Annular Hot-Stamping Blank With Emissivity-Tuned Thin Sheet
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Solution Overview
Problem
When producing structural members with integrated steel sheets of varying thicknesses, the faster cooling of thinner sheets leads to uneven hardenability, resulting in reduced shock absorption performance, torsion, and dimensional accuracy, particularly in annular shapes.
Innovation Solution
A blank for hot stamping comprising multiple steel sheets, where a first steel sheet with the smallest thickness has higher emissivity than a second steel sheet, ensuring quicker heating and longer retention in the austenite zone, thereby improving hardenability and uniformity across the member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple steel sheets with different thicknesses are joined to form an annular blank for hot stamping, then integration of members is achieved and productivity is improved, but the thinner steel sheet cools faster causing uneven hardenability and deterioration of mechanical properties
Solution Approach 1:
The patent applies local quality by providing the thinner first steel sheet with a surface-treated film having higher emissivity (60% or more) compared to the second steel sheet. This localized modification of thermal properties compensates for the thinner sheet's faster cooling rate, ensuring uniform hardenability across different thickness regions while maintaining the integrated annular structure's productivity benefits
2Weight of moving object
If the thinner steel sheet is used in the annular blank, then weight reduction and material efficiency are achieved, but the faster cooling rate causes ferrite transformation before shaping, reducing shock absorption performance
Solution Approach 1:
The patent changes the thermal parameter (emissivity) of the thinner steel sheet by applying a surface-treated film with emissivity of 60% or more. This parameter modification increases radiative heat absorption during heating and reduces cooling rate during quenching, preventing premature ferrite transformation and maintaining martensitic structure for adequate shock absorption performance in weight-reduced thinner sections
3Loss of time
If the blank is heated quickly to austenite temperature, then heating time is reduced and productivity is improved, but the thinner steel sheet may cool too quickly after heating, causing uneven microstructure
Solution Approach 1:
The patent applies local quality by selectively treating only the thinner first steel sheet with a high-emissivity surface film (emissivity ≥60%). This localized treatment accelerates heating response in the thinner section during the quick heating process, ensuring it reaches austenite temperature uniformly with thicker sections, while also controlling its cooling rate to prevent microstructure non-uniformity
Solution Approach 2:
The patent modifies the thermal radiation parameter (emissivity) of the thinner steel sheet to optimize both heating and cooling phases. The high-emissivity film enables faster heat absorption during rapid heating to austenite temperature, and controls heat loss during subsequent quenching, maintaining microstructure uniformity throughout the hot stamping cycle
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
Enhances the performance of structural members by ensuring uniform hardness and reducing torsion and dimensional inaccuracies, particularly in large annular shapes, by maintaining the austenite phase during shaping.
Implementation Method 1
the surface of the steel sheet provided with the surface-treated film is increased in emissivity and has higher heat transfer effect through radiation
Implementation Method 2
quenching the blank by holding the blank in the press tooling for heat dissipation (rapid cooling)
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A blank (20, 20A) for hot stamping includes multiple steel sheets. The multiple steel sheets are disposed to form an annular shape in plan view of the blank (20, 20A) and joined to each other. The multiple steel sheets include a first steel sheet (21) and a second steel sheet (22). The first steel sheet (21) has a smallest sheet thickness (tmin) among the multiple steel sheets. The second steel sheet (22) has a sheet thickness larger than the sheet thickness (tmin) of the first steel sheet (21). The first steel sheet (21) is configured so that an emissivity of at least one of both surfaces thereof is higher than an emissivity of both surfaces of the second steel sheet (22).