Austenitic Stainless Steel Slab Surface Defect Control
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Solution Overview
Problem
Austenitic stainless steel slabs produced by continuous casting often exhibit surface defects in the casting direction, leading to surface flaws in thin steel strips, which cannot be effectively prevented by existing methods such as oscillation mark smoothing or gradual cooling, and these defects are particularly challenging due to uneven cooling and solidification contraction.
Innovation Solution
A method combining decreased casting temperature and in-mold electro-magnetic stirring to achieve homogeneous gradual cooling, specifically controlling the temperature difference and stirring intensity to suppress surface defects in the casting direction, thereby preventing surface flaws without the need for surface grinding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional continuous casting methods are used, then production efficiency is maintained, but surface defects in casting direction occur leading to surface flaws in thin steel strips
Solution Approach 1:
The patent applies preliminary action by performing electro-magnetic stirring during the initial solidification stage in the mold to prevent surface defect formation before they occur. The stirring is applied at a specific timing (when solidification shell thickness is 5-10mm) to homogenize temperature distribution and prevent crack formation during solidification contraction, thereby eliminating surface defects before they can affect the final product quality.
Solution Approach 2:
The patent changes key process parameters by controlling the electro-magnetic stirring intensity (indicated by current values of 1500-3000A) and timing (when solidification shell reaches specific thickness). It also controls the temperature difference between molten steel and mold (ΔT = 10-50°C) to achieve optimal cooling conditions that prevent surface defects while maintaining production efficiency.
2Manufacturing precision
If surface grinding is applied to remove surface defects, then surface quality of thin steel strip is improved, but production cost increases
Solution Approach 1:
The patent converts the harmful effect of electro-magnetic stirring (which could potentially cause turbulence and defects) into a beneficial effect by carefully controlling the stirring intensity and timing. The stirring is applied only when the solidification shell reaches a specific thickness (5-10mm), transforming what could be a harmful disturbance into a beneficial homogenization effect that prevents surface defect formation without requiring subsequent grinding.
Solution Approach 2:
The patent applies self-service by enabling the casting process itself to produce defect-free surfaces through controlled electro-magnetic stirring during solidification. The process uses the molten steel's own electromagnetic properties and solidification characteristics to prevent defect formation, eliminating the need for external surface treatment processes like grinding.
3Manufacturing precision
If electro-magnetic stirring is applied to suppress surface defects, then surface quality is improved, but energy consumption increases
Solution Approach 1:
The patent applies partial action by using electro-magnetic stirring only during the critical solidification stage when the solidification shell reaches a specific thickness (5-10mm), rather than continuous stirring throughout the entire casting process. The stirring is applied at partial duration and with controlled intensity (1500-3000A current), achieving the necessary homogenization effect while minimizing energy consumption.
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
Significantly reduces the occurrence of surface defects in continuously cast austenitic stainless steel slabs, ensuring high-quality thin steel strips with minimal surface flaws even without surface treatment, and is applicable to austenitic stainless steel species while minimizing adverse effects on other steel species.
Implementation Method 1
a flowing force is applied to the molten steel in a depth position in the vicinity of the surface of the molten steel to the depth position of approximately 200 mm in the mold by an electro-magnetic stirrer
Implementation Method 2
the thickness of the solidification shell becomes uneven, and then the stress caused by the solidification contraction
Implementation Method 3
the cooling in the mold in the continuous casting process unevenly occurs
Implementation Method 4
the stress caused by the solidification contraction and the ferrostatic pressure is concentrated thereto to form a fine crack
Data Source
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AI summary
[Problem] To provide a continuous casting technique that significantly suppresses a surface defect occurring in the longitudinal direction (i.e., the casting direction) of a continuously cast slab of an austenitic stainless steel. [Solution] A method for producing an austenitic stainless steel slab by continuous casting of an austenitic stainless steel, including applying electric power to the molten steel in a depth region providing a solidification shell thickness of from 5 to 10 mm at least at a center position in the long edge direction, so as to cause flows in directions inverse to each other in the long edge direction on both long edge sides, thereby performing electro-magnetic stirring (EMS) to control a continuous casting condition satisfying 10 < ΔT < 50 × FEMS + 10. Herein, ΔT represents a difference between an average molten steel temperature (°C) and a solidification starting temperature (°C) of the molten steel, and FEMS represents a stirring intensity index shown by a function of a molten steel flow velocity in the long edge direction imparted by the electro-magnetic stirring and a casting velocity.