Titanium Cast Surface Remelting for Defect-Resistant Hot Rolling

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Solution Overview

Problem

Existing methods for manufacturing titanium cast products without a slabbing 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 titanium ingots before hot rolling, either through powder, chips, or thin films, and remelting the surface layer to create a fine-grained structure that reduces surface defects, achieving surface properties comparable to those with a traditional slabbing and finishing process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the slabbing step is omitted to improve production efficiency, then manufacturing time and cost are reduced, but surface defects occur due to deformation anisotropy in coarse grains during hot rolling

Engineering Contradiction:

Improveproduction efficiencyVSAvoidsurface quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The invention applies preliminary action by performing surface layer melting and resolidification before hot rolling to pre-refine the grain structure. By melting and resolidifying the surface layer to a depth of 1mm or more, fine grains are formed in advance, which prevents deformation anisotropy during subsequent hot rolling and eliminates surface defects without requiring the slabbing step.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention changes the physical state of the surface layer by controlling the melting and resolidification process. By adjusting the melting depth to 1mm or more and controlling the resolidification conditions, the grain structure is transformed from coarse to fine, fundamentally changing the material parameters to prevent surface defects during hot rolling.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If the surface layer is melted and resolidified to a depth of more than or equal to 1 mm to refine grains, then surface defects are reduced, but energy consumption increases

Engineering Contradiction:

Improvesurface qualityVSAvoidenergy consumption

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The invention applies local quality by selectively melting and resolidifying only the surface layer to a depth of 1mm or more, rather than treating the entire ingot. This localized treatment refines the grain structure where it is most needed (at the surface) while leaving the interior structure unchanged, thereby reducing the total energy consumption compared to full-ingot treatment.

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If additional finishing steps are introduced to remove surface defects, then surface quality is improved, but production efficiency decreases and costs increase

Engineering Contradiction:

Improvesurface qualityVSAvoidproduction efficiency

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The invention performs the grain refinement action preliminarily during the surface layer melting and resolidification step, which occurs before hot rolling. By refining the grains in advance, the need for subsequent finishing steps to remove surface defects is eliminated, thereby maintaining high production efficiency while achieving excellent surface quality.

Inventive Principle:

Principle #10Preliminary action

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 the production of titanium materials with improved surface quality and reduced manufacturing costs and energy consumption by eliminating the need for additional hot working and finishing steps, while maintaining surface properties equivalent to those achieved with conventional methods.

Implementation Method 1

remelting the surface layer to create a fine-grained structure

Methodology Applied

Scientific EffectMelting and resolidification: Melting

Implementation Method 2

an α stabilizer element or a neutral element is caused to be contained in a slab surface layer by placing or scattering a material (powder, chips, a wire, a thin film, and the like) containing the α stabilizer element or the neutral element on a rolling surface layer of an as-cast titanium material and remelting the slab surface layer together with the material

Methodology Applied

Scientific EffectPhase stability:

Data Source

PatentEP3202952B1Titanium cast product unlikely to exhibit surface defects and method of manufacturing the same

Publication Date: 2022.06.22 NIPPON STEEL CORPORATION

Figure 1

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%.