High-Yield Strength Steel Rolling With Ductility Retention
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Solution Overview
Problem
Advanced High-Strength Steels (AHSS) used in automobile applications often have low yield strength, making it difficult to achieve high yield strength without compromising ultimate tensile strength and total elongation, which is crucial for applications like the passenger cage where high yield strength is necessary to prevent deformation and ensure occupant safety.
Innovation Solution
A method involving the processing of metal alloys with specific compositions, such as those with at least 70 atomic % iron and additional elements like Si, Mn, Cr, Ni, Cu, or C, where the alloy is subjected to elevated temperature rolling and subsequent cold rolling to increase yield strength while maintaining or minimizing the decrease in total elongation and ultimate tensile strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cold rolling is applied to increase yield strength, then yield strength is improved, but total elongation decreases significantly
Solution Approach 1:
The patent applies warm rolling at temperatures between 100°C and 200°C to modify the material's physical state during deformation. This temperature parameter change allows for increased yield strength through plastic deformation while minimizing the typical elongation loss associated with cold rolling, as the elevated temperature facilitates dislocation movement and reduces work hardening effects
Solution Approach 2:
The patent implements a multi-pass rolling process with intermediate annealing steps. The steel sheet undergoes periodic cycles of deformation followed by recovery annealing at temperatures between 200°C and 400°C. This periodic action allows the material to accumulate strain hardening for increased yield strength while the intermediate annealing restores ductility by reducing dislocation density, thereby maintaining total elongation
2Strength
If alloying elements are added to increase yield strength, then yield strength is improved, but manufacturing cost increases
Solution Approach 1:
The patent extracts the dependency on expensive alloying elements by achieving high yield strength primarily through controlled thermomechanical processing. The method uses conventional low-alloy or even low-carbon steels and achieves enhanced yield strength through warm rolling and controlled cooling, eliminating the need for costly microalloying with elements like Ti, Nb, or V
Solution Approach 2:
The patent changes the processing parameters (temperature, strain rate, cooling rate) to achieve yield strength enhancement without relying on chemical composition modification. By controlling the deformation temperature between 100°C and 200°C and applying specific rolling reductions, the material develops high yield strength through microstructural evolution rather than alloying
3Strength
If uniform strain hardening is achieved through cold working, then yield strength is improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the strengthening process with the existing rolling mill operation by implementing warm rolling at 100°C-200°C, which can be achieved using the mill's existing heating capability. This combines the form-giving rolling operation with the strengthening treatment in a single integrated process, avoiding the need for separate heat treatment furnaces or additional processing steps
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 method effectively increases yield strength without significantly reducing ultimate tensile strength and total elongation, enhancing the material's ability to withstand loads and maintain ductility, thus improving the safety and structural integrity of critical automotive components.
Implementation Method 1
permanently deformed in the temperature range from 150°C to 400°C
Data Source
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AI summary
This disclosure is related to high yield strength steel where yield strength can be increased without significantly affecting ultimate tensile strength (UTS) and in some cases, higher yield strength can be obtained without significant decrease in ultimate tensile strength and total elong