Austenitic Steel Sheet Oxide Layer Formation
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Solution Overview
Problem
Existing manufacturing processes for cold-rolled iron-carbon-manganese austenitic steel sheets struggle to achieve high mechanical properties and corrosion resistance without a zinc-based coating, particularly during storage and transportation, where surface oxidation can occur, reducing corrosion resistance.
Innovation Solution
A process involving cold-rolling and recrystallization annealing in a reducing iron and oxidizing manganese atmosphere to form a thick, amorphous (Fe,Mn)O and crystalline MnO oxide layer on both sides of the sheet, enhancing corrosion resistance and mechanical properties, with specific chemical composition and annealing parameters to prevent oxidation and improve ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the steel sheet is delivered bare without zinc-based coating, then cost is reduced and processing simplicity is improved, but corrosion resistance deteriorates due to surface oxidation during storage and transportation
Solution Approach 1:
The patent converts the harmful oxidation that would normally degrade the steel surface into a beneficial protective oxide layer. By controlling the annealing atmosphere to be oxidizing with respect to manganese, a thick protective oxide layer (total thickness ≥ 0.5 microns) is formed on the steel sheet surface. This oxide layer, consisting of an amorphous (Fe,Mn)O sublayer and a crystalline MnO external layer, provides excellent corrosion resistance and eliminates the need for temporary protective oil films or zinc-based coatings.
2Reliability
If a temporary protective oil film is applied to prevent oxidation, then corrosion resistance is improved, but the risk of local modification by friction or contact is increased, reducing effectiveness
Solution Approach 1:
The steel sheet performs self-protection through the formation of a stable oxide layer during the annealing process. The controlled oxidation during annealing creates a protective barrier that eliminates the need for external protective measures such as oil films. The oxide layer forms inherently as part of the manufacturing process, providing continuous protection without requiring additional protective coatings that could be compromised during handling.
3Reliability
If the oxide layer thickness is increased to improve corrosion resistance, then protection is enhanced, but the complexity of controlling annealing parameters increases
Solution Approach 1:
The patent specifies precise parameter ranges for the annealing process to achieve the desired oxide layer thickness and composition. The annealing is conducted at temperatures between 500°C and 900°C in an atmosphere with controlled oxygen partial pressure (between 10^-20 and 10^-15 Pa), where the atmosphere is reducing with respect to iron but oxidizing with respect to manganese. These parameter changes enable the formation of a protective oxide layer with total thickness of at least 0.5 microns, providing optimal corrosion resistance.
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 process significantly improves corrosion resistance and mechanical properties, extending the time before red rust appears and reducing perforation corrosion, while maintaining high strength and elongation, even without a zinc-based coating, by forming a protective oxide layer that enhances the sheet's durability.
Implementation Method 1
a recrystallization annealing treatment is carried out on said sheet in a furnace having an atmosphere that is reducing with respect to iron and oxidizing with respect to manganese, the parameters of said annealing being chosen in such a way that said sheet is covered on both its sides with an essentially amorphous (Fe,Mn)O oxide sublayer and with an external crystalline manganese oxide (MnO) layer
Implementation Method 2
a recrystallization annealing treatment is carried out on said sheet in a furnace having an atmosphere that is reducing with respect to iron and oxidizing with respect to manganese
Data Source
AI summary
The invention relates to a process for manufacturing a corrosion-resistant cold-rolled sheet of iron-carbon-manganese austenitic steel, comprising the following steps: a sheet whose chemical composition comprises, the contents being expressed by weight: 0.35%≦C≦1.05%, 16%≦Mn≦24%, the balance of the composition consisting of iron and inevitable impurities resulting from its smelting, is provided; said sheet is cold-rolled; and a recrystallization annealing treatment is carried out on said sheet in a furnace containing a gas chosen from gases that are reducing with respect to iron, the parameters of said annealing being chosen in such a way that said sheet is covered on both its sides with an essentially amorphous (Fe,Mn)O oxide sublayer and with an external crystalline manganese oxide (MnO) layer, the total thickness of these two layers being equal to or greater than 0.5 microns.