Plated Steel Sheet Composition for Strength and Workability
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Solution Overview
Problem
Existing plated steel sheets require complex manufacturing methods to achieve high strength and workability, leading to unstable production and room for improvement in strength and workability.
Innovation Solution
A plated steel sheet composition comprising C, Si, Mn, Cr, Ti, B, P, S, and Al, with specific microstructures and controlled cooling rates, allowing for easier manufacturing and improved strength and workability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If complex manufacturing methods with multiple temperature ranges are used, then high strength and workability are achieved, but production stability deteriorates and manufacturing complexity increases
Solution Approach 1:
The patent specifies precise compositional parameters (C: 0.15-0.25%, Si: 0.80-2.20%, Mn: 1.50-2.80%, Cr: 0.15-1.50%, Ti: 0.012-0.100%, B: 0.0015-0.0100%) and microstructural parameters (retained austenite ≥5 vol%, bainite+tempered martensite ≤95 area%) to achieve high strength and workability through material composition rather than complex process control
Solution Approach 2:
The patent replaces complex, costly manufacturing processes with a simpler approach using specific alloying elements and basic heat treatment, making production more stable and accessible
2Strength
If complex manufacturing methods with multiple temperature ranges are used, then high strength and workability are achieved, but production stability deteriorates
Solution Approach 1:
The patent shifts control from complex process parameters (multiple temperature ranges, cooling rates) to material composition parameters and simple microstructural targets, improving production stability while maintaining high strength
Solution Approach 2:
Instead of controlling complex cooling processes to achieve desired properties, the patent specifies the target microstructure (retained austenite ≥5 vol%, bainite+tempered martensite ≤95 area%) and compositional ranges, allowing simpler process control to achieve the same results
3Strength
If conventional plated steel sheet compositions are used, then high strength is achieved, but workability deteriorates
Solution Approach 1:
The patent creates a composite microstructure containing multiple phases (retained austenite ≥5 vol%, bainite, tempered martensite, polygonal ferrite) with specific compositional elements (C, Si, Mn, Cr, Ti, B) that collectively provide both high strength and high workability
Solution Approach 2:
The patent uses Ti and B as microalloying elements that locally strengthen the steel through precipitation hardening and grain refinement, enabling high strength without sacrificing overall ductility and workability
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 plated steel sheet achieves high tensile strength (1150 MPa or more), high yield stress (850 MPa or more), high elongation (14% or more), and high hole expansion ratio (30% or more), contributing to vehicle weight reduction and improved formability.
Implementation Method 1
the steel sheet has a metal microstructure in which: a total of bainite and tempered martensite account for 95 area% or less; retained austenite accounts for 5 vol% or more
Implementation Method 2
a manufacturing method is strictly controlled, especially the reheating and subsequent cooling after hot rolling
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A plated steel sheet including a steel sheet and a plating layer disposed on a surface of the steel sheet, the steel sheet having a tensile strength of 1150 MPa or more, wherein the steel sheet included in the plated steel sheet has a predetermined composition and a metal microstructure in which a total of bainite and tempered martensite accounts for 95 area% or less, retained austenite accounts for 5 vol% or more, a total of polygonal ferrite and bainitic ferrite accounts for 5 area% or less, and a balance of the metal microstructure accounts for 5 area% or less.