JPS6345320A - T-head bolt - Google Patents

Abstract

PURPOSE:To permit production of a T-head bolt having high tensile strength made of stainless steel without requiring hardening and tempering by using a martensitic or ferritic stainless steel as a stock and subjecting the stock to cold or warm forging to produce said bolt at the time of producing the above-mentioned T-head bolt. CONSTITUTION:The bar-shaped stock of the martensitic or ferritic stainless steel contg. 10-13wt% Cr is subjected to complete annealing; thereafter, a series of working including cutting to a prescribed length, upsetting, forming of a head part 3, shaft drawing and trimming with a bolt former are executed by a cold or warm forging method. A stem part 2 is then subjected to thread rolling to form screw threads 2a; further, the bolt is immersed in an aq. HNO3 soln. kept at 30 deg.C by which the bolt is subjected to an immobilization treatment. The completely annealed structure which consists of ferrite as matrix and in which a small amt. of a CrC compd. exists here and there is thereby formed. The T-head bolt having >=60kgf/mm<2> tensile strength is thus obtd. without subjecting the bolt to hardening and tempering treatments.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a single head bolt made of stainless steel.

(Prior art) The TVt bolt is installed so that the head of the bolt joins the shaft to form a T-shape, and the tightening of pipe joints such as water pipes is uniform. It is used for.

As conventional single head bolts, those made of spheroidal graphite cast iron and those made of stainless steel are known. T-bolts made of spherical graphite S3 iron have a tensile strength of JIS G5502 type 1 of 40 kgf/me2 or more, and type 2 of 45 kgf/me2.
/m” or more.On the other hand, as a stainless steel single-head bolt, martensitic SUS 4
There is one that uses 03 grade, and its tensile strength is 60 kg.
f/am” or more.

The stainless steel one-head bolt is obtained by hot forging from a stainless steel bar, and its general processing steps are as follows.

Annealing of steel bar → cutting to required length → heating (1200℃
degree) → Forging → Passivation treatment by quenching and tempering → Thread rolling In this case, the above quenching is performed to homogenize the structure of the bolt head and details after hot forging or to improve the strength.
Furthermore, tempering is necessary because the martensitic structure produced by quenching significantly reduces toughness and increases residual stress. Therefore, this stainless steel one-head bolt has a uniform tempered structure throughout (see Fig. 16).

(Problems to be Solved by the Invention) Conventional stainless steel IT head bolts have high tensile strength, but they are expensive because they are hot forged, and they are also quenched and tempered, which makes them expensive. The problem is that it has become expensive. In addition, in the case where quenching and tempering are omitted, only the bolt head is hardened by heating and air cooling, and there is a problem that the strength becomes weak due to the difference in structure from the shaft part.

(Means and effects for solving the problems) The present invention has the following features:
As a means to solve the conventional problems, the head was installed in a T-shape together with the shaft, and the entire bolt was made of ferrite with a small amount of CrC compound dotted on it. This provides a single-head bolt with a completely annealed structure.

This one-head bolt is obtained by cold forging or warm forging of martensitic or ferritic stainless steel, and the entire bolt is made of ferrite with a small amount of C.
Since it has a completely annealed structure dotted with rC compounds, it can be used as is without quenching and tempering.

Of course, it is possible to further quench and temper the single-head bolt of the present invention to have a tensile strength of 60 kgf/nn+2 or more.

In addition, the metal flow obtained by the above forging is a continuous metal flow that curves from the center of the top of the bolt to both sides at the bolt head and converges at the bolt shaft, so there is no risk of the head breaking during use. It is possible to improve the strength of the bolt without any problems.

(Effects of the Invention) Therefore, according to the present invention, it is possible to provide a single-head bolt with excellent mechanical properties, and the cost of this single-head bolt can be reduced by, for example, about 40%, which is an excellent effect. is obtained.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In the one-head bolt 1 shown in FIG. 1, 2 is a shaft portion having a threaded portion 2a at the bottom, and a head 3 is attached to the upper end of this shaft portion 2 so that it forms a T-shape together with the shaft portion 2. It is connected to The nominal diameter of the one-head bolt 1 in this embodiment is 2011111, and the length of the head 3 is 55 m. That is, this ratio (head length/nominal diameter) is 2.75, and this ratio can also be set to, for example, 2.60 to 2.90. FIG. 2 is a plan view of the single-head bolt 1, and FIG. 3 is a bottom view thereof, in which a 1-shaped positioning recess 4 is engraved on the end surface of the shaft portion 2.

The structure of the single-head bolt 1 mentioned above is shown in a micrograph (500 mm) in Figure 4.
The entire bolt has a completely annealed structure with a small amount of CrC compound scattered on the ferrite base. In addition, in the part extending from the bolt head 3 to the shaft part 2, as shown in the photograph in FIG. A metal flow is formed.

The single-head bolt 1 is obtained by the treatment process shown in FIG. 6 including a forging process, and the test material is a martensitic stainless steel wire having the following components (main metal %).

C0.07 or less, Si 0.40 or less.

Mn O,l O-1,0,Cr 10. 0~13
．． 0. N O, 02 or less In the treatment process for the remaining Fe and impurity elements, the above-mentioned material is first completely annealed. This complete annealing is intended to improve the cutting and plastic workability of the material, and is carried out by holding the material at a temperature above its transformation point and completing the transformation by slow cooling. The relationship between the C content of the material (12C-r) and the tensile strength in the annealed state is as shown in Figure 7, and when the C content is 0.07% or less, the tensile strength is 47Kgf/l1II.
It can be seen that the forgeability is good. That is, as shown in Figure 8, which shows the relationship between the tensile strength of the material and the life of the forging die (the number of materials that can be forged before cracking occurs), when the tensile strength becomes 47 K g f /nn2 or less, The average mold life is over 2000 pieces.

Moreover, corrosion resistance can also be improved by reducing Cth1.

Next, using the bolt former 5 shown in FIG. 9, the material is cut to a required length, and a series of cold forging processes including upsetting, head forming, shaft drawing, and trimming are performed.

Although the material cutting portion of this bolt former 5 is omitted from illustration, the bolt former 5 performs each step surrounded by a two-dot chain line in the process diagram shown in FIG. Furthermore, when using a material that has been cut to a required length in advance, it is also possible to shift from the complete annealing process to the upsetting process. The bolt homer 5 will be explained below.

That is, in FIG. 9, 6 is an upper mold, 7 is a lower mold, and from the right side of the drawing are a (preliminary) upsetting section 8, a head forming section 9, a shaft drawing section 10. A trimming section 11 is provided, and a punch 12 and a die 13 for upsetting, and a punch 14 for head shaping.
and a die 15, a punch 16 and a die 17 for shaft drawing, and a punch 18 and receiver 19 for trimming.
is transported by an extrusion chuck, and the workpiece W4 is extruded and dropped into a product chute.

The machining conditions in the upsetting section 8 are as follows using the dimensional symbols shown in FIGS. 10 to 12.

Upsetting angle θ = 45 degrees, free upsetting ratio b/d = 1.5. Upsetting height ratio c/a=0.6°f/d=2.0. g/d=1.0 The quality of the bolt head 3 is determined by the upsetting, and the upsetting angle is preferably 30 to 60 degrees. That is, when the swaging angle is less than 30 degrees, a T-head bolt a is obtained in which the metal flow aluminum is irregularly distorted at the head due to head shaping, as shown in FIG.
If the swaging angle exceeds 60 degrees, as shown in FIG. 14, the metal flow b+ will break off near both sides of the bolt top (Tmm port 1), and in any case, the strength cannot be improved using the metal flow. The most preferable upsetting angle is about 45 degrees, and a streamlined metal flow shown in FIG. 5 can be obtained.

In the cold forging using the bolt former, the machined shape is non-axially symmetrical, that is, the machined shape during upsetting is symmetrical with the overhang part Wl following the product shape, as shown in Figure 12.
1. Wl 1 is formed, and cutting at the trimming portion 11 is unnecessary. Moreover, in this case, the positioning of the workpieces W1 to W4 in each of the workpieces 8 to 11 of the bolt former 5 is performed using the positioning recess (T-shaped) 4 at the bottom of the shaft, and the workpieces W1-W are positioned as they move. 4 does not rotate, and the above positioning prevents dents or damage to the mold due to runout of the workpiece W l-W 4.

After the cold forging, the forged product is thread rolled and further subjected to passivation treatment.

The passivation treatment is carried out, for example, by immersing the processed material in an aqueous HN○3 solution at 30°C for a predetermined period of time. In this case, since the passivation treatment is performed after thread rolling, the corrosion resistance of the threaded portion 2a can be improved.

The single head bolt obtained as above has a tensile strength of 50 kg.
f/m" or more, and the guaranteed load is 6100 kgf without causing permanent deformation. The reason for this excellent mechanical strength is that the metal flow shown in Figure 5 is formed in the completely annealed structure. This is because

Therefore, the single head bolt can be used as is for tightening pipe joints such as water pipes.

In addition, according to the single-head bolt manufacturing method of the embodiment, the wire rod is sequentially cut to the required length and cold forged, so compared to the case where hot forging is performed using a steel bar, the forging method is more effective. This difference increases processing speed and reduces costs, and there is virtually no generation of residual material or oxidation loss (due to the oxide film created by heating the material peeling off during hot forging) due to material cutting. This improves material yield and productivity. Further, since quenching and tempering treatments are not required, further cost reduction can be achieved.

Of course, the single head bolt in this example has a Cr equivalent of 9
．． 0 to 10.5, and it is possible to improve the strength by hardening and tempering. That is, in that case, the quenching temperature is 950 to 1000°C (for example, 9
70°C), and tempering can be performed by water cooling from 700 to 750°C (for example, 700°C). Through such heat treatment, the single-head bolt becomes a completely martensitic structure, and its tensile strength becomes 60 K g f /an2 or more.

In addition, in the above embodiment, by using the positioning recess (1-shaped) 4, the workpieces W1 to W4 can be conveyed accurately without wobbling during cold forging, resulting in a product with good head dimensional accuracy. is obtained.

Furthermore, since no heat treatment is required, the number of processing steps is reduced.

Further, in the above embodiment, a single head bolt is obtained by cold forging, but a single head bolt similar to the above embodiment can be obtained by warm forging. In other words, as shown in Figure 15, which shows the relationship between the deformation resistance and temperature of stainless steel m (SUS403), the deformation resistance significantly decreases at temperatures above 150°C, and
At temperatures between 00°C and 600°C, the decrease in deformation resistance decreases due to blue-hot brittleness, but at temperatures above 600°C, the deformation resistance decreases again. A T-head □ bolt similar to the previous example can be obtained by forging steel materials in a warm region (below the transformation point, particularly in a region where no oxide film is formed due to heating of the material).

[Brief explanation of the drawing]

Figures 1 to 5 relate to the single-head bolt of the embodiment; Figure 1 is a front view of the single-head bolt, Figure 2 is a top view of the same, Figure 3 is a bottom view of the same, and Figure 4 is a single-head bolt. 500x magnification 111'I microphotograph showing the metal group m (crystal structure) of , FIG. 5 is a photo showing the metal structure (metal flow) of a single-head bolt, FIG. Figure 7 is a characteristic diagram showing the relationship between the C content of the material and the tensile strength in the annealed state, Figure 8 is a characteristic diagram showing the relationship between the tensile strength of the material and the life of the forging die, and Figure 9 is a characteristic diagram showing the relationship between the tensile strength of the material and the life of the forging die. 10 is a front view showing the upper part of the material, FIG. 11 is a front view with the material upturned, FIG. 12 is a plan view of the same, and FIGS. 13 and 14. 15 is a characteristic diagram showing the relationship between the deformation resistance and temperature of stainless steel, and FIG. 16 is a 500 mm diagram showing the metal structure of a conventional single-head bolt. This is a photomicrograph magnified. l...1 bolt, 2...shaft, 2a
...Screw part, 3...Head, 5...
... Bolt Homa. Figure 6 drawing page 1-go (no change in content) Figure 5 Figure 4 Figure 16 Figure 7 α skill ωO C quantity (weight b) Figure 8 Se ■ Mamoru (afterlife Figure 12 Figure 13 Figure 14 Figure 15 Figure 5 twice (°C) Procedural amendment (method) November 6, 1985 Commissioner of the Patent Office Black 1) Akio Tonzo 1, Indication of the case 1989 Patent Application No. 189125 Address: 4-7-18 Imazu Kita, Tsurumi-ku, Osaka City, Osaka Prefecture Name: ``BE Zipper〒Mb Type All Company 4th Generation Manager Postal code: 650 Address: Asahi Seimei Sannomiya Building, 1-3-11 Sannomiya-cho, Chuo-ku, Kobe City, Hyogo Prefecture Showa 614f 40th month 8B (5a sending 61.10.28
) 6. Figure 5 of the drawing to be amended 7. Details of the amendment as shown in the attached sheet 8. List of attached documents

Claims (1)

[Claims] (1) It is a cold-warm formed bolt that is provided so that the head part joins the shaft part to form a T-shape, and the entire bolt has a ferrite base with a small amount of CrC compound dotted thereon. A T-head bolt characterized by a completely annealed structure.