JPS6237690B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a hot-forged nut, and more specifically to a hot-forged nut that reduces manufacturing costs by omitting the tempering process, and which also makes it possible to obtain nut properties comparable to conventional methods. The present invention relates to a manufacturing method. Nuts used for high-strength bolts are generally formed into a nut shape by hot or cold plastic working, and then processed through quenching and tempering to form the threaded part. This raises concerns about quench cracking as a heat treatment defect, shortened tap life due to non-uniform hardness after tempering, and defects in thread shape due to deterioration of machinability. Among these, quench cracking, which is a fatal defect, depends on the composition of the steel and the heating temperature, but the main cause is the difference in cooling rate at each part due to the shape of the wall thickness, and it becomes especially noticeable in rapid cooling conditions. Oil cooling treatment, in which the cooling rate is slower than water cooling, can solve the problem of quench cracking, but it is a material that has poor hardenability due to its composition and is more likely to cause uneven hardness. The present invention was made in view of the current situation, and its gist is that C0.25-0.55%,
Hot-formed at 1000-1150℃ using carbon steel containing 0.15-0.35% Si and 0.60-0.90% Mn, then heated to 850-900℃.
A method for producing a hot forged nut characterized by immediately cooling the nut with hot water to 80°C or more from the austenite temperature. The present invention will be explained in detail below. The present invention rapidly heats a carbon steel rod with a specific composition range, processes it into a nut shape, and uses the resulting sensible heat to immediately cool it from the austenitic state with hot water to obtain the required hardness, and is used as the material. The C content of carbon steel bars is regulated to 0.25-0.55%. If it is less than 0.25%, the required hardness cannot be obtained;
If it exceeds 0.55%, the hardness after cooling becomes an incompletely quenched structure with a hardness of H _RC 30 or more, which may reduce the tap life when machining the same part. The lower limit of Si as a deoxidizing agent was set to 0.15%, and the upper limit was set to 0.35% so as not to impair toughness, and the lower limit of Mn was set to 0.60% and the upper limit was set to 0.90% in consideration of hardenability. In addition, small amounts of P, S, or even trace amounts of Ni, Cr, etc. 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 1000°C in consideration of ease of processing and lowering of the finishing temperature.The upper limit is set at 1150°C to prevent overheating. The temperature was set in the range of 850°C to 900°C so as not to reduce the ductility. Moreover, the finishing temperature is the austenitizing temperature of these steels, and it can be cooled immediately after forming. Second, water, which is commonly used as a coolant, exhibits significantly lower cooling as the temperature increases, as shown in Table 1.

[Table] In the current quenching process, it is common to use a cooling rate that does not cause Ar′ transformation, that is, 25°C or less in the case of water, and the resulting martensitic structure is adjusted to the required hardness. Tempered. The present invention effectively utilizes the properties of water as shown in Table 1, and has a cooling capacity of 80°C, which is slightly greater than that of the air-cooled state.
By cooling in the above stability range, a mixed structure of ferrite, pearlite, and bainite is obtained, and strength is to be ensured. According to the method of the present invention, the required hardness H _RC of 20 to 25 can be obtained as shown in the examples described later, and no hardness was achieved in the guaranteed load (slipping test) test required for the mechanical properties of nuts. You can get nuts that are comparable to each other. 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 hardening. The chemical composition of the test steel is shown in Table 2, and the manufacturing process is shown in Table 3. Methods B, C, and D in the same table are the methods of the present invention,
A and E are comparative examples, and F is a conventional method.

【table】

【table】

[Table] Table 4 shows the mechanical properties of the nuts manufactured in this manner, such as hardness, variation, and guaranteed load.

[Table] As shown in Table 4, 0.22% low C material and 0.59%
High C materials have large variations in hardness, and low C materials lack hardness, whereas high C materials have high hardness, which may affect the tap life when threading. In contrast, the amount of C was limited. 0.25～
Methods B, C, and D of the present invention using steel materials within the 0.55% range
Good results comparable to conventional method F were obtained in hardness, variation, and proof load tests. As mentioned above, since the method of the present invention obtains the required hardness by cooling with hot water after rapid heating and forming, there are no heat treatment defects such as quench cracks that are usually a concern during hardening work, and the tempering process is easy. There are many things that can be omitted and contribute greatly to reducing manufacturing costs.

Claims (1)

[Claims] 1 C0.25~0.55%, Si0.15~0.35%, Mn0.60~
A method for producing a hot forged nut, characterized by hot forming at 1000 to 1150°C using carbon steel containing 0.90%, and immediately cooling with hot water to 80°C or higher from the austenite temperature of 850 to 900°C.