Steel for torsion bars

Abstract

To provide a steel for torsion bar that has high strength while maintaining excellent low-temperature ductility even after age hardening.SOLUTION: A steel for torsion bar has a predetermined chemical composition, satisfying the following formula (1) and formula (2). [Ti] / [N]≤4.0 (1), where [Ti] and [N] represent the content of Ti and N expressed in mass%, respectively. ΔHV<2.0HV (2), where ΔHV is defined by the following formula (3). ΔHV=HV2-HV1 (3), where HV1 and HV2 represent the Vickers hardness of steel for torsion bar before and after age hardening.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a steel material for seatbelt torsion bars that has excellent low-temperature ductility after age hardening. [Background technology]

[0002] Seatbelt devices are equipped with a retractor with a load limiter mechanism to cushion the impact on occupants. The torsion bar used in this retractor is designed to absorb the impact on occupants by rotating while twisting when the vehicle decelerates, so it is required to have high deformability (ductility) and high steel strength.

[0003] Patent Document 1 discloses a steel material for torsion bars, characterized in that the metal structure is made of ferrite or ferrite-pearlite and the ratio of cementite length is set to a certain amount or less. By controlling the metal structure of the steel matrix and grain boundaries, a steel with excellent ductility during high-speed deformation can be obtained.

[0004] Patent Document 2 discloses a steel bar that can be used for torsion bars, characterized in that the ferrite grain size in the surface layer and the interior of the rolled material is controlled to be uniform without being too refined. The steel bar disclosed in Patent Document 2 is said to have excellent deformability even in the as-hot-rolled state, and to have high strength and torsional properties. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-022397 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-105495 Summary of the Invention [Problem to be solved by the invention]

[0006] Since automobiles are used in cold regions, there is a demand for steel materials for torsion bars that have sufficient ductility (low-temperature ductility) even in sub-zero temperatures. Furthermore, the adverse effects of age hardening have been suggested, and even if high mechanical properties are achieved during manufacturing, ductility may decrease with age, resulting in the risk of not being able to absorb sufficient impact energy.

[0007] In Patent Document 1, the decrease in low-temperature ductility due to age hardening is not taken into consideration. In Patent Document 2, attention is paid to the fact that N in steel materials causes strain aging during cold working, and the N content is controlled. However, low-temperature ductility is not taken into consideration, and a detailed study is not conducted on the reduction in ductility due to age hardening.

[0008] Therefore, an object of an embodiment of the present invention is to provide a steel material for torsion bars that has high strength and excellent low-temperature ductility even after age hardening. [Means for solving the problem]

[0009] Aspect 1 of the present invention is C: 0.010~0.030% by mass Si:0.10~0.40% by mass Mn:0.20~0.50% by mass Al:0.010~0.060% by mass Nb:0.020~0.030% by mass Ti:0.005~0.025% by mass P: 0.020% by mass or less (including 0% by mass) S: 0.020% by mass or less (including 0% by mass) N: 0.0050% by mass or less (including 0% by mass) balance: the balance is composed of Fe and unavoidable impurities, This steel material for torsion bars satisfies the following formulas (1) and (2). [Ti] / [N]≦4.0 (1) Here, [Ti] and [N] represent the Ti and N contents, respectively, expressed in mass %. ΔHV<2.0HV (2) Here, ΔHV is defined by the following equation (3). ΔHV=HV2-HV1 (3) Here, HV1 and HV2 are the Vickers hardnesses of the steel material for the torsion bar before and after aging treatment, respectively.

[0010] Aspect 2 of the present invention is The steel material for a torsion bar according to aspect 1, wherein the reduction of area at −196° C. is more than 50%. [Effects of the Invention]

[0011] According to an embodiment of the present invention, it is possible to provide a steel material for torsion bars that has high strength and excellent low-temperature ductility after age hardening. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a graph showing the relationship between the difference in hardness ΔHV of a steel material before and after aging and the reduction of area. DETAILED DESCRIPTION OF THE INVENTION

[0013] The inventors conducted extensive research to obtain a steel material for seatbelt torsion bars that has excellent low-temperature ductility after age hardening. They discovered for the first time that, in a steel material having a specific chemical composition, by controlling the ratio of the Ti content to the N content to 4.0 or less and further controlling the difference in hardness ΔHV before and after aging to 2.0 HV or less, it is possible to achieve excellent low-temperature ductility after age hardening while maintaining high strength, and have completed the present invention. It is presumed that steel materials that have excellent low-temperature ductility after age hardening also have excellent low-temperature ductility before age hardening.

[0014] Hereinafter, a torsion bar steel material according to an embodiment of the present invention will be described. In this specification, "steel material for torsion bars" refers to steel material that has been subjected to cold working, and does not include steel material that is in the form of hot rolling.

[0015] <1.Chemical composition> The steel for torsion bars according to an embodiment of the present invention contains C: 0.010 to 0.030 mass%, Si: 0.10 to 0.40 mass%, Mn: 0.20 to 0.50 mass%, Al: 0.010 to 0.060 mass%, Nb: 0.020 to 0.030 mass%, Ti: 0.005 to 0.025 mass%, P: 0.020 mass% or less (including 0 mass%), S: 0.020 mass% or less (including 0 mass%), and N: 0.0050 mass% or less (including 0 mass%). In addition, the expression "containing 0% by mass" in relation to the content of an element means that it may be 0% by mass, may contain an amount that is unavoidably contained as an impurity (an amount at the impurity level), or may be intentionally added. Each element will be described in detail below.

[0016] (C:0.010~0.030% by mass) C is an essential element for imparting strength to steel materials. If the content is less than 0.010 mass%, the desired rolled material strength (350 MPa or more) cannot be obtained even if precipitation strengthening elements such as Ti and Nb are added or the rolling conditions are controlled. It is preferably 0.013 mass% or more, more preferably 0.015 mass% or more. On the other hand, if the content exceeds 0.030 mass%, the desired deformability cannot be obtained. It is preferably 0.027 mass% or less, more preferably 0.025 mass% or less.

[0017] (Si:0.10~0.40% by mass) Si is a useful element for acting as a deoxidizer and for ensuring the desired strength. To effectively exert these effects, 0.10% by mass or more is added. Preferably, 0.15% by mass or more, and more preferably, 0.20% by mass or more. However, if added in excess, the desired ferrite grain size cannot be obtained, and since the ferrite undergoes solid solution strengthening, the desired deformability cannot be ensured even if the rolling conditions are controlled. Therefore, the upper limit is set to 0.40% by mass. Preferably, the content is 0.35% by mass or less, and more preferably, 0.30% by mass or less.

[0018] (Mn:0.20~0.50% by mass) Like C, Mn is a useful element for increasing the strength of steel. To effectively exert this effect, 0.20% by mass or more is added. Preferably, 0.25% by mass or more, and more preferably, 0.30% by mass or more. However, if added in excess, significant segregation occurs, resulting in greater variations in strength. Therefore, the upper limit is set at 0.50% by mass. Preferably, the content is 0.45% by mass or less, and more preferably, 0.40% by mass or less.

[0019] (Al:0.010~0.060% by mass) Al is a useful element for deoxidation, and also has the effect of stabilizing ferrite grains by precipitating AlN (allowing for the stable production of ferrite with a desired average grain size). To effectively exert this effect, 0.010% by mass or more is added. Preferably, 0.015% by mass or more, and more preferably, 0.020% by mass or more. However, excessive addition increases nonmetallic inclusions and reduces deformability, so the upper limit is set at 0.060% by mass. Preferably, 0.050% by mass or less, and more preferably, 0.040% by mass or less.

[0020] (Nb: 0.020 to 0.030 mass%, and Ti: 0.005 to 0.025 mass%) These elements are all nitride / carbonitride forming elements and have the effect of suppressing hot rolling cracking by fixing free C and N to precipitate TiN in austenite or by precipitating Nb(C,N), etc. Furthermore, the remaining Ti that does not contribute to the precipitation of TiN precipitates in ferrite or at ferrite grain boundaries as TiC or composite carbides of Ti, Nb, and Cr, etc., thereby contributing to improved strength.

[0021] To effectively exert such an effect, Nb is controlled to 0.020 mass% or more and 0.030 mass% or less, and Ti is controlled to 0.005 mass% or more, preferably 0.008 mass% or more, and 0.025 mass% or less, preferably 0.020 mass% or less.

[0022] (P: 0.020% by mass or less (including 0% by mass)) Since P segregates at grain boundaries and reduces deformability, the upper limit is set to 0.020% by mass, preferably 0.015% by mass or less, and more preferably 0.010% by mass or less. The lower the P content, the better, but typically, at least about 0.001% by mass is contained.

[0023] (S: 0.020% by mass or less (including 0% by mass)) S forms sulfide-based inclusions, mainly MnS, which reduces deformability, so the upper limit is set to 0.020% by mass. It is preferably 0.015% by mass or less, and more preferably 0.010% by mass or less. The lower the S content, the better, but typically, at least about 0.001% by mass is contained.

[0024] (N: 0.0050% by mass or less (including 0% by mass)) Since N dissolves in ferrite and causes strain aging during cold working, the upper limit of N content is set to 0.0050 mass%, preferably 0.0045 mass% or less, and more preferably 0.0040 mass% or less.

[0025] (Relationship between Ti and N content) As mentioned above, Ti can fix free N and precipitate TiN in austenite. Excessive precipitation of TiN reduces the deformability of the steel, so the Ti and N contents are controlled to satisfy the following formula (1). [Ti] / [N]≦4.0 (1) Here, [Ti] and [N] represent the Ti and N contents, respectively, expressed in mass %.

[0026] (remainder) The basic components are as described above, and in one preferred embodiment, the balance is iron and unavoidable impurities. Examples of unavoidable impurities include elements that are introduced due to the circumstances of raw materials, materials, manufacturing facilities, etc. It should be noted that, for example, P and S are elements whose content is usually the lower the better and therefore are unavoidable impurities, but whose composition ranges are separately defined as above. Therefore, in this specification, when referring to "unavoidable impurities" that make up the balance, this concept excludes elements whose composition ranges are separately defined.

[0027] <2. Mechanical properties> The steel material for torsion bars according to the embodiment of the present invention has the following mechanical properties.

[0028] (Difference in hardness before and after aging ΔHV) In the torsion bar steel material of this embodiment, the hardness difference ΔHV defined by the following formula (3) satisfies formula (2). ΔHV<2.0HV (2) ΔHV=HV2-HV1 (3) Here, HV1 and HV2 are the Vickers hardnesses of the steel material for the torsion bar before and after aging treatment, respectively.

[0029] According to new findings by the present inventors, the difference in hardness ΔHV between before and after aging treatment correlates with low-temperature ductility. Figure 1 is a graph in which the reduction of area of ​​a steel material for torsion bars measured at liquid nitrogen temperature is plotted against ΔHV. As can be seen from Figure 1, by controlling ΔHV to less than 2.0 HV (i.e., satisfying formula (2)), excellent low-temperature ductility can be maintained even after age hardening.

[0030] In this embodiment, "age hardening" refers to age hardening after aging at room temperature for one year. When actually measuring HV2, an accelerated test (e.g., aging treatment at 75°C for 24 hours) is performed to achieve age hardening equivalent to that after aging at room temperature for one year. The steel material for torsion bars according to the embodiment of the present invention satisfies formula (2), and therefore can have excellent low-temperature ductility even after aging at room temperature for one year.

[0031] (Aperture (RA)) The reduction of area (RA) is an index that indicates the ductility of a material. The steel material for torsion bars of this embodiment preferably has a reduction of area of ​​more than 50% obtained from a low-temperature tensile test at liquid nitrogen temperature (-196°C), and has excellent low-temperature ductility. By controlling the hardness difference ΔHV to less than 2HV, the steel material for torsion bars after age hardening can have a reduction of area at low temperatures exceeding 50%, and can achieve excellent low-temperature ductility.

[0032] (Tensile strength (TS)) In order to obtain the strength required for a seat belt torsion bar, it is preferable that the tensile strength (TS) of the rolled material is 350 MPa or more. A tensile strength of 350 MPa or more can be achieved by satisfying the following chemical composition of the steel material: C: 0.010 to 0.030 mass %, Nb: 0.020 to 0.030 mass %, and Ti: 0.005 to 0.025 mass %.

[0033] <3. Manufacturing method> Next, a method for manufacturing a torsion bar steel material according to an embodiment of the present invention will be described.

[0034] A steel slab satisfying the above chemical composition is heated to a temperature range of 960 to 1050°C, rolled to a predetermined wire diameter within that temperature range, and finish-rolled at 920 to 1030°C. Next, the slab is rapidly cooled, mainly by adjusting the water flow, at a cooling rate of 600 to 6000°C / min until the adjusted cooling start temperature reaches 870 to 950°C, and then cooled at an average cooling rate of 10°C / sec or less to an adjusted cooling end temperature of 250 to 500°C.

[0035] Each step will be described in detail below.

[0036] (Steel billet heating temperature: 960-1050℃) This heating temperature is set to dissolve as much of the TiC and carbonitrides such as Nb(C,N) precipitated in the steel as possible, thereby improving strength through precipitation strengthening. Here, the "heating temperature of the steel billet" is measured using a radiation thermometer and strictly means the "surface temperature of the steel billet." Heating above 1050°C results in coarsening of the ferrite grain size, making it impossible to obtain the desired deformability. On the other hand, heating temperatures below 960°C do not dissolve the precipitates, and the desired strength cannot be obtained even if the subsequent heat treatment is controlled.

[0037] (Rolling temperature: 900~1150℃) This temperature is set to obtain the desired strength by precipitating Ti and Nb in the steel as carbonitrides such as TiC / Nb(C,N) during the series of rolling processes from rough rolling to intermediate rolling to finish rolling. Here, the "rolling temperature" is measured using a radiation thermometer and strictly refers to the "surface temperature of the steel billet." Rolling at temperatures above 1150°C fails to achieve the pinning effect of carbide precipitation, resulting in coarsening of the ferrite grain size after rolling and reduced deformability. On the other hand, rolling at temperatures below 900°C results in rolling in the ferrite transformation region, leading to cracks at the interface between ferrite and austenite during rolling.

[0038] More specifically, by controlling the temperatures of the rough rolling to 900 to 1150°C, the intermediate rolling to 925 to 1150°C, and the finish rolling to 920 to 1030°C in the series of rolling steps, respectively, it becomes possible to more efficiently exert the effects of the present invention.

[0039] Here, in the present invention, "rough rolling" refers to a process in which 7 to 10 rolling mills are used to roll 115 to 200 mm square billets at an area reduction rate of 75 to 95% to form square billets. "Intermediate rolling" refers to a process in which, following the rough rolling, 4 to 12 rolling mills are used to roll at an area reduction rate of 70 to 98% to form round billets. "Finish rolling" refers to a process in which, after the "intermediate rolling", the rolling temperature is adjusted by water cooling, and then 1 to 2 block mills are used to roll at an area reduction rate of 5 to 95%.

[0040] (Adjusted cooling start temperature: 870~950℃) After the finish rolling, the billet is rapidly cooled, primarily using water, at an average cooling rate of 600 to 6,000°C / min until the outermost surface temperature reaches a minimum of 500 to 900°C, and then wound onto a cooling belt (cooling conveyor). During this process, the billet recovers its temperature due to the heat (recuperation) retained in the billet. In this specification, this recovery temperature is referred to as the "adjusted cooling start temperature" (synonymous with the coiling temperature) and is defined as 870 to 950°C. Temperatures higher than 950°C result in thicker scale after cooling, which can peel off during cooling and form secondary scale. This can lead to problems in the subsequent descaling process. Furthermore, the resulting wire rod loses stiffness, making it difficult to wind into the desired ring shape. On the other hand, temperatures lower than 870°C result in abnormal grain growth of ferrite grains, which can lead to wire breakage during drawing.

[0041] (Average cooling rate to adjusted cooling end temperature (250-500°C): 10°C / sec or less) This defines the average cooling rate when cooling from the adjusted cooling start temperature (870 to 950°C) to a temperature of 250 to 500°C (adjusted cooling end temperature). The average cooling rate is set to ensure the desired strength, and by controlling it within the above range, carbonitrides of Ti and Nb, which contribute to improving strength, can be efficiently precipitated. The average cooling rate is preferably 3°C / sec or more and 8°C / sec or less, and more preferably 4°C / sec or more and 6°C / sec or less.

[0042] (cold working) After cooling, the steel sheet is subjected to cold working, which in this specification includes any of wire drawing, drawing, extrusion, and straightening. The difference in Vickers hardness ΔHV before and after aging can be controlled by the method and degree of cold working (working rate). For example, a desired ΔHV can be achieved by setting the cold working rate to 5.0% or less.

[0043] In this specification, the "cold working rate" in wire drawing is determined as a percentage (%) obtained by dividing the difference (reduction) in the cross-sectional area of ​​a steel material before and after cold working by the cross-sectional area of ​​the steel material before cold working (area reduction rate).The "cold working rate" in straightening is determined as a percentage (%) obtained by dividing the difference in length of a steel material before and after cold working by the length of the steel material before cold working. If the processing rate within the steel material is not constant (for example, in the case of bending straightening), the measurement is performed at the part where the processing rate is maximum (in the case of bending straightening, on the inner peripheral surface side).

[0044] When cold working is performed multiple times (for example, when wire drawing and straightening are performed), the cold working rate for each cold working step (referred to as the "working rate" for each cold working step) is determined, and the sum of these working rates (total working rate) is treated as the "cold working rate."

[0045] After removing scale from the steel material by immersing it in a bath of acid (hydrochloric acid, sulfuric acid, etc.) or by mechanically distorting it, the steel material may be subjected to wiredrawing pretreatment such as coating with zinc phosphate, calcium phosphate, or lime, and then wiredrawing and cold rolling may be carried out using metal soap or the like as a lubricant.

[0046] A person skilled in the art who has come into contact with the manufacturing method of the torsion bar steel material according to the embodiment of the present invention described above may be able to obtain the torsion bar steel material according to the present invention by trial and error using a manufacturing method different from the above-described manufacturing method. [Example]

[0047] (1) Preparation of test steel A 2-ton steel ingot having the chemical composition shown in Table 1 was melted in a converter. The steel ingot was then processed into a billet, which was then heated, hot-rolled, and cooled under the conditions shown in Table 2 to obtain rolled materials with a diameter of 9.7 mm (samples Nos. 1 to 6). The rolled material was machined to prepare a tensile test piece (JIS2241, No. 14A). The tensile strength (TS) was measured in accordance with JIS Z 2241:2011 and found to be 395 MPa.

[0048] Since coil-shaped rolled material was used, straightening was performed by passing it through guide rollers. In order to prevent cracks from occurring during cold working, it is common practice to perform annealing before wire drawing to soften the steel material and then perform cold working. Therefore, in this example, some steel materials were also annealed to confirm the effect on low-temperature ductility. In Table 2, wire (-) indicates that the treatment was not performed. As a result, within the scope of this example, the effect of annealing on ductility was small.

[0049] Below is a summary of the processes carried out for each sample, from rolling to evaluation (various measurements).

[0050] Samples No. 1 and 3: The above rolled material was straightened (bending straightened) and annealed at 500°C or 700°C for 90 minutes, and the steel material was evaluated (rolling → bending straightening → annealing → evaluation). Sample No. 2: The above rolled material was subjected to straightening (bending straightening) and the resulting steel material was evaluated without annealing (rolling → bending straightening → evaluation). Sample No. 4: The above rolled material was straightened (bending straightening), annealed at 700°C for 90 minutes, then pickled and coated, and then cold drawn. The further straightened steel material was used for evaluation (rolling → bending straightening → pickling → coating → wiredrawing → evaluation). Samples No. 5 and 6: The above rolled material was straightened (bending straightening), annealed at 700°C for 90 minutes, then pickled and coated, followed by cold wire drawing. The further straightened steel material was used for evaluation (rolling → bending straightening → annealing → pickling → coating → wire drawing → evaluation).

[0051] Furthermore, each sample was subjected to aging treatment, and evaluation was also carried out using the steel material after aging treatment. In order to reproduce a state where the specimen has been fully aged, an aging treatment of 75°C for 24 hours was carried out, which is considered to be equivalent to aging for one year at room temperature, using the Larson-Miller parameter (LMP = T × (20 + log t)) (Koichi Maruyama: Iron and Steel, 105 (2019), 767.). The aging conditions are not limited to 75°C x 24 hours as long as the LMP is approximately the same.

[0052] (2) Measurement of cold working ratio The cold working ratio was determined by the following procedure. In the examples, bending straightening and wire drawing were performed as cold working, so the "working ratio by bending straightening R1" (formula (4) described later) and the "working ratio by wire drawing R2" (formula (5) described later) were calculated. Then, as shown in formula (6) described later, the working ratios R1 and R2 were summed to calculate the cold working ratio R, which is shown in Table 3.

[0053] Regarding equation (4), because the processing rate in the steel material is not uniform during bending straightening, the length before straightening (L0) and the length after straightening (equivalent to L0 + ΔL) were measured on the inner peripheral side (the side subjected to tensile stress during bending straightening) where the processing rate is greatest. Regarding equation (5), since the working ratio within the cross section can be considered constant during wire drawing, the cross-sectional area of ​​the steel material was measured before and after wire drawing to calculate the working ratio.

[0054] R1(%)=100×ΔL / L0(4) Here, L0 is the length (mm) of the sample before straightening, and ΔL is the change in length (mm) of the sample due to straightening. R2(%)=100×ΔA / A0(5) Here, A0 is the cross-sectional area of ​​the sample before wire drawing (mm 2 ), ΔA is the change in cross-sectional area due to wire drawing (mm 2 ) R(%)=R1+R2 (6)

[0055] (3) Vickers hardness measurement The Vickers hardness of the steel (round bar) samples Nos. 1 to 6 was measured at three points on the cross section: two at the D / 4 section (D is the diameter of the steel) and one at the D / 2 section, under a load of 10 kgf, and the average value was calculated. The Vickers hardness was measured for each of the steel before and after aging treatment. The measurement results (average values) before and after aging treatment are shown in Table 3, labeled HV1 and HV2, respectively.

[0056] (4) Low-temperature tensile test Steel samples (round bars) No. 1 to No. 6 were subjected to aging treatment, and then tensile test pieces (JIS2241, No. 14A) were prepared. Tensile tests were then conducted in liquid nitrogen (-196°C) at a test speed of 0.25 mm / min, and the reduction of area (RA) was measured in accordance with JIS Z 2241:2011. The measurement results are shown in Table 3.

[0057] [Table 1]

[0058] [Table 2]

[0059] [Table 3]

[0060] Samples Nos. 1 to 3 are examples that satisfy the requirements of this embodiment, and the tensile strength TS of the rolled material exceeded 350 MPa, providing sufficient tensile strength. The cold working ratio R of the steel material during production was 5.0% or less. Furthermore, since ΔHV was less than 2.0 HV, the reduction of area RA of the steel material after aging treatment measured in a low-temperature environment exceeded 50%. Therefore, it was found that Samples Nos. 1 to 3 had excellent low-temperature ductility even after age hardening.

[0061] Samples Nos. 4 to 6 were comparative examples that did not satisfy the requirements of this embodiment. The cold working ratio R of the steel material at the time of production exceeded 5.0%, and the tensile strength TS of the rolled material exceeded 350 MPa, so that the steel material had sufficient tensile strength. However, since ΔHV was 2.0 HV or more, the reduction of area RA of the steel material after aging treatment measured in a low-temperature environment was 50% or less.

Claims

1. C: 0.015 to 0.030% by mass Si: 0.10 to 0.40% by mass Mn: 0.20 to 0.50% by mass Al: 0.010 to 0.060% by mass Nb: 0.020 to 0.030% by mass Ti: 0.005 to 0.025% by mass P: 0.005% by mass or less (including 0% by mass) S: 0.020% by mass or less (including 0% by mass) N: 0.0037% by mass or less (including 0% by mass) balance: the balance being Fe and unavoidable impurities; A steel material for a seatbelt torsion bar that satisfies the following formulas (1) and (2). [Ti] / [N]≦2.43 (1) Here, [Ti] and [N] represent the contents of Ti and N, respectively, expressed in mass %. ΔHV<2.0HV (2) Here, ΔHV is defined by the following equation (3). ΔHV=HV2-HV1 (3) Here, HV1 is the Vickers hardness of the steel material for the seatbelt torsion bar, and HV2 is the Vickers hardness of the steel material for the seatbelt torsion bar after aging treatment at 75°C for 24 hours.

2. The steel material for a seat belt torsion bar according to claim 1, wherein the reduction of area at -196°C is more than 50%.

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