Multi-phase Steel Composition for Strength and Weldability
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Solution Overview
Problem
Existing multi-phase steels face challenges in achieving a balance between high strength and deformability, while maintaining good weldability and microstructural stability, particularly in vehicle body construction.
Innovation Solution
A multi-phase steel composition with specific alloying elements such as C, Mn, Si, Al, Nb, Ti, and V, optimized to achieve a microstructure with at least 10% ferrite and 6% residual austenite, along with a controlled production process involving hot rolling and annealing, to enhance tensile strength, yield point, and elongation at break.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If carbon content is increased to achieve high tensile strength, then tensile strength is improved, but weldability deteriorates
Solution Approach 1:
The patent optimizes the carbon content parameter within a specific range (0.14-0.25% wt) rather than maximizing it, and compensates for strength through controlled combinations of other alloying elements (Mn: 1.7-2.5% wt, Si: 0.2-0.7% wt, Cr: 0.05-1% wt, Mo: 0.02-0.5% wt, V: 0.02-0.5% wt, Nb: 0.02-0.1% wt, Ti: 0.005-0.05% wt, B: 0.0005-0.005% wt) to achieve tensile strength ≥950 MPa while maintaining weldability
Solution Approach 2:
The patent creates a multi-phase composite microstructure consisting of ferrite (10-80% vol), residual austenite (6-20% vol), bainite (0-40% vol), and martensite (0-30% vol), where each phase contributes differently to strength and weldability, achieving a balance between these properties through microstructural design
2Strength
If alloying elements are added to increase tensile strength to at least 950 MPa, then strength is improved, but microstructural stability deteriorates
Solution Approach 1:
The patent precisely controls the content ranges of multiple alloying elements (C: 0.14-0.25% wt, Mn: 1.7-2.5% wt, Si: 0.2-0.7% wt, Cr: 0.05-1% wt, Mo: 0.02-0.5% wt, V: 0.02-0.5% wt, Nb: 0.02-0.1% wt, Ti: 0.005-0.05% wt, B: 0.0005-0.005% wt) to achieve the desired microstructural stability and strength simultaneously
Solution Approach 2:
The patent designs a composite microstructure with four phases (ferrite, residual austenite, bainite, and martensite) in specific volume proportions, where each phase provides different mechanical properties and stability characteristics, achieving overall microstructural stability through their synergistic combination
3Strength
If high strength is achieved through multi-phase microstructure, then tensile strength is improved, but deformability deteriorates
Solution Approach 1:
The patent creates a multi-phase composite microstructure where ferrite (10-80% vol) provides ductility and deformability, while residual austenite (6-20% vol) contributes to strength through TRIP effect, and bainite (0-40% vol) and martensite (0-30% vol) provide strength, achieving a balance between strength and deformability through phase composition
Solution Approach 2:
The patent creates local quality differences within the microstructure by distributing different phases (ferrite, residual austenite, bainite, martensite) in specific volume proportions, where each phase has different mechanical properties, allowing the material to exhibit both high strength and good deformability at the macro level
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 optimized steel achieves a tensile strength of at least 950 MPa, a yield point of at least 500 MPa, and an elongation at break of at least 15%, while maintaining good weldability and deformability, thereby addressing the balance of strength and formability requirements.
Implementation Method 1
the microstructure of which, in relation to its overall structure, comprises a ferrite content of at least 10% vol. and a residual austenite content of at least 6% vol.
Implementation Method 2
Nb is additionally to have a positive effect on the deformability of the steel, since its presence brings with it a refinement of the ferrite grain
Implementation Method 3
Al is used as an oxidising agent when smelting the known steel
Implementation Method 4
Cr is added to the known steel in contents of 0.05-1% wt., in order to reduce the effect of the heat introduced in the area of the weld seam by the welding process
Implementation Method 5
Mo and V contribute to the hardenability of the known steel
Data Source
AI summary
A multi-phase steel including in % wt. C: 0.14-0.25%, Mn: 1.7-2.5%, Si: 0.2-0.7%, Al: 0.5-1.5%, Cr: <0.1%, Mo: <0.05%, Nb: 0.02-0.06%, S: up to 0.01%, P: up to 0.02%, N: up to 0.01% and optionally at least one of Ti, B, and V according to the following stipulation: Ti: up to 0.1%, B: up to 0.002%, V: up to 0.15%, with the remainder iron and unavoidable impurities, wherein the microstructure has at least 10% vol. ferrite and at least 6% vol. residual austenite and the steel has a tensile strength Rm of at least 950 MPa, a yield point ReL of at least 500 MPa and an elongation at break A80 measured in the transverse direction of at least 15%. A method of producing the multi-phase steel.