Alpha+beta Titanium Alloy Plate Texture Control for Welded Pipe Strength
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Solution Overview
Problem
Current methods for manufacturing α + β type titanium alloy pipes struggle to achieve high strength and rigidity in the pipe longitudinal direction while maintaining low manufacturing costs, as existing processes often result in anisotropic mechanical properties and high production costs.
Innovation Solution
Developing a texture in α + β type titanium alloy sheets with a specific grain orientation and alloy composition, where the sheet width direction is set as the pipe longitudinal direction and the sheet longitudinal direction is set as the pipe circumference direction, utilizing uni-directional hot rolling and appropriate reheating temperatures to enhance T-texture development, thereby increasing tensile strength and Young's modulus in the pipe longitudinal direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If annealing is performed at β transus or higher to improve fracture toughness, then fracture toughness is improved, but strength and elastic modulus in pipe longitudinal direction become low and isotropic
Solution Approach 1:
The patent applies parameter changes by precisely controlling the reheating temperature range (β transus - 50°C to β transus + 50°C) and hot rolling finishing temperature (β transus - 100°C to β transus) to obtain a specific microstructure with acicular α phases distributed in a β matrix, achieving both high strength and good fracture toughness without annealing at β transus or higher
Solution Approach 2:
The patent creates a composite microstructure consisting of acicular α phases dispersed in a β matrix phase, which combines the high strength characteristics of acicular α phases with the ductility and fracture toughness of the β matrix, resolving the contradiction between strength and fracture toughness
2Ease of manufacture
If skew rolling process with large shear strain is used to improve hot workability, then hot workability is improved, but hot-rolling texture that causes high strength in pipe longitudinal direction cannot be obtained
Solution Approach 1:
The patent changes the processing parameters by performing hot rolling in a specific temperature range (finishing temperature at β transus - 100°C to β transus) after reheating, which enables the formation of a favorable hot-rolling texture with acicular α phases oriented to provide high strength in the pipe longitudinal direction while maintaining good hot workability
3Strength
If seamless pipe manufacturing methods (skew rolling or hot extrusion) are used to obtain high strength, then strength can be improved, but productivity is low and manufacturing cost is high
Solution Approach 1:
The patent applies parameter changes by optimizing the reheating temperature (β transus - 50°C to β transus + 50°C) and hot rolling finishing temperature (β transus - 100°C to β transus) to achieve a microstructure that provides high strength (tensile strength ≥1050 MPa, Young's modulus ≥130 GPa) in the pipe longitudinal direction, enabling welded pipe manufacturing to achieve seamless pipe-level strength while maintaining higher productivity and lower cost
Solution Approach 2:
The patent applies preliminary action by performing hot rolling with specific temperature control and reduction ratios to pre-establish the desired microstructure and texture in the plate before pipe forming and welding, ensuring that the final pipe product achieves the required mechanical properties without requiring complex post-processing or expensive seamless manufacturing processes
4Productivity
If sheet material is bent to manufacture welded pipe with sheet longitudinal direction as pipe circumference direction, then productivity is high and manufacturing cost is low, but strength and rigidity in pipe longitudinal direction are insufficient
Solution Approach 1:
The patent applies asymmetry by intentionally creating an asymmetric texture in the plate material where the microstructure and crystallographic orientation are optimized for strength in the sheet width direction (which becomes the pipe longitudinal direction after forming). This asymmetric microstructural design ensures that when the plate is bent with the sheet longitudinal direction as the pipe circumference direction, the resulting pipe achieves high strength and rigidity in the pipe longitudinal direction
Solution Approach 2:
The patent changes the microstructural parameters through controlled hot rolling to create acicular α phases with specific orientation distributions that provide high strength properties in the sheet width direction, enabling the welded pipe manufacturing process to achieve seamless pipe-level mechanical properties while maintaining high productivity
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
This approach results in α + β type titanium alloy pipes with tensile strength exceeding 1050 MPa and Young's modulus over 130 GPa, improving pipe-making properties and reducing manufacturing costs by enhancing ductility and bendability.
Implementation Method 1
a ratio of peak values of X-ray relative intensities from a basal plane in an α phase between a first group of grains and a second group of grains
Implementation Method 2
by hot rolling conditions and annealing is performed
Implementation Method 3
a ratio of peak values of X-ray relative intensities from a basal plane in an α phase
Data Source
Figure 1(a)~1(c)
Figure 2~3
Figure 4~5
AI summary
An α + β type titanium alloy sheet to be used for a welded pipe with a rolling direction of the sheet set to a circumference direction of the pipe includes: a composition containing, in mass%, 0.8 to 1.5% of Fe, 4.8 to 5.5% of Al, 0.020% or less of N, O in a range satisfying Q = 0.14 to 0.38, and a balance being composed of Ti and impurities, in which a texture in a sheet plane direction has: a first group of grains oriented in a region where of a (0002) pole figure of an α phase having a hexagonal crystal structure, an angle θ being the angle between a c axis and a sheet normal direction is 0 to 30°; and a second group of grains oriented in a region where the angle θ is 80 to 100° and of the (0002) pole figure of the α phase, an angle φ being the angle between a projection line of the c axis onto the sheet plane and a sheet width direction is -10 to 10°, and a ratio of peak values of X-ray relative intensities from a basal plane in the α phase between the first group of grains and the second group of grains (the second group of grains/the first group of grains) is 5.0 or more.