KR101678417B1 - Surface treating method for article and surface treated article by the same - Google Patents

Abstract

The present invention relates to a method of surface treating an article containing a substantial amount of chromium (Cr) such as a tool steel using plasma and an article surface-treated by this method.
The surface treatment method according to the present invention is characterized by comprising a first surface treatment for ionizing the surface of an article using hydrogen and nitrogen and a second surface treatment for ionizing the surface of the article using nitrogen and argon after the first surface treatment .

Description

TECHNICAL FIELD [0001] The present invention relates to a surface treatment method for an article, and a surface treated article using the surface treated article.

The present invention relates to a surface treatment method for an article and an article surface-treated by the method, and more particularly to a method for surface-treating an article containing a substantial amount of chromium (Cr) such as a mold steel or a tool steel using plasma The present invention relates to an article surface-treated by a method.

Recently, the surface of mold steel has been exposed to severe plastic deformation due to the requirement for forming of high strength steel. In accordance with this trend, many studies are being conducted to improve the life of the mold steel.

It is known that the destruction of the material mainly starts from the surface, and the surface treatment technology of the material is an important technology for extending the life of the material.

Of these surface treatment techniques, the gas nitriding treatment imparts excellent physical properties to the surface of the material, contributing greatly to the extension of the life of the material, and thus is one of the most useful techniques in industry.

When the steel is subjected to gas nitriding, it generally has the sectional structure shown in Fig. As shown in FIG. 1, a compound layer made of various nitrides is formed on the outermost layer of the gas nitrided steel, and a diffusion zone in which nitride is present is formed under the compound layer In the lower portion of the diffusion region, there is a core zone in which a base material in which diffused nitrogen is partially dissolved exists.

As the nitrogen compound constituting the compound layer, epsilon phase (ε phase, Fe ₃ N) and gamma prase phase (γ 'phase, Fe ₄ N) are mainly formed, while the ε phase improves abrasion resistance and fatigue resistance, And local stress, and the γ 'phase is relatively soft and less abrasive than the ε phase, but the toughness is better. The products nitrided through the control of the? Phase and? 'Phase have better abrasion resistance, fatigue resistance and corrosion resistance.

In the gas nitriding process, ion nitriding is also referred to as plasma nitridation or glow discharge nitriding. In the ion nitriding method, nitrogen is introduced from the surface of the material into the inside of the material through the glow discharge between the furnace and the specimen So that the surface region of the material is nitrided.

Ion nitration is environmentally friendly because it consumes less gas than other gas nitriding processes, has low process costs, has a short cycle time, can repeat the process, and has many advantages that can be processed on almost all steels There is a way.

However, as described above, in order to improve the lifetime of the metal mold, it is required to develop an ion nitriding method capable of realizing more improved surface physical properties.

L.L.G. da Silva, M. Ueda, R.Z. Nakazato, Surf. Coat. Technol. 201 (2007) 8291

It is an object of the present invention to provide a novel surface treatment method capable of improving the surface physical properties of an article as compared with the prior art, and an article surface-treated by the method.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first surface treatment for ionizing a surface of an article using a mixed gas of hydrogen and nitrogen; and a second surface treatment using a mixed gas of argon and nitrogen And performing a second surface treatment for ion nitriding the surface of the article.

Another aspect of the present invention for solving the above problems is characterized in that it is made of steel containing 4 wt% to 32 wt% of chromium (Cr), and the nitrogen concentration on the surface of the article is 48 atomic% or more To provide a surface treated article.

The surface treatment according to the present invention can be carried out by a two-step nitriding process that performs a first surface treatment of ion nitriding using a mixed gas of hydrogen and nitrogen and a second surface treatment of ion nitriding using a mixed gas of argon and nitrogen , Surface modification having excellent wear characteristics as compared with the conventional nitriding process can be performed.

Further, according to the present invention, a surface hardness similar to that of the conventional nitriding treatment can be obtained even when the nitriding is performed for a shorter time than the conventional nitriding treatment.

In addition, the article surface-treated in accordance with the present invention has higher hardness and wear resistance than articles surface-treated with the conventional nitrification process, and can be suitably used particularly for improving the life of the mold steel.

Figure 1 schematically illustrates a typical cross-sectional structure of a gas nitrided steel.
2 schematically shows a structure of a gas nitriding apparatus used in the present invention.
3 is a process diagram of the ion nitridation process according to the first embodiment of the present invention.
4 is a process chart of the ion nitridation process according to the second embodiment of the present invention.
Fig. 5 is a process chart of an ion nitriding process according to a comparative example.
Fig. 6 is a hardness profile of the base material and the specimen surface-treated in accordance with the comparative example, examples 1 and 2. Fig.
Fig. 7 is a graph showing the relationship between the values of the voltages applied to the base (a) and (e), the comparative examples (b) and (f), the embodiment 1 (c) )) Were observed with an optical microscope and a scanning electron microscope.
8 is a photograph of the surface texture of a specimen surface-treated in accordance with Comparative Example (a), Example 1 (b), and Example 2 (c) with a scanning electron microscope.
Fig. 9 shows the results of XRD analysis of the microstructure of the base material, the comparative example, the example 1, and the example 2. Fig.
10 to 13 are diagrams showing the microstructure of the base material (FIG. 9), the comparative example (FIG. 10), the example 1 (FIG. 11) and the example 2 (FIG. 12) observed by a transmission electron microscope It is a photograph.
14 schematically shows a nitrided cross-section microstructure according to Example 1 of the present invention.
Fig. 15 shows the result of performing quantitative component analysis in the depth direction using GD-OES.
16 schematically shows the wear test apparatus and the wear test process performed in the present invention.
Fig. 17 shows the results of the abrasion test of the base material and the specimens surface-treated in accordance with the comparative example, the example 1 and the example 2. Fig.

The singular forms used to describe the embodiments of the present invention are meant to include plural forms unless the phrases expressly mean the opposite. And includes meaning of specific characteristics, regions, integers, steps, and actions. Elements and / or components, and other particular features, regions, integers, steps, acts. Quot; does not exclude the presence or addition of elements, elements and / or groups.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Also, commonly used predefined terms are not to be construed as ideal or very formal meanings unless further defined and interpreted as having a meaning consistent with the relevant technical literature and the present disclosure.

The inventors of the present invention conducted researches to improve the surface properties such as the hardness and the wear resistance of an article (particularly, an article made of steel containing a large amount of chromium such as a metal mold) in comparison with a conventional ion nitriding method while using ion nitriding As a result, it has been found that when a nitriding treatment using a mixed gas of argon and nitrogen is performed after a typical ion nitriding process using a mixed gas of hydrogen and nitrogen, the surface-treated microstructure becomes fine, the nitrogen concentration becomes high, The microstructure changes, and the change of the microstructure contributes to the improvement of the surface physical properties, leading to the present invention.

The surface treatment method according to the present invention is a surface treatment method comprising: a first surface treatment for ionizing a surface of an article by using a mixed gas of hydrogen and nitrogen; and a second surface treatment for ionizing the surface of the article by using a mixed gas of argon and nitrogen 2 < / RTI > surface treatment.

The article may be applied without limitation as long as it is made of a material capable of nitriding treatment. Preferably, steel containing 4 to 32% by weight of Cr may be used, more preferably 6 to 32% by weight of Cr Mold steel can be used.

If the content of Cr is less than 4% by weight, the effect of improving the surface properties is not sufficient. If the Cr content exceeds 32% by weight, the corrosion resistance due to the exhaustion of Cr, The content of Cr is preferably 4 to 32% by weight.

In the first surface treatment step, it is preferable that the mixing ratio of hydrogen and nitrogen is in the range of 1: 4 to 4: 1 by volume ratio of hydrogen to nitrogen, and nitriding is difficult to occur when the mixing ratio is out of the range.

In the second surface treatment step, the mixing ratio of argon and nitrogen is preferably in the range of 1: 5 to 5: 1 by volume ratio of argon and nitrogen. When the mixing ratio is out of the range, fine crystal grains are not formed, Is lowered and the physical properties of the surface may deteriorate.

In the first surface treatment step, the surface treatment time may be at least 1 hour, preferably 2 hours or more. In the second surface treatment step, the surface treatment time may be at least 2 hours, preferably at least 4 hours, and most preferably at least 6 hours.

The nitrogen concentration at the outermost surface of the article after the first surface treatment and the second surface treatment is 48 atomic% or more which can not be obtained by a general nitriding treatment. When the nitrogen concentration is less than 48 atomic%, the hardness and The improvement in abrasion resistance is not sufficient. Therefore, it is preferably 48 atomic% or more, and more preferably, the nitrogen concentration is 50 atomic%.

Wherein the compound layer formed on the surface of the article after first performing a surface treatment and second surface treatment may preferably include FeN, Fe ₃ N, Fe ₄ N, and CrN.

In addition, the compound layer formed on the surface of the article after the first surface treatment and the second surface treatment is performed may be a region other than the chromium carbide boundary portion (for example, a base region other than the interface of chromium carbide) And may also include recrystallized tissue.

Further, the article can be used for any application in which surface hardness and abrasion resistance are required, and can be used, for example, for a mold or a tool.

≪ Example 1 >

Quenching and tempered 12Cr-1.5C tool steel rods were used as the base material for ion nitriding. The hardness of this material was 670HV.

Table 1 shows the specific composition of the base material.

ingredient C Cr Mo V Mn Si P S Fe weight% 1.52 12.8 0.99 0.38 0.53 0.4 0.04 0.02 Honey.

Table 2 shows the mechanical properties of the base material.

Tensile Strength (MPa) Yield strength (MPa) Elongation (%) Charpy V-Notch (J) 1736 1532 6 3

The tool steel rod was processed into a rod having a diameter of 30 mm and a length of 10 mm using an EDM (electric discharge machine), the surface was polished using sandpaper, polished using a 1 μm diamond suspension, and finally ethanol Was placed in an ultrasonic bath and ultrasonically cleaned for 3 minutes.

After the ultrasonic cleaning, ion cleaning was performed between the substrate and the nitrogen scavenger using a mixed gas of argon and hydrogen under the conditions of a pressure of 66.7 Pa, a temperature of 450 ° C, and a bias voltage of -700 V.

The ion nitridation for the base rod subjected to the cleaning treatment was carried out in two steps at a pressure of 0.4 Pa and a temperature of 450 캜.

As shown in FIG. 3, the first-stage nitridation process was performed for 2 hours under a bias voltage of -670 V using a mixed gas of nitrogen (N ₂ ) and hydrogen (H ₂ ). At this time, the mixing ratio of nitrogen and hydrogen was 1: 1 by volume.

Subsequently, the mixture was subjected to a two-step nitriding process using a mixed gas of argon (Ar) and nitrogen (N ₂ ) at a bias voltage of -670 V for 6 hours. At this time, the mixing ratio of argon and nitrogen was 1: 1 by volume.

That is, the total nitriding time in Example 1 was 8 hours in total, and after the nitriding treatment, the furnace was cooled to room temperature.

≪ Example 2 >

Ion nitridation for the base rod subjected to the cleaning treatment was carried out in two steps at a pressure of 0.4 Pa and a temperature of 450 캜 in the same manner as in Example 1.

As shown in FIG. 4, the first-stage nitridation process was performed for 2 hours under a bias voltage of -670 V by using a mixed gas of nitrogen (N ₂ ) and hydrogen (H ₂ ). At this time, the mixing ratio of nitrogen and hydrogen was 1: 1 by volume.

The two-stage nitridation process was performed for 1 hour under a bias voltage of -670 V using a mixed gas of argon (Ar) and nitrogen (N ₂ ). At this time, the mixing ratio of argon and nitrogen was 1: 1 by volume.

That is, the total nitriding time in Example 2 was 3 hours in total, and after the nitriding treatment, the furnace was cooled to room temperature.

<Comparative Example>

The ion nitridation condition for the base rod subjected to the cleaning treatment was nitriding treatment at a pressure of 0.4 Pa and a temperature of 450 캜.

As shown in FIG. 5, the nitriding treatment was performed for 8 hours under a bias voltage of -670 V using a mixed gas of nitrogen (N ₂ ) and hydrogen (H ₂ ). At this time, the mixing ratio of nitrogen and hydrogen was 1: 1 by volume.

After the nitriding treatment, it was cooled to room temperature in the furnace.

Hardness analysis

The microhardness was measured using a Vickers microhardener (FM-7). Specifically, the microhardness was measured under a load of 10 g and a holding time of 15 seconds. All hardness tests were repeated 20 times or more, The average value was applied.

Hardness results, as shown in FIG. 6, and Example 1, the surface hardness of up to 1500HV _0.05 in Example 2, the surface hardness of up to 1200HV _0.05 and the comparative example the maximum surface hardness showed 1250HV _0.05.

In other words, it can be seen that the ion nitriding test piece according to Example 1 of the present invention significantly improved the surface maximum hardness as compared with the comparative example, which is a typical ion nitriding method of the related art.

On the other hand, in the case of Example 2, although the nitriding treatment was performed for 5 hours shorter than the nitriding time of the comparative example, the surface hardness near to the comparative example is shown. However, as compared with Example 1, since the hardness is considerably different, it is understood that the nitriding treatment of the second step needs to be performed for at least 2 hours, preferably 4 hours or more, and more preferably 6 hours or more.

6, the cured products of Example 1 and Comparative Example were cured up to about 60 탆, but in Example 2, the cured products were cured up to about 40 탆. This is because the nitriding time is remarkably shorter than that of the example 1 or the comparative example.

Microstructure

All nitrided specimens were analyzed by optical microscope, scanning electron microscope and X-ray diffractometer, GD-OES, and transmission electron microscope.

Fig. 7 is a graph showing the relationship between the amount of the base material ((a), (e)), the comparative examples ((b) h)) were observed with an optical microscope and a scanning electron microscope.

In the base material, a tempered martensite structure consisting of a combination of coarse and small particles is observed, and this microstructure is a structure that appears when the AISI D2 steel is quenched and tempered.

On the other hand, a homogeneous compound layer was formed on the surface region in Example 1 ((c), (g)) and Comparative Examples ((b) and (f)), In Example 2 ((d) and (h)), which was remarkably shorter than that of Comparative Example 1, the heterogeneous compound layer was formed.

8 is a photograph of the surface texture of a specimen surface-treated in accordance with Comparative Example (a), Example 1 (b), and Example 2 (c) with a scanning electron microscope.

As shown in FIG. 8, the method according to Example 1 of the present invention shows a state in which the surface roughness formed on the surface is greater than the surface roughness of the comparative example. It seems to be due to the surface collision of argon ion during ion nitridation using mixed gas. On the other hand, since the two-stage ion nitriding time in Example 2 was very short, the surface state was maintained to be smooth compared with Example 1.

Fig. 9 shows the results of XRD analysis of the microstructure of the base material, the comparative example, the example 1, and the example 2. Fig.

As shown in Fig. 9, in the case of the base material, several peaks related to α-Fe and chromium carbide, which are the main phases of AISI D2 steel, are detected.

After the nitriding process, a peak related to the nitrides, such as iron oxides and chromium nitrides, is additionally detected in the surface region. The nitriding time of the comparative example and the example 1 are the same, It can be seen that the peak of the cargo (Fe ₃ N) shows a difference of about 40% stronger than that of the comparative example.

That is, on the surface of Example 1 of the present invention, more chromium nitride and iron oxide are formed than the comparative example.

10 to 13 are photographs of the microstructure of the base material, the comparative example, the example 1, and the example 2, respectively, observed with a transmission electron microscope (TEM).

As shown in FIG. 10, it can be seen that the base material is composed of a tempered martensite structure together with a precipitate composed of a metal carbide such as Cr-rich carbide such as Cr ₂₃ C ₆ .

Comparing the image it can be seen that if geotinde taken within 1㎛ depth from the surface, as shown in Figure 11, the comparative example, that consists primarily of freight and cheoljil, chromium nitride consisting of Fe ₃ N. In addition, along with the significantly finely divided particles, chromium nitride is mainly observed around the chromium carbide.

As shown in Fig. 12, the image of Example 1 was photographed within a depth of 1 mu m from the surface. Unlike the Comparative Example, as shown in Fig. 12, the fine grain structure was shown in the compound layer, It has been observed that various nitrides such as Fe ₃ N, Fe ₄ N, and CrN are present in the surface region.

The image of Example 2 was taken at a depth of 1 탆 from the surface. As shown in FIG. 13, in Example 2, a microstructure similar to that of Example 1 was observed at the upper portion indicated by a white dotted line, Microstructure similar to the comparative example is observed. From this, it can be seen that, in the case of Example 2, the change from the surface layer to the microstructure as in Example 1 did not occur sufficiently due to the unsatisfactory two-step nitriding time.

Fig. 14 schematically shows the nitrided cross-sectional microstructure according to Example 1 of the present invention through the above-described microstructure analysis results. As shown in FIG. 13, when the nitriding treatment is performed according to the first embodiment, grain refinement occurs, and a CrN rich structure is formed at the outermost surface of the surface, and a nitrogen concentration And such a structure is a structure different from the microstructure realized by the general ion nitriding process.

Component analysis

Fig. 15 shows the result of performing quantitative component analysis in the depth direction using GD-OES.

As shown in Fig. 15, the nitrogen concentration of the first embodiment, the second embodiment and the comparative example all show the maximum nitrogen concentration on the surface, and the concentration of nitrogen gradually decreases toward the inside.

The concentration of nitrogen measured at the outermost surface of Example 1 was about 55 atomic%, about 30 atomic% for Example 2 and about 43 atomic% for the comparative example.

On the other hand, although the chromium concentration was lower than that of the base region, the maximum chromium concentration of Example 1 was higher than that of Comparative Example and Example 2.

Abrasion test

16 schematically shows the wear test apparatus and the wear test process performed in the present invention. As shown in FIG. 16, the abrasion test of the surface-treated specimens according to Examples 1 and 2 and Comparative Examples of the present invention was performed using a ball-on-disk type friction meter.

Specifically, the specimen is placed on a clockwise rotating stage, and an SiC ball having a diameter of 5.5953 mm and a hardness of 2100 HV is loaded through the rod arm.

The abrasion test was carried out at room temperature with a load of 5 N, 10 N, and 20 N and a rotation speed of 100 rpm, 200 rpm, and 500 rpm.

Fig. 17 is a graph showing the relationship between the wear rate of the base material without surface treatment and the rotational speed (100 rpm, (b) 200 rpm, (c) 500 rpm) of the test piece subjected to the nitriding treatment according to the Comparative Example and Example 1 .

As shown in Fig. 17, the wear rate of the specimen increases with an increase in the applied load, and the specimen surface-treated according to the comparative example and the example 1 exhibits a lower wear rate than the non-surface-treated base material.

However, the wear rate of the specimen according to Example 1 gradually increased as the load increased from 5N to 20N, while the wear rate of the specimen according to the comparative example reached a level similar to that of the base material at 20N, see.

That is, there is almost no difference between Comparative Example and Example 1 of the present invention at a low rotational speed during the lowering. However, as the load is increased and the rotational speed is increased, Example 1 of the present invention exhibits superior wear resistance Able to know.

These excellent abrasion resistance are caused by grain refinement by grain recrystallization, which is a structure formed near the surface of the material after nitriding treatment, and iron atoms, which are sputtered on the surface of the workpiece in comparison with the impact process using argon, A high nitrogen concentration layer in which a large amount is absorbed and formed, a relatively large amount of chromium nitride existing on the surface due to a large amount of absorbed nitrogen, and a surface irregularity formed in response to argon impingement, etc. have.

Claims (11)

A first surface treatment for ionizing the surface of an article made of steel containing 4 to 32% by weight of Cr by using a mixed gas of hydrogen and nitrogen,
After the first surface treatment, a second surface treatment is performed in which ion nitridation is performed using a mixed gas of argon and nitrogen,
In the first surface treatment, the mixture ratio of hydrogen and nitrogen is 1: 4 to 4: 1 by volume ratio of hydrogen to nitrogen, the surface treatment time is 2 hours or more,
In the second surface treatment, the mixture ratio of argon and nitrogen is 1: 5 to 5: 1 by volume ratio of argon and nitrogen, and the surface treatment time is 4 hours or more.
The nitrogen concentration at the surface of the article after the second surface treatment is 48 atomic% or more,
To a predetermined depth from the surface of the article compound layer is formed, the compound layer comprises a FeN, Fe ₃ N, Fe ₄ N, CrN phase,
Wherein a compound layer is formed from the surface of the article to a predetermined depth, and the compound layer has a recrystallization structure in a region other than the boundary of chromium carbide formed on the steel. delete delete delete delete delete The method according to claim 1,
Characterized in that the article is for a mold. As a surface treated article,
The article is made of steel containing 4 wt% to 32 wt% of chromium (Cr)
The nitrogen concentration on the surface of the article is 48 atomic% or more,
To a predetermined depth from the surface of the article compound layer is formed, the compound layer comprises a FeN, Fe ₃ N, Fe ₄ N, CrN phase,
Wherein a compound layer is formed from the surface of the article to a predetermined depth, and the compound layer has a recrystallized structure in a region other than a boundary of chromium carbide formed on the steel. delete delete 9. The method of claim 8,
Wherein the article is a metal mold.

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