JP2014517151A - Improved bearing steel - Google Patents

Abstract

  The present invention relates to a bearing steel comprising at least 0.6% by weight of carbon, 0.007% by weight or less of phosphorus and optionally other alloying elements, the balance being iron or iron and impurities. The present invention further relates to a bearing comprising only this bearing steel.

Description

  The present invention relates to bearing steel. The invention further relates to a bearing manufactured from bearing steel.

  Bearings such as roller bearings and ball bearings are subjected to high loads during use. Therefore, the bearing should have high fatigue strength in addition to high hardness.

  Steel containing a large amount of carbon is known to have high hardness, but such steel has a problem of low fatigue strength.

  One object of the present invention is to provide a bearing steel with improved fatigue strength. It is also an object of the present invention to provide a bearing manufactured from bearing steel according to the present invention.

  According to a first aspect of the invention, this object is achieved by bearings comprising at least 0.6% by weight of carbon, 0.007% by weight or less of phosphorus and optionally other alloying elements, the balance being iron. Achieved with steel.

  It has been found that the balance may consist solely of impurities in addition to iron. Such impurities may be impurities or trace elements normally present in iron or steel. Thus, the bearing steel may contain at least 0.6 wt% carbon, 0.007 wt% or less phosphorus, and optionally other alloy elements, with the balance being iron or iron and impurities.

  Impurities may be present at a level of 0.5% by weight or less, preferably 0.425% by weight or less. Typical impurities may be, for example, Cu, As, Sn, Sb, Pb, Ti, or O, or combinations thereof. Impurities such as low levels of Ti and O lead to low levels of hard non-metallic inclusions, and this hard non-metallic inclusions combined with other low-level elements that tend to accumulate at austenite grain boundaries are high. A bearing steel having fatigue strength is provided. In particular, a small amount of phosphorus according to the present invention combined with low levels of impurities results in bearing steels with high fatigue strength.

  Iron can be essentially pure iron and is essentially free of impurities.

  The amount of carbon according to the present invention gives the steel a high hardness suitable for the steel used in the bearing. The amount of phosphorus according to the invention results in a bearing steel with high fatigue strength.

  The bearing steel may have phosphorus in an amount less than 0.007% by weight, preferably in the range of 0.003 to 0.007% by weight, such as 0.004 to 0.006% by weight. Steel with such an amount of phosphorus is produced efficiently in steel mills and may have high fatigue strength. Phosphorus at a level lower than 0.003% by weight is difficult and expensive to manufacture. Also, phosphorus levels higher than 0.007% by weight do not provide the desired high fatigue strength.

  It is an advantage according to the invention that a small amount of phosphorus combined with a suitable amount of carbon results in a bearing steel with high fatigue strength.

  The amount of carbon in the bearing steel may be 0.6 to 1.5 wt%, such as 0.7 to 1.3 wt% or 0.7 to 1.1 wt%. Preferably, the amount of carbon is 0.7 to 1.2% by weight, more preferably 0.8 to 1.1% by weight. For example, this amount may be from 0.9 to 1.0% by weight. Such an amount of carbon gives the bearing steel suitable properties such as high hardness. Even with high levels of carbon, for example 0.9 to 1.1% by weight, bearing steel has high fatigue strength when combined with 0.007% by weight or less of phosphorus.

  Thus, the bearing steel may be considered high carbon steel or ultra high carbon steel.

  The bearing steel may further contain sulfur, S, in an amount up to 0.02% by weight. The amount of sulfur may be 0.0001 to 0.02 wt%, such as 0.0001 to 0.016 wt% or 0.0001 to 0.011 wt%. According to one embodiment of the invention, the amount of sulfur is 0.0001 to 0.002 wt%, such as 0.0001 to 0.001 wt%, such as 0.0001 to 0.0002 wt%. It is. Such a small amount of sulfur results in a bearing steel having a high fatigue strength. According to another embodiment of the invention, the amount of sulfur is 0.002 to 0.02 wt%, such as 0.002 to 0.013 wt%, such as 0.003 to 0.012 wt%. 0.005 to 0.012 wt%, or 0.007 to 0.011 wt%. Even if the sulfur is so high, the bearing steel has a high fatigue strength even if the sulfur is so high and combined with a large amount of carbon and the amount of phosphorus according to the invention.

  In the bearing steel, the total amount of sulfur and phosphorus may be 0.02% by weight or less. Such total amounts of sulfur and phosphorus can result in bearing steels with high fatigue strength.

  The bearing steel may further contain aluminum in an amount of 0.01% by weight or more as an alloying element. Preferably, the amount of aluminum may be 0.015 wt% or more, or more preferably 0.02 wt% or more. The maximum amount of aluminum may be 0.05% by weight. Therefore, the amount of aluminum in the bearing steel may be 0.015 to 0.05% by weight.

  The bearing steel is further 0.1 to 0.7% by weight, preferably 0.3 to 0.7% by weight, most preferably above 0.5, for example from 0.51 to 0.6% by weight. Molybdenum and Mo in an amount up to 0.7% by weight may be included. Such a level of Mo may result in hard bearing steel with high fatigue strength. Furthermore, such an amount of Mo may be efficient in the production of bearing steel having a bainite structure.

  The bearing steel may have a bainite structure or may be bainite-quenched. It has been found that such bearing steel may also contain other structures besides the bainite structure. Preferably, more than 50 percent of such bearing steel has a bainite structure, for example 50 to 90 percent of the bearing steel.

 The bainite structure provides improved mechanical properties with high toughness and high crack propagation resistance. Thus, the bainite structure is beneficial for bearing steels and bearings because such steels and bearings are heavily loaded during normal and typical use. A combination of relatively high levels of carbon, low levels of phosphorus, relatively high levels of Mo, and / or relatively high levels of sulfur in accordance with related embodiments of the present invention results in bearing steel with high bearing fatigue strength. .

  Bainite quenching of bearing steel may be obtained according to the following method: austenitizing and quenching the steel; exposing the steel to an initial temperature (T1) higher than the initial martensite formation temperature (Ms); bainite transformation Meanwhile, T1 is lowered to a temperature lower than Ms but higher than the actual martensite formation temperature.

  By this bainite quenching method, the bainite quenching time of the bearing steel is shortened and the hardness is increased, and the bainite structure of the bearing steel may be obtained efficiently.

  The hardness of the bearing steel may be higher than 59 HRC, such as 59 to 62 HRC, or higher than 62 HRC.

  Thus, the bearing steel or bearing may have a substantially bainite structure and a hardness of at least 62 HRC.

  The bearing steel may also have a martensitic structure with high fatigue strength, or may be martensitic quenched.

  Bearing steel containing Mo in an amount of 0.1 to 0.7% by weight may be suitable for bearings having a material thickness above 0 and up to 150 mm. The bearing steel may have an amount of Mo of 0.1 to 0.5% by weight, which Mo is above 0, such as a material thickness of 15 to 100 mm, for example 15 to 45 mm. And may be suitable for bearings up to 150 mm.

  Bearing steel containing Mo in an amount of 0.5 to 0.7% by weight may be particularly suitable for bearings having a material thickness of 45 mm or more, such as 45 to 150 mm or 45 to 80 mm. Such a bearing may be, for example, a roller bearing with a wall thickness of 45 to 80 mm.

  Bearing steel used for bearings with a material thickness of less than 15 mm may have Mo in an amount of less than 0.35% by weight, or greater than 0 and up to 0.35% by weight. Such bearing steel may have a bainite structure.

  In particular, bearing steel containing Mo in an amount of 0.1 to 0.7% by weight may have a bainite structure.

  The bearing steel may contain chromium, Cr in an amount of 1.0 to 3.0% by weight, such as 1.3 to 2.0% by weight. An amount of Cr of 1.0 to 1.5% by weight may be particularly suitable for bearings whose material thickness is above 0 and up to 45 mm, such as 15 to 45 mm. A Cr content of 1.5 to 3.0% by weight, for example 1.5 to 2.0% by weight, is particularly suitable for bearings having a material thickness of 45 mm or more, for example 45 to 80 mm or 45 to 150 mm. Sometimes.

  Bearing steel containing Cr in an amount of 1.0 to 3.0 wt% may be suitable for a bainite structure.

  Any other alloying element may be selected from the group consisting of Si, Mn, S, Cr, Ni, Mo, V, and Al, or combinations thereof.

  Any such other alloying element may be suitable for imparting suitable properties to the steel.

If present in the bearing steel, suitable levels for any of these other alloying elements may be in the following ranges:
Silicon (Si): 0-2.5% by weight, eg 0.0001-2.5
Manganese (Mn): 0-2% by weight, eg 0.0001-2
Sulfur (S): 0-0.02% by weight, such as 0.0001-0.02
Chromium (Cr): 0-3 wt%
Nickel (Ni): 0-1% by weight, such as 0.0001-1
Molybdenum (Mo): 0-1% by weight
Vanadium (V): 0-1% by weight, such as 0.0001-1
Aluminum (Al): 0.01-0.050% by weight.

  Such levels of alloying elements may result in low hard non-metallic inclusions and high fatigue strength bearing steel.

  According to a second aspect of the invention, it contains at least 0.6% by weight of carbon, 0.007% by weight or less of phosphorus, and optionally other alloying elements, the balance being iron or iron and impurities. A bearing made of or consisting of bearing steel is provided.

  It may be preferred that the bearing consists of at least 0.6% by weight of carbon, 0.007% by weight or less of phosphorus and optionally only other alloy elements or essentially only.

  Therefore, the characteristics of the bearing steel may be imparted to the bearing as described above. Therefore, high fatigue strength may be imparted to the bearing.

  The bearing may be selected from the group consisting of a ball bearing and a roller bearing, the ball bearing comprising a deep groove ball bearing, an angular ball bearing, a thrust ball bearing, an angular thrust ball bearing, and a self-aligning ball bearing, or a combination thereof. The roller bearing may be selected from the group, and the cylindrical roller bearing, spherical roller bearing, thrust cylindrical roller bearing, needle roller bearing, toroidal roller bearing, CARB (registered trademark) toroidal roller bearing, compound needle roller bearing, tapered roller Selected from the group consisting of bearings, thrust tapered roller bearings, thrust needle roller bearings, thrust spherical roller bearings, compound cylindrical roller / conical roller bearings, track runner bearings, and indexing roller units, or combinations thereof Also good. At least one part of the bearing, such as a rolling element of the bearing or a bearing ring, may consist of bearing steel according to the invention.

  The bearing may be a ball bearing selected from the above group and a combination with a bearing.

  The bearing may have a material thickness above 0 and up to 150 mm, such as above 0 and up to 80 mm. Thus the bearing may have a material thickness above 0 and 45 mm, for example from 15 to 45 mm, or the bearing may have a material thickness of 45 mm or more, for example from 45 to 80 mm or from 45 to 150 mm. You may have.

  The above discussion about the bearing steel with respect to the first aspect of the invention may also be relevant for the bearing of the second aspect of the invention with respect to the bearing. Reference is now made to these discussions regarding bearings.

It is a figure which shows the result of the rotating beam fatigue test of samples A and B. It is a figure which shows the result of the steer case test of samples A and B.

  The advantages of the present invention will be appreciated and understood in the following comparative examples. It will be understood that comparative examples are included to enhance the understanding of the present invention, and that the comparative examples are by no means limited to the scope of the present invention.

  Two steel heats A and B were used to cast ingots A and B. Ingots A and B were forged into 350 mm round billets. Billets A and B were cut and machined into rotating beam samples A and B. Samples A and B were bainite quenched using a salt bath transformation at 235 ° C. and using a conventional bainite transformation cycle. Samples A and B were completed by high hardness turning, grinding, and polishing. The chemical composition of samples A and B obtained from heats A and B are listed in Table 1. Sample A is a comparative example.

  As shown in Table 1, Samples A and B are different in that the amount of phosphorus in Sample B is significantly less than Sample A, and Sample A has a phosphorus content that is 2.8 times higher than Sample B. . It can also be seen from Table 1 that the sulfur content in sample B is 2.5 times higher than the sulfur content in sample A. Furthermore, the amount of Al in sample B is 17% higher than in comparative example A. When samples A and B are compared, the content of other elements is the same or similar.

Rotating beam fatigue test and staircase test:
Several samples A and B were tested at a constant stress level of 1060 MPa to produce a staircase. The results from this test are shown in FIGS. From this test and results, it can be concluded that the average service life in the constant stress test of sample B according to the present invention is at least 5 times higher than that of Comparative Example A.

  The steer case test for Samples A and B, as shown in FIG. 2, represents a significant improvement in fatigue limit when Sample B according to the present invention is compared to Comparative Example A.

  It is clear from this test that the bearing steel having the chemical composition according to Sample B in Table 1 provides a significant improvement in properties including an improvement in fatigue strength. For example, it was concluded that small amounts of phosphorus had a beneficial effect on improving fatigue strength.

  According to one embodiment of the present invention, the bearing steel comprises 0.9 to 1.1 wt% carbon, 0.004 to 0.007 wt% phosphorus, and 0.5 to 0.7 wt% molybdenum. And optionally other alloy elements, the balance being iron or iron and impurities. Such bearing steel provides high fatigue strength.

  According to another embodiment of the present invention, the bearing steel comprises 0.9 to 1.1 wt% carbon, 0.004 to 0.007 wt% phosphorus, and 0.5 to 0.7 wt%. It may contain molybdenum, 0.002 to 0.016% by weight of sulfur, S, and optionally other alloying elements, the balance being iron or iron and impurities. Such bearing steel provides high fatigue strength.

Claims (13)

  Bearing steel comprising at least 0.6 wt% carbon, 0.007 wt% or less phosphorus, and optionally other alloying elements, the balance being iron or iron and impurities.   2. Bearing steel according to claim 1, wherein the amount of phosphorus is less than 0.007% by weight, preferably in the range of 0.004 to 0.007% by weight.   Bearing steel according to claim 1 or 2, wherein the amount of carbon is 0.6 to 1.5% by weight.   4. Bearing steel according to claim 3, wherein the amount of carbon is from 0.8 to 1.1% by weight.   The bearing steel according to any one of claims 1 to 4, further comprising as an alloying element sulfur in an amount of 0.02% by weight or less, preferably 0.002 to 0.016% by weight.   The bearing steel according to any one of claims 1 to 5, further comprising 0.015% by weight or more of aluminum as an alloying element.   Further comprising molybdenum as an alloying element in an amount of 0.1 to 0.7% by weight, preferably 0.4 to 0.7% by weight, most preferably above 0.5 and up to 0.6% by weight. The bearing steel according to any one of claims 1 to 6.   0.9 to 1.1 wt% carbon, 0.003 to 0.007 wt% phosphorus, 0.5 to 0.7 wt% molybdenum, and 0.002 to 0.016 wt% sulfur The bearing steel as described in any one of Claim 1 to 7 containing these.   The bearing steel according to claim 1, wherein the bearing steel has a bainite structure.   10. Any one of the other alloy elements is selected from the group consisting of Si, Mn, S, Cr, Ni, Mo, V, and Al alone, or a combination thereof. The bearing steel described.   A bearing comprising the bearing steel according to claim 1.   The bearing according to claim 11, wherein the bearing has a material thickness of 45 mm or less, preferably 15 to 45 mm.   The bearing according to claim 11, wherein the bearing has a material thickness of 45 mm or more, preferably 45 to 80 mm.

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