Continuously Cast Slab Microstructure for Cooling Crack Resistance
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Solution Overview
Problem
Conventional methods fail to adequately suppress thermal cracking in high-strength steel slabs due to insufficient control over prior austenite grain size and microstructure, leading to reduced toughness and increased cracking during cooling.
Innovation Solution
A continuously cast slab with controlled average prior austenite grain size of 0.5 mm to 2.0 mm, a total area ratio of bainite and ferrite of 90% or more, and an area ratio of ferrite of 0% or 3% or more, combined with specific cooling steps to prevent thermal cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the alloying level is increased to improve strength, then the strength of the steel slab is improved, but the toughness of the slab deteriorates, leading to increased thermal cracking during cooling
Solution Approach 1:
The invention changes the microstructural parameters by controlling the prior austenite grain size to 0.5-2.0 mm and regulating the area ratios of bainite (80-95%) and ferrite (5-20%) to optimize the balance between strength and toughness, preventing thermal cracking while maintaining high strength properties
Solution Approach 2:
The invention creates a composite microstructure consisting of bainite and ferrite phases with specific area ratios, where bainite provides strength and ferrite provides toughness, achieving a synergistic effect that prevents thermal cracking in high-strength steel slabs
2Ease of manufacture
If the prior austenite grain size is increased to simplify processing, then the manufacturing process is simplified, but the toughness of the slab deteriorates, increasing the risk of thermal cracking
Solution Approach 1:
The invention optimizes the prior austenite grain size parameter to a specific range of 0.5-2.0 mm, which provides sufficient toughness to prevent thermal cracking while maintaining reasonable processing characteristics, resolving the contradiction between manufacturing simplicity and material reliability
3Reliability
If the cooling rate is decreased to reduce thermal stress, then the thermal cracking is suppressed, but the productivity of the slab production deteriorates
Solution Approach 1:
The invention changes the microstructural parameters (prior austenite grain size and phase composition) to inherently resist thermal cracking, allowing the use of faster cooling rates that maintain high productivity while preventing cracking through material property optimization rather than slow cooling
4Reliability
If the area ratio of ferrite is increased to improve toughness, then the toughness of the slab is improved, but the strength of the slab deteriorates
Solution Approach 1:
The invention precisely controls the area ratio parameters of ferrite (5-20%) and bainite (80-95%) to achieve the optimal balance where sufficient ferrite provides toughness and crack resistance while the dominant bainite phase maintains high strength properties
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 solution effectively prevents thermal cracking during cooling, ensuring high yield and toughness of high-strength steel slabs by controlling grain size and microstructure.
Implementation Method 1
a total of an area ratio of bainite and an area ratio of ferrite in a microstructure of the slab is 90% or more
Implementation Method 2
stress is caused due to the difference in thermal shrinkage or in transformation expansion between the surface and the inside of the slab
Implementation Method 3
stress is caused due to the difference in thermal shrinkage or in transformation expansion between the surface and the inside of the slab
Data Source
AI summary
A continuously cast slab that can prevent thermal cracking during cooling therefor even if the toughness of the slab is low, and a method for producing the same. Specifically, provided is a continuously cast slab for high-strength steel with features such that the average prior austenite grain size at a position of 10 mm from the surface layer of the continuously cast slab is in the range of 0.5 mm to 2.0 mm; and in the microstructure of the slab, the total area ratio of bainite and ferrite is 90% more, and the area ratio of ferrite is 0%, or 3% or more.