JPH04143225A - Manufacture of long size steel with different strength in longitudinal direction - Google Patents

Abstract

PURPOSE:To manufacture a long size steel in which the ratio of the length in the high strength part and the low strength part is optional, in the longitudinal direction of a long size steel, by subjecting the high strength part to QT treatment and softening the low strength part other than the above without executing hardening. CONSTITUTION:At the time of manufacturing a long size steel, particularly a door impact beam for reinforcing the door of an automobile, a treating apparatus provided with quench coil 10 as primary heating means, a water-cooled ring 12 as cooling means and a temper coil 14 as secondary heating means is used. For example, while long size tube stock S is moved in the right direction, the output Q in the coil 10 is held to a certain one, and heating for hardening is executed. At this time, the amt. Q of water to be jetted in the ring 12 is held to prescribed value at which hardening is executable to the high temp. part B; when it comes to the turn of the low strength part A, it is regulated to zero, and annealing (softening treatment) is executed; when it comes to the turn of the high strength part once more, it is returned to the value at which hardening is executable; and hereafter, similar operation is executed. Moreover, the whole length in which the output T in the coil 14 has held to a certain one and subjected to hardening and annealing is heated to a tempering temp., and the high strength part B is tempered.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for producing a long steel material having different strengths in the longitudinal direction, and a method for producing a long steel material having different strengths in the longitudinal direction, which is particularly suitable for manufacturing door impact beams used for reinforcing automobile doors. Regarding.

[Conventional technology]

2. Description of the Related Art In order to improve the strength of automobile doors, a door impact beam is installed inside the door. This door impact beam is usually made of around 11 steel tubes, although it varies depending on the size of the car. However, the above-mentioned door impact beam requires great strength in order to withstand strong impacts, but both ends of the pipe are swaged to secure it to the door frame, etc.
q), appropriate softness is required. Door impact beams that require such performance have conventionally been manufactured by the methods described in (1) and (2) below. (1) After creating a short tube by cutting a long original tube into a predetermined length, the short tube is quenched by high-frequency heating, etc., except for both ends.
(tempering) processing (hereinafter also referred to as QT processing)
After that, swage processing is performed on both tube ends, which are moderately soft because QT treatment was not performed. (2) After applying QT treatment to the entire length of a long original tube, the original tube is cut to a predetermined length to create a short tube, and then both ends of the short tube are softened. After the softening treatment, the ends of both tubes are swaged.

[Problem to be solved by the invention]

However, in the method (1) above, when performing QT treatment on the short pipe after cutting, in order to prevent both ends of the pipe from being hardened, the QT treatment must be performed excluding both ends of the pipe, and the
For T treatment, for example, an induction heating coil is placed around a fixed short tube, and the coil is moved over a predetermined length range to perform quenching heating. There is a problem that production efficiency is low because only a small amount of water can be processed. In addition, in the method (2) above, the long original pipe is cut after being QT treated, but the QT treated steel pipe has a TS of 150 to 2.
The problem is that it is difficult to cut because it has a hardness of 00Kgf/ll112 class, and that the ends of the tube must be softened after cutting, so each short tube requires additional heat treatment. There is. In addition to methods (1) and (2) above, there is a method for manufacturing a steel pipe whose both ends are soft enough to be swaged. It is conceivable to manufacture a short pipe by manufacturing a steel pipe and cutting the steel pipe at its soft part. According to this method,
It is also possible to easily mass-produce short tubes that can be applied to door impact beams, etc., and can be swaged at both tube ends. However, although steel pipes having different thicknesses in the longitudinal direction have been manufactured, the production of long steel materials such as steel pipes having different strengths in the longitudinal direction has not been realized. The present invention has been made to solve the above-mentioned conventional problems, and can be applied, for example, to the manufacture of short tubes suitable for door impact beams whose ends are soft enough to be swaged. An object of the present invention is to provide a method for manufacturing a long steel material having different strengths in the longitudinal direction, which can easily and reliably produce long steel materials having different strengths in the longitudinal direction in a short process.

[Means for Achieving the Problem 1] The first invention provides a length treatment apparatus that uses a processing apparatus that includes a 17U heating means and a second heating means that heat a long steel material, and a cooling means that cools the long steel material with water. A method for manufacturing a long steel material having different strengths in the longitudinal direction, the long steel material being heated to a temperature equal to or higher than the transformation temperature Ac3 by a first heating means, and then the long steel material in a range where high strength is required in the longitudinal direction. The part is quenched by injecting a predetermined amount of cooling water from a water cooling means, and the long steel parts outside the above range are softened by cutting off the cooling water or injecting less water than during quenching. The above object has been achieved by heating at least the quenched long steel material portion to a temperature equal to or lower than the transformation temperature Ac1 using the second heating means to temper the steel material. A second invention also provides a method for manufacturing a long steel material having different strengths in the longitudinal direction using the processing apparatus, in which the first heating means heats the long steel material to a temperature equal to or higher than the transformation temperature Ac3, and then the cooling means The long steel material after heating is water-cooled and quenched, and then, by the second heating means, the long steel material portion in the range where high strength is required in the length direction is heated to a temperature equal to or lower than the transformation temperature Ac1. The above-mentioned problem is similarly achieved by tempering the long steel material and heating the portion of the long steel material outside the above range to a temperature exceeding the transformation temperature Ac1 to perform a softening treatment. A third aspect of the present invention further provides a method for manufacturing a long steel material having different strengths in the longitudinal direction using the processing apparatus, wherein the first heating means only applies to a portion of the long steel material in a range where high strength is required in the longitudinal direction. After heating to a temperature equal to or higher than the transformation temperature Ac3, a cooling means is used to water-cool and harden at least the heated long steel portion, and then a second heating means is used to transform at least the hardened long steel portion. The above-mentioned problem is similarly achieved by heating the part to a temperature of Ac1 or lower and tempering the part. [Operations and Effects] In the first invention, the long steel material is subjected to QT treatment in the range where high strength is required in the longitudinal direction (hereinafter also referred to as the high strength part), and in the long steel material outside the range The long steel parts that require softness (hereinafter also referred to as low-strength parts) are softened without being quenched, so that the strength can be increased in the length direction according to the length ratio of the high-strength parts and low-strength parts. It is possible to easily produce long steel materials with different strength, and the strength (softness) of the low-strength portion can be adjusted by adjusting the amount of water jetted during the softening treatment of the low-strength portion and changing the cooling rate. You can also do it. In addition, in the second invention, after hardening the long steel material, the high-strength parts are tempered, and the low-strength parts are softened by heating above the upper limit temperature of tempering. It is possible to easily produce a long bait with different strengths in different directions, and by adjusting the heating temperature during the softening treatment of the low-strength parts, the strength of the parts can also be adjusted. Furthermore, in the third invention, only the high-strength portion of the long steel material is heated above the quenching temperature and quenched by water cooling, and the quenched portion is tempered. 6 In the present invention, it is possible to easily manufacture long steel materials with different strengths in the longitudinal direction at a ratio of
The strength of the low strength part is the same as the original material, but with an appropriate M
The strength can also be adjusted by performing heat treatment at ambient temperatures. According to any of the first to third inventions described above, a long steel pipe with different strengths in the longitudinal direction is formed by repeatedly forming a low-strength part of a desired length with a high-strength part of a desired length in between. Can be easily manufactured. By cutting this long steel pipe at the low-strength portion, it is possible to easily produce a short steel pipe having a pipe end portion that is low in strength (soft) and therefore has high workability. Therefore, for example, it is possible to easily manufacture a door impact beam that requires swage workability at both tube ends.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. Fig. 1 is a schematic configuration diagram showing a processing apparatus applied to a method for manufacturing long steel materials having different strengths in the longitudinal direction according to a first embodiment of the first invention, together with a processing object, and Fig. 2 explains the operation. FIG. The processing device includes a quench coil (first heating means) 10
, a water cooling ring (cooling means) 12, and a temper coil (
(second heating means) 14, all of which are arranged around the long original tube at a predetermined position. Both the quench coil 10 and the temper coil 14 are high-frequency heating coils. In this embodiment, while the long original pipe (long steel material) S is moved rightward in the figure by the conveyor roll 16, the processing device performs the processing described in detail below, thereby moving the long original pipe (long steel material) in the length direction. Long steel pipes with different strengths can be manufactured continuously. FIG. 2 shows a case in which a long original tube S shown in the lower part of the figure is subjected to a softening treatment on a low-strength portion A indicated by diagonal lines, and a QT treatment on the other high-strength portion B. tube S
The output of the quench coil 10 for each part (hereinafter,
(also referred to as Q output), the amount of water injected from the water cooling ring 12 (hereinafter referred to as
Q) and the output of the tempering coil 14 (hereinafter also referred to as T output) are shown above corresponding to each part of the long original tube S, respectively. When manufacturing long steel pipes with varying strengths in the longitudinal direction at the ratio shown in Fig. 2 above using the processing equipment shown in Fig. 1 above, the Q output is kept constant while moving the long original pipe S in the direction of the arrow. Quenching heating is performed by keeping the on state of Q, at which time the water amount is
For high-strength part B, keep it at a predetermined value that can be quenched), and when it reaches low-strength part A, turn it to zero (off) and perform annealing (softening treatment), and when it reaches the high-strength part again, it can be quenched. Return to the value and perform the same operation from now on. In addition, the T output is maintained constant, and the entire length of the long tube that has been quenched and annealed is heated to the tempering temperature, and the high-strength portion B is heated to the tempering temperature.
Perform tempering on By performing the above series of operations, it is possible to continuously manufacture a long steel pipe consisting of a high-strength portion B and a low-strength portion A of a predetermined length and having different strengths in the length direction. Here, the Q output of the quench coil 10 may be of a magnitude that can heat the long original tube to a transformation temperature Ac3 or higher. Further, the amount of Q water from the water cooling ring 12 is sufficient as long as it can harden the raw pipe portion heated to the Ac3 or above, and the amount of Q water for the low strength portion A is as shown in FIG. 2 above. Not limited to the case where the injection of cooling water from the water cooling ring 12 is cut off to zero, it is sufficient that the amount of water is less than the amount of water used for quenching (for example, it may be about 50%).
By performing the softening treatment using a smaller amount of water than during quenching, it is possible to adjust the strength (softness) of the low-strength portion A. Further, the T output of the tempering coil 14 may be any value that can heat the hardened high-strength portion B to a temperature at which it can be tempered, and the temperature may be a transformation temperature Ac3 or higher and 100° C. or higher. Next, a specific example carried out to clarify the effects of this embodiment will be described. Using the processing apparatus shown in FIG. 1, 31°8 (φ)
The above-mentioned operation was performed on the long original tube of 5AE4130 of Xl, 6(t), and the low-strength part A (shaded part) was softened at the length ratio shown in Figure 3, and the high-strength part was QT-treated. B
(other than the shaded area), a long steel pipe with different strengths in the longitudinal direction was manufactured. At that time, the long raw tube S is heated to 900°C with the quench coil 10, and the water cooling coil 1 during the softening process is heated to 900°C.
The amount of water from No. 2 was set to zero, and the tempering heating temperature by the tempering coil 14 was set to 250°C. For the long steel pipe manufactured under the above conditions, the strength measurements of the high-strength part B after tempering and the low-strength part A after softening treatment are shown together with the measurement results of the G4 pipe as-quenched (not tempered). The strength measurement results shown in Table 1 are Vickers strengths measured at different distances from the outer surface of the tube. From Table 1 above, it can be seen that high-strength portion B has a high strength close to that of as-quenched steel pipe, while low-strength portion A has approximately half the strength of high-strength portion B. I understand. As described above, according to this embodiment, a long steel pipe having a large partial strength difference in the longitudinal direction can be easily manufactured. Furthermore, the long steel pipe can be easily cut at the low-strength portion A, and by cutting at the center, a length of 1000111 with low-strength portions of 100111 at both pipe ends can be obtained.
short tubes can be easily manufactured. This short tube can be suitably used as a door impact beam because both ends of the tube can be easily swaged. FIG. 4 is an explanatory view corresponding to FIG. 2, showing a method for manufacturing a long steel material having different strengths in the longitudinal direction according to a second embodiment of the present invention. In this second embodiment, the same processing apparatus as in the first embodiment was used, and the softening process was performed by changing the output of the tempering coil 14. That is, in this embodiment, after maintaining the amount of Q water from the water cooling ring 12 at the quenching amount and quenching the low-strength portion A, when the low-strength portion A passes through the tempering coil 14, the coil 14 to heat the low-strength portion A to a temperature at which it can be softened. Other than that, substantially the first
The operation is carried out under the same conditions as in the example. Now, if the tempering temperature for the high strength part B is T1,
Heating temperature T during softening treatment by the temper coil 14
2 needs to be higher than T1. That is, T2=TI+α, and this α can be, for example, 50'C. In this embodiment, the strength of the low-strength portion A can be adjusted by changing the softening temperature T2, and the temperature at which the temperature T2 is applied is the quenching heating temperature (
Ac3 or higher) can be mentioned. When this example was actually applied to the same long raw tube as in the first example, it was found that it was possible to easily produce a long steel tube with different strengths in the longitudinal direction, which is suitable for manufacturing door impact beams. was able to manufacture it. FIG. 5 is an explanatory view corresponding to FIG. 2, showing a method for manufacturing a long steel material having different strengths in the longitudinal direction according to a third embodiment of the present invention. This third embodiment also uses the same processing apparatus as the first embodiment, and performs the softening process by varying the output of the quench coil 10. That is, in this embodiment, the quench coil 10 is activated to heat the high-strength portion B of the long original tube, and the coil 10 is stopped for the low-strength portion A. While heating the parts to the quenching temperature in this way, a predetermined amount of cooling water is injected over the entire length of the water-cooled ring 12 to quench the quench-heated part (high-strength part B), and then the temper coil By operating 14 at a predetermined output, the hardened portion is tempered. According to this example, the high-strength portion B can be subjected to the QT treatment in the same way as in each of the above-mentioned examples, so that it can be given a large strength, and the low-strength portion A is not heated by quenching. Since it is a practical part, it can have the same strength as the original tube. As a result, as in each of the embodiments described above, it is possible to easily manufacture a long steel pipe having different strengths in the longitudinal direction, which is suitable for manufacturing a door impact beam. In this embodiment, the operation of the water cooling ring 12 and the tempering coil 14 may not be performed over the entire length of the long steel pipe as described above, but may be performed only on the high-strength portion B that has been quenched and heated. Although the present embodiment has been specifically described above, the present invention is not limited to what has been shown in the above embodiment, and various changes can be made without departing from the gist thereof. For example, the processing device applicable to the present invention may be any device as long as it has substantially the same functions as those shown in the embodiments. Further, the present invention is not limited to being applied to the manufacture of door impact beams, and it goes without saying that it can be applied to any long steel material such as bars, not just steel pipes. Further, although not shown in the embodiments, it goes without saying that the first, second, and third inventions are not limited to being implemented individually, but can also be implemented in arbitrary combinations.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a processing device applied to the first embodiment together with its operation. FIG. 2 is a schematic explanatory diagram for explaining the operation of the above embodiment. A perspective view showing a long steel pipe to which the embodiment is specifically applied, FIG. 4 is a schematic explanatory diagram for explaining the operation of the second embodiment, and FIG. 5 is an illustration for explaining the operation of the third embodiment. FIG. 10... Quench coil, 12... Water cooling ring, 14... Temper coil, A... Low strength part, B... High strength part.

Claims (3)

[Claims] (1) A method for manufacturing a long steel material having different strengths in the longitudinal direction using a processing device equipped with a first heating means and a second heating means for heating the long steel material, and a cooling means for cooling the long steel material with water. The long steel material is heated to a transformation temperature Ac by the first heating means.
After heating to a temperature of 3 or more, a predetermined amount of cooling water is injected from the water cooling means to the long steel part in the range where high strength is required in the length direction to perform quenching, and The cooling water is cut off or injected in a smaller amount than during quenching to soften the long steel part, and then the second heating means heats at least the quenched long steel part to a temperature below the transformation temperature Ac1. A method for producing a long steel material having different strengths in the longitudinal direction, the method comprising heating and tempering the material. (2) A method for manufacturing a long steel material having different strengths in the longitudinal direction using a processing device equipped with a first heating means and a second heating means for heating the long steel material, and a cooling means for cooling the long steel material with water. The long steel material is heated to a transformation temperature A by the first heating means.
After heating to a temperature of c3 or higher, the heated long steel material is water-cooled and quenched by a cooling means, and then, by a second heating means, the long steel material is heated in a range where high strength is required in the longitudinal direction. In the length direction, the steel part is heated to a temperature below the transformation temperature Ac1 to perform tempering, and the long steel part outside the above range is heated to a temperature exceeding the transformation temperature Ac1 to perform a softening treatment. A method for manufacturing long steel materials with different strengths. (3) A method for manufacturing a long steel material having different strengths in the longitudinal direction using a processing device equipped with a first heating means and a second heating means for heating the long steel material, and a cooling means for cooling the long steel material with water. The first heating means heats only a portion of the long steel material in a range where high strength is required in the longitudinal direction to a transformation temperature Ac.
After heating to a temperature of 3 or more, at least the heated long steel portion is water-cooled and quenched by a cooling means, and then, at least the hardened long steel portion is heated to a transformation temperature Ac1 or lower by a second heating means. 1. A method for producing a long steel material having different strengths in the longitudinal direction, the method comprising heating the portion to a temperature of 100 to temper the portion.