JP2021183717A - Slide member and method for producing the same and vibrating actuator - Google Patents

Abstract

To provide a slide member that is composed of martensitic stainless steel and has high hardness and suitable toughness.SOLUTION: A rolled material composed of a martensitic stainless steel is press-worked to make an intermediate material for a slide member, wherein the martensitic stainless steel contains, in wt.%, 0.08% or more and 0.4% or less of carbon, wherein a carbon equivalent is 2.3 or more and 3.5 or less, represented by [carbon equivalent=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14)], where C, Mn, Si, Ni, Cr, Mo, and V represent mass percentage of each element. The intermediate material is heated under predetermined conditions to produce a slide member that contains a martensite phase and an austenite phase, wherein a volume ratio of the austenite phase to a total of the martensite phase and austenite phase is 0.19 or more and 0.31 or less, and wherein a half-width of an X-ray diffraction peak in an α'(211) plane of the martensite phase is 1.17 or more.SELECTED DRAWING: Figure 6

Description

The present invention relates to a sliding member, a method for manufacturing the same, and a vibration type actuator.

A vibrating body equipped with an electric-mechanical energy conversion element is excited with a predetermined vibration, and a friction driving force is applied from the vibrating body to the contact body in contact with the vibrating body to relatively move the vibrating body and the contact body. Vibration type actuators are known. Generally, the vibrating body is configured by joining the piezoelectric body and the elastic body, and transmits the vibration generated by applying a voltage to the piezoelectric body to the contact body via the elastic body.

Here, since the surface of the elastic body that comes into contact with the contact body is a sliding surface on which a large frictional force is generated, the occurrence of wear is unavoidable. Therefore, when the vibration type actuator is used for a long period of time or for a long period of time, the surface condition of the contact surface changes due to wear, which lowers the vibration transmission efficiency, and the generated wear debris adversely affects the surrounding mechanical parts. Problems such as exerting occur. In order to suppress the occurrence of such a problem, an elastic body having a high hardness of the contact surface with respect to the contact body is required.

An example of a high hardness sliding member is martensitic stainless steel. Martensitic stainless steel increases in hardness due to martensitic transformation caused by quenching, but decreases in toughness (fracture toughness), so it forms a structure containing a certain retained austenite phase in order to achieve both toughness and hardness. There is a need. To solve such a problem, Patent Document 1 proposes a martensitic stainless steel having a large surface hardness while containing a large amount of retained austenite.

Japanese Unexamined Patent Publication No. 2003-342695

The elastic body that constitutes the vibrating body of the vibrating actuator is processed into an arbitrary shape before quenching, such as by forming protrusions at predetermined positions in order to enable highly efficient vibration transmission. Needs to be (transformed). Examples of such processing means include cold press working that causes plastic deformation.

In view of such workability, the martensitic stainless steel described in Patent Document 1 has a high carbon content of 0.4% by weight or more and has a high hardness as a material before quenching, so that it is cold. It is not suitable for deformation processing such as inter-press processing. On the other hand, if the carbon content is reduced and only the surface is made harder, it can be sufficiently used as an elastic body constituting a vibrating body. However, in order to increase the hardness of the material surface, it is necessary to perform nitriding treatment, etc., in which case, there is a problem that corrosion resistance is lowered due to nitriding, and a dedicated facility is required, which increases the manufacturing process. Problem arises.

An object of the present invention is to provide a sliding member having high hardness and excellent toughness by using martensitic stainless steel having a low carbon content without requiring a surface hardening treatment.

The sliding member according to the present invention is a sliding member made of martensite-based stainless steel, and the martensite-based stainless steel contains 0.08% or more and 0.4% or less of carbon in weight%. Moreover, using the mass% of C, Mn, Si, Ni, Cr, Mo, and V,'carbon equivalent = C + (Mn / 6) + (Si / 24) + (Ni / 40) + (Cr / 5) + The value of carbon equivalent represented by (Mo / 4) + (V / 14)'is 2.3 or more and 3.5 or less, and at least the sliding surface of the sliding member contains a martensite phase and an austenite phase. The volume ratio of the austenite phase to the total amount of the martensite phase and the austenite phase is 0.19 or more and 0.31 or less, and the X-ray diffraction peak on the α'(211) plane of the martensite phase. It is characterized in that the half price range of is 1.17 or more.

According to the present invention, it is possible to obtain a sliding member having high hardness and excellent toughness by using martensitic stainless steel having a low carbon content without requiring a surface hardening treatment.

It is an X-ray diffraction chart of the sliding member which concerns on embodiment of this invention. It is a figure which shows the shape of the intermediate material (test piece) which concerns on an Example and a comparative example. It is a figure which shows the quenching temperature profile used for making of an Example and a comparative example. It is a figure which shows the heat treatment condition in the quenching treatment of an Example and a comparative example. It is a figure which shows the evaluation result of an Example and a comparative example. It is a graph which shows the relationship between the Vickers hardness, the retained austenite ratio, and the α'(211) full width at half maximum in Examples and Comparative Examples.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Steel material for sliding members>
The sliding member according to the embodiment of the present invention is made of martensitic stainless steel. The martensitic stainless steel used for the sliding member contains 0.08% or more and 0.4% or less of carbon by weight. The carbon equivalent of martensitic stainless steel used for the sliding member is'carbon equivalent = C + (Mn / 6) + (Si / 24) + (Ni / 40) + (Cr / 5) + (Mo / 4) + (V / 14)'. Used. Here, C, Mn, Si, Ni, Cr, Mo, and V indicated by element symbols are mass% of each element.

As described above, in the vibration type actuator, a piezoelectric body is bonded to the sliding member to produce a vibrating body, and a predetermined AC voltage is applied to the piezoelectric body to vibrate the sliding member to make the sliding member. The contacting body and the vibrating body are moved relative to each other. Further, the material for producing the sliding member is required to be capable of plastic deformation processing into an arbitrary shape such as forming a protrusion at a predetermined position before quenching.

On the other hand, in order to increase the hardness after quenching, it is necessary that the carbon equivalent is 2.3 or more. However, if the carbon equivalent is excessive, the hardness of the material before quenching increases, and it becomes difficult to perform plastic deformation by means such as cold press working. Further, when the carbon equivalent is excessive, the corrosion resistance, fatigue strength and toughness are deteriorated.

In view of such circumstances, the martensitic stainless steel according to the present embodiment has a carbon equivalent of 2.3 or more and 3.5 or less. At this time, the carbon content is more preferably 0.26% or more and 0.40% or less in terms of weight%. Examples of the martensitic stainless steel whose composition is defined by JIS as a material having such a carbon equivalent include SUS410-based and SUS420-based stainless steel.

In stainless steel, nitrogen (N) improves hardness while lowering corrosion resistance. Therefore, the martensitic stainless steel according to the present embodiment is not subjected to surface nitriding treatment or the like, and thus nitrogen is substantially contained. It is not contained as. However, since nitrogen contained in the air is unavoidable in the general manufacturing environment of stainless steel, it is permissible if the content of nitrogen is 0.025% or less in weight%. ..

<Manufacturing method of sliding member>
Martensitic stainless steel is cold-pressed to obtain an intermediate material molded into any shape. For example, when it is used as an elastic body used for a vibrating body of a vibrating actuator, a protrusion or the like for efficiently transmitting the vibration of the piezoelectric body to the contact body is formed. Subsequently, the intermediate material after molding is heated to the austenite transformation point or higher, and then quenching treatment is performed to form a martensite phase to increase the hardness, thereby obtaining a sliding member.

Since the quenching treatment needs to be carried out in a non-oxidizing atmosphere in order to prevent oxidation, it is necessary to use a furnace in which the inside can be controlled to have a nitrogen atmosphere (inert gas atmosphere) or a vacuum atmosphere. As a heating means, a general high-temperature heater may be used, but only the vicinity of the sliding surface may be heat-treated by high-frequency heating, laser heating, or the like. Heating conditions such as quenching temperature and holding time need to be determined in consideration of the relationship with the structure after quenching, as will be described later. This is experimentally determined because the structure after quenching depends on the shape and size of the intermediate material, the arrangement of heaters (heating means), and the heat capacity of peripheral members (sample table, etc.). Because it is necessary.

In the quenching treatment, it is necessary to quench at a cooling rate higher than the upper critical cooling rate for martensitic transformation to occur after the heat treatment. As the cooling method, gas cooling, oil cooling, water cooling and the like can be selectively used. In the case of the above-mentioned martensitic stainless steel having a carbon equivalent of 2.3 or more and 3.5 or less, it is necessary to perform cooling treatment at a cooling rate of 80 ° C./min or more between the heat treatment temperature and 300 ° C. ..

<Structure of sliding member (martensitic stainless steel after quenching)>
The organizational characteristics of the sliding surface of the sliding member according to the embodiment of the present invention can be confirmed by the X-ray diffraction method (XRD). FIG. 1 is a diagram showing an example of an X-ray diffraction result (XRD chart) of a sliding member made of martensitic stainless steel according to the present embodiment.

The austenite phase ratio is calculated using the peak intensity Iγ of the γ (311) plane derived from the austenite phase and the peak intensity Iα ′ of the α ′ (211) plane derived from the martensite phase in the XRD chart. The austenite phase ratio is the volume ratio of the austenite phase to the total amount of the austenite phase and the martensite phase, and is represented by'austenite phase ratio = Iγ / (Iγ + Iα)'.

If the austenite phase ratio is too low, the toughness decreases, and if it is too high, the hardness decreases. Therefore, it is necessary to be in the range of 0.19 or more and 0.31 or less. From the viewpoint of further improving toughness and hardness, it is desirable that the austenite phase ratio is in the range of 0.20 or more and 0.30 or less.

The half width of the peak of the α'(211) plane, which is the growth direction in the martensite phase (hereinafter referred to as "211 plane half width"), is calculated. At the peak of the α'(211) plane, the peak width at half the intensity of the peak strength from which the background strength is removed is defined as the full width at half maximum of the 211 plane. The half-value width at the X-ray diffraction peak correlates with the crystallite size and the strain between the crystal lattices, and the smaller the crystallites and the larger the strain of the crystal lattice, the larger the half-value width.

The present inventors have found that in martensitic stainless steel, a width at half maximum of 211 faces is required to be 1.17 or more in order to develop high hardness while leaving a certain amount of austenite component after quenching. .. It is considered that the crystallite size and the amount of strain of the crystal act in a complex manner for this, but it is possible to increase the hardness by satisfying the above conditions.

It is considered that the organizational characteristics of the sliding member made of martensitic stainless steel according to the present embodiment are deeply related to the quenching conditions. When the heating is high temperature and long time, the decomposition of carbides contained in the matrix and the diffusion of carbon atoms proceed to lower the martensitic transformation temperature, resulting in excess retained austenite and lower hardness. In addition, the coarsening of the austenite particle size during heating causes the coarse martensite crystals to precipitate after the martensitic transformation, which also causes a decrease in hardness. On the other hand, when the temperature of the heat treatment is low and the time is short, the diffusion and solid solution of carbon atoms become insufficient and the hardness decreases.

As described above, it is considered that the crystal diameter of the martensite phase and the crystal strain caused by the solid solution of carbon change depending on the treatment conditions and appear as a half width at the X-ray diffraction peak. From the viewpoint of obtaining higher wear resistance as a sliding member, it is more desirable that the half width at half maximum of 211 planes is 1.35 or more.

Examples of the sliding member according to the present invention will be described below by taking an elastic body used as a vibrating body of a vibrating actuator as an example. However, the sliding member according to the present invention is not limited to such applications, and can be used as a sliding member of various machines and devices.

A rolled material whose JIS standard is SUS420J2 was used as a material. The specific composition of this rolled material (shown only for the above formula 1) is C: 2.6 to 4.0%, Cr: 12-14%, Si: 1% or less, Mn: 1% or less, P: 0.04% or less, S: 0.03% or less, carbon equivalent: 2.6 or more and 3.4 or less.

FIG. 2 is a diagram showing the shape of an intermediate material for obtaining a sliding member according to an example and a comparative example. Using a plate-shaped rolled material 1, a protrusion 2 for use as an elastic body for a vibrating body is formed by cold pressing, and then divided to form an intermediate material (hereinafter referred to as "test piece") shown in FIG. ) Was obtained. Subsequently, the prepared test piece was quenched using a heating furnace. A plurality of test pieces arranged on a heat-resistant ceramic plate were placed in a heating furnace so as to be close to the heater, and nitrogen gas was introduced into the heating furnace to create a nitrogen atmosphere in the heating furnace. An inert gas other than nitrogen gas may be used.

After that, heating with a heater was started. FIG. 3 is a diagram showing a temperature profile of quenching of a test piece. Further, FIG. 4 is a diagram showing heat treatment conditions in the quenching treatment. Here, the quenching process was performed under a plurality of conditions in which the temperature profile was changed. The quenching treatment condition is based on a temperature measurement value by a thermocouple installed in the vicinity of the heater, and the output of the heater is controlled (for example, PDI control) based on this temperature measurement value.

The treatment temperature was raised to a predetermined temperature shown in FIG. 4, and the temperature was maintained for the holding time shown in FIG. After that, the output to the heater was stopped and the test piece was immediately cooled by ejecting nitrogen gas onto the ceramic plate on which the test piece was placed. The cooling rate was set to about 100 ° C / min from the processing temperature to 300 ° C, and then the nitrogen gas was naturally cooled to near room temperature while maintaining the nitrogen atmosphere in the heating furnace, and then the supply of nitrogen gas was stopped. The moving member was taken out of the heating furnace.

The prepared test piece was subjected to Vickers hardness measurement, phase identification by X-ray diffraction method, and toughness evaluation. Only in Comparative Example 5, the Vickers hardness measurement and the phase identification by the X-ray diffraction method were performed after performing the sub-zero treatment in which the test piece was immersed in liquid nitrogen. A micro Vickers hardness tester HMV-2 manufactured by Shimadzu Corporation was used for measuring the Vickers hardness, and an X-ray diffractometer Ultima IV manufactured by Rigaku Co., Ltd. was used for X-ray diffraction. In X-ray diffraction, Cu was used as a target (CuKα ray), the output was 40 kV-40 mA, and 2θ was in the range of 30 ° to 100 °.

Further, in order to evaluate the toughness, a plate-shaped test piece having a size of 50 mm × 50 mm × 0.3 mm was prepared using the same rolled material as the rolled material used for producing each test piece, and the conditions shown in FIGS. 3 and 4 were met. Under the same conditions, test pieces corresponding to Examples and Comparative Examples were prepared. For each test piece, a test was carried out in which a load of 100 N was applied to the center of the support position while supporting two points with a width of 20 mm near the center. After the test, those with no change in appearance were judged as "◎ (good)", those that were not cracked only by dents were judged as "○ (possible)", and those that were cracked were judged as "× (defective)".

FIG. 5 is a diagram showing the test results (evaluation results) collectively. Regarding the Vickers hardness measurement results, those with insufficient hardness were evaluated as "x (defective)", and those with the desired hardness were evaluated as "○ (possible)" and "◎ (good)" in two stages. .. FIG. 6 is a diagram showing the relationship between the Vickers hardness measurement result, the retained austenite ratio obtained by X-ray diffraction, and the full width at half maximum of 211 planes. In FIG. 6, those having a Vickers hardness of Hv640 or more are indicated by “◯”, and those having a Vickers hardness of less than Hv640 are indicated by “x”. Further, the test pieces in the broken line frame shown in FIG. 6 are Examples 1 to 10, and the test pieces outside the broken line frame are Comparative Examples 1 to 4.

In Examples 1 to 10, the heating temperature is 980 ° C. or higher and 1090 ° C. or lower, and the holding time at the heating temperature is 0 minutes or longer and 30 minutes or shorter. The residual austenite ratio is 0.19 or more, the half width at half maximum is 1.17 or more, and the Vickers hardness is Hv640 or more. In particular, in Examples 2 to 8, Vickers hardness of Hv655 or more and good toughness can be obtained by having the retained austenite in the range of 0.2 or more and 0.3 or less and the half width at half maximum of 211 planes being 1.35 or more. ing.

On the other hand, in Comparative Examples 1 and 4, although the retained austenite is large, the half width at half maximum of 211 planes is as small as 1.1 or less, and the hardness is also small. In Comparative Examples 2 and 3, both the retained austenite ratio and the full width at half maximum of 211 planes are small, the hardness is small, and the toughness is also small (brittle). In Comparative Example 5, although the hardness was high, the retained austenite ratio was small, so that fracture was observed in the toughness test. This is considered to be due to the sub-zero processing.

As a result of composition analysis of the surfaces of all the test pieces by the XPS method using QuanteraSXM manufactured by ULVAC-PHI, nitrogen was not detected in all the test pieces (below the detection limit). From this result, it was confirmed that high hardness and toughness were obtained in the examples without impairing the corrosion resistance as compared with the material using the conventional nitriding treatment in order to obtain high hardness.

As described above, according to the present invention, it is possible to obtain a sliding member having high hardness, excellent wear resistance and high toughness without impairing corrosion resistance by using martensitic stainless steel. Although the present invention has been described in detail based on the preferred embodiments thereof, the present invention is not limited to these specific embodiments.

1 Rolled material 2 Protrusions

Claims (15)

A sliding member made of martensitic stainless steel,
The martensitic stainless steel contains 0.08% or more and 0.4% or less of carbon by weight, and carbon is used in terms of mass% of C, Mn, Si, Ni, Cr, Mo, and V. The value of carbon equivalent represented by equivalent = C + (Mn / 6) + (Si / 24) + (Ni / 40) + (Cr / 5) + (Mo / 4) + (V / 14)'is 2. 3 or more and 3.5 or less,
At least the sliding surface of the sliding member contains a martensite phase and an austenite phase.
The volume ratio of the austenite phase to the total amount of the martensite phase and the austenite phase is 0.19 or more and 0.31 or less, and the X-ray diffraction peak on the α'(211) plane of the martensite phase. A sliding member having a half-value width of 1.17 or more. The sliding member according to claim 1, wherein the martensitic stainless steel has a nitrogen content of 0.025% or less in terms of weight%. The sliding member according to claim 1 or 2, wherein the volume ratio is 0.20 or more and 0.30 or less. The sliding member according to any one of claims 1 to 3, wherein the half width of the X-ray diffraction peak on the α'(211) plane is 1.35 or more. The sliding member according to any one of claims 1 to 4, wherein the martensitic stainless steel has a carbon content of 0.26% or more and 0.40% or less in weight%. The sliding member according to any one of claims 1 to 5, wherein the Vickers hardness is Hv640 or more. It is a manufacturing method of sliding members.
The process of pressing a rolled material made of martensitic stainless steel to produce an intermediate material,
The intermediate material contains a martensite phase and an austenite phase, and the volume ratio of the austenite phase to the total amount of the martensite phase and the austenite phase is 0.19 or more and 0.31 or less, and the martensite phase is present. It has a step of performing a cooling treatment at a predetermined cooling rate after the heat treatment so that the half-value width of the X-ray diffraction peak on the α'(211) plane of the site phase is 1.17 or more.
The martensite-based stainless steel contains carbon of 0.08% or more and 0.4% or less in weight%, and carbon is used in terms of mass% of C, Mn, Si, Ni, Cr, Mo, and V. The value of carbon equivalent represented by equivalent = C + (Mn / 6) + (Si / 24) + (Ni / 40) + (Cr / 5) + (Mo / 4) + (V / 14)'is 2. A method for manufacturing a sliding member, which comprises 3 or more and 3.5 or less. The method for manufacturing a sliding member according to claim 7, wherein the martensitic stainless steel has a nitrogen content of 0.025% or less in terms of weight%. The method for manufacturing a sliding member according to claim 7 or 8, wherein the volume ratio is 0.20 or more and 0.30 or less. The method for manufacturing a sliding member according to any one of claims 7 to 9, wherein the half width of the X-ray diffraction peak on the α'(211) plane is 1.35 or more. The method for manufacturing a sliding member according to any one of claims 7 to 10, wherein the martensitic stainless steel has a carbon content of 0.26% or more and 0.40% or less in weight%. .. The heat treatment is performed by placing the intermediate material in a heating furnace and holding the heating furnace in a non-oxidizing atmosphere.
The method for manufacturing a sliding member according to any one of claims 7 to 11, wherein the cooling treatment is performed by introducing an inert gas into the heating furnace. The method for manufacturing a sliding member according to any one of claims 7 to 12, wherein the heat treatment is performed at a temperature of 980 ° C. or higher and 1090 ° C. or lower and a holding time of 0 minutes or longer and 30 minutes or shorter. .. The method for manufacturing a sliding member according to any one of claims 7 to 13, wherein the cooling treatment is performed at a cooling rate of 80 ° C./min or more from the heating temperature in the heat treatment to 300 ° C. .. A vibrating actuator including a vibrating body and a contact body in contact with the vibrating body.
The vibrating body is
The sliding member according to any one of claims 1 to 6, which comes into contact with the contact body, and the sliding member.
A vibration type actuator characterized by having a piezoelectric body adhered to the sliding member.

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