Complex Phase Steel Strip Balancing Edge Ductility and Formability
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Solution Overview
Problem
Prior art complex phase steel materials exhibit improved edge ductility but compromise on general ductility parameters like maximum uniform elongation and maximum total elongation, limiting the complexity of shaped articles that can be manufactured through deep drawing and stamping.
Innovation Solution
A high strength hot dip galvanized complex phase steel strip with a specific composition (0.13-0.19% C, 1.70-2.50% Mn, 0.40-1.00% Al, 0.05-0.25% Cr, 0.01-0.05% Nb, and trace amounts of Si, P, and optional elements) and microstructure (8-12% retained austenite, 20-50% bainite, less than 10% martensite, and ferrite) that balances strength and formability, allowing for complex shaped articles without compromising edge ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If complex phase steel materials are used to improve edge ductility, then edge ductility is improved, but general ductility parameters like maximum uniform elongation and maximum total elongation deteriorate
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.13-0.19%, Mn: 1.70-2.50%, Al: 0.40-1.00%, Cr: 0.05-0.25%, Nb: 0.01-0.05%, Si: ≤0.15%) and the microstructural phase parameters (retained austenite: 8-12%, bainite: 20-50%, martensite: <10%, ferrite: balance) to achieve a complex phase steel that simultaneously improves edge ductility and maintains general ductility, resolving the technical contradiction through optimized parameter combinations
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (ferrite, bainite, martensite, and retained austenite) with specific volume percentages. This composite phase structure combines the advantages of each phase: ferrite provides ductility, bainite provides strength, martensite provides hardness, and retained austenite provides work hardening capability through TRIP effect, thereby achieving both improved edge ductility and maintained general ductility
2Strength
If high strength is achieved in complex phase steel, then strength is improved, but formability deteriorates
Solution Approach 1:
The patent changes the parameters by optimizing the balance between strengthening elements (Mn, Cr, Nb for precipitation hardening) and formability elements (Al for TRIP effect, controlled C content), along with precise control of phase distribution parameters, to achieve high strength while maintaining excellent formability suitable for complex shaped articles
Solution Approach 2:
The patent employs a composite microstructure of four phases where each phase contributes different properties: ferrite matrix provides formability and ductility, bainite provides strength, martensite provides hardness, and retained austenite (8-12%) provides work hardening through TRIP effect during deformation, thereby achieving both high strength and good formability
3Stability of the object's composition
If silicon content is increased to stabilize austenite, then austenite stabilisation is improved, but galvanisation processability deteriorates
Solution Approach 1:
The patent extracts silicon from the alloy composition by limiting its content to ≤0.15%, removing the harmful effect of silicon on zinc wettability and galvanisation processability while maintaining austenite stabilisation through alternative mechanisms involving aluminium (0.40-1.00%) and controlled carbon content
Solution Approach 2:
The patent replaces silicon with aluminium as the primary austenite stabilising element. Aluminium, while present in higher quantities (0.40-1.00% vs ≤0.15% Si), does not interfere with galvanisation processability and provides similar or superior austenite stabilisation effects through different mechanisms, making it a more suitable additive for this application
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 steel strip achieves a combination of high strength and formability, with improved elongation and edge ductility, enabling the production of complex shaped articles without necking or cracking, and maintaining edge ductility performance.
Implementation Method 1
Si is traditionally used to effectuate the TRIP effect, due to retardation of carbide formation in the presence of Si which leads to carbon enrichment and, hence, stabilisation of austenite at room temperature
Implementation Method 2
Si is traditionally used to effectuate the TRIP effect, due to retardation of carbide formation in the presence of Si which leads to carbon enrichment and, hence, stabilisation of austenite at room temperature
Implementation Method 3
carbon enrichment and, hence, stabilisation of austenite at room temperature
Implementation Method 4
Manganese also contributes to solid solution strengthening which increases the tensile strength and strengthens the ferrite phase, thus helping to stabilise retained austenite
Implementation Method 5
high strength hot dip galvanised complex phase steel strip
Data Source
AI summary
The invention relates to a high strength hot dip galvanised complex phase steel strip consisting, in mass percent, of the following elements: 0.13-0.19 %C, 1.70- 2.50 %Mn, max 0.15 % Si, 0.40 - 1.00 % Al, 0.05 - 0.25 % Cr, 0.01 - 0.05 % Nb, max 0.10 % P, max 0.004 % Ca, max 0.05 % S, max 0.007 % N, and optionally at least one of the following elements: max 0.50 % Ti, max 0.40 % V, max 0.50 % Mo, max 0.50 % Ni, max 0.50 % Cu, max 0.005 % B, the balance being Fe and inevitable impurities, wherein 0.40 % < Al + Si < 1.05 % and Mn + Cr > 1.90 %, and having a complex phase microstructure, in volume percent, comprising 8-12 % retained austenite, 20 - 50 % bainite, less than 10 % martensite, the remainder being ferrite, as well as to a method of producing the same.