JP2010138459A - Titanium or titanium alloy sheet excellent in balance between press formability and strength - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium or titanium alloy sheet which is excellent in a balance between press formability and strength and is useful as a material for a heat exchanger or a chemical plant. <P>SOLUTION: The titanium or titanium alloy sheet is unidirectionally rolled in such a way that it has a lubricating coating applied to its surface, and the dynamic friction coefficient at the surface of the lubricating coating is controlled to <0.15. In the titanium or titanium alloy sheet, the elongation (L-El) in the rolling direction and the r value (T-r) in the direction perpendicular to the rolling direction satisfy the relation: (T-r)/(L-El)≥0.07. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a titanium or titanium alloy plate useful as a material for a heat exchanger or a chemical plant, and particularly relates to a titanium or titanium alloy plate having excellent press formability while ensuring a predetermined strength.

  Titanium or a titanium alloy plate (hereinafter “may be represented by a titanium plate”) has been used as a material for heat exchangers and chemical plants in recent years because it has excellent corrosion resistance and specific strength. In particular, it does not corrode at all against seawater, so it is often used in seawater heat exchangers.

  One of the main uses of titanium plates is plate-type heat exchangers. Titanium plates applied to these uses are formed into complex shapes from the viewpoint of improving heat transfer efficiency (heat exchange efficiency). The press formability as good as possible is desired. In addition, the strength is required to be high enough to cope with the high pressure of the heat exchanger. However, strength and press formability are contradictory properties, and the actual situation is that a titanium plate that can satisfy both of these properties has not been obtained.

  As a means for improving the press formability in a metal plate such as a steel plate, for example, Patent Document 1 and Patent Document 2 include, in addition to alloy design, a property improvement method by structure control for optimization of texture, crystal grain size, and the like. As disclosed in the above, a method of applying a lubricating film to the surface of a steel sheet is known. In these techniques, by forming a lubricating film on the surface of the steel sheet, deformation of the steel sheet into the mold is allowed and press formability is improved.

  In each of the above technologies, application to a titanium plate is also suggested as a type of metal plate for forming a lubricating film. In addition, as disclosed in Patent Document 3, Patent Document 4, and the like, it is also recognized that a lubricating film is applied to a steel sheet, and the effect of the lubricating film is exhibited when the r value and elongation of the original sheet are determined to be above a certain level. . According to these Patent Documents 3 and 4, it is generally shown that the elongation is high and the formability is improved as the r value is increased. By applying a lubricating film to a steel sheet having a higher formability, forming is performed. It is mentioned that the properties are further improved. However, when the influence of the lubricating film on the press formability of the titanium plate was examined, it was not always possible to obtain a good formability simply by forming the lubricating film on the surface of a high formability titanium thin plate having high elongation and a high r value. It turns out that is not always obtained.

That is, since the crystal structure of a titanium plate is a close-packed hexagonal lattice (hcp), it is known that the characteristic anisotropy of titanium is larger than that of a steel plate or the like. In a titanium plate produced by rolling in one direction, the rolling direction (hereinafter sometimes referred to as “L direction”) and the direction perpendicular to the rolling direction (hereinafter sometimes referred to as “T direction”) The characteristics are greatly different. For example, in the yield stress (YS), the characteristic of the titanium plate is such that the L direction is about 20% or more lower than the T direction, and the elongation in the L direction is about 40% or more higher than the T direction. . This difference in characteristics is considered to be the reason why the effect that is not effectively exhibited even if the technology that has been considered useful for the steel plate is applied to the titanium plate as it is.
Japanese Patent No. 3056446 JP 2004-232085 A JP 2003-65564 A Japanese Patent No. 3639060

  The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is excellent in the balance between press formability and strength, and titanium or titanium alloy plate useful as a material for heat exchangers and chemical plants. Is to provide.

The titanium or titanium alloy plate of the present invention capable of achieving the above object is a titanium or titanium alloy plate rolled in one direction, and a lubricating film is applied to the surface, and the dynamic friction coefficient of the surface of the lubricating film is The following (1) between the elongation in the rolling direction (L-El) and the r value (Tr) in the direction perpendicular to the rolling direction while being controlled to be less than 0.15 It has a gist in that it has a formula relationship.
T−r / L−E1 ≧ 0.07 (1)

  In the titanium or titanium alloy plate of the present invention, the plate thickness is preferably about 0.3 to 1.0 mm.

  According to the present invention, the lubricating film is applied to the surface, and the elongation in the rolling direction (L-El) in the titanium or titanium alloy plate and the r value (T-r) in the direction perpendicular to the rolling direction. In order to satisfy a predetermined relationship between them, a titanium or titanium alloy plate excellent in balance between press formability and strength can be realized, and such titanium or titanium alloy plate is extremely useful as a material for heat exchangers and chemical plants. It is.

  The present inventors examined the influence of the lubricating film on the press formability of titanium or a titanium alloy plate from various angles. As a result, the following knowledge was obtained. First, if the lubricity on the surface of the titanium plate is increased, plastic deformation in the T direction, which is low ductility, is likely to occur, so the press formability on the titanium plate may be worsened, and the press by increasing the lubricity It was found that in order to effectively exhibit the formability improvement effect, it is necessary to make the material itself difficult to deform in the T direction. As an index, the present inventors obtained an idea that a Rankford value (r value) should be selected and the r value in the T direction should be set to be somewhat high.

The r value (Rankford value) is the ratio (r = ε _w / ε _t ) of the logarithmic strain ε _w in the width direction (corresponding to the L direction in the present invention) and the logarithmic strain ε _{t in} the plate thickness direction in the uniaxial tensile test. It is known that the larger the r value, the larger the limit drawing ratio (the plate thickness at the mold part responsible for the load is less likely to be reduced).

  On the other hand, the press formability becomes better as the elongation in the L direction (L-El) is higher in the extent that the lubricity equivalent to that of ordinary press oil is given without applying a lubricating film to the surface of the titanium plate. . However, if the surface of the titanium plate is highly lubricated, the titanium plate is likely to flow macroscopically, and the uniform deformation region becomes large. This allows stress to concentrate in a relatively large area that cannot be overcome by local deformation, even if the area does not crack due to local deformation in a very high plastic strain region with a friction resistance equivalent to that of press oil. As a result, a high plastic strain region is formed, and on the contrary, a larger crack is caused than in the case where there is no lubricating film.

  In order to prevent such a situation, it is not preferable that the L direction becomes highly ductile (that is, the strength decreases in the L direction), and the elongation in the L direction is reduced to some extent. It has been found that by increasing the strength to some extent, plastic strain in the T direction must also be promoted to some extent.

Based on these findings, as a result of further studies, the ratio (T−r / L−) of the L direction elongation (L−E1) to the T direction r value (T−r) of the titanium plate itself as a substrate When El) is within a predetermined range, the inventors have found that good press formability can be secured while securing strength, and the present invention has been completed. Specifically, if there is a relationship of the following formula (1) between the elongation in the rolling direction (L-El) and the r value (T-r) in the direction perpendicular to the rolling direction, a lubricating film is applied. The excellent press formability of the titanium plate was achieved. A preferable value (lower limit) on the right side of the equation (1) is 0.08. Further, the upper limit of the value of the ratio (Tr / L-El) is not particularly limited, but is about 0.2 considering the tensile properties and production conditions of titanium.
T−r / L−E1 ≧ 0.07 (1)

  In the present invention, as described above, the ratio of the elongation (L-El) in the rolling direction (L direction) to the r value (T-r) in the direction perpendicular to the rolling direction (T direction) is controlled within an appropriate range. Thus, the above-described effects are exhibited, and the range of each parameter [elongation (L-El) and r value (Tr)] itself is not limited, but the tensile properties of titanium and Considering production conditions and the like, it is preferable that the elongation (L-EL) is 50% or less and the r value (T-r) is 1.8 or more.

  About the said elongation (L-El), it can adjust by changing the growth of a particle size by changing the final annealing temperature. The final annealing temperature is usually about 750 to 800 ° C., but by making this temperature relatively low (for example, about 700 ° C.), the elongation in the L direction can be lowered.

  In addition, although the annealing method of titanium may be performed in the laboratory by vacuum annealing (vacuum atmosphere or annealing in an atmosphere replaced with Ar after evacuation → no acid pickling thereafter), it is industrially productive. In general, annealing (after pickling) is performed in an air atmosphere for about 10 minutes.

  The r value (T−r) in the T direction can be adjusted by adjusting the number of reductions during cold rolling (normal rolling direction). That is, normally, cold rolling with a rolling reduction of about 50 to 75% is performed twice, but the r value (T−r) can be adjusted by increasing or decreasing the number of cold rolling. When considering the texture, the r value increases as the (0001) planes of the crystals accumulate in parallel with the plate thickness. This is due to the fact that the sliding surface of titanium is preferentially generated in the (0001) plane. Moreover, since the texture in which the r value becomes high, that is, the (0001) plane of the crystal accumulates parallel to the plate surface by performing cold rolling, the r value can be adjusted by increasing the number of rolling.

  About the reason why good formability can be obtained while maintaining the strength by satisfying the relationship of the above formula (1) when the r value in the T direction (Tr) and the elongation in the L direction (L-El) satisfy the relationship of the above formula (1). Although not all of the analysis of deformation behavior during press forming of titanium plates with particularly strong anisotropy has been grasped, the balance between the L direction elongation (L-El) and the T direction r value (Tr) Thus, it was considered that an appropriate deformation state could be secured without reducing the strength.

  The titanium plate of the present invention is based on the premise that a highly lubricious film is formed on the surface thereof, and it is useful to define the relationship of the above formula (1) by having high lubricity. Sex becomes remarkable. In other words, the dynamic friction coefficient of the lubricating film should be less than 0.15 in order to effectively exhibit the effect of improving the formability by forming the lubricating film by satisfying the relationship of the above formula (1). Necessary (see FIG. 3 below). When the dynamic friction coefficient is 0.15 or more, the material does not sufficiently flow in and the macroscopic uniformity is not improved, so that the above effect is hardly exhibited.

  As the material for forming the lubricating film, a conventionally known material can be used, and for example, an organic resin mainly composed of a polyurethane resin, a polyolefin resin, or the like can be preferably used (see Examples below). In addition, a lubricant film containing a silica-based inorganic solid lubricant can be used if necessary. However, if the blending ratio increases, the dynamic friction coefficient of the surface of the lubricant film increases, so that good lubricity is exhibited. It is preferable to adjust to a range in which the dynamic friction coefficient is made as small as possible. The dynamic friction coefficient on the surface of the lubricating film is basically determined to some extent by the type of resin film, but the same type is affected by the surface properties (surface irregularities) of the titanium plate used as the substrate. Even a lubricating film of the above will change slightly.

  The titanium alloy of the present invention is applied as a material for heat exchange equipment and chemical plants, and improves the press formability when applied to such a material, but when the plate thickness becomes too thick, a lubricating film is applied. Therefore, the effect of improving the formability is difficult to be exhibited. In other words, as the plate thickness increases, if the friction resistance is almost the same as that of press oil, if the region is a very high plastic strain region, the portion will not crack due to local deformation. On the contrary, the high plastic strain region is formed by concentrating on a relatively large region that cannot be covered by local deformation, resulting in cracks. For these reasons, the thickness of the titanium plate is preferably 1.0 mm or less.

  The lower limit of the thickness of the titanium plate (or titanium alloy plate) may be set in consideration of the required strength, etc., and may vary depending on the type of titanium or titanium alloy plate. For example, in the case of industrial pure titanium (1 type or 2 types) is preferably about 0.3 mm or more, and in the case of a titanium alloy containing a small amount of alloy elements, it may be thinner.

  The titanium plate to be used in the present invention basically assumes pure titanium (JIS type 1 or type 2) used industrially, and is required when such titanium is applied to a heat exchanger or a chemical plant member. The press formability is further improved. However, a titanium alloy containing a small amount of alloy elements to the extent that press formability is not hindered is also included in the titanium alloy targeted by the present invention. For example, containing elements such as Al, Si, and Nb is effective in increasing the strength of a titanium plate (that is, a titanium alloy plate). However, if the content of these elements increases, the strength becomes too high. Then, since the press formability expected in the present invention cannot be obtained, the content of these elements (the total content of one or more types) is preferably up to about 2%. In addition, although Fe is basically included as an inevitable impurity, it is also possible to apply a titanium alloy plate in which the strength is increased by actively including such Fe up to about 1.5%. .

  The titanium plate or titanium alloy plate targeted in the present invention is composed of titanium and unavoidable impurities in addition to the above-mentioned components (the remainder). The above-mentioned “inevitable impurities” are impurity elements inevitably contained in the raw sponge titanium, and are typically oxygen, iron (except when Fe is actively added), carbon, nitrogen In addition, hydrogen, chromium, nickel, and the like, and in the manufacturing process, elements that may be incorporated into the product, such as hydrogen, are also included in the inevitable impurities. Among these impurities, oxygen and iron in particular affect the properties (tensile strength and elongation) of the titanium plate or titanium alloy plate, and these properties differ depending on their contents (see table below). 1-3). The content ranges of inevitable impurities such as oxygen and iron are about 0.03 to 0.05% by mass of oxygen and about 0.02 to 0.04% by mass of iron.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  Various plate thicknesses (0.5 to 1.5 mm) were obtained by performing cold rolling using titanium plates or titanium alloy plates having various chemical composition compositions shown in Table 1 below. The titanium plate used was JIS type 1 and JIS type 2 equivalent pure titanium, and the titanium alloy plate contained 1.2% of Al, Si, Nb, etc. in total (denoted as “1.2ASN” in the table). , Fe containing 1.5% (referred to as “1.5Fe titanium alloy” in the table), and after atmospheric annealing (annealing time 10 minutes), pickling treatment (washing with hydrofluoric acid) was performed. Further, for JIS Class 1 equivalent pure titanium, the L direction elongation (L-El) was adjusted by the annealing temperature, and the r value in the T direction (Tr) was adjusted by the chemical composition and the number of cold rolling.

Various lubricating films shown below were applied to the obtained titanium or titanium alloy plate (application amount: 0.2 to 3.0 g / m ² ). Table 2 below shows the annealing temperature, the number of cold rolling operations, the plate thickness, the type of the lubricating coating, and the dynamic friction coefficient of the lubricating coating surface of the various titanium plates or titanium alloy plates at this time. In addition, even if it is the same kind of lubricating film, the dynamic friction coefficient of the surface may differ depending on the influence (surface unevenness | corrugation) of the titanium or titanium alloy plate surface as mentioned above.
[Lubrication film type]
Organic system 1: 90% by mass of polyurethane + 10% by mass of colloidal silica
Organic system 2: 90% by mass of polyolefin + 10% by mass of colloidal silica
Organic system 3: 80% by mass of polyolefin + 20% by mass of colloidal silica
Inorganic system 1: 70% by mass of colloidal silica + 25% by mass of polyurethane + 5% by mass of polyolefin
Inorganic system 2: colloidal silica 60% by mass + polyurethane 30% by mass + polyolefin 10% by mass

  For the titanium or titanium alloy plate before the lubrication film is applied, a test piece specified in ASTM is taken, and the yield stress in the L direction (L−) is determined based on the metal material tensile test method specified in ASTM E8. YS), tensile strength in the L direction (L-TS), total elongation (elongation in the L direction: L-El), and r value in the T direction (Tr). For the yield stress (YS), tensile strength (TS) and elongation (L-El), the test speed during the tensile test was 0.5% / min from the beginning to 0.5% strain, and thereafter 40%. % / Min. Further, for the measurement of the r value (T−r), the r value (T−r) was determined with the strain addition amount being 6% and the tensile test speed being 10% / min.

  About the titanium or titanium plate which apply | coated the lubricating film, the press moldability was evaluated by the method mentioned later. At this time, in order to contrast with the evaluation method of the present invention, the Erichsen value, which is a general evaluation method for press formability, was also measured. For the measurement of this Eleksen value, a test piece having a size of 90 mm × 90 mm was taken from the titanium plate or titanium alloy plate (coated with a lubricating film) obtained above, and Erichsen defined in JIS Z 2247 was used. The test was conducted. The press formability evaluation method used in the present invention is as follows.

  For each titanium or titanium alloy plate, the size 100 × 100 mm, the pitch: 10 mm, the maximum height 4 mm, the radius of curvature R = 0.4, 0.6, 0,. Using a mold having six kinds of ridgelines of 8, 1.0, 1.4, and 1.8 (mm), pressing was performed with an 8 ton hydraulic press. The press conditions at this time are a maximum load of 300 N, a press speed of 1 mm / second, and a press cut of 4 mm.

  As shown in FIG. 1, the crack measurement position of the press test piece obtained as described above is shown in FIG. 1 (FIG. 1A is a plan view and FIG. 1B is a cross-sectional view). It is a place. Regarding A, C, C ', and E, which are the base points of cracks, when visually judged, 2 points if healthy, 1 point if there is a tendency to necking (constriction phenomenon), 0 points if cracking has occurred As for [Equation (2) below], B and D, 1 point if healthy, 0.5 point if there is a tendency to necking, 0 point if there is a crack [Equation (3) below], and more Multiply the number of points by the reciprocal of the radius of curvature R [collectively "R (ij)"] to quantify the cracking condition (Equations (2) and (3) below) The ratio when no occurrence occurs is expressed as a score [formula (4) below], and is used as an index for evaluating the press formability in the present invention.

E (ij) = 1.0 × (healthy: 2, necking: 1, crack occurrence: 0) (2)
E (ij) = 0.5 × (healthy: 2, necking: 1, crack occurrence: 0) (3)
Score = [ΣE (ij) / R (ij)] / [ΣA _{, C, C ′, E2} / R (ij) + ΣB _{, D} 1 / R (ij)] × 100 (4)

  Measure the score when the lubricant film is applied and the score when the lubricant film is not applied, and calculate the ratio (score with application / score without application) to improve moldability by applying the lubricant film The effect of the present invention was confirmed depending on whether the effect can be further improved (that is, whether the value of the ratio is 1.0 or more).

  The measurement results are collectively shown in Table 3 below together with the tensile properties (L-YS, L-TS, L-El, Tr, and Tr / L-El) of the titanium plate or titanium alloy plate. Further, based on this result, the relationship between Tr / L-El and (score with application / score without application) is shown in FIG. 2, and Tr / L-El when the dynamic friction coefficient is high (0.15 or more). 3 and the relationship between the Erichsen value and the score (score when the lubricating film is applied) are shown in FIG. 4 (in each figure, No. indicates the test No.). .)

  As is apparent from the results of FIG. 2, it can be seen that when the value of Tr / L-El is 0.07 or more, the effect of improving the formability by applying the lubricating film is effectively exhibited.

  FIG. 3 shows the relationship between Tr / L-El and (score with application / score without application) when the dynamic friction coefficient of the lubricant film is high (0.15 or more). If it is not less than .15, it can be seen that it is difficult to obtain the effect of improving the press formability by applying the lubricating film.

  As is clear from the results of FIG. 4, the “score”, which is the evaluation standard for press formability in the present invention, has a good correlation with the Erichsen value, and the press formability can be accurately evaluated by the score. I understand.

It is a figure for demonstrating the method of evaluating press moldability. It is a graph which shows the relationship between Tr / L-El and (score with application / score without application). It is a graph which shows the relationship between Tr / L-El when a dynamic friction coefficient is high (0.15 or more) and (score with application / score without application). It is a graph which shows the relationship between an Eriksen value and a score.

Claims (2)

A titanium or titanium alloy plate rolled in one direction, the surface of which is coated with a lubricating film, the dynamic friction coefficient of the surface of the lubricating film is controlled to be less than 0.15, and the rolling direction of the titanium or titanium alloy sheet The press formability and strength are characterized by having the relationship of the following formula (1) between the elongation (L-El) of the steel and the r value (Tr) in the direction perpendicular to the rolling direction: Titanium or titanium alloy plate with excellent balance.
T−r / L−E1 ≧ 0.07 (1)   The titanium or titanium alloy plate according to claim 1, wherein the plate thickness is 0.3 to 1.0 mm.