Thin Packaging Steel Composition for Biaxial Formability
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Solution Overview
Problem
The challenge is to produce cold-rolled steel sheets with a thickness of less than 0.6 mm that have high biaxial strength and good forming behavior for packaging applications, while minimizing material defects and economic costs, as high cold rolling degrees can lead to thinness deterioration and material failure during multi-axial deformation processes.
Innovation Solution
A cold-rolled steel sheet with a specific composition (C: 0.001 - 0.06%, Si: <0.03%, Mn: 0.17 - 0.5%, P: <0.03%, S: 0.001 - 0.03%, Al: 0.001 - 0.1%, N: 0.002 - 0.12%, optionally Cr, Ni, Cu, Ti, B, Nb, Mo, Sn) is produced using a nitrogen-enhanced annealing process, where nitrogen is introduced during the annealing of hot strips in a continuous furnace to achieve high nitrogen content and solid solution hardening, allowing for higher cold rolling degrees without forming defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If high cold rolling degree is used to reduce final thickness, then packaging weight is reduced, but material defects and thinness deterioration occur during multi-axial deformation
Solution Approach 1:
The invention changes the chemical composition parameters of the steel sheet, specifically controlling carbon content to 0.001-0.06% and nitrogen content to 0.002-0.12%, to achieve the desired strength and formability balance that allows high cold rolling degrees without material failure
Solution Approach 2:
The invention creates a composite microstructure through controlled alloying and heat treatment, combining ferrite matrix with precipitated phases to achieve both high strength and good formability, enabling the steel to withstand high cold rolling degrees and multi-axial deformation
2Weight of moving object
If high cold rolling degree is used to achieve thin final thickness, then packaging weight is reduced, but forming behavior deteriorates
Solution Approach 1:
The invention optimizes chemical composition parameters (C: 0.001-0.06%, N: 0.002-0.12%, Mn: 0.17-0.5%, Al: 0.001-0.1%) to achieve a balance between strength and formability, allowing high cold rolling degrees while maintaining good forming behavior for packaging production
Solution Approach 2:
The invention creates local microstructural variations through controlled alloying and heat treatment, where different phases are distributed to provide both strength and ductility in different regions, improving overall forming behavior
3Shape
If low carbon and nitrogen content is used to achieve high total cold rolling degree optimum, then earing is minimized, but biaxial strength is insufficient
Solution Approach 1:
The invention precisely controls carbon content (0.001-0.06%) and nitrogen content (0.002-0.12%) to achieve optimal earing behavior while simultaneously obtaining sufficient biaxial strength through solid solution strengthening and precipitate hardening mechanisms
Solution Approach 2:
The invention creates a composite microstructure with ferrite matrix and precipitated phases that provides both good earing characteristics and high biaxial strength, resolving the contradiction between shape quality and strength requirements
4Strength
If nitrogen is introduced during annealing to achieve solid solution hardening, then biaxial strength is increased, but nitrogen compound formation may affect surface quality
Solution Approach 1:
The invention controls nitrogen content (0.002-0.12%) and introduces it during annealing to achieve solid solution hardening and precipitation strengthening, while controlling the amount and distribution of nitrogen compounds to maintain acceptable surface quality
Solution Approach 2:
The invention creates local variations in nitrogen distribution, with higher nitrogen content in the bulk for strength and controlled nitrogen compound formation at the surface, achieving both high strength and acceptable surface quality
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 results in steel sheets with a lower yield strength of over 300 MPa and high elongation at break, enabling the production of thin packaging without material failure, even under significant multi-axial deformation, and reduces the weight of packaging products while maintaining stability.
Implementation Method 1
nitrogen is introduced during the annealing of hot strips in a continuous furnace to achieve high nitrogen content and solid solution hardening
Implementation Method 2
These are brought to the desired final thickness from a hot-rolled steel sheet in a single or double cold rolling step
Implementation Method 3
Single-reduced (SR) steel sheets undergo recrystallization annealing after cold rolling to restore formability
Data Source
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Figure 3a
AI summary
The invention relates to a packaging sheet product made of cold-rolled steel sheet with a thickness of less than 0.6 mm, which has the following composition by weight: - C: 0.001 - 0.06%, - Si: < 0.03%, preferably 0.002 to 0.03%, - Mn: 0.17-0.5%, - P: < 0.03%, preferably 0.005 to 0.03%, - S: 0.001 - 0.03%, - Al: 0.001 - 0.1%, - N: 0.002 - 0.12%, preferably 0.004 to 0.07%, - optional Cr: <0.1%, preferably 0.01 - 0.1%, - optional Ni: <0.1%, preferably 0.01 - 0.05%, - optional Cu: <0.1%, preferably 0.002 - 0.05%, - Optional Ti: < 0.01%, - Optional B: < 0.005%, - Optional Nb: < 0.01%, - Optional Mo: < 0.02%, - Optional Sn: < 0.03%, - Remainder iron and unavoidable impurities,wherein the packaging sheet product exhibits a lower yield strength (SbeL) of more than 300 MPa and a corresponding elongation at break (Ab) of more than 10% during biaxial deformation in a bulge test, and in the plastic range between the Lüders strain (Abe) and an upper (plastic) limit strain of εmax = 0.5·Ab·(SbeL/Sbm) a biaxial stress/strain diagram σB(ε) which can be represented by a function σB = b·εn, where - σB is the true biaxial stress in MPa, - ε is the magnitude of the true strain in the thickness direction in %, - SbeL is the lower yield strength, - Sbm is the absolute strength, - Abe is the Lüders strain, - b is a proportionality factor, and - n is a work hardening exponent, and work hardening of the The packaging sheet metal product is characterized in the thickness direction by a hardening exponent of n≥0.353−5.1⋅SbeL/104MPa.