Composite Mill Roll Composition for Residual Stress Crack Control

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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 having specific chemical composition (1.70-2.70% C, 0.3-3% Si, 0.1-3% Mn, 1.1-3.0% Ni, 4.0-10% Cr, 2.0-7.5% Mo, 3-6% V, 0.1-2% W, 0.2-2% Nb, 0.01-0.2% B, and 0.01-0.1% N) and an inner layer of ductile cast iron, integrated with a controlled circumferential residual compressive stress of 150-350 MPa, tempered at 500-550°C after cooling.

Engineering Contradictions & Design Principles

VSEngineering 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

Engineering Contradiction:

Improvewear resistanceVSAvoidcracking resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention changes the chemical composition parameters of the outer layer by reducing alloying elements (Cr: 3-10%, Mo: 2-10%, V: 0.1-8%, W: 0.1-6%, Nb: 0.1-6%) compared to conventional high-speed steel, and controls cooling rates (10-60°C/hr) to reduce residual compressive stress from >300 MPa to 150-350 MPa, thereby improving cracking resistance while maintaining wear resistance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses a composite structure with an outer layer (Fe-based alloy with specific composition) and an inner layer (ductile cast iron), where the outer layer provides wear resistance and the inner layer provides toughness, integrating materials with different properties to simultaneously achieve wear resistance and cracking resistance

Inventive Principle:

Principle #40Composite materials

2Strength

If high-speed steel is used for the outer layer to improve wear resistance, then wear resistance is improved, but sticking resistance deteriorates

Engineering Contradiction:

Improvewear resistanceVSAvoidsticking

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The invention changes the chemical composition parameters by reducing Cr (3-10% vs. conventional 10-15%) and adding specific amounts of Mn (0.1-3%), Ni (1.1-3.0%), and B (0.01-0.2%), which modify the surface properties to reduce sticking tendency while maintaining wear resistance

Inventive Principle:

Principle #35Parameter changes

3Strength

If rapid cooling is applied to increase hardness, then wear resistance is improved, but residual compressive stress increases leading to cracking

Engineering Contradiction:

ImprovehardnessVSAvoidresidual compressive stress

Core Design Contradiction:

StrengthVSStress or pressure

Solution Approach 1:

The invention optimizes the cooling rate parameter within a specific range (10-60°C/hr) rather than using rapid cooling, and controls the tempering temperature (500-550°C) to achieve a balance between hardness (Shore 70-90) and residual compressive stress (150-350 MPa), preventing cracking while maintaining wear resistance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses controlled thermal processing (cooling rate control and tempering at 500-550°C) to manage thermal expansion and contraction, thereby controlling residual stress development during phase transformation and achieving the desired balance between hardness and stress

Inventive Principle:

Principle #37Thermal expansion

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 inward cracking propagation and enhances handling of the composite roll by maintaining low residual compressive stress across the usable diameter range, ensuring prolonged roll life and reduced maintenance costs.

Implementation Method 1

a cooling rate of 10-60°C/hr between the reheating temperature and 600°C

Methodology Applied

Scientific EffectPhase transformation (austenite to martensite): Phase Change

Implementation Method 2

the outer layer has Shore hardness of 70-90 at the initial diameter

Methodology Applied

Scientific EffectHeat treatment: Heat Treatment

Implementation Method 3

high-speed steel contains large amounts of alloying elements such as Cr, Mo, V, W, etc., and has extremely hard carbides crystallized, exhibiting excellent wear resistance

Methodology Applied

Scientific EffectCarbide crystallization: Crystallisation

Implementation Method 4

the outer layer has residual compressive stress of 150 MPa or less at the discard diameter

Methodology Applied

Scientific EffectResidual stress:

Data Source

PatentEP3821992B1Centrifugal cast composite roll for rolling and manufacturing method therefor

Publication Date: 2023.01.18 PROTERIAL LTD

Figure 1~2(a)
Figure 2(b)~3

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.