Gas Sensor Metal Shell Corrosion Resistance via Niobium
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Solution Overview
Problem
The existing gas sensors face corrosion issues at the welded portion between the metal cylinder and shell due to the formation of a Cr-depleted layer, which compromises the accuracy of gas concentration measurements, especially when exposed to corrosive substances in severe environments.
Innovation Solution
A gas sensor design that incorporates a metal shell with a specific chemical composition, including Fe ≥ 50.0 mass %, C 0.02-0.15 mass %, Cr 11.5-18.0 mass %, and Nb ≥ twice the C content, along with controlled Nb distribution to suppress the formation of chrome-depleted layers and enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If circumferential welding is performed on the metal cylinder and metal shell, then air tightness is ensured, but a Cr-depleted layer forms at the boundary causing corrosion
Solution Approach 1:
The invention changes the chemical composition parameters of the metal shell by strictly controlling the carbon content to 0.03 mass% or less and the chromium content to 16 mass% or more. This parameter adjustment prevents the formation of Cr-depleted layers during welding while maintaining air tightness through proper welding of the metal cylinder to the metal shell.
Solution Approach 2:
The invention uses a composite material approach by selecting specific stainless steel grades for the metal shell (with controlled C and Cr content) and the metal cylinder (SUS304). This material selection ensures that during circumferential welding, the metal components bond effectively to provide air tightness while the controlled composition prevents harmful Cr-depleted layer formation and subsequent corrosion.
2Ease of manufacture
If the metal shell uses SUS430 stainless steel with good cold forgeability, then manufacturing is easier, but corrosion resistance is slightly inferior
Solution Approach 1:
The invention changes the material selection from conventional SUS430 stainless steel to a specially controlled stainless steel composition with C≤0.03 mass% and Cr≥16 mass%. This parameter change maintains adequate cold forgeability for manufacturing while significantly improving corrosion resistance by preventing Cr-depleted layer formation during welding operations.
3Adaptability or versatility
If the gas sensor is exposed to corrosive substances in severe environments, then it can function in cold climate districts, but corrosion proceeds along the Cr-depleted layer compromising measurement accuracy
Solution Approach 1:
The invention changes the chemical composition parameters of the metal shell to C≤0.03 mass% and Cr≥16 mass%, which prevents the formation of Cr-depleted layers that would otherwise allow corrosion to proceed along the welded boundary. This ensures that even in severe environments with corrosive substances like snow melting agents, the air tightness and measurement precision are maintained over long periods.
Solution Approach 2:
The invention applies preliminary anti-action by pre-controlling the chemical composition of the metal shell before welding occurs. By limiting carbon content and ensuring adequate chromium content in advance, the material is pre-conditioned to resist the formation of Cr-depleted layers during welding, thereby preventing future corrosion pathways that would compromise measurement accuracy in corrosive environments.
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 design effectively prevents corrosion at the welded portion, ensuring accurate gas concentration measurements over a long period by forming niobium carbonate instead of chrome carbonate, thereby blocking water and corrosive substances from infiltrating the sensor.
Implementation Method 1
bonding of Cr and C
Implementation Method 2
chrome carbonate precipitates
Data Source
AI summary
A gas sensor including: a gas detection element; a metal shell extending in an axial direction; and a metal cylinder extending in an axial direction, wherein a leading end portion of the metal cylinder surrounds a base end portion of the metal shell and is fixed to the metal shell via a circumferential welded portion. The metal shell includes: Fe in an amount equal to or more than 50.0 mass %; C in an amount of 0.02 mass % to 0.15 mass %; Cr in an amount of 11.5 mass % to 18.0 mass %; and Nb in an amount equal to or more than twice amount of C in mass %.