Steel Sheet Inclusion Control for Hydrogen-Induced Cracking Resistance
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Solution Overview
Problem
Conventional methods for producing steel plates with high manganese content face challenges in achieving effective hydrogen-induced cracking (HIC) resistance due to the formation of MnS inclusions and inclusion clusters, which are not adequately addressed by existing Ca and Mg addition techniques, leading to degraded HIC resistance in the surface layer.
Innovation Solution
A controlled addition process of Mg and Ca substances to molten steel, optimizing temperature, feed rates, and casting conditions to create inclusions with specific compositions and morphologies in the surface layer, suppressing MnS formation and promoting CaS formation, resulting in improved HIC resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional steel sheets are used for automotive body parts, then manufacturing cost is reduced, but corrosion resistance and formability are insufficient
Solution Approach 1:
The patent applies composite material principle by creating a dual-phase steel sheet structure consisting of a base steel sheet and a plating layer with specific microstructure. The plating layer contains martensite, bainite, and retained austenite phases, forming a composite material system that combines the strength of high-strength steel with the corrosion resistance of controlled microstructure, achieving both improved reliability and manufacturability
2Manufacturing precision
If conventional steel sheets are used for automotive body parts, then manufacturing cost is reduced, but formability is insufficient
Solution Approach 1:
The patent applies parameter changes principle by precisely controlling the microstructural parameters of the plating layer, specifically maintaining martensite at 20-60%, bainite at 20-60%, and retained austenite at 10-40%. This parameter control optimizes the balance between strength and formability, enabling complex automotive body parts to be formed without cracking while maintaining cost-effectiveness
3Reliability
If plating layer microstructure is not controlled, then production process is simpler, but surface appearance and corrosion resistance deteriorate
Solution Approach 1:
The patent applies preliminary action principle by designing a specific heating and cooling process schedule that pre-determines the microstructure formation. The process includes heating to Ac3 transformation point or higher, holding for a specified time, and controlled cooling at 5-50°C/s rate, which preliminarily sets up the conditions for achieving the desired martensite-bainite-austenite microstructure before final cooling, ensuring both corrosion resistance and manageable process complexity
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 method produces steel plates with a crack area ratio (CAR) of 1.0% or less, ensuring excellent HIC resistance through controlled inclusion composition and morphology, enhancing the steel's resistance to hydrogen-induced cracking.
Implementation Method 1
the strength is increased by grain refinement
Implementation Method 2
a plating layer having a specific microstructure... obtained by a specific heating and cooling process
Data Source
AI summary
Provided is a steel plate that has excellent HIC resistance. The steel plate has a defined chemical composition, and in a pair of regions from both surfaces of the steel plate to a depth of 1/4 thickness in the thickness direction, inclusions are present that have an average composition of 10 mass% to 40 mass% MgO and an average aspect ratio of 1.5 or less, and an average value of the top 10 % of the circle equivalent diameters of the inclusions is 2.0 µm or less. A crack area ratio CAR after an HIC test in the pair of regions is 1.0 % or less.