JPS6257705B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a titanium plate with good bending workability and surface precision. Titanium is a metal that easily seizes, and it easily seizes under high pressure and high sliding speed, and the above characteristics are a disaster in the case of cold rolling. The characteristics of seizure during cold rolling of titanium sheets are that titanium adheres strongly to the roll surface during the rolling process, and once seizure occurs, the seizure becomes even more significant during subsequent rolling. Once seizure occurs, the friction coefficient increases rapidly, the rolling load increases, and it becomes extremely difficult to ensure stable rolling and a good plate shape. In order to prevent the above-mentioned seizure, especially in large-diameter roll rolling, where high-speed rolling is possible and it is easy to obtain a good plate shape, it is necessary to roll under sufficient lubrication conditions, and this request is made. Regarding this, we have developed the following improvement measures and have already filed a patent application. (1) A method of using highly saponified oil with a saponification value of 170 or more as a rolling lubricant (Japanese Patent Application Laid-open No. 145349/1983). (2) A method of forming an oxide film on the surface of a cold-rolled blank sheet and then cold rolling it (Japanese Patent Application Laid-Open No. 88858/1983). By carrying out the above methods (1) and (2) alone or in combination, seizure during cold rolling can be prevented. However, according to separate research conducted by the present inventors, even if seizure is prevented as much as possible, depending on the relationship between the crystal grain size of the titanium blank and the diameter of the rolling rolls, it may occur over the entire surface of the cold-rolled plate. It became clear that countless oil pits were generated and the surface accuracy was significantly reduced. Therefore, as a result of investigating the cause of oil pits and researching ways to improve them, we found that (A) the cause of oil pits is that a so-called fluid lubrication situation occurs in which a large amount of lubricating oil is introduced during roll bite. (B) As an improvement measure, when the average crystal grain size of the titanium blank is X (μm) and the diameter of the cold rolling roll is Y (mm), both are expressed by the following formula: X≦48672/Y ¹ ．． ³²⁸³ ...[] We confirmed that the method of performing cold rolling under the conditions satisfying the following relationship is effective, and filed a patent application (Japanese Patent Application No. 55-69174). That is, according to the inventors' previous research, it was found that there is a relationship between the oil pit depth (d: μm), the crystal grain size of the base plate (X: μm), and the cold rolling roll diameter (Y: mm). There is a correlation between d=0.287・X ^0.329・Y ^0.437 ...[] Once ^the maximum ^practically allowable oil pit depth d is determined, the average crystal grain size X of the titanium blank to be used and It can be arranged according to the relationship of the cold rolling roll diameter Y. On the other hand, in this industry, there is a demand from the customer side that "there should be no surface defects with a depth of 10 μm or more," so the maximum allowable oil pit depth d was set at 10 μm, and this was substituted into the formula [] above. Then, the following formula [] is established, and 10≧ ^{0.287・X 0.329 ・}Y ^0.437 … [ ^] By transforming this, the above formula [] is derived. That is, when the diameter Y of the cold rolling roll to be used is determined, the average crystal grain size X of the titanium blank is adjusted so as to satisfy the formula When cold rolling,
By adjusting the roll diameter Y so that the formula [] is fully satisfied, the maximum oil pit depth can be suppressed to 10 μm or less. However, further research revealed that even when cold rolling was carried out using the above technology,
Surface defects in the form of deep cracks were sometimes produced. The present invention was completed as a result of intensive research in order to establish a remedy for the above-mentioned problems, and its configuration consists of preparing a titanium base plate that satisfies the conditions of the above formula [], and 0.4 The gist is that after descaling using a fine shot blasting material whose volume is less than the volume equivalent to a mmφ sphere, the material is cold rolled. As mentioned above, even when cold rolling is carried out under conditions that satisfy the requirements of the formula [], surface defects in the form of deep cracks may occur in the rolled sheet (Reference Photo 1).
Experimental results show that when conventional, common titanium plate cold rolling methods (rolling methods with poor lubrication and risk of seizure) are used, surface defects due to seizure occur, but deep cracks such as those described above occur. It was confirmed that no surface defects of the shape (reference photo 2) were generated. From this, it seems necessary to consider from another angle in order to eliminate deep crack-like surface defects. When the cause of the crack-like defects was investigated, it became clear that the cause was a work-hardened layer formed on the surface of the titanium blank during shot blasting before cold rolling. In other words, since the surface of a titanium hot-rolled sheet is covered with a fine and strong oxide scale unique to titanium, the scale is usually destroyed by shot blasting prior to cold rolling, and then the surface layer is destroyed. The oxygen diffusion layer (approximately 30 to 50 μm) and the attached shot blasting material are removed by pickling. In the above-mentioned shot blasting process, a work-hardened layer is formed on the surface of the titanium blank due to shot impact energy, but the thickness of this work-hardened layer (thickness after pickling) is closely connected to the crack-like defects. It became clear that they were related. That is, FIG. 1 is a graph showing the influence of the thickness of the work-hardened layer (Hv, 100 g) on crack-like defects. The titanium blank and cold rolling conditions were as follows. Titanium base plate: Pure titanium hot-rolled plate (thickness: 3 mm, fine grain material, with a work-hardened layer by shot blasting and removed by pickling) Cold rolling conditions: tallow-based rolling oil, roll diameter 150 mm
φ, rolling speed 43 m/min, total reduction rate 50% As is clear from Fig. 1, the occurrence of cracking defects differs markedly depending on the presence or absence of a work-hardened layer. Therefore, in order to further clarify the influence of the degree of work hardening layer formed in the shotplast process on surface defects after cold rolling, the following experiment was conducted. That is, two types of pure titanium plates with different crystal grain sizes are treated using shot blasting materials with different dimensions, shapes and materials, and then pickled, and the thickness of the work-hardened layer of the obtained hot-rolled plates is determined. (Plate thickness cross-sectional direction)
was measured using a micro-Vickers hardness tester, cold rolling was performed under lubricated conditions that did not cause seizure, and the condition of the plate surface was observed. Table 1 shows the test materials, Table 2 shows the shot blasting method, and Table 3 shows the cold rolling method.

【table】

【table】

【table】

[Table] The grain size of the sample materials shown in Table 1 was adjusted by controlling the cooling conditions after hot rolling. The shot blasting method was varied in various ways as shown in Table 2, but in all cases the scale was completely removed by applying appropriate blasting force and time. Furthermore, the cold rolling conditions shown in Table 3 are good lubrication conditions that do not cause seizure. FIG. 2 shows the relationship between the work hardening thickness of the surface of each titanium plate obtained above and the dimensions of the shot material. As is clear from FIG. 2, the length of the work-hardened layer tends to become thinner as the dimensions of the shot material become smaller and as the crystal grain size becomes smaller. The shot material conventionally used for shot blasting titanium plates is a steel ball with a diameter of about 0.5 mm or more or a cut wire with a length of about 1 to 2 mm.
The machining depth can be significantly reduced by using fine shot material. Moreover, FIGS. 3 and 4 show the relationship between the work-hardened layer thickness and crack-like defects for fine-grained materials and coarse-grained materials. The symbols in the figures have the following meanings. ●: There is a crack-like defect at a rolling reduction of 50% ○: There is no crack-like defect at a rolling reduction of 50% ■: There is a crack-like defect at a rolling reduction of 75% □: There is no crack-like defect at a rolling reduction of 75% From Figures 3 and 4 You can think of it as follows.
The maximum defect depth in the absence of a work hardening layer is
As explained in the formula [] above, it is determined by the crystal grain size of the titanium blank and the rolling roll diameter, but when a work hardening layer exists, the same tendency is observed regardless of the crystal grain size, and work hardening Layer depth is 150μm
The maximum defect depth decreases as the thickness increases. This is thought to be because the crystal grains on the surface of the titanium plate were destroyed by the collision with the shot material, and the apparent crystal grain size became fine. However, when the depth of the work-hardened layer reaches 150 μm, crack-like defects begin to be observed, and thereafter, as the layer thickness increases, the crack-like defects become more noticeable and the maximum defect depth increases rapidly. In other words, in order to prevent crack-like defects on the surface of cold-rolled sheets, it is effective to control the shot blasting conditions so that the thickness of the work-hardened layer is 150 μm or less, and the relationship with the maximum defect depth is Considering this, a range of 50 to 150 μm is optimal. The most effective way to reduce the maximum hardened layer thickness is to reduce the size of the shot material used in the shot blasting process, as explained in Figure 2. Thickness of hardening layer (30
~50μm), the diameter is less than 0.4mm (grids and cut wires have the same volume)
By using this shot material, the thickness of the work-hardened layer after pickling can be reduced to 150 μm or less. By the way, reference photo 5 shows an example of the surface condition after rolling when the dimensions of the shot blast material are changed, and the crack-like defects caused by using shot materials with smaller dimensions are the same as those caused by using shot materials with larger dimensions. extremely small compared to other things. Furthermore, Figure 5 is a graph showing the relationship between the thickness of the work-hardened layer by shot blasting and the bending performance (3 mm thick, using a pure titanium plate made of fine crystal grain material). There is also a close relationship with From this figure, in order to satisfy the standard bending radius of 2.0T (twice the plate thickness) for a pure titanium 3mm plate, the thickness of the work-hardened layer must be 180μm or less, but this requirement is also true. defined by invention
Descaling treatment using shot material of 0.4 mm or less ensures that the requirements are met. In this way, in the present invention, the shot material is 0.4mm.
One of the features is that the thickness of the work-hardened layer is kept to 150 μm or less by using fine particles with a volume less than that equivalent to a φ sphere, and these effects are effective regardless of the material of the shot material. However, in view of the fact that work hardening is caused by the impact energy of the shot material, it is also extremely preferable to use a relatively soft and lightweight shot material, such as fused alumina powder. The present invention is roughly constructed as described above, and the relationship between the average grain size X (μm) of the titanium blank and the diameter Y (mm) of the cold rolling roll is expressed by the following formula: X≦ ⁴⁸⁶⁷² /Y ^1.3283 In addition to the configuration of the prior invention in which the titanium blank is cold rolled after being adjusted to meet the requirements, the descaling treatment of the titanium blank before cold rolling is carried out using fine shot blasting material whose volume is less than that equivalent to a 0.4 mm diameter sphere. By adding the requirement of suppressing the thickness of the work-hardened layer to 150 μm or less, it became possible to produce a cold-rolled titanium sheet with excellent surface precision and workability.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between distance from the surface after descaling treatment and hardness, Figure 2 is a graph showing the relationship between shot material dimensions and work hardening layer thickness, and Figures 3 and 4 are work hardening. A graph showing the relationship between layer thickness and maximum defect depth, and FIG. 5 is a graph showing the relationship between work hardening layer thickness and bending radius.

Claims (1)

[Claims] 1. When the average grain size of the titanium blank is X (μm) and the diameter of the cold rolling roll is Y (mm), the relationship between the two is expressed by the following formula: X ^≦ 48672/Y ^1.3283 A method for producing a titanium plate, which comprises adjusting the titanium plate to meet the requirements, performing descaling using fine shot blasting material having a volume equivalent to or less than a 0.4 mm diameter sphere, and then performing cold rolling. .