Super Duplex Seamless Pipe Composition for Deep-Sea Pitting Resistance
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Solution Overview
Problem
The existing technologies for manufacturing S32750 austenitic ferrite super duplex stainless steel seamless pipes for deep-sea manifolds face challenges in achieving high purity, good surface quality, strength, toughness, and excellent pitting corrosion resistance, while adapting to harsh underwater environments.
Innovation Solution
A method involving optimized metal components, two-phase ratio, and PREN balance, combined with high-purity smelting, controlled forging and hot piercing processes, and precise cold working to produce pipes with 40-60% ferrite content and 41≤PREN<45, ensuring no harmful precipitated phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional smelting and processing methods are used, then production cost and process simplicity are maintained, but the steel pipe cannot achieve high purity, excellent pitting corrosion resistance, and the required mechanical properties for deep-sea manifolds
Solution Approach 1:
The patent applies parameter changes by precisely controlling chemical composition parameters (Cr: 24-26%, Mo: 3-5%, Ni: 6-8%, N: 0.24-0.32%, Al: 0.012-0.018%) and processing parameters (smelting temperature, forging temperature 1050-1200°C, cooling rate) to achieve the required pitting corrosion resistance (PREN≥41) and mechanical properties while managing manufacturing complexity
Solution Approach 2:
The patent implements preliminary action through optimized smelting processes that pre-establish the correct phase composition (40-60% ferrite) and purity levels during initial manufacturing, preventing harmful precipitated phases from forming later and ensuring the steel pipe meets deep-sea manifold requirements from the outset
2Reliability
If high alloy content is increased to improve pitting corrosion resistance, then PREN value increases, but manufacturing cost and material complexity increase
Solution Approach 1:
The patent optimizes alloy content parameters by establishing specific ranges (Cr: 24-26%, Mo: 3-5%, Ni: 6-8%, N: 0.24-0.32%) that achieve the minimum PREN≥41 requirement without excessive alloying, balancing corrosion resistance with manufacturing cost and material complexity
Solution Approach 2:
The patent creates a composite microstructure consisting of 40-60% ferrite phase combined with optimized alloy elements, where the synergistic interaction between phases provides excellent pitting corrosion resistance (PREN≥41) without requiring excessive total alloy content
3Strength
If high strength is achieved through increased alloying and processing, then tensile strength and yield strength improve, but toughness and ductility may deteriorate
Solution Approach 1:
The patent controls phase composition parameters (40-60% ferrite) and chemical composition (Cr, Mo, Ni, N, Al contents) to achieve the optimal balance where tensile strength≥800 MPa and yield strength≥550 MPa are obtained while maintaining elongation≥25% and impact energy≥60 J through the stable two-phase microstructure
Solution Approach 2:
The patent employs a composite two-phase microstructure (40-60% ferrite + austenite) where the interaction between phases provides both high strength (tensile≥800 MPa, yield≥550 MPa) and good toughness (impact energy≥60 J at -46°C), preventing the deterioration of mechanical properties
4Reliability
If ferrite content is increased to improve corrosion resistance and phase stability, then pitting resistance and phase balance improve, but processing difficulty and formation rate of harmful phases increase
Solution Approach 1:
The patent controls the ferrite content parameter within the optimal range of 40-60% and adjusts chemical composition parameters (Cr, Mo, Ni, N, Al) to achieve phase stability (PREN≥41) while managing processing difficulty and preventing the formation of harmful precipitated phases during manufacturing
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 pipes exhibit tensile strength ≥800 MPa, yield strength ≥550 MPa, elongation ≥25%, impact energy ≥60 J at -46°C, and no pitting corrosion under 50°C for 24 hours, with improved mechanical properties and corrosion resistance.
Implementation Method 1
The ferrite content of the S32750 austenitic ferrite super duplex stainless steel seamless pipe for a deep sea manifold is 40-60%
Implementation Method 2
performing Al powder enhanced deoxidization in smelting in an argon oxygen decarburization (AOD) furnace to control the Al content to 0.012-0.018%, and reduce the oxygen content to 11-25 ppm
Implementation Method 3
introducing relatively weak argon in refining outside a ladle furnace (LF), and performing stirring to remove small-size inclusions by bubbles
Implementation Method 4
manufacturing a steel pipe mainly by cold rolling supplemented with cold drawing by using a cold rolling mill for controlling deformation, implementing solution heat treatment, and controlling a temperature and a time to manufacture a steel pipe with the same grain size as a finished product
Data Source
AI summary
Disclosed in the present disclosure is an S32750 austenitic ferrite super duplex stainless steel seamless pipe for a deep sea manifold and a method for preparing the same. The stainless steel seamless pipe includes the following components in percentage by mass: less than or equal to 0.03% of C, less than or equal to 0.80% of Si, less than or equal to 1.20% of Mn, less than or equal to 0.035% of P, less than or equal to 0.01% of S, 24.0-26.0% of Cr, 6.0-8.0% of Ni, 3.0-5.0% of Mo, less than or equal to 0.50% of Cu, 0.24-0.32% of N, 0.012-0.018% of Al, and the balance of Fe and impurities. The ferrite content of the stainless steel seamless pipe is 40-60%, and 41≤PREN<45. The stainless steel seamless pipe is prepared by metal collaborative design, smelting, pouring, forging, hot piercing and cold working.