Retained Austenite Steel Sheet Carbon Gradient Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Retained austenite steel sheets face challenges in achieving high elongation, V-bendability, and press-forming stability due to temperature dependence and mixed structures, which affect their performance in vehicle body structures.
Innovation Solution
The solution involves controlling the carbon concentration gradient and grain size distribution of the retained austenite phase to enhance its stability and uniform dispersion, ensuring high elongation, V-bendability, and press-forming stability across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the C concentration of austenite is increased to ensure a high fraction of retained austenite phase, then elongation is improved, but V-bendability deteriorates due to mixed structure
Solution Approach 1:
The patent applies local quality by creating distinct regions with different C concentration gradients. Small-diameter crystal grains have a Cgb/Cgc ratio of 1.05-1.20 while large-diameter crystal grains have a Cgb/Cgc ratio of 1.02-1.15. This local differentiation allows small grains to provide stability for elongation while large grains provide uniformity for V-bendability, resolving the contradiction between these two properties.
Solution Approach 2:
The patent creates a composite microstructure consisting of two types of crystal grains with different C concentration gradient characteristics. The small-diameter grains (≤10μm) with higher C concentration gradients provide TRIP effect for elongation, while large-diameter grains (>10μm) with lower C concentration gradients provide structural uniformity for V-bendability. This composite approach allows both properties to coexist.
2Stability of the object's composition
If TRIP steel sheet is used to achieve high strength and high elongation, then elongation is improved, but press-forming stability deteriorates due to temperature dependence
Solution Approach 1:
The patent changes the C concentration gradient parameters differently for small and large crystal grains. Small grains have Cgb/Cgc≥1.05 providing strong TRIP effect at lower temperatures, while large grains have Cgb/Cgc≥1.02 providing stable transformation at higher temperatures. This parameter differentiation ensures press-forming stability across the temperature range from 25°C to 150°C while maintaining high elongation.
3Stability of the object's composition
If uniform structure is created to enhance local ductility, then elongation is improved, but V-bendability deteriorates due to mixed structure
Solution Approach 1:
The patent applies local quality by creating distinct regions with different C concentration gradients. Small-diameter crystal grains have a Cgb/Cgc ratio of 1.05-1.20 while large-diameter crystal grains have a Cgb/Cgc ratio of 1.02-1.15. This local differentiation allows small grains to provide stability for elongation while large grains provide uniformity for V-bendability, resolving the contradiction between these two properties.
Solution Approach 2:
The patent creates a composite microstructure consisting of two types of crystal grains with different C concentration gradient characteristics. The small-diameter grains (≤10μm) with higher C concentration gradients provide TRIP effect for elongation, while large-diameter grains (>10μm) with lower C concentration gradients provide structural uniformity for V-bendability. This composite approach allows both properties to coexist.
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 approach results in steel sheets with improved elongation, V-bendability, and press-forming stability that are not dependent on temperature changes during press forming, making them suitable for vehicle body structures.
Implementation Method 1
a TRIP (Transformation Induced Plasticity) steel sheet containing a retained austenite phase exhibits high strength and high elongation due to the TRIP effect
Data Source
Figure 1~3
AI summary
A steel sheet is provided, including: as chemical components, by mass%, 0.05% to 0.35% of C; 0.05% to 2.0% of Si; 0.8% to 3.0% of Mn; 0.01% to 2.0% of Al; equal to or less than 0. 2% of P; equal to or less than 0.05% of S; equal to or less than 0.01% ofN; and the balance including iron and inevitable impurities, wherein an area ratio of equal to or higher than 50% of a total of a ferrite phase, a bainite phase, and a tempered martensite phase is contained, an area ratio of equal to or higher than 3% of a retained austenite phase is contained, and crystal grains of the retained austenite phase having a number ratio of equal to or higher than 50% satisfy Expression 1, assuming that a carbon concentration at a position of center of gravity is Cgc and a carbon concentration at a grain boundary is Cgb.