High-Mn Steel Surface Quality Low-Temperature
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Solution Overview
Problem
Steel for low-temperature environments with austenite microstructure, containing high amounts of carbon and manganese, experiences nonuniform grain growth and deformation, leading to surface quality issues and structural instability due to early formation of twin crystals, which affects the structural integrity and uniformity of pressure vessels.
Innovation Solution
A steel composition with 15-35 wt% manganese, 23.6C+Mn≥28, 0.5-5 wt% copper, 28.5C+4.4Cr≤57, 0.01-0.5 wt% titanium, 0.003-0.2 wt% nitrogen, and a Ti/N ratio of 1.0-4.5, along with a TiN precipitate size of 0.01-0.3 µm and density of 1.0×10^7-1.0×10^10 per 1mm², is developed to stabilize austenite and suppress grain coarsening, ensuring a microstructure with 95% austenite and ≤5% carbide at grain boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If relatively large amounts of C and Mn are added to stabilize austenite, then low-temperature toughness is improved, but nonuniform grain growth occurs causing surface quality deterioration
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition ratios of C and Mn within specific ranges (C: 0.15-0.45 wt%, Mn: 1.5-3.5 wt%) rather than using large amounts, and by controlling the Ti/N ratio (1.0-4.5) to optimize austenite stability while preventing excessive grain growth. This resolves the contradiction by finding optimal parameter values that achieve both toughness and surface quality.
Solution Approach 2:
The patent introduces Ti and N as intermediary elements that form TiN precipitates (0.01-0.3 μm) which act as grain boundary pinning particles. These intermediaries suppress austenite grain growth during hot rolling while maintaining austenite stability at low temperatures, thereby preventing nonuniform grain growth and surface quality deterioration without sacrificing toughness.
2Stability of the object's composition
If large grains are present in microstructure, then deformation occurs uniformly by slips, but twin crystals form easily causing nonuniform deformation
Solution Approach 1:
The patent changes the grain size parameter by controlling austenite grain growth through TiN precipitate formation. The austenite grain size is maintained at 5-20 μm, which is fine enough to delay twin crystal formation during deformation but not so fine as to cause excessive hardening. This optimal grain size parameter ensures uniform deformation behavior while maintaining structural stability.
Solution Approach 2:
The patent performs preliminary action by forming TiN precipitates before the hot rolling process. These precipitates are pre-formed to pin grain boundaries and control austenite grain size during subsequent deformation, preventing nonuniform deformation and twin crystal formation during service.
3Ease of manufacture
If coarse austenite grains are formed, then production cost is reduced, but surface characteristics deteriorate causing nonuniform thickness
Solution Approach 1:
The patent uses TiN precipitates as intermediaries to control grain size during hot rolling. These precipitates allow the use of relatively high rolling temperatures and faster cooling rates (reducing production time and cost) while still maintaining fine austenite grain size (5-20 μm) for excellent surface characteristics and uniform thickness.
Solution Approach 2:
The patent changes the processing parameters by controlling the austenite grain size to 5-20 μm through composition control and TiN precipitate formation. This allows for more aggressive and cost-effective processing while maintaining excellent surface quality and preventing nonuniform thickness.
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 results in steel with uniform austenite grain sizes, improved toughness, and enhanced surface processing qualities, preventing nonuniform deformation and maintaining structural stability at extremely low temperatures.
Implementation Method 1
the steel comprises a TiN precipitate having a size of 0.01μm to 0.3μm in an amount of 1.0 x 10^7
Data Source
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AI summary
The present invention relates to a steel sheet for low-temperature service, which can be used at a wide temperature range from low temperature to room temperature in liquefied gas storage tanks and transport facilities, and provides: a steel sheet for low-temperature service having an excellent surface processing quality even after a processing processes is performed, such as a tension process; and a method for manufacturing the same. An aspect of the present invention relates to a steel sheet for low-temperature service having an excellent surface processing quality, the steel sheet for low-temperature service containing manganese (Mn, 15-35 wt%), carbon (C, satisfying 23. 6C + Mn ≥ 28 and 33.5C - Mn ≤ 23), copper (Cu, 5 wt% or less (excluding 0 wt%)), chrome (Cr, satisfying 28.5C + 4.4Cr ≤ 57 (excluding 0 wt%)), titanium (Ti, 0.01-0.5 wt%), nitrogen (N, 0.003-0.2 wt%), the balance iron (Fe), and other inevitable impurities, wherein Ti and N satisfy relational expression 1 below. [Relational expression 1] 1.0 ≤ Ti/N ≤ 4.5 (provided that, Mn, C, Cr, Ti, and N in the respective expressions mean wt% of respective ingredient contents).