Non-magnetic Stainless Steel for Fusion Cladding
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Solution Overview
Problem
The 316LN stainless steel used in Tokamak devices faces challenges with composition control, leading to local intergranular and pitting corrosion, and its mechanical properties are inadequate to meet the requirements for high service temperature, pressure, and neutron irradiation resistance.
Innovation Solution
A high-alloy austenitic stainless steel with controlled Cr, Mn, Co, and Si content is developed, featuring a non-magnetic composition with 17%<Cr<23%, 17%<Mn<23%, 17%<Co<23%, and 0.5%<Si<3%, followed by a heat treatment process including melting, homogenization, forging, and quenching to achieve ultrahigh strength, hardness, and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If N atoms are added to improve strength through solid solution strengthening, then tensile strength increases, but N atoms have low solution solubility in molten iron causing composition control difficulties and local intergranular corrosion
Solution Approach 1:
The patent changes the chemical composition parameters by replacing N with Co and adjusting Cr and Mn content. Specifically, it uses 17-23% Cr, 17-23% Mn, and 17-23% Co to achieve the desired strength without the solubility problems of N. This parameter change resolves the contradiction by finding an alternative alloying strategy that achieves strength improvement while maintaining compositional control.
Solution Approach 2:
The patent replaces the difficult-to-control N element with Co, which has better solubility and controllability in molten iron. This substitution allows for more reliable composition control during manufacturing while still achieving the desired mechanical properties through solid solution strengthening.
2Reliability
If Cr content is increased to improve corrosion resistance, then pitting corrosion resistance improves, but δ-Fe phase region expands reducing mechanical properties and creating magnetic properties
Solution Approach 1:
The patent applies local quality by creating a balanced composition where Cr is concentrated at grain boundaries and corrosion-prone surfaces to provide localized corrosion protection, while the bulk material maintains optimal mechanical properties through the combined effect of Cr, Mn, and Co. This allows high corrosion resistance without requiring excessive overall Cr content that would harm mechanical properties.
Solution Approach 2:
The patent changes the composition parameters by optimizing Cr content to 17-23% (not excessively high) and balancing it with 17-23% Mn and 17-23% Co. This parameter optimization prevents the expansion of δ-Fe phase region while maintaining excellent corrosion resistance, resolving the contradiction between corrosion resistance and mechanical properties.
3Reliability
If high Cr content is used to ensure corrosion resistance, then non-magnetic properties are maintained, but mechanical properties are reduced
Solution Approach 1:
The patent creates a composite alloying system combining Cr, Mn, and Co in specific proportions (17-23% each). This composite approach allows the Cr to provide corrosion resistance and non-magnetic properties, while Mn and Co contribute to mechanical strength through their own solid solution strengthening effects and interaction with the austenite phase, thereby balancing all requirements.
Solution Approach 2:
The patent optimizes the Cr content parameter to 17-23%, which is sufficient for corrosion resistance and non-magnetic properties but not excessively high to harm mechanical properties. This parameter optimization, combined with Mn and Co addition, resolves the contradiction by finding the optimal balance point.
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 resulting stainless steel exhibits yield strength of 500-600 Mpa, tensile strength of 1,000-1,100 Mpa, and superior corrosion resistance, making it suitable for nuclear fusion applications as an outer cladding material with maintained toughness and resistance to deformation.
Implementation Method 1
melting a raw material and casting it to a mold to obtain a stainless steel block
Implementation Method 2
homogenizing the stainless steel block at 1,100-1,250° C. for 6-12 hours
Implementation Method 3
forging the homogenized stainless steel block at 1,050-1,150° C. with a final forging temperature of 850-950° C.
Implementation Method 4
holding the forged plate at 1,000-1,250° C. for 10-30 minutes and then put it in water for quenching to obtain the non-magnetic stainless steel
Implementation Method 5
the mechanical properties of the steel can be greatly improved by solid solution of a large number of N atoms
Data Source
AI summary
The present invention provides a non-magnetic stainless steel with high strength and corrosion resistance and a preparation method thereof. The non-magnetic stainless steel composed of the following components according to percentage by weight: 17%<Cr<23%, 17%<Mn<23%, 17%<Co<23%, 0.5%<Si <3%, and the balance of iron and inevitable impurities thereof. The preparation method includes: (1) melting a raw material and casting it to a mold to obtain a stainless steel block; (2) homogenizing the stainless steel block at 1,100-1,250° C. for 6-12 hours; (3) forging the homogenized stainless steel block at 1,050-1,150° C. with a final forging temperature of 850-950° C. to obtain a plate having a thickness of 5-15 mm; and (4) holding the forged plate at 1,000-1,250° C. for 10-30 minutes and then put it in water for quenching. The non-magnetic stainless steel of the present invention has superior pitting corrosion resistance and mechanical properties. After a certain heat treatment process, the stainless steel has ultrahigh strength, hardness and toughness and excellent corrosion resistance and low-temperature toughness, and can be used for preparing an outer cladding material of a superconductor in the nuclear fusion industry.