Packaging Steel Sheet Nitrogen Gradient for Strength and Formability
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Solution Overview
Problem
Existing methods for producing thin steel sheets for packaging applications face limitations in achieving high strength and formability, particularly in deep drawing and stretch forming processes, due to the upper limit of unbound nitrogen content, which affects cold-rollability and formability.
Innovation Solution
A method involving a controlled nitrogen diffusion process during heating, creating a multilayer microstructure with a recrystallized core and non-recrystallized fringe regions, enhancing the recrystallization temperature in the fringe region by incorporating nitrogen, thereby achieving a three-layer 'sandwich structure' with high strength and ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If unbound nitrogen is introduced into steel to increase strength, then yield strength increases, but cold-rollability deteriorates
Solution Approach 1:
The patent applies local quality by creating a non-uniform nitrogen distribution within the steel sheet thickness. The nitrogen content is concentrated in specific regions (such as near the surface or in controlled zones) rather than being uniformly distributed throughout the entire steel sheet. This localized nitrogen enrichment allows strength enhancement in critical areas while maintaining lower nitrogen content in other regions, thereby preserving cold-rollability and formability where high strength is not the primary requirement.
2Strength
If nitrogen content is increased beyond 100 ppm, then strength increases, but formability deteriorates
Solution Approach 1:
The patent implements local quality by controlling nitrogen distribution to be non-uniform across the steel sheet thickness. By concentrating nitrogen in specific zones (such as surface regions or intermediate layers) while maintaining lower nitrogen content in other areas, the invention achieves enhanced strength in critical regions without compromising the formability of the overall material. This selective nitrogen placement allows the steel to meet strength requirements while retaining adequate ductility and formability for deep drawing and stretch forming operations.
3Loss of substance
If thinner steel sheets are used for resource efficiency, then resource consumption decreases, but strength and stability deteriorate
Solution Approach 1:
The patent applies parameter changes by fundamentally altering the nitrogen content and distribution parameters within the steel sheet. By introducing controlled amounts of unbound nitrogen (exceeding 100 ppm in certain regions) and creating specific nitrogen concentration profiles through the thickness, the invention achieves significant strength enhancement in thin steel sheets. This parameter modification allows thinner sheets to maintain adequate strength and stability while preserving the resource efficiency benefits of reduced material thickness.
4Strength
If nitrogen is added to increase strength, then yield strength increases, but elongation at break decreases
Solution Approach 1:
The patent employs local quality by creating a non-uniform nitrogen distribution where nitrogen is concentrated in specific regions rather than being uniformly distributed. This localized enrichment strategy enhances yield strength in critical areas while maintaining lower nitrogen content in regions where ductility is paramount. The resulting gradient structure allows the steel to exhibit high strength where needed while preserving adequate elongation at break through the overall material composition.
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 method produces steel sheets with strengths over 800 MPa and elongation at break of at least 5%, suitable for deep drawing applications, while maintaining formability and avoiding surface roughening.
Implementation Method 1
nitrogen from the nitrogen donor is incorporated at least into a near-surface (fringe) region of the steel sheet by diffusion of (atomic) nitrogen from the nitrogen donor into the near-surface (fringe) region
Implementation Method 2
The cold-rolled steel sheet is heated to a predetermined (maximum) heating temperature (TE) in the presence of a nitrogen donor
Implementation Method 3
The introduction of unbound nitrogen into the steel is referred to as nitrogenizing, nitriding or nitridation and is a well-known method for solid solution strengthening of steel and steel products
Data Source
AI summary
A method for producing a steel sheet for packaging includes: cold-rolling a hot-rolled steel sheet made from a steel having a carbon content of 10 to 1000 ppm by weight, the steel of the hot-rolled steel sheet having a predetermined recrystallization temperature (TR); heating the cold-rolled steel sheet to a predetermined heating temperature (TE), where TR≤TE, the heating performed at least partially in the presence of a nitrogen donor at least until TR is reached such that when the cold-rolled steel sheet is heated, nitrogen from the nitrogen donor is diffused at least into a near-surface region of the cold-rolled sheet steel and incorporated in the near-surface region, as a result of which the TR in the near-surface region is increased by a value ΔT, where TE<TR+ΔT. Using this method, high-strength steel sheets having a multilayer microstructure can be produced.