Composite Rolling Roll Composition for Low Residual Stress
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Solution Overview
Problem
Centrifugally cast composite rolls for hot strip mills face issues with high residual compressive stress leading to cracking and delayed failure, despite having excellent wear resistance and sticking resistance, which affects their efficiency and longevity.
Innovation Solution
A centrifugally cast composite roll with an outer layer made of an Fe-based alloy and an inner layer of ductile cast iron, where the outer layer has a controlled circumferential residual compressive stress of 150-350 MPa at the discard diameter, achieved by specific chemical composition and a production method involving centrifugal casting, reheating, and controlled cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-speed steel is used for the outer layer to improve wear resistance, then wear resistance is improved, but residual compressive stress increases leading to cracking and delayed failure
Solution Approach 1:
The patent changes the chemical composition parameters of the outer layer by replacing high-speed steel with an Fe-based alloy containing specific amounts of Cr (4.0-10.0%), Mo (2.0-7.5%), V (3.0-6.0%), and other elements. This composition change, combined with controlled cooling rates (10-60°C/hr), achieves the desired balance between wear resistance and reduced residual compressive stress, preventing cracking while maintaining hardness of 58-65 HRC
Solution Approach 2:
The patent uses a composite structure with an Fe-based outer layer and a ductile cast iron inner layer. The outer layer contains specifically controlled amounts of alloying elements (Cr, Mo, V, Nb, B, Ni, Mn, Si) to create a material that combines wear resistance with lower residual stress, while the ductile cast iron inner layer provides toughness and structural support, together resolving the contradiction between wear resistance and cracking resistance
2Strength
If high-speed steel roll is used to achieve excellent wear resistance, then wear resistance is improved, but sticking resistance decreases causing cobble formation
Solution Approach 1:
The patent changes the material composition from high-speed steel to an Fe-based alloy with optimized chemical parameters including Cr (4.0-10.0%), Mo (2.0-7.5%), V (3.0-6.0%), and controlled carbon content (1.70-2.70%). This parameter change results in a surface that maintains wear resistance through hard carbide formation while improving sticking resistance by preventing excessive adhesion to steel strips during hot rolling
3Ease of repair
If the outer layer is ground from initial diameter to discard diameter to remove damages, then wear damages are removed, but the usable roll diameter range is reduced
Solution Approach 1:
The patent applies beforehand cushioning by designing an outer layer with inherently low residual compressive stress (150-500 MPa) that prevents crack initiation and propagation. This preventive approach reduces the frequency and depth of grinding operations needed, thereby extending the usable roll diameter range from initial to discard diameter and improving productivity
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 the propagation of cracks and delays failure, enhancing the roll's handling and operational efficiency by maintaining low residual compressive stress throughout its usable diameter range.
Implementation Method 1
a centrifugally cast composite roll for rolling comprising an outer layer having excellent wear resistance and an inner layer having excellent toughness, which are integrally fused to each other
Implementation Method 2
the outer layer has a controlled circumferential residual compressive stress of 150-350 MPa at the discard diameter, achieved by specific chemical composition and a production method involving centrifugal casting, reheating, and controlled cooling
Data Source
AI summary
A centrifugally cast composite roll for rolling comprising an outer layer and an inner layer, which are integrally fused to each other, the outer layer being made of an Fe-based alloy comprising by mass 1.70-2.70% of C, 0.3-3% of Si, 0.1-3% of Mn, 1.1-3.0% of Ni, 4.0-10% of Cr, 2.0-7.5% of Mo, 3-6.0% of V, 0.1-2% of W, 0.2-2% of Nb, 0.01-0.2% of B, and 0.01-0.1% of N, the balance being Fe and inevitable impurities, and the inner layer being made of ductile cast iron.