Hot-Rolled Al-Coated Steel Sheet With Controlled Coiling Temperature
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods fail to produce coated steel sheets with thicknesses between 1.8 mm and 5 mm that maintain excellent coating adhesion after hot-stamping, and control coating thickness within the targeted range of 10 to 33 μm, while ensuring weldability and productivity.
Innovation Solution
A method involving hot-rolling with controlled coiling temperatures and pickling followed by Al or Al alloy coating through continuous hot-dipping, with specific chemical compositions to minimize intergranular oxidation and ensure coating adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If hot-rolling is used to produce steel sheets with thickness higher than 1.6 mm, then the thickness requirement is met, but the coating adhesion after hot-stamping becomes unsatisfactory
Solution Approach 1:
The invention changes the coiling temperature parameter to a specific range (450-650°C) to control the microstructure and surface properties of the hot-rolled steel sheet, thereby improving coating adhesion while maintaining the ability to produce thick sheets (1.6-5 mm). This parameter optimization resolves the contradiction between thickness and coating adhesion.
2Reliability
If the pickling process is slowed down to improve coating adhesion, then coating adhesion improves, but the control of coating thickness and weldability deteriorates, and productivity is reduced
Solution Approach 1:
The invention changes the coiling temperature parameter to control the surface state and microstructure of the steel sheet before pickling. This allows the pickling process to be optimized for both coating adhesion and productivity, as the pre-conditioned surface requires less aggressive or prolonged pickling to achieve good adhesion, thus maintaining productivity and coating thickness control.
3Reliability
If cold-rolling is used to produce coated steel sheets, then coating adhesion can be maintained, but sheets with thickness between 1.8 mm and 5 mm cannot be produced due to equipment limitations and insufficient flatness
Solution Approach 1:
Instead of using cold-rolling to achieve good coating adhesion (the conventional approach), the invention inverts the sequence by using hot-rolling with controlled coiling temperature to achieve both the required thickness (1.6-5 mm) and good coating adhesion. This eliminates the need for subsequent cold-rolling while maintaining adhesion properties.
4Ease of manufacture
If the coating thickness is not tightly controlled, then the manufacturing process is simpler, but weldability deteriorates and coating thickness falls outside the targeted range of 10-33 μm
Solution Approach 1:
The invention changes the coiling temperature to a controlled range that inherently promotes uniform coating deposition and controls the formation of intermetallic layers during hot-dip coating. This parameter control enables tight coating thickness control (10-33 μm) without excessive process complexity, as the controlled coiling temperature creates more predictable surface conditions for coating.
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
Achieves improved coating adhesion and controlled coating thickness, maintaining weldability and productivity, suitable for producing high-strength steel parts.
Implementation Method 1
hot-rolling the semi-product with a final rolling temperature FRT, so as to obtain a hot-rolled steel product... cooling the hot-rolled steel product down to a coiling temperature Tcoil
Implementation Method 2
pickling the hot-rolled steel substrate
Implementation Method 3
coating the hot-rolled steel substrate with Al or an Al alloy by continuous hot-dipping in a bath
Data Source
AI summary
A method for manufacturing a hot-rolled and coated steel sheet having a thickness between 1.8 mm and 5 mm. The method contains the steps of: providing a semi-product having a composition containing: 0.04%≤C≤0.38%, 0.40%≤Mn≤3%, 0.005%≤Si≤0.70%, 0.005%≤Al≤0.1%, 0.001%≤Cr≤2%, 0.001%≤Ni≤2%, 0.001%≤Ti≤0.2%, Nb≤0.1%, B≤0.010%, 0.0005%≤N≤0.010%, 0.0001%≤S≤0.05%, 0.0001%≤P≤0.1%, Mo≤0.65%, W≤0.30%, Ca≤0.006%, hot-rolling with a final rolling temperature FRT, to obtain a hot-rolled steel product having a thickness between 1.8 mm and 5 mm, then cooling down to a coiling temperature Tcoil satisfying: 450° C.≤Tcoil≤Tcoilmax with Tcoilmax=650−140×fγ, Tcoilmax being expressed in degrees Celsius and fγ designating the austenite fraction just before the coiling, and coiling to obtain a hot-rolled steel substrate, pickling and coating the hot-rolled steel substrate with Al or an Al alloy by continuous hot-dipping in a bath, to obtain a hot-rolled and coated steel sheet containing a hot-rolled steel sheet and an Al or an Al alloy coating, having a thickness between 10 and 33 μm, on each side of the hot-rolled steel sheet.