Centrifugal Casting Hot-Rolling Composite Roll
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Solution Overview
Problem
Hot strip mill rolls face challenges with wear resistance, sticking resistance, and accident resistance due to thermal and mechanical loads, leading to surface damage and cracking, particularly in rear finishing stands where overlapped rolling occurs, resulting in insufficient hardness and fracture toughness in existing composite rolls.
Innovation Solution
A centrifugally cast hot-rolling composite roll with an outer layer composed of cast iron containing specific chemical compositions and structures, including graphite and MC carbides, and an intermediate layer with controlled Cr and Nb content, integrated with a ductile cast iron shaft portion, to enhance wear resistance, sticking resistance, and fracture toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hardening is conducted at 800-950°C to improve wear resistance, then the outer layer achieves high hardness, but temperature difference between surface and inner portion generates residual compression stress that leads to cracking
Solution Approach 1:
The patent changes the hardening temperature parameter from the conventional 800-950°C range to a lower range of 200-450°C. This parameter change reduces the temperature difference between surface and inner portion, thereby minimizing residual compression stress while still achieving the required hardness through controlled carbide precipitation and matrix transformation at the lower temperature range.
2Strength
If the outer layer contains high Cr content (3.0-10.0%) to improve wear resistance, then carbide hardness increases, but graphite precipitation is suppressed resulting in poor sticking resistance and fracture toughness
Solution Approach 1:
The patent changes the Cr content parameter from high levels (3.0-10.0%) to a controlled range of 0.5-2.0%. This parameter change allows sufficient Cr to form hard carbides for wear resistance while preventing excessive Cr from suppressing graphite precipitation. The balanced Cr level maintains both wear resistance through carbide formation and sticking resistance through adequate graphite content.
Solution Approach 2:
The patent applies local quality by creating a specific carbide distribution pattern where Cr-rich carbides are precipitated in controlled amounts and locations within the matrix. The Cr content is optimized to form discrete hard carbide particles that provide wear resistance without forming continuous networks that would suppress graphite precipitation throughout the entire outer layer.
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 excellent wear resistance, sticking resistance, and accident resistance with high fracture toughness, preventing surface damage and cracking, and ensuring radial uniformity and good bonding between layers, thus improving the quality of rolled products.
Implementation Method 1
produced by centrifugal casting
Data Source
AI summary
A centrifugally cast hot-rolling composite roll comprising (a) an outer layer made of cast iron having a chemical composition comprising by mass 2.5-3.5% of C, 1.3-2.4% of Si, 0.2-1.5% of Mn, 3.5-5.0% of Ni, 0.8-1.5% of Cr, 2.5-5.0% of Mo, 1.8-4.0% of V, and 0.2-1.5% of Nb, the balance being Fe and inevitable impurities, a mass ratio of Nb/V being 0.1-0.7, and a mass ratio of Mo/V being 0.7-2.5, and meeting the condition of 2.5 ≤ V + 1.2 Nb ≤ 5.5, and having a structure comprising 0.3-10% by area of a graphite phase; (b) a shaft portion made of ductile cast iron in which the area ratio of ferrite is 35% or less; and (c) an intermediate cast iron layer.