Bainite-Ferrite Steel Pipe for High-Pressure Hydrogen Service
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Solution Overview
Problem
Current materials used in high pressure hydrogen piping, such as SUS316L stainless steel, lack economic efficiency and do not effectively address hydrogen embrittlement, which deteriorates the strength properties of metal materials in hydrogen environments.
Innovation Solution
A steel pipe with a specific chemical composition and metallographic structure, comprising a mixed structure of bainite and ferrite, is developed. The steel pipe has a tensile strength of 500 MPa or more and 900 MPa or less in a hydrogen atmosphere, with a hardness of 160 HV1 or more and 280 HV1 or less, and is designed with a ratio of outer to inner diameter that satisfies a specific formula to ensure safety and economic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SUS316L stainless steel is used for high pressure hydrogen piping, then safety is improved through proven track record and hydrogen compatibility, but economic efficiency deteriorates due to low strength requiring thick pipe walls and small bores
Solution Approach 1:
The patent changes the material parameters by specifying a carbon steel composition with controlled carbon content (0.17-0.27%) and specific alloying elements (Si: 0.05-0.40%, Mn: 0.30-2.00%, P: 0.035% or less, S: 0.035% or less, Cu: 0-0.50%, Mo: 0-1.0%, V: 0-0.15%) to achieve both high strength and hydrogen embrittlement resistance, replacing the conventional SUS316L stainless steel
Solution Approach 2:
The patent creates a composite microstructure consisting of bainite and ferrite phases through controlled cooling and heat treatment processes, combining the high strength characteristics of bainite with the toughness and hydrogen embrittlement resistance of ferrite
2Productivity
If high strength materials are used to reduce pipe wall thickness, then economic efficiency is improved, but hydrogen embrittlement resistance deteriorates
Solution Approach 1:
The patent optimizes the chemical composition parameters, particularly controlling carbon content at 0.17-0.27% (not too high to avoid excessive brittleness, not too low to maintain strength) and adding specific alloying elements that enhance hardenability and microstructure control to achieve both high strength and hydrogen embrittlement resistance
Solution Approach 2:
The patent creates different microstructural zones within the pipe wall through controlled cooling rates, with the outer layer having a microstructure optimized for hydrogen embrittlement resistance and the inner layer optimized for strength, achieving local optimization of properties
3Productivity
If carbon steel is used for high pressure piping, then economic efficiency is improved due to low material cost, but hydrogen embrittlement resistance deteriorates significantly
Solution Approach 1:
The patent modifies the conventional carbon steel composition by adding specific amounts of alloying elements (Si: 0.05-0.40%, Mn: 0.30-2.00%, Cu: 0-0.50%, Mo: 0-1.0%, V: 0-0.15%) that enhance hardenability and control microstructure formation, transforming ordinary carbon steel into a high-strength, hydrogen-resistant material
Solution Approach 2:
The patent utilizes phase transition during cooling and heat treatment to transform the microstructure from conventional pearlite-ferrite to a refined bainite-ferrite mixed structure, which provides both high strength and improved hydrogen embrittlement resistance while maintaining carbon steel's economic advantages
Data Source
AI summary
Provided is a steel pipe for high pressure hydrogen piping, for use in fuel cell vehicles, having a chemical composition consisting of, by mass %, 0.17 to 0.27% C, 0.05 to 0.40% Si, 0.30 to 2.00% Mn, 0.035% or less P, 0.035% or less S, 0 to 0.50% Cu, 0 to 1.0% Mo, 0 to 0.15% V, and a balance being Fe and impurities. The steel pipe has a metallographic structure composed of a mixed structure of bainite and ferrite in a middle part of the thickness of the steel pipe, a tensile strength in a hydrogen atmosphere of 500 MPa or more and 900 MPa or less, and a hardness in the middle part of the thickness of the steel pipe of 160 HV1 or more and 280 HV1 or less, and a defect on the inner surface of the steel pipe has a depth of 200 μm or less at a maximum.