Hot Dip Galvanized UHSS Sheets: Gas Cooling for High Flatness
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Solution Overview
Problem
Current methods for producing zinc-coated ultra-high strength steel (UHSS) using water quenching result in distortion and reduced sheet flatness, leading to low roll forming efficiency and incompatibility with continuous galvanizing production lines.
Innovation Solution
A method involving heating a steel sheet to a temperature between 800° C and 950° C, followed by gas cooling at a controlled rate of 2° C/s to 15° C/s, and then hot dip galvanizing to form a zinc coating, while maintaining high flatness and compatibility with continuous galvanizing lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If water quenching is used to harden the steel sheet, then high strength is achieved, but temperature gradients cause distortion and reduced sheet flatness
Solution Approach 1:
The patent changes the cooling medium from water to gas (air), and controls the cooling rate within a specific range (2-15°C/s). This parameter change eliminates the harmful temperature gradients caused by water quenching while maintaining the ability to achieve high strength through controlled martensitic transformation.
Solution Approach 2:
The patent introduces dynamic control of the cooling process by specifying a cooling rate range rather than a fixed value. This allows optimization of both strength and flatness based on specific production requirements, making the process adaptable to different steel compositions and product specifications.
2Strength
If water quenching is used to achieve high strength, then steel strength is improved, but the process becomes incompatible with continuous galvanizing production lines
Solution Approach 1:
The patent changes the cooling method to gas cooling with a controlled cooling rate, which is compatible with the continuous galvanizing process. This allows the steel sheet to be cooled and hardened while maintaining temperature and flatness suitable for subsequent galvanizing operations on a continuous production line.
3Strength
If water quenching is used to harden the steel, then high strength is achieved, but sheet flatness deteriorates leading to low roll forming efficiency
Solution Approach 1:
The patent changes the cooling method to gas cooling with controlled cooling rate (2-15°C/s), which maintains sheet flatness while achieving high strength. This eliminates the need for post-quenching flatness correction operations, thereby improving roll forming efficiency and overall productivity.
4Reliability
If chromium content is increased to improve corrosion resistance and hot dip galvanizability, then coating quality is improved, but manufacturing cost increases
Solution Approach 1:
The patent optimizes the chromium content within a specific range (1.2-6.0 wt.%) to achieve the desired balance between corrosion resistance, hot dip galvanizability, and manufacturing cost. This parameter optimization ensures sufficient performance while avoiding excessive chromium addition that would unnecessarily increase material costs.
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 achieves high flatness in UHSS sheets, improving roll forming efficiency and enabling continuous galvanizing production, while maintaining high strength and toughness through controlled microstructure formation.
Implementation Method 1
heating a steel sheet to a temperature in a predetermined range from 800° C. to 950° C. for a soaking period
Implementation Method 2
cooling the steel sheet using gas cooling having a cooling rate in a predetermined range from 2° C./s to 15° C./s
Implementation Method 3
cooling the steel sheet using gas cooling having a cooling rate in a predetermined range from 2° C./s to 15° C./s to a first predetermined temperature
Implementation Method 4
hot dip galvanizing the steel sheet at the second predetermined temperature to form a zinc coating
Data Source
AI summary
A coated steel sheet includes a steel sheet comprising iron (Fe); carbon (C) in a range from 0.05% to 0.35 wt. %; manganese (Mn) in a range from 0.1% to less than 2 wt. %; chromium (Cr) in a range from 1.2% to 6.0 wt. %; silicon (Si) in a range from 0.01% to less than 0.6 wt. %; aluminum (Al) in a range from 0.5% to 1.3 wt. %; vanadium (V) in a range from 0.01% to 0.5 wt. %; niobium (Nb) in a range from 0.01% to 0.2 wt. %; and titanium (Ti) in a range from 0.01% to 0.3 wt. %. A zinc coating is formed on an outer surface of the steel sheet.