20-28%, Mo: 0.5-2.0%, Cu: 2.0-4.0%, Co: 0.02-0.5%) that simultaneously achieve high corrosion resistance and maintain proper phase balance. These parameter ranges are optimized to prevent excessive austenite formation while ensuring adequate corrosion protection.
Solution Approach 2:
The patent applies local quality by distributing alloying elements preferentially to different phases during solidification and heat treatment. Chromium and molybdenum are concentrated in the ferrite phase to enhance its corrosion resistance, while nickel and copper are distributed to control austenite formation, creating locally optimized properties in each phase.
3Stability of the object's composition
If solution treatment temperature is increased to prevent σ-phase precipitation, then σ-phase precipitation is reduced, but energy consumption increases and distortion risk increases
Solution Approach 1:
The patent applies parameter changes by optimizing the solution treatment temperature to a specific range (960-1045°C) that is sufficient to prevent σ-phase precipitation and maintain phase balance, but not excessively high to cause unnecessary energy consumption or distortion. This optimized temperature parameter achieves the desired microstructure with minimal energy input.
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 resulting duplex stainless steel exhibits improved low-temperature toughness and resistance to embrittlement, ensuring effective performance in corrosive environments and maintaining phase balance without compromising corrosion resistance.
Implementation Method 1
subjecting the hot-worked material to solution treatment at a temperature of 960 to 1045° C.
Data Source
AI summary
A duplex stainless steel with good low-temperature toughness is provided. The duplex stainless steel has a chemical composition of, in mass %: up to 0.03% C; 0.1 to 0.8% Si; up to 2.3% Mn; up to 0.040% P; up to 0.010% S; up to 0.040% sol. Al; 3 to 7% Ni; 20 to 28% Cr; 0.5 to 2.0% Mo; more than 2.0% and not more than 4.0% Cu; 0.02 to 0.5% Co; 0.1 to 0.35% N; up to 0.010% O; and other elements, the steel having a microstructure including an austenite phase and a ferrite phase, the ferrite phase having an area percentage of 30 to 60%, the steel satisfying the following Formula, (1);0.70×NiL≤NiH (1),where NiH and NiL are obtained by using an electron-beam microanalyzer to measure Ni content and, in a distribution of Ni content, determining two maximum frequencies, and treating the one with a higher Ni content as NiH and treating the one with a lower Ni content as NiL.