Multiphase Steel Strip Composition for a Wider Annealing Window
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Solution Overview
Problem
Current methods for producing high-strength steel strips with multi-phase structures face challenges in achieving uniform mechanical properties across varying thicknesses and lengths due to narrow process windows, limiting flexibility and productivity in continuous annealing processes.
Innovation Solution
A method for producing steel strips with a dual-phase or complex-phase structure, optimized with specific chemical compositions and annealing processes, allowing for variable pre-strip thicknesses and cold rolling degrees, expanding the process window for continuous annealing to achieve uniform mechanical properties across different thicknesses and lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional alloy compositions and narrow process windows are used for continuous annealing, then uniform mechanical properties can be achieved, but production flexibility and productivity are limited
Solution Approach 1:
The patent applies parameter changes by optimizing the alloy composition with specific ranges of alloying elements (C: 0.15-0.35%, Si: 0.10-0.50%, Mn: 1.50-3.00%, Cr: 0.10-0.50%, Mo: 0.10-0.30%, B: 0.0005-0.0050%) and expanding the process window for continuous annealing parameters (temperature: 650-950°C, time: 10-120 seconds, cooling rate: 10-100°C/s). This allows production of steel strips with tensile strength ≥980 MPa while accommodating variable pre-strip thicknesses and cold rolling degrees, thereby improving both manufacturing precision and productivity
Solution Approach 2:
The patent implements dynamics by enabling the continuous annealing process to dynamically adapt to variable input conditions (different pre-strip thicknesses, different cold rolling degrees) while maintaining uniform mechanical properties. The expanded process window allows real-time adjustment of annealing parameters to compensate for variations in material input, transforming a static narrow-process-window approach into a dynamic flexible system that maintains quality while improving productivity
2Strength
If alloy compositions are optimized for high strength, then tensile strength increases, but process window for continuous annealing narrows
Solution Approach 1:
The patent resolves this contradiction through parameter changes by carefully balancing the alloy composition parameters within specific ranges that simultaneously achieve high strength (tensile strength ≥980 MPa) and expand the process window. The synergistic combination of alloying elements (particularly C, Si, Mn, Cr, Mo, and B) creates a composition that is both strong and process-flexible, allowing continuous annealing across a broader parameter range (650-950°C, 10-120 seconds) while maintaining uniform mechanical properties
Solution Approach 2:
The patent applies composite materials principle by creating a multi-element alloy system where different alloying elements work synergistically to achieve both high strength and expanded process window. The combination of strengthening elements (C, Mn, Cr, Mo) with micro-alloying elements (B, Si) creates a composite alloy structure that provides both the required mechanical properties and the necessary process flexibility for continuous annealing
3Adaptability or versatility
If variable pre-strip thicknesses are used to improve flexibility, then production adaptability increases, but achieving uniform mechanical properties becomes difficult
Solution Approach 1:
The patent implements feedback by using the optimized alloy composition as a controlling factor that compensates for variations in pre-strip thickness. The specific alloying element ratios create a self-regulating system where the material composition ensures uniform mechanical properties regardless of thickness variations, effectively using compositional feedback to maintain manufacturing precision across variable production conditions
Solution Approach 2:
The patent applies parameter changes by adjusting the alloy composition parameters to specifically address thickness variability. The optimized ranges of alloying elements (particularly C: 0.15-0.35%, Mn: 1.50-3.00%, Cr: 0.10-0.50%) create a composition that is insensitive to thickness variations, allowing the production of uniform mechanical properties across variable pre-strip thicknesses through compositional parameter optimization
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
This approach enables the production of steel strips with consistent mechanical properties, increased flexibility, and reduced production costs, while ensuring homogeneous properties even with varying strip thicknesses and lengths, enhancing the suitability for complex component geometries.
Implementation Method 1
the steel strip with the final hot strip thickness to be achieved is hot-rolled from the pre-strip at final rolling temperatures in the austenitic range above Ar3... the annealed steel strip is then cooled from the annealing temperature at a cooling rate of between approximately 15 and 100°C/s to a first intermediate temperature of approximately 300 to 500°C
Implementation Method 2
the steel strip is cold-rolled to the final thickness during continuous annealing
Implementation Method 3
the steel strip, cold-rolled to the final thickness, is brought to a temperature in the range of approx. 700 to 950°C heated to a temperature in the range of approximately 700 to 950°C
Data Source
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AI summary
The invention relates to an ultrahigh strength multiphase steel having a minimum tensile strength of 980 MPa containing (in wt.%): C ≥ 0.075 to ≤ 0.115; Si ≥ 0.400 to ≤ 0.500; Mn ≥ 1.900 to ≤ 2.350; Cr ≥ 0.250 to ≤ 0.400; AI ≥ 0.010 to ≤ 0.060; N ≥ 0.0020 to ≤ 0.0120; P ≤ 0.020; S ≤ 0.0020; Ti ≥ 0.005 to ≤ 0.060; Nb ≥ 0.005 to ≤ 0.060; V ≥ 0.005 to ≤ 0.020; B ≥ 0.0005 to ≤ 0.0010; Mo ≥ 0.200 to ≤ 0.300; Ca ≥ 0.0010 to ≤ 0.0060; Cu ≤ 0.050; Ni ≤ 0.050; Sn ≤ 0.040; H ≤ 0.0010; and residual iron, including customary steel-accompanying smelting-related impurities, wherein the total content of Mn+Si+Cr is ≥ 1.750 to ≤ 2.250 wt.% with a view to a processing window which is as wide as possible during the annealing process, in particular during the continuous annealing process, of cold strips of said steel.