Cold Rolled Steel Flat Product for Packaging
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Solution Overview
Problem
The production of thin flat steel products for packaging faces challenges in achieving adequate strength and flatness while minimizing climate-damaging emissions and costs, particularly with rapid temperature changes during induction heating and water quenching in annealing processes.
Innovation Solution
A method involving continuous annealing of cold-rolled steel strips with inductive heating to high temperatures followed by two-stage cooling, where primary cooling occurs at a lower rate to prevent martensite formation and maintain a ferrite-based microstructure, and secondary cooling is rapid to achieve high energy efficiency and flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rapid cooling with water is used after induction heating to achieve high tensile strength through martensite formation, then tensile strength is improved to more than 550 MPa, but flatness of the steel strip deteriorates
Solution Approach 1:
The cooling process is segmented into two distinct stages: a first cooling stage at a controlled rate (10-1000 K/s) to prevent excessive flatness defects, followed by a second rapid cooling stage (>1000 K/s) to achieve the desired microstructure. This segmentation allows each cooling stage to serve a specific function without compromising the other.
Solution Approach 2:
The first cooling stage performs a preliminary cooling action that prepares the steel strip for the subsequent rapid cooling by establishing a controlled temperature reduction that prevents flatness defects. This preliminary action ensures that when rapid cooling occurs, the strip is already in a state that can withstand the thermal stresses without excessive deformation.
2Use of energy by moving object
If induction heating with rapid temperature changes is used for recrystallization annealing, then energy efficiency is improved and climate-damaging emissions are reduced, but flatness of the steel strip deteriorates
Solution Approach 1:
The cooling process following induction heating is segmented into two stages with different cooling rates. The first stage uses a moderate cooling rate (10-1000 K/s) to maintain flatness, while the second stage uses rapid cooling (>1000 K/s) to achieve the desired microstructure. This segmentation resolves the contradiction between energy efficiency and flatness by allowing the induction heating to provide energy efficiency while the controlled two-stage cooling preserves flatness.
3Shape
If conventional heating methods with fossil fuels are used for annealing, then flatness is maintained, but climate-damaging emissions increase
Solution Approach 1:
The conventional mechanical/thermal heating system using fossil fuels is replaced with an induction heating system that uses electromagnetic fields to heat the steel strip directly. This substitution eliminates the need for combustion processes, thereby eliminating climate-damaging emissions while maintaining or improving process efficiency.
Solution Approach 2:
The heating method parameter is changed from conventional thermal conduction/radiation heating with fossil fuels to induction heating using electromagnetic induction. This parameter change fundamentally alters the energy source and heating mechanism, eliminating harmful emissions while enabling precise temperature control through the two-stage cooling process to maintain flatness.
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 produces flat steel products with strengths and elongations suitable for standard grades, ensuring cost-effectiveness, environmental sustainability, and maintaining excellent flatness, while reducing investment and operating costs compared to conventional annealing methods.
Implementation Method 1
the cold-rolled steel strip is inductively heated to the annealing temperature in the continuous annealing furnace
Implementation Method 2
annealing of the flat steel product at temperatures above the recrystallization temperature takes place after a (primary) cold rolling in order to restore the original structural condition of the steel
Implementation Method 3
the austenite phase formed in the steel during induction heating to the annealing temperature is converted into martensite
Data Source
AI summary
A cold rolled steel flat product for packaging made of a low carbon steel having a thickness of less than 0.49 mm and a method of making. The steel flat product has a martensite-free microstructure and represents a standard grade for packaging with tensile strengths from 300 to 550 MPa, which can be produced from a cold-rolled steel sheet with a carbon content from 0.01% to 0.1% by weight by inductive annealing of the steel sheet and subsequent water cooling for quenching the recrystallization-annealed steel sheet. To achieve flatness of 5 I-units or less, the induction annealed steel sheet is first primarily cooled in the manufacturing process to a take-off temperature at a rate of less than 1000 K/s, with the take-off temperature being below the transformation temperature of 723° C., and thereafter a secondary cooling by water cooling with a water temperature of less than 80° C. at a rate of more than 1000 K/s.