TRIP Steel Strip Cooling Sequence for Direct Casting-Rolling
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Solution Overview
Problem
Current processes for producing TRIP steel strips are inefficient and require additional cold-rolling and annealing steps, leading to high energy consumption and increased costs, while also resulting in surface defects and inhomogeneous microstructures.
Innovation Solution
A continuous integrated casting-rolling process that eliminates the need for cold-rolling and annealing by controlling cooling rates and temperatures to achieve a predominantly austenitic microstructure, which is then converted into ferritic and bainitic phases, allowing direct production of TRIP steel strips with enhanced mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If additional cold-rolling and annealing steps are used to produce TRIP steel strips, then manufacturing precision and microstructure control are improved, but energy consumption and production costs increase
Solution Approach 1:
The patent applies preliminary action by establishing the desired austenitic microstructure during the hot-rolling process itself, before final cooling. Through controlled cooling rates and temperature maintenance in the finishing mill, the steel is prepared in advance with the correct phase composition, eliminating the need for subsequent cold-rolling and annealing operations.
Solution Approach 2:
The patent utilizes parameter changes by precisely controlling cooling rates (from 5-50 K/s in the finishing mill) and maintaining specific temperature ranges (620-700°C) to transform the microstructure during hot-rolling. These parameter adjustments enable direct production of TRIP steel with the required mechanical properties without additional processing steps.
2Strength
If additional cold-rolling and annealing steps are implemented, then mechanical properties and microstructure homogeneity are improved, but production time and process complexity increase
Solution Approach 1:
The patent merges the microstructure control function into the hot-rolling process itself. The finishing mill performs both the shaping function and the phase transformation function simultaneously through controlled cooling, combining multiple operations into a single integrated process that reduces total production time.
Solution Approach 2:
The patent maintains continuous useful action by keeping the steel in the austenitic phase throughout the hot-rolling process and then transforming it directly to the final microstructure during controlled cooling. This continuous process eliminates interruptions and additional heating/cooling cycles that would otherwise be required.
3Ease of manufacture
If conventional hot-rolling processes are used without controlled cooling, then production simplicity is maintained, but microstructure homogeneity and mechanical strength deteriorate
Solution Approach 1:
The patent applies dynamics by implementing variable cooling rates at different stages of the process. The cooling rate is dynamically adjusted from 5-50 K/s in the finishing mill to achieve uniform austenitic microstructure, then slowed to -25 K/s to 20 K/s during transport to allow controlled phase transformation, optimizing both simplicity and precision.
Solution Approach 2:
The patent utilizes phase transitions by controlling the transformation from austenite to ferrite and martensite during the cooling process. By maintaining the steel in the austenitic phase during hot-rolling and then controlling the cooling rate through the phase transformation point, uniform microstructure and high mechanical strength are achieved.
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 process reduces energy consumption, eliminates surface defects, and ensures high homogeneity and mechanical strength, enabling the production of TRIP steel strips with improved microstructural stability and reduced production costs.
Implementation Method 1
the finished strip is supplied to a first cooling group of the cooling sector, wherein in the first cooling group a core of the finished strip is force-cooled to a second exit temperature
Implementation Method 2
a second cooling rate of the core of the finished strip is established, wherein the second cooling rate of the core of the finished strip is -25 K/s, in particular 0 K/s, to 20 K/s inclusive
Implementation Method 3
In the third cooling group the core of the finished strip is force-cooled to a third exit temperature which is not more than the bainite starting temperature so that a first portion of the austenite of the finished strip is at least partially converted into bainite
Implementation Method 4
Due to the phase transitions taking place during transport and a resulting heat of transition the second cooling rate may also be negative
Data Source
AI summary
A process for production of a TRIP steel strip that includessupplying a finished strip to a first cooling group of a cooling sector to force-cool the core of the finished strip to a second exit temperature (TA2) in the range 620° C. to 700° C., whereby, upon exiting the first cooling group, the core has a predominantly austenitic microstructure, transporting the finished strip to a third cooling group establishing, during the transport, a second cooling rate of the core of the finished strip in the range −25 K/s to 20 K/s to convert a first portion of the austenitic microstructure into a ferritic microstructure, force-cooling the core of the finished strip in the third cooling group to a third exit temperature (TA3) which is not more than the bainite starting temperature (BS) to at least partially convert a second portion of the austenite into a bainitic microstructure.