Composite Rolling Roll Outer Layer for Wear and Crack Resistance
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Solution Overview
Problem
Existing centrifugally cast composite rolls for hot rolling suffer from excessive crack initiation and high residual stress, leading to potential spalling during cobble incidents, with previous solutions failing to provide adequate wear resistance and surface deterioration resistance comparable to high-speed steel cast iron rolls.
Innovation Solution
A centrifugally cast composite roll with an outer layer composition of C: 1.5 to 3.5%, Si: 0.3 to 3.0%, Mn: 0.1 to 3.0%, Ni: 1.0 to 6.0%, Cr: 1.5 to 6.0%, Mo: 0.1 to 2.5%, V: 2.0 to 6.0%, Nb: 0.1 to 3.0%, B: 0.001 to 0.2%, and N: 0.005 to 0.070%, containing 5 to 30% M3C carbide by area ratio, and subjected to a tempering treatment without quenching, at 400°C to 550°C, to achieve optimal Shore hardness and residual stress levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high carbon content (2.2-3.5% C) and high alloying elements (Cr: 4-15%, Mo: 2-10%, V: 3-10%) are used to improve wear resistance, then wear resistance is improved, but crack initiation becomes more likely and rolling incident resistance deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters by strictly limiting P to 0.001-0.05% (down from conventional 0.1-0.6%) and B to 0.001-0.05% (down from conventional 0.05-0.5%), while optimizing C to 2.0-3.5% and alloying elements (Cr: 1.0-10.0%, Mo: 1.0-5.0%, V: 1.0-5.0%). This parameter optimization resolves the contradiction by reducing impurity content that causes embrittlement while maintaining carbide-forming elements for wear resistance, achieving both high wear resistance and rolling incident resistance
Solution Approach 2:
The invention creates a composite microstructure containing M3C carbide (30-70% by area ratio), M2C carbide (10-30% by area ratio), and M7C3 carbide (10-30% by area ratio) through controlled cooling and tempering processes. This composite carbide structure provides both wear resistance from the hard carbides and crack resistance by distributing stress across multiple carbide types, preventing deep crack initiation
2Strength
If quenching treatment is applied to achieve high hardness, then wear resistance is improved, but residual stress increases and crack development accelerates
Solution Approach 1:
The invention extracts the quenching step from the conventional heat treatment process, using only tempering treatment at 200-600°C after centrifugal casting. This removal of the quenching operation eliminates the rapid cooling that generates high residual stress and accelerates crack development, while the tempering process alone achieves sufficient hardness (HRC 50-60) without the harmful stress effects
Solution Approach 2:
The invention converts the potential harm of high residual stress from quenching into a benefit by using the tempering process to achieve controlled hardness while simultaneously reducing residual stress. The tempering treatment at 200-600°C allows the material to achieve the desired hardness level while the slow cooling process prevents stress concentration, turning what would normally be a harmful stress condition into a beneficial low-stress high-hardness state
3Ease of manufacture
If phosphorus content is increased to 0.1-0.6% to improve fluidity during casting, then casting processability is improved, but P segregates in grain boundaries causing embrittlement
Solution Approach 1:
The invention dramatically reduces the phosphorus content parameter from conventional 0.1-0.6% to 0.001-0.05%, representing a 10-60 times reduction. This extreme parameter change eliminates P segregation in grain boundaries that causes embrittlement, while the improved fluidity is achieved through optimized silicon content (1.0-3.0%) and controlled cooling rates during centrifugal casting
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 suppresses crack development and enhances wear resistance and surface deterioration resistance to levels comparable to high-speed steel cast iron rolls, while maintaining rolling incident resistance at the level of high alloy grain cast iron rolls, particularly in the later stands of hot finish rolling mills.
Implementation Method 1
a tempering treatment without quenching, at 400°C to 550°C, to achieve optimal Shore hardness and residual stress levels
Implementation Method 2
Centrifugally cast composite roll for rolling
Data Source
AI summary
There is provided a centrifugally cast composite roll for rolling having excellent wear resistance and surface deterioration resistance at levels of a high-speed steel cast iron roll and having rolling incident resistance at a level of a high alloy grain cast iron roll. Its outer layer includes chemical components by mass ratio: C: 1.5 to 3.5%; Si: 0.3 to 3.0%; Mn: 0.1 to 3.0%; Ni: 1.0 to 6.0%; Cr: 1.5 to 6.0%; Mo: 0.1 to 2.5%; V: 2.0 to 6.0%; Nb: 0.1 to 3.0%; B: 0.001 to 0.2%; N: 0.005 to 0.070%; and the balance being Fe and inevitable impurities, wherein: a chemical composition of the outer layer satisfies Formula (1) and has 5 to 30% of M3C carbide by area ratio; an outer layer Shore hardness (A) of a roll surface satisfies Formula (2); and a residual stress (B) of the roll surface satisfies Formula (3),2×Ni+0.5×Cr+Mo>10.0 (1)Hs 75≤A≤Hs 85 (2)100 MPa≤B≤350 MPa (3).