Ultrafine-Grain Austenite Stainless Steel Via Controlled Cooling
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Solution Overview
Problem
Existing austenite stainless steels face limitations in strength, ductility, and corrosion resistance, with high alloy content leading to increased costs and decreased formability, and existing grain refinement methods suffer from low productivity and high costs.
Innovation Solution
Austenite stainless steel composition with specific alloying elements (C, Si, Mn, P, S, Cr, Ni, Cu, N) and manufacturing process including hot rolling, cold rolling, and annealing to achieve ultrafine grain diameter and stability parameters, ensuring high strength, ductility, and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If severe plastic deformation is used to refine grains, then grain size is reduced, but productivity decreases and product size is limited
Solution Approach 1:
The patent changes the processing parameters by using hot rolling at specific temperatures (900-1100°C) followed by controlled cooling rates (5-50°C/s) to achieve grain refinement without severe plastic deformation. This parameter optimization allows obtaining ultrafine grains (5 μm or less) while maintaining high productivity and no product size limitation
Solution Approach 2:
The patent replaces the mechanical severe plastic deformation method with a thermodynamic approach using hot rolling and controlled cooling. Instead of applying strong shear stress mechanically, the patent uses temperature control and phase transformation to achieve grain refinement, thereby avoiding productivity loss and size limitations
2Manufacturing precision
If long-time heat treatment is performed to obtain fine grains, then grain size is reduced, but manufacturing time increases and costs increase
Solution Approach 1:
The patent uses periodic action through controlled cooling rates (5-50°C/s) after hot rolling to achieve rapid grain refinement. Instead of long-time heat treatment, the patent employs a time-efficient cooling process that transforms the microstructure quickly, reducing manufacturing time from over 48 hours to a much shorter duration while achieving the same fine grain size
Solution Approach 2:
The patent utilizes phase transitions during controlled cooling from the austenite phase to achieve grain refinement. By controlling the cooling rate through specific ranges, the patent triggers phase transformation that produces ultrafine grains without requiring long-time heat treatment, thereby reducing both time and cost
3Strength
If high alloy content is used to increase strength, then yield strength is improved, but manufacturing cost increases and formability decreases
Solution Approach 1:
The patent changes the approach from increasing alloy content to optimizing processing parameters. By controlling hot rolling temperature (900-1100°C) and cooling rate (5-50°C/s), the patent achieves ultrafine grain structure that provides high strength (600 MPa tensile strength) without requiring high alloy content, thereby maintaining ease of manufacture and price competitiveness
Solution Approach 2:
The patent creates a composite microstructure through ultrafine grain formation and phase transformation during controlled cooling. This microstructural composite provides enhanced strength properties comparable to high-alloy steels but with lower alloy content, improving both strength and manufacturing cost characteristics
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 achieves high strength (600 MPa), high ductility (30% elongation), and improved corrosion resistance with a pitting potential of 200 mV or more, while maintaining price competitiveness.
Implementation Method 1
severe plastic deformation (SPD) has drawn attention. Severe plastic deformation is a method for realizing fine grains by generating new grain boundaries in existing grain boundaries by applying a strong sheer stress to a material
Implementation Method 2
Patent Document 0002 discloses a method including heat treatment performed at a temperature of 600 to 700° C. for a long time over 48 hours
Data Source
AI summary
Provided are an austenite stainless steel having high strength, high ductility, and improved corrosion resistance by realizing ultrafine grain characteristics and a manufacturing method therefor.The austenite stainless steel according to an embodiment of the present disclosure includes, in weight %, at least 0.05% but not more than 0.1% of C, at least 0.2% but not more than 0.7% of Si, at least 2.0% but not more than 4.0% of Mn, more than 0% but less than 0.1% of P, more than 0% but less than 0.01% of S, at least 17% but not more than 19% of Cr, at least 2.0% but not more than 4.0% of Ni, at least 1.0% but not more than 2.5% of Cu, at least 0.15% but not more than 0.25% of N, and the balance being iron (Fe) and inevitable impurities and is 5 μm or less in average grain diameter of the thickness center.