JP2011194470A - Squeezing-contraction processing method of high-strength electroseamed steel pipe, and processed component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a squeezing-contraction processing method preventing occurrence of any crack of a weld seam part in the squeezing-contraction processing for a high-strength electroseamed steel pipe of TS980 MPa or above.SOLUTION: In the squeezing-contraction processing method for squeezing a pipe end in a tapered shape, or contracting the partial length or the entire length of the pipe by pressing a stock pipe consisting of an electroseamed steel pipe 1 into a hole die 2, the electroseamed steel pipe with its weld seam part being heated to 450-550°C immediately after the electroseam welding is used as the stock tube.

Description

  The present invention relates to a method for reducing the diameter of a mouth-stretched high-strength ERW steel pipe and a processed part. This processed part is preferably applied to automobile parts such as a front arm and a cross member.

  For example, as described in Non-Patent Document 1, in pipe end processing of pipe materials, mouth drawing and widening are processing techniques that are frequently used. Among these, there are two types of mouth drawing methods: rotary swaging and parallel swaging that pushes a blank tube into a hole die. These squeezing processes are characterized in that since the stress field at the time of processing is mainly compressive stress, there are few problems of cracking and a large diameter reduction ratio can be easily obtained. In the parallel swaging method, it is necessary to prevent seizure to the hole die by using a lubricant. However, compared to the rotary swaging method, the equipment is inexpensive and noise during processing is often used.

  Further, in the parallel swaging process, it is possible to process the pipe material whose diameter is reduced by increasing the pushing length of the pipe material or pushing the entire length of the pipe material into the hole die.

Toyota, Suzuki, Sato: JFE Technical Report No.4, May 2004, p.28-32

  The above-mentioned process of pushing the pipe end of the raw pipe into the hole die to reduce the diameter into a taper shape, or the process of pressing the partial length or the entire length of the raw pipe into the hole die to reduce the diameter (collectively referred to as aperture reduction) The diameter machining) is usually performed for ERW steel pipes of TS440MPa class or less. On the other hand, Non-Patent Document 1 discloses an example of performing the above-mentioned diameter reduction processing on a TS780MPa class or less steel pipe, but there is no example of performing it on a high-strength ERW steel pipe of TS980MPa class or more. .

  Using a TS980MPa class or higher ERW steel pipe (as the ERW weld), when the diameter reduction ratio exceeds a certain value, the weld seam part at the end of the pipe ends at the end of the diameter reduction. In some cases, the weld seam part full-length crack may be generated starting from the crack. It is assumed that the mechanism of cracking is either delayed fracture due to hydrogen absorption, or cracking due to hydrogen absorption and martensitic transformation of residual γ. In diameter machining, welded seam cracks often occur in processed products for high-strength ERW steel pipes of TS980MPa class or higher, so it cannot be said that sufficient contributions can be made to increase the strength and thickness of automobile parts. There was a problem.

The present invention has been made to solve the above problems, and the gist thereof is as follows.
(1) In a diameter reduction processing method in which a pipe end made of an ERW steel pipe is pushed into a hole die to squeeze the end of the pipe into a taper shape or to reduce the partial length or total length of the pipe. A diameter reducing diameter processing method characterized by using an ERW steel pipe whose weld seam is heated to 450 to 550 ° C. immediately after ERW welding.
(2) The aperture drawing diameter reducing method according to (1), wherein a high-strength ERW steel pipe of TS980 MPa class or higher is used as the element pipe.
(3) The aperture reduction / reduction processing method according to (1) or (2), wherein distortion removal annealing is performed on the entire pipe body of the pipe after the aperture reduction or diameter reduction.
(4) The electric resistance welded steel pipe has a composition of C: 0.05 to 0.20 mass%, Si: 0.5 to 2.0 mass%, Mn: 1.0 to 3.0 mass%, P: 0.1% by mass or less, S: 0.01% by mass or less, remaining Fe and inevitable impurities, and the structure is a two-phase structure of a ferrite phase and a martensite phase, or a residual austenite phase in the two phases. The diameter-reducing method according to any one of (1) to (3), which is an added three-phase structure.
(5) A processed part processed by the mouth-drawing diameter reducing method described in any one of (1) to (4).

  According to the present invention, it is possible to process high-strength steel pipes of TS980 MPa class or higher by aperture drawing diameter reduction processing, which can greatly contribute to increasing the strength and thinning of automobile parts.

Schematic diagram showing an example of diameter reduction processing method

In the present invention, when subjecting an element pipe made of an electric resistance steel pipe to a diameter reduction process, an electric resistance steel pipe whose weld seam portion is heated to 450 to 550 ° C. immediately after the electric resistance welding is used as the element pipe. This heating is referred to as “seam heating” for convenience.
FIG. 1 is a schematic diagram illustrating an example of full-length diameter reduction processing in the mouth-drawing diameter reduction processing method. (a) In the first step, the tube 1 is pushed from the tube end (tip) on the side pushed first into the hole die 2 to a predetermined length, and then taken out from the hole die 2 once. (b) In the second step, the front and rear ends are replaced, the tube 1 is pushed into the hole die 2 from the unprocessed rear end to the full length, and then removed from the hole die 2. Further, by appropriately changing the indentation length in FIG. 1, it is possible to perform either processing such as aperture restriction at the pipe end or reduction in diameter of the partial length.

  By using the ERW steel pipe subjected to the above seam heating as a raw pipe, cracking of the weld seam crack at the end of the pipe of the diameter-reduced processed product and further cracking of the weld seam full length crack starting from that crack The frequency is greatly reduced. When the seam heating temperature (final temperature) is less than 450 ° C., the effect of reducing the frequency of cracking after processing is poor. On the other hand, when this temperature exceeds 550 ° C., the strength decrease becomes large and the desired strength level cannot be satisfied. In addition, this temperature is preferably 450 to 500 ° C., and it is good to hold this temperature for a time within 5 seconds. As a heating device for performing seam heating immediately after ERW welding in the ERW steel pipe production line, a high-frequency induction heating type seam annealer can be preferably used.

The ERW steel pipe used as the base pipe is preferably a high-strength ERW steel pipe of TS980 MPa class or higher. If this is used, the effect of heating the seam part (the effect of preventing the weld seam cracking at the end of the pipe of the diameter-reduced diameter processed product and also the weld seam full length cracking from that crack) will be lower. This is because it is more prominent than when a high-strength ERW steel pipe is used as the base pipe.
In addition, it is preferable to perform strain relief annealing on the entire pipe body of the pipe that has been closed or reduced in diameter. As a result, delayed fracture and cracks are less likely to occur, and the frequency of occurrence of weld seam cracks at the end of the pipe of the diameter-reduced diameter processed product and further weld seam cracks starting from the cracks can be further reduced. Because. The strain relief annealing is preferably performed under conditions of a temperature: 450 to 550 ° C. and a holding time of about 1 minute.

  The composition of the electric resistance steel pipe used for the base pipe is as follows: C: 0.05 to 0.20 mass%, Si: 0.5 to 2.0 mass%, Mn: 1.0 to 3.0 mass%, P: 0.1% by mass or less, S: 0.01% by mass or less, remaining Fe and inevitable impurities, and the structure is a two-phase structure of a ferrite phase and a martensite phase, or a residual austenite phase in the two phases. The added three-phase structure is preferable. The reason is as follows.

C: 0.05-0.20 mass%
C improves the strength of the electric resistance welded steel pipe and produces a retained austenite phase that provides excellent workability. However, when the content is less than 0.05% by mass, these effects are poor, and when it exceeds 0.20% by mass, the electric stitching is performed. The strength of the steel pipe rises excessively and the workability deteriorates. Therefore, C is set to 0.05 to 0.20 mass%.

Si: 0.5-2.0 mass%
Si improves the balance between tensile strength and elongation of the electric resistance welded steel pipe by solid solution strengthening, promotes the ferrite transformation to generate a ferrite phase, and has the effect of concentrating C in the residual austenite phase. The residual austenite phase is stabilized by C enrichment. However, when Si is less than 0.5% by mass, these effects are poor. On the other hand, if it exceeds 2.0% by mass, scale is likely to occur in the hot rolling process for producing the material steel plate of the ERW steel pipe, and the surface properties of the ERW steel pipe are deteriorated. Therefore, Si is 0.5 to 2.0% by mass.

Mn: 1.0 to 3.0% by mass
Mn improves the hardenability of the ERW steel pipe and stabilizes the retained austenite phase. However, if it is less than 1.0% by mass, these effects are poor, whereas if it exceeds 3.0% by mass, the ERW steel pipe is poor. The strength of the steel increases excessively and the workability deteriorates. Therefore, Mn is set to 1.0 to 3.0% by mass.

P: 0.1% by mass or less P promotes ferrite transformation to generate a ferrite phase. However, if it exceeds 0.1% by mass, ductility of the ERW steel pipe decreases and workability deteriorates. Therefore, P is set to 0.1% by mass or less.
S: 0.01% by mass or less S combines with other elements to generate sulfides. When S exceeds 0.01% by mass, the sulfide aggregates in the structure of the electric resistance welded steel pipe and becomes an inclusion, which causes a decrease in the strength of the electric resistance welded steel pipe. Therefore, S is set to 0.01% by mass or less.

The balance excluding the above components is Fe and inevitable impurities.
The structure of the ERW steel pipe is preferably a two-phase structure of a ferrite phase and a martensite phase in order to ensure high strength and sufficient ductility, and in order to further increase the ductility, A three-phase structure in which a residual austenite phase is added is preferable. The phase ratio of the two-phase to three-phase structure is preferably 20 to 70% by volume of ferrite phase, 30 to 80% by volume of martensite phase, and 0 to 15% by volume of retained austenite phase.

By using the electric resistance welded steel pipe having the above composition and structure as a raw pipe, it is possible to suppress the occurrence of cracks in the squeezed portion with a heat holding time of several seconds.
The processed part processed by the aperture reduction process method of the present invention can be made stronger and thinner than the conventional aperture reduction process part, and can contribute to weight reduction and energy saving of an automobile.

  A TS980MPa class ERW steel pipe (outer diameter 48.6 mm x wall thickness 2.0 mm x length 450 mm) with or without seam heating was used as the base pipe. Table 1 shows the composition and structure of the blank tube, and Table 2 shows the seam heating conditions. With respect to these raw pipes, the diameter reduction processing of 20 pieces per one condition was performed under various conditions shown in Table 2 by a processing method in which the indentation length was appropriately changed in FIG. The hole size of the hole die is the inlet side hole diameter: raw pipe outer diameter + 6.3mm, outlet side hole diameter: raw pipe outer diameter x (reduction ratio (%) / 100), between the inlet side hole and the outlet side hole Tapered hole length: 43.5 mm. In processing, molybdenum disulfide was applied as a lubricant to prevent the pipe from sticking to the hole die. About the pipe | tube of 10 days after finishing a process, the welding seam part crack generation | occurrence | production situation of a pipe end part was investigated, and the crack number in the process number in each condition was calculated | required. The results are shown in Table 2.

  From Table 2, the number of cracks is zero for both the inventive example and the comparative example at a diameter reduction rate of 10%, but the comparative example except No. 11 shows a considerably high number of cracks at a diameter reduction rate of 30%. The invention example shows a significantly lower number of cracks than the comparative example, and in particular, the number of cracks is zero in the example taking account of strain relief annealing. In the comparative example of No. 11, although the number of cracks was zero, the strength was insufficient.

  A TS1180MPa class ERW steel pipe (outer diameter 48.6mm x wall thickness 1.8mm x length 450mm) with or without seam heating was used as the base pipe. Table 3 shows the composition and structure of the raw tube, and Table 4 shows the seam heating conditions. With respect to these raw tubes, the diameter reduction processing of 20 pieces per condition was performed under various conditions shown in Table 4 by a processing method in which the indentation length was appropriately changed in FIG. The hole size of the hole die is the inlet side hole diameter: raw pipe outer diameter + 6.3mm, outlet side hole diameter: raw pipe outer diameter x (reduction ratio (%) / 100), between the inlet side hole and the outlet side hole Tapered hole length: 43.5 mm. In processing, molybdenum disulfide was applied as a lubricant to prevent the pipe from sticking to the hole die. About the pipe | tube of 10 days after finishing a process, the welding seam part crack generation | occurrence | production situation of a pipe end part was investigated, and the crack number in the process number in each condition was calculated | required. The results are shown in Table 4.

  From Table 4, the number of cracks is zero for both the inventive example and the comparative example when the diameter reduction rate is 10%, but the comparative example except No. 11 shows a considerably high number of cracks when the diameter reduction rate is 25%. The invention example shows a significantly lower number of cracks than the comparative example, and in particular, the number of cracks is zero in the example taking account of strain relief annealing. In the comparative example of No. 11, although the number of cracks was zero, the strength was insufficient.

1 pipe (ERW steel pipe)
2 hole die

Claims (5)

  In the diameter reduction processing method for narrowing the pipe end length or total length by pressing the pipe made of ERW steel pipe into the hole die, the pipe end is tapered, A method for reducing the diameter of a mouth-drawing, comprising using an ERW steel pipe whose weld seam is heated to 450 to 550 ° C. immediately after ERW welding.   2. The aperture drawing diameter reducing method according to claim 1, wherein a high-strength ERW steel pipe of TS980 MPa class or higher is used as the raw pipe.   3. The diameter reduction processing method according to claim 1 or 2, wherein strain reduction annealing is performed on the entire pipe body of the pipe after the diameter reduction or diameter reduction.   The ERW steel pipe has a composition of C: 0.05 to 0.20 mass%, Si: 0.5 to 2.0 mass%, Mn: 1.0 to 3.0 mass%, P: 0.1. 3% by mass or less, S: 0.01% by mass or less, remaining Fe and inevitable impurities, and the structure is a two-phase structure of a ferrite phase and a martensite phase, or a residual austenite phase is added to the two phases. It is a phase structure | tissue, The aperture drawing diameter reducing processing method of any one of Claims 1-3 characterized by the above-mentioned. A processed part formed by the mouth-drawing diameter reducing method according to any one of claims 1 to 4.

Images