Ferritic Stainless Steel Housing with Austenitized Surface for Magnetic Shielding
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Solution Overview
Problem
Existing timepiece case members made from ferritic stainless steel lack the necessary hardness, corrosion resistance, and surface properties required for a decorative external part, while austenitic stainless steel is difficult to process and costly to manufacture, and methods to enhance ferritic stainless steel using nitrogen austenitizing result in uneven nitrogen concentration and discontinuous ferrite phases, compromising magnetic shielding performance.
Innovation Solution
A housing made from ferritic stainless steel with an austenitized surface layer and a uniform internal ferrite phase layer, where the austenitizing process is controlled to maintain a contiguous ferrite phase, providing both decorative and magnetic shielding properties without the need for a dedicated magnetic shield, using a manufacturing method that involves nitrogen absorption and chromium nitride formation to achieve a stable austenitized surface layer and ferrite phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ferritic stainless steel is used for case member components, then ease of manufacture and magnetic shielding properties are improved, but hardness, corrosion resistance, and surface properties deteriorate
Solution Approach 1:
The invention changes the chemical composition parameters of the ferritic stainless steel by adding specific amounts of nitrogen (0.01-1.0 wt%) and chromium (10-25 wt%). This compositional parameter change enables the material to achieve both ease of manufacture and improved hardness/corrosion resistance without requiring post-processing heat treatments that would compromise magnetic shielding properties.
2Strength
If austenitic stainless steel is used for case member components, then hardness, corrosion resistance, and surface properties are improved, but ease of manufacture and manufacturing cost deteriorate
Solution Approach 1:
The invention changes the phase structure parameter by controlling the steel to remain ferritic rather than transforming to austenite. By adjusting composition parameters (adding nitrogen and chromium) while maintaining ferritic phase, the invention achieves austenite-like hardness and corrosion resistance through compositional modification rather than phase transformation, thereby preserving ease of manufacture.
3Strength
If nitrogen austenitizing is applied to ferritic stainless steel, then surface properties are improved, but uniformity of nitrogen concentration and contiguity of ferrite phase deteriorate
Solution Approach 1:
The invention performs preliminary action by pre-adding nitrogen and chromium elements to the ferritic stainless steel composition before manufacturing. This preliminary compositional adjustment ensures uniform distribution of alloying elements throughout the material, eliminating the need for subsequent nitrogen austenitizing treatment that would cause non-uniform nitrogen concentration and disrupt ferrite phase contiguity.
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 solution enables a timepiece with improved decorative and magnetic shielding properties, reducing product size and manufacturing costs, while ensuring reliable magnetic shielding by maintaining a uniform ferrite phase and enhancing surface characteristics.
Implementation Method 1
The austenitizing process using nitrogen gas enables the nitrogen atoms to penetrate the ferrite phase from both front and back sides of the work piece
Implementation Method 2
the portion in which the nitrogen concentration rises to at least a predetermined level changes to the austenite phase
Implementation Method 3
a manufacturing method that involves nitrogen absorption and chromium nitride formation to achieve a stable austenitized surface layer and ferrite phase
Implementation Method 4
an internal layer portion having an internal ferrite phase that functions as a magnetic shield for the magnetically shielded component
Data Source
AI summary
A device has a magnetically shielded component that is magnetically shielded from an external magnetic field, and a housing. The housing is made from a ferritic stainless steel that has an austenitized surface layer rendered on the surface, and an internal layer portion having an internal ferrite phase that functions as a magnetic shield for the magnetically shielded component.