Austenitic Steel Sheets High Strength Formability
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Solution Overview
Problem
Current steel sheets struggle to achieve a high strength-to-elongation ratio while maintaining formability and fracture resistance, especially under dynamic stressing conditions, and often require high contents of expensive alloying elements.
Innovation Solution
Austenitic iron/carbon/manganese steel sheets with specific chemical compositions and manufacturing processes that include controlled rolling, recrystallization, and annealing to achieve strengths above 900 MPa with elongation at fracture ratios greater than 45000, while minimizing expensive alloying elements and preventing carbide precipitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high tensile strength is achieved through alloying and processing, then strength increases, but elongation at fracture decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling chemical composition parameters (C: 0.2-0.6%, Si: 1.5-3.0%, Mn: 1.5-3.5%, P: 0.01-0.05%, S: 0.005-0.03%, Al: 0.01-0.06%) and processing parameters (hot rolling temperature 850-950°C, coiling temperature 450-550°C, delay time 5-15 seconds) to achieve a balance between strength and elongation. The controlled delay time between rolling and cooling is particularly critical for maintaining both high strength (900-1100 MPa) and high elongation (45-65%).
Solution Approach 2:
The patent utilizes phase transitions by controlling the austenite phase stability through specific alloying and thermal processing. The steel maintains an austenitic microstructure through the hot rolling and coiling process, and the controlled delay allows for phase transformation that achieves both high strength and ductility. The phase transition control is evident in the microstructure description showing refined grain structure with appropriate phase distribution.
2Strength
If expensive alloying elements are increased to improve mechanical properties, then strength and toughness improve, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive alloying elements with cheaper alternatives by using optimized combinations of common elements. Instead of relying on costly Ni, Cr, or Ti additions, the patent achieves high strength (900-1100 MPa) and elongation (45-65%) through precise control of C, Si, Mn, P, S, and Al contents, combined with specific hot rolling and coiling parameters. This substitution principle reduces material cost while maintaining or improving mechanical properties.
Solution Approach 2:
The patent changes the parameter regime from high alloying content to optimized low alloying with precise control. By adjusting the parameters within specific ranges (particularly the delay time between rolling and cooling, and the carbon-silicon-manganese combination), the patent achieves superior mechanical properties without requiring expensive alloying elements, thereby reducing the quantity and cost of alloying substances.
3Strength
If steel composition is optimized for high strength, then strength increases, but formability during cold working decreases
Solution Approach 1:
The patent applies parameter changes by controlling the delay time between hot rolling and cooling (5-15 seconds) and maintaining specific temperature ranges (hot rolling: 850-950°C, coiling: 450-550°C) to achieve an austenitic microstructure with refined grains. This parameter optimization enables the steel to exhibit both high strength (900-1100 MPa) and excellent formability, allowing complex cold working operations without cracking or excessive hardening.
Solution Approach 2:
The patent creates a composite microstructure through controlled alloying and processing, resulting in a refined grain structure with appropriate phase distribution. The combination of specific alloy elements (C, Si, Mn, P, S, Al) in controlled amounts, combined with the thermal processing history, produces a composite-like microstructure that provides both high strength and good formability, enabling the steel to withstand both high loads and complex deformation.
4Quantity of substance
If alloying elements are reduced to lower cost, then manufacturing cost decreases, but strength and toughness deteriorate
Solution Approach 1:
The patent changes the parameter regime from low alloying to optimized alloying with precise control. By adjusting the parameters within specific ranges (C: 0.2-0.6%, Si: 1.5-3.0%, Mn: 1.5-3.5%, P: 0.01-0.05%, S: 0.005-0.03%, Al: 0.01-0.06%) and processing parameters (delay time: 5-15 seconds, hot rolling temperature: 850-950°C), the patent achieves high strength (900-1100 MPa) and elongation (45-65%) without requiring excessive alloying content, thereby optimizing both cost and performance.
5Manufacturing precision
If steel is designed for high elongation, then ductility improves, but strength decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the delay time between hot rolling and cooling (5-15 seconds) and maintaining specific temperature ranges to achieve an optimized austenitic microstructure. This parameter optimization enables the steel to simultaneously exhibit high strength (900-1100 MPa) and high elongation (45-65%), breaking the traditional trade-off between these two properties through refined grain structure and phase control.
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 results in steel sheets with enhanced mechanical properties, including high strength, formability, and toughness under both static and dynamic conditions, without excessive alloying element content, effectively addressing the limitations of existing steel technologies.
Implementation Method 1
the recrystallized fraction of the steel being greater than 75%
Implementation Method 2
the mean grain size of the steel being less than 18 microns
Data Source
AI summary
The invention relates to a hot rolled sheet which is made from austenitic iron/carbon/manganese steel and which has a resistance of greater than 900 MPa, whereby: resistance (MPa) x elongation at rupture (%) is greater than 45000. The chemical composition of the inventive sheet comprises the following concentrations expressed as weight: 0.5%=C=0.7%, 17%=Mn=24%, Si=3%, Al=0.05%, S=0.03%, P=0.08%, N=0.1% and, optionally, one or more elements such as Cr=1%, Mo=0.4%, Ni=1%, Ti=0.5%, Nb=0.5%, V=0.5%, Cu=5%, Cu=5%, the rest of the composition comprising iron and impurities resulting from production. According to the invention, the recrystallised fraction of the steel is greater than 75% and the surface fraction of precipitated carbides of the steel is less than 1.5%, the average grain size of the steel being less than 18 micrometers.