Steel Sheet Hydrogen Embrittlement Resistance via Mn Segregation
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Solution Overview
Problem
Current high-strength steel sheets face challenges in hydrogen embrittlement resistance, as existing technologies fail to effectively inhibit hydrogen segregation to grain boundaries, leading to reduced strength and increased susceptibility to cracking.
Innovation Solution
A steel sheet with a specific chemical composition and microstructural arrangement, including a balance of ferrite, martensite, and tempered martensite, where manganese is micro-dispersed to create stronger segregation sites that divert hydrogen away from grain boundaries, thereby enhancing embrittlement resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional high-strength steel sheets are used to achieve high tensile strength, then strength is improved, but hydrogen embrittlement resistance deteriorates due to hydrogen segregation to grain boundaries
Solution Approach 1:
Manganese acts as an intermediary element that creates alternative segregation sites (Mn-rich precipitates and inclusions) within the steel matrix. These Mn-rich regions serve as mediators to intercept and trap hydrogen atoms, preventing their migration to grain boundaries. The Mn concentration in these regions is controlled to be 1.5-4.0 mass%, creating effective hydrogen trapping sites that protect the grain boundary structure.
Solution Approach 2:
The invention converts the typically harmful effect of Mn segregation (which can cause brittleness) into a beneficial hydrogen trapping mechanism. By controlling Mn distribution to create discrete Mn-rich precipitates and inclusions, the steel utilizes these segregations as hydrogen sinks, transforming what would be defect sites into protective features that enhance hydrogen embrittlement resistance while maintaining high strength.
2Reliability
If Mn is added to improve hydrogen embrittlement resistance, then embrittlement resistance is improved, but manufacturing precision deteriorates due to Mn segregation
Solution Approach 1:
The invention applies local quality by creating Mn-rich regions with specific characteristics (1.5-4.0 mass% Mn) distributed throughout the steel matrix, while maintaining the overall steel composition with 0.15-2.0 mass% Mn. These localized Mn-rich precipitates and inclusions provide hydrogen trapping functionality without causing excessive macroscopic segregation, achieving both hydrogen embrittlement resistance and acceptable microstructure uniformity.
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 significantly improves hydrogen embrittlement resistance while maintaining high tensile strength, preventing cracking and ensuring excellent formability and weldability.
Implementation Method 1
a standard deviation a of Mn concentration satisfies a ≥0.15×Mnave, and a region with a Mn concentration of higher than (Mnave+1.3a) has a circle-equivalent diameter of less than 10.0 μm
Data Source
AI summary
Provided are: a steel sheet having a high strength and excellent hydrogen embrittlement resistance; and a method of producing the same. The steel sheet has prescribed chemical composition and structure, in which a standard deviation σ of Mn concentration satisfies σ≥0.15 Mnave (wherein, Mnave represents an average Mn concentration) and a region with a Mn concentration of higher than (Mnave+1.3σ) has a circle-equivalent diameter of less than 10.0 μm. The method of producing the steel sheet includes: the hot rolling step that includes finish rolling a slab having a prescribed chemical composition under prescribed conditions; the step of coiling the thus obtained hot-rolled steel sheet at a coiling temperature of 450 to 700° C.; and the step of cold rolling the hot-rolled steel sheet and subsequently annealing this steel sheet at 800 to 900° C.