JPS5974262A - Steel for gear - Google Patents

Abstract

PURPOSE:To obtain a steel for a gear having improved strength and capable of forming a small-sized gear by reducing the amount of Mn in a steel having a specified composition, regulating the amounts of P an O, and adding a proper amount of Ni or Mo as required. CONSTITUTION:This steel for a gear consists of, by weight, 0.15-0.40% C, <=0.35% Si, <=0.55% Mn, <=0.020% P, <=0.020% S, 0.3-2.0% Cr, 0.020-0.080% Al, 0.010-0.030% N, <=15ppm O and the balance Fe with inevitable impurities. <=5.0% Ni and/or <=0.5% Mo may be contained in the steel. By the composition the austenite grains can be made fine, and a small-sized gear having superior strength and causing no breakage can be obtd.

Description

[Detailed description of the invention]

The present invention relates to a high-strength steel for gears that allows gears with excellent strength to be obtained. Conventionally, chromium steel (such as SCr420) and chrome-molybdenum steel (such as 30M420) are often used as gear steels, and these steels are formed into gears and then subjected to surface hardening treatment such as carburizing or nitriding. Usually, it is used for On the other hand, as a result of the recent efforts to reduce the weight of automobiles, there has been an increasing demand for smaller gears such as transmission gears and differential gears that have been subjected to surface hardening treatments such as carburizing or nitriding. The reality is that gears need to be made stronger. However, there has been a problem in that it is difficult to achieve such high strength of gears using conventional gear steels. The present invention has been made in view of these conventional problems, and aims to provide a steel for gears that can provide gears that have excellent strength and can be made smaller. As a result of intensive research to obtain gears with excellent strength, the inventors developed the current 5Cr420 and S CM420 gears.
The amount of Mn is lower than that of
i, Mo is added to lower the amount of P, which is a grain boundary embrittling element, and is an inclusion forming element.

[0] It has been found that the gear strength can be improved by regulating the amount and adding appropriate amounts of A1 and N to refine the austenite crystal grains. That is, the gear steel according to the present invention has, in weight %,
C: 0.15~0, 40%, Si: 0.35%
Below, Mn: 0.55% or less, P: 0.020% or less,
S: 0.020% or less, Cr: 0.3-2.0%,
A4: 0.020-0.080%, N: 0.010-0
．． 030%, [:0): 15 ppm or less, as necessary, one or two of Ni: 5.0% or less, Mo: 0.5% or less, and further Nb, Ti, Zr, V, T
It is characterized by containing the element Fli, which is effective in preventing coarsening of crystal grains such as a. The reasons for limiting the component range (weight %) of the gear steel according to the present invention will be explained below. C: O, 15-0.40% C is an effective element for securing the depth of the surface hardening layer necessary to improve the wear resistance and fatigue resistance of gears during surface hardening treatment after tooth forming. , and for this purpose 0.1
Contain 5% or more. However, if it is too large, toughness, cold forgeability, and machinability will deteriorate, so the content should be 0.40% or less. Si: 0.35% or less Si is an effective element as a deoxidizing and desulfurizing element during melting, but if it is too large, an abnormal surface layer will be formed after surface hardening treatment, so the content should be 0.35% or less. Mn: 0.55% or less Mn is an effective element as a deoxidizing and desulfurizing element during melting, but if it is too large, the gear strength will be significantly lowered, so it should be kept at 0.55% or less. P: 0.020% or less If the amount of P is too large, the gear strength will decrease significantly, so 0.
．． 0.020% or less. S: 0.020% or less S is an inclusion-forming element, and if the S content is too high, gear breakage is likely to occur starting from inclusions, so 0.020% or less S is an inclusion-forming element.
0.020% or less. Cr20.3~2.0% Cr is an element necessary to ensure the hardenability of steel, and M
It is added to compensate for the decreased amount of n, but 0.3%
If it is less than 2.0%, such an effect cannot be obtained.
If it exceeds 6%, the hardness of the 6th part becomes large and causes high strain, so it is set in the range of 0.3 to 2.0%. To A! , : 0.020-0.080%, N: 0.01
0-0.030% A1 and N form the compound AiN; 1. It is an effective element for refining austenite crystal grains and preventing the occurrence of strain, and for this purpose it is necessary to contain 0.020% or more of Ai and 0.010% or more of N. However, when All exceeds 0.080%, A4N becomes coarse,
Since it loses the effect of grain refinement and reduces the cleanliness of the steel, it is set to less than o, oao%. Also, N is 0
．． If it exceeds 0.30%, blows are likely to occur, so
The content shall be 0.030% or less. (0): 15ppm or less

[0] is an inclusion-forming element, and if it is too large, the cleanliness of the steel will deteriorate, teeth will be more likely to break due to the inclusions, and the fatigue strength of the gear will also decrease, so 15 pp.
It must be less than m. Ni: 5.0% or less Ni is an effective element for increasing gear strength, but 5.
If it exceeds 0%, the above-mentioned effect will be saturated and it will also cause high strain, so if added, it should be 5.0% or less. Mo: 0.5% or less MO, like Ni, is an effective element for increasing gear strength, but if it exceeds 0.5%, the above effects will be saturated and it will also cause high strain, so it should not be added. 0.
5% or less. Nb, Ti, Zr, V, Ta Nb, Ti, Zr, V, Ta
etc. are elements that form carbonitrides M (C, N) and contribute to improving gear strength by refining austenite crystal grains together with AiN.
If it is less than 0.01%, such an effect cannot be obtained, and if it is less than 0.10%,
If Nb is contained, the above effect will be saturated, so if Nb is contained, it is preferably in the range of 0.01 to 0.10%, and in addition, Ti, Zr, and V. For the same reason, Ta is preferably contained within an appropriate range. Examples will be described below. Steel having the chemical composition shown in Table 1 was melted, formed into ingots, and rolled to obtain steel materials for gears. Next, gears having specifications shown in Table 2 were formed from the obtained gear steel materials. Next, carburizing and quenching and tempering were performed according to the procedure shown in FIG. 1, and then the gear strength was measured using a power circulation gear testing machine. In this measurement, the maximum Hertzian stress at which tooth breakage did not occur even after 107 repetitions of the test was evaluated. The results are also shown in Table 1. As shown in Table 2 and Table 1, it is clear that all of the invention steels have high gear strength, and the Mn content is 0.35.
% (G), 0.50% (H). 0.60% (J), 0.80% (K), 0.95% (L
), the gear strength gradually decreases as shown in Figure 2, indicating that keeping the Mn content below 0.55% is effective in increasing gear strength. Ta. Even when the P content or S content is high (M,
N), when Ai or N content is low (0, P),
(0) When the content is high (Q), the unfavorable result was that the gear strength was low. As explained above, by using the steel for gears according to the present invention, it is possible to obtain gears with excellent gear strength and low risk of breakage, and it is also possible to reduce the size of the gear, and to reduce the weight of the gear and the material used. It has a significant effect in that it is possible to reduce the amount used.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the surface hardening treatment conditions applied to gears in Examples of the present invention, and FIG. 2 is a graph showing the results of investigating the influence of Mn content on gear strength. Procedural amendment (voluntary) January 25, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi 16 Indication of case 1982 Patent application No. 182129 2° Issued “0 Name Steel for gears 3, Person making amendment case” Relationship Patent Applicant Address: 66 Kawide, Hoshizaki-cho, Nagoya City-ku, Aichi Prefecture Name (Name) (371) Daido Steel Co., Ltd. Representative Aki 1) Masaya 4, Agent

Claims (2)

[Claims] (1) In weight%, C: 0.15-0.40%, Si: 0
．． 35% or less, Mn: 0.55% or less, P: 0.020
% or less, S: 0.020% or less, Cr: 0.3 to 2.0
%, A4: 0.020-0.080%, N: 0.010
~0.030%, (0): 15 ppm or less, the balance being Fe and inevitable impurities. (2) In weight%, C: 0.15-0.40%, Si: 0
．． 35% or less, Mn: 0.55% or less, P: 0.020
% or less, S: 0.020% or less, Cr: 0, 3~
2, 0%, Ai: 0.020~o, oao%, N:
0.010 to 0.030%, (0): 15 ppm or less,
A gear steel comprising one or two of Ni: 5.0% or less and Mo: 0.5% or less, the balance being Fe and inevitable impurities.