JPH0622728B2 - Descaling method for shape memory alloy thin plate - Google Patents

Description

Description: TECHNICAL FIELD The present invention is capable of suitably removing oxide scale generated in the process of rolling a thin sheet of a shape memory alloy material without causing complex deformation of the thin sheet. It concerns a scaling method.

Conventional technology and its drawbacks A long thin plate made of a shape memory alloy (generally called a ribbon material) is manufactured by cold rolling a material of a shape memory alloy, and its plate thickness is About 2 mm
It is the following. The shape memory alloy thin plate is used in various industrial fields, and the following problems are pointed out when the thin plate is manufactured by cold rolling. That is, the shape memory alloy has low ductility as a characteristic, and is significantly work-hardened and embrittled by cold rolling. For this reason, if continuous rolling is performed on the shape memory alloy material, rolling cracks will occur in the thin plate, resulting in product defects. Therefore, it is necessary to perform intermediate annealing for removing internal stress at every reduction rate of 20 to 30%. There is. Therefore, in the step of cold rolling a thin sheet of shape memory alloy, the number of times of intermediate annealing tends to increase inevitably.

If a reducing gas containing a hydrogen component is used as the atmosphere in the furnace during this annealing, the shape memory alloy has a drawback that it absorbs hydrogen and becomes significantly brittle. Therefore, generally, annealing is performed in the atmosphere or in an inert gas atmosphere such as argon, but when the shape memory alloy is exposed to high temperature, oxide scale is generated on the surface of the material, and therefore the material is No bright skin can be obtained on the surface. Therefore, vacuum annealing that blocks contact with oxygen can prevent scale generation due to oxidation on the material surface, but since this is a batch type annealing, it takes a long time for each annealing to produce. Efficiency is reduced. Further, since the intermediate annealing is repeated many times, if vacuum annealing is applied to this, the thin plate manufacturing cost rises.

Therefore, in general, it is necessary to take a method of removing the oxide scale formed on the surface of the shape memory alloy in a separate step after annealing in the air or in an inert gas atmosphere. However, as a means of removing oxide scale,
When the pickling method of immersing in an acid solution such as sulfuric acid or hydrochloric acid is used, hydrogen is generated as oxide scale and metal components elute, and this hydrogen penetrates into the shape memory alloy material and becomes extremely brittle (pickling brittleness ), There is a drawback that it cannot withstand the subsequent processing. Therefore, as a means for removing the oxide scale, the actual condition is to use a mechanical descaling method such as sandblasting in which a mixed air of compressed air and fine sand is blown, or grinding with a grindstone.

However, the shape memory alloy that has been annealed is significantly softened as a result of the removal of internal stress, and when such annealed structure is subjected to the above-mentioned mechanical descaling, the shape is affected by particle impact and grinding during sandblasting. The vicinity of the surface layer of the memory alloy material is locally deformed. Furthermore, the heat generated by these workings causes a local temperature rise in the material. The cooling will be repeated. As a result, as shown in FIG. 1, the mechanically descaled shape memory alloy thin plate 1 undergoes a complex composite deformation including transverse waves 2, longitudinal waves 3, and twists 4, and the subsequent rolling. It causes a problem that processing becomes impossible.

OBJECT OF THE INVENTION The present invention has been proposed in view of the present situation in which intermediate annealing must be performed in the coexistence of oxygen when cold-rolling a thin sheet of shape memory alloy, and as a result, oxide scale is generated. It is an object of the present invention to provide a novel means capable of suitably performing mechanical descaling without causing deformation of the material of the shape memory alloy.

Means for Solving the Problems In order to overcome the above-mentioned problems and preferably achieve an intended purpose, a method for descaling a shape-memory alloy thin plate according to the present invention comprises a cold-rolled shape-memory alloy material. In the thin plate manufacturing method of manufacturing a shape-memory alloy thin plate having a required thickness by repeatedly performing the intermediate annealing and the intermediate annealing, the thin plate after the intermediate annealing is subjected to cold temper rolling with a reduction rate of 5% or more and processed. The surface of the thin plate which has been hardened and then work hardened is subjected to mechanical descaling by sandblasting or grinding to remove oxide scale.

Example Next, a descaling method for a shape memory alloy thin plate according to the present invention will be described with reference to preferred examples. In this method, an annealed shape memory alloy material is cold-rolled by, for example, temper rolling (skin pass) with a reduction rate of 5% or more to work-harden the alloy structure, and mechanical descaling is performed in this state. That is the content. That is, by annealing the material of the shape memory alloy, the material is softened by removing the internal stress as described above.
Therefore, when this material is subjected to an appropriate reduction by a tempering roll and subjected to a slight cold rolling, the increase in hardness and strength explained by the refinement due to the slip of the metal crystal and the occurrence of dislocation in the crystal ( Work hardening). Therefore, even if mechanical descaling such as sandblasting or grinding with a grindstone is applied to the shape-hardening alloy material after work hardening, the above-mentioned complex deformation does not occur, and a flat thin plate shape is secured. Is.

The plate surface can be made to have a glossy surface by further cold finishing rolling this material. When further softness is required, a batch-type vacuum annealing is performed only for the final annealing to obtain a shape-memory alloy thin plate having a bright skin with no oxide scale.

Comparative Example 55.2% Ni (nickel) and balance Ti (titanium) Ni-
Φ10mm wire made of Ti-based shape memory alloy
Five pieces were prepared by warm rolling at 0 ° C. to form a sheet having a thickness of 2 mm and a sheet width of 14 mm. After cold rolling this flat plate material to a plate thickness of 1.8 mm, its surface was ground to completely remove oxide scale. Plate thickness after grinding is 1.7 mm
Met. This flat plate material is further cold rolled to a plate thickness of 1.5.
mm, and then annealed by heating in an argon gas atmosphere at 700 ° C. for 1 minute and then water cooling. Oxide scale was generated on the surface of this flat plate material.

The flat plate material that has generated this oxide scale has a reduction ratio of 0 to 10
After cold rolling in the range of%, the oxide scale on the surface was removed by sandblasting or grinding with a grindstone, and the flatness as a flat plate shape was measured. That is, the results of measuring the maximum height Hmm per length L = 20 mm in FIG. 1 are shown in Table 1 below.

The thin plate that has been mechanically descaled while being annealed in this way is extremely inferior in flatness, and cannot be caught in the rolling roll in the next cold rolling step. However, the thin plate subjected to mechanical descaling after cold rolling at a rolling reduction of 5% or more has good flatness, and the next cold rolling can be performed with the shape as it is. The reduction rate is expected to be 5% or less, but practically it is difficult to adjust the reduction with a thickness difference of 0.05 mm or less, and it is generally considered that the cold-rolled sheet thickness is 2 mm or less. Considering this, it is practical that the minimum rolling reduction is 5% or more.

As described above, according to the descaling method of the present invention,
Allowing intermediate annealing in a state where oxide scale is generated on the surface of the shape memory alloy material, and subjecting the thin plate after this intermediate annealing to cold temper rolling with a reduction rate of 5% or more to work harden it and then work harden it. The surface of the thin plate is subjected to mechanical descaling. That is, even if mechanical descaling is applied to a thin plate made of a shape memory alloy by work hardening, local deformation at that time can be prevented, so that the temperature above and below the martensitic transformation temperature and the reverse transformation temperature can be prevented. Even if heated and cooled (due to descaling heat generation) in the vicinity, composite deformation does not occur, and a thin plate that remains flat can be obtained. Further, since the present method enables continuous annealing, it is possible to significantly improve the production efficiency of the shape memory alloy thin plate as compared with batch annealing.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing a state in which a composite deformation has occurred in a material when descaling is performed on a shape memory alloy thin plate that has only been subjected to intermediate annealing.

Claims (1)

[Claims] 1. A thin plate manufacturing method for manufacturing a shape memory alloy thin plate having a required thickness by repeatedly subjecting a shape memory alloy material to cold rolling and intermediate annealing, wherein the thin plate after the intermediate annealing is rolled down. It is characterized in that it is subjected to cold temper rolling at a rate of 5% or more to work-harden, and then the surface of this work-hardened thin plate is subjected to mechanical descaling by sandblasting or grinding to remove oxide scale. Method for descaling thin sheet made of shape memory alloy.