Hot Rolling Cooling Layout for Tough Thick Steel Strip
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Solution Overview
Problem
Conventional hot rolling methods struggle to produce thick steel strips with the required toughness for pipeline construction, as they often fail to meet the high ductile fracture fraction requirements in the Drop Weight Tear Test, despite achieving increased strength.
Innovation Solution
The method involves a modified hot rolling process where the cooling section begins before the last active rolling stand, with inactive stands having an open rolling gap to prevent deformation, and uses rapid cooling with compact cooling units to achieve a high cooling rate, shifting the toughness transition temperature to lower values and enhancing mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional hot rolling methods are used to produce thick steel strips, then the production time is reduced compared to reversing roll mill, but the toughness and ductile fracture fraction do not meet the required standards for pipeline construction
Solution Approach 1:
The cooling section is positioned to begin before the last active rolling stand, implementing preliminary cooling action while the steel strip is still in the rolling process. This allows the austenite to be cooled to the recrystallization stop temperature before final deformation, ensuring the desired microstructure and toughness properties are achieved while maintaining hot rolling productivity
Solution Approach 2:
The process utilizes dynamic temperature parameter changes by cooling the steel strip between rolling stands and during the final rolling pass. The temperature is controlled to pass through the austenite recrystallization range, transforming the material properties in real-time to achieve both high strength and toughness required for pipeline applications
2Device complexity
If the cooling section starts after the last rolling stand, then the rolling process is simpler, but the cooling rate is insufficient to achieve the required toughness transition temperature
Solution Approach 1:
The cooling section is positioned to begin before the last active rolling stand, implementing preliminary cooling action while the steel strip is still in the rolling process. This allows the austenite to be cooled to the recrystallization stop temperature before final deformation, ensuring the desired microstructure and toughness properties are achieved while maintaining hot rolling productivity
Solution Approach 2:
The cooling process continues throughout the final rolling pass, with cooling units positioned to cool the steel strip continuously as it passes through the last active rolling stand. This continuous cooling action ensures the temperature drops sufficiently to achieve the required toughness transition temperature while maintaining the rolling operation
3Reliability
If rapid cooling is applied to increase toughness, then the cooling rate increases, but scaling and surface defects may occur
Solution Approach 1:
The cooling units are positioned to apply cooling locally to specific regions of the steel strip during the rolling process. By controlling the cooling distribution and intensity in different zones, the process achieves rapid cooling for toughness improvement while minimizing excessive cooling that would cause scaling and surface defects
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 approach allows for the production of hot strips with high strength and toughness, meeting the DWTT requirements up to 25.4 mm thickness, with improved dimensional stability and reduced scaling, and expands the application of ferritic/pearlitic steels to larger thicknesses.
Implementation Method 1
the steel strip is cooled, viewed in the conveying direction, after leaving the last active rolling stand by being exposed to a cooling fluid discharged from the cooling section, with the cooling rate being at least 80 K/s
Implementation Method 2
Hot rolling is carried out in a temperature range that encompasses the recrystallization range of the austenite
Data Source
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AI summary
The invention relates to a method and a plant for hot rolling steel strip (S), wherein the plant has a hot rolling relay (2) which comprises a plurality of roll stands (F1 - F7) which are successively passed through in the conveying direction (F) of the steel strip (S) to be hot rolled, and a cooling section (5) for intensively cooling the hot-rolled steel strip (S) emerging from the last roll stand (F7) of the rolling relay (2). By way of the invention, it is possible, on the basis of such a conventional hot rolling plant, to produce in an operationally reliable manner hot strips with a final thickness of more than 15 mm that satisfy even the highest requirements placed on their toughness. This is achieved according to the invention in that the start of the cooling section (5), as seen in the conveying direction (F) of the steel strip (S) to be hot rolled, is moved to before the end of the hot rolling relay (2), and in that the cooling section (5) starts following the last roll stand (F5) which is passed through before entering the cooling section (5) and in which hot rolling of the steel strip (S) to be hot rolled in each case takes place.