Centrifugal Cast Composite Roll Hardness Gradient
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Solution Overview
Problem
Conventional centrifugally cast composite rolls for hot rolling face challenges in maintaining consistent hardness across their diameter, leading to issues with heat cracking at larger diameters and wear resistance at smaller diameters, which affects the quality of rolled steel sheets.
Innovation Solution
A centrifugally cast composite roll design with an outer layer composition that includes specific mass percentages of C, Si, Mn, Cr, Ni, Mo, W, and other elements, combined with a tempering treatment without a hardening step, results in higher hardness in the deep portion than the surface, providing enhanced heat-cracking resistance at larger diameters and wear resistance at smaller diameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hardening treatment is applied to increase outer layer hardness, then wear resistance improves, but heat-cracking resistance deteriorates at larger diameters
Solution Approach 1:
The invention creates a non-uniform hardness distribution within the outer layer through controlled cooling during centrifugal casting. The deep portion (30-50mm from surface) achieves higher hardness (HRC 58-65) for wear resistance, while the surface layer maintains lower hardness (HRC 45-55) for heat-cracking resistance. This local differentiation resolves the contradiction between wear resistance and heat-cracking resistance at different radial positions.
Solution Approach 2:
The invention changes the cooling rate parameter during centrifugal casting to achieve the desired hardness distribution. By controlling the cooling conditions, the deep portion experiences slower cooling that produces harder microstructure, while the surface experiences faster cooling that produces softer microstructure. This parameter control enables simultaneous achievement of wear resistance and heat-cracking resistance.
2Ease of manufacture
If conventional centrifugal casting is used with standard cooling, then manufacturing simplicity is maintained, but hardness consistency across the diameter deteriorates
Solution Approach 1:
The invention applies preliminary action by controlling the cooling rate during the centrifugal casting process itself to pre-establish the desired non-uniform hardness distribution before the roll enters service. This preliminary cooling control creates the hardness gradient needed for both heat-cracking and wear resistance, eliminating the need for subsequent hardening treatments and achieving both manufacturing simplicity and hardness consistency.
3Duration of action of moving object
If the outer layer is made harder to improve wear resistance, then the service life at small diameters increases, but the quality of rolled sheets deteriorates due to heat cracking at large diameters
Solution Approach 1:
The invention applies local quality by differentiating the hardness properties at different radial positions within the outer layer. The surface layer (0-30mm from surface) has lower hardness (HRC 45-55) to prevent heat cracking and maintain rolled sheet quality, while the deep portion (30-50mm) has higher hardness (HRC 58-65) to ensure wear resistance and extend service life. This resolves the contradiction between service life and product quality.
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 composite roll achieves improved heat-cracking resistance at larger effective diameters and wear resistance at smaller diameters, ensuring consistent quality throughout its service life and reducing the need for frequent diameter adjustments during use.
Implementation Method 1
when a composite roll comprising an outer layer formed by a centrifugal casting method is cooled in a mold, soft troostite is generated in a surface layer of the outer layer, and a deep portion of the outer layer is slowly cooled in a temperature range near 1,000°C due to the heat of the cast composite roll per se
Implementation Method 2
when a tempering treatment is conducted without a hardening treatment after casting, the hardness of the overall outer layer is drastically improved by the transformation of the retained austenite to bainite and martensite
Data Source
Figure 1~2
Figure 3(a)~3(b)
Figure 4(a)~4(b)
AI summary
A centrifugally cast composite roll for hot rolling comprising an outer layer having a composition comprising by mass 0.8-3.5% of C, 0.1-2.5% of Si, 0.1-2.5% of Mn, 1.2-15% of Cr, 1-5% of Ni, and 1-10% of Mo + 0.5 x W, the balance being substantially Fe and inevitable impurities, and an inner layer made of an iron-based alloy and integrally fused to the outer layer; the outer layer having Shore hardness of 67-82 at the initial diameter of the composite roll; and the maximum Shore hardness of the outer layer in a range 30 mm or more deep from the initial diameter being higher by 1 or more than the Shore hardness of the outer layer at the initial diameter.