Cold-Rolled Steel Composition for High Hole Expansion and Bendability
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Solution Overview
Problem
Existing methods for producing wide steel strips with high yield strength and good local formability, such as hole expansion ratio and bendability, are costly and lack process stability, particularly in continuous annealing lines, and often require expensive alloying elements.
Innovation Solution
A cold rolled steel strip with a specific composition and production process involving controlled alloying elements (C, Si, Mn, Al, Ti, Nb) and a continuous annealing method at controlled temperatures and cooling rates to achieve a microstructure of ≥95% ferrite and <5% perlite, cementite, carbides, and carbonitrides, ensuring mechanical properties of 800-950 MPa yield strength, 830-1000 MPa tensile strength, ≥9% total elongation, ≥60% hole expansion ratio, and ≤1.0 bendability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional hot-rolled steel is used, then production cost is lower and production process is simpler, but surface quality is poor and dimensional accuracy is insufficient
Solution Approach 1:
The patent applies parameter changes by transforming the steel production process from hot-rolling to cold-rolling at controlled temperatures (room temperature or slightly above), changing the rolling pressure parameters, and adjusting the composition parameters of the steel alloy to achieve superior surface quality and dimensional accuracy while maintaining production feasibility
Solution Approach 2:
The patent employs composite materials by creating a multi-layer steel structure consisting of a base steel layer and a surface-treated layer with specific compositional characteristics, achieving enhanced surface quality and corrosion resistance through the composite structure formed during the cold-rolling and surface treatment process
2Manufacturing precision
If cold-rolled steel with high surface quality is produced, then surface quality and dimensional accuracy improve, but production cost increases
Solution Approach 1:
The patent optimizes production cost by controlling the temperature parameters during cold-rolling (room temperature to slightly above), adjusting the rolling pressure to minimize energy consumption, and optimizing the chemical composition parameters of the steel alloy to reduce material costs while maintaining high surface quality
Solution Approach 2:
The patent applies self-service by utilizing the natural properties of the steel material during the cold-rolling process, where the material's own elasticity and plasticity are exploited to achieve the desired surface quality without requiring additional complex surface treatment operations, thereby reducing overall production cost
3Strength
If conventional steel production methods are used, then production cost is lower, but corrosion resistance and strength are insufficient
Solution Approach 1:
The patent creates a composite material structure with a base steel layer providing structural strength and a surface layer providing corrosion resistance, achieved through controlled cold-rolling and surface treatment processes that form a protective composite structure enhancing both strength and corrosion resistance
Solution Approach 2:
The patent enhances strength and corrosion resistance by changing the chemical composition parameters of the steel alloy, controlling the temperature and pressure parameters during cold-rolling to optimize microstructure, and adjusting the surface treatment parameters to create a protective surface layer, all while managing production costs through efficient process 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 provides a cost-effective, high-volume production of wide steel strips with improved mechanical properties and process stability, suitable for components requiring high strength and local formability, while minimizing waste and ensuring easy weldability.
Implementation Method 1
the surface quality and dimensional accuracy of the steel slab are improved through cold-rolling
Implementation Method 2
the surface quality and dimensional accuracy of the steel slab are improved through cold-rolling
Data Source
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AI summary
The invention relates to a cold rolled steel strip or sheet having a composition comprising of 0.02 – 0.10 C, 0.05 – 0.5 Si, 0.6 – 1.1 Mn, 0.015 – 1.5 Al, 0.03 – 0.12 Ti, 0.01 –0.06 Nb, where Ti+ Nb is 0.05 – 0.15. The strip or sheet having a Yield strength (Rp0.2) of 800 – 950 MPa, a Tensile strength (Rm) of 830 –1000 MPa, a Total elongation (A80) ≥ 9%, and a hole expansion ratio (λ) ≥ 60 %. The microstructure comprising in vol%: ferrite ≥ 95 %, and perlite, cementite, carbides, nitrides, and/or carbonitrides < 5 %. The bendability (Ri/t) is ≤ 1.0. The invention also relates to a continuous process of producing the strip or sheet.