Duplex Stainless Seamless Pipe Microstructure for Low-Temperature Toughness
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Solution Overview
Problem
There is a growing demand for duplex stainless seamless steel pipes with enhanced low-temperature toughness to withstand harsher oil well environments, and existing technologies do not adequately address this need.
Innovation Solution
A duplex stainless seamless steel pipe with a specific chemical composition and microstructure, including 30.0 to 70.0% ferrite and austenite volume ratio, and a layered distribution of ferrite and austenite phases, along with a defined number of intersections between these phases, is produced through controlled heating and rolling processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chromium content is increased to improve corrosion resistance, then corrosion resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chromium content within a specific range (20-30%) rather than simply increasing it indefinitely. This optimized parameter range achieves the necessary corrosion resistance for oil well environments while avoiding excessive manufacturing complexity. The solution also involves adjusting other compositional parameters (Ni: 3-12%, Mo: 0.2-5.0%, Al: 0.01-0.05%) in coordination to achieve the desired balance between corrosion resistance and manufacturability.
2Reliability
If duplex stainless steel composition is optimized for corrosion resistance, then corrosion resistance is improved, but low-temperature toughness deteriorates
Solution Approach 1:
The patent resolves this contradiction through comprehensive parameter optimization, specifying precise ranges for multiple alloying elements: Cr (20-30%), Ni (3-12%), Mo (0.2-5.0%), Al (0.01-0.05%), along with controlled impurity levels (O: <0.0020%, S: ≤0.0003%). This multi-parameter optimization achieves a balance where the steel exhibits both excellent corrosion resistance in seawater and improved low-temperature toughness, overcoming the traditional trade-off between these two properties.
Solution Approach 2:
The patent utilizes the composite nature of duplex stainless steel, which contains two phases (ferrite and austenite), to simultaneously achieve corrosion resistance and low-temperature toughness. The specific compositional ranges are designed to optimize the dual-phase microstructure, where the ferrite phase provides corrosion resistance while the austenite phase contributes to low-temperature ductility and toughness.
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 steel pipe achieves excellent low-temperature toughness, ensuring effective performance in extreme conditions.
Implementation Method 1
a heating step for heating the starting material after the starting material preparation step at a heating temperature TA° C. of 1000 to 1280° C.
Implementation Method 2
a solution heat treatment step for holding the hollow shell after the elongating-rolling step at 950 to 1080° C. for 5 to 180 minutes
Data Source
AI summary
The duplex stainless seamless steel pipe according to the present disclosure has the chemical composition described in the description and a microstructure composed of 30.0 to 70.0% of ferrite, and austenite. In an observation field of view region of a square shape with a side of 1.0 mm, the region including a center portion of wall thickness and including an L direction and a T direction. A number of intersections NT, which is the number of intersections between the line segments T1 to T4 which is four line segments extending in the T direction and a ferrite interface, is 40.0 or more. A number of intersections NL, which is the number of intersections between the line segments L1 to L4 which is four line segments extending in the L direction and the ferrite interface, and the number of intersections NT satisfy Formula (1).NT/NL≥2.0 (1)