Austenized Ferritic Stainless Steel Watch Component

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Solution Overview

Problem

The existing nitrogen absorption treatment for ferritic stainless steel in watch components results in non-uniform nitrogen transfer, leading to areas where the ferrite phase is eroded, compromising magnetic resistance due to a thin magnetic resistance functional layer.

Innovation Solution

A watch component made from austenized ferritic stainless steel with a base containing specific compositions and a nitrogen content of 1.0 to 1.6% by mass, featuring a mixed layer where the ferrite and austenized phases are mixed, ensuring a thickness ratio of 45% or less of the surface layer, enhancing nitrogen diffusion and magnetic resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If nitrogen absorption treatment is applied to ferritic stainless steel to obtain required hardness and corrosion resistance, then the surface layer is austenized, but the nitrogen transfer rate is non-uniform causing erosion of ferrite phase and degradation of magnetic resistance function

Engineering Contradiction:

Improvemagnetic resistance functionVSAvoiduniformity of nitrogen transfer

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies local quality by creating distinct layers with different nitrogen concentrations: a surface layer with high nitrogen content (austenized phase) for hardness and corrosion resistance, and a base layer with low nitrogen content (ferrite phase) for magnetic resistance. This localized differentiation of nitrogen distribution resolves the contradiction by allowing the surface to have high nitrogen transfer while maintaining the base's uniform ferrite structure.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent ensures continuous control of nitrogen diffusion by implementing a gradient structure where nitrogen concentration gradually decreases from the surface to the base. This continuous gradient prevents abrupt phase changes and maintains uniform nitrogen transfer throughout the material, ensuring both surface performance and magnetic resistance function.

Inventive Principle:

Principle #20Continuity of useful action

2Strength

If nitrogen absorption treatment is applied to achieve sufficient austenized phase thickness for hardness and corrosion resistance, then the surface layer becomes thicker, but the ferrite phase is significantly eroded reducing magnetic resistance function

Engineering Contradiction:

Improvehardness and corrosion resistanceVSAvoidferrite phase thickness

Core Design Contradiction:

StrengthVSLoss of substance

Solution Approach 1:

The patent applies preliminary action by pre-establishing a base material with controlled composition and structure before nitrogen absorption treatment. The base contains specific alloying elements (Cr: 16-20%, Mo: 1.0-2.5%, Nb: 0.05-0.50%, Cu: 0.1-0.8%) that prepare the ferrite phase to resist nitrogen diffusion, preserving its thickness while still allowing sufficient nitrogen uptake in the surface layer for required hardness and corrosion resistance.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes material parameters by controlling the composition of the base material and the nitrogen absorption treatment conditions. By adjusting alloying element concentrations and nitrogen potential/temperature/time parameters, the patent achieves optimal nitrogen distribution where the surface layer attains sufficient austenized phase thickness for mechanical properties while the base layer maintains adequate ferrite phase thickness for magnetic resistance.

Inventive Principle:

Principle #35Parameter changes

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 ensures uniform austenization, improving corrosion resistance and magnetic resistance, meeting the requirements for a first-class magnetic resistant watch by maintaining a sufficient ferrite phase thickness and reducing treatment time.

Implementation Method 1

In an austenization treatment using nitrogen gas, i.e., in a nitrogen absorption treatment, nitrogen enters the ferrite phase from the surface layer of the treatment target material

Methodology Applied

Scientific EffectNitrogen absorption: Absorption (physical)

Implementation Method 2

nitrogen enters the ferrite phase from the surface layer of the treatment target material

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS11644795B2Watch component and watch

Publication Date: 2023.05.09 SEIKO EPSON CORP

AI summary

A watch component includes an austenized ferritic stainless steel including a base including a ferrite phase, a surface layer formed on a surface of the base, the surface layer including an austenized phase, and a mixed layer formed between the base and the surface layer, the mixed layer being a layer in which the ferrite phase and the austenized phase are mixed. In a cross section taken along a depth direction from the surface, a thickness of the mixed layer is 45% or less of a thickness of the surface layer.