JPH01108347A - Gear excellent in impact resistance - Google Patents

Abstract

PURPOSE:To obtain a gear excellent in impact resistance and having high reliability by subjecting a steel having a specific composition consisting of C, Si, Mn, P, S, Cr, Mo, Al, N, O, and Fe to tooth profile forming and then applying proper carburizing, hardening, and tempering to the above. CONSTITUTION:A steel having a composition which consists of, by weight, 0.10-0.30%, preferably 0.10-0.20%, C, <0.15%, preferably <0.10%, Si, 0.50-1.50%, preferably 0.50-0.80%, Mn, <0.015% P, <0.020%, preferably <0.005%, S, 0.50-1.50%, preferably 0.50-1.00%, Cr, 0.30-0.70% Mo, 0.010-0.050% Al, 0.005-0.025% N, <0.0015% O, and the balance essentially Fe and in which Mo/(10Si+100P+Mn+Cr) is regulated to >0.10, preferably 0.15, is used as a stock and subjected to tooth profile forming by means of cold forging. This gear body is subjected to carburizing, hardening, and tempering, by which effective hardening depth after the above treatment is regulated to 0.6-1.0mm in a region of >=550 Vickers hardness. Further, shot peening of 0.4-1.0A arc height is applied, if necessary.

Description

[Detailed description of the invention]

OBJECTS OF THE INVENTION - (Industrial Application Field) The present invention relates to gears that are used in machinery such as automobiles and particularly have excellent impact strength. (Prior Art) In recent years, there has been a strong desire for higher quality gears used in machinery. In particular, automobiles are becoming more powerful and lighter, and demands for higher strength and toughness are increasing. Under these circumstances, one of the inventors of the present invention previously proposed in Japanese Patent Application No. 128787/1987 the prevention of grain boundary oxidation by reducing Si, the increase in grain boundary strength by adding MO to reduce P, AJI,
We are proposing high-strength, high-toughness steel for gears based on measures such as grain refinement by adding N and Nb and increasing grain boundary strength by adding Ni. (Problem to be solved by the invention) However, power transmission gears for automobiles are being used in even more severe conditions as the gears themselves are becoming smaller as automobiles become more compact and lightweight. However, there have been cases where gears have been damaged by impact loads during rapid start-up, acceleration, or gear shifting processes, and there has been a need to develop gears with even higher toughness and strength. (Object of the Invention) The present invention has been made to solve the above-mentioned problems, and its purpose is to provide high toughness that will not break even when subjected to an impact load, and to provide reliable Our goal is to provide high quality gear.

[Structure of the invention]

(Means for Solving the Problems) With the aim of developing high-toughness gears, the inventors of the present invention have conducted intensive studies on not only alloy components but also gear manufacturing methods, heat treatment methods, etc., and have found that the toughness of carburizing steel Mo/(10Si+100P) newly discovered in steel as an evaluation index.
By using a material with a large ratio expressed by +Mn+Cr), applying heat treatment (1) surface work hardening with optimized conditions, and tooth forming by cold forging, we are able to create gears with extremely high impact strength. I've come to find out what I can do. The present invention is based on the above knowledge, and the gear according to the present invention has C: 0.10 to 0.30%, Si: 0.
Less than 15%, Mn 20, 50-1.50%%P: 0. O
Less than 15%, SiO, less than 020%, Cr: 0.50~
1.50%, Mo: 0, 30-0.70%, A
Sentence = 0.010-0.050%, N: 0.005-0.
025%, O: less than 0.0015%, remainder qualitatively Fe
and Mo/(10Si+100P+Mn+Cr) is 0, lO
Made of larger steel, with a Vickers hardness of 550
Carburizing and quenching to achieve an effective hardened layer depth of 0.6 to 1.0 mm, as well as shot peening to achieve an arc height of 0.4 to 1.0 A, if necessary. It is characterized by being Further, a more desirable gear in the present invention has C: 0.10 to 0.20%, Sl: less than 0.10%, in weight%.
Mn: 0.50 to 0.80%, P: less than 0.015%,
S: less than 0.005%, Cr: 0.50-1.00%,
Mo: 0.30-0.70%, A text: 0.010-0.
050%, N: 0.005-0.025%, 0:0.0
less than 015%, the remainder substantially consisting of Fe, and Mo/
(10Si+100P+Mn+Cr) is made of steel with a value larger than 0.15, and the effective hardened layer depth is 0.0000.
It is characterized by being carburized, quenched and tempered to a thickness of 6 to 1.0 mm, and shot peened to an arc height of 0.4 to 1.0A, if necessary. (Function) Next, the function and effect of each component in the present invention and the reasons for limiting the numerical values will be described. Mo/ (10Si+100P+Mn+Cr): 0.1
Greater than 0 As a result of careful study of various data obtained in the process of examining alloy components, the present inventor found that the toughness of case hardened steel can be summarized by the above parameters, and that there is a good correlation between the impact value and the above parameters. I found out that it shows. In other words, Figure 1 shows steels with various compositions being carburized and quenched (
The 10mm RC notch Charpy impact value when carburized at 91O℃, held at 830℃ and then quenched], tempered and air-cooled at 160℃ is calculated as M o / (lO5i + 100P + Mn
+cr) It can be seen that a good correlation is shown. In practical gears, when considering impact loads such as sudden starts, 2K steel is suitable for gears.
An impact value of about 7cm gf-m is required, and for that purpose M o / (10S i +100P+
Mn+Cr) The ratio expressed must be greater than 0.10, but if you want to ensure greater safety, for example, when forming the tooth profile by cold forging, the ratio should be 0.15.
It can be said that it is more desirable to make it larger. C: O, IO ~ 0.30% C requires 0.10% or more in order to maintain the strength of the outer part of the gear. However, if the C content is too high, the strength of the bottom part will become too high and the toughness will decrease, so it is limited to 0.30% or less. In addition, when forming by cold forging, the content is set to 0.20% or less in consideration of forgeability. Si: less than 0.15% St has a strong tendency to form oxides and promotes grain boundary oxidation, so it is desirable to have a lower content, but it is acceptable if it is less than 0.15%. In addition, when performing cold forging, from the point of view of forgeability,
．． Limited to less than 10%. Mn: 0, 50-1, 50% Mn is an effective component for improving hardenability, and 0.50% or more is required to maintain the core strength of the gear. On the other hand, if the amount is too high, the strength of the outer part becomes too high and the toughness decreases, and the tendency to form oxides increases and promotes grain boundary oxidation, so 1.50
%, but when forming a tooth profile by cold fIJim forming, it is necessary to keep it below O, aO% in order to ensure forgeability. P: Less than 0.015% P segregates at austenite grain boundaries during carburizing and heating and deteriorates the toughness of the carburized layer, so the lower the content, the better;
If it is less than ois%, it is practically acceptable. S i 0 , less than 0.020% S forms inclusions such as MnS and serves as a starting point for impact fracture, so the lower the content, the better, but if it is less than 0.020%, there is no substantial problem. However, when performing cold forging, the forgeability deteriorates, so the content should be less than 0.005%. Cr: 0.50-1.50% Like Mn, Cr improves hardenability and is added in an amount of 0.50% or more to maintain the strength of the outer part of the gear, but if it is added too much, the strength of the outer part becomes too high. Since it deteriorates toughness, the upper limit is set at 1.50%. Note that when cold forging is performed, the content is limited to 1.00% or less from the viewpoint of forgeability. Mo: 0.30~O. 70% Mo is an element that not only improves hardenability but also increases the toughness of the carburized layer and contributes to improving the impact resistance of gears.
At least 0.30% of the area exhibits this effect.
is necessary, but the effect no longer increases even if added in excess of 0.70%. Al: 0.010 to 0.050% N: 0.005 to 0.025% These elements form fine AJIN grains, have a function of refining austenite grains, and improve toughness. However, either Al or N4J- is 0.010%, 0
．． If the content is less than 0.005%, the above effects cannot be achieved, and if the content is less than 0.050% or 0.025%, respectively.
Addition of more than 10% does not increase the effect any further. 0: Less than 0.0015% O forms oxides and becomes a starting point for fatigue fracture, so a lower content is preferable, but if it is less than 0.0015%, there is no substantial problem. Effective hardening layer depth: 0.6 to 1.0 m Generally, only one surface layer of a gear is hardened to provide wear resistance and fatigue resistance, and the sixth part is carburized to provide toughness and ductility. It is used after being quenched and tempered. The present inventor has determined that the effect of the surface hardening treatment can be maximized by controlling the depth of the effective hardening layer (Vickers hardness of 550 or more) within the range of 0.6 to 1.0 mm. We have found that variations in performance as a product can be prevented.In other words, if the effective hardened layer depth is less than 0.6 mm, wear resistance and fatigue strength cannot be ensured, and conversely, if it exceeds 1.0 mm, impact resistance will decrease. This control can be performed by adjusting the carbon potential, carburizing/diffusion time, etc. Arc height = 0.4 to 1.0 A When increasing not only impact resistance but also fatigue strength. However, shot peening is effective when the arc height is less than 0.4A, and when it exceeds 1.0A, the toughness is rather reduced, so shot peening was limited to the above range. This refers to the height of deformation on the material surface caused by the deformation of the material surface, and is measured by an Almen strip, and this control can be performed by adjusting the shot grain, blasting speed, blasting time, coverage, etc. We have found that both fatigue strength and impact strength can be improved by forming fiber flow. When performing cold forging, we also take into account forgeability.
The range of each component of C, Si, Mn, S, and Cr is limited to a lower range. (Example) Steel having the alloy components shown in Table 1 is melted, rolled into a 90 mm diameter steel bar, normalized, and then machined or cold forged and machined to create a pitch circle diameter near 0 mm. , module: 2.5. Number of teeth = 28. Pressure angle: 2
The gears were processed into 0° gears, then carburized and quenched and tempered, and some of the gears were shot peened to obtain gear test pieces. This gear test piece was tested in a gear impact tester (hammer weight i: 138K) equipped with a hammer 1 and a moment arm 2 as shown in FIG.
g, pendulum length = 1.2 m. Maximum impact load: 4000Kg, maximum hammer speed: 3.
4m/5ec) and power circulation gear testing machine (rotation speed:
3500r, p, m, gear: module 2.5. Number of teeth:
28 and 32), the gear impact breaking load and gear fatigue limit were measured. In addition, carburizing and quenching reduces the carbon potential to 0.8~
0.9, carburized at 910°C for 3 hours, and diffused for 2.5 hours.
The standard conditions were oil cooling after holding at 830°C for 30 minutes, then air cooling after tempering at 160°C for 2 hours, and the effective hardened layer depth was adjusted mainly by changing the carburization and diffusion times. In addition, shot peening is performed using an impeller type processing machine, shot grains: 5B-6F, projection speed: 40~
80m/sec, projection time: 2 minutes, coverage 2300
% as the standard, and the arc height was adjusted mainly by changing the shot grain and projection speed. The arc height was measured using a commercially available Almen Strip A. These results are shown in Table 2. As is clear from the results shown in this table, examples 1 to 3 of the present invention
The gears have the appropriate alloy composition of the steel material and are heat-treated with an appropriate depth of effective hardening layer, so the impact breaking load and fatigue limit are both well-balanced.
Mo in steel / (10Si+100P+Mn+Cr)
Comparative Examples 4, 5, and 7 using Comparative Steels F, G, and I, which have a low ratio represented by This is the result. In addition, the 0 content is high and A! 2. ,N,l
In Comparative Example 6 using Comparative Steel H with a low . Furthermore, it is clear from Comparative Examples 8 and 9 that even when steel with appropriate composition is used, incorrect selection of carburizing and quenching conditions results in gears with an imbalance between impact breaking load and fatigue limit. In Examples 10 to 12 of the present invention in which shot peening was applied under appropriate conditions, the fatigue limit was particularly improved, but as seen in Comparative Example 14, excessive shot peening actually lowered the impact breaking load. The gears of Examples 15 and 16 of the present invention, which were cold-forged using steel E in a compositionally more desirable range, exhibited extremely excellent impact breaking load and fatigue limit, and were further shot-peened. It is clear from Examples 17 and 18 of the present invention that, although the impact rupture load is slightly lowered by applying this, the fatigue limit is further improved.

【Effect of the invention】

As explained above, the gear according to the present invention uses a material steel that is optimized in terms of alloy composition, and combines this with the most effective carburizing and quenching, surface work hardening treatment, and further tooth forming by cold forging. When applied to various types of machinery such as automobiles, it can be used to reduce size and weight, improve performance, and provide extremely high impact resistance and fatigue strength.
This has a great effect on increasing trustworthiness.

[Brief explanation of the drawing]

Figure 1 shows Mo/(10Si+100P+M n
+Cr) and impact toughness, i2
The figure is a schematic diagram showing a gear impact tester used for evaluating the impact resistance of gears in Examples of the present invention. Patent applicant Nissan Motor Co., Ltd. Patent applicant
Daido Steel Co., Ltd. Representative Patent Attorney Shio O
Barrel box 1

Claims (1)

[Claims] (1) In weight%, C: 0.10 to 0.30%, Si: 0
．． Less than 15%, Mn: 0.50-1.50%, P: less than 0.015%, S: less than 0.020%, Cr: 0.50-1.50%, Mo
: 0.30-0.70%, Al: 0.010-0.050%, N: 0.005-0.02
5%, 0: less than 0.0015%, the remainder substantially consists of Fe, and Mo/(10Si+100P+Mn+Cr) is 0.10
The material is made of larger steel, and the effective hardened layer depth after carburizing and quenching and tempering is 0.
A gear with excellent impact resistance, characterized by a diameter of 6 to 1.0 mm. (2) In weight%, C: 0.10-0.30%, Si: 0
．． Less than 15%, Mn: 0.50-1.50%, P: less than 0.015%, S: less than 0.020%, Cr: 0.50-1.50%, Mo
: 0.30-0.70%, Al: 0.010-0.050%, N: 0.005-0.02
5%, O: less than 0.0015%, the remainder substantially consists of Fe, and Mo/(10Si+100P+Mn+Cr) is 0.10
The material is made of larger steel, and the effective hardened layer depth after carburizing and quenching and tempering is 0.
6 to 1.0mm, and the arc height is 0.
．． A gear having excellent impact resistance, characterized by being shot peened to a value of 4 to 1.0A. (3) In weight%, C: 0.10-0.20%, Si: 0
．． Less than 10%, Mn: 0.50-0.80%, P: less than 0.015%, S: less than 0.005%, Cr: 0.50-1.00%, Mo
: 0.30-0.70%, Al: 0.010-0.050%, N: 0.005-0.02
5%, O: less than 0.0015%, the remainder substantially consists of Fe, and Mo/(10Si+100P+Mn+Cr) is 0.15
The teeth are formed by cold forging using a larger steel material, and the effective hardening layer depth after carburizing and tempering is 0.6 to 1.0 mm in the area of Vickers hardness of 550 or more. Gears with excellent impact resistance. (4) In weight%, C: 0.10-0.20%, Si: 0
．． Less than 10%, Mn: 0.50-0.80%, P: less than 0.015%, S: less than 0.005%, Cr: 0.50-1.00%, Mo
: 0.30-0.70%, Al: 0.010-0.050%, N: 0.005-0.02
5%, O: less than 0.0015%, the remainder substantially consists of Fe, and Mo/(10Si+100P+Mn+Cr) is 0.15
It is formed into a tooth shape by cold forging using larger steel as a material, and the effective hardening layer depth after carburizing and quenching and tempering is 0.6 to 1.0 mm in the area of Vickers hardness of 550 or more. A gear having excellent impact resistance, characterized by being shot peened to have an arc height of 0.4 to 1.0A.