Zr Alloy Sheet Flatness via Beta Quenching and Alpha Stretching
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Solution Overview
Problem
Existing methods for producing sheets for nuclear reactor components, such as channel boxes and water channels, face challenges in achieving optimal flatness and straightness due to phase transformations during quenching, which introduce tensions and affect corrosion properties.
Innovation Solution
A method involving forging, hot rolling, cold rolling, and heat treatment in the α-phase temperature range after β quenching, with stretching to release tensions and enhance secondary phase particle growth, ensuring improved flatness, straightness, and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If β quenching is performed to improve corrosion properties and randomize crystal grain texture, then corrosion resistance is improved, but tensions are introduced that reduce flatness and straightness
Solution Approach 1:
The patent applies a two-stage heat treatment process with specific parameter changes: first β quenching at high temperature (950-1150°C) to improve corrosion resistance and randomize texture, then a second heat treatment at lower temperature (600-800°C) to relieve tensions and restore flatness. This parameter change strategy resolves the contradiction by optimizing different parameters at different stages.
Solution Approach 2:
The second heat treatment is designed as a preliminary anti-action to counteract the harmful effects (tensions) introduced by the first β quenching process. By applying controlled heating after quenching, the patent pre-compensates for and neutralizes the distortion and tension effects, thereby maintaining both corrosion resistance and dimensional precision.
2Reliability
If multiple rolling steps are used to achieve final thickness to enable β quenching, then material properties are improved, but production time and process complexity increase
Solution Approach 1:
The patent performs β quenching at or near the final thickness stage, which is a preliminary action that enables the subsequent second heat treatment to be more effective in relieving tensions. By timing the quenching operation at the optimal moment in the rolling sequence, the process maximizes material property improvement while minimizing total production time.
Solution Approach 2:
The patent utilizes the phase transition characteristics of the Zr-based alloy at different temperatures. By controlling the heating and cooling rates during β quenching and the subsequent heat treatment, the phase transition from α to β and back is leveraged to achieve desired microstructure and properties efficiently, reducing the need for excessive rolling passes.
3Reliability
If heat treatment in α-phase temperature range is performed after quenching to improve corrosion properties, then corrosion resistance is enhanced, but additional process steps are required
Solution Approach 1:
The patent merges the second heat treatment step with the existing production line by integrating it after the β quenching process. This combination approach allows the corrosion-resistant microstructure to be achieved without requiring a completely separate production line, thereby enhancing corrosion properties while limiting the increase in overall process complexity.
Solution Approach 2:
The second heat treatment is conducted at specifically controlled parameters (600-800°C for 5-30 minutes) that are optimized to achieve the desired corrosion resistance improvement. By precisely controlling temperature and time parameters, the patent achieves enhanced corrosion properties with a relatively simple and efficient process step.
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 method produces sheets with enhanced flatness, straightness, and corrosion properties, reducing the need for subsequent treatments and enabling effective use in nuclear light water reactor components like channel boxes and water channels.
Implementation Method 1
phase transformations during quenching, which introduce tensions
Implementation Method 2
carrying out an α+β quenching or a β quenching of the sheet
Implementation Method 3
heat treatment of the sheet in the α-phase temperature range of said alloy
Implementation Method 4
enhance secondary phase particle growth
Data Source
AI summary
The invention concerns a method of producing and treating a sheet suited to be used as a component or as a part of a component in a fuel assembly for a nuclear light water reactor, which method comprises:a) producing a sheet of a Zr-based alloy by forging, hot rolling and cold rolling in a suitable number of steps,b) carrying out an α+β quenching or a β quenching of the sheet when the sheet has been produced to a thickness which is equal to or almost equal to the final thickness of the finished sheet,c) heat treating the sheet in the α-phase temperature range of said alloy, wherein the sheet is stretched during the heat treatment according to step c).The invention also concerns a use of a sheet that is produced and treated according to this method, and to methods and fuel assemblies of which said sheet forms a part.