Composite Hot-Rolling Roll Composition for Carbide Distribution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Centrifugally cast composite rolls for hot rolling in steel strip mills face challenges with wear resistance and casting defects, particularly in the usable range, and often have issues with the distribution and segregation of MC carbides, leading to poor boundary integrity between the outer and inner layers.
Innovation Solution
Optimizing the composition of the outer layer with specific ranges of V and Nb, limiting the V/Nb ratio and V equivalent, to ensure MC carbides are distributed mainly within the usable range, and incorporating additional elements like B, W, Ti, Al, and Co to enhance wear resistance and structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-alloy indefinite chilled cast iron is used for the outer layer to improve incident resistance, then sticking resistance and crack resistance are improved, but wear resistance deteriorates compared to high-chromium cast iron or high-speed steel
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the outer layer, specifically limiting C to 2.7-3.5%, Si to 1.0-2.5%, and Cr to 2.0-4.0%, while also controlling the Cr/C ratio to 0.70 or less. This compositional parameter optimization enables the outer layer to achieve both high incident resistance and high wear resistance by balancing the microstructure formation, resolving the contradiction between these two properties.
Solution Approach 2:
The patent employs composite materials by creating an outer layer with a complex microstructure containing graphite, cementite, and carbides distributed in a matrix. This composite microstructure, achieved through controlled alloying and centrifugal casting, combines the benefits of different phases: graphite provides toughness and incident resistance, while cementite and carbides provide wear resistance, thus resolving the contradiction between incident resistance and wear resistance.
2Object-generated harmful factors
If MC carbides are increased to improve wear resistance, then wear resistance is improved, but casting defects increase and boundary integrity between outer and inner layers deteriorates
Solution Approach 1:
The patent applies parameter changes by controlling the Cr content to 2.0-4.0% and the Cr/C ratio to 0.70 or less, which regulates the formation of cementite and carbides. This parameter control ensures sufficient wear-resistant phases are formed in the outer layer while preventing excessive carbide precipitation that would cause casting defects and poor boundary integrity with the inner layer.
3Productivity
If the usable range of the roll is extended to improve productivity, then productivity is improved, but the roll diameter decreases from initial to discard diameter requiring frequent stock removal
Solution Approach 1:
The patent applies parameter changes by optimizing the chemical composition to create a uniform microstructure with controlled graphite, cementite, and carbide distribution throughout the outer layer. This uniform structure ensures consistent wear resistance across the entire usable range from initial to discard diameter, allowing the roll to maintain performance throughout its full operational life and extend the usable range while minimizing the need for stock removal.
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 optimized composite roll achieves excellent wear resistance across the usable range with suppressed casting defects and a good boundary between the outer and inner layers, suitable for severe rolling conditions in hot-strip mills.
Implementation Method 1
a centrifugal casting method is used to form an outer layer
Implementation Method 2
MC carbides are distributed mainly in a usable range from an initial diameter to a discard diameter
Implementation Method 3
an outer layer having excellent wear resistance and an inner layer integrally fused to the outer layer
Data Source
AI summary
A centrifugally cast composite roll for hot rolling comprising an outer layer made of an Fe-based alloy having a chemical composition comprising by mass 2.6-3.6% of C, 0.1-3% of Si, 0.3-2% of Mn, 2.3-5.5% of Ni, 0.5-3.2% of Cr, 0.3-1.6% of Mo, 1.8-3.4% of V, and 0.7-2.4% of Nb, 1.4≤V/Nb≤2.7, a V equivalent (Veq=V+0.55Nb) being 2.60-4% by mass, and the balance being Fe and impurities, and an inner layer made of an iron-based alloy and integrally fused to the outer layer.