JPS58138537A - Manufacture of hot forging nut - Google Patents

Abstract

PURPOSE:To cause no defect due to heat treatment such as burn-cracking, etc., and also to omit a tempering proces, by quickly heating a carbon steel rod of specified component range, working it to a nut shape, executing hot water cooling by utilizing its sensible heat, and obtaining necessary hardness. CONSTITUTION:Carbon steel used as a blank material contains 0.25-0.55% C content, 0.15-0.35% Si as a deoxidizing agent, and 0.60-0.90% Mn by taking hardenability into consideration. As a hot forming temperature, the lower limit is set to 1,000 deg.C, the upper limit is set to 1,150 deg.C in order to prevent overheating, a finish temperature is set to a range of 850 deg.C-900 deg.C, and by executing hot water cooling of >=80 deg.C, a mixed structure of ferrite, pearlite and bainite is obtained and the strength is secured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a hot forged nut, and more specifically, it aims to reduce manufacturing costs by omitting the tempering process, and to obtain nut properties comparable to conventional methods. The present invention relates to a method for manufacturing hot-forged nuts.

Nuts used for tensile strength bolts are generally formed into a nut shape by hot or cold plastic working, and then subjected to heat treatment such as quenching and tempering to form the threaded part.
Depending on the type of steel, problems such as heat treatment defects such as quench cracking, reduced tap life due to non-uniform hardness after tempering, and defects in the torsion shape due to deterioration of rigidity may arise. Among these, quench cracking, which is a fatal defect, is caused by the composition of the steel,
Although it depends on the heating temperature, the main factor is the difference in the cooling rate of each part depending on the wall thickness, and this is especially noticeable in rapid cooling conditions.However, in oil cooling treatment where the cooling rate is slower than water cooling, quenching cracks may occur. Although this problem can be solved, it is also a material that has poor hardenability due to its composition and tends to cause uneven hardness of noodle scraps.

The present invention was made in view of the current situation, and the main points of the present invention are as follows: id, C0.25-0.55%, S
i0.15~0.35%, MnO,tO~0.90%
The method for producing a hot forged nut is characterized in that it is hot-formed at 1000 to 1150°C using carbon steel containing carbon steel, and immediately cooled with hot water to 80°C or higher from an austenite temperature of 850 to 900°C.

The present invention will be explained in detail below.

The present invention rapidly heats a steel bar in the II4I four-component range, processes it into a nut shape, and immediately cools it from the austenitic state with hot water using the sensible heat to obtain the required hardness t, which is used as the material. The C content of the carbon steel rod is 0
．． 25~o, 55% K regulated. 0.25%
If it is less than 0.55%'i, the required hardness cannot be obtained, while if it exceeds 0.55%'i, the hardness after cooling becomes an incompletely quenched structure with HRc of 30 or more, which may reduce the tap life when machining blank parts.

The lower limit of St as a defrosting agent was set to 0.15%, and the upper limit of t-0.3541 was set to 0.60% and the upper limit of Mn was set to 0.9091i in consideration of hardenability so as not to impair toughness.

In addition, a small amount of p, s, or even Ni, Cr, etc. of the device may be unavoidably included as impurities.

In addition, the hot forming temperature varies slightly depending on the carbon content, but the lower limit is set at 100°C in consideration of ease of processing and lowering of the finishing temperature.
The upper limit is set at 1150°C to prevent overheating by 0°C, and the finishing temperature is set at 85°C to avoid increasing hardness due to strain hardening and reducing ductility.
The temperature range was 0°C to 900°C.

Also, the finishing temperature of these steel austeners) It is also the temperature at which it becomes hard, so it can be cooled immediately after molding.

Second, water, which is commonly used as a coolant, exhibits significantly lower cooling as the temperature increases, as shown in Table 1.

In the quenching process of the first expression, it is common to use a cooling rate that does not cause Ar' transformation, that is, in the case of water, a cooling rate of 25°C or less, and the resulting martensitic structure is adjusted to the required hardness. tempered to In the present invention, by effectively utilizing the properties of water as shown in Table 1, and by cooling in a stable range of 80°C or higher, which has a cooling capacity slightly greater than that of an air-cooled state, ferrite and pearlite bainite can be mixed. The aim is to obtain structure and ensure strength.

According to the method of the present invention, the required hardness HRc2o to 25 can be obtained as shown in the examples described later, and there is no inferiority in the proof load (slipping test) test required for the mechanical properties of nuts. You can get nuts.

Furthermore, since the method of the present invention does not require tempering treatment after nut forming, manufacturing costs can be reduced, and as the amount of C increases, there are no heat treatment defects such as quench cracks that are a concern with normal quenching.

The chemical composition of the test steel is shown in Table 2, and the manufacturing process is shown in Table 3.

In the same table, methods B, C, and D are the methods of the present invention, A and E are comparative examples, and F is the conventional method.

Table 2 Table 3 Table 4 shows the mechanical properties of the nuts thus produced, such as hardness, variation, guaranteed load, etc.

Table 4 As shown in Table 4, KO, 22- low C material and 0.591
1.High C materials have large variations in hardness.Furthermore, low C materials lack hardness, while high C materials have high hardness and 16 screws are machined.
There is a strong possibility that the life of the tap will be affected. On the other hand, with the present invention methods B, C, and D, which limit the amount of C and use steel materials within the range of 90, 2 S-0, 51, the hardness, variation, and guaranteed load tests are also superior to the conventional method PK. You can get equally good results.

As mentioned above, since the method of the present invention obtains the required hardness by cooling the bales with hot water, there is no heat treatment defect of the cast crack cape, which is a concern during normal hardening work, and There is a special feature that makes it possible to omit the tempering process, which contributes to a reduction in manufacturing costs.

Applicant: Nippon Steel Corporation -1'

Claims (1)

[Claims] CO, 25-0.55%, SiO, 15-0.35
%, hot forming at 1000 to 1150°C using carbon steel containing Mn 0.60 to 0.90
A method for producing a hot forged nut characterized by immediately cooling the austenite temperature of 0°C with hot water to 80°C or higher.