KR100336634B1 - heat treatment method for surface hardening for steel of bearing - Google Patents
heat treatment method for surface hardening for steel of bearing Download PDFInfo
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- KR100336634B1 KR100336634B1 KR1019990029750A KR19990029750A KR100336634B1 KR 100336634 B1 KR100336634 B1 KR 100336634B1 KR 1019990029750 A KR1019990029750 A KR 1019990029750A KR 19990029750 A KR19990029750 A KR 19990029750A KR 100336634 B1 KR100336634 B1 KR 100336634B1
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- 238000000034 method Methods 0.000 title claims abstract description 38
- 238000010438 heat treatment Methods 0.000 title claims abstract description 30
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 29
- 239000010959 steel Substances 0.000 title claims abstract description 29
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 34
- 239000007789 gas Substances 0.000 claims abstract description 29
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 18
- 229910001209 Low-carbon steel Inorganic materials 0.000 claims abstract description 16
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 9
- 229910052799 carbon Inorganic materials 0.000 claims description 14
- 239000002344 surface layer Substances 0.000 claims description 14
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 9
- 238000005496 tempering Methods 0.000 claims description 8
- 229910000975 Carbon steel Inorganic materials 0.000 claims 1
- 238000005461 lubrication Methods 0.000 abstract description 10
- 238000009792 diffusion process Methods 0.000 abstract description 5
- 238000005255 carburizing Methods 0.000 description 9
- 229910001566 austenite Inorganic materials 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 238000005121 nitriding Methods 0.000 description 6
- 230000007547 defect Effects 0.000 description 5
- 238000009826 distribution Methods 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 239000010410 layer Substances 0.000 description 4
- 239000011148 porous material Substances 0.000 description 4
- 238000010791 quenching Methods 0.000 description 4
- 230000000717 retained effect Effects 0.000 description 4
- 230000015556 catabolic process Effects 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 230000035515 penetration Effects 0.000 description 3
- 230000000171 quenching effect Effects 0.000 description 3
- 238000005096 rolling process Methods 0.000 description 3
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 229910000669 Chrome steel Inorganic materials 0.000 description 1
- 101000622427 Homo sapiens Vang-like protein 1 Proteins 0.000 description 1
- 102100023517 Vang-like protein 1 Human genes 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000001273 butane Substances 0.000 description 1
- 150000001721 carbon Chemical group 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000009661 fatigue test Methods 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 239000002737 fuel gas Substances 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 230000001050 lubricating effect Effects 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 125000004433 nitrogen atom Chemical group N* 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 230000002028 premature Effects 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/40—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rings; for bearing races
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
본 발명은, 열처리용 가스(흡열형 가스)의 분위기에서 저탄소강를 열처리하는 표층경화 열처리 방법에 있어서, 600∼750℃부터 900∼980℃까지 온도를 상승시키는 중에 상기 열처리용 가스 100중량부에 대해 암모니아 가스 2~10 중량부를 투입하고, 900∼980℃에서 열처리용 가스 100중량부에 대해 인리치 가스 0.8 ~ 1.4 중량부를 투입하는 베어링용 강재의 표층경화 열처리방법으로서, 질소의 확산 깊이를 깊게 하고 이물질이 혼입되지 않은 청정한 윤활조건 및 이물질이 혼입된 윤활조건에서도 베어링의 수명을 향상시킬 수 있다.The present invention is a surface hardening heat treatment method for heat-treating low carbon steel in an atmosphere of heat-treatment gas (endothermic gas), wherein the temperature is increased from 600 to 750 ° C to 900 to 980 ° C with respect to 100 parts by weight of the heat-treatment gas. As a surface-hardening heat treatment method for bearing steel which adds 2 to 10 parts by weight of ammonia gas and 0.8 to 1.4 parts by weight of in-rich gas to 100 parts by weight of heat treatment gas at 900 to 980 ° C., the diffusion depth of nitrogen is deepened. The life of the bearing can be improved even under the condition of clean lubrication without foreign matter and lubrication with foreign matter.
Description
본 발명은 베어링용 강재의 표층경화 열처리방법에 관한 것이다.The present invention relates to a surface hardening method of bearing steel.
일반적으로, 베어링용 강재는 고탄소 크롬강(STB2)에 전경화(full hardening) 열처리를 하거나 저탄소강(SCR420H 등)에 침탄 열처리를 실시하여 사용되었다.In general, steel for bearings was used by performing full hardening heat treatment on high carbon chrome steel (STB2) or by carburizing heat treatment on low carbon steel (SCR420H, etc.).
최근에는 베어링은 그 크기는 작고 부하용량은 커질 것이 요구되고 있다. 특히, 자동차의 트랜스 밋션에 사용되는 베어링에서는 윤활유 중에 주변 부품으로부터 떨어져 나온 금속 마모분, 조각, 파편등의 이물이 많이 존재하게 되므로, 상기 이물에 의해 베어링 궤도면에 손상을 입히고 베어링의 수명을 급속히 저하시키게 되므로, 이에 대한 베어링용 강재의 열처리 방법의 개발이 요구되고 있다.In recent years, bearings have been required to have a smaller size and a larger load capacity. Particularly, in bearings used for transmission of automobiles, many foreign materials such as metal wear, fragments, and debris that are separated from peripheral parts are present in the lubricant, which causes damage to the bearing raceway and rapidly prolongs the life of the bearings. Since it will reduce, development of the heat treatment method of the steel for bearings is calculated | required.
종래의 베어링용 강재의 침탄 열처리 방법에 의하면, 높은 면압에 의한 온도상승이나 금속마모분 등에 의한 손상에 따른 수명의 감소를 억제할 수가 없었다.According to the carburizing heat treatment method of the conventional steel for bearings, it is not possible to suppress the decrease in the life due to the increase in temperature due to high surface pressure or the damage caused by metal wear and the like.
또한, 종래 침탄질화 열처리 방법이 개시되어 있으나, 종래 침탄질화 열처리방법은 베어링, 특히 구름베어링에 요구되는 충분한 깊이의 침탄질화층을 형성할 수 없었다.In addition, the conventional carburizing nitriding heat treatment method has been disclosed, but the conventional carburizing nitriding heat treatment method could not form a carburizing nitriding layer having a sufficient depth required for bearings, especially rolling bearings.
구름 베어링은 점접촉 또는 좁은 면적이 접촉하여, 이러한 좁은 부위에 과대한 하중이 집중적으로 작용하기 때문에 표층 경도를 증대시키기 위해 경화층의 두께(즉, 침탄 질화층의 깊이)를 충분하게 만족시키도록 제작되어야만 한다.Since rolling bearings are in point contact or a small area contact, excessive load is concentrated on these narrow areas so as to sufficiently satisfy the thickness of the hardened layer (ie, the depth of the carburized nitride layer) to increase the surface hardness. It must be made.
그러나, 침탄과 질화의 고유 특성상, 침탄은 면심입방격자(FCC) 구조인 고온에서 탄소 침투가 빨라지지만, 이와 반대로 질화의 경우에는 체심입방격자(BCC) 구조인 570℃를 기점으로 하여 온도가 올라가면 침투속도가 느려지는 등의 상반된 메커니즘을 가지고 있다. 따라서, 구름베어링과 같은 경박단소형 자재에는 충분한 깊이의 침탄질화층을 형성시키는 것이 가장 큰 난점 중 하나였다.However, due to the intrinsic characteristics of carburization and nitriding, carburization accelerates carbon at high temperature, which is a face-centered cubic (FCC) structure, whereas in case of nitriding, when the temperature rises from 570 ° C, which is a body-centered cubic (BCC) structure, It has the opposite mechanism of slowing down penetration. Therefore, forming a carburized nitride layer of sufficient depth has been one of the biggest difficulties in light and thin short and small materials such as rolling bearings.
또한, 일반적으로 알려진 침탄 후에 재차 온도를 내려 질화처리하는 2단계공정은 공정시간이 너무 길고, 또한 이 공정의 경우, 탄소와 질소비를 최적으로 제어하지 못하면 표층부의 질소의 운동으로 인해 기공(void) 및 입계산화(grain boundary oxidation)가 발생하여 오히려 깨끗한 윤활조건에서도 수명이 감소하는 현상이 나타나는 등의 비효율적인 면을 내포하고 있었다.In addition, the two-stage process of lowering the temperature again after the known carburization generally takes a long process time, and in this process, if the carbon and nitrogen ratio cannot be optimally controlled, voids may occur due to the movement of nitrogen in the surface layer. ), And grain boundary oxidation occurs, resulting in a decrease in life even under clean lubrication conditions.
또, 기어류 등에 적용하는 800∼880℃에서 침탄질화하는 공정에 있어서는 침탄깊이가 충분하지 않고 또한 표층에 필요 이상의 과잉 잔류 오스테나이트의 존재하여, 내피로성이 현저히 감소하는 특성이 있었다.In the step of carburizing and nitriding at 800 to 880 ° C applied to gears or the like, the carburizing depth was not sufficient, and excessive residual austenite was present in the surface layer, and the fatigue resistance was remarkably reduced.
또한, 이와 같은 내피로성을 저해하는 베어링의 파손 메커니즘은, 표층에서 흠이나 미소 크랙 등이 발생하여 파손에 이르게 하는 표층기점 파괴와, 표층으로부터 0.1∼0.5mm 깊이의 최대 전단응력 지점에서 반복된 응력으로 인해 조직변화에 의해 크랙이 발생하여 파손에 이르게 하는 내부기점 파괴로 나누어 지는데, 사용 조건에 따라 표층기점 또는 내부기점 파괴가 구별되어 발생하거나 또는 동시에 나타나는 경우가 있었다.In addition, the failure mechanism of the bearing that impairs the fatigue resistance includes surface layer breakage that causes scratches or microcracks in the surface layer and leads to breakage, and repeated stress at the maximum shear stress point 0.1 to 0.5 mm deep from the surface layer. Because of this, cracks are generated due to organizational changes, and they are divided into internal breakdowns that lead to breakdown. Depending on the conditions of use, surface or internal breakdowns may be distinguished or appear simultaneously.
따라서, 본 발명은 상기한 점을 감안하여 이루어진 것으로서, 본 발명의 목적은, 질소의 확산 깊이를 깊게 하고 이물질이 혼입되지 않은 청정한 윤활조건 및 이물질이 혼입된 윤활조건에서도 수명을 향상시키는 베어링용 강재의 표층경화 열처리 방법을 제공하는 데 있다.Accordingly, the present invention has been made in view of the above-mentioned point, and an object of the present invention is to provide a bearing steel material which improves life under clean lubrication conditions in which the diffusion depth of nitrogen is deep and no foreign matters are mixed and lubrication conditions in which foreign matters are mixed. It is to provide a surface hardening heat treatment method of.
도1은 종래 베어링용 강재의 표층경화 열처리방법의 온도와 시간관계를 나타내는 그래프,1 is a graph showing the temperature and time relationship of the surface hardening method of the conventional bearing steel;
도2은 본 발명의 실시예에 의한 베어링용 강재의 표층경화 열처리방법의 온도와 시간관계를 나타내는 그래프,2 is a graph showing the temperature and time relationship of the surface hardening method of the bearing steel according to an embodiment of the present invention;
도3은 종래의 열처리 방법과 본 발명의 열처리 방법에 의해 열처리된 시편의 회전접촉 피로수명을 나타내는 그래프,3 is a graph showing the rotational contact fatigue life of the specimen heat-treated by the conventional heat treatment method and the heat treatment method of the present invention;
도4는 종래의 열처리 방법과 본 발명의 열처리 방법에 의해 열처리된 시편의 표층경도를 나타내는 그래프이다.4 is a graph showing the surface hardness of the specimen heat-treated by the conventional heat treatment method and the heat treatment method of the present invention.
본 발명에 의한 베어링용 강재의 표층경화 열처리방법은, 열처리용 가스(흡열형 가스)의 분위기에서 저탄소강을 열처리하는 표층경화 열처리 방법에 있어서, 600∼750℃부터 900∼980℃까지 온도를 상승시키는 중에 상기 열처리용 가스 100중량부에 대해 암모니아 가스 2~10 중량부를 투입하고, 900∼980℃에서 열처리용 가스 100중량부에 대해 인리치 가스 0.8 ~ 1.4 중량부를 투입하는 것을 특징으로 한다.600℃ 이하에서는 암모니아 가스를 투입해도 강재의 표층에 질소의 침투속도가 너무 느리므로 생산공정에서 비효율적이고, 750℃에서 강재의 표층에 질소의 침투속도가 가장 빠르므로, 암모니아 가스는 600∼750℃부터 시작하여 투입하게 된다. 그리고 900∼980℃는 일반적인 공지의 침탄온도로서, 이 온도에서 침탄이 행해진다.The surface hardening method of the bearing steel material of this invention raises the temperature from 600-750 degreeC to 900-980 degreeC in the surface hardening method which heat-processes low carbon steel in the atmosphere of heat processing gas (endothermic type gas). 2 to 10 parts by weight of ammonia gas is added to 100 parts by weight of the heat treatment gas, and 0.8 to 1.4 parts by weight of the rich gas is added to 100 parts by weight of heat treatment gas at 900 to 980 ° C. Below a ℃, even if ammonia gas is injected, nitrogen penetration into the surface of the steel is too slow, which is inefficient in the production process. Since the penetration rate of nitrogen into the surface of the steel is the fastest at 750 ℃, the ammonia gas starts from 600 to 750 ℃. To start with. And 900-980 degreeC is a general well-known carburizing temperature, and carburizing is performed at this temperature.
이러한 본원발명의 구성은 낮은 온도에서 우선 투입된 질소원자가 나중에 투입된 탄소원자와 상호반응하면서 더욱 깊게 확산된다. 상기 저탄소강의 표층에 질소와 탄소를 침투시키는 시간은 2~6시간으로 하는 것이 바람직하다.The composition of the present invention diffuses deeper as the nitrogen atom first introduced at low temperature interacts with the later introduced carbon atom. It is preferable to make time for infiltration of nitrogen and carbon to the surface layer of the said low carbon steel to be 2 to 6 hours.
상기 암모니아 가스가 과잉공급되면 표층부에 질소가 과다하게 침투하여, 담금질 후 잔류 오스테나이트가 과잉으로 형성되어, 경도가 저하하고 입계산화 및 기공등의 표면결함이 발생하여 내마모성이 감소하고 피로수명에 악영향을 미치므로, 암모니아 가스의 투입량은 열처리 효과에 큰 인자로 작용한다.즉, 암모니아 가스의 투입량이 2중량부 이하일 경우에는 질소의 효과는 거의 없고 10중량부 이상일 경우에는 강재 표면부에 과잉의 질소가 투입됨으로 인해 잔류오오스테나이트 량의 과다와 기공등의 표면결함이 생기므로, 바람직하지 못하다.그리고, 인리치 가스의 투입량이 0.8 중량부 이하일 경우에는 강재의 표면과 내부의 농도차이로 인하여 이미 침투된 질소의 역확산이 일어나서 기공등의 결함이 생기고 1.4중량부 이상일 경우에는 입계산화 및 기공등의 표면결함이 생기므로, 바람직하지 못하다.When the ammonia gas is excessively supplied, nitrogen is excessively penetrated into the surface layer, and residual austenite is excessively formed after quenching, resulting in a decrease in hardness, surface defects such as grain boundary oxidation and pores, and thus reducing wear resistance and fatigue life. As a result, the amount of ammonia gas added acts as a large factor in the heat treatment effect. In other words, when the amount of ammonia gas is added in an amount of 2 parts by weight or less, the effect of nitrogen is almost zero. It is not preferable because the addition of nitrogen leads to an excessive amount of residual austenite and surface defects such as pores. When the amount of the inlet gas is 0.8 parts by weight or less, it is caused by a difference in concentration between the surface of the steel and the interior. Defect of nitrogen that has already penetrated occurs and defects such as pores occur, and when it is 1.4 parts by weight or more, grain boundary oxidation Since the advent of surface defects such as pores and undesirable.
상기 저탄소강의 표층에 질소와 탄소를 침투시킨 후, 저탄소강을 80~150℃의 오일에서 담금질한 다음, 150 ~ 300℃에서 1~2시간 뜨임처리를 하는 것이 바람직하다. 상기 담금질 및 뜨임후 표층의 조직은 마르텐 사이트 70~80%와, 잔류 오스테나이트 20~30%로 되며, 표층경도는 60∼64 HRc로 유지되고 심부경도는 30∼50 HRc로 된다. 이 담금질과 뜨임처리 조건은 일반적인 공지의 조건이다.After nitrogen and carbon infiltrate the surface layer of the low carbon steel, it is preferable to quench the low carbon steel in an oil of 80 ~ 150 ℃, and then temper treatment for 1 to 2 hours at 150 ~ 300 ℃. After quenching and tempering, the texture of the surface layer is 70 to 80% of martensite and 20 to 30% of retained austenite, and the surface hardness is maintained at 60 to 64 HRc and the core hardness is 30 to 50 HRc. These quenching and tempering conditions are generally known conditions.
상기 20~30%의 잔류 오스테나이트는 연한 조직(soft microstructure)으로서 충격을 완화시킬 뿐만 아니라 이물질에 대한 저항성을 향상시키는 역할을 수행할 뿐만 아니라 베어링의 조기파손이 유발하는 것을 억제함으로써 발열에 대한 안정성을 증대시킨다.The 20 to 30% of retained austenite is a soft microstructure, which not only mitigates the impact but also improves the resistance to foreign substances, and suppresses the occurrence of premature failure of the bearing, thereby preventing heat generation. To increase.
상기 저탄소강은 '0.17∼0.23 중량％ C, 0.15∼0.35 중량％ Si, 0.55∼0.9중량％ Mn, 0.85∼1.25중량％ Cr, 0.03중량％ 이하 P'를 포함한 조성으로 되어 있는 것이 바람직하다.It is preferable that the said low carbon steel is a composition containing 0.17-0.23 weight% C, 0.15-0.35 weight% Si, 0.55-0.9 weight% Mn, 0.85-1.25 weight% Cr, and 0.03 weight% or less P '.
또한, 상기 저탄소강은 '0.17∼0.23 중량％ C, 0.15∼0.35 중량％ Si, 0.55∼0.9중량％ Mn, 0.85∼1.25중량％ Cr, 0.35∼2.0중량％ Ni, 0.50중량％ 이하 Mo, 0.03중량％ 이하 P'를 포함한 조성으로 되어 있을 수도 있다.상기 저탄소강의 조성은 일반적으로 베어링용 강재로 많이 사용되는 조성이다.In addition, the low carbon steel is' 0.17 to 0.23 wt% C, 0.15 to 0.35 wt% Si, 0.55 to 0.9 wt% Mn, 0.85 to 1.25 wt% Cr, 0.35 to 2.0 wt% Ni, 0.50 wt% or less Mo, 0.03 wt% The composition containing% or less P 'may be sufficient. The composition of the said low carbon steel is a composition generally used for bearing steel materials generally.
베어링용 강재는 베어링으로 사용하기 위해, 열처리 후 연삭가공에 의해 0.1∼0.3 mm 정도 제거되기 때문에 안정적인 표층경화 깊이가 0.5∼0.8 mm 정도 형성되도록 하는 것이 바람직하다.In order to use the bearing steel as a bearing, it is desirable to have a stable surface hardening depth of about 0.5 to 0.8 mm since 0.1 to 0.3 mm is removed by grinding after heat treatment.
이하, 본 발명에 대해 실시예를 통하여 상세히 설명한다.Hereinafter, the present invention will be described in detail through examples.
<실시예><Example>
먼저, C : 0.17∼0.23 중량％, Si : 0.15∼0.35 중량％, Mn : 0.55∼0.9중량％, P : 0.03 중량％ 이하, Cr : 0.85∼1.25중량 %를 함유하는 저탄소강재를 외경이 60mm, 내경이 30mm, 두께가 5.5mm 인 원판 상태로 가공하여 준비했다.First, an outer diameter of a low carbon steel material containing C: 0.17 to 0.23% by weight, Si: 0.15 to 0.35% by weight, Mn: 0.55 to 0.9% by weight, P: 0.03% by weight or less, Cr: 0.85 to 1.25% by weight, It prepared by processing into the disk state whose internal diameter is 30 mm and thickness is 5.5 mm.
도2에 나타낸 바와 같이, Rx가스가 충진된 노내에 상기 저탄소강재를 투입하여 700℃부터 900℃까지 온도를 상승시키는 중에 상기 Rx 가스 100중량부에 대해 암모니아 가스 10 중량부를 투입하고, 900℃에서 Rx 가스 100중량부에 대해 인리치 가스 1중량부를 투입하여 3~4시간 유지시켰다.As shown in Fig. 2, 10 parts by weight of ammonia gas was added to 100 parts by weight of the Rx gas while the low carbon steel was charged into a furnace filled with Rx gas to raise the temperature from 700 ° C to 900 ° C, and at 900 ° C. 1 part by weight of the rich gas was added to 100 parts by weight of the Rx gas and maintained for 3 to 4 hours.
다음에 800℃로 온도를 내려 100℃오일에 담가 담금질 한 후, 160℃에서 2시간동안 뜨임처리했다.The temperature was then lowered to 800 ° C. and immersed in 100 ° C. oil, followed by tempering at 160 ° C. for 2 hours.
상기 Rx가스는 연료가스(천연가스, 도시가스, 프로판, 부탄등)에 일정비율의 공기를 혼합하여 외열식 로를 이용해서 만든 가스의 일종으로서, 흡열형 가스(endothermic gas)라고도 하며, 열처리 가스로 널리 사용된다.The Rx gas is a kind of gas made by mixing an air of a certain ratio with fuel gas (natural gas, city gas, propane, butane, etc.) using an external heat furnace, and is also called an endothermic gas. Widely used.
상기 인리치 가스(enriched gas)는 침탄성 분위기의 카본 포텐셜을 증가하기 위해 사용되는 탄화수소등의 가스이다.The enriched gas is a gas such as a hydrocarbon used to increase the carbon potential of the carburized atmosphere.
<비교실시예>Comparative Example
먼저, 상기 본 발명의 실시예와 같은 조성 및 크기의 저탄소강재를 준비했다.First, a low carbon steel of the same composition and size as in the embodiment of the present invention was prepared.
도1에 나타낸 바와 같이, Rx가스가 충진된 노내에 상기 저탄소강재를 투입하여 930℃까지 온도를 상승시키고, 930℃에서 상기 Rx 가스 100중량부에 대해 인리치 가스 1중량부를 투입하여 6시간 유지시켰다.As shown in FIG. 1, the low carbon steel is charged into a furnace filled with Rx gas to raise the temperature to 930 ° C, and 1% by weight of the rich gas is added to 100 parts by weight of the Rx gas at 930 ° C for 6 hours. I was.
다음에 840℃로 온도를 내려 100℃오일에 담가 담금질 한 후, 160℃에서 2시간동안 뜨임처리했다.The temperature was then lowered to 840 ° C. and immersed in 100 ° C. oil, followed by tempering at 160 ° C. for 2 hours.
<시험예 1><Test Example 1>
상기 실시예의 방법과 비교실시예의 방법으로 열처리한 각 시편의 피로시험을 다음과 같이 실시하였다..The fatigue test of each specimen heat-treated by the method of the said Example and the method of a comparative example was performed as follows.
시험조건 :Exam conditions :
열처리한 상기 각 시편을 베어링 가공 공정과 같이 100∼300 μm 연삭하고, 표층 조도가 0.05∼0.20 μm이 되도록 연마한 후, 디스크 타입(DISC TYPE)의 회전접촉 피로 시험기를 사용하여, 다음 <표1>과 같은 '청정 윤활조건'과 '이물질이 혼입된 윤활조건' 하에서 실시하였다.The heat-treated specimens were ground to 100 to 300 μm in the same manner as in the bearing machining process, and polished to have a surface roughness of 0.05 to 0.20 μm. Then, using a DISC TYPE rotary contact fatigue tester, the following <Table 1 > Under 'clean lubrication conditions' and 'lubricating conditions in which foreign substances are mixed'.
<표1><Table 1>
도3에 도시한 바와 같이, 실시예(본 발명)에 따라 침탄질화 열처리된 강의 피로수명이 비교실시예(종래 예)에 따라 열처리된 강의 피로수명보다 각 조건(청정 윤활조건 및 이물질 혼입 윤활조건)에서 모두 현저히 증가함을 알 수 있다.As shown in Fig. 3, the fatigue life of the carburized nitrification heat treated steel according to the embodiment (the present invention) is better than the fatigue life of the steel heat treated according to the comparative example (the conventional example) (clean lubrication condition and foreign matter mixing lubrication condition). It can be seen that both increase significantly.
<시험예 2><Test Example 2>
상기 실시예(본 발명)의 방법과 비교실시예(종래 예)의 방법의 뜨임온도를 변화시키면서 각 시편을 1시간동안 뜨임처리하여 그 표면경도(HRc)와 잔류오스테나이트량( % )을 측정하는 시험을 하였다.While varying the tempering temperature of the method of Example (invention) and the method of Comparative Example (conventional example), each specimen was tempered for 1 hour to obtain its surface hardness (HR c ) and residual austenite (%). The test to measure was carried out.
시험결과가 <표2>에 기재되어 있다.The test results are shown in <Table 2>.
표시된 바와 같이, 본 발명의 방법에 의해 열처리된 강의 잔류 오스테나이트량은 종래 방법에 의해 열처리된 강의 잔류 오스테나이트량 보다 5∼6％ 더 많이 형성되지만, 뜨임 온도에 따른 변화량은 더 적음을 알수 있다.As indicated, the amount of retained austenite of the steel heat-treated by the method of the present invention is formed 5-6% more than the amount of retained austenite of the steel heat-treated by the conventional method, but it can be seen that the change according to the tempering temperature is smaller. .
또한, 본 발명의 방법에 의해 열처리된 강이 종래 방법에 의해 열처리된 강보다 뜨임 온도에 따른 경도변화가 적어서 안정적임을 알 수 있다. 따라서, 국부적인 체적변화(micro-strain)에 의해서 발생될 수 있는 크랙 생성이 억제됨으로써, 크랙에 대한 내성 및 이물질에 대한 내성이 향상되어 피로 수명을 더욱 증대시킬 수 있게 된다.In addition, it can be seen that the steel heat-treated by the method of the present invention is less stable than the steel heat-treated by the conventional method due to the tempering temperature. Therefore, crack generation, which may be caused by local micro-strain, is suppressed, thereby improving resistance to cracks and resistance to foreign substances, thereby further increasing fatigue life.
<표2><Table 2>
<시험예 3><Test Example 3>
상기 실시예(본 발명)의 방법과 비교실시예(종래 예)의 방법으로 열처리한 각 시편의 표층부 미소경도분포를 공지의 경도측정기를 사용하여 측정하였다.The surface hardness of the surface layer microhardness distribution of each specimen heat-treated by the method of the said Example (invention) and the comparative example (conventional example) was measured using the well-known hardness tester.
도4에는 그 결과가 그래프로 표시되어 있다. 도시한 바와 같이, 비교실시예(종래 예)에 따라 열처리된 강의 표층부 경도분포는 탄소의 확산분포에 따라 거의 직선적으로 감소하였고 유효경화 깊이가 1.2mm로 나타났다. 실시예(본 발명)에 따라 열처리된 강의 표층부 경도분포는 탄소와 질소의 영향으로 0.9mm까지 경도가 높게 나타났고 유효경화 깊이는 1.4mm로 나타났다.4 shows the results graphically. As shown, the hardness distribution of the surface layer of the steel heat-treated according to the comparative example (a conventional example) decreased almost linearly with the diffusion distribution of carbon and the effective hardening depth was 1.2 mm. The hardness distribution of the surface layer portion of the steel heat-treated according to the embodiment (invention) showed a high hardness up to 0.9 mm under the influence of carbon and nitrogen and an effective hardening depth of 1.4 mm.
즉, 최대전단응력이 작용되는 영역에서, 종래예의 열처리 방법에 의한 강의경도보다 본 발명의 열처리방법에 의한 강의 경도가 50∼100 Hv 상승되어 피로수명을 증대시킨다.That is, in the region where the maximum shear stress is applied, the hardness of the steel by the heat treatment method of the present invention is increased by 50 to 100 Hv than the hardness of the conventional heat treatment method to increase the fatigue life.
또한, 본 발명의 방법은 질소를 먼저 침투시킨 후 침탄시킴으로써, 질소의 확산깊이를 0.9mm까지 깊게 확산시킬 수 있고, 그 결과, 강의 표층으로부터 0.1mm 까지의 미소경도가 650 Hv 이상이고, 중심 미소경도가 500 Hv 정도인 경도분포를 가지는 강을 얻을 수 있다.In addition, the method of the present invention can infiltrate nitrogen first and then carburize to deeply diffuse the diffusion depth of nitrogen to 0.9 mm. As a result, the microhardness from the surface layer of the steel to 0.1 mm is 650 Hv or more, and the center minute Steel having a hardness distribution with a hardness of about 500 Hv can be obtained.
본 발명에 의한 베어링용 강재의 표층경화열처리 방법에 의하면, 질소의 확산 깊이를 깊게 하고 이물질이 혼입되지 않은 청정한 윤활조건 및 이물질이 혼입된 윤활조건에서도 베어링의 수명을 향상시킬 수 있다.According to the surface hardening heat treatment method of the steel for bearings according to the present invention, it is possible to deepen the diffusion depth of nitrogen and to improve the life of the bearing even under the condition of clean lubrication conditions in which foreign substances are not mixed and in lubrication conditions in which foreign substances are mixed.
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