High-Nitrogen Stainless Steel Pipe Nitrogen Diffusion Process
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Solution Overview
Problem
Conventional austenite stainless steel pipes with high nickel content, used in compressed hydrogen gas storage tanks, face challenges of low strength and ductility, and existing nitrogen absorption and diffusion processes lead to crystal grain enlargement and faults like blowholes, making it difficult to produce high-nitrogen austenite stainless steel pipes with both high strength and ductility for large dimensions.
Innovation Solution
A nitrogen absorption and diffusion process is applied to austenite stainless steel pipes at temperatures near 1000 to 1100°C, creating a gradient structure with high nitrogen concentration near the surface and decreasing nitrogen concentration towards the center, minimizing crystal grain enlargement, and subsequent annealing and plastic working enhance strength and ductility, while grain refinement treatments further improve mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If nitrogen absorption and diffusion process is performed at high temperature (1200°C or above), then nitrogen concentration in steel increases and strength improves, but crystal grain enlargement occurs and ductility decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the nitrogen absorption and diffusion temperature to be below the critical temperature for crystal grain enlargement. This temperature parameter control allows nitrogen to be absorbed and diffused into the steel without causing excessive crystal grain growth, thereby maintaining ductility while achieving high strength through nitrogen concentration in the steel matrix.
Solution Approach 2:
The patent employs preliminary action by performing nitrogen absorption and diffusion treatment before the steel undergoes service conditions. The nitrogen is pre-absorbed and diffused into the steel matrix at controlled temperatures, creating a high-strength, ductile material structure in advance, which prevents hydrogen gas embrittlement and ensures optimal mechanical properties before the steel is put into application.
2Strength
If nitrogen is added to austenite stainless steel to increase strength, then offset yield strength increases to about three times as high, but manufacturing defects like blow holes and segregation occur
Solution Approach 1:
The patent replaces the conventional melting-solidification process with a nitrogen absorption and diffusion process. Instead of adding nitrogen during steelmaking (which causes blow holes and segregation due to phase transformation), the patent uses thermal diffusion to introduce nitrogen into the solid steel matrix, substituting a thermal-chemical process for a mechanical-melting process and thereby eliminating manufacturing defects.
Solution Approach 2:
The patent uses nitrogen gas atmosphere as an intermediary medium to transfer nitrogen into the steel. By exposing the steel to nitrogen-containing atmosphere at controlled temperatures, nitrogen acts as an intermediary that diffuses into the steel matrix without causing the defects associated with direct nitrogen addition during melting, achieving high strength with excellent product quality.
3Reliability
If high nickel content is used in austenite stainless steel for hydrogen gas storage tanks, then corrosion and heat resistance improve, but strength and ductility decrease
Solution Approach 1:
The patent creates a composite material structure by combining high nickel content austenite stainless steel with nitrogen-diffused zones. The base material provides excellent corrosion and heat resistance due to high nickel content, while the nitrogen-diffused regions provide enhanced strength and ductility. This composite approach allows the material to simultaneously achieve reliability in corrosive environments and mechanical strength for hydrogen storage tank applications.
Solution Approach 2:
The patent applies local quality by creating a nitrogen concentration gradient within the steel, with higher nitrogen concentration near the surface and decreasing concentration toward the center. This local variation in nitrogen distribution provides enhanced strength and ductility where needed (at the surface and near-surface regions) while maintaining the overall corrosion and heat resistance properties of the high nickel austenite stainless steel bulk material.
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 process results in high-nitrogen austenite stainless steel pipes with enhanced strength, ductility, and corrosion resistance, suitable for large dimensions, effectively preventing hydrogen gas embrittlement, and achieving properties unattainable by conventional methods.
Implementation Method 1
heating said steel pipe together with said nitrogen source substance at a temperature of 800 to 1100°C in a range of temperatures not higher than the critical temperature for crystal grain enlargement of the steel pipe material to cause nitrogen to be absorbed into the surface of the pipe and diffused into the solid phase
Implementation Method 2
nitrogen to be absorbed into the surface of the pipe and diffused into the solid phase
Implementation Method 3
applying to said heat-treated pipe material annealing treatment in said range of temperatures in vacuum, inert gas including argon gas or an atmosphere of a gas with a reducing substance including H2 gas added thereto, to result in a decrease of nitrogen concentration gradient
Data Source
AI summary
A process for manufacturing a high nitrogen stainless steel pipe material includes keeping an outside surface and/or an inside surface of an austenite stainless steel pipe material in contact with a substance that becomes a nitrogen (N) source, heating the steel pipe together with the nitrogen source substance at a temperature of 800° C. to 1100° C. in a range of temperatures not higher than the critical temperature for crystal grain enlargement of the steel pipe material to cause nitrogen to be absorbed into the surface of the pipe and diffused into the steel solid phase, and applying to the heat-treated pipe material annealing treatment in the range of temperatures in vacuum, inert gas including argon gas or an atmosphere of a gas with a reducing substance including H2 gas added thereto, to result in a decrease of nitrogen concentration gradient.