Duplex Stainless Steel Composition for Stronger Non-Filler Welds
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Solution Overview
Problem
Existing duplex stainless steel materials face a decrease in weld metal strength during non-filler welding, which is not adequately addressed by existing technologies, leading to reduced pressure resistance in applications like seawater heat exchangers.
Innovation Solution
A duplex stainless steel material with specific chemical compositions and inclusion of elements like Ca, Ti, and Co, which form CaS and Ti nitrides to refine grain size and enhance work hardening, ensuring the weld metal strength equals or exceeds that of the base material portion without using nitrogen in the shielding gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If non-filler welding is performed without adding nitrogen to the shielding gas, then production costs decrease and construction time is reduced, but weld metal strength decreases
Solution Approach 1:
The patent changes the chemical composition parameters of the base material by controlling the content of Al, B, Ca, Ti, Co, and other elements to achieve sufficient weld metal strength without adding nitrogen to the shielding gas. This resolves the contradiction by modifying material parameters rather than changing welding process parameters.
Solution Approach 2:
The patent eliminates the need for expensive nitrogen-added shielding gas by using a cost-effective base material composition that inherently provides sufficient strength. This replaces the expensive consumable (nitrogen-enriched gas) with a cheaper, built-in material solution.
2Device complexity
If non-filler welding is performed without using a welding consumable, then device complexity is reduced, but weld metal strength decreases
Solution Approach 1:
The base material itself provides the necessary strength through its specially controlled composition, eliminating the need for external welding consumables. The material serves its own strengthening function through its inherent alloying elements (Al, B, Ca, Ti, Co, etc.), making the system self-sufficient.
3Strength
If nitrogen is added to the Ar shielding gas to increase weld metal strength, then weld metal strength increases, but gas purification cost increases and electrode life shortens
Solution Approach 1:
The patent replaces the expensive nitrogen-enriched shielding gas with a standard shielding gas by incorporating strengthening elements directly into the base material composition. This eliminates the need for costly gas purification and extends electrode life while maintaining weld metal strength.
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 chemical composition and inclusion mechanisms synergistically enhance weld metal strength, maintaining or exceeding base material strength during non-filler welding, thus improving pressure resistance and reducing production costs and construction time.
Implementation Method 1
CaS and Ti nitrides that refine grain size are formed
Implementation Method 2
enhance work hardening
Implementation Method 3
Ti nitrides that refine grain size are formed
Data Source
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AI summary
Provided is a duplex stainless steel material in which the strength of the weld metal produced by non-filler welding using a shielding gas not containing nitrogen is greater than or equal to that of the base material portion. The duplex stainless steel material of this disclosure contains, in mass%: C: 0.001 to 0.030%, Si: 1.00% or less, Mn: 0.05 to 5.00%, P: 0.035% or less, S: 0.0008% or less, Cr: 21.00 to 28.00%, Ni: 4.00 to 9.50%, Mo: 0.80 to 5.50%, Cu: 0.01 to 3.50%, Al: 0.001 to 0.050%, N: 0.400% or less, B: 0.0001 to 0.0050%, Mg: 0.0050% or less, Ca: 0.0005 to 0.0100%, Ti: 0.002 to 0.100%, and Co: 0.05 to 2.00%, and formula (1) and formula (2) below are satisfied. Ca/S≥2.00 1000×Ti+2×N×Co0.2×0.5×Ca/S1.6≥50.00