Multi-phase Steel Alloy Process Window Expansion
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Solution Overview
Problem
Current alloy concepts for multiphase steels have a narrow process window, making it difficult to achieve uniform mechanical properties across varying sheet thicknesses and widths during continuous annealing, leading to inefficiencies and increased waste in steel production.
Innovation Solution
A new alloy composition with specific weight percentages of C, Si, Mn, Cr, Al, Nb, N, S, and P, combined with micro-alloying using niobium, expands the process window for continuous annealing, allowing for consistent mechanical properties across different strip cross-sections and thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If current alloy concepts for multiphase steels are used, then the steel achieves required strength levels, but the process window for continuous annealing is narrow, making it difficult to achieve uniform mechanical properties across varying sheet thicknesses and widths
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the steel alloy. Specifically, it limits carbon content to 0.075-≤0.105%, silicon to 0.200-≤0.300%, manganese to 1.000-≤2.000%, chromium to 0.280-≤0.480%, and adds niobium micro-alloying at ≥0.005 to ≤0.025%. These compositional parameter changes widen the annealing process window, enabling uniform mechanical properties across varying sheet thicknesses and widths during continuous annealing.
2Strength
If the alloy composition is optimized for high strength, then tensile strength reaches 580-900 MPa, but yield ultimate ratio increases above 67%, reducing formability
Solution Approach 1:
The patent resolves this contradiction through parameter changes in alloy composition. By limiting carbon to 0.075-≤0.105% and silicon to 0.200-≤0.300%, while adding niobium micro-alloying (≥0.005 to ≤0.025%), the steel achieves tensile strength of 580-900 MPa with yield ultimate ratio below 67%. This compositional parameter optimization enables both high strength and good formability.
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (ferrite, martensite, bainite, and residual austenite) through controlled alloying. This multiphase composite structure, achieved by combining specific amounts of C, Si, Mn, Cr, and Nb, provides both high strength and low yield ultimate ratio, resolving the contradiction between strength and formability.
3Strength
If carbon content is increased to improve strength, then tensile strength increases, but weldability deteriorates due to increased carbon equivalent
Solution Approach 1:
The patent applies parameter changes by optimizing the carbon content to a narrow range of 0.075-≤0.105%, which is lower than conventional high-strength steels. This reduced carbon parameter, combined with niobium micro-alloying (≥0.005 to ≤0.025%), achieves tensile strength of 580-900 MPa while maintaining low carbon equivalent for improved 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 widened process window ensures more reliable and homogeneous mechanical properties in continuously annealed hot or cold strips, enabling the production of stress-optimized components with varying thicknesses and strengths, while improving weldability and reducing production costs.
Implementation Method 1
extreme grain refinement is caused by a delayed re-crystallization or by precipitations of micro-alloy elements
Implementation Method 2
dual phase microstructure and a yield strength ratio of less than 67% with which the process window for the continuous annealing of hot and cold rolled strips can be widened
Data Source
AI summary
A high-strength multi-phase steel having tensile strengths of no less than 580 MPa, preferably with a dual-phase structure for a cold-rolled or hot-rolled steel strip having improved forming properties, in particular for lightweight vehicle construction is disclosed, containing the following elements (contents in % by mass): C 0.075 to ≤0.105; Si 0.200 to ≤0.300; Mn 1.000 to ≤2.000; Cr 0.280 to ≤0.480; Al 0.10 to ≤0.060; P ≤0.020; Nb ≥0.005 to ≥0.025; N ≥0.0100; S ≥0.0050; the remainder iron, including conventional steel-accompanying elements not mentioned above.