Continuous Steel Casting With Intentional Slab Bulging for Segregation Control
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Solution Overview
Problem
Current continuous casting methods fail to adequately reduce center segregation in steel slabs, leading to hydrogen-induced cracking, especially in line pipe steel materials, due to variations in solidification completion positions and bulging issues, which are not effectively addressed by existing soft reduction techniques.
Innovation Solution
A continuous casting method that involves intentional bulging of the slab's wide side surfaces and controlled rolling reduction in a soft reduction zone, with a specific rolling reduction speed and total rolling reduction amount, while ensuring the solid phase fraction at the slab's thickness center is within a certain range to minimize segregation and prevent internal cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If soft reduction is applied with rolling reduction amount corresponding to solidification shrinkage and thermal shrinkage, then center segregation is reduced, but variation in solidification completion position causes insufficient effect at certain locations
Solution Approach 1:
The patent applies dynamic adjustment of rolling reduction amount based on real-time detection of solidification completion position. The rolling reduction amount is not fixed but varies dynamically to match the actual solidification state at different locations, ensuring optimal center segregation reduction effectiveness across the entire slab width.
Solution Approach 2:
The patent implements a feedback mechanism where the solidification completion position is detected and used to adjust the rolling reduction amount. This closed-loop control ensures that the rolling reduction is optimized based on actual solidification conditions, resolving the issue of insufficient effect at locations with varying solidification completion positions.
2Manufacturing precision
If rolling reduction is increased to prevent void formation and negative pressure, then center segregation is reduced, but internal cracking may occur
Solution Approach 1:
The patent optimizes the rolling reduction amount by changing the parameter from fixed conventional values to dynamically adjusted values based on solidification completion position and bulging amount. This parameter optimization ensures sufficient compression to prevent void formation while staying below the threshold that would cause internal cracking.
Solution Approach 2:
The patent applies rolling reduction selectively based on detected bulging amounts and solidification states. Rather than applying uniform excessive rolling reduction throughout, it applies partial rolling reduction only where and when needed, preventing both void formation and internal cracking by avoiding over-compression in already solidified regions.
3Strength
If solid phase fraction is increased in reformation zone to prevent cracking, then slab strength is improved, but segregation control becomes more difficult
Solution Approach 1:
The patent ensures that solidification is substantially completed before the slab enters the reformation zone by controlling solid phase fraction to be 0.8 or more upstream of this zone. This preliminary solidification action prevents cracking during reformation while minimizing segregation by ensuring most solute redistribution occurs before the critical reformation process.
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 the variation of segregation degree in the slab width direction, enhances hydrogen-induced cracking resistance, and prevents internal cracking, meeting the stringent quality requirements for line pipe steel materials.
Implementation Method 1
performing rolling reduction on the wide side surfaces of the slab, performed after the bulging of the wide side surfaces of the slab, in a soft reduction zone in which the roller gap of a plurality of pairs of slab support rollers is reduced stepwise toward the downstream side in the casting direction
Implementation Method 2
In a solidification process of steel, solute elements such as carbon (C), phosphorus (P), sulfur (S), and manganese (Mn) are concentrated in the unsolidified liquid side through redistribution during the solidification
Implementation Method 3
solute elements such as carbon (C), phosphorus (P), sulfur (S), and manganese (Mn) are concentrated in the unsolidified liquid side through redistribution during the solidification
Implementation Method 4
Voids are formed or a negative pressure is generated at the thickness central portion of the slab during continuous casting by solidification shrinkage or thermal shrinkage of the slab
Data Source
AI summary
A continuous casting method of steel includes the step of bulging wide side surfaces of a slab having there inside an unsolidified layer with a total intentional bulging amount of 3 to 10 mm by increasing stepwise toward a downstream side in a casting direction a roller gap of a plurality of pairs of slab support rollers disposed in a continuous casting machine.