JPS60243223A - Manufacture of gear - Google Patents

Abstract

PURPOSE:To eliminate refining and tempering when a steel is worked into a gear and subjected to induction hardening to manufacture a reduction gear for a hoist, by using a low-C Mn-B steel having a specified composition as the steel so as to improve the hardenability. CONSTITUTION:A steel consisting of, by weight, 0.25-0.42% C, 0.8-1.5% Mn, 0.0008-0.003% B, 0.15-0.3% Si, <=0.03% P, <=0.03% S and the balance Fe is worked Fe is worked into a gear by direct toothing, and the teeth of the gear are subjected to induction hardening to form a hardened martensitic structure. At this time, the hardening time is made longer than that of S45C used widely as a starting material. By the longer hardening time, surface hardness and strength comparable to those of an S45C gear can be attained while eliminating refining and tempering.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention provides a reduction gear for hoisting machines such as hoists that requires high strength and high wear resistance. For this purpose, 845G is used as the raw material, and the manufacturing method is as follows.
After cutting the steel bar, it is tempered and gear-cut, then induction hardened, and then tempered at 180 to 200°C. In general, during induction hardening, in addition to heat removal from the surface, there is heat removal due to heat conduction to the 6th part, and the bottom of the gear tooth is also easily hardened, so it has better heat conduction than alloy steel.
Furthermore, 845C, which is inexpensive, is widely used.

However, since 845C has poor hardenability, when induction hardening is performed, which is rapid heating, it facilitates austenite formation in the heated area, prevents ferrite from remaining in the base after hardening, and creates a uniform martensite structure. Therefore, it is necessary to perform thermal refining (quenching/high temperature tempering) as a pretreatment.

In addition, in 845G, since 0% is high, the hardness of the tooth surface reaches Hv800 in the hardened state and has high notch sensitivity, and since it has no toughness, it is tempered at 200℃ to increase the hardness. It is necessary to lower it and give it appropriate toughness.

However, these heat refining and tempering processes require a lot of time, and since there are many steps, there are restrictions on the work area, making it difficult to organize a rational line, and it has the disadvantage of poor productivity. there were.

[Purpose of the invention]

An object of the present invention is to provide a gear with excellent productivity by ensuring strength and wear resistance, omitting the pre- and post-treatments of heat refining and tempering.

[Summary of the invention]

When induction hardening is performed on 845C material, refining and tempering are required as pre- and post-treatments for the reasons mentioned above. Therefore, in order to omit these steps, the material must first have good hardenability.

Ni is an additional element that improves hardenability.

Examples include Cr and MO, but considering the economical efficiency, addition of B and Mn may be considered. B has the characteristic of greatly improving hardenability even when added in an extremely small amount.

Mn also has the same effect as above, is relatively cheaper than Ni, C, and r, and further improves hardenability due to the mutual effect with B.

Next, it is necessary to have a low C%. The surface hardness when a uniform martensitic structure is formed by induction hardening is determined by the C content, so if the hardness is to be kept within a certain range, the C% must be lower than that of 845G.

・This time, we were able to obtain the appropriate components and heat treatment conditions for a gear that has the same strength as conventional gears and can omit heat refining and tempering.

In the present invention, C is the most important element that controls strength, and if it is less than 0.25%, the strength required in the present invention cannot be obtained due to lack of strength. Also, 0.
If it exceeds 42%, quenching distortion and quenching cracks tend to occur during rapid cooling such as water quenching, resulting in a lack of reliability, and the surface hardness after quenching becomes high, requiring tempering. Furthermore, the effect of B on improving hardenability is more pronounced as the C% is lower.

Therefore, the C content was set to 0.25 to 0.42%.

B greatly improves hardenability even in extremely small amounts, comparable to impurities. As a result of evaluating the strength and toughness of the Mn-B material depending on the amount of B added, the appropriate amount of B added is around 0.001%. Since it is very difficult to control the amount added in PPM order, the B content was set to 0.0008% to 0.003%.

Next is Mn, which is also an element that improves hardenability and has the effect of increasing strength.

If the content is less than 0.8%, which is about 845C, the effect will be small, and if it is more than 1.5%, austenite will tend to remain during quenching, and there is a risk that the strength will decrease. Therefore, the Mn content was set to 0.8% to 1.5%.

In addition, Si is generally included in rust as a deoxidizing agent, and its content is 0.15 to 0.3%.

Furthermore, if both P and S exceed 0.03%, the toughness decreases, so the content needs to be 0.03% or less.

[Embodiments of the invention]

'Hereinafter, the present invention will be explained in detail.

Table 1 shows the chemical compositions of Mn-B steel, which is the gear material of the present invention, and 845G, which is the current material.

For 845G, gear cutting was performed after heat treatment (850°C x 40 minutes oil cooling → 650°C x 50 minutes air cooling), and for Mn-B steel, gear cutting was performed directly. Gear specifications are shown in Table 2.

Thereafter, induction hardening was performed, and then, for 545C, tempering was performed at 200°C for 50 minutes.

Table 1 Sample chemical composition 2 Table 3 Induction hardening conditions Table 3 shows the induction hardening conditions, and Figures 1 and 2 show the hardness of the tooth tip and tooth bottom of the gear after all processes are completed. Shown below.

In the figure, by using M n -B@ as the material and making the high frequency heating time longer than that of 545C material, 545
It was possible to obtain the same tooth tip hardness and tooth root hardness as those subjected to G refining.

Furthermore, the results of measuring the mechanical properties of 845G after quenching and tempering and after quenching of Mn-B steel are shown in FIG.

In Fig. 3, Mn-B steel has 54
It was possible to obtain mechanical properties equivalent to those of 5G quenched and tempered steel.

Based on the above, Mn-B steel was used and the heating time was 84F.
By making the length longer than C, the same surface hardness and strength can be obtained even if heat refining and tempering are omitted.

〔Effect of the invention〕

According to the present invention, the hardenability of the material with low C content is improved by the Mn and B elements, and by controlling the heating time, refining and tempering can be omitted, so the heat treatment time is shortened and the process is reduced. It is effective in manufacturing gears with excellent performance.

[Brief explanation of the drawing]

Figure 1 is a hardness distribution diagram from the tooth tip of 545C and M n -B gears, Figure 2 is a hardness distribution diagram from the tooth bottom of 545C and M n -B gears, and Figure 3 is a mechanical hardness distribution diagram. It is a comparative diagram of properties. Agent Patent Attorney Akio Takahashi Page 1 continued 0 Inventor Akira Izumiyama To 1-1-1 Higashitaga-cho, Hitachi City Taga Factory, Hitachi, Ltd.

Claims (1)

[Claims] 1. C: 0.25-0.42%, Mn in weight percent
: 0.8~1.5%, B: 0.0008~0
．． 003%, Si: 0.15-0.3%, P: 0.03
% or less, S: 0.03% or less, the remainder is Fe, and after processing the gear into a gear, the teeth of the gear are subjected to a quenching treatment, and the gear has a rutinsite structure after quenching. Production method. 2. In claim 1, the surface hardness after heat treatment is Hv 570 to 690 at the tooth bottom, and Hv 45
A method for manufacturing a gear, characterized in that the hardening depth to 0 is equal to or more than the module of the gear x 0.3, and the structure is a martensitic structure.