Duplex Stainless Steel Tube Composition for Stable Internal Weld Beads
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Solution Overview
Problem
Duplex stainless steel tubes used in heat exchangers and fuel injectors face challenges in forming stable internal weld beads during welding, leading to potential corrosion and weld defects due to excessive heat input, which can result in incomplete melting and reduced toughness of the weld heat affected zone.
Innovation Solution
A duplex stainless steel tube with a specific chemical composition and surface roughness, including controlled levels of elements such as S, Sn, O, and Ca, to stabilize the formation of internal weld beads and enhance the toughness of the weld heat affected zone, ensuring a balanced phase structure and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If heat input in welding is reduced to prevent weld reinforcement sagging, then corrosion resistance is improved, but welding completeness deteriorates resulting in weld defects
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the duplex stainless steel, specifically limiting S to 0.0001-0.0050%, Sn to 0.0001-0.0100%, and O to 0.0004-0.0150%, while maintaining Cr at 21.5-25.5% and Ni at 2.50-5.50%. This compositional parameter control modifies the material properties to achieve both low heat input weldability and complete welding, resolving the contradiction between corrosion resistance and welding completeness
2Shape
If heat input in welding is reduced to prevent weld reinforcement sagging, then internal bead shape is improved, but toughness of weld heat affected zone deteriorates
Solution Approach 1:
The patent uses parameter changes by optimizing the chemical composition ranges, particularly Cr (21.5-25.5%), Ni (2.50-5.50%), and alloying elements like Mo (0.10-0.50%), Cu (0.10-2.50%), and N (0.050-0.200%). These parameter adjustments ensure the material maintains adequate toughness in the weld heat affected zone even when welding heat input is reduced for better internal bead shape control
3Reliability
If heat input in welding is increased to ensure complete melting, then welding completeness is improved, but weld reinforcement sagging worsens causing excessive height
Solution Approach 1:
The patent applies parameter changes by controlling the chemical composition to enable welding with reduced heat input. Specifically, the controlled ranges of S (0.0001-0.0050%), Sn (0.0001-0.0100%), and O (0.0004-0.0150%), combined with Cr (21.5-25.5%) and Ni (2.50-5.50%), allow the material to achieve complete welding at lower heat inputs, preventing weld reinforcement sagging while ensuring adequate melting
4Reliability
If heat input in welding is increased to ensure complete melting, then welding completeness is improved, but corrosion resistance worsens due to corrosive fluid accumulation
Solution Approach 1:
The patent resolves this contradiction through parameter changes in chemical composition, specifically limiting S to 0.0001-0.0050%, Sn to 0.0001-0.0100%, and O to 0.0004-0.0150%, while maintaining Cr at 21.5-25.5% and Ni at 2.50-5.50%. This enables welding with reduced heat input that ensures complete melting while preventing weld reinforcement sagging, thereby maintaining both welding completeness and corrosion resistance
Data Source
AI summary
There is provided a duplex stainless steel tube including a chemical composition consisting of, in mass %, C: 0.008 to 0.030%, Si: 0.10 to 0.70%, Mn: 0.80 to 2.60%, P: 0.030% or less, S: 0.0001 to 0.0050%, O: 0.0004 to 0.0150%, Sn: 0.0001% or more to less than 0.0100%, Cu: 0.10 to 2.50%, Ni: more than 2.50 to 5.50% or less, Cr: 21.5 to 25.5%, Mo: 0.10 to 0.50%, N: 0.050 to 0.200%, Al: 0.200% or less, and optional elements, with the balance: Fe and impurities, wherein 4S+8O+Sn is 0.0040 to 0.0900, and 4S+Sn is 0.0180 or less.