Black Ferritic Stainless Steel Sheet for Weld-Stable Oxide Blackness
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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 controlled oxide coating, optimized through hot-rolling, cold-rolling, and annealing processes, ensures excellent weldability, corrosion resistance, and maintains blackness after welding by regulating elements like C, Si, Mn, Cr, Mo, Ti, and Al within defined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If oxidation treatment is applied to impart black tone on stainless steel, then designability and blackness are improved, but weldability deteriorates due to oxide coating entanglement during welding
Solution Approach 1:
The patent changes the chemical composition parameters of the stainless steel by strictly controlling the content of harmful elements (P≤0.04%, S≤0.005%, C≤0.03%, Si≤1.0%, Mn≤2.0%) and optimizing beneficial elements (Cr: 16-26%, Ti: 0.05-1.0%, Al: 0.05-1.0%, Mo: 0.05-2.0%). This compositional parameter optimization ensures that the oxide coating formed has better adhesion properties and does not entangle during welding, thus maintaining both black tone appearance and weldability.
Solution Approach 2:
The patent creates a composite structure where the base stainless steel material is combined with a controlled oxide coating layer. By optimizing the base material composition (particularly Cr, Ti, Al, and Mo contents), the oxide coating forms as a beneficial composite layer that provides black coloration while maintaining good adhesion and preventing entanglement during welding operations.
2Shape
If oxidation treatment is applied to impart black tone, then designability is improved, but corrosion resistance of welded portion deteriorates
Solution Approach 1:
The patent optimizes the chemical composition parameters, particularly increasing Cr content (16-26%) which forms a protective passive layer, and controlling Ti (0.05-1.0%), Al (0.05-1.0%), and Mo (0.05-2.0%) contents. This compositional optimization ensures that both the base material and the oxide coating layer have enhanced corrosion resistance, maintaining protection even in the welded heat-affected zone while preserving the black tone appearance.
3Ease of manufacture
If oxidation treatment is applied to eliminate painting step, then manufacturing cost is reduced, but blackness uniformity after welding deteriorates
Solution Approach 1:
The patent optimizes the chemical composition parameters (Cr: 16-26%, Ti: 0.05-1.0%, Al: 0.05-1.0%, Mo: 0.05-2.0%, with strict controls on P, S, C, Si, and Mn) to ensure uniform oxide coating formation. This compositional control promotes consistent oxidation behavior during the blackening treatment, and the optimized alloying elements ensure that the oxide layer remains stable and uniform even after welding heat exposure, eliminating the need for painting while maintaining appearance quality.
4Ease of manufacture
If oxidation treatment is applied to impart black tone, then painting treatment is eliminated, but toughness of welded portion deteriorates due to oxide coating entanglement
Solution Approach 1:
The patent optimizes the chemical composition by controlling harmful elements (P≤0.04%, S≤0.005%, C≤0.03%, Si≤1.0%, Mn≤2.0%) and optimizing beneficial elements (Cr: 16-26%, Ti: 0.05-1.0%, Al: 0.05-1.0%, Mo: 0.05-2.0%). This compositional optimization ensures that the oxide coating has appropriate adhesion properties that prevent entanglement during welding, thereby maintaining the toughness and mechanical strength of the welded portion while eliminating the need for additional painting treatments.
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, toughness, and corrosion resistance, maintaining the black tone and designability without the need for additional painting, suitable for applications like exhaust gas system members.
Implementation Method 1
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
Implementation Method 2
The oxidation method can utilize an annealing treatment in the manufacturing process of the stainless steel
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.