JP4850657B2 - β-type titanium alloy - Google Patents

Description

  The present invention relates to a β-type titanium alloy.

  The β-type titanium alloy is a titanium alloy in which a β-type stabilizing element such as V or Mo is added to leave a β phase that is stable at room temperature. The β-type titanium alloy is excellent in cold workability, and the α phase is finely precipitated by aging heat treatment, a high strength of about 1400 MPa is obtained in tensile strength, and the Young's modulus is relatively low. It is applied to various uses such as golf club heads and fasteners.

  The conventional β-type titanium alloys are Ti-15 mass% V-3 mass% Cr-3 mass% Sn-3 mass% Al (hereinafter, description of mass% is omitted), Ti-13V-11Cr-3Al, Ti-3Al-8V-6Cr-4Mo-4Zr is a typical one.

  On the other hand, a β-type titanium alloy to which Fe, which is a relatively inexpensive β-type stabilizing element, has been proposed.

  The invention described in Patent Document 1 is a Ti-Al-Fe-Mo-based β-type titanium alloy having a Moeq (Mo equivalent) larger than 16, and a typical composition thereof is that Al is 1 to 2 mass. %, Fe is 4 to 5% by mass, Mo is 4 to 7% by mass, and O is 0.25% by mass or less.

  The inventions described in Patent Document 2, Patent Document 3, and Patent Document 4 are Ti-Al-Fe-Cr-based β-type titanium alloys, to which V and Mo are not added, and in mass%, Fe is 1-4%, 8.8% or less (However, Fe + 0.6Cr is 6 to 10), 5% or less, Cr is 6-13%, 2-12% respectively (Fe + 0.6Cr is 6-10) 10 to 20% of range.

  The inventions described in Patent Document 5, Patent Document 6, and Patent Document 7 are respectively Ti-Al-Fe-Cr-V-Mo-Zr system, Ti-Al-Fe-Cr-V-Sn system, Ti-Al system. -Fe-Cr-V-Mo based β-type titanium alloy. In both cases, Fe and Cr are both added, and both or one of V and Mo is contained. Furthermore, in patent document 5 and patent document 6, 2-6 mass% Zr and 2-5 mass% Sn are added, respectively.

Japanese Patent No. 2859102 Japanese Patent Laid-Open No. 03-61341 JP 2002-235133 A JP 2005-60821 A JP 2005-154850 A JP 2004-270009 A JP 2006-111934 A

  As described above, Patent Documents 1 to 7 are β-type titanium alloys to which Fe and Cr, which are relatively inexpensive β-type stabilizing elements, are added.

  However, since Fe, which is an inexpensive β-stabilizing element, easily segregates during solidification in the dissolution process, Patent Document 1 (Ti—Al—Fe—Mo system) contains 4 to 5% by mass of Fe, If it is added in a large amount exceeding 4% by mass, the possibility of variation in material properties and age-hardening properties increases due to component segregation. Moreover, patent document 1 does not contain V.

  In Patent Document 2, Patent Document 3, and Patent Document 4, a relatively inexpensive β-stabilizing element Cr is used in addition to Fe, and neither V nor Mo is added. Since Cr segregates in the same tendency as Fe, even in these β-type titanium alloys in which the β-stabilizing elements are only Fe and Cr and a large amount of these are added, the material properties and age hardening are caused by component segregation. When variations occur in the characteristics, a region with high strength and a region with low strength are generated, and the difference in strength between these regions is large, when the material is applied to a spring such as a coil spring, the region with low strength is The possibility that the fatigue life becomes the starting point of the fatigue failure is increased. Patent Literature 5, Patent Literature 6, and Patent Literature 7 are based on a Ti—Al—Fe—Cr—V—Mo system, and V and Mo are added alone or both. In both Patent Document 5, Patent Document 6, and Patent Document 7, both Fe and Cr that are easily segregated are added, and Mo is as low as 6% by mass or less with respect to the total amount, and the effect of reducing component segregation is sufficient. is not. In Patent Document 6, Mo is not added.

  In addition, the β-type titanium alloy can be strengthened by aging heat treatment, but the aging heat treatment for 8 to 24 hours does not always have a tensile strength of 1400 MPa or more, and there is a problem that ductility is low even at a strength of 1400 MPa or more. .

  Patent Document 6 also contains 2 to 5% by mass of Sn, which is a neutral element (an element that is neither α-stabilized nor β-stabilized). As can be seen from the periodic table, Sn has a large atomic weight of 118.69, whereas Zr, which is the same neutral element, is 91.22, and it further increases the density of the titanium alloy. In applications where a titanium alloy is applied for the purpose of weight reduction (high specific strength) (springs, golf club heads, fasteners, etc.), it is advantageous to avoid the addition of Sn.

  Further, when the α-phase is precipitated by aging heat treatment to increase the strength of the β-type titanium alloy, the Young's modulus increases, and the low Young's modulus, which is a feature of the β-type titanium alloy, cannot be fully utilized. This is because the α phase is about 20 to 30% and the Young's modulus is larger than the β phase. In order to obtain a high strength while maintaining a relatively low Young's modulus, it is necessary to increase the strength before the aging heat treatment as a base to suppress the precipitation amount of the α phase by the aging heat treatment.

  From the above, the present invention controls the additive element and its composition to suppress the influence of component segregation that occurs when a large amount of Fe, which is a relatively inexpensive β-stabilizing element, is added. An object of the present invention is to provide Ti-Al-Fe-V-Mo and Ti-Al-Fe-V-Mo-Zr-based β-type titanium alloys having material properties. By applying the β-type titanium alloy of the present invention as a material for a spring such as a coiled spring of an automobile or a motorcycle, a golf club head, or a fastener such as a bolt or nut, a product having stable material characteristics is provided. It is for the purpose.

  Furthermore, in order to make it easy to obtain a low Young's modulus while having high strength, in the β-type titanium alloy of the present invention, the Ti—Al—Fe—V—Mo system and Ti—Al— with increased strength before aging heat treatment are used. An object of the present invention is to provide a Fe-V-Mo-Zr-based β-type titanium alloy.

The gist of the present invention for solving the above problems is as follows.
(1) By mass%, Al is contained in a range of 2 to 5%, Fe is 2.5 to 4.5%, V is 6 to 10%, and Mo is 6.5 to 10%. [1] A β-type titanium alloy having an oxygen equivalent Q in the formula of 0.15 to 0.30 and the balance of Ti and inevitable impurities.
Equivalent oxygen Q = [O] +2.77 [N] (1) formula
Here, [O] is the O content (mass%), and [N] is the N content (mass%).
(2) The β-type titanium alloy according to (1), further containing Zr in a range of 2 to 6% by mass.
( 3 ) A processed product obtained by work-hardening the β-type titanium alloy according to (1) or (2) .
(4) By mass%, Al is contained in a range of 2 to 5%, Fe is 2.5 to 4.5%, V is 6 to 10%, Mo is 6.5 to 10%, and the balance is Ti. And a processed product that has been work-hardened β-type titanium alloy composed of inevitable impurities.
(5) Further, the processed product of the β-type titanium alloy according to (4), wherein the β-type titanium alloy contains Zr in a range of 2 to 6% by mass.

  Here, (4) “work-hardened product” refers to plates, rods, and other molded products that have been subjected to processing such as rolling, wire drawing, forging, and press molding. The strength is higher than that in the annealed state.

  According to the present invention, the Ti—Al—Fe—V—Mo system and the Ti—Al—Fe—V—Mo— which suppress the influence of component segregation that occurs when a large amount of Fe, which is a relatively inexpensive β-stabilizing element, is added. A Zr-based β-type titanium alloy can be provided. This makes it possible to obtain stable product material characteristics even in a β-type titanium alloy utilizing Fe, which is a relatively inexpensive additive element, in various applications represented by springs, golf club heads, fasteners and the like. Furthermore, in order to make it easy to obtain a low Young's modulus while having high strength, it is possible to provide a β-type titanium alloy having increased strength before aging heat treatment in the β-type titanium alloy of the present invention.

  The present inventors suppress the influence of component segregation by containing a relatively low amount of Fe as a β-stabilizing element and by containing both V and Mo in a predetermined amount to 10% by mass. The present inventors have found that stable aging material characteristics can be achieved, leading to the present invention. Further, the oxygen equivalent Q (= [O] +2.77 [N]) of the formula [1] is set to 0.15 to 0.30, or the work hardening state is left, or both. It has been found that the tensile strength before aging heat treatment can be further increased. Thus, by increasing the tensile strength before aging heat treatment, high tensile strength can be achieved by aging heat treatment while maintaining a relatively low Young's modulus.

  The basis for setting each element of the present invention will be described below.

  Al is an α-stabilizing element and promotes precipitation of α-phase during aging heat treatment, thus contributing to precipitation strengthening. If the Al content is less than 2% by mass, the contribution to the precipitation strengthening of the α phase is too small, while if it exceeds 5% by mass, excellent cold workability cannot be obtained. Therefore, in this invention, Al is made into the range of 2-5 mass%. When emphasizing cold workability, 2 to 4% by mass of Al is preferable.

  By adding a predetermined amount of both V and Mo in addition to Fe as a β-stabilizing element, the influence of component segregation can be mitigated. V has a small segregation during solidification and is distributed almost uniformly, and Mo is concentration-distributed in a tendency opposite to that of Fe. In other words, the Fe concentration is low at the site where the Mo concentration is high, and vice versa at the site where the Mo concentration is low. In this way, the stability of the β phase can be ensured based on the uniformly distributed V, and the influence of Fe segregation can be mitigated by Mo. Thereby, the influence of component segregation is suppressed, and it becomes possible to add much relatively inexpensive Fe.

  Here, the degree of component segregation can be determined by observing the structure obtained by etching the cross section after the aging heat treatment for precipitating the α phase. Due to the segregation of the β-stabilizing element, the precipitation rate and amount of the α-phase are different, and therefore a difference appears in the metal structure depending on the segregation site. FIG. 1 is an example in which the uneven distribution of the fine α-phase precipitation amount is significantly caused by unilateral segregation of the β-phase stabilizing element in the β-type titanium alloy, and FIG. 2 shows the β-phase in the β-type titanium alloy. An example in which the uneven distribution of the fine α-phase precipitation distribution is suppressed by devising the composition of the stabilizing element will be shown. FIGS. 1 and 2 both show examples in which a hot-rolled β-type titanium alloy bar is solution annealed in the β single phase region and then subjected to aging heat treatment at 500 ° C. for 24 hours. 1 and 2, after polishing the L cross section of the rod (cross section parallel to the longitudinal direction of the rod), the rod was immersed in an etching solution for titanium (containing hydrofluoric acid and nitric acid), and the structure was observed. It is easy. In FIG. 1, the effect of component segregation appears greatly, and a portion where the precipitation amount of α phase is small (a light gray band sandwiched between dark gray regions) and a portion where a large amount (dark gray region) can be clearly identified visually. . This dark gray region is hard because there is a lot of α phase and finely precipitated, while the light gray region is softer than this, and in the example of FIG. 1, the Vickers hardness of the dark gray region is about 440. On the other hand, the value in the light gray band is as low as about 105 points. This is a phenomenon caused by the segregation of the β-stabilizing element as described above, and naturally has a great influence on the material. On the other hand, FIG. 2 ((a), (b), (c)) is an example in which the light gray coarse area as shown in FIG. In addition, when 6 points of Vickers hardness are measured at random within each cross section of (a), (b), and (c) of FIG. 2, the width of the value is about 10 to 20, compared with the example of FIG. Very small. In the present invention, this determination method is used, and is hereinafter referred to as “segregation determination method”. The Vickers hardness was measured with a load of 9.8N.

  As a result of evaluation by the segregation judgment method, when Al is 2 to 5% by mass, Fe is 1 to 4.5%, V is 6 to 10%, Mo is 6.5 to 10%. The effect of segregation can be greatly reduced. On the other hand, in order to obtain a good strength-ductility balance in the tensile properties after aging heat treatment, it is necessary to add 2.5% by mass or more of Fe. When the Fe concentration is less than 2.5% by mass, the influence of component segregation tends to be reduced. However, in the strength-ductility balance after the aging heat treatment, the tensile strength is 1400 MPa or more in the aging heat treatment for 24 hours or less. The growth is not as high as 10%. By adding 2.5 mass% or more of Fe, an aging material can be improved, and a tensile strength of 1400 MPa or more and an elongation of 10% or more can be obtained.

  Therefore, in claim 1 of the present invention, the mass ranges from 2 to 5%, Fe from 2.5 to 4.5%, V from 6 to 10%, and Mo from 6.5 to 10%. did. In addition, when Fe, Mo, and V are less than the lower limit, a stable β phase may not be obtained. On the other hand, comparatively expensive V and Mo do not need to be added excessively beyond the upper limit, and if Fe exceeds the upper limit, the influence of component segregation may become obvious.

  In the present invention, preferably, by mass%, Al is 2 to 4%, Fe is 2.8 to 4.2%, V is 8.6 to 10%, and Mo is 8.6 to 10%. . In this preferable range, the lower limits of V and Mo are increased, and the effect of suppressing the influence of component segregation is further enhanced.

  Zr is a neutral element like Sn and contributes to increasing the strength, and has a smaller tendency to increase the density than Sn. Since Zr is in the range of 2 to 6% by mass, the tensile strength after aging heat treatment is improved, and the decrease in total elongation is very small. Therefore, Claim 2 of the present invention provides the β-type titanium alloy of Claim 1, Furthermore, it shall contain 2-6 mass% of Zr. Preferably, by mass, Al is 2 to 3.5%, Fe is 2.5 to 4.5%, V is 7 to 9%, Mo is 7 to 9%, and Zr is 2 to 5%. Range. Considering the increase in density due to the addition of Zr, the upper limit of V, Mo, Zr is lowered, and the ductility tends to decrease in response to the increase in strength due to the addition of Zr, so the upper limit of the Al amount is lowered. .

The β-type titanium alloy having the above composition can increase the strength before aging heat treatment by O and N. On the other hand, if the amounts of O and N are too high, it may be impossible to maintain excellent cold workability. The contribution of O and N to the strength can be evaluated by the oxygen equivalent Q in the formula [1] (= [O] + 2.77 × [N]). This Q is 1.77 when the contribution to the solid solution strengthening ability of the β-type titanium alloy per 1% by mass of oxygen concentration, that is, the contribution to the increase in tensile strength, is 2.77 times that of oxygen. Therefore, the nitrogen concentration is multiplied by 2.77 to be converted into an oxygen concentration. According to claim 1 of the present invention, because it can achieve both excellent cold working and improving the strength, the β-type titanium alloy according to claim 1, the oxygen equivalent Q in the range of 0.15 to 0.30.

Further, even by work hardening in addition to the chemical composition, since it is possible to increase the strength before aging heat treatment, in the claims 3 to 5 of the present invention, rolling (including cold rolling) and drawing (cold drawing etc. ) And a work-hardened state by processing such as pressing or forging. The shape is a board, a bar wire, and various molded products obtained by molding these.

  The titanium alloy of the present invention inevitably contains H, C, Ni, Cr, Mn, Si, S, etc., as in the case of ordinary pure titanium or titanium alloy. It is less than 0.05% by mass. However, as long as the effects of the present invention are not impaired, the content is not limited to less than 0.05% by mass. Since H is a β-stabilizing element and tends to delay the precipitation of the α phase during aging heat treatment, the H concentration is preferably 0.02% by mass or less.

  The β-type titanium alloy of the present invention described above is composed of ferromolybdenum, ferrovanadium, low-grade sponge titanium, pure titanium, and various titanium alloy scraps as a relatively inexpensive raw material in addition to the Fe metal simple substance. Etc. can be used.

  Claim 1 of the present invention will be described in more detail using the following examples.

  The ingot melted in vacuum was heated at 1100 to 1150 ° C. and hot forged to produce an intermediate material, and then heated at 900 ° C. and hot forged into a rod having a diameter of about 15 mm. Thereafter, solution annealing was performed at 850 ° C. and air cooling was performed.

  In order to evaluate the cold workability of this solution annealed material, descaling (soaking with nitric hydrofluoric acid after shot blasting) was performed, followed by lubrication and cold drawing with dies up to 50% in cross-section reduction rate. did. It was observed with the naked eye whether there were cracks or breaks in the surface between each cold drawing. The case where breakage or cracking occurred until the cross-section reduction rate reached 50% was evaluated as “X”, and the case where no cross-section reduction occurred was evaluated as “◯”. Further, the influence of component segregation was evaluated by the segregation determination method described above. In the method shown in FIG. 1 and FIG. 2, the solution annealed material is further subjected to an aging heat treatment at 500 ° C. for 24 hours, the L section is polished and etched with an etching solution for titanium, and the metal structure is visually observed. Accordingly, when the aspect is as shown in FIG. 1, it is judged as “X”, and when it is as shown in FIG. Further, the material subjected to aging heat treatment at 500 ° C. for 24 hours was processed into a tensile test piece having a parallel part of 6.25 mm in diameter and 32 mm in length in order to evaluate the aging material, and a tensile test was performed at room temperature.

  Table 1 shows the components, the possibility of cold drawing, the evaluation results of the segregation determination method, the tensile properties after aging heat treatment, and the like. The oxygen equivalent Q was about 0.175, and the H concentration was 0.02% by mass or less.

No. 1 in Table 1 in which the components are in the range of claim 1 of the present invention (Al, Fe, V, Mo , and oxygen equivalent Q ). Nos. 1 to 19 are “◯” because there is no defect such as a crack even in cold drawing with a cross-section reduction rate of 50%, and the result of the segregation determination method also shows a uniform macro structure.

  On the other hand, No. in which the Al concentration deviates from the lower limit. No. 21, even when subjected to aging heat treatment at 500 ° C. for 24 hours, the macro structure is light gray, the increase in cross-sectional hardness is small, the tensile strength is low, and the precipitation of α phase is slower than that of the conventional β-type titanium alloy. . No. in which the amount of Al deviates from the upper limit. No. 22 cannot be said to have excellent cold workability because cracks occur during cold drawing. In addition, No. No. 22 was not evaluated after aging heat treatment because cracking occurred during cold drawing.

  No. in which the Fe concentration deviates from the lower limit. No. 20 has a tensile strength after aging heat treatment, the strength is less than 1400 MPa, and the elongation is as small as 7%. On the other hand, the Fe concentration exceeded the upper limit. 25, No. in which the amount of V or Mo deviates from the lower limit. 23, no. No. 24 is markedly affected by component segregation, and the evaluation result of the segregation determination method is “x”. In addition, the sample whose result of the segregation judgment method was “x” was not subjected to the tensile test after the aging heat treatment because of the large variation in material.

  In the samples of Table 1, No. 5,6,9,11,13,16,18 are the preferred ranges of claim 1 in mass%, Al 2-4%, Fe 2.8-4.2%, and V 8. 6 to 10%, Mo is in the range of 8.6 to 10%, and the aging heat treatment is already in the state of “○” at 10 hours when the aging heat treatment is less than 24 hours, and the component segregation The impact was smaller.

  Claim 2 of the present invention will be described in further detail using the following examples.

  Table 2 shows an embodiment of claim 2 to which Zr is added. The manufacturing method, evaluation method, and the like are the same as those in the above-mentioned [Example 1]. In all samples in Table 2, the oxygen equivalent Q was about 0.175, and the H concentration was 0.02% by mass or less.

  From Table 2, it can be seen from No. 2 that Zr is within the range of claim 2. As for 2-1 to 2-14, there is no defect, such as a crack, even in cold drawing with a cross-section reduction rate of 50%, and the result of the segregation judgment method also shows a uniform macro structure, which is a judgment of “◯”. The tensile properties after aging heat treatment are also good. When Zr is in the range of 2 to 6% by mass, it has excellent cold workability and segregation is suppressed. Compared with the invention example of Table 1 to which Zr is not added, the invention example of Table 2 has a high tensile strength of aging heat treatment, and there is almost no decrease in total elongation.

  On the other hand, no. No. 2-15 is No. 2 in Table 1 where Zr was not added. 1 and the tensile strength after the aging heat treatment hardly increased. No. Zr exceeding 6 mass% and as large as 7.3 mass%. No. 2-16 has a low total elongation of less than 10% after aging heat treatment.

  No. in which the amount of V or Mo deviates from the lower limit. In 2-17 and 2-18, the influence of component segregation is significant, and the evaluation result of the segregation determination method is “x”. In addition, the sample whose result of the segregation judgment method was “x” was not subjected to the tensile test after the aging heat treatment because of the large variation in material.

Claims 1 and 2 of the present invention will be described in more detail using the following examples.

Table 3 shows examples in which the O and N concentrations are variously changed. The manufacturing method, evaluation method, and the like are the same as those in the above-mentioned [Example 1]. In all the samples in Table 3, the H concentration was 0.02% by mass or less. In the examples of Table 1 and Table 2, the value of oxygen equivalent Q is within the scope of claim 1 .

  When samples having equivalent components other than the oxygen equivalent Q are compared, the larger the oxygen equivalent Q, the higher the tensile strength of the solution annealed material. No. in Table 3 where Q is about 0.114 to 0.121 and smaller than 0.15. Compared with 3-1, 3-6, 3-9, 3-14, and 3-18, the sample with Q of 0.15 or more clearly has a higher tensile strength of the solution annealed material. On the other hand, No. in Table 3 where Q exceeds 0.3. 3-5, 3-13, 3-17, 3-22, cold drawing is possible without defects such as cracks until the cross-sectional reduction rate (drawing rate) of cold drawing is 50%. The critical cold drawing rate (cross-sectional reduction rate that enables cold drawing without defects such as cracks) is as small as 69% and 65%.

  When Q is in the range of 0.15 to 0.3, the tensile strength of the solution-annealed material is relatively high, and even if the cold drawing rate exceeds 80%, defects such as cracks do not occur and the limit cold drawing The linearity exceeds 80% and has very good cold workability. In addition, the results of the segregation determination method also show a uniform macro structure, and the determination of “◯” indicates that the tensile properties after aging heat treatment are good with a total elongation of 10% or more. Table 3 also shows that the tensile strength after the aging heat treatment is increased in response to the oxygen equivalent Q, and a high strength can be obtained even if the amount of precipitation of the α phase is reduced. In that respect, when the strength after the aging heat treatment is equal, the amount of the precipitated α phase can be reduced, so that a low Young's modulus is easily obtained.

In addition, No. of Table 3 where Q is smaller than about 0.114 to 0.121 and 0.15. 3-1, 3-6, 3-9, 3-14, 3-18, the tensile strength of the solution heat-treated material is 938 to 969 MPa, compared with the invention example in which Q is 0.15 to 0.3. Slightly low.

As shown in Table 3, it can be seen that the tensile strength as cold drawn with a drawing rate of 50% is about 30 to 40% higher than that of the solution annealed material before aging heat treatment. As described above, a material that is work-hardened while being cold worked has a higher strength before aging heat treatment, and a material having higher strength and lower Young's modulus can be easily obtained. This corresponds to the invention of any one of claims 3 to 5 of the present invention. In the examples of Tables 1 and 2, the material as cold-drawn after a drawing rate of 50% is 30-40% higher in tensile strength than the solution annealed material before aging heat treatment, and is work-hardened. is doing.

  In the samples of Tables 1 to 3, the preferred range of the present invention is mass%, “Al is 2 to 4%, Fe is 2.8 to 4.2%, V is 8.6 to 10%, and Mo is In the case of “8.6 to 10%”, the evaluation of the segregation judgment method was already in the state of “◯” at the time of 10 hours when the aging heat treatment was less than 24 hours, and the influence of the component segregation was smaller.

  In the above embodiment, the rod-shaped material has been described in detail. However, the effect of the present invention similar to that of the above-described rod can be obtained even with a material that is hot-rolled from an intermediate material for hot forging into a plate shape having a thickness of about 10 mm. Is obtained.

It is a figure which shows the macro structure of the L cross section of the rod heat-treated. It is a figure which shows the macro structure of the L cross section of the rod heat-treated.

Claims (5)

By mass%, 2-5% of Al, 2.5 to 4.5% of Fe, the V 6 to 10%, containing within an amount of 6.5 to 10% of Mo, (1) type of oxygen A β-type titanium alloy having an equivalent Q of 0.15 to 0.30 and the balance of Ti and inevitable impurities.
Equivalent oxygen Q = [O] +2.77 [N] (1) formula
Here, [O] is the O content (mass%), and [N] is the N content (mass%).   The β-type titanium alloy according to claim 1, further comprising Zr in a range of 2 to 6% by mass. Claim 1 or 2 remains workpiece obtained by work hardening a β-type titanium alloy according to. It contains 2 to 5% of Al, 2.5 to 4.5% of Fe, 6 to 10% of V, and 6.5 to 10% of Mo with the balance being Ti and inevitable. Processed product with work hardened β-type titanium alloy consisting of impurities. Further, the β-type titanium alloy according to claim 4, wherein the β-type titanium alloy contains Zr in a range of 2% to 6% by mass%.