High-Alloy Continuously Cast Slab Microstructure for Cooling Crack Prevention
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Solution Overview
Problem
Conventional methods for suppressing thermal cracking in high-alloy, high-strength steel slabs during cooling fail to control the grain size of prior austenite and microstructure, leading to insufficient toughness and frequent cracking.
Innovation Solution
Control the average prior austenite grain size to 100 μm to 0.5 mm and maintain a microstructure with at least 10% ferrite, 10% pearlite, and 1% to 30% bainite to enhance toughness, using controlled cooling rates and composition adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the alloying level is increased to produce high-strength steel, then the strength of the steel is improved, but the toughness of the slab decreases significantly
Solution Approach 1:
The invention changes the microstructural parameters by controlling the grain size of prior austenite to 100 μm to 0.5 mm and adjusting the area ratios of ferrite (10-30%), pearlite (10-40%), and bainite (30-70%). This parameter control resolves the contradiction by creating a fine-grained multi-phase microstructure that simultaneously provides high strength and adequate toughness, preventing thermal cracking during cooling.
2Productivity
If the slab is cooled rapidly to increase productivity, then the production efficiency is improved, but thermal cracking occurs more frequently due to stress concentration
Solution Approach 1:
The invention performs preliminary action by controlling the microstructure before the harmful cooling process occurs. By pre-establishing a fine-grained prior austenite structure with controlled phase distribution, the slab gains inherent resistance to thermal stress during subsequent cooling, allowing rapid cooling without cracking.
Solution Approach 2:
The invention creates a composite microstructure consisting of multiple phases (ferrite, pearlite, and bainite) in specific proportions within the steel matrix. This composite structure provides both strength and toughness, enabling the material to withstand the thermal stresses of rapid cooling that would cause cracking in single-phase structures.
3Device complexity
If conventional cooling methods are used without microstructure control, then the process complexity is reduced, but the grain boundaries become embrittled and cracking propagates
Solution Approach 1:
The invention applies parameter changes by precisely controlling the grain size (100 μm to 0.5 mm) and phase distribution (ferrite 10-30%, pearlite 10-40%, bainite 30-70%). This controlled microstructure prevents grain boundary embrittlement and crack propagation while maintaining a relatively simple cooling process, resolving the contradiction between process simplicity and material reliability.
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
Prevents cracking during the cooling process of high-alloy, high-strength steel slabs by ensuring appropriate grain size and microstructure, thereby improving yield and reducing surface defects.
Implementation Method 1
the transformation of austenite to ferrite occurs
Implementation Method 2
Precipitates and ferrite are more likely to be formed at grain boundaries than within grains
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 prevents cracking during a cooling process therefor even if such a slab is a high-alloy slab with low toughness. Specifically, a continuously cast slab for high-strength steel features the average prior austenite grain size at a position 10 mm from the surface layer of the continuously cast slab in the range of 100 μm to 0.5 mm; and in the microstructure of the slab, the area ratio of ferrite is 10% or more, the area ratio of pearlite is 10% or more, and the area ratio of bainite is in the range of 1% to 30%. The continuously cast slab preferably contains, in mass %, C: 0.10 to 0.40%, Si: 0.10 to 2.50%, and Mn: 1.00 to 5.00%.