Layered Steel Sheet Structure for Thin-Gauge Bending Resistance
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Solution Overview
Problem
Existing methods for improving bending resistance in steel sheets, particularly in thin-gauge applications, face challenges in achieving high hardness without compromising bending resistance, and often require shape modifications or heat treatment that are not feasible in all applications.
Innovation Solution
A steel sheet with a hard layer and an inner layer, where the hard layer has an average micro-Vickers hardness of 400 HV or more and less than 800 HV, and the inner layer has a hardness 50 HV or more lower than the hard layer, along with a screw dislocation density of 2.0×10^13 m/m^3 or more, optimized through integrated hot rolling and annealing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the thickness of steel sheet is reduced to achieve weight reduction, then the weight decreases, but the bending resistance deteriorates
Solution Approach 1:
The patent applies local quality by creating a two-layer steel sheet structure where the surface layer has different properties (higher strength, lower elongation) than the base layer. This allows the thin steel sheet to maintain high bending resistance at the surface while keeping the overall weight reduced through thin gauge design.
Solution Approach 2:
The patent employs composite materials by combining two different steel grades in a single sheet structure. The surface layer uses high-strength steel (e.g., DP1000 or higher) while the base layer uses lower-strength steel with better formability, creating a composite structure that achieves both weight reduction and maintained bending resistance.
2Strength
If the strength of steel sheet is increased to improve bending resistance, then the bending resistance improves, but the formability deteriorates
Solution Approach 1:
The patent applies local quality by creating a two-layer steel sheet structure where the surface layer has different properties (higher strength, lower elongation) than the base layer. This allows the thin steel sheet to maintain high bending resistance at the surface while keeping the overall weight reduced through thin gauge design.
Solution Approach 2:
The patent employs composite materials by combining two different steel grades in a single sheet structure. The surface layer uses high-strength steel (e.g., DP1000 or higher) while the base layer uses lower-strength steel with better formability, creating a composite structure that achieves both weight reduction and maintained bending resistance.
3Strength
If heat treatment is applied to improve bending resistance, then the bending resistance improves, but the process complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-forming the two-layer structure during the steel sheet manufacturing process itself, rather than requiring subsequent heat treatment or processing steps. The different steel grades are bonded together in a controlled rolling process, achieving the desired mechanical properties without additional complex post-processing.
Data Source
AI summary
There is provided a steel sheet including an inner layer and a hard layer formed on one or both surfaces of the inner layer, wherein each content of C and Mn in the hard layer is more than each content of C and Mn in the inner layer, a thickness of the hard layer is 20 μm or more and a total of the thickness of the hard layer is ⅖ or less of the entire sheet thickness, an average micro-Vickers hardness of the hard layer is 400 HV or more and less than 800 HV, an average micro-Vickers hardness of the inner layer is 350 HV or more and is 50 HV or more smaller than a hardness of the hard layer, and a screw dislocation density of the inner layer is 2.0×1013 m/m3 or more.