JP3226777B2 - Age hardened steel product and surface treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for firmly applying a PVD coating on the surface of an age hardened steel and to a steel product obtained therefrom.

[0002]

2. Description of the Related Art PVD (Physical Vapor)
Deposition processing is a method in which, in a vacuum chamber, a target metal atom irradiated with an electron beam and struck out is attached to the surface of an object to be processed which is arranged to face the target metal. In this process,
If a small amount of nitrogen is interposed in the vacuum chamber and a hard nitride-forming substance such as Ti is used as the target metal, the target metal atoms that are knocked out become nitrides and are deposited on the surface of the workpiece. Since it adheres, a hard film can be formed on the surface of the object.

[0003] The PVD process is a CVD (Chemical Vapor Depos) utilizing a chemical reaction at a high temperature.
(ion) It can be processed at a lower temperature than the processing,
It is used as a surface hardening treatment method for products requiring little dimensional deformation due to heat and requiring high dimensional accuracy. On the other hand, the age-hardened steel is a steel containing an age-hardenable element such as Cu, Mo, and Al such as SUS630, SUS631, maraging steel, etc., and the age-hardenable element is solid-dissolved in a matrix by a solution heat treatment. It is a steel whose hardness can be increased by performing a hardening treatment.

[0004] Age hardened steel has a relatively low hardness in a solution treatment state, so that it is easy to perform cold forming, cutting, and the like. Age hardened steel is heated at a relatively low temperature of around 500 ° C. High hardness can be obtained. By subjecting age-hardened steel to PVD processing, it is possible to use the excellent workability and high hardness of age-hardened steel, and to obtain a product with high surface hardness without impairing dimensional accuracy. It is used as a steel product, for example, a mold having a complicated shape, a shaft part, a bearing part, and a high-strength bolt requiring wear resistance.

[0005]

Conventionally, when PVD treatment is applied to age-hardened steel, the solution hardening treatment and age-hardening treatment are applied to the age-hardened steel to adjust the required material hardness, and then the PVD treatment is performed. The formation of a hard coating on the surface layer has been performed. However, according to this method, there is a problem that the hard coating often peels off during use, thereby shortening the service life of the product.

The present invention has been made in view of the above situation, and an object of the present invention is to provide a method for forming a hard coating which has excellent adhesion and is difficult to peel off on the surface of an age-hardened steel product by PVD treatment. To provide.

[0007]

Means for Solving the Problems In order to achieve the above object, a method for surface-treating an age-hardened steel product according to the present invention comprises the following steps: (1) in producing an age-hardened steel product, Next, a PVD process is performed, and then the PVD process is performed.
Temperature higher than the processing temperature in the range of 300 ° C to 650 ° C
It is characterized by performing age hardening treatment within the enclosure .

Further, age hardened steel product of the present invention, (2) age hardening steel solution heat treated, then PVD process, temperature 30 then higher than the processing temperature of the PVD process
By age hardening treatment in the range of 0 ℃ of 650 ° C., characterized by being applied a PVD coating on the surface.
The age hardened steel crystal is, for example, a mold, a shaft part, a bearing part, a high-strength bolt, and the like.

[0009]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, age hardened steel is
It is an iron-based alloy, preferably after a solution heat treatment, from 300 to
Age-hardened by heating at 650 ° C. The solution heat treatment is a process in which an element causing the age hardening is dissolved in the matrix by the age hardening process, and is performed to age harden the age hardened steel by the age hardening process. This treatment also reduces the hardness of the age-hardened steel and facilitates forming operations such as cold forming and cutting.

The PVD process is performed to form a hard coating on the surface of the age hardened steel. Depending on the type of film formed on the surface, it is possible to improve the surface quality of an age-hardened steel product such as improvement in wear resistance and corrosion resistance by increasing the hardness of the surface. In order to improve the adhesion between the PVD film to be formed and the surface of the age-hardened steel, in the PVD process, the age-hardened steel which is an object to be processed is heated. The temperature is at least lower than the heating temperature of the age hardening treatment to be performed thereafter,
Preferably, the temperature is 20 ° C. or lower than the age hardening treatment temperature. It should be noted that some age hardening occurs in the steel due to the heating in the PVD process, but this does not prevent the effect of the present invention.

The age hardening process is performed after the PVD process. The heating temperature of the age hardening treatment is preferably 300 to 650 ° C.
By heating at the above-mentioned temperature, the age-hardened steel hardens and shrinks isotropically. Due to shrinkage of the age-hardened steel, a compressive residual stress acts on the PVD coating formed on the surface of the age-hardened steel, thereby preventing peeling of the PVD coating.
If the heating temperature in the age hardening treatment is lower than 300 ° C., it takes a long time to reach the required hardness, and the generation of the compressive stress is too small to prevent peeling of the PVD coating. If the temperature exceeds 650 ° C., overaging occurs in a short time, high hardness cannot be obtained, and the characteristics of the formed PVD coating are impaired.

The age hardened steel product of the present invention has a small heat treatment strain and a hard PVD coating on the surface,
Since it has excellent wear resistance, it is suitable for application to, for example, a mold requiring precision. In addition, since the heat treatment strain is small and a hard PVD coating is applied on the surface, it is suitable for precision shafts, long threaded rods, bearing parts, and the like that require small wear and wear resistance.

[0013]

Embodiments of the present invention will be described below. Table 1 shows the chemical composition of the age hardened steel subjected to the experiment. The steel shown in Table 1 was subjected to the solution heat treatment shown in Table 2, and processed into a smooth rotating bending fatigue test piece having a parallel portion diameter of 8 mm. The temperature shown in Table 2 was applied to the fatigue test piece in the solution heat treatment state.
PVD processing was performed under time conditions. The PVD process was performed in a dilute nitrogen atmosphere using Ti as a target material. Next, an age hardening treatment was performed under the conditions shown in Table 2 and the test was performed.

[0014]

[Table 1]

[0015]

[Table 2]

As a comparative example, a fatigue test specimen similar to that described above was prepared from steel 1 which had been subjected to a solution heat treatment at 830 ° C. × 1 hr air cooling, subjected to age-hardening treatment at 480 ° C. × 5 hr air cooling, and then to 460 ° C. × The test was performed by performing a PVD treatment for 5 hours. The PVD process was performed in a dilute nitrogen atmosphere using Ti as a target material, as in the example.

The core hardness was measured for the cross section of the grip portion of the fatigue test piece. In addition, the surface hardness of the grip portion surface of the fatigue test piece was measured. The surface residual stress and the peeling resistance of the parallel part surface of the fatigue test piece were measured. Surface residual stress is X
The measurement was performed using a linear residual stress measuring device. In addition, a scratch test was performed for the peel resistance, and AE (Acoustic Em)
issue). The fatigue strength was determined by applying a skin bending stress of 490 to 1280 MPa to a parallel portion of the fatigue test piece, performing a rotary bending fatigue test, and measuring the number of rotations before breaking. Table 3 shows the measurement results. Regarding the peel resistance and the fatigue strength, the value of the comparative example was set to 1, and the strength ratio of the example was shown.

[0018]

[Table 3]

According to Table 3, in the comparative example, the residual skin stress is the tensile residual stress (+), while in the embodiment of the present invention, the residual skin stress is the compressive residual stress (-). Or even the tensile residual stress is significantly smaller than that of the comparative example. Each of the examples of the present invention is superior to the comparative example in peel resistance and fatigue strength. 83 for steel 1
A solution heat treatment of air cooling at 0 ° C. × 1 hr was performed, and a metal mold for plastic injection molding was prepared by cutting. This is 4
A TiN film was formed on the mold cavity by performing a PVD process at 60 ° C. for 4 hours. Then 480 ° C. in nitrogen
An age hardening treatment of heating and cooling for 1.5 hours was performed. The mold was mounted on a plastic injection molding machine and subjected to plastic injection molding. As a result, the mold life was excellent without the TiN film peeling off.

Steel 1 was subjected to a solution heat treatment at 830 ° C. × 1 hr air cooling, and formed into M12 hexagon bolts by cold heading. This was subjected to PVD treatment at 450 ° C. for 4 hours to form a TiN coating on the surface. Then in nitrogen for 50
As a result of performing the age hardening treatment at 0 ° C. × 1.5 hours under heating and cooling, a high-strength bolt was obtained in which the TiN film on the surface was not peeled off by tightening.

[0021]

As described above, according to the present invention, PVD
It is possible to provide a method for forming a hard coating having excellent adhesion and hard to peel off on the surface of an age-hardened steel product by the treatment. The age-hardened steel product of the present invention is excellent in abrasion resistance because the hard coating is hard to peel off, and has high fatigue strength. For example, when applied to a mold, a long-life mold can be obtained.
Further, since the age-hardened steel product of the present invention has high surface hardness and high fatigue strength, it exhibits excellent characteristics even when applied to shaft parts, bearing parts, high-strength bolts and the like that require wear resistance.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-64024 (JP, A) JP-A-51-256242 (JP, A) JP-A-64-68458 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C23C 14/00-14/58 C21D 6/00

Claims (2)

(57) [Claims] 1. In the manufacture of an age-hardened steel product, the age-hardened steel is subjected to a solution heat treatment, followed by a PVD treatment, and then from 300 ° C. to 65 ° C., which is higher than the treatment temperature of the PVD treatment.
A method for surface-treating an age-hardened steel product, comprising performing an age-hardening treatment within a range of 0 ° C. 2. A solution heat treatment of the age hardened steel,
An age-hardened steel product having a surface coated with a PVD coating by performing a VD process and then performing an age hardening process in a temperature range of 300 ° C. to 650 ° C. higher than the processing temperature of the PVD process.