Mist Quenching of Steel Sheet to Prevent Warpage
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Solution Overview
Problem
Existing methods for quenching steel sheets in continuous annealing systems often result in shape defects such as warpage and deformation due to excessive rapid cooling, with limited effectiveness in inhibiting these issues when only water flow density or temperature variation is controlled.
Innovation Solution
A quenching apparatus and method that uses mist cooling with controlled water flow density and restraining rolls arranged within the martensite transformation temperature range to moderate cooling rates and prevent deformation, ensuring the steel sheet is cooled from the martensite start temperature to finish temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rapid cooling is applied to manufacture high strength steel sheet, then tensile strength is improved, but shape defects such as warpage and wavelike deformation occur due to out-of-plane deformation
Solution Approach 1:
The invention changes the cooling parameters by controlling water flow density within a specific range (50-200 L/m²min) and restraining the steel sheet at a specific temperature range (Ms-100°C to Mf+100°C). This parameter control allows rapid cooling to achieve high tensile strength while preventing excessive thermal stress that causes shape defects
Solution Approach 2:
The invention applies preliminary restraining action before the steel sheet completes cooling. By placing restraining rolls that contact the steel sheet surface in the temperature range of Ms-100°C to Mf+100°C, the system prevents out-of-plane deformation from occurring during the critical phase transformation period, thereby preventing shape defects before they fully develop
2Speed
If water flow density is increased to enhance cooling effect, then cooling rate is improved, but temperature variation in width direction increases causing non-uniform cooling
Solution Approach 1:
The invention optimizes the water flow density parameter to a specific range (50-200 L/m²min) that balances cooling rate and temperature uniformity. This parameter setting ensures sufficient cooling speed for martensite transformation while preventing excessive water accumulation that would cause non-uniform cooling in the width direction
3Shape
If restraining rolls are used to prevent warpage, then shape stability is improved, but cooling rate variation occurs due to excessive rapid cooling
Solution Approach 1:
The invention changes the restraining temperature parameter to the range of Ms-100°C to Mf+100°C, which is the critical phase transformation zone. By restraining the steel sheet in this specific temperature range rather than throughout the entire cooling process, the system maintains shape stability during the most critical deformation period while allowing controlled cooling rate variation in less critical zones
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
Effectively inhibits shape defects by stabilizing the cooling rate and reducing warpage, allowing for the production of high-strength steel sheets with improved mechanical properties.
Implementation Method 1
spraying mist onto both surfaces of a continuously transported metal sheet to cool the metal sheet
Implementation Method 2
water contained in mist, which is sprayed onto the strip, dripping down along the surface of the strip
Data Source
AI summary
A quenching apparatus and a quenching method for a metal sheet with which it is possible to inhibit shape defects from occurring in the metal sheet when quenching is performed and a method for manufacturing a steel sheet. The quenching apparatus is placed on an exit side of a soaking zone in a continuous annealing furnace, and the apparatus includes a cooling fluid-spray device having plural spray nozzles for spraying mist onto both surfaces of a continuously transported metal sheet, and at least one pair of restraining rolls for restraining the metal sheet on both surfaces thereof in a region from a cooling start point to a cooling finish point in the cooling fluid-spray device.