Galvanized TRIP Steel Sheet for Strength and V-Bendability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-strength steel sheets with tensile strength of 980 MPa or more face challenges in achieving both high elongation and V-bendability, as existing techniques fail to adequately enhance both properties simultaneously.
Innovation Solution
The stability of the retained austenite phase is increased by imparting residual compression stress through optimal control of roll diameter, tension, and number of passes during over-aging treatment, combined with precise control of austenite phase enrichment and grain size, resulting in improved elongation and V-bendability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-strength steel sheet with tensile strength of 980 MPa or more is produced, then strength is improved, but elongation and V-bendability deteriorate
Solution Approach 1:
The invention applies parameter changes by controlling the residual stress state of retained austenite through specific over-aging treatment conditions (temperature, time, and applied load). By adjusting these parameters, the retained austenite is transformed into a compressively stressed state, which simultaneously improves both strength and V-bendability. The key parameter change is the residual stress state of the retained austenite phase.
Solution Approach 2:
The invention utilizes a composite microstructure consisting of multiple phases (ferrite, bainite, and retained austenite with compressive residual stress). This composite structure at the microstructural level allows the material to exhibit both high strength and improved V-bendability, as each phase contributes different properties that complement each other.
2Strength
If high-strength steel sheet with tensile strength of 980 MPa or more is produced, then strength is improved, but elongation deteriorates
Solution Approach 1:
The invention applies parameter changes by controlling the residual stress state of retained austenite through specific over-aging treatment conditions (temperature, time, and applied load). By adjusting these parameters, the retained austenite is transformed into a compressively stressed state, which simultaneously improves both strength and V-bendability. The key parameter change is the residual stress state of the retained austenite phase.
Solution Approach 2:
The invention utilizes a composite microstructure consisting of multiple phases (ferrite, bainite, and retained austenite with compressive residual stress). This composite structure at the microstructural level allows the material to exhibit both high strength and improved V-bendability, as each phase contributes different properties that complement each other.
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
This approach results in a high-strength hot-dip galvanized steel sheet with enhanced ductility and V-bendability, making it suitable for automotive applications and offering high industrial value through stable production processes.
Implementation Method 1
a retained (or residual) austenite steel having retained austenite in the steel structure may be known to, despite high strength, exhibit very high elongation by making use of a TRIP effect
Implementation Method 2
when the roll diameter, tension and number of passes in repeated bending during an over-aging (OA) treatment are optimally controlled so as to impart a residual compression stress to the retained austenite phase
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A high-strength hot-dip galvanized steel sheet containing a main component, the steel sheet having at least 40 wt.% of ferrite as a main phase in terms of the volumetric ratio, and 8-60% inclusive of residual austenite, the remaining structure comprising one or more of bainite, martensite, or pearlite. Austenite particles within a range where the average residual stress (sigmaR) thereof satisfies the expression -400MPa<=sigmaR<=200MPa (formula (1)) are present in an amount of 50% or more in the hot-dip galvanized steel sheet. The surface of the steel sheet has a hot-dip galvanized layer containing less than 7 wt.% of Fe, the remainder comprising Zn, Al and inevitable impurities.