Hot Rolled Steel Sheet Scale Adhesion via Layer Control
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Solution Overview
Problem
Hot rolled steel sheets face issues with scale adhesion during manufacturing and processing, leading to surface deterioration and corrosion, particularly when the scale exfoliates, which is not adequately addressed by existing methods that rely on controlling cooling rates and adding costly elements like Cu and Ni.
Innovation Solution
A hot rolled steel sheet with a chemical composition that includes a scale layer structure composed of wustite, magnetite, and hematite, where the thickness fractions of hematite and magnetite are controlled to be below a certain fraction of the total scale thickness, enhancing adhesion without the need for additional alloying elements like Cu, Cr, and Ni.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Cu, Ni, or Si elements are added to the steel composition to improve scale adhesion through anchoring effect, then scale adhesion improves, but manufacturing cost increases
Solution Approach 1:
The invention changes the chemical composition parameters by strictly limiting Cu to 0.10% or less, Cr to 0.10% or less, and Ni to 0.10% or less, thereby eliminating the need for expensive alloying while achieving excellent scale adhesion through controlled scale layer structure formation
Solution Approach 2:
The invention replaces expensive alloying elements (Cu, Ni, Cr) with a cost-effective approach using controlled scale layer structure that forms naturally through processing parameters, eliminating the need for costly additive materials
2Reliability
If cooling rate after finish rolling and coiling temperature are controlled to reduce scale thickness to 20 μm or less, then scale adhesion improves, but microstructure control of the steel sheet becomes limited
Solution Approach 1:
The invention changes the control parameters from cooling rate and coiling temperature to finish rolling temperature (850°C or higher) and inter-stand water spraying, thereby achieving both excellent scale adhesion and maintained microstructure control flexibility
Solution Approach 2:
The invention performs preliminary action by controlling the scale layer structure formation during hot rolling through water spraying and temperature control, creating an optimal scale structure before coiling that ensures excellent adhesion without limiting subsequent microstructure control
3Reliability
If coiling temperature is set to 600°C or lower to form magnetite-rich scale structure, then scale adhesion improves, but there is no description regarding coiling temperature of 300°C or lower
Solution Approach 1:
The invention changes the coiling temperature parameter to 300°C or lower, which is significantly lower than the conventional 600°C or lower, thereby achieving excellent scale adhesion with a cost-effective approach that forms an optimal scale layer structure
Solution Approach 2:
The invention performs preliminary action by controlling the scale layer structure during hot rolling and cooling processes before coiling, creating a stable structure that maintains excellent adhesion even at very low coiling temperatures of 300°C or lower
4Reliability
If scale thickness is reduced to suppress crack occurrence during coiling and processing, then scale adhesion improves, but surface properties and appearance may deteriorate
Solution Approach 1:
The invention changes the scale structure parameters by controlling the thickness fractions of hematite and magnetite layers relative to total scale thickness, achieving excellent adhesion while maintaining surface appearance through optimized scale layer composition rather than simple thickness reduction
Solution Approach 2:
The invention uses a composite scale layer structure consisting of multiple oxide layers (hematite and magnetite in specific thickness ratios) that combines the adhesion benefits of magnetite-rich structure with the surface protection benefits of controlled hematite content
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 approach results in excellent surface properties and improved scale adhesion, preventing exfoliation during processing and maintaining a favorable appearance, while reducing costs associated with expensive alloy additions.
Implementation Method 1
Since a hot rolled steel sheet passes through an oxidative atmosphere during hot rolling, scale (iron oxide) is inevitably formed on the surface of the steel sheet
Implementation Method 2
in a finish rolling step, cooling water or nitrogen gas is sprayed between individual rolling stands, and the oxygen concentration on the surface of a steel sheet is controlled
Data Source
AI summary
This hot rolled steel sheet is a hot rolled steel sheet including a base steel sheet and a scale formed on a surface of the base steel sheet, in which the base steel sheet has a predetermined chemical composition, the scale has a layer structure composed of wustite, magnetite, and hematite in order from the base steel sheet side or a layer structure composed of the wustite and the magnetite in order from the base steel sheet side, and, when a thickness of the scale is represented by s, a thickness of the hematite is represented by h, and a thickness of the magnetite is represented by m, the s, the h, and the m satisfy formula (1) and formula (2).(h+m)/s<0.20 Formula (1)h≤m/4 Formula (2)