JPS6112991B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a sliding member that has excellent surface self-lubricating properties and wear resistance, as well as excellent strength and toughness of the material itself.

Examples of sliding members include cylinders, cylinder liners, cylinder cores, and piston rings. FIG. 1 shows an example of the structure of a pressure die-casting device equipped with an injection cylinder as a sliding member, in which a mold cavity 3 of a predetermined shape is formed between a fixed mold 1 and a movable mold 2. Fixed mold 1
An injection cylinder (injection sleeve) 4 is attached to the injection cylinder 4, and a plunger 5 is slidably disposed within the injection cylinder 4, and the molten metal injected into the injection cylinder 4 from the pouring port 6 is pushed out by the plunger 5. The structure is such that the material is supplied under pressure into the mold cavity 3 and a die-cast product is obtained after solidification.

The injection cylinder 4 used in such a pressure die-casting device is heated to a high temperature of, for example, about 650°C in the case of aluminum alloy die-casting, and a temperature of 500°C to
Because it is repeatedly slid against the plunger 5 under high pressure of approximately 1500 kg/ ^cm2 , it has excellent lubricity, wear resistance, oxidation resistance, and strength at high temperatures.
It is required to have properties such as tempering resistance and heat check resistance, as well as properties that can withstand erosion.

Conventionally, in manufacturing the above-mentioned injection cylinder 4, hot die steel, for example, is used as the material, and after being machined to a predetermined dimension leaving a grinding allowance, it is then quenched and tempered. The material was tempered to about H _R C 40 to 50, then subjected to a long nitriding treatment to form a nitrided layer with a hardened layer depth of about 0.3 to 0.5 mm, and finally finished polished.

However, in such conventional cases, the wear resistance of the surface was achieved only by nitriding, which tends to result in insufficient lubricity, especially when hot molten metal is injected from the pouring port 6. When the injection cylinder 4 is heated and thermally deformed, galling is likely to occur, which shortens the life of the injection cylinder 4 and increases the frequency of replacement. If a long life is to be obtained only by such nitriding treatment, a sliding member is separately prepared to adjust the increase in clearance between the injection cylinder 4 and the plunger 5 caused by wear. The problem was that it had to be done.

Furthermore, in order to improve the lubricity between the injection cylinder 4 and the plunger 5, graphite powder is supplied to the sliding parts, but the graphite powder scatters, reducing usage efficiency and causing problems in the working environment. This has the problem of worsening the temperature and furthermore, there is a risk of causing seizure.

In addition, attempts have been made to improve the self-lubricating properties of the surfaces of sliding members such as the injection cylinder 4 by sulfurizing them in a salt bath. In the case of a salt bath containing NaCN), the formation of a nitrided layer is also slightly observed at the same time as the formation of a sulfurized layer. However, the thickness of the nitrided layer formed at the same time as the sulfurized layer is at most 0.1
In addition, the hardness of this nitrided layer is considerably lower than that in the case of nitriding treatment alone, and the hardness of this nitrided layer is mainly to improve the self-lubricating property of the surface due to sulfurization, and it has sufficient hardening depth and durability. Since it is not possible to obtain abrasion resistance, there has been a problem that the sliding member is still insufficient from the viewpoint of long life. In addition, in order to increase the hardening depth of the nitrided layer in the sulfurizing treatment using the salt bath mentioned above, it is possible to lengthen the sulfurizing time, but since the sulfurizing layer becomes thicker due to the long sulfurizing treatment. , it is easy to cause surface roughness, surface peeling, and even dimensional changes, which increases the polishing finish amount, increases polishing time, and reduces the hardened surface layer. had. Furthermore, immediately after carburizing, it is immersed in a low-temperature sulfurizing bath,
There is also a method of forming a sulfurized layer during martempering (Japanese Patent Laid-Open No. 50-114355), but the thickness of the sulfurized layer formed in this case is at most 2 to 3 μm.
However, there was a problem in that it could not withstand long-term use, especially under heavy sliding conditions.

This invention was made by focusing on the above-mentioned conventional problems, and has excellent self-lubricating properties and wear resistance, and the material itself has extremely excellent strength and toughness, and can be used under heavy sliding conditions. Another objective is to obtain a sliding member with a long service life.

This invention is characterized in that, in manufacturing a member suitable for surface sliding, a surface hardening treatment is applied to a steel surface that has been previously tempered by quenching and tempering, and then a sulfurizing treatment is applied. In the embodiment, as surface hardening treatment, the hardened layer depth is 0.3
~0.5mm nitriding treatment or hardened layer depth 0.5~0.7
Carburized to 0.1 mm to 0.4 mm, and sulfurized to a depth of 0.1 to 0.4
mm, a sliding member with extremely excellent wear resistance and lubricity is manufactured by the synergistic effect of the improvement in wear resistance by the surface hardening treatment and the improvement in self-lubricity by the sulfurization treatment. It is said that

Carbon tool steel (SK), alloy tool steel (SKS, SKD, SKT, SKH) and other appropriate steels can be used as the steel to be subjected to the above-described surface hardening treatment and sulfurization treatment. Then, the selected steel material is subjected to the necessary annealing treatment to make it into a homogeneous material that is sufficiently spherical, and this material is processed into a predetermined shape and dimension including a predetermined finishing allowance, and then quenched and tempered. , H _{R C} to a hardness of about 40 to 50. Thereafter, the steel surface is subjected to surface hardening treatment, for example, to a hardened layer depth of 0.3 mm or more. At this time, the reason why the hardened layer depth is preferably 0.3 mm or more is to obtain sufficient wear resistance as a sliding member. As this surface hardening treatment, it is best to perform nitriding treatment with a hardened layer depth of approximately 0.3 to 0.5 mm or carburization treatment with a hardened layer depth of approximately 0.5 to 0.7 mm, and carbonitriding treatment may be performed as necessary. Good too.

Among these nitriding treatments, liquid nitriding is possible, but gas nitriding or ion nitriding is preferable.
degree). Here, the hardening layer depth is 0.3~0.5mm
The reason for this is that if it is smaller than 0.3 mm, it will not be possible to obtain the necessary long-term wear resistance, so 0.5 mm
If it becomes larger than , the nitriding treatment time becomes longer. On the other hand, as the carburizing treatment, it is possible to perform liquid carburizing, but it is preferable to perform gas carburizing using an atmospheric furnace. Here, the hardened layer depth is set to 0.5 to 0.7 mm because if it is smaller than 0.5 mm, it will not be possible to obtain the necessary long-term wear resistance, and if it is larger than 0.7 mm, the carburizing treatment time will be longer. It depends.

Next, after the above-mentioned surface hardening treatment, a sulfurization treatment is performed to a depth of about 0.1 to 0.4 mm. This sulfurization treatment is conveniently carried out by a liquid method using a neutral or reducing salt bath, but it can also be carried out by a gas method using a gas such as H ₂ S. When using a salt bath, it is convenient to use a salt bath agent prepared by adding a sulfur compound salt to a mixed salt. In this case, as mentioned above, if the salt bath agent contains nitrogen (for example, if it contains NaCN), nitriding is usually performed at the same time as sulfurization. however,
Since the nitriding depth in this case is only 0.1 mm at most, it is not possible to obtain sufficiently satisfactory wear resistance, and sulfurizing treatment alone is not suitable for sliding parts such as injection cylinders that aim for long life. do not have. Here, if the depth of the sulfurized layer is less than 0.1 mm, good self-lubricating properties cannot be obtained, so it is essential that the depth of the sulfurized layer is 0.1 mm or more. On the other hand,
Even if a sulfurized layer with a depth greater than 0.4 mm is formed, it will not contribute much to improving self-lubricating properties, and the time required for sulfurization will become longer, and the surface will become rough. It is better to set it to less than mm.

In a surface treated with this type of surface treatment, the following steps are formed from the outermost surface of the sliding member: a sulfide film with high self-lubricating properties, a carburized or nitrided/sulfurized diffusion layer, a carburized or nitrided diffusion layer, and the base material. Therefore, the sulfide film on the outermost surface can provide extremely excellent self-lubricating properties, and at the same time, when the sulfide film is damaged, carburization or nitriding/sulfiding, which is extremely hard and has lubricating properties, can be applied. This can be sufficiently compensated for by the diffusion layer, and it is possible to maintain good self-lubricating properties and wear resistance of the sliding member over a long period of time. The carburized or nitrided diffusion layer formed between the carburized or nitrided/sulfurized diffusion layer and the substrate can sufficiently prevent the surface layer from chipping or missing during use, and the presence of each of these layers Because of this, it can exhibit very excellent sliding properties as a sliding member, and because it has been heat-treated in advance, the material itself has excellent strength and toughness.

Example Here, the process was carried out according to the process diagram shown in FIG. As for steel material, C: 0.39%, Si:
1.00%, Mn: 0.40%, Cr: 5.15%, Mo: 1.4%,
An alloy tool steel (JIS SKD 61 equivalent material) consisting of V: 0.8%, balance Fe and normal impurities is used, which is heated to 820 to 870°C and then slowly cooled to undergo sufficient spheroidizing annealing treatment (hardness H _R C23 or below). Next, the final finished dimensions of 220 mm outside diameter, 120 mm inside diameter, and 700 mm length are set, and the required finishing allowance is set for machining, and the outside diameter section is turned and the inside diameter section is bored to obtain the cylinder material. It was molded into. Next, heat this cylinder material to 1030~1040℃.
After heating to a temperature of , air-cooling quenching was performed to obtain a quenched hardness of H _R C47 or higher. In this hardening,
In order to prevent oxidation and decarburization of the cylinder material, it is desirable to use a vacuum quenching furnace or an atmosphere quenching furnace, and it is desirable to use an in-furnace quenching method to suppress quenching distortion as much as possible. Next, the cylinder material after quenching is heated to 590°C and then air cooled for tempering, and the hardness H _R
It was tempered to obtain C42-48. This tempering is applied to the hardened cylinder material mentioned above.
This is done in order to impart appropriate hardness and good toughness, and it is desirable to do it in multiple batches if necessary. In this case, the first tempering may be performed by heating to the above-mentioned tempering temperature, and the last tempering may also be performed in the surface hardening treatment described below.

Therefore, the cylinder material after the above-mentioned first tempering is polished leaving a slight finishing allowance, and then surface hardening treatment is performed.

When performing nitriding treatment as a surface hardening treatment, the above cylinder material is charged into a nitriding furnace,
It was held at 590°C for 48 hours in an ammonia gas atmosphere. Due to this nitriding treatment, the hardness is Hv900~1100,
A nitrided layer with a depth of 0.3-0.5 mm was obtained.

On the other hand, when performing carburizing treatment as a surface hardening treatment, the cylinder material was placed in a carburizing gas (RX gas) atmosphere furnace adjusted by a gas conversion furnace and held at 860° C. for 6 hours. Through this carburizing treatment, a carburized layer with a hardness of Hv550 to 700 and a depth of 0.5 to 0.7 mm was obtained.

Next, each cylinder material subjected to the above-mentioned surface hardening treatment was subjected to a sulfurization treatment. During this sulfurizing treatment, a salt bath was used, and a mixed salt consisting of NaCN + NaCl + Na ₂ CO ₃ was added with a sulfur compound salt consisting of Na ₂ S ₂ O ₃ , and this was maintained at 570 ° C.
Each cylinder material was immersed in this salt bath for 3 to 6 hours. Through this sulfurization treatment, the hardness is Hv750~850,
A sulfurized layer with a depth of 0.3-0.4 mm was obtained. In addition to the above, examples of sulfur compound salts include Na ₂ S, Na ₂ SO ₄ ,
Na ₂ SO ₃ etc. can also be used. Thereafter, final polishing and inner diameter honing were performed to produce an injection cylinder for a pressure die-casting machine as shown in FIG. 1.

According to the results of one experiment in which the obtained injection cylinder was assembled into a pressure die-casting device shown in Fig. 1 and die-casting of aluminum alloy was carried out,
It was able to withstand up to approximately 400,000 shots.

Also, for comparison, the same as the above example
Using SKD61, the cylinder material was previously tempered to H _R C40-50 and was sulfurized using the same salt bath composition as above to obtain a hardness of Hv600-700 and a depth of 0.1-0.3mm.
After forming a sulfurized layer, an injection cylinder was manufactured by final polishing, and was similarly installed in the pressure die-casting machine shown in Figure 1 to die-cast an aluminum alloy under the same conditions, resulting in approximately 200,000 shots. The need for replacement arose.

In addition, although the above-mentioned embodiment was explained by taking the injection cylinder of a pressure die-casting device as an example, it goes without saying that the present invention can be applied to various other sliding members such as cylinder liners, cylinder cores, and piston rings.

As described above, according to the present invention, after quenching and tempering are performed in advance to refine the structure and improve strength and toughness, a hardened layer depth of, for example, 0.3 mm is applied to the tempered steel surface. By performing the above surface hardening treatment, a hardened layer of the predetermined depth is obtained before the sulfurization treatment, and then, for example, the sulfurization treatment is performed to a depth of 0.1 to 0.4 mm. After improving the strength and toughness of the core of the member, the wear resistance and lubrication of the sliding member are improved by the synergistic effect of the surface hardening treatment to improve wear resistance and the sulfurization treatment to improve self-lubricity. It is possible to achieve extremely excellent properties such as the ability to be used for a long period of time without any trouble even under heavy sliding conditions.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view of a pressure die-casting device incorporating an injection cylinder to which the present invention can be applied, and FIG. 2 is an explanatory view of the manufacturing process of a sliding member in one embodiment of the present invention.

Claims (1)

[Claims] 1. In manufacturing a member suitable for surface sliding, a steel surface that has been previously quenched and tempered is subjected to a surface hardening treatment, and then a sulfurization treatment is performed. A method for manufacturing a sliding member. 2. The method of manufacturing a sliding member according to claim 1, wherein the surface hardening treatment is a nitriding treatment with a hardened layer depth of 0.3 to 0.5 mm. 3. The method for manufacturing a sliding member according to claim 1, wherein the surface hardening treatment is a carburizing treatment with a hardened layer depth of 0.5 to 0.7 mm. 4. The method for manufacturing a sliding member according to claim 1, 2 or 3, wherein the depth of the sulfurization treatment is 0.1 to 0.4 mm.