Ferritic Stainless Steel Nitriding via Carburizing

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Solution Overview

Problem

Conventional nitriding methods for ferritic stainless steel fail to form a sufficient nitrided layer on workpieces with low carbon concentration, limiting the improvement of hardness and corrosion resistance.

Innovation Solution

A method involving a carburizing step to form a carburized layer on ferritic stainless steel workpieces, followed by a nitriding step at a temperature equal to or higher than the transformation point in an atmosphere containing N2 gas, which allows for the formation of a nitrided layer that enhances hardness and corrosion resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional nitriding method is used on ferritic stainless steel with low carbon concentration, then the process is simple, but the nitrided layer cannot be formed sufficiently

Engineering Contradiction:

Improvenitrided layer formationVSAvoidprocess complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies preliminary action by performing a carburizing treatment before nitriding to increase the carbon concentration in the steel substrate. This preliminary carbon enrichment enables subsequent nitriding to form a sufficient nitrided layer, which would otherwise be impossible on low-carbon ferritic stainless steel.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the carbon concentration parameter of the steel substrate by introducing carbon through carburizing treatment. This parameter change transforms the material properties to enable effective nitriding, resolving the contradiction between maintaining simple processing and achieving reliable nitrided layer formation.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If carburizing step is added before nitriding, then nitrided layer formation is improved, but the manufacturing process becomes more complex

Engineering Contradiction:

Improvenitrided layer formationVSAvoidprocess steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the carburizing and nitriding processes into a combined carbonitriding treatment. By using a single atmosphere containing both carbon-containing gases and nitrogen, the patent achieves both carbon enrichment and nitrogen diffusion in one operation, reducing process complexity while maintaining effective nitrided layer formation.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent creates a multi-functional treatment process where a single heating atmosphere performs both carburizing and nitriding functions simultaneously. This universal approach eliminates the need for separate process equipment and procedures, addressing the contradiction between process effectiveness and manufacturing complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Length of stationary object

If heating temperature is increased to form nitrided layer, then nitrided layer penetration depth increases, but surface carbon concentration decreases

Engineering Contradiction:

Improvenitrided layer penetration depthVSAvoidsurface carbon concentration

Core Design Contradiction:

Length of stationary objectVSQuantity of substance

Solution Approach 1:

The patent applies preliminary carbon enrichment through carburizing treatment before nitriding. This ensures that even when high-temperature nitriding causes carbon diffusion and surface carbon concentration decrease, there is sufficient carbon reservoir in the substrate to maintain adequate surface carbon levels while achieving deep nitrided layer penetration.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent maintains continuous carbon supply to the surface during the nitriding process by performing carburizing first and then nitriding without interrupting the carbon enrichment effect. This continuous action ensures that carbon concentration is maintained at the surface while nitrogen penetrates deeply, resolving the contradiction between penetration depth and surface carbon concentration.

Inventive Principle:

Principle #20Continuity of useful 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 method effectively improves the hardness and corrosion resistance of ferritic stainless steel products by forming a nitrided layer that can penetrate deeply and reduce surface carbon concentration, making the material suitable for applications requiring both properties.

Implementation Method 1

forming a nitrided layer on a surface of the workpiece by heating the workpiece at a temperature equal to or higher than a transformation point of the ferritic stainless steel in an atmosphere containing an N2 gas

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

forming a carburized layer on a workpiece made of ferritic stainless steel

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS10508331B2Method for manufacturing ferritic stainless steel product

Publication Date: 2019.12.17 DENSO CORP

AI summary

A method for manufacturing a ferritic stainless steel product includes forming a carburized layer on a workpiece made of ferritic stainless steel, and forming a nitrided layer on a surface of the workpiece by heating the workpiece at a temperature equal to or higher than a transformation point of the ferritic stainless steel in an atmosphere containing an N2 gas.