JPH06306572A - Gear - Google Patents

Abstract

PURPOSE:To improve impact strength and fatigue strength by carburizing a material, having a composition where C, Si, Mr, P, S, Ni, Cr, Fe, etc., are specified, and regulating C concentration,' abnormally carburized layer, respectively. CONSTITUTION:This gear is constituted of a metallic material having a composition consisting of, by weight, 0.15-0.25% C, <=0.1% Si, 0.2-0.8% Mn, <=0.015% P, 0.01-0.015% S, 0.4-0.6% Ni, 0.2-0.8% Cr, 0.6-1% Mo, 0.01-0.05% Al, 0.005-0.025% N, 0.02-0.5% Nb, <=0.002% O, and the balance Fe. Further, [10Si+Mn+Cr] is regulated to <=2% to control abnormally carburized layer to <=6mum, by which the impact strength and fatigue strength of a gear can be improved. Moreover, > crystalline grain size is regulated to >=#9(JIS), by which strength in the crystalline grain can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear having excellent impact characteristics and fatigue characteristics.

[0002]

2. Description of the Related Art Conventionally, gears are made of a case-hardened steel that has been carburized, and the surface has wear resistance and the interior maintains toughness.

[0003]

However, in the above-mentioned conventional gear, since a grain boundary oxide layer is formed in the material, cracks are easily generated from this, and alloy elements are added unnecessarily to improve toughness. In this case, there was a problem that machinability was reduced.

[0004]

The present invention, as means for solving the above-mentioned conventional problems, comprises 0.15 to 0.25% by weight of C, 0.1% by weight or less of Si, and 0.2 to 0.8 of Mn. % By weight, P 0.015% by weight or less, S0.010 to 0.01
5% by weight, Ni 0.4-0.6% by weight, Cr 0.2-
0.8% by weight, Mo 0.6 to 1.0% by weight, Al 0.0
1 to 0.05% by weight, N 0.005 to 0.025% by weight, Nb 0.02 to 0.5% by weight, O 0.002% by weight
Hereinafter, the balance is Fe, and 10Si + Mn + Cr ≤2.
0, which has a C concentration of 0.7-0.
The present invention provides a gear that is carburized to have a content of 9% by weight, has an abnormal carburizing layer of 6 μm or less, and is made of a material having a grain size of # 9 or more.

[0005]

The operation of the present invention is as follows. C is 0.1
If the content is less than 5% by weight (hereinafter simply referred to as%), the strength of the gear core cannot be secured, and if the content exceeds 0.25%, the toughness of the gear is deteriorated. If the content of Si exceeds 0.1%, the grain boundary oxide layer increases and the strength near the grain boundaries decreases. Since the conventional case-hardening steel contains 0.15 to 0.35% of Si, the above-mentioned cracks are likely to occur. Mn improves the hardenability, but if the content is less than 0.2%, the hardenability cannot be secured, and if it exceeds 0.8%, the grain boundary oxide layer tends to increase. When P exceeds 0.015%, P has a grain boundary deflecting action and tends to embrittle the grain boundaries. S forms a compound having ductility like Mn, reduces the impact value in the lateral direction and improves machinability, but if the content is less than 0.010%, machinability cannot be secured,
Further, if the content exceeds 0.015%, the toughness decreases.
If the Ni content is less than 0.4%, the intragranular strength cannot be secured, and if the Ni content exceeds 0.6%, the machinability deteriorates. If the Cr content is less than 0.2%, the hardenability cannot be secured, and if the Cr content exceeds 0.8%, the grain boundary oxide layer tends to increase. Mo has the effect of suppressing the grain boundary deviation effect of P to improve the grain boundary strength and suppresses the formation of an incompletely quenched structure, but if the content is less than 0.6%, the grain boundary strength can be secured. However, if the content exceeds 1.0%, the effect is saturated. If the Al content is less than 0.010%, it is not possible to ensure the refinement of crystal grains, and if the Al content exceeds 0.05%, the effect is saturated. If the crystal grains are made finer, the crack propagation resistance increases, which is effective in improving the toughness of the carburized layer. N has a grain refining effect similar to Al, but 0.005
If the content is less than%, the above effect cannot be secured, and 0.025
The effect is saturated when the content exceeds%. Nb has a grain refinement effect similar to Al, but if the content is less than 0.02%, the above effect cannot be secured, and if it exceeds 0.5%, the effect is saturated. If the content of O exceeds 0.002%, it causes fatigue fracture due to the formation of alumina inclusions.

When the abnormal carburization layer (grain boundary oxidation layer) is 6 μm or less, the impact strength and fatigue strength of the gear are improved. The relationship between the depth of the grain boundary oxide layer and the elements contained in the material is 10 Si
+ Mn + Cr as parameter, grain boundary oxide layer is 6μm
In order to be below, it is necessary to set the above parameter to 2.0 or less. Further, by setting the crystal grain size to be # 9 (JIS) or more, the strength inside the crystal grain is increased.

[0007]

[Example] Steels having alloy components shown in Table 1 were melted. After rolling and normalizing, it was processed into a test piece. The test piece was carburized and tempered under the following conditions. Carburization and diffusion were performed at 910 ° C. using propane gas as a carbon source, and then the mixture was kept at 830 ° C. for 30 minutes and cooled with oil. The test piece thus treated was further tempered at 160 ° C. for 2 hours and then air-cooled.

[0008]

[Table 1]

Test items: Normalization hardness, grain boundary oxide layer depth, austenite grain size, machinability: evaluated by a 5000 mm life speed by high speed drilling Gear fatigue test: pitch circle diameter 70 mm, module 2.
5, Life of 10 ⁷ times evaluated with 28 gears Rotating bending fatigue test: Ono type smooth test piece with 8 mm parallel part Carburizing impact test: Izod test using the same gear as the gear fatigue test Table 2 shows the above test results Shown in.

[0010]

[Table 2]

The steels A and B of the present invention have good fatigue strength and impact strength, and also have a hardness N after normalization.
Since the value is almost the same as unadded steel, there is almost no deterioration in machinability. The comparative steels of C and D are conventional case-hardening steels, but since Si is excessively large, grain boundary oxidation is remarkably observed, and particularly, impact strength is greatly reduced as compared with other steels. The comparative steels of E and H have an excessively high Ni content and have a good impact value, but their machinability is significantly reduced. Since the comparative steels of F and G have too little Ni and Mo, respectively, low values for fatigue strength and impact strength are recognized.

The relationship between the grain boundary oxide layer depth D (μm) and the parameter X (10Si + Mn + Cr) is shown in the graph of FIG. 1, and the relationship between D and X is almost linear.
It can be seen that when X is 2.0 or less, D is 6 μm or less.

[0013]

Therefore, according to the present invention, a gear having excellent impact strength and fatigue strength can be obtained.

[Brief description of drawings]

FIG. 1 is a graph in which the grain boundary oxide layer depth D (μm) is plotted on the vertical axis and the parameter X is plotted on the horizontal axis.

Claims (1)

[Claims] 1. C0.15 to 0.25% by weight, Si 0.1
% By weight, Mn 0.2 to 0.8% by weight, P 0.015
% By weight or less, S0.010 to 0.015% by weight, Ni
0.4 to 0.6% by weight, Cr 0.2 to 0.8% by weight, M
o 0.6-1.0 wt%, Al 0.01-0.05 wt%, N 0.005-0.025 wt%, Nb 0.02-
0.5% by weight, 0.002% by weight or less of O, the balance Fe, and 10Si + Mn + Cr ≤2.0, which has a C concentration of 0.7 to 0.9% by weight. Gears which have been carburized so that they are made of a material having an abnormal carburizing layer of 6 μm or less and a grain size of # 9 or more