Wire Rod Pearlite Grain Refinement for Low-Temperature Toughness
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Solution Overview
Problem
Conventional PC steel stranded wires used in LNG tank dikes lack sufficient low-temperature elongation and toughness, risking fracture when exposed to extremely low temperatures, such as -162°C, due to inadequate material properties.
Innovation Solution
A wire rod with a specific chemical composition (C: 0.60 to 1.20%, Si: 0.30 to 1.30%, Mn: 0.30 to 0.90%, P: 0.020% or less, S: 0.020% or less, N: 0.0025 to 0.0060%, Cr: 0 to 1.00%, V: 0 to 0.800%, Al: 0.005 to 0.100%, Ti: 0.003 to 0.050%, and B: 0.0005 to 0.0040%) and manufacturing process (heating, rough-rolling, finish-wire-rolling, coiling, and air blast cooling) that reduces the average grain size of pearlite blocks to 23µm or less and limits the number density of coarse pearlite blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PC steel stranded wire is used in LNG tank dike, then the structure provides basic reinforcement, but the wire lacks sufficient low-temperature elongation and toughness, risking fracture at -40°C or lower temperatures
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.60-1.20%, Si: 0.80-1.30%, Mn: 0.30-0.90%, etc.) and microstructural parameters (pearlite block grain size ≤23μm, number density of coarse pearlite blocks ≤20 pieces/mm²) to achieve both high strength and excellent low-temperature elongation, resolving the contradiction between strength and low-temperature toughness
Solution Approach 2:
The patent creates a composite microstructure consisting of fine pearlite blocks distributed throughout the wire rod matrix, combining the strength benefits of pearlite with controlled grain refinement to achieve both high strength and improved low-temperature ductility, effectively resolving the contradiction between strength and low-temperature elongation
2Reliability
If the wire rod grain size is reduced to improve low-temperature elongation, then low-temperature toughness improves, but the manufacturing complexity increases
Solution Approach 1:
The patent changes the manufacturing parameters by specifying precise chemical composition ranges and controlled cooling rates (air blast cooling) during production, which naturally produce the required fine pearlite block structure (≤23μm) without requiring additional complex processing steps, thus improving low-temperature elongation while maintaining manufacturing simplicity
Solution Approach 2:
The patent employs self-service by allowing the controlled chemical composition and air blast cooling process to automatically generate the desired fine-grained pearlite microstructure during normal manufacturing operations, eliminating the need for separate grain refinement treatments or complex additional processing steps
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 wire rod exhibits enhanced low-temperature elongation and toughness, preventing fractures at -40°C and improving the reliability of PC steel stranded wires in LNG tank dike applications.
Implementation Method 1
manufacturing process (heating, rough-rolling, finish-wire-rolling, coiling, and air blast cooling) that reduces the average grain size of pearlite blocks to 23µm or less
Data Source
Figure 1~2
Figure 3~4
Figure 5A
AI summary
A wire rod according to the present invention includes a predetermined chemical composition and the remainder thereof includes Fe and impurity, wherein the average value of a grain size of a pearlite block in a cross section perpendicular to a wire rod axial direction is 23µm or less, and wherein a number density of the pearlite blocks having a grain size of 40µm or more in the cross section perpendicular to the wire rod axial direction is 0 to 20 pieces/mm2.