Black Ferritic Stainless Steel Composition for Weld-Stable Oxide Coatings
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Solution Overview
Problem
Black stainless steel sheets produced by oxidation methods face issues with weldability, toughness, and corrosion resistance, as the oxide coating can entangle during welding, affecting the blackness and corrosion resistance of the welded portion.
Innovation Solution
A ferrite-based stainless steel sheet with specific alloy compositions and surface oxide coating properties, ensuring excellent weldability, toughness, and corrosion resistance, with controlled components like Cr, Ti, and Al, and a uniform black tone maintained after welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an oxide coating is formed on the surface of stainless steel by oxidation method to impart black tone, then the designability and cost-effectiveness are improved, but the weldability and toughness deteriorate due to oxide coating entanglement during welding
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the stainless steel (C: 0.005-0.030%, Si: 0.01-1.50%, Mn: 0.01-2.00%, P: 0.005-0.040%, Cr: 13.00-20.00%, Ti: 0.03-0.10%, Al: 0.01-0.50%, N: 0.005-0.030%) to achieve a balance between black tone appearance and weldability. This compositional parameter optimization prevents oxide coating entanglement while maintaining the blackening effect.
Solution Approach 2:
The patent creates a composite material system by combining multiple alloying elements (Cr, Ti, Al, Si, Mn) in specific proportions to form a stainless steel composition that simultaneously provides black oxide coating formation capability and good weldability. The synergistic effect of these elements creates a material that resolves the contradiction between aesthetic appearance and welding performance.
2Ease of manufacture
If the oxide coating is formed to achieve uniform black tone, then the designability is improved, but the corrosion resistance may be affected by heating during welding
Solution Approach 1:
The patent uses parameter changes by optimizing the Cr content (13.00-20.00%) and Ti content (0.03-0.10%) to ensure that the oxide coating maintains both uniform black appearance and corrosion resistance after welding heating. The controlled composition ensures stable performance under thermal conditions.
Solution Approach 2:
The patent applies preliminary action by pre-optimizing the chemical composition before welding to ensure that the material has inherent resistance to welding-induced degradation. The composition is designed in advance to maintain corrosion resistance and black tone stability during subsequent welding operations.
3Ease of manufacture
If painting treatment is applied to achieve black appearance, then the designability is improved, but the manufacturing cost and process complexity increase
Solution Approach 1:
The patent extracts the blackening function from a separate painting process and integrates it directly into the material itself through oxidation treatment. By forming the black oxide coating as an inherent surface layer of the stainless steel, the patent eliminates the need for additional painting steps, reducing process complexity while maintaining designability.
Solution Approach 2:
The patent merges the aesthetic function (black appearance) with the base material by forming an oxide coating directly on the stainless steel surface. This integration combines the structural material and the aesthetic coating into a single unified system, eliminating separate painting processes and reducing overall manufacturing complexity.
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 provides a black stainless steel sheet with improved weldability, maintaining blackness and corrosion resistance, and preventing coat peeling, suitable for applications like exhaust gas system members without the need for additional painting.
Implementation Method 1
a surface in which an oxide coating is formed on the base, wherein the surface has a lightness index (L*) satisfying L*≤45, chromaticity indices (a*, b*) satisfying −5≤a*≤5 and −5≤b*≤5
Implementation Method 2
In the oxidation method, a stainless steel is heated under an oxidizing atmosphere to form an oxide coating imparting a black tone on a surface
Data Source
AI summary
Provided is a black stainless steel sheet that has excellent weldability, that can ensure good toughness and corrosion resistance, and that can maintain the blackness of the surface thereof, even after being welded. This black ferrite-based stainless steel sheet having excellent weldability includes, as a base, a stainless steel containing, in mass %, 0.020% or less of C, 1.0% or less of Si, 0.35% or less of Mn, 0.04% or less of P, 0.005% or less of S, 11-25% of Cr, 1.0% or less of Mo, 0.020% or less of N, 0.4% or less of Al, 10(C+N) to 0.3% of Ti, 0.05% or less of Nb, and 0.01% or less of O, and has a surface in which an oxide coating is formed on the base, wherein the surface has a lightness index (L*) satisfying L*≤45, chromaticity indices (a*, b*) satisfying −5≤a*≤5 and −5≤b*≤5, and a blackness (E) satisfying E=(L*2+a*2+b*2)1/2≤45.