KR20010027622A - Method for surface treatment of forging die - Google Patents
Method for surface treatment of forging die Download PDFInfo
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- KR20010027622A KR20010027622A KR1019990039429A KR19990039429A KR20010027622A KR 20010027622 A KR20010027622 A KR 20010027622A KR 1019990039429 A KR1019990039429 A KR 1019990039429A KR 19990039429 A KR19990039429 A KR 19990039429A KR 20010027622 A KR20010027622 A KR 20010027622A
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/34—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in more than one step
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/02—Pretreatment of the material to be coated
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
- C23C8/16—Oxidising using oxygen-containing compounds, e.g. water, carbon dioxide
- C23C8/18—Oxidising of ferrous surfaces
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/24—Nitriding
- C23C8/26—Nitriding of ferrous surfaces
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/36—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases using ionised gases, e.g. ionitriding
- C23C8/38—Treatment of ferrous surfaces
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/80—After-treatment
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- Engineering & Computer Science (AREA)
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- Mechanical Engineering (AREA)
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- Organic Chemistry (AREA)
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Abstract
Description
본 발명은 단조금형의 표면처리 방법에 관한 것으로, 보다 자세하게는 마이크로펄스 플라즈마를 이용하여 복잡한 형상의 금형표면에 대하여 균일하게 경화층이 형성되도록 하여 내마모성의 개선이 이루어지도록 하는 한편 플라즈마 질화처리에 이어지는 후속공정으로서의 산화물층 형성을 통해서 내식성 및 내충격성의 향상이 이루어질 수 있도록 한 단조금형의 표면처리 방법에 관한 것이다.The present invention relates to a surface treatment method of a forging die, and more particularly, by using a micropulse plasma to form a hardened layer uniformly on the surface of the mold of a complex shape to improve the wear resistance while following the plasma nitridation treatment The present invention relates to a forging mold surface treatment method which can improve corrosion resistance and impact resistance by forming an oxide layer as a subsequent step.
일반적으로 커넥팅 로드나 스핀들을 비롯한 각종 자동차 부품의 생산에 사용되는 단조금형의 경우에는 내마모성의 향상으로 위해 금형의 표면에 대한 경화처리가 행해지게 되는 데, 이러한 단조금형의 종래 표면처리 방식으로는 경질크롬 도금법과 가스질화가 주로 행해지고 있다.In general, forging molds used for the production of various automotive parts including connecting rods and spindles are hardened to the surface of the mold for improved wear resistance. The chromium plating method and gas nitriding are mainly performed.
그런데 상기 종래의 경질크롬 도금의 경우에는 단조금형의 표면에 형성된 크롬도금층이 400℃ 이상의 온도에서 연화되는 특성이 있으며, 도금층 자체가 다공성(porous) 조직으로 이루어져 있기 때문에 내마모성의 향상에 제한이 따르며 도금층의 응력으로 인하여 모재에 변형이 발생하는 단점이 지적되고 있다. 그리고, 경질크롬 도금법은 도금시에 유해한 공해물질이 배출되는 문제점이 있다.However, in the conventional hard chromium plating, the chromium plating layer formed on the surface of the forging die has a softening property at a temperature of 400 ° C. or higher. It is pointed out that the deformation occurs in the base material due to the stress of. In addition, the hard chromium plating method has a problem that harmful pollutants are discharged during plating.
한편, 질화처리 방법중의 하나인 가스질화는 모재의 표면에 질화물을 형성시켜 경도의 향상이 이루어지도록 하는 방식으로서 단조금형뿐만 아니라 커터나 드릴을 비롯한 각종 공구류의 경화처리에 많이 적용되고 있으나, 결정입계(grain boundary)에 질화물이 급격히 생성되는 경우가 있고, 이러한 경우에는 질화물의 입계편석(Nitriding Needle)에 기인하여 표면 질화물층의 박리현상이 나타나게 되는 문제점이 있다.On the other hand, gas nitriding, one of the nitriding methods, is used to harden various tools such as cutters and drills, as well as forging dies, by forming nitride on the surface of the base material to improve hardness. In some cases, nitride is rapidly formed at grain boundaries, and in this case, there is a problem that peeling of the surface nitride layer occurs due to a nitride needle.
특히, 가스질화를 이용하여 단조금형을 질화시키는 경우에는 최외표면에 화이트 레이어(White Layer)가 형성됨과 동시에 입계에서 니들(Needle)이 형성되는 데, 니들이 생성된 단조금형에서는 단조작업시 가해지는 충격에너지가 니들에 집중되고 이에 따라 크랙을 발생시키는 원인이 되기도 한다.In particular, when nitriding a forging die using gas nitriding, a white layer is formed on the outermost surface and a needle is formed at the grain boundary. Energy is concentrated on the needle, which in turn can cause cracks.
그리고, 상기 방법 이외의 단조금형 경화처리 방법으로서 900℃ 이상의 염욕중에서 약품을 사용하여 표면을 경화처리하는 일명 T.D(Toyoda Diffusion Process)처리와 플라즈마 질화처리가 알려지고 있다.As forging die-hardening treatment methods other than the above-mentioned methods, the so-called T.D (Toyoda Diffusion Process) treatment and the plasma nitriding treatment which harden the surface using chemical | medical agent in 900 degreeC or more salt bath are known.
상기 T.D처리의 경우에는 처리 후 심한 변형이 발생하므로 후 가공공정을 필요로 하는 문제점이 따르고 있다.In the case of the T.D treatment, since a severe deformation occurs after the treatment, there is a problem that requires a post-processing process.
상기 플라즈마 질화처리는 처리후에도 변형이 수반되지 않는다는 장점과 함께 환경친화적이라는 측면에서 많은 관심을 끌고 있긴 하나 복잡한 형상의 단조금형에 대해서는 균일한 경화층을 생성시키는 것이 곤란하다는 형상의 제한성과 코팅층의 낮은 밀착력등의 해결되어야 할 문제점을 안고 있다.The plasma nitridation treatment has attracted a lot of attention in terms of environmental friendliness with the advantage that it does not involve deformation even after the treatment, but it is difficult to produce a uniform hardened layer for complex forging molds. It has problems to be solved such as adhesion.
본 발명은 상기 종래 단조금형의 표면처리 방식에서 지적되고 있는 제반 문제점을 감안하여 창안된 것으로, 바이폴라 마이크로펄스 플라즈마(Bipolar Micropulse Plasma)를 이용하여 플라즈마 상태에서의 질소원자와 전자를 제어함으로써 불규칙하고 복잡한 표면형상을 갖는 금형의 전체 영역에 걸쳐 균일한 표면처리가 이루어지도록 함으로써 형상의 제한성 극복을 통한 내마모성의 향상을 도모한 단조금형의 표면처리 방법을 제공하는 데 목적을 두고 있다.The present invention was devised in view of various problems pointed out in the surface treatment method of the conventional forging mold, and irregular and complicated by controlling nitrogen atoms and electrons in a plasma state using a bipolar micropulse plasma. It is an object of the present invention to provide a forging die surface treatment method aimed at improving abrasion resistance through overcoming the limitation of the shape by performing uniform surface treatment over the entire area of the mold having the surface shape.
본 발명의 다른 목적은 플라즈마 질화처리에 후속되는 확산공정을 통해서 금형의 표면에 형성된 질소화합물을 분해시킴과 동시에 금속 내부로 확산되도록 함으로써 금형의 최외표면 경도를 낮춰서 내충격성의 향상이 이루어지도록 한 단조금형의 표면처리 방법을 제공하는 데 있다.Another object of the present invention is to forge a mold to improve the impact resistance by lowering the outermost surface hardness of the mold by decomposing nitrogen compounds formed on the surface of the mold through the diffusion process following plasma nitridation and diffusing into the metal. It is to provide a surface treatment method of.
본 발명의 또 다른 목적은 플라즈마 질화처리에 이은 확산공정의 완료 후에 산화피막을 형성시켜 금형의 내식성 및 고온윤활성의 향상이 이루어지도록 한 단조금형의 표면처리 방법을 제공하는 데 있다.It is still another object of the present invention to provide a forging die surface treatment method in which an oxide film is formed after completion of a plasma nitriding treatment followed by a diffusion process to improve corrosion resistance and high temperature lubrication of a mold.
본 발명의 상기 목적을 달성하는데 가장 중요한 기술적 사항으로서의 마이크로펄스 플라즈마 표면처리 방식의 배경기술과 기본원리 및 특성을 간략하게 살펴보면 다음과 같다.The technical background and basic principles and characteristics of the micropulse plasma surface treatment method as the most important technical matters for achieving the above object of the present invention will be briefly described.
일반적으로 철계 소재의 표면에 플라즈마 표면처리를 통하여 수명을 향상시키기 위해서는, 플라즈마 상태에서 표면반응이 활성화되어 진행하여야 하며, 또한 형상의 제한성에 무관하게 제품 전체에 플라즈마가 균일하게 형성되어야만이 된다.In general, in order to improve the life through the plasma surface treatment on the surface of the iron-based material, the surface reaction must be activated and proceed in the plasma state, and the plasma must be uniformly formed throughout the product regardless of the limitation of the shape.
상기 두가지의 조건을 만족시키기 위해서는 모재로부터 분리된 철원자의 수가 많아야 하고, 플라즈마 상태에서 존재하는 중성 질소원자의 수가 많아야 한다.In order to satisfy the above two conditions, the number of iron atoms separated from the base material must be large, and the number of neutral nitrogen atoms present in the plasma state must be large.
그리고, 이들 두 종류의 원자가 상호 반응을 일으킬 확율은 플라즈마의 파워가 증가됨에 따라서 증대되므로 높은 전압을 사용하는 것이 유리하다 할 것이나, 플라즈마 질화에 사용할 수 있는 전압은 아크 영역으로 이동되기 전까지의 영역으로 한정되어 있다.The probability that these two types of atoms will react with each other increases as the power of the plasma increases, so it would be advantageous to use a higher voltage, but the voltage that can be used for plasma nitridation is transferred to the area before moving to the arc region. It is limited.
또한 피처리재의 형상이 복잡할 수록 높은 압력 및 전압으로 C.F.T.(Cathode Fall Thickness)를 얇게 형성시켜야 하는데 플라즈마가 존재하는 상태에서의 압력증가는 진공상태의 와해를 의미하기 때문에 플라즈마를 유지시키기 위해서는 더욱 높은 전압의 사용이 불가피하게 된다.In addition, the more complicated the shape of the material to be processed, the thinner the CFT (Cathode Fall Thickness) should be formed at a higher pressure and voltage. The increase in pressure in the presence of the plasma means the breakdown of the vacuum state. The use of voltage is inevitable.
특히, 자동차부품용 단조금형과 같이 복잡한 표면형상을 갖는 제품에 대하여 기존의 플라즈마 질화처리 방식으로 표면처리르 하는 경우에는 충격에너지를 유발하는 이온 및 H.C.D(Hollow Cathode Discharge)를 발생시키는 전자에 의해서 국부적인 과열(over heating)이 발생하여 소재가 오히려 연화되는 역효과가 나타나게 된다.Particularly, in case of surface treatment using a conventional plasma nitridation method for a product having a complex surface shape such as a forging die for automobile parts, it is localized by ions causing impact energy and electrons generating HCD (Hollow Cathode Discharge). Phosphorus overheating occurs and the adverse effect of the softening of the material appears.
이에 따라, 본 발명의 방법에서는 바이폴라 마이크로펄스 플라즈마를 이용하여 단조금형과 같이 형상이 복잡한 경우에 충격에너지를 유발하는 이온 및 전자를 제어함으로써 소재의 국부적인 과열이 억제되도록 하여 형상에 무관하게 균일한 표면반응이 일어나도록 하고 있다.Accordingly, in the method of the present invention, bipolar micropulse plasma is used to control ions and electrons that cause impact energy when the shape is complex, such as forging dies, so that local overheating of the material is suppressed, thereby making it uniform regardless of the shape. Surface reactions occur.
즉, 본 발명에서는 금형에 순간적으로 양극을 인가시킴에 의해 전자들을 소멸시키고 플라즈마 표면처리시 발생하는 쉴드(shield)를 제거하여 지속적으로 균일한 플라즈마 상태를 유지시킴으로써 금형의 과열없이 표면처리가 가능하도록 함과 아울러 재료의 안정성을 증가시키기 위해 아크의 발생시 μs 단위로 인가전압을 정지시키게 된다.That is, in the present invention, the anode is instantaneously applied to the mold to dissipate the electrons and remove the shield generated during the plasma surface treatment to maintain a uniform plasma state so that the surface treatment can be performed without overheating the mold. In addition, to increase the stability of the material, the applied voltage is stopped in μs when the arc is generated.
도1은 본 발명의 실시예 시편에 대한 종단면도.1 is a longitudinal cross-sectional view of an embodiment specimen of the present invention.
도2는 본 발명의 방법에 의해 처리된 실시예 시편의 표면으로부터 내부로의 경도 프로파일.2 is a hardness profile from the surface to the interior of an example specimen treated by the method of the present invention.
본 발명의 단조금형의 표면처리 방법은, 진공로중에 장입된 단조금형의 주위에 플라즈마를 형성시키고 수소가스와 알곤가스를 이용하여 표면에 대한 세척 및 가열을 행하는 세척(sputtering)공정과, 마이크로펄스 플라즈마를 이용하여 질소원자가 금형의 내부로 확산되도록 하는 질화(Nitriding)공정과, 내충격성의 향상을 위해 표면에 형성된 질소화합물의 분해 및 내부로의 확산이 이루어지도록 하는 확산(Glowing)으로 이루어지며 이에 부가하여 금형의 표면에 산화피막을 형성시켜 내식성 및 고온윤활성이 증대되도록 하는 산화(Oxidizing)공정이 추가적으로 수행될 수도 있다.The forging die surface treatment method includes a sputtering step of forming a plasma around a forging die charged in a vacuum furnace, and washing and heating the surface using hydrogen gas and argon gas, and a micropulse. Nitriding process that allows nitrogen atoms to diffuse into the mold by using plasma, and Glowing, which allows decomposition and diffusion of nitrogen compounds formed on the surface to improve impact resistance. By forming an oxide film on the surface of the mold, an oxidation process may be additionally performed to increase corrosion resistance and high temperature lubrication.
상기 세척공정은 일종의 전처리 공정으로서, 후속되는 질화공정시 질소원자의 확산을 용이하게 하기 위한 공정이다. 단조금형의 내마모 특성 향상을 위해서는 금형의 표면으로 질소원자가 얼마만큼 확산되고 철계와 반응하여 질소화합물을 형성하는 가가 중요하게 작용하는 데, 세척공정에서는 금형주위에 플라즈마를 형성시키고 수소와 알곤가스를 이용하여 금형표면에 흡착된 불순물 및 산화피막을 제거시키게 된다. 그리고, 세척공정에서는 전체 처리시간의 단축을 위하여 진공로의 온도를 400 ∼ 530℃로 유지시켜 금형이 질화에 필요한 온도로 가열되도록 한다.The washing step is a kind of pretreatment step, which facilitates diffusion of nitrogen atoms in the subsequent nitriding step. In order to improve the wear resistance of the forging mold, how much nitrogen atom diffuses to the surface of the mold and reacts with the iron system is important. In the washing process, plasma is formed around the mold and hydrogen and argon gas are applied. It is used to remove the impurities and oxide film adsorbed on the mold surface. In the washing process, the temperature of the vacuum furnace is maintained at 400 to 530 ° C. in order to shorten the overall processing time so that the mold is heated to the temperature required for nitriding.
다음, 질화공정은 금형의 표면에 실제로 질화물 및 확산층이 형성되도록 하는 가장 중요한 단계이다. 탄소원자와 유사한 크기를 갖는 질소원자는 바이폴라 마이크로펄스 플라즈마 질화처리에 의해서 금속내부로 확산이 이루어지게 되는 데, 그 반응이 빠르게 진행되는 경우에는 입계에 질소화합물이 형성되어 내충격성에 악영향을 미치게 된다. 반면에, 반응이 너무 느리게 진행되는 경우에는 확산층의 깊이가 줄어들어서 내마모 특성을 충분히 향상시킬 수 없게 된다.Next, the nitriding process is the most important step to actually form the nitride and diffusion layers on the surface of the mold. Nitrogen atoms having a size similar to that of carbon atoms are diffused into the metal by bipolar micropulse plasma nitriding. When the reaction proceeds rapidly, nitrogen compounds are formed at grain boundaries, which adversely affects impact resistance. On the other hand, if the reaction proceeds too slowly, the depth of the diffusion layer is reduced so that the wear resistance cannot be sufficiently improved.
따라서, 단조금형의 내충격 특성과 내마모 특성 모두를 만족시키기 위해서는 반응속도를 적절히 제어하여야 하는 데, 그러한 단조금형의 반응속도는 단조금형의 형상, 총 장입량 등에 따라서 변화되므로 이들 변수의 조정에 주의를 필요로 한다.Therefore, in order to satisfy both impact resistance and abrasion resistance characteristics of the forging mold, the reaction speed must be appropriately controlled.The reaction speed of such forging mold is changed according to the shape of the forging mold, the total loading amount, etc., so pay attention to the adjustment of these variables. in need.
한편, 질화공정에서는 수소, 질소 및 메탄 등의 가스가 사용되며 일부 알곤가스가 사용되기도 한다.Meanwhile, in the nitriding process, gases such as hydrogen, nitrogen, and methane are used, and some argon gas is also used.
다음, 확산공정은 질화공정을 통해서 금형의 표면에 형성된 질소화합물을 분해시킴과 동시에 금속내부로의 확산이 이루어지도록 하여 내충격성이 향상되도록 하는 단계이다. 확산공정을 거친 후의 금형에서는 화이트 레이어 및 입계 질소화합물이 잔존하여서는 안된다. 질화처리시 최외 표면에 발생되는 화이트 레이어는 주로 Fe2-3N 또는 Fe4N으로서 경도가 Hv1000 이상의 매우 취성이 높은(brittle) 특성을 지닌다. 따라서 화이트 레이어는 단조공정중에 박리현상이 발생되고 박리된 화합물은 마찰 마모(abrasive ware)를 초래하게 되기 때문에 본 발명의 질화시에는 화이트 레이어의 생성을 최대한 억제시키도록 분위기를 제어하게 된다.Next, the diffusion process is a step of decomposing the nitrogen compound formed on the surface of the mold through the nitriding process and at the same time to diffuse into the metal to improve the impact resistance. In the mold after the diffusion process, the white layer and the intergranular nitrogen compounds should not remain. The white layer generated on the outermost surface during nitriding is mainly Fe 2-3 N or Fe 4 N, and has a very brittle characteristic of hardness of Hv1000 or more. Therefore, since the peeling phenomenon occurs during the forging process and the peeled compound causes abrasion ware, the white layer controls the atmosphere to suppress the generation of the white layer as much as possible during the nitriding of the present invention.
또한 확산공정시에는 표면의 경도를 낮춤과 동시에 활성화시켜야 한다. 이같은 확산공정의 결과로 금형의 최외표면은 그 내부에 비해서 경도가 낮아지게 되나 인성은 증대된다.In addition, during the diffusion process, the surface hardness should be lowered and activated at the same time. As a result of the diffusion process, the outermost surface of the mold is lower in hardness than the inside thereof, but the toughness is increased.
확산공정에서 사용되는 가스로는 수소와 일부 알곤이 이용되며, 플라즈마의 균일한 분포가 매우 중요한 역할을 하고 있다.Hydrogen and some argon are used as the gas used in the diffusion process, and the uniform distribution of plasma plays a very important role.
본 발명의 단조금형 표면처리 방법은 상기의 세척→질화→확산으로 이어지는 3단계 공정에 의해서 완료될 수 있으나, 고온 내마모 특성과 표면 윤활성 및 내식성이 요구되는 경우에는 산화공정이 추가적으로 수행된다.The forging die surface treatment method of the present invention can be completed by a three-step process leading to the above washing → nitriding → diffusion, but an oxidation process is additionally performed when high temperature wear resistance and surface lubricity and corrosion resistance are required.
상기 산화공정은 노내 분위기를 진공상태(약 0.2 - 0.3mbar 정도)로 유지한 가운데 노내부로 수증기를 공급하여 경화처리된 금형의 표면에 산화피막으로서의 Fe3O4를 형성시키게 된다. 일반적으로 열간단조시에는 단조금형의 표면온도가 피단조품의 매스 플로우(mass flow)에 의해 약 800℃ 이상으로 상승하게 되는 데, 질화층이 600℃ 이상의 온도에서 열분해가 시작되는 점을 감안할 때 금형의 수명단축이 충분히 예상된다. 이때 본 발명의 산화피막은 피단조품으로부터 질화층으로 전해지는 열전달을 억제시키는 역할을 함으로써 질화층의 열분해가 방지되도록 함과 아울러 산화피막이 부동태(passive layer)로 작용하여 금형표면에 더 이상 산화가 진행되는 것을 방지하게 된다.The oxidation process maintains the furnace atmosphere in a vacuum state (about 0.2-0.3 mbar) to supply water vapor into the furnace to form Fe 3 O 4 as an oxide film on the surface of the hardened mold. In general, during hot forging, the surface temperature of the forging die rises to about 800 ° C. or higher due to the mass flow of the forged product. In view of the fact that the pyrolysis starts at a temperature of 600 ° C. or higher, the mold It is expected that the shortening of the service life will be sufficient. At this time, the oxide film of the present invention serves to inhibit heat transfer from the forged product to the nitride layer, thereby preventing thermal decomposition of the nitride layer, and the oxide film acts as a passive layer to further oxidize the mold surface. To prevent it.
상기 산화공정을 통해 형성된 산화피막은 조밀하며 화학반응을 이용하므로 물리적인 방법에 의해 형성된 피막층보다 우수한 결합력을 나타낸다.Since the oxide film formed through the oxidation process is dense and uses a chemical reaction, it shows superior bonding strength than the film layer formed by the physical method.
본 발명을 실시예와 관련하여 보다 구체적으로 설명한다.The present invention is described in more detail with reference to examples.
실시예Example
도1에 도시된 바와같은 단면형상을 갖는 SKD61 소재로 이루어진 시편을 마련하였다. 시편의 내부에 형성된 홈의 깊이(d)는 17.5mm 이고, 폭(w)은 3.5mm 이다.A specimen made of SKD61 material having a cross-sectional shape as shown in FIG. 1 was prepared. The depth d of the groove formed in the specimen is 17.5 mm, and the width w is 3.5 mm.
먼저, 시편을 진공로중에 장입하고 시편 주위에 플라즈마를 형성시킨 상태에서 노 내부로 수소와 알곤가스를 주입하여 시편의 표면에 잔류하는 불순물 및 산화피막을 제거시켰다. 이와같은 세척공정은 전압 780V, 압력 0.5 ∼ 2mbar, 온도 400 ∼ 530℃, 유지시간 약 0.7시간 및 바이폴라비 50:1의 조건하에서 행하였다.First, the specimen was charged in a vacuum furnace and hydrogen and argon gas was injected into the furnace while plasma was formed around the specimen to remove impurities and oxide films remaining on the surface of the specimen. This washing process was performed under the conditions of voltage 780V, pressure 0.5-2 mbar, temperature 400-530 degreeC, holding time about 0.7 hours, and bipolar ratio 50: 1.
이어서, 시편의 표면에 질화물 및 확산층을 형성시키는 질화공정을 수행하였다. 이때에는 수소, 질소, 메탄 가스가 사용되었으며, 노내 조건은 전압 500 ∼ 560V, 압력 4 ∼ 6mbar, 온도 약 530℃, 유지시간 약 10시간 및 바이폴라비 20 ∼ 25:1로 유지하였다. 상기 질화공정시에는 반응속도를 적절히 조절하여 화이트 레이어의 발생 및 입계 질소화합물의 형성이 최대한 억제되도록 하였다.Next, a nitriding process was performed to form a nitride and a diffusion layer on the surface of the specimen. At this time, hydrogen, nitrogen, methane gas was used, and the furnace conditions were maintained at a voltage of 500 to 560 V, a pressure of 4 to 6 mbar, a temperature of about 530 ° C., a holding time of about 10 hours, and a bipolar ratio of 20 to 25: 1. During the nitriding process, the reaction rate was properly adjusted to suppress the generation of the white layer and the formation of the grain boundary nitrogen compound as much as possible.
다음, 상기의 질화공정에 의해서 질화처리된 시편의 표면에 형성되어 있는 질소화합물을 분해시킴과 동시에 내부로의 확산이 이루어지도록 하였다. 이때에는 수소와 일부 알곤 가스를 사용하였으며 플라즈마가 균일하게 분포되도록 하였다. 확산공정의 조건은 전압 530 ∼ 610V, 압력 5 ∼ 7mbar, 온도 530℃, 유지시간 약 3시간 및 바이폴라비 15:1로 하였다.Next, the nitrogen compound formed on the surface of the nitrided specimen was decomposed by the nitriding process and diffused into the interior. At this time, hydrogen and some argon gas were used to uniformly distribute the plasma. The conditions of the diffusion process were voltage 530-610V, pressure 5-7 mbar, temperature 530 degreeC, holding time about 3 hours, and bipolar ratio 15: 1.
마지막 공정으로서 노 내부가 단순히 0.2 ∼ 0.3mbar의 진공상태가 유지되도록 한 가운데 수증기를 투입하여 시편의 표면에 두께 3 ∼ 4μm의 Fe3O4산화피막이 형성되도록 하였다.As a final process, the inside of the furnace was simply maintained in a vacuum of 0.2 to 0.3 mbar while steam was added to form a 3 to 4 μm thick Fe 3 O 4 oxide film on the surface of the specimen.
상기의 방법을 통해서 표면처리된 본 발명의 실시예 시편과 종래 방법에 의해 표면처리된 비교예 시편에 대하여 특성을 비교함과 아울러 이들 특성이 소정의 평가기준의 범위내에 있는가를 살펴보았던 바, 그 결과는 아래의 표1과 같다.As a result of comparing the characteristics of the specimens of the present invention surface-treated by the above-described method and the comparative specimens surface-treated by the conventional method and examining whether these characteristics are within a predetermined evaluation criteria, the results were as follows. Is shown in Table 1 below.
상기 표1에서와 같이 본 발명의 실시예 시편은 경도분포와 표면처리의 균일성을 비롯한 모든 평가항목에 있어서 평가기준을 만족하고 있으며, 비교예 시편에 비해서 우수한 특성을 나타내고 있다.As shown in Table 1, the sample of the present invention satisfies the evaluation criteria in all evaluation items including hardness distribution and uniformity of surface treatment, and showed superior characteristics compared to the comparative sample.
그리고, 본 발명의 방법에 따라 표면처리된 시편은 확산공정에 의해서 표면부의 질소화합물이 분해되고 또한 내부로 확산됨에 따라 최외표면부의 경도가 내부에 비해서 오히려 낮은 특성을 나타내게 되는 데, 도2는 이러한 본 발명 시편의 경도 프로파일을 나타내고 있다.In addition, the specimen surface-treated in accordance with the method of the present invention exhibits a characteristic that the hardness of the outermost surface portion is lower than that inside as the nitrogen compound of the surface portion is decomposed by the diffusion process and diffused into the interior. The hardness profile of the specimen of the present invention is shown.
이상에서 살펴본 바와같이, 본 발명 단조금형의 표면처리 방법에서는 마이크로펄스 플라즈마 처리를 통하여 복잡한 형상과 불균일한 표면을 갖는 단조금형에 균일한 경화처리가 이루어지도록 함으로써 형상의 제한성 극복과 함께 내마모성의 향상을 통한 금형의 전체적인 수명증대를 도모할 수 있는 효과가 있다.As described above, in the surface treatment method of the forging mold of the present invention, by forging a uniform curing treatment to the forging mold having a complex shape and a non-uniform surface through a micropulse plasma treatment to overcome the limitation of the shape and to improve the wear resistance Through this, it is possible to increase the overall life of the mold.
그리고, 본 발명에서는 질화공정의 수행후에 플라즈마 열처리를 행하여 금형표면의 질소화합물의 분해 및 내부로의 확산이 이루어지도록 하여 최외표면의 경도를 낮춤과 함께 인성의 증대가 이루어지도록 함으로써 내충격성이 향상되도록 하는 장점이 있다.In addition, in the present invention, after performing the nitriding process, plasma heat treatment is performed to decompose the nitrogen compound on the surface of the mold and to diffuse it into the inside so that the impact resistance is improved by lowering the hardness of the outermost surface and increasing the toughness. There is an advantage.
또한, 본 발명의 방법에서는 표면처리된 금형의 표면에 산화피막을 형성하여 열간단조시 피단조 제품으로부터의 열이 금형내부로 전열되는 것을 차단함으로써 질화경화층의 열분해를 억제하여 결과적으로 금형의 수명연장이 이루어지도록 함과 아울러 상기 산화피막이 부동태층으로 작용하여 더이상의 산화를 억제함으로써 고온 내식성이 향상된다.In addition, in the method of the present invention, an oxide film is formed on the surface of the surface-treated mold to prevent heat from the forged product to be transferred to the inside of the mold during hot forging, thereby suppressing thermal decomposition of the nitride hardened layer and consequently the life of the mold. In addition to the extension, the oxide film acts as a passivation layer to suppress further oxidation, thereby improving high temperature corrosion resistance.
이에 더하여, 본 발명의 방법은 전체 공정이 단일 장치내에서 수행되므로 생산성이 뛰어나며 또한 환경친화적인 플라즈마 질화처리 방식의 채택에 의해 공해요인이 배제되는 효과도 아울러 지니고 있다.In addition, the method of the present invention has the effect of eliminating pollution by adopting an environmentally friendly plasma nitriding treatment method because the whole process is performed in a single apparatus.
따라서, 본 발명의 방법은 링기어, 스핀들, 크랭크 및 커넥팅 로드 등을 비롯한 각종 자동차용 부품의 단조시에 유용하게 활용될 수 있음은 물론 그 외에도 압출금형, 사출금형 및 다이캐스팅 금형등에도 응용되어 사용될 수 있을 것으로 기대되고 있다.Therefore, the method of the present invention can be usefully used for forging various automotive parts including ring gears, spindles, cranks, connecting rods, etc., as well as being applied to extrusion molds, injection molds, and die casting molds. It is expected to be able.
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
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KR100503497B1 (en) * | 2002-11-25 | 2005-07-26 | 한국기계연구원 | Heat treating method for improving the wear-resistance and corrosion-resistance of chromium platings |
KR100864700B1 (en) * | 2007-04-25 | 2008-10-23 | 박석봉 | Surface hardening method for large molding steel |
KR20160009503A (en) | 2014-07-15 | 2016-01-26 | 금오공과대학교 산학협력단 | Extrusion mold of surface-treated and method for treating thereof |
KR20160009505A (en) | 2014-07-15 | 2016-01-26 | 금오공과대학교 산학협력단 | Surface treating method of extrusion die and Extrusion die |
KR20160009504A (en) | 2014-07-15 | 2016-01-26 | 금오공과대학교 산학협력단 | Surface treating method of extrusion die, Extrusion die and Extrude process system |
Families Citing this family (4)
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JP2003120534A (en) * | 2001-10-05 | 2003-04-23 | Hitachi Ltd | Compressor for refrigeration, and manufacturing method of connecting rod thereof |
KR100624043B1 (en) | 2005-02-28 | 2006-09-19 | 주식회사 케이피티 | Metal surface hardening method |
KR100837789B1 (en) | 2007-03-02 | 2008-06-13 | 정익수 | Nitriding treatment method |
KR101719452B1 (en) | 2016-04-27 | 2017-03-23 | 박래규 | Surface treatment method of hot forging mold and the hot forging mold |
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1999
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
KR100503497B1 (en) * | 2002-11-25 | 2005-07-26 | 한국기계연구원 | Heat treating method for improving the wear-resistance and corrosion-resistance of chromium platings |
KR100864700B1 (en) * | 2007-04-25 | 2008-10-23 | 박석봉 | Surface hardening method for large molding steel |
KR20160009503A (en) | 2014-07-15 | 2016-01-26 | 금오공과대학교 산학협력단 | Extrusion mold of surface-treated and method for treating thereof |
KR20160009505A (en) | 2014-07-15 | 2016-01-26 | 금오공과대학교 산학협력단 | Surface treating method of extrusion die and Extrusion die |
KR20160009504A (en) | 2014-07-15 | 2016-01-26 | 금오공과대학교 산학협력단 | Surface treating method of extrusion die, Extrusion die and Extrude process system |
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