DE102010003902A1 - Alloy steel for vacuum carburizing at low temperatures - Google Patents

Abstract

The present invention relates to an alloyed steel for vacuum carburizing at low temperatures, and more particularly to an alloyed steel for vacuum carburizing at low temperatures, when carrying out the heat treatment of vacuum carburizing and quenching at 810 ° C. or so of an available minimum carburizing temperature of a conventional vacuum carburizing furnace , it is possible to ensure a sufficient ferrite phase (α) to suitably improve a heat deformation due to the heat treatment of a ring gear and to suit the shape restrictions such as roundness or cylindricity of the ring gear to be produced appropriately. An alloyed steel according to the invention for vacuum carburizing at low temperatures, said alloyed steel consisting of a main element of Fe, said alloyed steel being formed such that dissolved oxygen (DO) in an alloy system containing 0.17 ~ 0.24 weight percent C , 0.8 ~ 1.2 wt% Cr, 0.4 ~ 0.8 wt% Mn, 0.80 ~ 1.20 wt% Si, 0.020 wt% or less P, 0.020 wt% or less S, 0.015 ~ 0.045 wt% V, and the like remaining weight percent of Fe is 10 ppm or less.

Description

Cross-reference to related applications

Pursuant to 35 USC §119 (a), the present application claims the benefit of Korean Patent Application No. 10-2009-0117993 filed on December 01, 2009, the contents of which are hereby incorporated by reference.

Background of the invention

Field of the invention

The present invention generally relates to an alloyed steel for vacuum carburizing at low temperatures, and more particularly to an alloyed steel for vacuum carburizing at low temperatures, wherein, when the heat treatment of vacuum carburizing and quenching is carried out at 810 ° C. or so of an available minimum carburizing temperature of a conventional vacuum carburizing furnace, is possible to ensure a sufficient ferrite phase (α) to suitably improve a heat deformation due to the heat treatment of a ring gear and to suit the shape restrictions of the ring gear to be produced, such as, but not limited to, the roundness or cylindricity suffice.

Description of the Prior Art

Generally, in gear-type components of a vehicular transmission, heat treatment of carburizing and quenching is usually performed. When the heat treatment of carburizing and quenching is performed, deformation of the components may occur. In certain cases where excessive deformation occurs, problems may arise in assembling the components or developing unusual noises.

1 shows an example of a known ring gear.

As in 1 is shown, a ring gear is a cylindrical component, wherein the ring gear is a main component of a planetary gear, which can be used as an essential power transmission system or drive system of an automatic transmission. The ring gear is preferably an internal gear whose teeth have been suitably machined by a broaching method. Since the ring gear has a large diameter and is thin, it is very susceptible to heat deformation. In addition, although the surface working of the teeth of a known external gear is easily performed after the heat treatment such as grinding or the like, the ring gear is one of the components whose processing after the heat treatment is difficult.

There are various heat treatment methods for a ring gear that involve heat deformation.

In order to minimize the heat distortion of the ring gear, for example, various methods of gas carburizing, furnace cooling, high frequency heating and quenching of a chuck have been used. By performing the final treatment of quenching a chuck, that is, by applying high-frequency heating, assembling the chuck, and then quenching, it is possible to satisfy the shape restrictions such as roundness, cylindricity, and the like.

However, the method described above involves a lengthy and expensive processing. In addition, since the procedure must be performed individually for each component, the efficiency of the treatment may decrease accordingly. Further, when the chuck is cooled, the shape of the teeth of the gear may be correspondingly unevenly deformed by local uneven cooling, and accordingly, development of abnormal sounds may occur.

Recently, methods of vacuum carburizing and gas quenching have been used which have considerable profitability and uniform cooling. It is thus possible to improve the noise caused by uneven deformation; in terms of shaping, such as roundness, cylindricity or the like, however, improvements are still required.

Accordingly, there is a need for new compositions and methods for vacuum carburizing at low temperatures.

The information disclosed in the background section above is merely for a better understanding of the background of the invention, and therefore, it may include information that is not prior art, as is already known to one of ordinary skill in the art in this country.

Brief summary of the invention

In one aspect, the present invention provides an alloyed steel for vacuum carburizing at low temperatures, wherein at 810 ° C or so of an available minimum carburizing temperature of a conventional vacuum carburizing furnace, it is possible to achieve a sufficient ferrite phase (α).

In preferred embodiments, the present invention provides an alloyed steel for vacuum carburizing at low temperatures, wherein the alloyed steel preferably consists of a major element of Fe, wherein the alloyed steel is formed such that dissolved oxygen (DO) in an alloying system containing 0.17 ~ 0.24 weight percent C, 0.8 ~ 1.2 weight percent Cr, 0.4 ~ 0.8 weight percent Mn, 0.80 ~ 1.20 weight percent Si, 0.020 weight percent or less P, 0.020 weight percent or less than S, 0.015~0.045 weight percent V, and the remaining weight percent of Fe comprises 10 ppm or less.

With the alloyed steel for low temperature vacuum carburizing of the present invention, in certain preferred embodiments, where the heat treatment of carburizing and quenching at 810 ° C. or the like of an available minimum carburizing temperature of a conventional vacuum carburizing furnace is performed, a sufficient ferrite phase (FIG. α) in order to suitably improve the heat distortion due to the heat treatment of the ring gear and to suitably satisfy the shape restrictions such as the roundness or cylindricity of the ring gear to be produced.

It is understood that the term "vehicle" or "vehicle" or any similar term as used herein refers to motor vehicles in general, such as passenger cars, including sports utility vehicles (SUVs), buses, trucks, various utility vehicles, Watercraft, including various boats and ships, airplanes, and the like, as well as hybrid vehicles, electric vehicles, hybrid electric hybrid vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (eg, fuels derived from non-petroleum resources).

As used herein, a hybrid vehicle refers to a vehicle that uses two or more sources of power, such as vehicles that are both gasoline powered and electrically powered.

The foregoing features and advantages of the present invention will become apparent from the accompanying figures, which are incorporated in and constitute a part of the specification, and the following detailed description, which together serve to exemplify the principles of the present invention are described in more detail in these.

Brief description of the figures

The above and other features of the present invention will be described in detail below with reference to certain exemplifying embodiments thereof illustrated in the attached figures, which are given below for purposes of illustration only and are not intended to limit the present invention applies:

1 is a perspective view illustrating a known ring gear of the prior art.

2 Fig. 13 is a view for explaining a concept of vacuum carburizing at low temperatures and showing a state of Fe-C (iron-carbon).

It should be understood that the appended drawings are not necessarily to scale but depict a somewhat simplified representation of the various preferred features which illustrate the principles of the invention. Particular design features of the present invention as disclosed herein, including, for example, particular dimensions, orientations, locations, and shapes, will be determined in part by the particular intended application and conditions of use.

Detailed Description of the Preferred Embodiments

As described herein, the present invention provides an alloyed steel for vacuum carburizing at low temperatures. The alloyed steel preferably contains mainly Fe.

In preferred aspects, the present invention provides an alloyed steel for vacuum carburizing at low temperatures, wherein the alloyed steel consists of a major element of Fe, the alloyed steel being formed such that dissolved oxygen (DO) in an alloy system containing 0, 17 ~ 0.24 weight percent C, 0.8 ~ 1.2 weight percent Cr, 0.4 ~ 0.8 weight percent Mn, 0.80 ~ 1.20 weight percent Si, 0.020 weight percent or less P, 0.020 weight percent or less S, 0.015~0.045 weight percent V and the remaining weight percent Fe comprises 10 ppm or less.

An alloyed steel for vacuum carburizing at low temperatures according to preferred embodiments of the present invention will be explained in detail.

The method of carburizing at low temperatures has been studied as a substitute for the conventional method of quenching a chuck with a view to improving the shape such as roundness, cylindricity or the like using the method of vacuum carburizing. 2 illustrates an example of a process of vacuum carburizing at low temperatures and shows a state of Fe-C (iron-carbon).

With reference to 2 For example, the carburizing process was carried out during the carburizing process at low temperatures in a temperature range between the two dual phases A1 ~ A3 in which an austenite phase (γ) and a ferrite phase (α) coexist. The method of carburizing at low temperatures accordingly improves the heat distortion because a certain amount of the ferrite phase (α) is suitably maintained without a phase change in temperature elevation and carburization of products and also in the quenching process. However, in the case of a vacuum carburizing furnace now mass-produced, mass production by means of carburizing at a temperature of 800~810 ° C is possible according to the characteristics of the apparatuses used. Therefore, in a case where a conventionally used carburizing material is carburized and quenched at an available carburizing temperature of 810 ° C, the heat deformation can not be sufficiently improved because the ferrite phase (α) can not be sufficiently ensured.

As shown in the following Table 1, the alloyed steel for vacuum carburizing at low temperatures according to preferred embodiments of the present invention consists of Fe and preferably Fe as a main component, the alloyed steel being formed such that dissolved oxygen (DO) is 10 ppm or less to a degree of purity of the alloy in an alloy system comprising 0.17 ~ 0.24 weight percent C, 0.8 ~ 4.2 weight percent Cr, 0.4 ~ 0.8 weight percent Mn, 0.80 ~ 1, 20 wt% Si, 0.020 wt% or less P, 0.020 wt% or less S, 0.015-0.045 wt% V, and the remaining wt% Fe to obtain (to reduce the level of impurities). <Table 1> Compositions of Alloys of the Steel of the Present Invention and a Conventional Comparative Steel (Unit of Proportion: Percent by Weight) classification C Cr Mn Si P S V O (ppm) Fe Steel of the invention 0.17 ~ 0.24 0.8 ~ 1.2 0.4 ~ 0.8 0.8 ~ 1.2 below 0.02 below 0.02 0.015 ~ 0.045 under 10 rest Comparative steel (SCr420H) 0.17 ~ 0.23 0.85 ~ 1.25 0.55 ~ 0.9 0.15 ~ 0.35 below 0.03 below 0.03 - under 25 rest

In preferred exemplary embodiments, the alloyed steel for vacuum carburizing at low temperatures in accordance with the present invention may be configured predominantly as follows.

The alloy steel of the present invention is designed to ensure a sufficient ferrite phase (α) at 810 ° C. or so of an available minimum carburizing temperature of a conventional vacuum carburizing furnace. Since the alloyed steel is configured such that a temperature A3 of the alloy steel of the present invention with reference to FIG 2 While this may preferably also ensure above 850 ° C, 30 ~ 50% of the ferrite phase (α) may also be present in a deep core of the alloyed steel during carburizing and quenching at 810 ° C ~ 830 ° C.

The alloyed steel according to the invention is explained in detail below.

In certain preferred embodiments, carbon (C) can make up a content of 0.17 ~ 0.24 weight percent so that sufficient hardness of the core is obtained after high frequency carburizing. In certain preferred embodiments, where the proportion is less than the normal amount, too much ferrite phase (α) is included, so that the hardness of the core decreases and, correspondingly, the hardness of the alloyed steel decreases. In certain examples where the proportion is more than the normal amount, too little ferrite phase (α) is contained, and therefore, it is insufficient to sufficiently improve the heat distortion.

Preferably, chromium (Cr), which is an essential element for enhancing the fatigue strength of a steel for gears, may account for 0.8 ~ 1.2 weight percent. Since chromium is the temperature A3 as well as the temperature of A1, referring to 2 , the amount of chromium is preferably restricted accordingly. In certain embodiments, more than 0.8 percent by weight of chromium is added to lower the temperature A1 accordingly and to suitably ensure fatigue strength; However, the amount is limited to 1.2 percent by weight, otherwise sufficient ferrite phase (α) corresponding to the lowered temperature A3 can not be ensured.

According to further preferred embodiments, manganese (Mn) may account for 0.4 ~ 0.8 weight percent, thereby reducing it compared to conventional carburizing steel.

Although manganese (Mn) may suitably increase the strength of the alloyed steel, the element may cause uneven heat distortion because it accordingly induces segregation during steelmaking. In particularly preferred embodiments, more than 0.4 weight percent manganese (Mn) is added to lower the temperature A1; however, the amount of manganese (Mn) is limited to 0.8 weight percent to reduce segregation.

In order to ensure a sufficient amount of the ferrite phase (α) by appropriately raising the temperature A3, it is preferable to increase the content of silicon (Si) and to add a sufficient amount of vanadium (V).

In further preferred embodiments, the silicon (Si) preferably constitutes 0.80 ~ 1.20 weight percent, so that the temperature A3 is suitably increased and also suitably increases the contact fatigue (pitting resistance) property. In certain exemplary embodiments, for example, when the content of silicon (Si) is smaller than the normal amount, since the temperature A3 is not sufficiently raised, it is difficult to secure a sufficient amount of the ferrite phase (α). Further, in a case where the content of silicon (Si) is more than 1.2% by weight is too strong a known solid solution hardening, so that the moldability excessively decreases and, accordingly, the forging process and the manufacturing process can become correspondingly heavy. The alloyed steel of the present invention is preferably suitable for a vacuum carburization treatment because the amount of silicon is very high compared to the conventional steel. In certain preferred embodiments where carburization is suitably carried out in a conventional gas carburizing furnace, oxide layers may be formed on the surface by the oxidizing atmosphere and the hardness of the alloyed steel may be correspondingly reduced.

According to further embodiments, the vanadium (V) is preferably 0.015~0.045 weight percent, so that the temperature A3 correspondingly increases and grain refining is further maximized. Since the vanadium (V) is an element for strengthening fine deposits, the amount of vanadium (V) in other preferred embodiments has been preferably restricted to more than 0.015 weight percent in order to suitably improve the hardness of the core according to the solidification of fine deposits, and as well increase the temperature A3. Further, the amount of vanadium (V) was limited to less than 0.045 weight percent because vanadium (V) is very expensive.

In other exemplary embodiments, the dissolved oxygen (DO) was formed at 10 ppm or less. Since the hardness of the core in the alloyed steel of the present invention is comparatively low to that of the conventional alloyed steel for carburizing, the required properties of a surface layer (a carburizing layer) are taken into account and, accordingly, the dissolved oxygen was restricted to 10 ppm or less. If the dissolved oxygen is more than 10 ppm, it may preferentially affect the occurrence of contact surface generation.

Examples

The following Table 2 shows the chemical compositions and the deformation temperature of the essential phase of the alloy steel of the present invention and the comparative steel. <Table 2> classification Chemical ingredient (percent by weight) Deformation temperature of the phase (° C) available carburizing temperature (° C) C Cr Mn Si P S V O (ppm) Fe A1 A3 Steel of the invention 0.22 1.0 0.6 1.1 0,015 0.01 0.04 8th rest 761 852 770 ~ 840 Comparative steel (SCr420H) 0.2 1.1 0.8 0.2 0,015 0,015 - 17 rest 743 803 755 ~ 790

In the case of the comparative steel as conventional steel, when it is carburized at 810 ° C. or so of an available minimum carburizing temperature of a conventional vacuum carburizing furnace, it can be predicted that there will be no ferrite phase (α) since it is in the range of a single phase of austenite Phase (γ) is carburized above the temperature A3. In the case of the alloy steel of the present invention, a sufficient amount of the ferrite phase (α) can be secured, and therefore the heat distortion can be improved.

The comparative examples are shown in the following Table 3, each carburized at an actual temperature of 810 ° C. <Table 3> classification Conditions of heat treatment Physical properties for the heat treatment Average size after heat treatment (μm) Remarks Hardness (Hv) (surface e / deep core) the amount of α in the core (%) roundness cylindricity Embodiment (steel of the invention) Vacuum carburizing (810 ° C) → high-pressure gas cooling (130 bar, helium) 730/340 about 35 38 42 Carburizing the steel of the invention at low temperatures Comparative Example (Conventional Steel) 1 760/390 about 2 53 72 Carburizing the conventional steel at low temperatures 2 Gas carburizing (920 ° C) → furnace cooling → high-frequency heating → quenching of a clamping device (oil cooling) 750/400 0 36 40 Quenching of the clamping device * Test component used: Rear ring gear of a 6-speed automatic transmission (The inner diameter of the gear is, according to IBD: 122.45 mm (gear of Fig. 1) * The average size after the heat treatment is an average of 20 test products.

In certain examples where the alloy steel of the present invention was suitably subjected to vacuum carburizing at a low temperature at a temperature of 810 ° C, it was shown that the heat deformation after the heat treatment is higher than that of the conventional steel in which the same heat treatment was performed, was significantly improved. In the case of the conventional carburizing material, the deep core ferrite phase (α) was not sufficiently ensured during carburizing at this temperature. In the case of the alloy steel of the present invention, the ferrite phase (α) was sufficiently ensured.

Besides, the result almost corresponded to that of the conventional method of quenching the jig.

As described above, the alloy steel for vacuum carburizing at low temperatures according to the present invention is capable of a case where the heat treatment of carburizing and quenching is performed at 810 ° C. or so of an available minimum carburizing temperature of a conventional vacuum carburizing furnace to ensure a sufficient ferrite phase (α) in order to improve the heat deformation due to the heat treatment of a ring gear and to satisfy the shape restrictions such as the roundness or the cylindricity of the ring gear to be produced.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• KR 10-2009-0117993 [0001]

Claims (5)

Alloyed steel for vacuum carburizing at low temperatures, the alloyed steel consisting of a major element of Fe, the alloyed steel being formed such that dissolved oxygen (DO) in an alloying system containing 0.17 ~ 0.24 weight percent C, 0 , 8 ~ 1.2 weight percent Cr, 0.4 ~ 0.8 weight percent Mn, 0.80 ~ 1.20 weight percent Si, 0.020 weight percent or less P, 0.020 weight percent or less S, 0.015 ~ 0.045 weight percent V, and the remaining weight percent at Fe, 10ppm or less. Alloy steel for vacuum carburizing at low temperatures, wherein the alloyed steel is 0.17 ~ 0.24 weight percent C, 0.8 ~ 1.2 weight percent Cr, 0.4 ~ 0.8 weight percent Mn, 0.80 ~ 1.20 Weight percent Si, 0.020 weight percent or less P, 0.020 weight percent or less S, 0.015 ~ 0.045 weight percent V, and the remaining weight percent of Fe. The low temperature vacuum carburizing alloy steel according to claim 2, wherein the alloyed steel is formed such that the dissolved oxygen (DO) is 10 ppm or less. An alloyed steel for vacuum carburizing at low temperatures, wherein the alloyed steel contains Fe, wherein the alloyed steel is formed such that the dissolved oxygen (DO) is 10 ppm or less. An alloyed steel for low temperature vacuum carburizing according to claim 4, wherein said alloy is 0.17 ~ 0.24 weight percent C, 0.8 ~ 1.2 weight percent Cr, 0.4 ~ 0.8 weight percent Mn, 0.80 ~ 1 , 20 wt% Si, 0.020 wt% or less P, 0.020 wt% or less S, 0.015-0.045 wt% V, and the remaining wt% Fe.

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