Dual-Phase Steel Substrate for High Strength and Crack Resistance
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Solution Overview
Problem
Cold-rolled flat steel products with high strength tend to form edge cracks, impairing processability and requiring improved weldability, while existing high-strength steels with good formability are costly to produce.
Innovation Solution
A dual-phase steel substrate with a composition of 10-40 vol.% martensite, 30-90 vol.% ferrite, and limited residual austenite, optimized with specific alloying elements like C, Mn, Si, Cr, Ti, and B, to achieve a tensile strength of 750-940 MPa, improved weldability, and enhanced forming properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-strength steel is used to achieve tensile strength of at least 950 MPa, then strength is improved, but edge crack resistance deteriorates and processability is impaired
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.050-0.105%, Si: 0.10-0.60%, Mn: 2.10-2.80%, Cr: 0.20-0.80%, Ti: 0.02-0.10%, B: 0.0005-0.0050%) and microstructural parameters (martensite: 20-70%, residual austenite: up to 8%, ferrite/bainite: remainder) to achieve tensile strength of 950 MPa or more while maintaining edge crack resistance. The controlled alloying and phase distribution resolve the contradiction between high strength and resistance to edge cracking during forming operations.
2Strength
If high-strength steel with significant strength differences between structural constituents is used, then strength is improved, but elastic limit ratio deteriorates and formability is reduced
Solution Approach 1:
The patent employs a composite microstructure consisting of multiple phases (martensite, residual austenite, ferrite, and/or bainite) with specific volume fractions. This composite structure combines the high strength of martensite with the ductility and formability contributions from residual austenite and ferrite, achieving tensile strength ≥950 MPa while maintaining adequate elastic limit ratio and formability for complex shape components.
3Strength
If high-strength steel is used to meet strength requirements, then strength is improved, but weldability deteriorates
Solution Approach 1:
The patent resolves the weldability-strength contradiction through parameter changes in chemical composition, specifically limiting carbon content to 0.050-0.105% and controlling carbon equivalent through balanced alloying (Si: 0.10-0.60%, Mn: 2.10-2.80%, Cr: 0.20-0.80%, Ti: 0.02-0.10%, B: 0.0005-0.0050%). This composition achieves tensile strength of 950 MPa or more while maintaining carbon equivalent levels that ensure good weldability for automotive body construction applications.
Data Source
AI summary
A cold-rolled flat steel product has a tensile strength of 750-940 MPa, a high strength, an improved weldability and optimized shaping properties, and can be produced at low cost. The cold-rolled flat steel product consists of a steel composed, in percent by mass, of C: 0.040-0.100%; Mn: 2.10-2.50%; Si: 0.10-0.40%; Cr: 0.30-0.90%; Ti: 0.020-0.080%, B: 0.0005-0.0020%; N: 0.003-0.010%; Al: up to 0.10%; Ca: up to 0.005%; P: up to 0.025%; S: up to 0.010%; optionally one or more of the following elements: Mo: up to 0.20%; Nb: up to 0.050%; Cu: up to 0.10%; V: up to 0.020%; Ni: up to 0.10%, the remainder being iron and unavoidable impurities, and total content of impurities is limited to at most 0.5% by mass and contents of phosphorus (“P”) and sulfur (“S”) belong to the impurities.