Casting Slab Surface Crack Reduction via Ferrite Phase Control
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Solution Overview
Problem
Existing methods for reducing surface cracks in continuous casting slabs either require high temperatures, affecting equipment accuracy and energy consumption, or large amounts of cooling water, and fail to inherently improve the steel's plasticity.
Innovation Solution
Controlling the surface layer temperature of the casting slab within the austenite-to-ferrite transition range (900°C-600°C) to achieve a ferrite phase proportion of 35% or more before the straightening point, using a continuous cooling characteristic CCT curve to determine the cooling rate and maintaining this temperature through controlled cooling with water or air, ensuring the surface layer remains in the austenite-to-ferrite transition temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature operation is used to prevent ferrite phase transition and precipitation, then surface cracks are reduced, but equipment accuracy and service life are greatly affected
Solution Approach 1:
The invention applies preliminary action by controlling the surface layer temperature in advance before the casting slab enters the straightening section. By pre-controlling the temperature to maintain austenite single-phase structure before critical deformation occurs, the method prevents ferrite phase transition and precipitation that would otherwise lead to surface cracks during straightening, thereby solving the contradiction between crack prevention and temperature control
Solution Approach 2:
The invention segments the temperature control approach by specifically targeting only the surface layer temperature (within 10mm from the surface) rather than controlling the entire casting slab temperature. This localized temperature control allows the surface layer to maintain austenite structure while the internal structure can follow normal solidification, thus preventing surface cracks without subjecting the entire continuous casting machine to high-temperature operation
2Reliability
If intensive cooling quenching is used to eliminate ferrite precipitation, then surface layer plasticity is improved, but a large amount of cooling water is consumed affecting energy and environment
Solution Approach 1:
The invention applies local quality by focusing cooling efforts exclusively on the surface layer within 10mm from the casting slab surface. By making the surface layer the specific target for temperature control and phase structure management, the method achieves high surface layer plasticity through controlled austenite structure without requiring intensive cooling of the entire slab, thus significantly reducing cooling water consumption and energy usage
3Reliability
If controlled cooling is applied to maintain austenite structure, then surface layer plasticity is improved, but precise temperature control is required
Solution Approach 1:
The invention applies parameter changes by establishing specific quantitative parameters for surface layer temperature control: maintaining temperature within the austenite region, controlling the surface layer depth to within 10mm from the surface, and ensuring ferrite phase proportion remains below 35%. These defined parameters provide clear control targets that improve surface layer plasticity while making the temperature control process more manageable and less precise than unguided intensive cooling
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 method effectively reduces surface cracks by enhancing the plasticity of the surface layer, preventing stress concentration and crack formation during straightening, while optimizing energy use and equipment performance.
Implementation Method 1
the surface layer temperature of the casting slab is controlled so that the surface layer temperature of the casting slab is constant in the vicinity of the phase transition temperature of the steel for a long time
Implementation Method 2
controlled cooling to the casting slab in the casting machine before entering the straitening section
Data Source
Figure 1A~2
AI summary
Provided is a method for reducing surface cracks of a casting slab by using ferrite phase. Cooling water is used to control the surface layer temperature of the casting slab before a straightening section of a casting machine, so that the surface layer of the casting slab is kept constant for a long time in the vicinity of the austenite-to-ferrite phase transition temperature of the steel; due to the long-time constant temperature, a ferrite layer is formed on the surface layer of the casting slab, thereby improving the proportion of ferrite in the surface layer structure of the casting slab, improving the plasticity of the surface layer structure of the casting slab by high plasticity property of the ferrite, and thus reducing cracks generated on the inner surface of the casting slab under the tensile stress in a straightening area. The method can not only control the surface layer structure of the casting slab, but also improve the plasticity of the surface layer of the casting slab, and reduce surface cracks of the casting slab.