JP2864026B2 - Manufacturing method of high strength rivets from low carbon steel wire for cold forging. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a high-strength rivet from a low-carbon steel wire for cold forging. More specifically, the present invention relates to a method for reducing the amount of C and suppressing aging. The present invention relates to a method for manufacturing a high-strength rivet, which improves the workability by giving an effect and finally improves the strength as a rivet more than before.

<Conventional Technology> In a frame of a medium-sized or heavy-duty truck or the like, a side member which is an open section member is formed by fastening a plurality of cross members of the same shape by rivets.

The fastening rivets used in this case are C: 0.12-0.
After performing wire drawing (for so-called sizing) to a predetermined diameter on a carbon steel wire rod containing about 17%, it is cut into a predetermined size and formed into a rivet shape by cold forging.
This was subjected to an annealing treatment for removing residual stress, improving toughness, and improving workability, and was further subjected to shot blasting to remove oxide scale to obtain a final product.

However, since the strength of the rivet according to the conventional manufacturing method as described above is lower than that after cold forging due to the annealing treatment, when a truck or the like having a frame fastened by such a rivet travels, When an unexpected shear stress is applied to the rivet due to bending and torsion applied to the rivet, the rivet may be broken.

On the other hand, measures such as increasing the rivet diameter, increasing the number of fastening rivets, and changing the rivet arrangement are usually considered, but all of these involve major design changes and sometimes require capital investment. Had been invited up.

On the other hand, Japanese Patent Application Laid-Open No. 57-206515 discloses that an aluminum-killed low-carbon steel wire containing 0.10 to 0.18% carbon is made from a soft state.
Disclosed is a method for manufacturing a rivet wire, which comprises performing cold drawing at a workability in the range of 18 to 30%, annealing at 600 to 700 ° C, and performing finish drawing at 10% or less. This rivet is used for fastening a laminated body such as an iron core of an electromagnet, and as a wire for that purpose, when used as a rivet, a gap is not formed between the through hole made in the laminated body and the rivet. What is required is a material having a predetermined strength that is soft to be deformable and does not need to have a large cross-sectional area. is there.

<Problems to be Solved by the Invention> However, in the method of manufacturing a rivet wire described in the above-mentioned Japanese Unexamined Patent Publication, since the annealing treatment is performed in the same manner as in the conventional example, the rivet manufactured by such a method is used. When used for the fastening of a frame such as a truck under much more severe load conditions than a laminated body such as a magnet core, an unexpected shear stress is applied to the rivet due to bending and torsion also applied to the frame, The rivet may break.

An object of the present invention is to provide a method of manufacturing a high-strength rivet which has good workability, can improve the strength as a rivet more than before, and can omit the conventional process, except for the disadvantages of the conventional example and the one disclosed in Japanese Patent Application Laid-Open No. Sho. To provide.

<Means for Solving the Problems> According to the present invention to achieve the object of the present invention, C: 0.
A low-carbon steel containing 15% or less, and in a wire rod having N fixed in the component, 200 to 5% during cooling after hot rolling or after cooling.
After aging suppression treatment to fix C by heating to 00 ° C, wire drawing with diameter reduction rate of 15% or more to increase tensile strength is performed, and then rivets are formed by cold forging. And a method for manufacturing a high-strength rivet using a carbon steel wire for cold forging.

Steel types applicable to the production method of the present invention are carbon steel of C: 0.15% or less and carbon steel for machine structural use. Such steel types include, for example, JIS (Japanese Steel Industry Standard) S12C or less, C: 0.15% or less, Si: 0.35% or less, Mn: 0.60% or less, P: 0.040% or less, S: 0.040% In the following, Cu: 0.30% or less, Ni: 0.20% or less, Cr: 0.20% or less, Ni + Cr: 0.35% or less, and a component system that satisfies the following formula in order to fix solute N as a precipitate. , The balance is Fe and carbon steel as impurities.

Further, the aging suppression treatment according to the production method of the present invention fixes N in the above-described component system, and after hot rolling, heating C to 200 to 500 ° C. during or after cooling to precipitate C as carbide and fixation. By doing so, age hardening due to C and N is suppressed.

<Operation> The reasons for determining the composition of the steel and the processing conditions of the wire used in the production method of the present invention will be explained. C is necessary to give the required strength to the steel by solid solution strengthening. For the above purpose, when C: exceeds 0.15%, the deformation resistance increases during the working of steel, so the upper limit of the content of C is set to 0.15%. N is precipitated by the above component balance and suppresses age hardening.

With respect to the other components, the ratio does not increase the age hardening within the range of the JIS, that is, does not deteriorate the workability.

The low-carbon steel wire for cold forging used in the rivet of the present invention is produced by converting a steel having the above components into a converter, ingot, ingot, and after rolling, further aging suppression processing, and It is obtained by performing a wire drawing treatment to increase the tensile strength with a diameter reduction rate of 15% or more.

As a method of the aging suppression treatment, for example, N is fixed as a precipitate by component adjustment, and after the rolling, heating to 200 to 500 ° C. during or after cooling to precipitate C as a carbide, and fixing. Thereby, age hardening can be suppressed.

The reason why the number of drawing times is not particularly limited is that a predetermined tensile strength and a predetermined diameter can be obtained if the total diameter reduction rate is the same even if the number of drawing times is different.

<Examples> The conventional rivet (A to C) wire rods shown in Table 1 were obtained by processing the wire rods having a diameter of 10.5 mm by rolling as shown in each column of Table 1 as they were rolled. The drawn wire is 10.5mm in diameter and 10mm in diameter for sizing.

In contrast, in the rivet (D, E) wire of the present invention,
After the above-mentioned aging suppression treatment is performed on the wire rod having a diameter of 13 mm by rolling, first, the first stage wire drawing process is performed at a diameter reduction rate of 13%, and then the second stage wire drawing process is also performed at a diameter reduction rate of 11.5%. And finished to a diameter of 10 mm.

The tensile strength is shown in Table 1. The wire of the rivet D of the present invention is 30 to 43% as compared with the wire of the conventional rivet (A to C). The strength of the rivet E is 33% higher than that of the rivet wire, and the wire of the rivet E is also 9.5 to 21% as compared with the wire of the conventional rivet. Compared to the riveted wire rod, the strength has been increased by 12%. The wire is cut into a predetermined size and then formed into a rivet by cold forging. When the frame is swaged by the rivets (D, E) of the present invention, the swaging direction is the same as that of the wire drawing process. Since it is performed in the direction opposite to the direction, the caulking load may correspond to the strength before the wire drawing process.

Table 1 also shows the material property test results of the conventional rivets (A to C) and the rivets (D, E) of the present invention according to JIS and the like. According to this, only the rivets D and E of the present invention obtained favorable evaluations in the comprehensive evaluation.

FIG. 1 shows an SN diagram of the conventional rivets (A to C) and the rivets (D, E) of the present invention with a 10% probability of fracture determined from the results of a tensile shear fatigue test. For example, compared to the rivet A, the rivet D of the present invention has a fatigue strength of 1.1 to 1.25 times that of the rivet A, and the life extension in a high cycle region is particularly remarkable.

FIG. 2 shows the results of the Charpy impact test of the rivet A and the rivet D. The rivet D shows a higher value than the rivet A over the entire test temperature.

<Effect of the Invention> The method for producing a high-strength rivet using a low-carbon steel wire for cold forging according to the present invention is a method for producing a low-carbon steel containing C: 0.15% or less and fixing a N in a component to a wire. During the cooling after the cold rolling or after the cooling, the steel is heated to 200 to 500 ° C. and subjected to an aging suppression treatment for fixing C, and then the diameter reduction rate 15 for increasing the tensile strength is increased.
% Or more, and then the rivet is formed by cold forging. Therefore, the workability is improved by lowering the C content and having the effect of suppressing aging, and annealing is performed. However, by performing wire drawing with a diameter reduction rate of 15% or more, the strength as a rivet can be finally improved by at least 9% or more of the conventional rivet wire rod, and the conventional steps such as annealing are omitted. Therefore, there is a great effect that there is no increase in cost.

[Brief description of the drawings]

FIG. 1 is an SN diagram of a 10% fracture probability obtained from the tensile shear fatigue test results of each rivet, and FIG. 2 is a graph showing the impact temperature of the conventional rivet (A) and the rivet material of the present invention (D). 6 is a graph showing a change due to.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsu Murayama 2100 Endo, Fujisawa-shi, Kanagawa Prefecture Press Engineering Co., Ltd. Fujisawa Plant (72) Inventor Shigeo Ohara 1-3-1 Otemachi, Chiyoda-ku, Tokyo Sumitomo Metal Inside the Industrial Co., Ltd. (72) Kenji Kurokawa 1st, Konomi-cho, Kokurakita-ku, Kitakyushu-shi, Fukuoka Prefecture Inside the Kokura Works, Sumitomo Metal Industries, Ltd. (56) References JP-A-57-206515 (JP, A)

Claims (1)

(57) [Claims] 1. A low-carbon steel containing C: 0.15% or less, wherein C is fixed by heating to 200 to 500 ° C. during or after cooling after hot rolling on a wire rod in which N is fixed in the composition. Diameter reduction rate 15 to increase tensile strength after aging suppression treatment
%. A method for producing a high-strength rivet from a carbon steel wire rod for cold forging, wherein a rivet is formed by cold forging after subjecting to a wire drawing of at least 30%.