Stainless Steel Substrate Solid Solution Nb for Fuel Cell Separator

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Solution Overview

Problem

Stainless steel substrates used as fuel cell separators face corrosion issues in harsh environments due to the dissolution of Nb-containing intermetallic compounds, leading to pitting corrosion, despite the addition of Nb for improved corrosion resistance.

Innovation Solution

A stainless steel substrate with Nb in a solid solution state and substantially no precipitates of Nb-containing intermetallic compounds is achieved by heating the substrate under an inert atmosphere to dissolve these compounds and then quenching it, suppressing precipitation and enhancing corrosion resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If Nb is added to stainless steel to improve corrosion resistance, then sensitization is inhibited and corrosion resistance is improved, but Nb-containing intermetallic compounds precipitate and dissolve in corrosive environments, leading to pitting corrosion

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidpitting corrosion

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The invention changes the physical state parameter of Nb from precipitated intermetallic compounds to solid solution state through controlled heat treatment and quenching processes. This parameter change prevents the formation of dissolvable precipitates while maintaining Nb's corrosion-resistant properties in solid solution form

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention utilizes phase transition by heating the stainless steel to austenite region and then rapidly quenching it to obtain martensite structure with Nb in solid solution state. This phase transition process dissolves Nb-containing intermetallic compounds and traps Nb atoms in solid solution, preventing their re-precipitation

Inventive Principle:

Principle #36Phase transitions

2Reliability

If heat treatment is applied to dissolve Nb-containing intermetallic compounds, then corrosion resistance is improved, but additional processing steps and energy consumption are required

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidmanufacturing process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention performs preliminary action by adding Nb to the steel composition before casting and rolling. The Nb remains in the steel matrix through subsequent processing steps, and the final heat treatment simply needs to dissolve precipitates and create solid solution, rather than adding Nb at later stages. This preliminary incorporation simplifies the overall process

Inventive Principle:

Principle #10Preliminary action

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 resulting substrate exhibits superior corrosion resistance in corrosive fuel cell environments, reducing the occurrence of pitting corrosion and maintaining performance in harsh conditions.

Implementation Method 1

heating the substrate under an inert atmosphere to dissolve these compounds

Methodology Applied

Scientific EffectDissolution:

Implementation Method 2

then quenching it, suppressing precipitation and enhancing corrosion resistance

Methodology Applied

Scientific EffectQuenching:

Data Source

PatentUS10833335B2Stainless steel substrate

Publication Date: 2020.11.10 TOYOTA JIDOSHA KK

AI summary

The present disclosure provides a stainless steel substrate used for a fuel cell separator that comprises Nb and is excellent in corrosion resistance. The embodiments relate to a stainless steel substrate used for a fuel cell separator, comprising Nb in a solid solution state, and comprising substantially no precipitate of a Nb-containing intermetallic compound.