High-Strength Steel Sheet Texture Control for Rigidity
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Solution Overview
Problem
Current methods for producing high-strength steel sheets with tensile strength of 780 MPa or more and high Young's modulus struggle to achieve excellent deep drawability and stretch flangeability while maintaining cost-effectiveness, often requiring expensive elements and failing to provide uniform rigidity in all directions.
Innovation Solution
A high-strength steel sheet production method involving a chemical composition with controlled amounts of Nb and V, hot rolling at high coiling temperatures, and subsequent cold rolling to develop α-fiber and γ-fiber textures, followed by annealing to optimize microstructure and Young's modulus in all directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the thickness of steel sheets is reduced to increase strength, then weight of automobile bodies is reduced, but rigidity of vehicle body deteriorates
Solution Approach 1:
The patent changes the material parameters by increasing the Young's modulus of the steel sheet through controlled crystal orientation (texture). By adjusting the manufacturing process to achieve specific texture characteristics (higher Young's modulus in rolling direction and transverse direction), the patent enables thin steel sheets to maintain high rigidity while reducing weight
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite and martensite phases with specific area ratios (ferrite: 50-90%, martensite: 10-50%). This multi-phase composite structure provides both high strength and high Young's modulus, resolving the contradiction between weight reduction and rigidity maintenance
2Strength
If anisotropy is given to crystal orientation to increase Young's modulus in a specific direction, then Young's modulus in that direction is increased, but Young's modulus in other directions remains insufficient for multi-directional loads
Solution Approach 1:
The patent applies local quality by creating different texture characteristics in different directions. Specifically, it achieves higher Young's modulus in the rolling direction (through {100} texture) and simultaneously maintains high Young's modulus in the transverse direction (through {110} texture), allowing the material to respond appropriately to loads from various directions while maintaining overall structural integrity
3Strength
If the strength of steel sheet is increased, then tensile strength is increased, but formability deteriorates
Solution Approach 1:
The patent uses a composite microstructure of ferrite and martensite phases. The ferrite phase (50-90% area ratio) provides excellent formability and ductility, while the martensite phase (10-50% area ratio) provides high strength. This composite structure enables the steel sheet to achieve tensile strength of 780 MPa or more while maintaining good formability
Solution Approach 2:
The patent creates local quality differences within the microstructure by controlling the distribution and characteristics of ferrite and martensite phases. The ferrite regions provide ductility for forming operations, while the martensite regions provide strength, allowing the material to exhibit both high strength and good formability simultaneously
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 method produces steel sheets with tensile strength of 780 MPa or more, high Young's modulus, and excellent deep drawability and stretch flangeability, improving automotive body rigidity and reducing weight, thereby enhancing fuel efficiency.
Implementation Method 1
cause most of interstitial elements C and N to precipitate as carbides or nitrides
Implementation Method 2
subjecting the steel sheet to hot rolling with a finisher delivery temperature from 850° C. to 1000° C. and then coiling the steel sheet at a coiling temperature of 500° C. to 800° C. to develop α-fiber and γ-fiber textures
Implementation Method 3
subjecting the steel sheet to cold rolling at a rolling reduction of 40% or more to develop α-fiber and γ-fiber textures
Implementation Method 4
subjecting the steel sheet to annealing to have a ferrite single-phase microstructure
Data Source
AI summary
A steel sheet has a microstructure that contains ferrite in an area ratio of 20% or more, martensite in an area ratio of 5% or more, and tempered martensite in an area ratio of 5% or more. The ferrite has a mean grain size of 20.0 μm or less. An inverse intensity ratio of γ-fiber to α-fiber in the ferrite is 1.00 or more and an inverse intensity ratio of γ-fiber to α-fiber in the martensite and the tempered martensite is 1.00 or more.