Multiphase Steel Composition for Strength-Ductility Balance
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Solution Overview
Problem
Existing low-cost multiphase steels struggle to achieve high strength, high yield ratio, high elongation, high hole expansion, and good bending performance simultaneously, particularly for automotive chassis and suspension systems, due to the challenges of balancing alloying element additions and microstructural uniformity.
Innovation Solution
A low-carbon multiphase steel composition with controlled amounts of manganese, chromium, titanium, and silicon, combined with a specific microstructure and manufacturing process, including controlled cooling rates and rolling temperatures, to achieve a microstructure of ferrite and lower bainite with fine carbide precipitation, minimizing precious alloying elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-strength phase components (martensite and bainite) are added to ensure strength, then tensile strength is improved, but yield ratio deteriorates due to insufficient plasticity
Solution Approach 1:
The patent applies local quality by creating a dual-phase microstructure where hard phases (bainite and martensite) and soft phases (ferrite) coexist in specific proportions and distributions. The hard phases provide tensile strength while the soft ferrite phases provide plasticity, and their localized arrangement ensures both strength and high yield ratio simultaneously
Solution Approach 2:
The patent uses composite materials principle by combining multiple phase components (ferrite, bainite, and martensite) in a multiphase steel structure. This composite microstructure allows the steel to exhibit both high tensile strength from the hard phases and high yield ratio from the synergistic interaction between hard and soft phases
2Stability of the object's composition
If softer phase components (ferrite) are added to ensure plasticity and elongation, then elongation is improved, but tensile strength deteriorates
Solution Approach 1:
The patent applies local quality by creating a dual-phase microstructure where hard phases (bainite and martensite) and soft phases (ferrite) coexist in specific proportions and distributions. The hard phases provide tensile strength while the soft ferrite phases provide plasticity, and their localized arrangement ensures both strength and high yield ratio simultaneously
Solution Approach 2:
The patent uses composite materials principle by combining multiple phase components (ferrite, bainite, and martensite) in a multiphase steel structure. This composite microstructure allows the steel to exhibit both high tensile strength from the hard phases and high yield ratio from the synergistic interaction between hard and soft phases
3Stability of the object's composition
If a large amount of alloying elements (niobium, molybdenum, vanadium, nickel, aluminum) are added to achieve precipitation reinforcement, then yield ratio and elongation are improved, but manufacturing cost deteriorates
Solution Approach 1:
The patent applies this principle by replacing expensive precious alloying elements (niobium, molybdenum, vanadium, nickel) with cheaper alternatives (manganese, silicon, titanium, chromium) that can achieve similar or better strengthening effects through different mechanisms, significantly reducing manufacturing cost while maintaining or improving performance
Solution Approach 2:
The patent uses parameter changes by optimizing the chemical composition parameters within specific ranges (C: 0.03-0.07%, Si: 0.10-0.50%, Mn: 1.30-1.90%, Cr: 0.20-0.50%, Ti: 0.07-0.14%) to achieve the desired microstructure and properties without relying on expensive alloying elements, thereby reducing cost while maintaining high yield ratio
4Ease of manufacture
If low-carbon composition (carbon content less than 0.1%) is used to ensure weldability, then weldability is improved, but tensile strength deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling carbon content within a specific range (0.03-0.07%) and optimizing the interactions with other alloying elements (Si, Mn, Cr, Ti) to achieve both low carbon equivalent for good weldability and high tensile strength through synergistic strengthening mechanisms
Solution Approach 2:
The patent uses composite materials principle by combining multiple strengthening mechanisms (solid solution strengthening from Si and Mn, precipitation strengthening from Ti, and phase transformation strengthening) to compensate for the limited strength contribution from low carbon content, achieving high tensile strength while maintaining excellent weldability
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 a steel plate with tensile strength ≥780 MPa, yield strength ≥680 MPa, elongation ≥15%, hole expansion ratio ≥85% (punched hole) or ≥115% (reamed hole), and 180° bending performance without cracking, while maintaining low production costs.
Implementation Method 1
a low-carbon multiphase steel composition with controlled amounts of manganese, chromium, titanium, and silicon
Implementation Method 2
combined with a specific microstructure and manufacturing process, including controlled cooling rates and rolling temperatures, to achieve a microstructure of ferrite and lower bainite with fine carbide precipitation
Data Source
AI summary
Disclosed are a low-cost ultra-high-strength multiphase steel plate/steel strip and its manufacturing method. Said steel plate/steel strip comprises the following components in percentage by weight: 0.03 to 0.07% of C, 0.1 to 0.5% of Si, 1.3 to 1.9% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, 0.01 to 0.05% of Al, 0.2 to 0.5% of Cr, 0.07 to 0.14% of Ti, less than 0.03% of (Ni+Nb+Mo+V), and the balance being Fe and other inevitable impurities; and Mn+1.5Cr+5 (Ti+Al+Cu)+10(Mo+Ni)+20(Nb+V)<3.0; Mn+2Cr+4Ti+4Nb+4V+4Mo—Si/3+2C≤3.0. The steel plate is mainly used for the manufacturing of automotive chassis and suspension system parts.