Hot-Rolled Steel Sheet Microstructure for Strength and Shearing
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Solution Overview
Problem
Existing hot-rolled steel sheets lack high strength, high limit fracture sheet thickness reduction ratio, and excellent ductility and shearing properties, which are crucial for vehicle body components to achieve both weight reduction and collision resistance while maintaining end surface accuracy during press forming.
Innovation Solution
A hot-rolled steel sheet with a specific chemical composition and microstructure, including controlled amounts of elements like C, Si, Mn, Ti, Nb, V, and a balanced microstructure of residual austenite, ferrite, pearlite, bainite, and martensite, optimized for high strength, ductility, and shearing properties, with a crystal grain size less than 3.0 µm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional hot-rolled steel plates are used, then manufacturing cost is reduced, but surface quality deteriorates due to heavy scale formation requiring shot blasting
Solution Approach 1:
The patent changes the chemical composition parameters of the steel plate by controlling carbon content (0.05-0.15%), silicon content (0.01-0.05%), and aluminum content (0.01-0.05%). These parameter changes modify the scale formation characteristics during hot rolling, enabling the scale to be easily removed by water blasting instead of requiring shot blasting, thus resolving the contradiction between manufacturing cost and surface quality
2Strength
If high-strength steel plates with tensile strength ≥1320 MPa are produced, then mechanical strength is improved, but surface quality deteriorates due to severe scale formation
Solution Approach 1:
The patent achieves high tensile strength (≥1320 MPa) through specific compositional parameters (C: 0.05-0.15%, Si: 0.01-0.05%, Al: 0.01-0.05%) and controlled cooling rates (5-50°C/s). Simultaneously, these parameter changes modify scale formation to be water-blast removable, resolving the contradiction between mechanical strength and surface quality
3Manufacturing precision
If shot blasting is used to remove scale, then surface quality is improved, but productivity deteriorates due to additional processing time and cost
Solution Approach 1:
The patent creates a scale layer that is intentionally designed to be easily removable by water blasting, a cheap and quick method. The scale forms during hot rolling but can be completely removed by water blasting without requiring expensive and time-consuming shot blasting, thus improving productivity while maintaining surface quality
Data Source
Figure 1~2
AI summary
This hot-rolled steel sheet has a predetermined chemical composition, has a microstructure including, by area%, residual austenite of less than 3.0%, ferrite of 15.0% or more and less than 60.0%, and pearlite of less than 5.0%, in which an entropy value obtained by analyzing an SEM image of the microstructure using a gray-level co-occurrence matrix method is 10.7 or more, an inverse difference normalized value is 1.020 or more, a cluster shade value is -8.0 × 105 to 8.0 × 105, and a standard deviation of an Mn concentration is 0.60 mass% or less, and has a tensile strength of 980 MPa or more.