KR0138441B1 - Surface hardening method of forged steel product - Google Patents
Surface hardening method of forged steel productInfo
- Publication number
- KR0138441B1 KR0138441B1 KR1019940040150A KR19940040150A KR0138441B1 KR 0138441 B1 KR0138441 B1 KR 0138441B1 KR 1019940040150 A KR1019940040150 A KR 1019940040150A KR 19940040150 A KR19940040150 A KR 19940040150A KR 0138441 B1 KR0138441 B1 KR 0138441B1
- Authority
- KR
- South Korea
- Prior art keywords
- forging
- steel
- temperature
- oil
- surface hardening
- Prior art date
Links
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 27
- 239000010959 steel Substances 0.000 title claims abstract description 27
- 238000000034 method Methods 0.000 title claims abstract description 17
- 238000005242 forging Methods 0.000 claims abstract description 38
- 238000010791 quenching Methods 0.000 abstract description 14
- 230000000171 quenching effect Effects 0.000 abstract description 14
- 238000001816 cooling Methods 0.000 abstract description 9
- 238000010438 heat treatment Methods 0.000 description 21
- 229910052799 carbon Inorganic materials 0.000 description 19
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 18
- 239000010410 layer Substances 0.000 description 16
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 6
- 238000005255 carburizing Methods 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 238000005299 abrasion Methods 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 229910000954 Medium-carbon steel Inorganic materials 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000005121 nitriding Methods 0.000 description 3
- 229910052698 phosphorus Inorganic materials 0.000 description 3
- 238000005096 rolling process Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 239000002344 surface layer Substances 0.000 description 3
- 238000005275 alloying Methods 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 230000035515 penetration Effects 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- 241000428199 Mustelinae Species 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 238000012805 post-processing Methods 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 230000006032 tissue transformation Effects 0.000 description 1
- 238000009966 trimming Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Forging (AREA)
- Heat Treatment Of Articles (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
Abstract
본 발명은 단조용 강재의 표면경화방법에 관한 것으로, 단조용 강재를 1150-1350℃로 가열하고, 햄머(hammer)나 프레스로 소정의 속도이상으로 단조하여 표면온도를 1000℃ 이상으로 유지한 후, 소입용 오일에 유냉시키므로써 강재의 표면에 내마모성이 큰 표면경화층을 형성시키게 된 것이다.The present invention relates to a method of hardening the surface of a forging steel, the forging steel is heated to 1150-1350 ℃, forging by a hammer or a press at a predetermined speed or more to maintain the surface temperature above 1000 ℃ By oil-cooling the quenching oil, the surface hardening layer having a high wear resistance is formed on the surface of the steel.
Description
제1도는 본 발명에 따라 제조된 단조용 강재의 표면조직 사진이다.1 is a photograph of the surface texture of the forging steel produced in accordance with the present invention.
본 발명은 단조용 강재의 표면경화방법에 관한 것으로, 특히 고주파, 침탄, 질화와 같은 별도의 표면경화 처리공정없이 단조공정시의 온도제어와 냉각매질, 냉각속도 등을 제어하여 단조품표면에 경도가 매우 높고 내마모성이 우수한 표면경화층을 형성하는 단조용 강재의 표면경화방법에 관한 것이다.The present invention relates to a method of hardening the surface of a forging steel, in particular, by controlling the temperature during the forging process, cooling medium, cooling rate, etc. without a separate surface hardening process such as high frequency, carburizing, nitriding, the hardness of the forged product surface The present invention relates to a method of hardening the surface of a forging steel to form a surface hardening layer having a very high wear resistance.
일반적으로 기계구조용 강은 중탄소, 저합금 소재를 열간 압연후 소정의 열처리를 실시하여 원하는 기계적 성질을 얻게 되는바, 특히 표면 내마모성이 요구되는 경우에는 고주파 유도전류에 의해서 소요의 깊이까지 급가열해서 급랭시키므로서 조직변태를 일으키는 고주파 담금질이나, 강의 표면에 고체, 액체 또는 가스체 등의 침탄제를 사용하여 강의 표면에 탄소를 침투시키므로서 소정의 표면경화층을 얻게 되는 침탄, 질소와 탄소를 강의 표면에 확산시킨 후 급랭시키는 질화 등의 표면경화처리를 추가적으로 실시하였다.In general, mechanical structural steels obtain desired mechanical properties by performing a predetermined heat treatment after hot rolling of a medium carbon or low alloy material. In particular, when surface wear resistance is required, a rapid heating to a required depth is required by a high frequency induction current. High frequency quenching, which causes tissue transformation by quenching, or carburizing agents such as solids, liquids, or gaseous bodies, infiltrating carbon into the surface of the steel, thereby obtaining carburizing, nitrogen, and carbon, which obtain a predetermined surface hardening layer. After surface diffusion, surface hardening treatment such as nitriding was further carried out.
이러한 표면경화처리는 제강과정에 있어서 화학성분 특히 합금원소의 퍼센트는 변화시키지 않고 강의 표면층에서만 화학성분의 변화를 일으키므로써 내마멸성, 내식성 또는 내마모성을 향상시키는 것이나 그 처리과정을 위해서는 별도의 제조공정이 추가되므로써 생산원가가 상승되고 또한 숙련된 열처리제어가 요구되기 때문에 이에 따른 열처리불량이 발생되는 문제점이 있었다.The surface hardening treatment does not change the percentage of chemical components, especially alloying elements, in the steelmaking process, but changes the chemical composition only in the surface layer of the steel to improve abrasion resistance, corrosion resistance or abrasion resistance, but a separate manufacturing process is added for the treatment process. As a result, the production cost is increased, and since the skilled heat treatment is required, there is a problem in that heat treatment defects occur.
이에 본 발명은 상기한 문제점을 해결하기 위한 것으로, 종래의 고주파 담금질, 침탄, 질화 등의 별도의 표면경화처리를 하지 않고도 표면처리강재와 동등 내지는 그 이상의 내마모성을 얻을 수 있는 단조용 강재의 표면경화방법을 제공하는 것이다.Accordingly, the present invention is to solve the above problems, the surface hardening of the steel forgings that can achieve abrasion resistance equivalent to or higher than the surface treatment steel without a separate surface hardening treatment such as conventional high-frequency quenching, carburizing, nitriding, etc. To provide a way.
상기한 목적을 달성하기 위한 본 발명의 단조용강재의 표면경화방법은 단조용 강재를 1150-1350℃로 가열하고, 햄머(hammer)나 프레스로 소정의 속도이상으로 단조하여 표면온도를 1000℃ 이상으로 유지한 후, 소입용 오일에 유냉시키게 된 것을 특징으로 한다.Surface hardening method of the forging steel of the present invention for achieving the above object is to heat the forging steel to 1150-1350 ℃, forging at a predetermined speed or more by a hammer or press to the surface temperature 1000 ℃ or more After maintaining, the oil for quenching is characterized in that it is cooled.
강의 표면경화는 고체, 액체 또는 가스체로 된 탄소, 질소 및 기타 합금 원소를 강의 표면을 둘러쌓아 직접 접촉시켜 강의 표면의 화학조성만을 변화시키는 것으로, 특히 탄소는 철에 침투되는 양 및 속도가 온도와 함께 증가하는 것으로, 예를들면 탄소는 V철에서 723℃로 0.8% 고용되나 1130℃로 약 2% 고용되며, 또한 925℃에서 1100℃가 되면 탄소가 철속으로 침투하는 속도가 7배이상이 된다.Surface hardening of steel changes only the chemical composition of the steel surface by directly contacting carbon, nitrogen, and other alloying elements in solid, liquid or gaseous form around the surface of the steel. Together, for example, carbon is employed in V iron at 0.8% at 723 ° C, but at about 2% at 1130 ° C, and at 925 ° C to 1100 ° C, the rate of carbon penetration into iron is more than seven times. .
따라서 본 발명의 공정은 단조용 강재를 환봉절단하여 소정의 온도로 가열하고, 소정의 단조공정을 거친 뒤, 1000℃ 이상의 소입온도로 유냉처리하므로써, 오일내의 탄소가 활성화되고, 이 활성화된 탄소가 강재의 표면에 침투하게 되어, 표면층의 탄소량을 증가시켜 주므로써 표면경도가 증가하게 되는 것이다.Therefore, in the process of the present invention, the forging steel is round-cut and heated to a predetermined temperature, and after undergoing the forging process, oil-cooled at a quenching temperature of 1000 ° C. or higher to activate carbon in the oil. It penetrates into the surface of the steel, thereby increasing the amount of carbon in the surface layer to increase the surface hardness.
이하에서 본 발명을 상세히 설명한다.Hereinafter, the present invention will be described in detail.
종래의 단조공정은 환봉절단→가열→단조→담금질 뜨임→가공→표면경화 열처리→후가공등으로 이루어져 있으나 본 발명은 환봉절단→가열→단조→오일담금질→뜨임→가공으로 이루어진 것으로, 종래 공정과의 가장 큰 차이점은 단조공정후 직접 유냉만을 실시하므로써 표면경화처리를 하게 되어 별도의 표면경화처리를 할 필요가 없게 되는 것이다.Conventional forging process consists of round bar cutting → heating → forging → quenching tempering → processing → surface hardening heat treatment → post-processing, etc. The present invention consists of round bar cutting → heating → forging → oil quenching → tempering → processing, The biggest difference is that the surface hardening treatment is performed by performing only oil cooling directly after the forging process, so that a separate surface hardening treatment is not necessary.
이러한 제조공정을 더욱 상세히 설명하면, 단조용 강재 환봉을 절단 및 1150-1350℃로 가열한 후 햄머나 프레스에서 금형사이에 놓고 타격한다.In more detail, such a manufacturing process, the forging steel round bar is cut and heated to 1150-1350 ℃ and then placed between the mold in the hammer or press hit.
이때 가열온도를 1150-1350℃로 한정한 이유는, 단조작업이 이루어지기 위해서는 단조시 온도가 1050-1150℃가 확보되어야만 성형작업이 가능하게 되고, 이러한 단조시의 작업온도를 유지하기 위해서는 가열한 후 단조공정까지 이동 시간이 공정라인에 따라 차이가 있지만 통상의 콘베이어 이송시에 대략 20초정도 소요되는 것을 감안할 때 제품의 표면온도가 대략 100℃ 정도 낮아지는 것을 고려하여 설정된 것이다.In this case, the heating temperature is limited to 1150-1350 ° C., in order to perform the forging operation, the forming operation is possible only when the temperature is forging at 1050-1150 ° C., and the heating temperature is maintained to maintain the working temperature during the forging. Although the movement time until the forging process is different depending on the process line, it is set in consideration of lowering the surface temperature of the product by about 100 ° C. in consideration of the fact that it takes about 20 seconds for the conveyance of a normal conveyor.
즉, 가열온도가 1150℃ 이하인 경우에는 가열후 단조작업시까지 이동되면 단조작업시는 최소의 온도인 1050℃ 이하로 되어 소성변형에너지가 증가하여 작업성이 급격히 떨어지기 때문에 가열온도는 1150℃ 이상으로 한정한다.In other words, if the heating temperature is 1150 ℃ or less, if it is moved to the forging operation after heating, the heating temperature is 1150 ℃ or more because the plastic deformation energy increases and the workability is sharply decreased because the plastic deformation energy increases during the forging operation. It is limited to.
그리고, 가열온도가 1350℃ 이상인 경우에는 제품표면에 과열에 의한 탈탄이나 일부 부위에서 용융되는 현상이 발생하여 작업이 곤란하게 되기 때문에 가열온도는 1350℃ 이하로 한정한다.In the case where the heating temperature is 1350 ° C or higher, decarburization due to overheating or melting at a part of the surface of the product occurs, which makes work difficult, so the heating temperature is limited to 1350 ° C or lower.
상기와 같은 가열온도에서 얻어진 제품은 타격시 가해지는 소성변형에너지가 열에너지로 바뀌게 되므로 타격부위의 온도는 온도상승효과가 생기게 되고, 더욱이 오목한 형상을 만들게 되는 경우는 온도상승효과가 크게 되는 경향이 있다.Since the plastic deformation energy applied at the time of the hitting is changed to the thermal energy, the product obtained at the heating temperature as described above has a temperature rising effect, and if the concave shape is made, the temperature rising effect tends to be large. .
그리고 단조후 플래쉬(flash)를 제거하는 트리밍(Trimming) 처리후 오일에 담금질을 실시하면 타격에 의해 온도가 상승된 고온부가 냉각 오일중의 탄소가 활성화되어 강재의 표면에 침투하게 되어 고경도의 표면경화층이 생성된다.When quenching in oil after trimming treatment to remove flash after forging, high temperature part whose temperature rises due to blow activates carbon in cooling oil and penetrates the surface of steel to harden surface. A layer is created.
이때 소입온도는 강재의 표면경화층의 탄소량 및 두께를 결정하는 중요한 것이므로, 상기 가열단계에서의 온도 및 단조시의 타격속도를 조절하므로써 소입온도를 1000℃ 이상으로 제어하는 것이 중요하다.At this time, the quenching temperature is important to determine the carbon amount and thickness of the surface hardening layer of the steel, it is important to control the quenching temperature to 1000 ℃ or more by adjusting the temperature in the heating step and the blow rate during forging.
여기서 소입온도가 1000℃ 이하로 되는 경우 탄소에 침투되는 탄소가 철속으로 침투되는 양이 적어지고 침투속도나 감소되어 원하는 표면경화층을 생성할 수 없게 되어, 소입온도를 1000℃ 이상으로 한정한 것이다.In this case, when the quenching temperature is lower than 1000 ° C, the amount of carbon that penetrates the carbon into the iron decreases and the penetration rate decreases, so that the desired surface hardened layer cannot be formed, and the quenching temperature is limited to 1000 ° C or higher. .
이러한 반응을 통해 생성된 표면의 두께는 10㎛-0.15mm정도이며, 이 경화층의 두께는 가열온도, 타격력에 의해 제어되는 소입온도와 냉각속도에 의해 결정되는 것이다.The thickness of the surface produced through this reaction is about 10 μm-0.15 mm, and the thickness of the hardened layer is determined by the quenching temperature and cooling rate controlled by the heating temperature and the impact force.
이렇게 제조된 단조용 강재는 제1도의 표면조직사진에서, 내부조직(a)은 펄라이트(pearlite)조직과 페라이트(ferrite)조직으로 되어 있고, 표면경화층(C)은 카바이드(carbide)조직으로 되어 있으며, 그 중간에 확산층(B)이 형성된 것을 알 수 있다.The forging steel thus manufactured is shown in the surface texture photograph of FIG. 1, and the internal structure (a) is composed of a pearlite structure and a ferrite structure, and the surface hardening layer (C) is made of a carbide structure. It can be seen that the diffusion layer (B) is formed in the middle.
또한 상기 단조용 강재의 표면경화층을 스펙트로메터로 분석해 보면 모재의 탄소성분이 0.4-0.5%인 것에 비해 표면층의 탄소성분은 최대 3.5%까지 높게 나타나고 조직도 주물 급냉응고 조직과 유사한 카바이드 칠(Carbide Chill)조직으로 경도가 Hv650-850으로 높게 나타난다.(모재경도 Hv350)In addition, when the surface hardening layer of the forging steel is analyzed by spectrometer, the carbon component of the base layer is higher than the carbon component of 0.4-0.5%, and the carbon component of the surface layer appears to be up to 3.5% higher. Hardness is high as Hv650-850 as a tissue (Material hardness Hv350)
이와 같은 표면경화층은 일반강에게 통상적으로 실시하는 고온 뜨임[550-650℃]으로도 변화가 발생되지 않아 내마모성에도 변화가 없는 특징을 갖는다.Such a surface hardening layer has a characteristic that there is no change in abrasion resistance because no change occurs even at high temperature temper [550-650 ° C.], which is usually performed on ordinary steel.
[실시예 1]Example 1
진공 용해후 압연비 8S이상으로 제작하여 만든 중탄소강 환봉(SM45C; C:0.43wt%, Si:0.20wt%, Mn:0.90wt%, P:0.02wt%, S:0.01wt%)을 1250℃로 가열한 후, 햄머에서 단조후 유냉을 실시하였다.Medium-carbon steel round bar (SM45C; C: 0.43wt%, Si: 0.20wt%, Mn: 0.90wt%, P: 0.02wt%, S: 0.01wt%) made by rolling ratio more than 8S after vacuum melting was 1250 ℃ After the heating, the forging was performed in a hammer, followed by oil cooling.
이때 오일의 온도는 60℃, 단조시의 타격횟수는 2회/sec, 최종 유냉시 부품의 표면온도는 1100℃였다.At this time, the oil temperature was 60 ° C, the number of blows during forging was twice / sec, and the surface temperature of the final oil-cooled part was 1100 ° C.
이 결과 얻어진 표면경화층의 두께는 0.1mm, 경도는 Hv 750, 표면탄소 농도는 2.6%였다.The resulting surface hardened layer had a thickness of 0.1 mm, a hardness of Hv 750 and a surface carbon concentration of 2.6%.
[실시예 2]Example 2
진공 용해후 압연비 8S이상으로 제작하여 만든 중탄소강 환봉(SM45C; C:0.43wt%, Si:0.20wt%, Mn:0.90wt%, P:0.02wt%, S:0.01wt%)을 1250℃로 가열한 후 프레스에서 단조후 유냉을 실시하였다.Medium-carbon steel round bar (SM45C; C: 0.43wt%, Si: 0.20wt%, Mn: 0.90wt%, P: 0.02wt%, S: 0.01wt%) made by rolling ratio more than 8S after vacuum melting was 1250 ℃ After heating in the press, forging was carried out for oil cooling.
이때 오일의 온도는 60℃, 단조시의 타격횟수는 1회/sec, 최종 유냉시 부품의 표면온도는 1050℃였다.At this time, the oil temperature was 60 ° C, the number of blows during forging was once / sec, and the surface temperature of the final oil-cooled part was 1050 ° C.
이 결과 얻어진 표면경화층은 두께 50㎛, 경도는 Hv 650, 표면탄소농도는 2.3%였다.The resulting surface hardened layer had a thickness of 50 µm, a hardness of Hv 650 and a surface carbon concentration of 2.3%.
[실시예 3]Example 3
진공 용해후 압연비 8S이상으로 제작하여 만든 중탄소강 환봉(SM45C; C:0.43wt%, Si:0.20wt%, Mn:0.90wt%, P:0.02wt%, S:0.01wt%)을 1250℃로 가열한 후, 프레스에서 단조후 유냉을 실시하였다.Medium-carbon steel round bar (SM45C; C: 0.43wt%, Si: 0.20wt%, Mn: 0.90wt%, P: 0.02wt%, S: 0.01wt%) made by rolling ratio more than 8S after vacuum melting was 1250 ℃ After heating in the furnace, oil cooling was performed after forging in a press.
이때 오일의 온도는 60℃, 단조시의 타격횟수는 1회/sec, 최종 유냉시 부품의 표면온도는 1050℃였다.At this time, the oil temperature was 60 ° C, the number of blows during forging was once / sec, and the surface temperature of the final oil-cooled part was 1050 ° C.
이 결과 얻어진 표면경화층의 두께는 50㎛, 경도는 Hv 650, 표면탄소 농도는 2.3%였다.The resulting surface hardened layer had a thickness of 50 µm, a hardness of Hv 650 and a surface carbon concentration of 2.3%.
이상에서 상술한 바와 같이 본 발명은 종래의 표면경화처리공정을 별도로 시행함이 없이 단조후 유냉으로만 조직이 안정된 카바이드(Carbide) 표면경화층을 얻을 수 있는 것으로, 고주파, 침탄 열처리에 의해 생성된 마르텐사이트(Martensite) 경화층보다 내마모성이 우수할 뿐아니라, 별도의 추가공정이 없어 경제적인 것이다.As described above, the present invention provides a carbide surface hardened layer whose structure is stable only by oil cooling after forging, without separately performing a conventional surface hardening treatment. Martens produced by high frequency and carburizing heat treatment It is more economical than the martensite hardened layer and there is no additional process.
이상에서 서술된 실시예는 모든 점에서 단순한 예시에 불과한 것이고, 이를 한정적으로 해석해서는 안되며, 단지 본 발명의 진지한 정신 및 범위내에 존재하는 변형예는 모두 본 발명의 청구범위에 속하는 것이다.The embodiments described above are merely examples in all respects and should not be construed as limiting. Only modifications existing within the serious spirit and scope of the present invention shall fall within the claims of the present invention.
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