Austenitic Steel Welded Joint Nitrogen Stabilization
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Solution Overview
Problem
High-strength austenitic steel welded joints used in high-pressure hydrogen applications face challenges in achieving stable nitrogen content under various welding conditions, leading to potential weld defects and inadequate hydrogen embrittlement resistance without prolonged heat treatment.
Innovation Solution
Austenitic steel welded joints are produced using base and welding materials with specific chemical compositions that stabilize the austenitic phase and allow for solute strengthening by nitrogen, even with lower nitrogen content in the welding material, ensuring high strength and hydrogen embrittlement resistance without heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a welding material containing a large amount of N (0.15 to 0.35% N) is used to achieve high strength through solute strengthening, then the tensile strength of the welded joint can exceed 800 MPa, but welding materials are limited in their applicability and weld defects such as blowholes may occur under some welding conditions
Solution Approach 1:
The invention changes the chemical composition parameters of the welding material, specifically reducing N content from 0.15-0.35% to less than 0.15%, while adjusting other alloying elements (C: 0.03-0.10%, Si: 0.10-0.70%, Mn: 1.00-3.00%, Ni: 8.00-23.00%, Cr: 17.00-25.00%, Mo: 0.01-4.00%, V: 0.01-0.50%, Nb: 0.01-0.50%, Al: 0.01-0.05%) to achieve the same high strength effect without causing weld defects
Solution Approach 2:
The invention creates a composite alloying strategy by combining multiple strengthening mechanisms: solute strengthening from N (at lower concentrations), precipitation strengthening from V and Nb nitrides, and solid solution strengthening from Ni and Cr, achieving synergistic effects that provide both high strength and weldability
2Strength
If a welding material containing a large amount of N is used to provide high strength through solute strengthening, then the strength requirement can be met, but N may be separated from the weld metal during welding, making it difficult to provide a certain N content in the weld metal in a stable manner under a wide range of welding conditions
Solution Approach 1:
The invention optimizes the chemical composition parameters by reducing N content to less than 0.15% and adjusting the ratios of other alloying elements, particularly increasing Ni (8.00-23.00%) and Cr (17.00-25.00%), which stabilize the austenitic phase and prevent N segregation during welding, ensuring stable N content retention under various welding conditions
Solution Approach 2:
The invention uses Ni and Cr as intermediary elements that stabilize the austenitic matrix structure, preventing N segregation and promoting uniform distribution of N in the weld metal, thereby ensuring stable composition under a wide range of welding conditions
3Strength
If prolonged heat treatment after welding is performed to provide high strength in the welded portion, then the tensile strength can reach 800 MPa or higher, but manufacturing time is extended and manufacturing costs increase
Solution Approach 1:
The invention performs preliminary action by optimizing the chemical composition of the welding material before welding to achieve high strength without subsequent heat treatment. The specific composition (C: 0.03-0.10%, Si: 0.10-0.70%, Mn: 1.00-3.00%, Ni: 8.00-23.00%, Cr: 17.00-25.00%, Mo: 0.01-4.00%, V: 0.01-0.50%, Nb: 0.01-0.50%, Al: 0.01-0.05%, N: less than 0.15%) is designed to produce self-hardening weld metal that achieves 800 MPa or higher tensile strength directly after welding
Solution Approach 2:
The invention extracts the heat treatment step from the manufacturing process by designing a welding material composition that achieves high strength through controlled alloying and solidification, eliminating the need for prolonged heat treatment and reducing manufacturing time and costs
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 provides welded joints with high tensile strength and excellent hydrogen embrittlement resistance, eliminating the need for heat treatment and reducing manufacturing costs while preventing weld defects like blowholes.
Implementation Method 1
WO 2004/083476, WO 2004/083477 and WO 2004/110695 propose increasing Mn to increase the solubility of N and including V or including a combination of V and Nb to take advantage of solute strengthening of N
Implementation Method 2
including V or including a combination of V and Nb to take advantage of solute strengthening of N and precipitation strengthening of nitride
Data Source
AI summary
A welded joint having high strength and good hydrogen embrittlement resistance is provided. A welded joint is a welded joint obtained by welding a base material using a welding material. The base material has a chemical composition of, in mass %: C: 0.005 to 0.1%; Si: up to 1.2%; Mn: 2.5 to 6.5%; Ni: 8 to 15%; Cr: 19 to 25%; Mo: 0.01 to 4.5%; V: 0.01 to 0.5%; Nb: 0.01 to 0.5% Al: less than 0.05%; N: 0.15 to 0.45%; O: up to 0.02%; P: up to 0.05%; and S: up to 0.04%, and a balance being iron and impurities, and which satisfies Equation (1). The welding material has a chemical composition which satisfies Equations (1) and (2).Ni+0.65Cr+0.98Mo+1.05Mn+0.35Si+12.6C≥29 (1)0.31C+0.048Si−0.02Mn−0.056Cr+0.007Ni−0.013Mo≤−1.0 (2)