Clad Steel Plate Microstructure for Strength-Toughness and Ductility
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Solution Overview
Problem
Clad steel plates lack sufficient ductility, which is crucial for applications requiring complex shape processing, such as chemical tankers, despite offering high strength and toughness.
Innovation Solution
The chemical composition and microstructure of the base steel plate are optimized by forming a hard bainite and martensite phase on the surface and a soft ferrite phase in the inner portion, with a controlled hardness difference between the surface and inner portions, to enhance ductility while maintaining high strength and toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the base steel plate is made with high strength and toughness, then strength and toughness are improved, but ductility deteriorates
Solution Approach 1:
The invention applies local quality by creating different microstructures in different regions of the base steel plate. The inner portion contains ferrite phase (30-80% area ratio) providing ductility, while the surface portion contains bainite and martensite phases (80% or more area ratio) providing strength and toughness. This regional differentiation resolves the contradiction between overall strength and local ductility.
Solution Approach 2:
The invention uses composite materials by combining multiple phases (ferrite, bainite, martensite) within the base steel plate to achieve a balance of properties. The ferrite phase contributes to ductility and formability, while the bainite and martensite phases provide strength and toughness, creating a composite microstructure that satisfies multiple requirements simultaneously.
2Strength
If the surface portion is made hard to improve strength, then strength is improved, but ductility deteriorates due to excessive hardness difference
Solution Approach 1:
The invention applies parameter changes by precisely controlling the hardness difference between the surface and inner portions within a specific range (25-80 HV). This quantitative parameter control ensures that the surface is hard enough for strength while preventing excessive hardness difference that would cause strain localization and reduce ductility. The tempering temperature (500-750°C) and holding time (5-120 minutes) are also optimized to achieve this balance.
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 clad steel plate achieves excellent ductility, strength, and toughness, making it suitable for complex shape processing applications like chemical tankers, while ensuring corrosion resistance.
Implementation Method 1
when the surface portion and the inner portion of the base steel plate have different cooling rates and a hard microstructure mainly composed of bainite phase and martensite phase is formed in the surface portion of the base steel plate, while a soft microstructure containing at least a certain amount of ferrite phase is formed in the inner portion of the base steel plate
Implementation Method 2
it is important to perform tempering treatment under appropriate conditions with the surface portion of the base steel plate being made into a hard microstructure while the inner portion thereof into a soft microstructure
Data Source
Figure 1
AI summary
Provided is a clad steel plate including: a base steel plate; and a cladding metal made of a corrosion-resistant alloy bonded or joined to one surface of the base steel plate, wherein the base steel plate includes: a predetermined chemical composition, a microstructure of a surface portion containing, in terms of area fraction, at least one of a bainite phase or a martensite phase in an amount of 80 % or more in total, and a microstructure of an inner portion containing, in terms of area fraction, a ferrite phase in an amount of 30 % or more, and the difference in hardness between the surface portion and the inner portion of the base steel plate is 20 or more to 80 or less in terms of Vickers hardness. The clad steel plate is excellent in ductility while securing high strength and high toughness.