Flat Steel Scale Layer Adhesion via Wustite Control
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Solution Overview
Problem
Conventional hot-rolled flat steel products have a scale layer with low and fluctuating adhesion, leading to manufacturing and quality defects during further processing, such as spalling, contamination, and increased cleaning costs due to non-homogeneous scale layers.
Innovation Solution
A flat steel product with a steel substrate having a carbon content of less than 0.8% and a scale layer with a maximum residual wüstite proportion of 30% at the interface, ensuring high adhesive strength through controlled rolling and cooling processes to form a homogeneous and firmly adhering scale layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional hot-rolled flat steel products are produced with standard cooling processes, then production efficiency is maintained, but the scale layer has low and fluctuating adhesion leading to spalling and manufacturing defects
Solution Approach 1:
The patent applies parameter changes by controlling the cooling rate within a specific range (2-30°C/s) and maintaining the final rolling temperature above 700°C. These parameter adjustments transform the scale layer composition to contain magnetite and iron phases with controlled wüstite content, achieving adhesion strength of at least 80% while maintaining conventional production efficiency
Solution Approach 2:
The patent creates a composite scale layer structure consisting of multiple iron oxide phases (magnetite Fe3O4, wüstite FeO, and iron Fe) with specific volume proportions. This composite structure, where magnetite forms the matrix and iron precipitates are distributed within it, provides both high adhesion to the steel substrate and resistance to spalling during subsequent processing
2Reliability
If the scale layer is removed by pickling or blasting to avoid spalling, then manufacturing defects are reduced, but additional work steps are required and the scale can no longer serve as a lubricant
Solution Approach 1:
The patent converts the traditionally harmful scale layer, which causes spalling and contamination, into a beneficial component by controlling its composition and adhesion. The scale layer with magnetite-matrix structure and iron precipitates becomes a protective layer that prevents spalling, reduces contamination during laser cutting and roll forming, and eliminates the need for pickling or blasting operations
Solution Approach 2:
The scale layer serves multiple functions simultaneously: it acts as a lubricant during forming processes, provides a protective barrier against oxidation, and maintains surface quality without requiring additional cleaning or pickling steps. The controlled adhesion strength of at least 80% ensures the scale remains beneficial throughout subsequent manufacturing operations
3Object-affected harmful factors
If shorter cleaning intervals or increased rework are implemented to counteract scale spalling, then contamination is reduced, but costs increase
Solution Approach 1:
The patent transforms the scale layer from a source of contamination through spalling into a protective barrier that prevents contamination. The firmly adhering scale layer with magnetite-iron composite structure eliminates dust generation during forming and cutting operations, thereby reducing contamination of optical measuring devices and component surfaces without requiring increased cleaning frequency or rework
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 solution results in a scale layer that remains intact during forming, cutting, and welding processes, reducing rework costs, extending cleaning intervals, and allowing direct painting or galvanizing, thereby improving production efficiency and quality.
Implementation Method 1
a scale layer contacting the steel substrate, which in direct contact at the interface between the steel substrate and the scale layer has a maximum proportion of residual wüstite of 30%, preferably a maximum of 20% and particularly preferably a maximum of 10%
Implementation Method 2
controlled rolling and cooling processes to form a homogeneous and firmly adhering scale layer
Data Source
Figure 1a~2
Figure 3~4
AI summary
The invention relates to a flat steel product comprising a steel substrate and a scale layer contacting the steel substrate, as well as a method for producing the flat steel product. The steel substrate has a carbon content of C, for which C is ≤ 0.8 wt.%. Furthermore, the scale layer contacting the steel substrate has a residual wüstite content of at most 30% in direct contact at the interface between the steel substrate and the scale layer.