JP7163642B2 - Carburizing and quenching equipment and carburizing and quenching method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carburizing and quenching apparatus and a carburizing and quenching method.

It is known that the hardness of steel is improved by dissolving carbon therein. On the other hand, since steel can only dissolve up to 0.02% of carbon at room temperature, it is necessary to raise the temperature to 900°C or higher to transform the phase of steel into the austenite phase and dissolve carbon. . After that, in the quenching treatment, the steel is transformed into the martensitic phase by quenching from a high temperature, and the steel with improved hardness can be used at room temperature while the carbon remains dissolved in the crystal. For this reason, a carburizing and quenching method in which a step of carburizing treatment at a high temperature, followed by a cooling step in which the temperature is lowered to a temperature suitable for quenching treatment, and a step of performing quenching are performed in succession is generally often practiced.

As an improvement of such a carburizing and quenching method, for example, Patent Document 1 discloses a carburizing and quenching method that can obtain carbon steel having an austenite grain size of #10 or more while being a non-forged product of a raw material made of low-carbon steel. is disclosed. In this method, carburizing is performed by heating to the austenitizing temperature or higher in the first step, cooling to below the austenitizing temperature in the second step, and rapid heating to just above the austenitizing temperature again in the third step to obtain austenite crystals. The grains are finely controlled, and quenching is performed in the fourth step. High-frequency contour heating is recommended for heating in the third step (reheating step). When held at a high temperature, crystal grains grow according to the holding time, but rapid heating in a short time by high-frequency contour heating suppresses the growth of austenite crystal grains and improves the strength characteristics by refining the crystal grains. This is because the improvement effect can be maximized.

JP-A-2005-48292

The inventors of the present invention believe that since high-frequency contour heating requires new equipment investment, when mass production is performed based on the method of Patent Document 1 using a carburizing furnace, the obtained parts usually It was found that the dimensional accuracy is lower than that of carburizing and quenching. Specifically, in the method of Patent Document 1, as shown in FIGS. 6 and 7, a plurality of parts 102 are placed on each tray 101 and conveyed between heating sources (continuous carburizing furnaces) 103 on both sides. However, when the plurality of parts were subjected to the third step (reheating step) at the same time, the dimensional accuracy was lowered. FIG. 6 is a schematic plan view showing the third step (reheating step) when mass production is performed using existing heating equipment in a conventional carburizing and quenching apparatus. FIG. 7 shows a tray and a plurality of parts placed and conveyed on the tray in the third step (reheating step) when mass production is performed using existing heating equipment in a conventional carburizing and quenching apparatus. 1 shows a schematic side view of FIG.

Specifically, heating by a continuous carburizing furnace requires a long time for heating compared to high-frequency contour heating. The longer the heating time, the larger the crystal grains grow. The larger the crystal grains, the higher the hardenability and the larger the volume expansion due to the transformation of the austenite phase to the martensite phase.
For this reason, for example, there is a difference in the heating rate between a part near the heat source and a part far from the heat source, which causes a difference in the growth time of crystal grains. varied greatly.
Also, for example, even in one part, the surface near the heat source and the surface far from the heat source have different heating rates, different crystal grain growth times, and different amounts of deformation. As a result, the generated heat treatment strain increased and the amount of deformation increased in the obtained parts.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a carburizing and quenching apparatus and a carburizing and quenching method that can mass-produce parts with sufficiently excellent dimensional accuracy at sufficiently low cost.

The present invention
An apparatus for carburizing and quenching parts made of steel, comprising:
The carburizing and quenching device includes a tray for placing and transporting the plurality of parts,
The tray relates to a carburizing and quenching apparatus having a shielding plate between the plurality of parts and a heat source for shielding radiant heat from the heat source.

The present invention also provides
A method for carburizing and quenching a part made of steel, comprising:
Using a tray for placing and transporting the plurality of parts,
The tray relates to a carburizing and quenching method, wherein the tray has a shield plate between the plurality of parts and the heat source for shielding radiant heat from the heat source.

In the case of refining crystals or preventing coarsening by the heat history given to parts after carburizing, the carburizing and quenching apparatus and the carburizing and quenching method of the present invention can be processed at the same time even if mass production is performed using a carburizing furnace. It is possible to sufficiently prevent the difference in the amount of heat treatment deformation from increasing between a plurality of parts and between a surface near the heat source and a surface far from the heat source in each part. As a result, it is possible to more sufficiently prevent a decrease in dimensional accuracy between the plurality of parts obtained.
The carburizing and quenching apparatus and the carburizing and quenching method of the present invention are sufficiently superior in terms of cost performance because they are mass-produced using existing equipment that is indispensable for carburizing and quenching.

FIG. 4 is a schematic plan view showing an example of a third step (reheating step) when mass production is performed using existing heating equipment in the carburizing and quenching apparatus of the present invention. FIG. 4 is a schematic plan view showing another example of the third step (reheating step) when mass production is performed using existing heating equipment in the carburizing and quenching apparatus of the present invention. FIG. 10 is a schematic plan view showing still another example of the third step (reheating step) when mass production is performed using existing heating equipment in the carburizing and quenching apparatus of the present invention. Schematic showing a tray and a plurality of parts placed on the tray and conveyed in the third step (reheating step) when mass production is performed using existing heating equipment in the carburizing and quenching apparatus of the present invention. A side view is shown. FIG. 4 shows a schematic plan view showing the third step (reheating step) in the carburizing and quenching apparatus of the example. The heat pattern in each step of the carburizing and quenching apparatus of the example is shown. Evaluation results of a plurality of parts obtained by the carburizing and quenching apparatus of the example are shown. FIG. 4 is a cross-section of the continuous furnace in the carburizing and quenching apparatus of the example, showing a schematic cross-sectional view when the inside of the continuous furnace is viewed from the front in the conveying direction of the tray. The schematic plan view which shows the 3rd process (reheating process) in the carburizing hardening apparatus of a comparative example is shown. The evaluation results of a plurality of parts obtained by the carburizing and quenching apparatus of the comparative example are shown together with the evaluation results of the example. The heat pattern in each step of the carburizing and quenching apparatus of the reference example is shown. The evaluation results of a plurality of parts obtained by the carburizing and quenching apparatus of the reference example are shown together with the evaluation results of the example. A schematic plan view showing a third step (reheating step) when mass production is performed using existing heating equipment in a conventional carburizing and quenching apparatus. Schematic side view showing a tray and a plurality of parts placed on the tray and conveyed in the third step (reheating step) when mass production is performed using existing heating equipment in a conventional carburizing and quenching apparatus Figure shows.

The carburizing and quenching apparatus of the present invention is an apparatus excellent in mass productivity for processing a plurality of parts made of steel. Steel is an alloy of iron that contains carbon. ). Preferred steels are special steels, especially chromium steels.

The parts to be treated by the carburizing and quenching apparatus of the present invention may be parts and products that require strength, particularly strength and dimensional accuracy, such as automotive parts. Automobile parts are preferably power transmission parts from the viewpoint that higher strength and higher dimensional accuracy are required. Examples of power transmission parts include gears (gears), shafts (including those integrated with gears), sprockets, and the like. In the present invention, it is possible to more effectively achieve both strength and dimensional accuracy in the final reduction drive gear shaft of a manual transmission, which requires high strength.

The carburizing and quenching apparatus of the present invention normally carries out a first step of carburizing, a second step of cooling, a third step of heating, and a fourth step of hardening. When the carburizing and quenching apparatus of the present invention includes gas carburizing means as the carburizing treatment means as described later, the carburizing and quenching apparatus may include a continuous gas carburizing furnace. A continuous gas carburizing furnace is a furnace for carburizing, and can continuously perform the first to third steps, preferably the first to fourth steps.

The first step is a carburizing step, in which a plurality of parts are heated above the austenitizing temperature to carburize them. Carburizing is a heat treatment that causes carbon to form a solid solution in the material. From the viewpoint of strength, carburizing is preferably carried out so that the surface carbon concentration is set near the eutectoid point (0.7 to 0.9%).

As carburizing means, gas carburizing, vacuum carburizing, plasma carburizing, or the like is appropriately used. Carburizing is preferably gas carburizing or vacuum carburizing from the viewpoint of cost and mass productivity. Particularly in the case of gas carburizing, the heating temperature is not particularly limited as long as the carburizing reaction occurs, and from the viewpoint of productivity, it is preferable to use a high temperature as long as the melting point of the material is not exceeded. On the other hand, from the viewpoint of quality, the crystals of steel exposed to high temperatures for a long period of time become coarse, impairing the mechanical properties. For example, when obtaining a power transmission part (especially a gear shaft for driving the final reduction of a manual transmission), from the viewpoint of compatibility between productivity and mechanical properties (strength), the heating temperature is set, for example, to the austenitizing temperature of Tos (° C. ), it may be Tos+120 to Tos+180 (° C.), particularly Tos+140 to Tos+160 (° C.). Heating can be achieved by adjusting the temperature within the furnace (eg, the temperature of the carburizing zone in a continuous gas carburizing furnace).

The second step is cooling below the austenitizing temperature. By performing austenitization again by cooling in this step and heating in the third step described later, the austenite crystal grains that have been exposed to high temperatures for a long time during carburization are reprecipitated, thereby refining the austenite grains. (Austenite grain size is #10 or more) can be realized. As a result of these, the strength is more sufficiently improved as compared with the case where the second step and the third step are not performed.

The cooling temperature is usually Tos1-400 to Tos1-600 (°C), particularly Tos1-500 to Tos1-580 (°C), where Tos1 (°C) is the austenitizing temperature at the surface carbon concentration after carburization. The time required for cooling to such a cooling temperature (cooling time) may generally be 30 to 10 minutes. However, at this time, rapid cooling cannot be performed because strain due to martensitic transformation occurs if rapid cooling is performed. Cooling can be achieved by preparing a cooling chamber, filling it with an inert gas at normal temperature such as nitrogen, and stirring. In the above cooling temperature range, Tos1 may be the austenitizing temperature Tos of the steel material of the part to be subjected to the carburizing and quenching apparatus and carburizing and quenching method of the present invention.

The third step is heating above the austenitizing temperature, especially just above the austenitizing temperature. Assuming that the non-carburized part is quenched, the heating temperature is generally Tos2 + 20 to Tos2 + 60 (°C), especially Tos2 + 30 to Tos2 + 50 (°C), where Tos2 (°C) is the austenitizing temperature at the material carbon concentration. It is preferable to As the set temperature of the equipment, it is preferable to set the temperature slightly higher than this temperature in order to quickly heat the cooled processed product, specifically Tos2+50 to Tos2+100 (° C.), especially Tos2+60 to Tos2+80. (°C). In particular, it is necessary to lower the temperature below the carburizing temperature. The time required for heating to such a heating temperature (heating time) is the time to sufficiently complete the transformation to the austenite phase. minutes to 30 minutes. Heating can be achieved by adjusting the temperature within the furnace (eg, the temperature of the heating zone within a continuous gas carburizing furnace). By such heating, the austenite crystal grains are further and sufficiently refined, so sufficient strength is ensured. In the above heating temperature range and set temperature range, Tos2 may be the austenitizing temperature Tos of the steel material of the part subjected to the carburizing and quenching apparatus and carburizing and quenching method of the present invention.

For example, as shown in FIG. 1A, the carburizing and quenching apparatus of the present invention has heating means (heating sources) 3 for this step on both sides in the conveying direction C of trays 1 to be described later. As a heating means, existing heating equipment such as an electric heater heating furnace and a gas burner heating furnace can be used. In the present invention, even when such existing heating equipment is used, a plurality of parts having sufficient strength and excellent dimensional accuracy can be obtained. FIG. 1A shows a schematic plan view showing an example of the third step (reheating step) when mass production is performed using existing heating equipment in the carburizing and quenching apparatus of the present invention.

In the third step, the plurality of parts 2 placed on each tray is usually processed while continuously advancing two or more trays. For example, for two trays that advance continuously, the processing of a plurality of components placed on the front tray 1 in the transport direction C and the processing of a plurality of components placed on the rear tray 1 are continuous. Equivalent to processing. Further, for example, the processing of a plurality of components placed on the same single tray 1 corresponds to simultaneous processing.

In the third step, as shown in FIG. 1A, a plurality of trays 1 are usually advanced adjacent to each other, but they may be advanced at predetermined intervals. In the present invention, it is preferable that the plurality of trays 1 be adjacent to each other in the third step. As will be described later, even if the shielding plate 10 has a shape that is open in the direction opposite to the conveying direction C in a plan view, the two adjacent trays 1 may be placed on the front side of the rear tray 1 in the conveying direction C. This is because the shielding plate 10b also shields the radiant heat from the plurality of parts of the tray 1 in front. "Adjacent" means not only "in contact" with each other as shown in FIG. 1A, but also in a "separated state" with a narrower interval than other processes (for example, 100 mm or less, especially 10 to 50 mm). It also includes relationships.

When advancing a plurality of trays 1 adjacently in the third step, for example, as shown in FIGS. speeds up and exits the third process section, and then slows down (returns). At the same time, the new tray 1'''' speeds up to enter the third step and then slows down to advance next to the preceding tray 1'''. 1A to 1C are schematic plan views showing an example of changes over time in the third step (reheating step) when mass production is performed using existing heating equipment in the carburizing and quenching apparatus of the present invention. show. In FIGS. 1A to 1C, the length of the arrow indicating the conveying direction (advancing direction) C also indicates the magnitude of the speed.

The fourth step is a step of quenching. Quenching is performed for the purpose of obtaining the martensite phase by quenching the austenite phase. Lattice defects are generated in the crystal when the martensite phase is transformed, so the temperature becomes room temperature while carbon is forced into a solid solution. As a result, a high-hardness steel in which a large amount of carbon is solid-dissolved can be obtained, and the strength of the treated product can be improved.

In the quenching treatment (rapid cooling), it is essential to rapidly cool the austenite phase. To that end, quenching is accomplished by contacting the treated article with a cooling agent. For example, the coolant can be water, quenching oil, salt, inert gas such as high pressure nitrogen.

The method of supplying the coolant is not particularly limited as long as the surface of the component and the coolant come into contact with each other. It can be a method. From the viewpoint of further improving the strength of the parts by uniform treatment, it is preferable to adopt a method of immersing the parts in a bath filled with a coolant.

In the present invention, it is preferable to perform quenching treatment in the fourth step after soaking in the third step. Soaking means to keep the entire processed product uniformly at a temperature suitable for quenching. Here, the temperature suitable for quenching means that in order for the treated product to be in the austenite phase, it must be above the austenitizing temperature of the material, and in addition, it must be as low as possible to suppress the generation of thermal stress that causes heat treatment strain. It is necessary.

In the present invention, it is preferable to perform the quenching treatment in the fourth step after the temperature is lowered to a temperature suitable for the quenching treatment (for example, 830° C.) by soaking in the third step. By lowering the temperature to a temperature (830° C.) suitable for quenching treatment, thermal stress is not generated more than necessary, thereby aiming to reduce heat treatment deformation. The temperature suitable for the quenching treatment is usually Tos2+10 to Tos2+50 (°C), especially Tos2+20 to Tos2+30 (°C), where Tos2 (°C) is the austenitizing temperature at the material carbon concentration, assuming the quenching of the non-carburized portion. is. The time required for cooling to such a temperature (cooling time) may generally be 20 minutes or longer. Cooling can be achieved by adjusting the temperature within the furnace (eg, the temperature of the cooling zone within a continuous gas carburizing furnace). In the temperature range suitable for the quenching treatment, Tos2 may be the austenitizing temperature Tos of the steel material of the part subjected to the carburizing quenching apparatus and the carburizing quenching method of the present invention.

In the present invention, soaking is preferably performed at a temperature suitable for quenching treatment (for example, 830° C.) in the third step. Immediately after the temperature lowering step described above, temperature variations are likely to occur due to the heat of the parts (workpieces) and trays with different temperatures adjacent to each other in the furnace. By soaking this for a sufficient time, the temperature variation before the start of quenching, here, the variation between the parts loaded on the processing tray and the variation occurring inside the part, can be reduced. The purpose is to reduce the speed variation. During soaking at this temperature, it is necessary to set the surface carbon concentration near the eutectoid point (0.7 to 0.9%) so that decarburization does not occur. Moreover, you may carry out in an ammonia atmosphere. As a result, the effect of suppressing the formation of an abnormal surface layer due to carbonitriding can be obtained, and the effect of suppressing breakage from the surface can be obtained.

The carburizing and quenching apparatus of the present invention includes a tray 1 for placing and transporting a plurality of parts. In the present invention, the plurality of parts are placed on the tray 1 in at least the third step, preferably the first to third steps, more preferably the first to fourth steps in the carburizing and quenching apparatus, and the tray 1 is placed. It is supplied to a predetermined process while being conveyed by advancing. The number of trays 1 is not particularly limited as long as a plurality of components are placed and conveyed per tray, and may be one or two or more. From the viewpoint of mass production, it is preferable to use two or more trays, particularly three or more trays.

The tray 1 has a shielding plate 10 erected on the tray. At least in the third step, the shield plate shields radiant heat from the heat source between the plurality of components placed on the tray and the heat source. As a result, in at least the third step, not only between the part near the heat source and the part far from the heat source, but also between the surface near the heat source and the surface far from the heat source in one part, uniform Heat treatment is possible. For this reason, the difference in heating rate and the difference in crystal grain growth time are reduced between them, and as a result, the deformation amounts are more sufficiently equal among the plurality of parts obtained, and the dimensional accuracy is improved. On the other hand, if the shielding plate is not formed on the tray but is formed on the main body of the carburizing and quenching apparatus to block radiant heat from the heat source to the parts, the shielding plate itself is heated by the heat source and becomes a new heat source. Since radiant heat is emitted, uniform heat treatment cannot be performed.

As shown in FIG. 1A, the tray 1 has a shielding plate 10 so that the plurality of components 2 (in particular, all of the plurality of components 2) placed on the tray 1 are surrounded by the shielding plate 10 in plan view. is doing. As shown in FIG. 1A, when two or more trays 1 are used, each of the trays 1 has a plurality of parts 2 (especially all of the parts 2) placed on the tray 1 as a shielding plate in plan view. It is preferable to have the shielding plate 10 so that it is surrounded by the . A plan view refers to a state in which a tray on which a plurality of articles are placed is placed on a horizontal surface and viewed from directly above in the height direction, and is the same as a plan view. The shielding plate 10 may surround the sides of the tray 1 without gaps.

That the plurality of components 2 (particularly all of the plurality of components 2) placed on the tray 1 is surrounded by shielding plates in plan view means that at least in side view (two side views) (see, for example, FIG. 2), preferably means that all of the plurality of parts are hidden by the shield plate in side view (two side views) and front view. A side view is a horizontal direction in which a tray on which a plurality of articles are placed is placed on a horizontal plane, and is a direction perpendicular to the conveying direction (i.e., advancing direction) C of the tray (see FIG. 1A). ) (for example, FIG. 2), which is the same as the side view. Therefore, in the side view, there are two side views from both sides (D) of the conveying direction (that is, advancing direction) C. As shown in FIG. A front view is a state when a tray on which a plurality of articles are placed is placed on a horizontal surface and viewed in a direction opposite to the conveying direction (that is, advancing direction) C of the present invention, and is the same as the front view. is. Placement is placement with the surface (flat surface) having the largest area constituting the appearance of the tray as the bottom surface. It should be noted that the tray 1 does not necessarily have to have an external shape consisting of planes. As long as a plurality of parts can be placed on the tray 1, from the viewpoint of uniformity of heat treatment and easiness of treatment in the case of performing rapid cooling treatment with a coolant in the fourth step, for example, as described later, a flat surface is used. It preferably has a mesh shape in appearance.

The shape of the shielding plate 10 is not particularly limited as long as it surrounds the plurality of components 2 placed on the tray 1 in plan view. The shielding plate 10 may have, for example, a closed shape or an open shape in a direction opposite to the conveying direction C in plan view. That the shielding plate 10 has a closed shape in plan view means that the shielding plate 10 has a cylindrical shape as a whole. The tubular shape may be a cylindrical shape or a polygonal tubular shape such as a rectangular tubular shape. That the shielding plate 10 has a shape that opens in a direction opposite to the conveying direction C in a plan view means that the overall cylindrical shape of the shielding plate 10 has, for example, as shown in FIGS. 1A to 1C and 3A. , a shape in which part or all of the side opposite to the conveying direction C is missing. The cylindrical shape before chipping may be a cylindrical shape, or may be a polygonal cylindrical shape such as a rectangular cylindrical shape. For example, the plan view shape of the shielding plate 10 shown in FIG. It is a shape in which the entire opposite side is missing. The shielding plate 10 having such a plan view shape shown in FIG. 1A has side shielding plates 10a and 10c and a front shielding plate 10b. FIG. 3A shows an example of a schematic plan view showing the third step (reheating step) in the carburizing and quenching apparatus of the present invention, and specifically shows the shielding plate and parts placed on the tray.

The shielding plate 10 having a shape that opens in the direction opposite to the conveying direction C in a plan view is particularly effective in the case where a plurality of trays 1 advance adjacently in the third step, as described above. be. For example, when two trays 1 advance side by side, the front side shielding plate 10b of the rear tray 1 in the transport direction C also shields the radiant heat from a plurality of components placed on the front tray 1. The amount of material used for the shielding plate can be saved.

The height H (see FIG. 2) of the shield plate 10 is not particularly limited as long as uniform heat treatment is achieved, and may be, for example, equal to or higher than the height of the parts 2 stacked. From the viewpoint of more uniform heat treatment, the height of the shielding plate 10 is preferably 1.0×h to 1.2×h, more preferably 1.0×h to 1.2×h, where h (mm) is the stacked height of the component 2. is between 1.0×h and 1.1×h. Even if the height of the shielding plate 10 is too high, it is difficult to achieve a more uniform heat treatment.

The thickness of shielding plate 10 is not particularly limited as long as uniform heat treatment (especially refinement of crystal grains) is achieved. The thickness of the shielding plate 10 is preferably 2 to 8 mm, more preferably 4 to 6 mm, from the viewpoint of more uniform heat treatment (especially further refinement of crystal grains). By setting the shielding plate 10 to such a thickness, the shielding plate 10 has an appropriate heat capacity and heating time is avoided, which is preferable from the viewpoint of further miniaturization of crystal grains.

The material constituting the shielding plate 10 is not particularly limited as long as it can shield the radiant heat, and it is essential that it sufficiently withstands the carburizing temperature, which is the highest temperature during processing. Examples of the material forming the shielding plate 10 include martensitic, ferritic, austenitic, and precipitation hardened heat-resistant steels and stainless steels. Among others, the shielding plate 10 is preferably made of austenitic heat-resistant steel. Austenitic steel does not undergo transformation due to temperature, has good heat resistance, has low magnetic permeability, and has a high radiant heat shielding effect, so that heat treatment deformation can be effectively suppressed.

The material constituting the tray 1 is not particularly limited as long as it can hold the parts over the first to fourth steps, and examples thereof include martensitic, ferritic, austenitic, and precipitation hardened heat resistant steels. . Among them, the tray 1 is preferably made of austenitic heat-resistant steel.

In the tray 1, no members are arranged on the top and bottom of the tray 1, that is, above the plurality of components 2 and below the tray 1 when the plurality of components 2 are placed on the tray 1. preferable. In the fourth step, when performing a rapid cooling treatment with a coolant, more uniform quenching is achieved without blocking the supply of the coolant to the surface of the part or blocking the flow of the coolant during immersion. This is because the strength of the parts can be further improved. The drive for transporting the trays may be carried out, for example, on the furnace side, in which case no members for transporting the trays 1 may be arranged below the trays 1, or A guide or the like may be arranged.

The tray 1 preferably has a mesh shape in plan view from the viewpoint of uniformity of heat treatment and easiness of treatment when rapid cooling with a coolant is performed in the fourth step. The fact that the tray 1 has a mesh shape means that it has a lattice shape in plan view, as shown in FIG. 3A, for example. The lattice shape may be any lattice shape. For example, as shown in FIG. triangular lattice shape), parallel lattice shape, and the like.

Arrangement of the plurality of components 2 on the tray 1 is not particularly limited as long as a uniform heat treatment is achieved, and is usually a uniform arrangement. The plurality of components 2 may be arranged at the positions of lattice points, for example, when the tray 1 is assumed to have a lattice shape in plan view. When the tray 1 actually has a lattice shape in plan view as shown in FIG. 3A, it is preferable that the trays are arranged at the positions of the actual lattice points.

When the tray 1 has a lattice shape in plan view, the thickness t1 (see FIG. 3A) of the material forming the lattice shape in plan view is such that uniform heat treatment (especially refinement of crystal grains) is achieved. is not particularly limited. The thickness is preferably 2 to 8 mm, more preferably 4 to 6 mm, from the viewpoint of more uniform heat treatment (especially further refinement of crystal grains). By making the material constituting the lattice shape have such a thickness in plan view, the tray 1 has an appropriate heat capacity, and prolonged heating is avoided, so from the viewpoint of further refinement of the crystal grains. preferable.

When the tray 1 has a grid shape in plan view, the thickness t2 (see FIG. 2) of the material forming the grid shape in a side view is determined by the placement (holding) of the plurality of parts 2 and the uniform heat treatment ( In particular, it is not particularly limited as long as the refinement of crystal grains is achieved. The thickness is preferably 5 to 50 mm, more preferably 10 to 30 mm, from the viewpoint of more uniform heat treatment (especially further refinement of crystal grains). By making the material constituting the lattice shape have such a side view thickness, the tray 1 has an appropriate heat capacity, and a long heating time is avoided, so from the viewpoint of further refinement of the crystal grains. preferable.

Auxiliary tools may be used to place the plurality of components 2 on the tray 1 . For example, as shown in FIG. 2, when the component 2 has a cylindrical shape (or columnar shape), a cylindrical assisting tool 11 having an inner diameter larger than the outer diameter of the shape is fixed to the tray 1 in advance. , the placement may be achieved by inserting the part 2 into the aid 11 concerned.

In the carburizing and quenching apparatus and the carburizing and quenching method of the present invention, when reheating is performed in the third step after cooling in the second step, the obtained parts have more sufficient strength.

<Example 1>
A plurality of gear shafts (shafts integrally provided with gears; forgings) (hereinafter simply referred to as “parts”) of the same shape made of case-hardened steel (equivalent to SCR420) with the following composition were carburized and quenched. . The austenitizing temperature Tos of this material was 800°C. The loading height h of the parts was 280 mm.
composition:
C: 0.13-0.18%, Si: 0.15-0.35%, Mn: 0.6-0.85%, P: 0.03% or less, S: 0.03% or less, Cr : 0.9-1.2%.

Specifically, using a continuous gas carburizing furnace, a first step (S1 ), the second step (S2) of cooling below the austenitizing temperature, the third step (S3) of heating again to the austenitizing temperature or higher, and the fourth step (S4) of quenching.

In more detail, it was as follows.
As shown in FIG. 3A, the transport of a plurality of components by the tray 1 was performed by continuously advancing three trays on which 20 components 2 were placed per tray 1. As shown in FIG. The shield plate 10 used an austenitic stainless steel plate with a plate thickness of 5 mm. The height H of the shielding plate 10 was 1.1×h with respect to the stacking height h of the parts on the tray. The tray 1 had a rectangular lattice shape in plan view, and the thickness t1 in plan view of the material forming the lattice shape was 15 mm, and the thickness t2 in side view was 40 mm. The material constituting the tray 1 was austenitic heat-resistant steel.
The continuous gas carburizing furnace had heating sources on both sides of the tray in the portion (zone) corresponding to the third step. The heating source was an electric heater, arranged as shown in FIG. 3D. FIG. 3D is a cross-sectional view of the continuous furnace, and is a schematic cross-sectional view when the inside of the continuous furnace is viewed from the front in the conveying direction C of the tray 1, and the arrangement of the heat source 3, the shielding plate 10, and the tray 1. Show relationship.

First step (S1):
Carburization was performed by heating the surface temperature of the part to a temperature above the austenitizing temperature (950° C.).
Second step (S2):
The part temperature was cooled to about 250° C. for re-austenitization. Cooling was performed by injecting nitrogen gas into the tray extracted from the carburizing furnace, and the cooling time was 15 minutes.
Third step (S3):
Subsequently, the cooled tray was put into another continuous carburizing furnace again, and the parts were heated with a target temperature of 830°C to 850°C. The heating time was 30 minutes. At this time, the set furnace temperature of the continuous furnace is set at 870° C., which is higher than the target value of the component temperature. This is a continuous furnace operation method for the purpose of completing heating in a shorter time. Before the temperature inside the furnace and the temperature of the parts reach equilibrium, that is, near the target temperature, the process proceeds to the next zone where the temperature setting of the continuous furnace is changed. In the next zone, the furnace temperature was set to 830° C. suitable for quenching, and was kept at this set furnace temperature for 30 minutes or more in order to equalize the temperature variation of the parts due to rapid heating.
Fourth step (S4):
The parts sufficiently soaked in the third step were put into a quenching bath together with the tray and quenched. A salt bath agent was used as a coolant for quenching, and the set temperature was 230°C. Therefore, after the immersion in the salt bath, the quenching was completed by cooling to room temperature by air cooling.

FIG. 3C shows the evaluation results, which will be described later in detail, of the parts obtained in the examples.

<Comparative example>
As shown in FIG. 4A, a plurality of parts were carburized and quenched in the same manner as in Example except that 20 parts were placed on each tray without providing a shield plate on the tray.
Specifically, parts of the same material and the same shape were used in order to clearly confirm the effects of the present invention. In addition, carburizing and quenching were carried out in the same heat pattern of FIG. 3B as in the example by the mounting method shown in FIG. did FIG. 4B shows the evaluation results, which will be described later in detail, of the parts obtained in the comparative example.

<Reference example>
As shown in FIG. 4A, carburizing and quenching were carried out with the heat pattern shown in FIG. A plurality of parts were carburized and quenched in the same manner as in the example, except that the
Specifically, the same materials and parts with the same shape as those of the examples were used. In addition, while no shield plate is provided on the tray, the stacking position and number are not changed from the embodiment, and the fourth step is performed after the first step in the loading method shown in FIG. 4A, as shown in FIG. 5A. Carburizing and quenching were performed with a heat pattern. This is normal carburizing and quenching. FIG. 5B shows evaluation results of the parts obtained in the reference example, which will be described in detail later.

<Evaluation>
Evaluation was carried out using a loading jig (that is, a shielding plate) according to the present invention, carburizing and quenching in which cooling and reheating were performed before quenching (example), and carburizing performed under the same conditions as in the example without using a loading jig. The amount of heat treatment deformation was compared under three conditions of quenching (comparative example) and normal carburizing and quenching (reference example).
Specifically, the evaluation was performed based on variations in the tooth trace (shape) of the gear portion of the component with respect to the dimensions to be evaluated. "Tooth trace variation" is a value that indicates how much the shape of a gear tooth in the tooth trace direction, which affects gear meshing tooth contact, varies within a single gear. This means that sensory evaluation of noise is adversely affected. However, all evaluation values are expressed as percentages when the maximum value of "tooth trace variation" in the example is set to 100 (FIG. 3C (example), FIG. 4B (comparative example) and See FIG. 5B (reference example)).
From FIGS. 3C and 4B, it can be confirmed that the dimensional accuracy due to heat treatment deformation is greatly improved by the effect of arranging the shield plate.
From FIGS. 3C and 5B, the same dimensional accuracy is obtained in the normal carburizing and quenching (reference example) and the example, so the present invention clearly suppresses the deterioration of the dimensional accuracy caused by the second and third steps. It proves that it can be done.
The average value (Ave) and the maximum value (Max) of the "tooth trace variation" were calculated for the examples, comparative examples and reference examples, and the results are shown in Table 1. In carburizing and quenching (comparative example) in which cooling and reheating were performed before quenching without a loading jig (that is, a shield plate), there were A deterioration of about 60% occurred when comparing an individual with the worst dimensional accuracy (Max). In the present invention (Example), not only is it possible to prevent such deterioration, but it is also possible to improve the maximum value (Max) by about 10%.
In addition, in the example, as in the comparative example, after cooling in the second step, reheating is performed in the third step, so the parts obtained in the example have the same degree of heat resistance as the parts obtained in the comparative example. It is clear that it has a strong strength.

INDUSTRIAL APPLICABILITY The carburizing and quenching apparatus and the carburizing and quenching method of the present invention are useful in the field of manufacturing automobile parts, particularly in the field of manufacturing power transmission parts (for example, final reduction drive gear shafts and secondary shafts of manual transmissions).
If there is a desire to improve the strength performance of the part without changing the shape and characteristics (material) of the part, a tray equipped with a shield plate is prepared and prepared based on the carburizing and quenching apparatus (method) of the present invention. By simply changing the heat pattern setting, the existing carburizing and quenching equipment can be used to meet the demand at low cost.

1: tray 2: parts 3: heating source 10: shielding plate

Claims (10)

An apparatus for carburizing and quenching parts made of steel, comprising:
The carburizing and quenching device, advancing two or more trays side by side;for placing and transporting a plurality of said partsSaidincluding a tray,
The tray isIn plan view,pluralSaidpartsso that is surrounded byBetween the heating source, there is a shielding plate that shields the radiant heat from the heating sourcedeath,
The shielding plate is erected on the tray and has a shape that opens in a direction opposite to the conveying direction in a plan view. Carburizing and quenching equipment. 2. The carburizing and quenching apparatus according to claim 1 , wherein said shield plate is made of an austenitic stainless steel material. 3. Carburizing and quenching apparatus according to claim 1 or 2 , wherein the steel is case hardening steel. The carburizing and quenching apparatus according to any one of claims 1 to 3 , wherein the parts are automobile parts. 5. The carburizing and quenching apparatus according to claim 4 , wherein the automotive part is a power transmission part. 6. The carburizing and quenching apparatus according to claim 5 , wherein said power transmission component is a final reduction drive gear shaft of a manual transmission. A method for carburizing and quenching a part made of steel, comprising:
advancing two or more trays side by side; for placing and transporting a plurality of said partsSaidusing a tray
The tray isIn plan view,pluralSaidpartsso that is surrounded byA shield plate is provided between the heat source and shields the radiant heat from the heat source.death,
The shielding plate is erected on the tray and has a shape that opens in a direction opposite to the conveying direction in a plan view. Carburizing and quenching method. The carburizing and quenching method includes a first step of carburizing the plurality of parts by heating them to an austenitizing temperature or higher, a second step of cooling them to below the austenitizing temperature, and a third step of heating them again to the austenitizing temperature or higher. and a fourth step of performing quenching treatment,
8. The carburizing and quenching method according to claim 7 , wherein said tray is a tray for placing and transporting said plurality of parts in at least said third step. The carburizing and quenching method uses a continuous gas carburizing furnace,
9. The carburizing and quenching method of claim 8, wherein at least said first step, said second step and said third step are performed in said continuous gas carburizing furnace. 10. The carburizing and quenching method according to claim 8 or 9, wherein the heating in the third step is heating by an electric heater heating furnace.

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