Multiphase Hot-Rolled Steel Composition for Formable 1000 MPa Sheet
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Solution Overview
Problem
Existing advanced high strength steels (AHSS) face challenges such as tool wear, shear fracture, edge cracking, welding difficulties, and high production costs during stamping and forming, along with issues related to alloy elements like carbon, silicon, and aluminum affecting surface quality and weldability, limiting design flexibility and manufacturing uncertainty.
Innovation Solution
A hot rolled, complex metallographic structured steel sheet with a specific composition and microstructure, including elements like carbon, manganese, silicon, and molybdenum, and a multi-phase microstructure of bainite, martensite-austenite, and ferrite, which enhances forming performance, weldability, and durability without boron addition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength steel is used to improve vehicle durability and crashworthiness, then strength and weight targets are met, but tooling wear, shear fracture, and edge cracking occur during stamping and forming
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (carbon: 0.15-0.30%, silicon: 0.01-1.00%, aluminum: 0.01-1.00%, manganese: 1.50-3.50%, boron: 0.0005-0.0100%) and microstructure parameters (bainite: 15-45% by volume, martensite+austenite: 5-35% by volume, tempered and non-tempered martensite: <15% by volume, ferrite: remainder) to achieve tensile strength >1000 MPa while eliminating tooling wear and forming defects
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (bainite, martensite, austenite, and ferrite) in specific proportions to achieve both high strength and improved formability. This multi-phase composite structure resolves the contradiction by combining the strength benefits of martensite with the formability benefits of softer phases
2Strength
If boron is added to achieve high strength, then tensile strength increases, but weldability deteriorates and manufacturing uncertainty increases
Solution Approach 1:
The patent optimizes the boron content parameter to a narrow range (0.0005-0.0100%) to achieve the necessary hardenability and strength while minimizing the negative impact on weldability. This precise parameter control allows the steel to meet high strength targets without the excessive boron content that causes welding difficulties
3Weight of moving object
If high strength steel is used to reduce product weight, then fuel efficiency improves, but production costs increase due to hot-stamping and high temperature press forming
Solution Approach 1:
The patent changes the material parameters to achieve high strength through controlled composition and microstructure rather than through expensive processing. The specific alloying strategy and microstructure control enable the steel to be formed at lower temperatures, eliminating the need for costly hot-stamping and high temperature press forming operations
4Strength
If carbon, silicon, and aluminum are increased to achieve high strength, then tensile strength improves, but surface quality deteriorates
Solution Approach 1:
The patent optimizes the parameters of carbon (0.15-0.30%), silicon (0.01-1.00%), and aluminum (0.01-1.00%) to achieve the necessary strength while controlling surface quality. By carefully balancing these compositional parameters and controlling the microstructure, the patent achieves high strength without the surface defects that result from excessive alloying
Data Source
AI summary
A hot rolled, ultra-high strength, complex metallographic structured or multi-phase structured steel that improves formability during stamping or forming process, while possessing one or more of the following properties: excellent castability, rollability and coatability, excellent structural performance, excellent stretch formability, excellent stretch flangeability, excellent dent resistance, excellent durability, excellent impact performance, excellent intrusion and crash resistance without the purposeful addition of boron.