Titanium Slab Surface Defect Control via Solidification Orientation
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Solution Overview
Problem
Titanium slabs produced by electron beam melting furnaces often exhibit surface defects when hot rolled due to coarse crystal grains and casting structure issues, leading to yield degradation and increased production costs from necessary surface treatments.
Innovation Solution
Control the solidification direction of titanium slabs by adjusting the angle between the casting and solidification directions to between 70 to 90 degrees, and ensure a crystal grain layer thickness of 10 mm or greater, along with a specific width-to-thickness ratio and length-to-width ratio, to minimize surface defects during hot rolling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a thinner rectangular mold is used to produce as-cast slab directly for hot rolling, then production cost is reduced by omitting breakdown process, but casting surface properties and cast structure are considerably affected with deep defects and coarse crystal grains
Solution Approach 1:
The patent applies preliminary action by performing surface smoothing treatment on the as-cast slab before hot rolling. The slab surface smoothing treatment unit smooths the casting surface in advance to remove deep defects such as pits, bumps, and wrinkles, preventing them from becoming prominent surface defects after hot rolling. This preliminary smoothing action resolves the contradiction by preparing the surface in advance, allowing direct hot rolling without breakdown process while maintaining surface quality.
2Productivity
If as-cast slab with coarse crystal grains is directly hot rolled without breakdown process, then production efficiency is improved, but uneven deformation develops into large surface defects degrading yield
Solution Approach 1:
The patent applies preliminary action by performing surface smoothing treatment on the as-cast slab before hot rolling. The slab surface smoothing treatment unit smooths the casting surface in advance to remove deep defects such as pits, bumps, and wrinkles, preventing them from becoming prominent surface defects after hot rolling. This preliminary smoothing action resolves the contradiction by preparing the surface in advance, allowing direct hot rolling without breakdown process while maintaining surface quality.
3Reliability
If surface of as-cast slab is smoothed by machining or other treatment to remove deep defects, then surface defects after hot rolling are reduced, but yield declines due to considerable material removal
Solution Approach 1:
The patent applies parameter changes by controlling the thickness of the as-cast slab within a specific range (100mm to 200mm) and adjusting the electron beam melting parameters (beam current, melting speed, mold temperature) to optimize the casting process. These parameter changes allow the slab to be produced with fewer deep surface defects and a more favorable cast structure, reducing the need for extensive surface removal while maintaining surface quality after hot rolling.
4Device complexity
If breakdown process is omitted to reduce production cost, then manufacturing simplicity is improved, but coarse crystal grains cause uneven deformation and surface defects
Solution Approach 1:
The patent applies preliminary action by performing surface smoothing treatment on the as-cast slab before hot rolling. The slab surface smoothing treatment unit smooths the casting surface in advance to remove deep defects such as pits, bumps, and wrinkles, preventing them from becoming prominent surface defects after hot rolling. This preliminary smoothing action resolves the contradiction by preparing the surface in advance, allowing direct hot rolling without breakdown process while maintaining surface quality.
Solution Approach 2:
The patent applies parameter changes by controlling the thickness of the as-cast slab within a specific range (100mm to 200mm) and adjusting the electron beam melting parameters (beam current, melting speed, mold temperature) to optimize the casting process. These parameter changes allow the slab to be produced with fewer deep surface defects and a more favorable cast structure, reducing the need for extensive surface removal while maintaining surface quality after hot rolling.
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 allows titanium slabs to be hot rolled into high-quality strip coils with significantly reduced surface defects, enabling direct feeding into general-purpose hot-rolling mills without breakdown processes, thus reducing energy and labor costs while maintaining surface quality.
Implementation Method 1
a method of producing the titanium slab with an electron beam melting furnace
Implementation Method 2
the solidification direction, i.e., the crystal growth direction from the surface layer toward the interior
Data Source
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AI summary
The present invention provides a titanium slab for hot rolling which can be fed into a general purpose hot-rolling mill for producing strip coil, without passage through a breakdown process such as blooming or a straightening process, and can further suppress surface defect occurrence of the hot-rolled strip coil, and a method of producing and a method of rolling the same, characterized in that in the cast titanium slab an angle θ formed by the crystal growth direction (solidification direction) from the surface layer toward the interior and a direction parallel to the slab casting direction (longitudinal direction) is 45 to 90°, and moreover, there is a surface layer structure of 10 mm or greater whose θ is 70 to 90°, and further characterized in that a crystal grain layer of 10 mm or greater is formed whose C-axis direction inclination of a titanium α phase is, as viewed from the side of the slab to be hot rolled, in the range of 35 to 90° from the normal direction of the surface to be hot rolled. The titanium slab concerned is produced using an electron beam melting furnace by casting at an extraction rate of 1.0 cm/min or greater.