Ferritic Stainless Steel Flange Welding with Niobium
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Solution Overview
Problem
Heat exchangers for recirculated exhaust gases face issues with nitrogen in ferritic stainless steel reacting with boron in solder materials, leading to the formation of boron nitrides that hinder furnace welding, resulting in inadequate welds and increased costs due to the need for nickel-containing materials.
Innovation Solution
Incorporating niobium into the ferritic stainless steel flanges to form niobium nitrides, which react with the nitrogen, preventing it from reacting with boron in the solder material, thus avoiding the formation of boron nitrides and ensuring a stable weld during furnace welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ferritic stainless steel is used for flanges to reduce cost, then material cost is reduced, but nitrogen in the steel reacts with boron in solder material to form boron nitrides that hinder furnace welding
Solution Approach 1:
The patent converts the harmful reaction between nitrogen and boron into a beneficial process by adding niobium that preferentially reacts with nitrogen to form niobium nitrides. This removes the harmful nitrogen from the system, preventing boron nitride formation and enabling successful furnace welding while maintaining cost-effective ferritic stainless steel flanges.
Solution Approach 2:
Niobium acts as an intermediary element that mediates between nitrogen and boron. The niobium preferentially reacts with nitrogen to form stable niobium nitrides, preventing nitrogen from reacting with boron in the solder material. This intermediary reaction enables the welding process to proceed successfully.
2Reliability
If nickel-containing austenitic stainless steel is used for flanges, then welding performance is improved, but material cost increases significantly
Solution Approach 1:
The patent changes the chemical composition parameters of the ferritic stainless steel by adding niobium (0.01-1.0% by weight). This compositional modification fundamentally changes the material's behavior during welding, enabling furnace welding performance comparable to nickel-containing steels while maintaining the cost advantages of nickel-free ferritic steel.
Solution Approach 2:
The patent creates a composite material system by combining ferritic stainless steel with niobium addition. This composite composition leverages the cost advantages of ferritic steel while incorporating niobium's beneficial effects on high-temperature strength and weldability, achieving a balance between cost and performance.
3Reliability
If mechanical connection or arc welding is used for ferritic flanges, then furnace welding issues are avoided, but assembly complexity and manufacturing cost increase
Solution Approach 1:
By changing the chemical composition of the ferritic stainless steel to include niobium, the material's weldability parameters are improved. This enables the use of furnace welding (a simpler, more reliable process) instead of more complex mechanical connections or arc welding procedures, reducing assembly complexity while maintaining joint reliability.
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
This solution provides improved resistance to oxidation and corrosion, allows direct furnace welding of ferritic stainless steel flanges to austenitic stainless steel components, maintains the use of standard soldering processes, and reduces material costs by using less noble materials, ensuring reliable and cost-effective heat exchanger assembly.
Implementation Method 1
the ferritic stainless steel of the flange comprises a percentage of niobium capable of reacting with the nitrogen contained in the ferritic stainless steel itself so as to form niobium nitrides
Implementation Method 2
said flange being secured to said heat exchange bundle by furnace welding, and said weld furnace using a solder material composed of an alloy comprising boron
Implementation Method 3
a heat exchange bundle made from stainless steel, intended for the circulation of gases with exchange of heat with a refrigerant fluid
Data Source
Figure 1
AI summary
The invention relates to a heat exchanger (1), in particular for recirculated engine exhaust gases, including a heat exchange bank (2) made of stainless steel, intended for circulating gases with heat exchange, with a coolant and at least one flange (3) to be coupled to the gas recirculation line made of ferritic stainless steel, said flange (3) being secured to said heat exchange bank (2) by oven welding, said oven welding process using a welding material (4) consisting of an alloy including boron. According to the invention, the ferritic stainless steel of the flange (3) also includes a percentage of niobium capable of reacting with the nitrogen contained in the actual ferritic stainless steel so as to form niobium nitrides.