Austenitic Stainless Steel Grain Refinement
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Solution Overview
Problem
Commercially available 304 series and 301 series austenitic stainless steels have low yield strengths, limiting their application in structural materials requiring high strength, and existing manufacturing methods, such as skin pass rolling and long heat treatments, increase costs and reduce productivity.
Innovation Solution
A method for manufacturing ultra-fine grain 304 series and 301 series austenitic stainless steels by controlling the austenitic stability parameter (ASP) value, [100*N]/[Ni+Cu] value, cold rolling reduction ratio, and annealing temperature to achieve high strength and ductility, without skin pass rolling, and with a grain size less than 5 μm, to satisfy the requirements of 301 series ¼H crude materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If skin pass rolling is applied to increase yield strength, then yield strength is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the microstructural parameters by controlling grain size to ultra-fine levels (average 5 μm or less) and controlling the phase composition (martensite phase 10-50%, retained austenite 5-20%). This parametric control of microstructure achieves high yield strength (500 MPa or more) without requiring skin pass rolling, thereby avoiding the additional manufacturing cost while meeting strength requirements.
2Manufacturing precision
If long heat treatment is applied to control grain size, then grain size is improved, but productivity deteriorates
Solution Approach 1:
The patent performs preliminary grain refinement during the hot rolling and cold rolling processes themselves, rather than relying on subsequent long heat treatments. By controlling the rolling parameters and tempering conditions, the ultra-fine grain structure (average 5 μm or less) is achieved during the forming process, eliminating the need for prolonged 48-hour heat treatments and significantly improving productivity.
3Manufacturing precision
If ultra-fine grains are obtained by cold rolling and low temperature annealing, then grain size is improved, but simultaneous achievement of excellent yield strength, tensile strength, and elongation is difficult
Solution Approach 1:
The patent creates a composite microstructure consisting of multiple phases: martensite (10-50%) providing strength, retained austenite (5-20%) providing ductility and elongation, and ultra-fine grain structure (average 5 μm or less) providing overall mechanical performance. This multi-phase composite microstructure, achieved through controlled rolling and tempering, simultaneously delivers excellent yield strength (500+ MPa), tensile strength (850+ MPa), and elongation (25%+).
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 method achieves a yield strength of 500 MPa or more, a tensile strength of 850 MPa or more, and an elongation of 25% or more, while reducing manufacturing costs and improving productivity, making it suitable for structural components like vehicle outer panels and construction components.
Implementation Method 1
Ultra-fine grains are realized in 300 series stainless steels generally by transforming an austenite phase into a martensite phase by cold rolling
Implementation Method 2
performing annealing at a low temperature
Data Source
AI summary
Disclosed is an austenitic stainless steel including, in percent by weight (wt %), 0.005 to 0.03% of C, 0.1 to 1% of Si, 0.1 to 2% of Mn, 0.01 to 0.4 of Cu, 0.01 to 0.2 of Mo, 6 to 9% of Ni, 16 to 19% of Cr, 0.01 to 0.2% of N, and the balance of Fe and inevitable impurities, wherein an austenitic stability parameter (ASP) value calculated by 551−462 (C+N)−9.2Si−8.1Mn−13.7Cr−29 (Ni+Cu)−18.5Mo is from 30 to 60, a [100*N]/[Ni+Cu] value is 1.4 or more, an average grain size is less than 5 μm, and a fraction (%) of grains with a grain size of 5 μm or more is less than 10%.