AHSS Delayed Cracking Prevention During Drawing
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Solution Overview
Problem
Advanced High Strength Steels (AHSS) used in vehicle components are prone to hydrogen-assisted delayed cracking during drawing operations, limiting their formability and leading to material scrap due to the combination of high tensile strength, continuous stress, and hydrogen ion concentration.
Innovation Solution
A method involving the processing of metal alloys with at least 50% iron and additional elements like Si, Mn, B, Cr, Ni, Cu, Al, or C, where the alloy is melted, cooled at a rate of ≤250 K/s, and formed into sheets with specific tensile properties and magnetic phase volumes to achieve improved resistance to delayed cracking by controlling critical draw speed and ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength steel is used to achieve high tensile strength, then strength is improved, but delayed cracking resistance deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the steel alloy by adding specific elements (Ti, Nb, V, B, Al, Mn, Si, Cu, Ni, Cr, Mo) within defined ranges. This modifies the material's microstructure and hardenability, enabling high tensile strength while improving resistance to hydrogen-assisted delayed cracking through controlled phase transformation and grain refinement
Solution Approach 2:
The patent creates a composite microstructure by combining multiple alloying elements that work synergistically. The interaction between these elements produces a complex microstructure with refined grains and controlled phase distribution, achieving both high strength and improved delayed cracking resistance through the combined effects of different mechanisms
2Strength
If high strength steel is used to achieve high tensile strength, then strength is improved, but formability deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters to achieve a balance between strength and formability. By controlling the content of alloying elements and their interactions, the steel achieves high tensile strength while maintaining adequate ductility and formability through controlled microstructure development during processing
3Shape
If drawing operation is performed on high strength steel, then complex geometry is achieved, but hydrogen-assisted delayed cracking occurs
Solution Approach 1:
The patent applies preliminary protective measures by adding specific alloying elements (Ti, Nb, V, B, Al, Mn, Si, Cu, Ni, Cr, Mo) before the drawing operation. These elements pre-condition the steel's microstructure to resist hydrogen embrittlement and delayed cracking that would otherwise occur during subsequent drawing operations, allowing complex geometries to be formed without cracking
Solution Approach 2:
The patent converts the potentially harmful effect of hydrogen during drawing into a beneficial outcome by using specific alloying elements that trap or neutralize hydrogen. The hydrogen that would cause delayed cracking is instead managed through the alloying strategy, allowing the drawing operation to proceed successfully while achieving complex geometries
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 method enhances the resistance to delayed cracking in AHSS, allowing for increased draw ratios and reduced hydrogen-induced fractures, thereby improving the formability and reducing material scrap in vehicle component manufacturing.
Implementation Method 1
cooling at a rate of ≤250 K/s or solidifying to a thickness of ≥2.0 mm and forming an alloy having a Tm and matrix grains of 2 to 10,000 μm
Implementation Method 2
processing said alloy into sheet with thickness ≤10 mm by heating said alloy to a temperature of 650° C. and below the Tm of said alloy and stressing of said alloy
Data Source
AI summary
This invention relates to prevention of delayed cracking of metal alloys during drawing which may occur from hydrogen attack. The alloys find applications in parts or components used in vehicles, such as bodies in white, vehicular frames, chassis, or panels.