Press-Hardened Steel Processing Without Coatings or Descaling
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Solution Overview
Problem
Current methods for forming press-hardening steel components require pre-applied coatings for oxidation avoidance and subsequent descaling operations, which can be cumbersome and inefficient, and aim to improve strength, ductility, and fracture resistance while maintaining high strength-to-weight ratios.
Innovation Solution
A method involving a multi-zone furnace for austenitizing steel alloy blanks with controlled temperature and gas flow rates, followed by stamping and quenching to form press-hardened steel components without pre-applied coatings, utilizing nitrogen-containing gases and specific heating and cooling rates to achieve desired microstructures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If pre-applied coatings are used for oxidation avoidance during hot stamping, then oxidation resistance is improved, but process complexity and manufacturing time increase due to additional coating and descaling operations
Solution Approach 1:
The patent removes the coating layer from the process by using a controlled atmosphere furnace that prevents oxidation through nitrogen gas protection rather than protective coatings. This extracts the harmful element (coating) while maintaining its protective function through atmospheric control.
Solution Approach 2:
The patent employs a nitrogen-containing atmosphere in the furnace to create an inert environment that prevents oxidation of the steel blank during heating and forming. This inert atmosphere replaces the need for protective coatings while effectively preventing harmful oxidation.
2Strength
If high cooling rates above 27 K/s are used to form martensitic structure, then strength is improved, but ductility and fracture resistance deteriorate
Solution Approach 1:
The patent applies different cooling rates to different regions of the steel component during forming. By controlling the cooling rate locally, the process achieves martensitic structure in regions requiring high strength while maintaining slower cooling rates in regions where ductility and fracture resistance are prioritized.
Solution Approach 2:
The patent uses dynamic control of the forming and cooling process, where the cooling rate is adjusted during the forming operation. The process transitions from high cooling rates for strength-critical areas to lower cooling rates for ductility-critical areas, optimizing both strength and fracture resistance through dynamic parameter adjustment.
3Object-affected harmful factors
If multiple process steps including coating application and descaling are used, then oxidation protection is achieved, but productivity decreases due to extended manufacturing time
Solution Approach 1:
The patent combines the heating, oxidation protection, and forming operations into a single integrated process step using a controlled atmosphere furnace. This merging eliminates separate coating application and descaling steps, maintaining oxidation protection while significantly improving manufacturing efficiency.
Solution Approach 2:
The patent maintains continuous protection against oxidation throughout the entire heating and forming process by using a nitrogen atmosphere that persists for the duration of the operation. This continuous protection eliminates the need for intermittent coating applications and descaling operations, improving productivity while maintaining oxidation resistance.
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 eliminates the need for pre-applied coatings and descaling, achieving high-strength press-hardened steel components with enhanced strength, ductility, and fracture resistance, suitable for various industrial applications, including automotive and aerospace sectors.
Implementation Method 1
austenitizing a steel alloy blank to form a heated blank using a furnace having two or more zones
Implementation Method 2
The austenitization is often followed by pressing and quenching of the sheet steel using dies. For example, in direct processes, the press-hardening steel components may be formed and pressed simultaneously between dies that are also configured to quench the steel sheet. In the instance of indirect processes, the press-hardening steel components may be cold-formed to form an intermediate partial shape that is then subject to austenitization and subsequently pressing and quenching. In each instance, the quenching of the press-hardening steel components often transforms microstructures from austenite to martensite
Implementation Method 3
Many processes for forming press-hardening steel components include the austenitization of a sheet steel blank using a furnace. For example, austenitization may occur at temperatures greater than or equal to about 880° C. to less than or equal to about 950° C.
Implementation Method 4
the quenching of the press-hardening steel components often transforms microstructures from austenite to martensite, and the quenching includes using differential cooling to adjust the strength and elongation properties of the press-hardening steel components
Implementation Method 5
the quenching includes using differential cooling to adjust the strength and elongation properties of the press-hardening steel components. For example, cooling rates above 27 K/s in a boron-manganese steel (e.g., 22MnB5) often leads to the formation of a martensitic structure, while lower cooling rates force the formation of a more ductile microstructure with lower strength, such as bainite and ferrite-pearlite
Data Source
AI summary
A method for preparing a press-hardened steel component is provided. The method includes forming a heated blank by heating a steel alloy blank to a first temperature in a first zone of a furnace having two or more zones, and after the heating of the steel alloy blank to the first temperature, heating the steel alloy blank to a second temperature in a second zone of the furnace. The second temperature is greater than the first temperature. The first zone has a first flow rate for a protective gas, and the second zone has a second flow rate for the protective gas that is greater than the first flow rate. The method further includes stamping and quenching the heated blank at a constant rate to a temperature between a martensite finish temperature of the steel alloy defining the steel alloy blank and room temperature to form the press-hardened steel component.