JPH06277777A - Manufacture of threading member having satisfactory wear resistance - Google Patents

Abstract

PURPOSE:To secure intrinsic strength of a bolt and to enhance wear resistance of thread ridges by forming a nitriding layer or a carbonizing layer in a thread rolling part and then performing thread rolling. CONSTITUTION:By applying a nitriding process(carburizing process) on a base material for thread rolling, a nitriding layer 1 (or a carburizing layer 2) is preformed. After that, a bolt is manufactured by performing thread rolling. With the thread rolling, even if the thickness of the nitriding layer 1 (carburizing layer 2) becomes gradually thinner in the depth direction of a twisted part 3, the layer remains with the thickness sufficient to show a wear resistance; also, in a thread groove bottom 4, the nitriding layer 1 (carburizing layer 2) does not remain or remains only a little if any, an excellent wear resistance is shown, and the generation of cracks and breakage is prevented in the thread groove bottom. Thus, the base material per se can bring out the intrinsic strength in the thread groove bottom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a threaded member such as a bolt having excellent wear resistance.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of bolts, a rolling material is thread-rolled with a flat die, a round die or the like, and then heat-treated as required. In particular, what is called a high-strength bolt is subjected to quenching and tempering after thread rolling to provide necessary strength.

[0003]

Thus, the strength required for the bolt can be imparted by quenching and tempering, but since no consideration is given to wear resistance, tightening / loosening (installation) is required.・ For bolts that are frequently removed, the thread is extremely worn.

Therefore, in order to improve the wear resistance of the thread portion, a method of increasing the strength of the base material can be considered, but in reality, if the strength is too high, delayed fracture will occur.

On the other hand, as shown in FIG. 3, after the thread rolling of the rolling material 10 (or after the subsequent heat treatment),
The nitriding layer 1 is formed by performing nitriding treatment or carburizing treatment.
Alternatively, a method in which the carburized layer 2 is formed on the thread portion 3 is conceivable, but the nitrided layer 1 or the carburized layer 2 has excellent wear resistance, but is fragile, so that even the thread groove bottom portion 4 has the same thickness. If it is formed by, the cracks are likely to occur due to the tensile stress at the time of tightening. Then, once a crack is generated, cracking or breakage of the base material progresses starting from the crack, and the base material may be broken.

Therefore, an object of the present invention is to provide a method of manufacturing a thread cutting member capable of improving the wear resistance of the thread portion while ensuring the original strength of the bolt.

[0007]

Means for Solving the Problems The above-mentioned problem is to form a nitriding layer or a carburizing layer by subjecting at least a rolling portion of a rolling material to a nitriding treatment or a carburizing treatment in advance when manufacturing a threaded member. It is possible to solve the problem by performing thread rolling after that.

[0008]

According to the present invention, as shown in FIGS. 1 and 2, after the rolling material 10 is subjected to the nitriding treatment or the carburizing treatment, the thread rolling is carried out. Even if the thickness of the nitriding layer 1 (carburized layer 2) is gradually reduced in the depth direction of the screw thread portion 3, it remains with a sufficient thickness to exhibit wear resistance, and the thread groove bottom portion 4 has Nitrided layer 1
Since the (carburized layer 2) does not remain or is very small even if it remains, the nitride layer 1 (carburized layer 2) does not crack or break when the screw is tightened, and the original wear resistance In addition to maintaining the above, the base material itself exhibits the original strength at the bottom of the thread groove.

[0009]

The present invention will be described in more detail below with reference to the embodiments shown in the drawings. According to the present invention, as shown in FIG. 2, the rolling material 10 is previously subjected to a nitriding treatment (carburizing treatment) to form the nitrided layer 1 (or the carburized layer 2).
After that, the bolt is manufactured by performing thread rolling. The profile of the thread portion after thread rolling is shown in FIG.

Even if the thickness of the nitrided layer 1 (carburized layer 2) gradually decreases in the depth direction of the thread portion 3 due to the rolling, it remains with a sufficient thickness to exhibit wear resistance. Further, at the bottom of the thread groove, the nitride layer 1 (carburized layer 2) does not remain, or even if it remains, it becomes extremely small and exhibits excellent wear resistance, and cracks and fractures are prevented from occurring at the bottom 4 of the thread groove. it can.

Although the present embodiment has been described by taking the bolt as an example, the present invention can be applied to other thread cutting members such as a turnbuckle. In addition, even a square screw has the same advantages as the present invention.

On the other hand, the relationship between the maximum thickness T of the nitriding (carburizing) layer and the thread height H is T = (0.1-0.2)
We find that H is desirable.

(Experimental example) Next, the effect of the present invention will be clarified by an experimental example. As the sample steel, SMn443 was used. Then, after subjecting this test steel to spheroidizing annealing, a material of hexagon bolt with M16 and a nominal length of 50 mm was produced by cold forging.

After that, three types of bolts were manufactured in the following steps. In the production of the bolts, as shown in the following process, quenching and tempering were carried out for each bolt under the same conditions to make the base metal strength constant.

Nitriding material (material of the present invention) Bolt material → Nitriding treatment → Induction hardening → Tempering → Thread rolling (520 ℃ × 60Hr) (900 ℃ × 1min) (400 ℃ × 20min) (M16, P1.5) Carburized material (material of the present invention) Bolt material → Carburized → Induction hardening → Tempering → Thread rolling (925 ℃ × 3Hr) (900 ℃ × 1min) (400 ℃ × 20min) (M16, P1.5) Normal material ( Normal material) Bolt material → Thread rolling → Induction hardening → Tempering (M16, P1.5) (900 ℃ × 1 min) (400 ℃ × 20 min) The bolt thus obtained was used as a test material and the torque was 2000 kg.
After the tightening at f-cm was repeated 100 times, the wear amount of the thread portion was measured. The amount of wear was measured by cutting the bolts vertically and then embedding them in resin,
With respect to C, D and E, the amount of wear at a position of 0.5 mm from the screw bottom was measured with a microscope. The amount of wear was calculated as an average value of five thread ridges as shown in the following equation. Abrasion amount = (A + B + C + D + E) / 5- (a + b + c +
d + e) / 5 Table 1 shows the results when the test was performed 5 times for three types of bolts.

[0016]

[Table 1]

As a result, as is clear from Table 1, it was found that the bolt processed according to the present invention had a significantly smaller amount of wear than the bolt processed by the conventional method.

[0018]

As described above, according to the present invention, it is possible to remarkably improve the wear resistance of the thread portion.

[Brief description of drawings]

FIG. 1 is a profile of a hardened layer when thread rolling is performed after nitriding (carburizing) treatment according to the present invention.

FIG. 2 is a hardened layer profile for showing a correlation between a nitriding (carburizing) treated layer and a thread rolling portion.

FIG. 3 is a profile of a hardened layer when a nitriding (carburizing) treatment is performed after thread rolling in a comparative example.

FIG. 4 is an explanatory diagram of measurement conditions for wear resistance.

[Explanation of symbols]

1 ... Nitrided layer, 2 ... Carburized layer, 3 ... Thread groove bottom, 10 ... Rolling material.

Claims (1)

[Claims] 1. When manufacturing a threaded member, a nitriding treatment or a carburizing treatment is applied to at least a rolling portion of a rolling material in advance to form a nitrided layer or a carburized layer. A method for manufacturing a threaded member having excellent wear resistance, which is characterized by performing manufacturing.