Titanium Cast Surface Alloying for Defect-Resistant Hot Rolling
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Solution Overview
Problem
Existing methods for manufacturing titanium cast products without a slabing step often result in surface defects due to deformation anisotropy, requiring additional finishing steps that increase costs and reduce production efficiency.
Innovation Solution
Incorporating an α stabilizer element or neutral element into the surface layer of commercially pure titanium ingots through remelting with materials like powders or wires, creating a layer with a concentration higher than the base metal by at least 0.1% to 2.0% mass%, which suppresses crystal grain growth and reduces surface defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the slabing step is omitted to improve production efficiency, then manufacturing cost and time are reduced, but surface defects occur due to deformation anisotropy in coarse grains
Solution Approach 1:
The invention applies preliminary heat treatment to the surface layer of the ingot before hot rolling. By heating the surface layer to the β phase transformation temperature or higher and then cooling it, the coarse surface grains are transformed into fine equiaxed grains in advance. This preliminary action eliminates the deformation anisotropy that would otherwise cause surface defects during hot rolling, allowing the slabing step to be omitted while maintaining surface quality
Solution Approach 2:
The invention changes the thermal parameters (temperature and time) of the surface layer through controlled heating and cooling cycles. By heating to specific temperature ranges (β phase transformation temperature or higher) and controlling the cooling rate, the grain structure of the surface layer is fundamentally altered from coarse columnar grains to fine equiaxed grains, resolving the surface quality issue while maintaining production efficiency
2Manufacturing precision
If the finishing step is introduced to remove surface defects, then surface quality is improved, but manufacturing cost and time increase
Solution Approach 1:
The invention extracts the essential function of the finishing step (removing surface defects) and integrates it into the hot rolling process itself. By modifying the surface layer grain structure before hot rolling, the deformation during rolling naturally produces a smooth surface without requiring subsequent finishing operations to remove defects
Solution Approach 2:
The invention merges the surface treatment function with the hot rolling process. The heat treatment step that modifies surface grains is combined with the subsequent hot rolling operation, where the pre-treated surface layer deforms uniformly to produce the desired surface quality, eliminating the need for separate finishing 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
This approach allows for surface properties comparable to those achieved with traditional slabing and finishing steps, reducing manufacturing costs and improving energy efficiency by eliminating the need for additional hot working and pickling processes.
Implementation Method 1
heating a surface layer to a temperature in a β phase transformation temperature range
Implementation Method 2
performing cooling to transform a structure of the surface layer into fine equiaxed grains
Implementation Method 3
remelting the surface layer together with the material
Data Source
AI summary
Provided is a titanium cast product for hot rolling made of commercially pure titanium, the titanium cast product including a melted and resolidified layer in a range of more than or equal to 1 mm in depth on a surface serving as a rolling surface, the melted and resolidified layer being obtained by adding one or more elements out of any one of or both of at least one α stabilizer element and at least one neutral element to the surface, and melting and resolidifying the surface. An average value of a total concentration of the at least one α stabilizer element and the at least one neutral element in the range of more than or equal to 1 mm in depth is higher than a total concentration of the at least one α stabilizer element and the at least one neutral element in a base metal by, in mass %, more than or equal to 0.1% and less than 2.0%.