Hearth Roll Thermal Spray Coating for Fe-Mn Buildup Resistance
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Solution Overview
Problem
Existing thermal spray coatings for hearth rolls in continuous annealing furnaces suffer from reduced thermal shock resistance, crack resistance, and inadequate buildup resistance, particularly for Fe and Mn-based substances, due to high chromium carbide content and aluminum oxidation leading to MnAl double oxide formation.
Innovation Solution
A thermal spray coating for hearth rolls comprising a Co-based alloy, transition metal carbide, and double oxides, with specific molar ratios and content percentages to enhance Fe and Mn buildup resistance, thermal shock resistance, and crack resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the content of chromium carbide is increased to improve buildup resistance, then Fe-based buildup resistance is improved, but thermal shock resistance and crack resistance are degraded
Solution Approach 1:
The patent optimizes the content of chromium carbide within a specific range (10-30 mass%) rather than using high concentrations, and adjusts the Al content (5-20 mass%) to control oxide formation. This parameter optimization resolves the contradiction by finding the optimal balance point where sufficient buildup resistance is achieved without excessive carbide content that would harm thermal shock and crack resistance
Solution Approach 2:
The patent creates a composite thermal spray coating material comprising multiple components: Co-based alloy (50-80 mass%), chromium carbide (10-30 mass%), and aluminum (5-20 mass%). This composite structure combines the buildup-resistance-providing carbide with the ductility-providing Co-based alloy and the oxide-forming aluminum, achieving a balance where the composite as a whole provides both buildup resistance and adequate thermal shock/crack resistance
2Object-affected harmful factors
If aluminum is included in the thermal spray powder to improve Fe-based buildup resistance, then Fe-based buildup resistance is improved, but Mn-based buildup is promoted due to Al2O3 reacting with MnO to generate MnAl double oxide
Solution Approach 1:
The patent precisely controls the aluminum content within 5-20 mass% and chromium carbide content within 10-30 mass%, creating an optimal chemical environment where aluminum provides sufficient Fe-based buildup resistance while limiting the formation of MnAl double oxide. The controlled stoichiometry prevents excessive reactive oxide formation that would promote Mn-based buildup
Solution Approach 2:
The patent creates different functional zones within the coating structure: the chromium carbide-rich regions provide Fe-based buildup resistance, while the controlled aluminum distribution provides localized oxide barriers. This spatial differentiation of material properties allows the coating to simultaneously resist both Fe-based and Mn-based buildup through locally optimized chemistry
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 proposed coating improves Fe and Mn buildup resistance, thermal shock resistance, and crack resistance while reducing carbide content, maintaining optimal performance in high-temperature environments.
Implementation Method 1
aluminum included in the thermal spray powder becomes Al2O3 during thermal spraying, and the Al2O3 reacts with MnO included in the steel plate to generate a MnAl double oxide
Implementation Method 2
an increase in the content of chromium carbide causes thermal shock resistance and crack resistance of the thermal spray coating to be degraded
Data Source
AI summary
A hearth roll for a continuous annealing furnace, the hearth roll comprising a thermal spray coating on a surface of the hearth roll, wherein the thermal spray coating comprises main components consisting of a Co-based alloy, a carbide of a transition metal, and a double oxide; and impurities, the double oxide consists of one or two types of a first double oxide consisting of Al and a rare earth element and a second double oxide consisting of a transition metal and a rare earth element, and when the main components are 100 mass %, a content of the Co-based alloy is 25 mass % or more and 50 mass % or less, a content of the carbide is 5 mass % or more and 30 mass % or less, and a content of the double oxide is 20 mass % or more and 45 mass % or less.