Dual-Phase Steel Sheet Formability via Alloy and Coiling Control
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Solution Overview
Problem
There is a need for high-strength flat steel products with improved forming properties, particularly in vehicle construction, to meet requirements for lightweight construction, crash safety, and complex component structures, where existing dual-phase steels may not provide sufficient elasticity and strength.
Innovation Solution
A method for producing a flat steel product with specific alloying elements (C, Si, Mn, Al, and Cr) and a coiling temperature of 540 to 620 °C, followed by optional cold rolling and annealing, to achieve enhanced mechanical properties such as increased elasticity and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional dual-phase steels with 70 to 90 vol% ferrite and martensite are used, then high tensile strength and good formability are achieved, but the yield strength ratio is not sufficiently low and elongation capacity is limited
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition ranges of alloying elements (C: 0.05-0.20 wt.%, Si: 0.01-0.50 wt.%, Mn: 1.00-3.00 wt.%, Al: 0.05-2.50 wt.%, Cr: 0.01-1.00 wt.%) and processing parameters (coiling temperature: 540-620°C, annealing temperature: 780-880°C, annealing time: 15-300 seconds) to optimize the microstructure. This results in a dual-phase steel with 70-90 vol% ferrite and 10-30 vol% martensite, achieving tensile strength of 580-710 MPa and elongation of at least 23%, while maintaining low yield strength ratio and excellent formability.
2Strength
If higher carbon content is added to increase strength, then tensile strength improves, but total elongation and formability deteriorate
Solution Approach 1:
The patent optimizes the carbon content parameter within a specific range (0.05-0.20 wt.%) to balance strength and elongation. By controlling carbon at this moderate level and compensating with other alloying elements (particularly Mn: 1.00-3.00 wt.% and Cr: 0.01-1.00 wt.%), the steel achieves tensile strength of 580-710 MPa while maintaining total elongation of at least 23%, resolving the trade-off between strength and elongation.
Solution Approach 2:
The patent creates a composite microstructure consisting of two distinct phases: soft ferrite (70-90 vol%) providing ductility and toughness, and hard martensite (10-30 vol%) providing strength. This dual-phase composite structure enables the steel to simultaneously achieve high tensile strength (580-710 MPa) and high total elongation (at least 23%), as the soft ferrite matrix allows plastic deformation while the dispersed martensite islands provide strength reinforcement.
3Strength
If complex alloying is used to improve mechanical properties, then strength and formability are enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent employs parameter changes by establishing specific composition ranges for five alloying elements (C, Si, Mn, Al, Cr) and controlling key processing parameters (coiling temperature: 540-620°C, annealing temperature: 780-880°C, annealing time: 15-300 seconds). This systematic parameter optimization achieves the desired mechanical properties (tensile strength: 580-710 MPa, elongation: ≥23%) through a well-defined manufacturing process, balancing performance enhancement with process controllability.
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 results in a flat steel product with improved tensile strength (580 MPa to 710 MPa) and elongation at break (at least 23%), suitable for safety-relevant components in vehicle construction, such as longitudinal and cross members, while maintaining surface quality and formability.
Implementation Method 1
The microstructure of typical DP steels consists of 70 to 90 vol% ferrite, with the remainder being martensite. In addition to martensite, small amounts of other carbon-rich transformation microstructures such as bainite and/or thermodynamically metastable retained austenite may be present.
Implementation Method 2
subsequent annealing in a continuous furnace with an optional subsequent coating
Data Source
AI summary
The present invention relates to a method for producing a steel flat product, a corresponding steel flat product, components made from such a steel flat product, and the use of the steel flat product.