CN1973144A - Rolling bearing - Google Patents

Abstract

A large number of fine recesses are randomly provided on the surfaces of at least rolling bodies of a rolling bearing. The surface roughness parameter Ryni of the surface where the recesses are provided is set within the range of 0.4 - 1.0 m, and an Sk value is set to -1.6 or less.

Description

Rolling bearing

Technical field

The present invention relates to rolling bearing, described rolling bearing can be applicable to the roller bearing that for example is used for as the shaft supporting part of automotive trannsmission system.

Background technique

JP-A-02-168021 and JP-A-06-42536 have disclosed such rolling bearing separately: wherein the surface of rolling element is provided with small irregular part (irregularity) formed thereon and forms ability to improve oil film.In this conventional art, as to the damage that causes because of insufficient lubrication, as the countermeasure of peeling off damage of roller bearing, in the raceway face of the rolling contact surfaces of roller and/or interior outer race, be provided with depression, each depression all has small spill.When with parameters R qni presentation surface roughness the time, ratio R qni (L) between axial surface roughness Rqni (L) and the peripheral surface roughness Rqni (C)/Rqni (C) becomes 1.0 or littler, and, the parameter S k value of surface roughness is set as-1.6 or littler, thereby, if match surface is rough surface or smooth finished surface, then prolonged the life-span of rolling bearing.

Summary of the invention

In recent years, exist to reduce as the size of part automotive trannsmission system etc., that use rolling bearing and improve the trend of its power output, and oil body is tending towards descending.In other words, in the Environmental Conditions of rolling bearing, load and temperature are improving.Therefore, for bearing, compare before lubricated environment is followed and become harsher.Reduction fatigue life and the separation under the contaminating impurity environment that the surperficial initial type (surfaceoriginating type) that causes because of lubrication failure separates, causes because of higher contact pressure are tending towards easy generation.In this case, needing can be under any lubricating condition, under the lubricated condition of low viscous harsh lubricated, contaminating impurity environment or detergent oil, improves the life-span.

Traditional micro recessed is formed, thereby make in parameters R qni presentation surface roughness, the ratio R qni (L) of axial surface roughness Rqni (L) and peripheral surface roughness Rqni (C)/Rqni (C) is equal to or less than 1.0 (Rqni 〉=0.10), and, the value of surface roughness parameter Sk is equal to or less than-1.6, thereby,, also can realize life-time dilatation even if match surface is rough surface or smooth finished surface.Yet under low viscosity and thin lubricated condition, when oil film as thin as a wafer the time, its effect possibly can't be brought into play.

At least on the surface of rolling element, comprise the countless micro recessed that form at random according to the described rolling bearing of the embodiment of the invention.The average area of described depression is at 30 to 100 μ m ²Scope in, and Rymax is in 0.4 to 1.0 scope.At least on the surface of rolling element, be formed with countless micro recessed randomly, thereby, even if, also can strengthen oil film and form ability and realize life-time dilatation in low viscosity and thin when lubricated under the oil film condition as thin as a wafer.Particularly, be set in 30 to 100 μ m by average area with described depression ²Scope in, and Rymax is set in 0.4 to 1.0 the scope, even if then can prevent that also oil film lacks when lubricated thin.Compare with traditional product, even if under oil film condition as thin as a wafer, also can obtain the long life-span.

In the external member, inner member and the rolling element that constitute rolling bearing, have at least one to have nitrogen-enriched layer.Austenite grain size in the nitrogen-enriched layer can be in the scope that is higher than crystallite dimension No.10.After forming nitrogen-enriched layer, by setting austenite grain size less so that crystallite dimension number becomes greater than No.11, then rolling fatigue life improves significantly, thereby can obtain outstanding resistance to cracking and to the antagonism of the aging dimensional changes that is produced.

Known ground, rolling bearing are the machine elements that supports rotation or axis of rocking by the rolling motion of rolling element (ball or roller).Usually, rolling element is placed between the raceway of the raceway of inner race and outer race rotationally.Yet, also have the type that does not have the type of inner race and do not have outer race, wherein, in not having the rolling bearing of inner race, the outer surface of axle directly serves as raceway face, and in not having the rolling bearing of outer race, the interior perimeter surface of gear is directly served as raceway face.When using as during the term of " inner member " and " external member " and so on, such intention being arranged: promptly prevent to get rid of the inner race that has raceway face separately and outer race and axle, gear etc.And, when using " at least on the surface at rolling element " such expression, there is such intention: promptly prevent to get rid of the rolling bearing that in raceway face, also is formed with micro recessed, and, at rolling element is under the situation of roller, has such intention: promptly prevent to get rid of micro recessed and not only be formed in the raceway face, also be formed on the rolling bearing in the end face.

When the surface roughness on the surface of representing to be formed with on it described depression with parameters R qni, the ratio between axial surface roughness Rqni (L) and the peripheral surface roughness Rqni (C) " Rqni (L)/Rqni (C) " can be equal to or less than 1.0.Parameters R qni be by in measuring length of interval to square the carrying out integration and determine that the square root of the mean value in this interval obtains of the height tolerance from the roughness center line to roughness curve, it is known as r.m.s. roughness (ISO4287:1997) again.Rqni determines by numerical calculation by cross section curve that writes down under the amplification situation and roughness curve, and measures by broad ways with along the contact pilotage (tracer) that circumferential direction moves roughmeter.

Nitrogen-enriched layer is formed in the layer that the nitrogen content in seat ring (outer race or inner race) or the rolling element top layer increases.This layer can form by processing such as for example carbonitriding, nitriding, nitrogen immersions.Nitrogen content in the nitrogen-enriched layer is preferably in 0.1% to 0.7% scope.When nitrogen content less than 0.1% the time, do not have effect, so the life-span of rolling especially can reduce under the contaminating impurity condition.When nitrogen content greater than 0.7% the time, form the hole (hole called void) that is called the hole, to such an extent as to or remained austenite content can't obtain hardness too greatly, thereby cause the life-span to become shorter.About being formed on the nitrogen-enriched layer on the seat ring, nitrogen content is the value in the 50 μ m top layers of the raceway face after the grinding, and this value can wavelength dispersion type X-ray microanalysis device (EPMA) obtains by for example using.

And when austenite grain size became greater than crystallite dimension No.10, the austenite crystal diameter became thinner, thereby can significantly improve rolling fatigue life.When austenite grain size was lower than crystallite dimension No.10, rolling fatigue life did not significantly improve, and therefore, made austenite grain size in being higher than the scope of No.10.Usually, austenite grain size is equal to or higher than crystallite dimension No.11.Ideally, the austenite crystal diameter is as much as possible little.Yet, be difficult to obtain to be higher than the crystallite dimension of crystallite dimension No.13.Note, the austenite crystal of aforesaid bearing part in having the surface portion of nitrogen-enriched layer and surface portion not change between these two in the interior inside.Therefore, the position that becomes the object of crystallite dimension number in above-mentioned scope is top layer part and inside.Austenite crystal is meant the crystal grain based on austenite crystal border vestige, and wherein, even if for example after Quenching Treatment, just the austenite crystal border vestige before quenching still is retained on the austenite crystal.

Nitrogen content in the nitrogen-enriched layer can be in 0.1% to 0.7% scope.

At member is under the situation of seat ring, and nitrogen content can be the interior value of raceway face upper epidermis 50 μ m after the grinding.

To more obvious according to above-mentioned and other purposes of the present invention and characteristic point from the following description made from reference to accompanying drawing.

Description of drawings

Fig. 1 is the sectional view of needle bearing.

Fig. 2 is the sectional view that is used for the needle bearing of life test.

Fig. 3 is roughness curve figure, shows the finished surface state of the rolling element of test bearing.

Fig. 4 is roughness curve figure, shows the finished surface state of the rolling element of test bearing.

Fig. 5 is roughness curve figure, shows the finished surface state of the rolling element of test bearing.

Fig. 6 is the schematic cross sectional views of testing apparatus.

Fig. 7 is the figure that the life test result is shown.

Fig. 8 is the sectional view of taper roller bearing.

Fig. 9 A is the figure that the described Measuring Metallic Contact Rate of example according to the present invention is shown.

Fig. 9 B is the figure that the described Measuring Metallic Contact Rate of comparative example according to the present invention is shown.

Figure 10 is the overall schematic of two cylinder test devices (double cylindrical test apparatus).

Figure 11 is a schematic cross sectional views, illustrates according to the described rolling bearing of the embodiment of the invention.

Figure 12 is the figure that illustrates according to the embodiment of the invention, as to be used for rolling bearing heat treatment method.

Figure 13 is the figure that illustrates the modification of according to the embodiment of the invention, as to be used for rolling bearing heat treatment method.

Figure 14 A is the figure of described, microstructure, the particularly austenite crystal that bearing part is shown of example according to the present invention.

Figure 14 B is the figure that the microstructure of traditional bearing parts, particularly austenite crystal are shown.

Figure 15 A is the schematic representation on the austenite crystal border of Figure 14 A.

Figure 15 B is the schematic representation on the austenite crystal border of Figure 14 B.

Figure 16 is the view that the test specimen that is used for static pressure breakdown strength test (determining of rupture stress value) is shown.

Figure 17 A is the front schematic view of rolling fatigue life testing machine.

Figure 17 B is the side view of the testing machine of Figure 17 A.

Figure 18 is the view that the test specimen that is used for static fracture toughness test is shown.

Embodiment

Rolling bearing comprises inner race, outer race and rolling element, as critical piece.In at least one of the rolling surface of rolling element and the raceway face of end face and inner and outer race (and the rib surface, the cone back side under the inner race situation at taper roller bearing (cone back face rib surface)), be formed with countless micro recessed randomly, thereby obtain fine rough surface (fine roughsurface).In fine rough surface, the average area of described depression is at 30 to 100 μ m ²Scope in, and the Rymax on surface that wherein is formed with described depression is in 0.4 to 1.0 scope.And, when determining each surperficial surface roughness on each direction in axial direction and circumferential direction and it represented with parameters R qni, ratio R qni (L) between axial surface roughness Rqni (L) and the peripheral surface roughness Rqni (C)/Rqni (C) is equal to or less than 1.0, and, on axial direction and circumferential direction, surface roughness parameter Sk value is equal to or is lower than-1.6.As for obtaining the surface treatment that so fine rough surface carries out,, yet also can use bullet methods such as (shot) although can carry out the finished surface of special tumbling (special barrel finishing) to obtain to be scheduled to.Be set in 30 to 100 μ m by average area with described micro recessed ²Scope in, and the Rymax that will wherein be formed with the surface of described depression is set in the scope of 0.4 to 1.0 μ m, forms effect even if then also can show high oil film under oil film condition as thin as a wafer.Therefore, even if under the harsh lubricating condition of the extreme of oil film parameter Λ=0.13, also can obtain sufficiently long life-span effect.

Following method of measurement and the condition that parameters R ymax and Rqni are described with example.Please note, when with the surface properties of these parametric representations when determining as the parts of the rolling element of rolling bearing and bearer ring and so on, even if is enough reliable by measure the value that obtains a position as typical value, but, preferably measure two positions, for example, these two positions along diametric(al) toward each other.

Calculation of parameter standard: JIS B 0601:1994 (surfcom JIS 1994)

End type: Gaussian

Measure length: 5 λ

Cutoff wavelength: 0.25mm

Measure multiplying power: * 10000

Measuring speed: 0.30mm/s

Measuring position: roller center

Measure number: 2

Measuring device: surface roughness measurement device surfcom 1400 A (TOKYO SEIMITSUCO., LTD.)

About the micro recessed in the rolling contact surfaces that is arranged on roller, when described depression drops in 5 to 20% the scope with respect to the area percentage of whole rolling contact surfaces, removing each equivalent diameter is that 3 μ m Φ or littler depression sum up when calculating, and the average area of described depression drops on 30 to 100 μ m ²Scope in.When the Rymax of described depression outside the scope of 0.4 to 1.0 μ m the time, greater than 20%, and the average area of described depression is greater than 100 μ m with respect to the area percentage of rolling contact surfaces for described depression ², the effective length of contact is tending towards reducing, and long-life effect is tending towards reducing.

When the quantitative measurment of carrying out depression,, can utilize commercially available picture system to quantize by by amplifying the image that roller surface obtains.And, use according to described surface properties test method of JP-A-2001-183124 and surface properties testing apparatus, can allow to realize stable, measurement accurately.Suppose in image should the surface planar section be expressed as white portion and small depression is expressed as black part assigns to analyze.Measuring condition is described as follows.And, when the area of described depression and average area are when measuring as the parts of the rolling element of rolling bearing and raceway face and so on, even if is enough reliable by measure the value that is obtained a position as typical value, but, preferably measure in for example two positions.

Area percentage: the ratio of the area of being filled by pixel (black part) in the field of view scope, it is less than binary-state threshold ((brightness of the brightness of light part+dark part)/2)

Average area: the area of black part and/total amount

Measure the visual field: 826 μ m * 620 μ m (during less than Φ 4, hope is 413 μ m * 310 μ m at the roller diameter)

Measuring position: roller center

Measure number: 2

Fig. 1 illustrates first example of rolling bearing.Rolling bearing 1 is a needle bearing, and wherein, needle roller 2 is merged in the outer race 3, and needle roller 2 serves as rolling element.Needle roller 2 supports coupling axle 4.Following is the result of life test, and this life test is carried out on polytype needle bearing of manufacturing, and handle with surface treatment so that different finished surfaces is provided on the needle roller surface of these needle bearings.The outer diameter D r that is used for the needle bearing of life test is 33mm, and inner diameter d r is 25mm, and the diameter D of needle roller 2 is 4mm, and the length L of needle roller 2 is 25.8mm, and it adopts 15 needle rollers, and is provided with retainer 5 as shown in Figure 2.3 kinds of dissimilar bearings that comprise needle roller are as test bearing, its surface is processed to have different roughness, that is, after the grinding through superlinishing bearing A (comparative example), form bearing B (comparative example) and the bearing C (example) have or not several micro recessed on it at random.The state of the finished surface of the needle roller of each test bearing is shown in Fig. 3 to 5.Specifically, respectively, Fig. 3 illustrates the surface roughness of bearing A, and Fig. 4 illustrates the surface roughness of bearing B, and Fig. 5 illustrates the surface roughness of bearing C.And the tabulation of the characteristic value parameter of the finished surface of test bearing is shown in the table 1.Notice that in Fig. 1, parameter S k represents the skewness (skewness) (ISO 4287:1997) of roughness curve, and serve as the index of the sample statistics value that is used to understand the nonsymmetry that irregular part distributes.When this distribution image equally is symmetry time in Gaussian distribution, Sk value becomes near 0, and under the situation of the convex portion in the irregular part of removal, the Sk value becomes negative value, and, under opposite situation, the Sk value become on the occasion of.The Sk value can wait and controls by pack into the kind of number (workcharging number), abrading block (chip) and size of rotating speed, process time, the work of selecting roll grinding machine.For example, be equal to or less than-1.6 by on width direction and circumferential direction, the Sk value being set at simultaneously, these micro recessed constitute oil sump (oil basin), therefore, even if when implementing compression, also can produce following effect: promptly, leakage of oil is few on glide direction and Vertical direction, oil film forms good, and oil film forms in good condition, and surface failure is suppressed to minimum.Notice that the Rqni of each among bearing B and the C (L/C) value is equal to or less than 1.0, and the Rqni of bearing A (L/C) value is approximately 1.0.

Table 1

Bearing	Rqni	Sk	Ryni (μm)	Rymax	Area percentage (%)	Average area (μ m 2)	Rqni (L/C)
								A (comparative example)	0.01 to 0.03	-0.8 to 0.9	0.1 to 0.2	0.1 to 0.3	-	-	-
B (comparative example)	0.10 to 0.20	-5.0 to-2.0	1.1 to 1.5	1.1 to 2.0	24 to 40	105 to 150	≤1.0
								C (example)	0.05 to 0.09	-4.9 to-1.6	0.4 to 1.0	0.4 to 1.0	5 to 20	30 to 100	≤1.0

As testing apparatus be radial load testing machine 11 as schematically showing among Fig. 6, wherein, test bearing 1 is connected to the both sides of rotatingshaft 12, and, rotate and load is applied in thereon to test.Used inner race (coupling axle) is processed to have the Ra of 0.10 to 0.16 μ m in the test, and this obtains by polishing processing.Outer race is processed with the same manner.Test conditions is as follows.

Bearing radial load: 2000kgf

Rpm：4000rpm

Oiling agent: Cresec oil H8 (2cst under test conditions)

Fig. 7 is illustrated in the result that oil film parameter Λ is a life test under 0.13 the condition.Vertical shaft among the figure is represented the L10 life-span (h).Apparent from figure, bearing A has 78h, and bearing B has 82h, and bearing C has 121h.As shown in data, even if under extremely harsh lubricating condition, promptly oil film parameter Λ is that described bearing C also can access long life-span effect according to this example under 0.13 the condition.

Then, Fig. 8 illustrates the taper roller bearing as the second exemplary rolling bearing.Taper roller bearing is a radial bearing, and it uses taper roller 16 as rolling element.A plurality of taper rollers 16 are placed between the raceway of the raceway of outer race 13 and inner race 14 in the free rolling mode.During operation, the rolling contact surfaces 17 of each taper roller 16 contacts with the raceway rolling of outer race 13 and inner race 14, and the large end face 18 of taper roller 16 is with the internal surface sliding contact of the cone back side rib 15 of inner race 14.Like this, in the situation of taper roller 16, countless micro recessed can be formed in the large end face 18 and in the rolling contact surfaces 17 randomly.In a similar fashion, in the situation of inner race 14, countless micro recessed can be formed in the internal surface of cone back side rib 5 and in the raceway face randomly.

The life test of carrying out on E (comparative example) and bearing F and the G (example) (with reference to table 2) at traditional taper roller bearing A and B (comparative example), bearing C is described, wherein, tradition taper roller bearing A and B comprise the taper roller with smooth processing rolling contact surfaces, and bearing C comprises having the taper roller that wherein forms the rolling contact surfaces that has or not several micro recessed at random to E.Used bearing A is a taper roller bearing to G, and in each of these bearings, the external diameter of outer race is 81mm, and the internal diameter of inner race is 45mm.Note, after grinding, stand superfinish according to the rolling contact surfaces of the roller of described bearing A of comparative example and B and be not processed to have depression.According to the described bearing C of comparative example to E be subjected to special tumbling according in the rolling contact surfaces of the roller of described bearing F of example and G each, thereby formed countless micro recessed randomly thereon.Notice that the Rqni (L/C) of roller bearing C each in the G is equal to or less than 1.0, and the Rqni of each among roller bearing A and the B (L/C) is approximately 1.0.

Table 2

Test bearing		Average area (μ m 2)	Ryni (μm)	Area percentage (%)	Sk	Rqni (L/C)	Rymax	Life-span (h)
									Comparative example	A	-	0.32	-	-0.9	-	0.5	11.5
B	-	0.41	-	-0.7	-	0.7	9.2
								C		132	1.47	25	-4	≤1.0	1.9	15.5
D	113	1.12	19	-3.2	≤1.0	1.2	50.5
								E		30	0.32	5	-1.8	≤1.0	0.5	19.8
Example	F	94	0.95	17	-2.6	≤1.0	1										129.6
								G	52	0.52	5	-1.8	≤1.0	0.6	Be equal to or higher than 200

Two cylinder test machines as shown in Figure 10 are used to carry out peeling test, with the assessment Measuring Metallic Contact Rate.In Figure 10, actuator) and be driven side cylinder 24 (the F cylinder: each driven member) all is connected to an end of each corresponding cylinder driving side cylinder 22 (D cylinder:.Two rotatingshafts 26,28 can be driven by the intervention of different motors by belt wheel 30,32 respectively.At the axle of D cylinder 22 sides 26 by motor driving, thereby and make F cylinder 24 freely roll can be by 22 drivings of D cylinder.According to the comparative example and the example of F cylinder 24, prepared two types surface treatment.The details that comprises test conditions is shown in the table 3.

Table 3

Testing machine	Two cylinder test machines (with reference to Fig. 9)
				Driving side cylinder (D cylinder)	 40 * L12, inferior radius of curvature R 60 SUJ2 standard items+outer surface superfinish
Be driven side cylinder (F cylinder)	 40 * L12, straight SUJ2 standard items+outer surface superlinishing surface is handled
					Comparative example	Example
	Average area (μ m 2)	145	83
				Ryni(μm)	1.21	0.73
	Area percentage (%)	20	15

Rpm	2000rpm
		Load	2156N(220kgf)
Maximum contact pressure Pmax	2.3Gpa
		Osculating ellipse (2a * 2b)	2.34mm×0.72mm
Load applies number of times	2.4×10 5Inferior (2h)
		Ambient temperature	Normal temperature
The fueling method	Use the felt pan fueling
		Lubricant oil	JOMO HI SPEED FLUID(VG1.5)

The comparing data of Measuring Metallic Contact Rate is shown in Fig. 9 A and the 9B.In each figure, horizontal axis is represented the transit time, and vertical shaft is represented Measuring Metallic Contact Rate.Fig. 9 A illustrates the Measuring Metallic Contact Rate according to the rolling contact surfaces of the roller of the described bearing of example.Fig. 9 B illustrates the Measuring Metallic Contact Rate according to the rolling contact surfaces of the roller of the described bearing of comparative example.When between these figure, comparing, compare with comparative example, can clearly realize that the improvement of Measuring Metallic Contact Rate in example.In other words, according to the oil film formation rate (=100%-Measuring Metallic Contact Rate) of the described bearing of example when the operation beginning beguine according to the oil film formation rate height of the described bearing of comparative example 10%, when off-test (after 2 hours) beguine according to the oil film formation rate height of the described bearing of comparative example 2%.

Then, Figure 11 illustrates the cross section as the deep groove ball bearing of another exemplary rolling bearing.This rolling bearing comprises outer race 34, inner race 36, a plurality of rolling element 38 and retainer 40 as its critical piece, and wherein, a plurality of rolling elements 38 are placed between the raceway of the raceway of outer race 34 and inner race 36 in the free rolling mode.In this case, rolling element 38 is balls, and is kept with predetermined interval by retainer 40 on circumferential direction.Have at least one to comprise nitrogen-enriched layer in the bearing part, wherein, above-mentioned bearing part is for constituting outer race 34, inner race 36 and the rolling element 38 of rolling bearing.Comprise that heat treatment that carbonitriding handles will be described as the concrete example of the processing that is used to form nitrogen-enriched layer.

Figure 12 is the figure that illustrates according to the embodiment of the invention, as to be used for rolling bearing heat treatment method.Figure 13 is the figure that is used to illustrate its modification.Figure 12 illustrates the heat treatment figure (pattern) that has carried out primary quenching and Qa method.Figure 13 shows material and is lower than the A1 transition temperature and is after this heated heat treatment figure with the method for finally being quenched once more quenching to be cooled to midway.In these figure, handling T ₁In, when carbon and nitrogen spread in the base steel material, the infiltration of carbon proceeded to abundant degree, and after this base steel material is cooled to and is lower than A ₁Transition temperature.Then, processing T in the drawings ₂In, the base steel material is heated to once more is equal to or higher than A ₁Transition temperature and be lower than and handle T ₁In its temperature, be subjected to oil quench then.

Compare with traditional carbonitriding quenching, promptly after handling, carbonitriding only carries out primary quenching and without any other processing, owing to above-mentioned heat treatment, cracking resistance accesses raising, simultaneously the top layer part is by carbonitriding, thereby can reduce aging caused size changing rate.In by the heat treatment figure of Figure 12 or 13 microstructure that produce, according to rolling bearing of the present invention, austenite grain size is equal to or less than half of traditional austenite grain size.Be subjected to above-mentioned heat treated bearing part and have long rolling fatigue life, therefore can improve resistance to cracking and reduce aging caused size changing rate.For crystal grain thinning, carried out heat treatment process so that reduce the secondary quenching temperature.Therefore, among its top layer and inside, the quantity of retained austenite crystal grain reduces.Thereby, can obtain outstanding resistance to cracking and aging caused size changing rate.

Figure 14 A and 14B are the views that bearing part microstructure, particularly austenite crystal are shown separately.Figure 14 A illustrates according to exemplary bearing parts of the present invention.Figure 14 B illustrates the traditional bearing parts.That is, Figure 14 A illustrates according to the austenite grain size in the raceway of the described rolling bearing of the embodiment of the invention, and wherein, the heat treatment figure of Figure 12 is applied to above-mentioned rolling bearing.In order to compare, the austenite grain size of the Bearing Steel that obtains by the prior heat treatment method is shown in Figure 14 B.And Figure 15 A and 15B illustrate the austenite grain size of Figure 14 A and 14B respectively with schematic form.According to the structure that shows these austenite grain sizes, traditional austenite grain size is corresponding to JIS model die size No.10, and, when adopting the heat treatment method of Figure 12 or 13, can obtain to have separately the fine-grain of JIS model die size No.12.And, to measure according to microtomy, the average grain size of Figure 14 A is 5.6 μ m.

Then example will be described.

Example 1

By using JIS standard SUJ2 material (1.0 mass percent C-0.25 mass percent Si-0.4 mass percent Mn-1.5 mass percent Cr), carried out following test, promptly, (1) hydrogen measurement amount, (2) crystallite dimension is measured, (3) pendulum impact test, (4) failure stress values is measured, and the test of (5) rolling contact fatigue.Table 4 shows the result of these tests.

Table 4

Sample

A

B

C

D

E

F

The tradition carbonitriding

Normal quenching

							Handle
									The secondary quenching temperature (℃)	780	800	815	830	850	870	-	-
Hydrogen amount (ppm)	-	0.37	0.48	0.38	0.42	0.40	0.72	0.33
									Crystallite dimension (JIS)	-	12	11.5	11	30	15	10	10
Pendulum impact value (J/cm 2)	-	6.65	5.45	6.30	6.20	6.30	5.33	6.70
									Failure stress values (MPa)	-	2840	2780	2550	2850	2700	2330	2770
Rolling fatigue life is than (L 10)	-	5.4	4.2	3.5	2.9	2.8	3.1	1

The production history of each sample is described below.

Sample A is to D (example of the present invention): carbonitriding is handled 850 ℃, 150 minutes retention times.Given atmosphere is the mixed gas of RX gas and ammonia.In heat treatment figure as shown in Figure 12, the time that arrives 850 ℃ from the carbonitriding treatment temperature begins to carry out primary quenching, then, after sample being heated in the temperature range that falls into 780 ℃ to 830 ℃, carry out secondary quenching, wherein, 780 ℃ to 830 ℃ temperature range is lower than the carbonitriding treatment temperature.Notice that the secondary quenching temperature is that 780 ℃ sample A is not fully quenched, so it is not put within the subjects.

Sample E and F (comparative example): carrying out carbonitriding processing to the identical course of D with example A of the present invention, and, by the carbonitriding treatment temperature is set at 850 ℃ or higher, promptly 850 ℃ carry out secondary quenching to 870 ℃.

Traditional carbonitriding product (comparative example): carbonitriding is handled 850 ℃, 150 minutes retention times.Given atmosphere is the mixed gas of RX gas and ammonia.Begin to quench and without any other processes from the time that obtains the carbonitriding treatment temperature, and, do not carry out secondary quenching.

Normal quenching product (comparative example): do not carry out carbonitriding and handle, and product is heated to 850 ℃ to be quenched.Do not carry out secondary quenching.

Then test method will be described.

(1) hydrogen measurement amount

As the hydrogen amount, the DH-103 type hydrogen analyzer that is produced with LECO company is analyzed the amount of non-dispersive hydrogen in the steel.Do not measure the amount of diffusivity hydrogen.Below show the specification of the DH-103 type hydrogen analyzer that LECO company produced.

Analyst coverage: 0.01 to 50.00ppm

Accuracy of analysis: ± 0.1ppm or ± 3%H (wherein bigger that)

Sensitivity for analysis: ± 0.1ppm

Detecting method: thermal conductivity method

The sample size of representing with weight: 10mg is to 35mg (maximum value: diameter 12mm * length 100mm)

Furnace temperature scope: 50 ℃ to 1100 ℃

Reagent: anhydrone Mg (ClO ₄) ₂, ascarite NaOH

Carrier gas: nitrogen, gas dosage gas (gas dosing gas): hydrogen, the purity of two kinds of gases is 99.99% or higher, and pressure is 40psi (2.8kgf/cm ²).

The summary of measurement procedure is as follows.The sample of being obtained by special-purpose sample collector is inserted into hydrogen analyzer, is contained in the sample collector simultaneously.Diffusible hydrogen in it is introduced into the thermal conductivity detector by the nitrogen carrier gas.In example 1, diffusible hydrogen does not experience measurement.Then, sample is taken out from sample collector and in resistance-heated furnace, heat, and non-diffusible hydrogen is introduced into the thermal conductivity detector by the nitrogen carrier gas.By measuring the thermal conductivity in the thermal conductivity detector, can know the amount of non-diffusible hydrogen.

(2) crystallite dimension is measured

Carrying out crystallite dimension based on the austenite grain size test method of JIS G 0551 steel measures.

(3) pendulum impact test

Pendulum impact test method based on JIS Z 224 metallic material is carried out pendulum impact test.As test specimen, used U-shaped gap test piece (JIS No.3 test specimen) according to JIS Z 2202.

(4) failure stress values is measured

Figure 16 illustrates the test specimen that is used for static pressure breakdown strength test (determining of rupture stress value).Load applies along the P direction among the figure, and is continuously applied up to destroying the load that takes place measured.After this, the breaking load that is obtained is converted into stress value by the Stress calculation formula of following bent beam.Notice that test specimen is not limited only to the test specimen shown in Figure 16, can use the test specimen of other structures.

When using symbol σ ₁Fiber stress on the convex surfaces of test specimen of expression Figure 16, and use symbol σ ₂During the recessed lip-deep fiber stress of expression, σ ₁And σ ₂Can determine by following formula (mechanical engineer's handbook A4 roll of material intensity A 4-40).In this case, symbol N represents to comprise the axial force in the cross section of ring specimen axis, and symbol A represents cross-section area, symbol e ₁The expression inside radius, symbol e ₂The expression outer radius.And symbol kappa is represented the section modulus of bent beam.

σ ₁＝(N/A)+{M/(Aρ ₀)}[1+e ₁/{κ(ρ ₀+e ₁)}]

σ ₂＝(N/A)+{M/(Aρ ₀)}[1-e ₂/{κ(ρ ₀-e ₂)}]

k＝-(1/A)∫A{η/(ρ ₀+η)}dA

(5) rolling fatigue life

The test conditions of rolling fatigue life test is shown in the table 5.Each schematic representation of rolling fatigue life testing machine naturally of Figure 17 A and 17B.Figure 17 A is a front elevation, and Figure 17 B is a side view.In Figure 17 A and 17B, rolling fatigue life test specimen 48 drive by drive roller (driving roll) 48 and with rotation when ball 46 contact.Ball 46 is 3/4 inch ball, guides by guide reel 44, and, applying high contact pressure on the rolling fatigue life test specimen 48 and when rolling fatigue life test specimen 48 was accepted high contact pressure, ball 46 rolled at ball 46.

The test result of the example 1 shown in the table 4 is described below.

(1) hydrogen amount

The hydrogen amount of the traditional carbonitriding product that stays after the experience carbonitriding is handled is 0.72ppm, and this is a very high value.Its reason is considered to because of the ammonia (NH that is included in the carbonitriding processing atmosphere ₃) decompose, thereby hydrogen is entered in the steel.On the other hand, in D, the hydrogen amount is reduced to 0.37 to 0.40ppm at sample B, and this approximately is above-mentioned value half.The such hydrogen amount and the hydrogen amount of normal quenching product are in same level.

Because aforesaid oxygen amount reduces, can alleviate the Hardening Of Steel (stiffening) that the dissolving because of hydrogen causes.Just, because the reduction of hydrogen amount, improved largely to the pendulum impact value of D according to the sample B of example of the present invention.

(2) crystallite dimension

About crystallite dimension, the secondary quenching temperature is lower than under the situation of quenching (primary quenching) temperature in carbonitriding is handled, promptly at sample B under the situation of D, austenite grain size is refined to crystallite dimension No.11 to 12 significantly.The crystallite dimension of the austenite crystal of sample E and F, traditional carbonitriding product and normal quenching product is No.10, and above-mentioned crystal grain beguine is slightly much bigger to the crystal grain of D according to the sample B of example of the present invention.

(3) pendulum impact test

According to table 4, when the pendulum impact value of traditional carbonitriding product is 5.33J/cm ²The time, be higher value according to the sample B of the example of the present invention pendulum impact value of each in the D, promptly 6.30 to 6.65J/cm ²Among these, what have low secondary quenching temperature is tending towards showing higher pendulum impact value.The pendulum impact value of normal quenching product is higher value 6.70J/cm ²

(4) failure stress values is measured

Above-mentioned failure stress values is corresponding to resistance to cracking.According to table 4, the failure stress values of traditional carbonitriding product is 2330MPa.In contrast to this, the sample B that is obtained is the improvement value to the failure stress values of D, and promptly 2650 to 2840MPa.The failure stress values of normal quenching product is 2770MPa, and resulting sample B is to reduce and a benefit of the effect that the austenite crystal refinement causes because of hydrogen content to the improved resistance to cracking of D.

(5) rolling contact fatigue test

According to Fig. 4, because the normal quenching product does not have carbonitrided case on its top layer part, so its rolling fatigue life L ₁₀Be minimum.In contrast to this, the rolling fatigue life of traditional carbonitriding product is 3.1 times big.Sample B rolling fatigue life of each in the D is compared with traditional carbonitriding product and is significantly increased.Sample E and the F rolling fatigue life and the rolling fatigue life of traditional carbonitriding product separately is basic identical.

Sum up The above results, in each of D, hydrogen content reduces at the sample B of example of the present invention, and austenite grain size is refined to and is higher than No.11, and pendulum impact value, resistance to cracking and rolling fatigue life are improved.

Example 2

Then, example 2 will be described.Following X material, Y material and Z material experience a series of tests.As heat treatment material, JIS standard SUJ2 material (1.0 mass percent C-0.25 mass percent Si-0.4 mass percent Mn-1.5 mass percent Cr) generally is used for X each to the Z material.X is as follows to the manufacturing history of Z material.

X material (comparative example): normal quenching (do not carry out carbonitriding handle) only.

Y material (comparative example): after carbonitriding is handled, quench and without any other processes (traditional carbonitriding quenching).845 ℃ of carbonitriding treatment temperatures, and 150 minutes retention times.The atmosphere that carbonitriding is handled is RX gas+ammonia.

Z material (example of the present invention): the Bearing Steel of the heat treatment figure of experience Figure 12.845 ℃ of carbonitriding treatment temperatures, and 150 minutes retention times.The atmosphere that carbonitriding is handled is RX gas+ammonia.Last quenching temperature is 800 ℃.

(1) rolling fatigue life

As mentioned above, the test conditions of rolling fatigue life and testing apparatus are shown in table 5 and Figure 17 A, the 17B.The result of rolling fatigue life test is shown in the table 6.

Table 5

Test specimen	 12 * L22 cylinder test specimen
		Test number (TN)	10
The coupling steel ball	3/4 inch (19.05mm)
		Contact pressure	5.88GPa
Loading velocity	46240opm
		Lubricant oil	Turbine VG68 self-contained lubrication

Table 6

Material type	Life-span (loading number of times)		L 10The ratio
				L 19(×10 4Inferior)	L 59(×10 4Inferior)
	Material X	8017				18648	1.0
Material Y			24656	33974	3.1
	Material Z	43244				69031	5.4

According to table 6, the Y bill of material of comparative example reveals 3.1 times of big L of X material ₁₀Life-span (life-span of a fracture in 10 test specimens), wherein the X material with comparative example in same mode only experience normal quenching.In this case, observe the longer life effect that causes because of the carbonitriding processing.On the other hand, the life-span of revealing 5.4 double-lengths of life-span of 1.74 double-lengths of B material and X material according to the Z bill of material of example of the present invention.The refinement of microstructure is considered to this improved effective reason.

(2) pendulum impact test

Carry out pendulum impact test by aforesaid method with the U-shaped gap test piece according to JISZ2242.Test result is shown in the table 7.

Table 7

Material type	Pendulum impact value (J/cm 2)	The ratio of impact value
			Material X	6.7	1.0
Material Y	5.3	0.8
			Material Z	6.7	1.0

The pendulum impact value of the Y material (comparative example) that the experience carbonitriding is handled also is not more than the pendulum impact value of the X material (comparative example) of experience normal quenching, and for the Z material, has then obtained the identical value of pendulum impact value with the X material.

(3) static fracture toughness value test

Figure 18 illustrates the test specimen that is used for static fracture toughness test.Approximately the precrack of 1mm is introduced into the barbed portion of test specimen.After this, the static load that causes because of three-point bending is applied in thereon, and has determined breaking load P.Be used to calculate fracture toughness value (K ₁The c value) be formula (I).Test result is shown in the table 8.

$\mathrm{Klc}=(\mathrm{PL}\sqrt{a}/{\mathrm{BW}}^2)\{5.8-9.2(a/W)+4.36{(a/W)}^2-75.3{(a/W)}^3+77.5{(a/W)}^4\}\·\·\·\left(I\right)$

Table 8

Therefore the degree of depth of precrack is not having difference according to comparative example between described X material and the Y material greater than the degree of depth of carbonitrided case.Yet, compare with comparative example, can obtain about 1.2 times of big values according to the Z material of example of the present invention.

(4) static pressure breakdown strength test

The test specimen of shape as shown in above-mentioned Figure 16 is used as static pressure and destroys test specimen.In the drawings, load to carry out the test of static pressure breakdown strength along the P direction.Test result is shown in the table 9.

Table 9

Material type	Test number (TN)	Static pressure breakdown strength (kgf)	The ratio of static pressure breakdown strength
				Material X	3	4200	1.00
Material Y	3	3500	0.84
				Material Z	3	4300	1.03

The Y bill of material that the experience carbonitriding is handled reveals the lower slightly value of X material than the experience normal quenching.Yet, to compare with the Y material according to the Z material of example of the present invention, its static pressure breakdown strength is improved, and is in the X material and compares favourable level.

(5) aging caused size changing rate

Follow surface hardness and remained austenite content together at (degree of depth 50 μ m) shown in the table 10 in the measurement result that keeps the aging caused size changing rate under 130 ℃ of temperature, the 500 hours retention times condition.

Table 10

Material type	Test number (TN)	Surface hardness (HRC)	Remaining γ amount (%)	Size changing rate (* 10 -3)	The ratio of size changing rate
						Material X	3	62.5	8.8	18	1.0
Material Y	3	63.6	30.5	35	1.9
						Material Z	3	60.0	11.8	22	1.2

Compare with the size changing rate of the bigger Y material of remained austenite content, be suppressed to being lower than half according to the size changing rate of the Z material of example of the present invention.

Example 3

The result of the test that table 11 is illustrated under the condition of incorporating impurity into, nitrogen content and the relation between the life-span of rolling are carried out.In this test, used the taper roller bearing shown in Fig. 8.In example 1 to 5, all outer races 13, inner race 14 and taper roller 16 are manufactured when having used the heat treatment figure shown in Figure 12.And, on the surface of taper roller, be formed with the countless micro recessed shown in table 1 and the table 2 at random.Notice that comparative example 1 is the normal quenching product, comparative example 2 is common carbonitriding products.Although comparative example 3 shows the situation of following the same processing of example of the present invention but having only nitrogen amount surplus of having used.Test result is as follows.

Test bearing: taper roller bearing 30206 (inside/outside seat ring and roller are made (being made by SUJ2) according to JIS by second level high-carbon-chromium bearing steel)

Radial load: 17.64kN

Thrust load: 1.47kN

Rpm：2000rpm

Hard impurity content ratio: 1g/L

Table 11

No.	Nitrogen content (%)	Retained austenite (%)	Hardness (Hv)	In the rolling life-span (h) of incorporating under the impurity condition	Austenite grain size	Remarks
							1	0.11	14	725	321	11.8	Example 1
2	0.16	18	735	378	12.0	Example 2
							3	0.18	20	730	362	11.9	Example 3
4	0.32	22	730	395	12.1	Example 4
							5	0.61	24	715	434	12.2	Example 5
6	0	8	770	72	9.8	Comparative example 1
							7	0.32	32	710	155	10.0	Comparative example 2
8	0.72	31	700	123	12.0	Comparative example 3

Can understand from table 13, about example 1 to 5, nitrogen content and life-span are in ratio substantially when incorporating impurity into.Note, preferably, consider nitrogen content be 0.72 comparative example 3 incorporate into rolling life-span under the impurity condition be reduced to minimum, so nitrogen content on be limited to 0.7.

Here disclosed embodiment only is example in all fields, and should not be considered to restriction.Scope of the present invention is given by the scope of claim, rather than given by foregoing description.Scope of the present invention should be included in the method that is equal to the claim scope and all modifications within the scope.

Claims (5)

1. a rolling bearing comprises rolling element, and described rolling element has the countless micro recessed that form at random at least in its surface, and wherein, the average area of described depression is at 30 to 100 μ m ²Scope in, and Rymax is in 0.4 to 1.0 scope.

2. rolling bearing as claimed in claim 1, wherein: at least one in the external member of described rolling bearing, inner member and the described rolling element has nitrogen-enriched layer; And the austenite grain size in the described nitrogen-enriched layer is in the scope that is higher than crystallite dimension No.10.

3. rolling bearing as claimed in claim 1 or 2, wherein, when the surface roughness on the surface of representing to be formed with on it described depression with parameters R qni, the ratio between axial surface roughness Rqni (L) and the peripheral surface roughness Rqni (C) " Rqni (L)/Rqni (C) " is equal to or less than 1.0.

4. as claim 2 or 3 described rolling bearings, wherein, the nitrogen content in the described nitrogen-enriched layer is in 0.1% to 0.7% scope.

5. rolling bearing as claimed in claim 4, wherein: in described external member, described inner member and the described rolling element described at least one comprise seat ring; And described nitrogen content is the value in the 50 μ m top layers on the raceway face after the grinding.

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