Metal treatment – Stock – Ferrous
Reexamination Certificate
2001-09-27
2003-06-24
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Ferrous
C148S906000, C384S492000, C384S912000
Reexamination Certificate
active
06582532
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to large-sized bearing parts used for industrial equipment or so, and a steel suitable for the bearing parts of this kind and, it is possible to provide an inexpensive bearings of which rolling fatigue strength and breaking resistance are excellent or at least equivalent as compared with carburized (cemented) bearings of conventional type, and are possible to be easily improved into target quality through a simplified process as compared with the conventional heat treatment process.
PRIOR ART
As a bearing for the industrial equipment or so, a large-sized bearing with an outside diameter of 150mm or more, and a thickness of 30mm or more may be used. The bearing of this kind is required to have sufficient strength even in severe working environment in order to prevent the equipment from a trouble caused by a damage in the bearing. Further, it is especially important in the large-sized bearing not to be broken in brittle even by excessive load applied momentarily (to be excellent in breaking resistance).
In the past, carburizing, which is a method suitable to obtain parts excellent in toughness at an internal portion, is widely applied in order to improve the breaking resistance of the bearing parts, and case-hardening steels such as SCM 420, SNCM420, SNCM815 or so which are specified in JIS G 4105 and G 4103 have been used in this purpose.
However, the carburizing is expensive in the processing cost as compared with quenching and tempering treatment which is applied to the general purpose bearings, and it has not been possible to provide inexpensive bearings through the carburizing.
Furthermore, deformation and dimensional change are caused in the ring, and the bearing parts are to be finished by machining after the carburizing, and it is necessary to cut out in a depth of the order of 0.5 mm in this time. Accordingly, it is necessary to form a carburizing layer of 2 mm or more at the time of immediately after the carburizing. In order to obtain such the carburizing layer with a thickness of 2 mm or more, the parts have to be subjected to the carburizing for at least 10 hrs. or more, and there is a problem in the carburized bearing parts also from a viewpoint of the productivity.
On the other side, high carbon bearing steels such as SUJ3, SUJ5 or so which are specified in JIS G 4805 have been used in a case of applying quenching and tempering treatment. In this case, the parts are hardened as high as HRC50 or above even in the internal portion thereof according to the ordinary quenching treatment and remarkably deteriorated in the breaking resistance, therefore it becomes necessary to take measures to lower the internal hardness of the parts by controlling cooling rate at the quenching treatment.
In such the quenching treatment, operational procedures are carried out such that outer layer of the bearing is exclusively quench-hardened by abruptly cooling the outer layer through a cooling nozzle disposed in the oil tank for injecting the coolant at the time of quenching the bearing into the oil tank, successively the cooling rate is controlled so as not to harden the internal portion of the bearing according to martensitic transformation by regulating the cooling nozzle.
However, the above-mentioned quenching treatment contains weak points that hardness of the bearing is apt to fluctuate owing to segregation of chemical compositions in the steel materials, and the control of cooling rate becomes difficult owing to deterioration of the coolant, clogging of the coolant nozzle or so, thereby also causing scattering in the hardness.
DISCLOSURE OF THE INVENTION
The present invention is made in order to solve the aforementioned problems in the prior art, and it is an object to provide large-sized bearing parts with excellent breaking resistance and rolling fatigue strength at a low cost.
The quenching and tempering treatment is carried out in a short time as compared with the carburizing and excellent in the productivity, accordingly it seems to be possible to reduce the cost if the quenching and tempering treatment becomes possible to be applied by using appropriate steel materials, and it appears to be possible to improve the productivity and reduce the production cost if the quenching and tempering treatment becomes possible to be carried out easily without complicated control of the cooling rate. Furthermore, it is expected to improve the breaking resistance by making the quench-and-tempered bearing to have hardness distribution similar to that of carburized one, and it seems to enable the bearing to be advantageous from the viewpoint also of the strength.
Therefore, as a result of detailed investigations concerning the above-mentioned factors, it has been found that it is possible to produce a large-sized bearing with objective hardness distribution by defining designated quench-hardenability to the steel materials in a case where H-value (quenching intensity) of the oil tank is in the order of 0.2~0.5 in general purpose oil-quenching treatment.
Furthermore, it has become clear that it is possible to provide -the large-sized bearing having breaking resistance and rolling fatigue strength excellent more than or equal to these of carburized one by using the aforementioned steel materials and defining the hardness of products at the outer layer and the internal portion, respectively.
That is, a steel for a large-sized bearing according to this invention is characterized by having quench-hardenability of HRC64 or more at J 1.5 mm, HRC63 to 66 at J 7 mm, HRC37 to 50 at J 15 mm, HRC30 to 45 at J 20 mm and HRC28 to 38 at J 45 mm, which is measured according to a method of hardenability test for steel specified in JIS G 0561 as recited in claim 1. The method specified in JIS G 0561 is widely known as Jominy end quenching method.
Furthermore, in the steel for a large-sized bearing according to this invention, the chemical compositions may consist by mass percentage of
0.80 to 1.30% of C,
more than 0.35% and not more than 0.80% of Si,
0.30 to 0.90% of Mn,
0.90 to 1.50% of Cr,
the remainder being Fe and incidental impurities, and the quench-hardenability according to a method of hardenability test for steel specified in JIS G 0561 may be HRC64 or more at J 1.5 mm, HRC63 to 66 at J 7 mm, HRC37 to 50 at J 15 mm, HRC30 to 45 at J 20 mm and HRC28 to 38 at J 45 mm, as recited in claim 2.
Similarly in the steel for a large-sized bearing according to this invention, the chemical compositions may consist by mass percentage of
0.80 to 1.30% of C,
more than 0.35% and not more than 0.80% of Si,
0.30 to 0.90% of Mn,
0.90 to 1.50% of Cr,
one or both of not more than 0.25% of Mo and 0.20 to 1.50% of Ni,
the remainder being Fe and incidental impurities, and the quench-hardenability according to a method of hardenability test for steel specified in JIS G 0561 may be HRC64 or more at J 1.5 mm, HRC63 to 66 at J 7 mm, HRC37 to 50 at J 15 mm, HRC30 to 45 at J 20 mm and HRC28 to 38 at J 45 mm, as recited in claim 3.
Similarly in the steel for a large-sized bearing according to this invention, S, P, O and Ti of the incidental impurities may be limited up to 0.010% of S, 0.020% of P, 0.0010% of O and 0.0030% of Ti, respectively, as recited in claim 4.
Further, large-sized bearing parts excellent in breaking resistance and rolling fatigue life characteristics according to this invention is characterized by being made from a steel according to any one of claims 1 to 4 and having a ring-shape with an outside diameter of 150 mm or more and a thickness of 30 mm or more, and having a hardness of HRC58 to 65 at a surface thereof and of HRC25 to 45 at a central portion thereof after quenching and tempering treatment, as recited in claim 5.
(Hardenability)
Jominy hardenability of SUJ2 steel to be used in a general purpose bearing, SUJ3 steel to be used in a large-sized bearing and a suitable steel according to this invention, which is measured in conformity to the method specified in JIS G 0561, is shown in FIG.
1
.
For example, in a case where the large-sized bearing with a r
Hattori Kiyoyuki
Kizawa Katsuhiko
Kurebayashi Yutaka
Nakamura Sadayuki
Koyo Seiko Co. Ltd.
Yee Deborah
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