How to improve the mill bearing life

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First, the impact of material factors bearing life

Early failure in the form of rolling bearings, main has broken, plastic deformation, wear, corrosion, and fatigue, contact fatigue under normal conditions. In addition to the

service conditions, the failure of the bearing parts, mainly affected by the hardness, strength, toughness, abrasion resistance, corrosion resistance and the internal stress

state constraints. There are several key internal factors that affect the performance and status.ball bearing companies

1.1 hardened steel martensite
Granular pearlite original organization of high-carbon chromium steel, quenching and tempering state quenched martensite carbon content significantly affect the mechanical

properties of the steel. Strength, toughness and contact fatigue life of about 0.55%, the crush capacity of about 0.42%, when the the GCr15 steel quenched martensite carbon

content of 0.5% to 0.56%, can be resistant to the most failure capacity of about 0.5% mechanical properties.

It should be noted that the martensite is obtained in this cas e hidden martensite, and the measured carbon content is the average carbon content. In fact, the amount of the

carbon in the martensite in the micro area is not uniform, close carbide around the carbon concentration is higher than away from the carbide raw ferrite portion, so that they

start at different temperatures of the martensitic transformation , thereby inhibiting the the martensite grain growth and micromorphology display and hidden martensite. It can

avoid the quenching of the high carbon steel prone to microcracking, and its sub-structure for the strength and toughness of a high dislocation plate lath martensite. Therefore,

only when high-carbon steel quenching cryptocrystalline martensite when the bearing, carbon parts could obtain anti-failure capacity matrix.industrial bearings

1.2 hardened steel, the residual austenite

Of h igh-carbon chromium steel after normal after quenching, and may contain 8% ~ 20% Ar (residual austenite). Bearing parts in the Ar has advantages and disadvantages, Ar

content should be appropriate, in order to better bring. As the amount of Ar austenitizing and quenching conditions, how much it will affect the of quenched martensite carbon

content, and the number of undissolved carbides, more difficult to correctly reflect the amount of Ar mechanical properties. Fixed Albright conditions, the use of austenitic

body of thermal stabilization treatment process, to get a different amount of Ar, Ar content after quenching and tempering of GCr15 steel hardness and contact fatigue life in

this study. Austenite content, hardness, and contact fatigue life increases, reaches a peak and then the attendant reduction, but the peak of the Ar content, hardness peak

appeared in about 17% Ar, and contact fatigue life peak around 9%. When the test load is reduced, due to the increased amount of Ar contact fatigue life decreases. This is when

a small amount of Ar has little effect on the intensity decreases, toughening role. Because the load is small, Ar is a small amount of deformation, reduced the stress peak

deformation Ar processing to strengthen and to stress strain induced martensite transformation and strengthening. However, if the load is large, Ar large plastic deformation

with base experience local stress concentration rupture so that the lower life expectancy. It should be noted that the beneficial effect of Ar must be under Ar steady state, if

the spontaneous transition to martensite, the toughness of the steel will drastically reduced embrittlement.

1.3 hardened steel undissolved carbides

Undissolved carbides in the number of hardened steel, morphology, size distribution, both by the chemical composition of the steel and q uenching before the impact of the

original tissue, but also by austenitizing conditions, the undissolved carbides bearing life less impact study. Carbide is a hard and brittle phase addition to the benefit of

wear resistance, bearing due to be (in particular, non-spherical carbide) matrix cracks caused by stress concentration, which will reduce the toughness and fatigue resistance.

Quenching undissolved carbides in addition to its own impact on the performance of steel, but also affect the quenched martensite carbon content and Ar content and distribution,

and thus additional impact on the performance of steel. In order to reveal the undissolved carbides performance using different carbon content steel after quenching its of

martensitic carbon content and Ar content without dissolved carbon content after tempering at 150 ℃, martensite carbon content and higher hardness, which undissolved carbides

small amount of increased value is not on the hardness increased, reflecting the strength and toughness of the crushing load is decreased, the stress concentration sensitive

contact fatigue life significantly reduced. Therefore, the quenching of undissolved carbides too much steel mechanical properties and failure resistance is harmful. Appropriate

to reduce the carbon content of the bearing steel one way is to increase the service life of parts.

Quenching of undissolved carbides in addition to the number of affect material properties, size, morphology, distribution also have an impact on the material properties. In

order to avoid the undissolved carbides hazards bearing steel, the undissolved carbides (a small number), small (small size), uniform (the size of each other the difference is

small and evenly distributed), round (each piece carbide were highly spherical). It should be noted that a small amount of undissolved carbides bearing steel after quenching is

necessary, not only can maintain sufficient resistance to abrasion, but also cryptocrystalline martensite fine grain prerequisite.double row angular bearing

1.4 of residual stresses after quenching and tempering

Bearing parts after quenching and tempering, still has a large internal stress. Part of the residual stress advantages and disadvantages of the two states. After the heat

treatment of steel parts, as the surface residual stress increases, the fatigue strength of the steel along with it, the contrary, the surface residual stress is a tensile

stress, so that the fatigue strength of the steel decreases. Since the parts of the fatigue failure occurs in the bear excessive tensile stress, when the surface of a large

residual compressive stress, it will offset the equivalent value of the tensile stress, leaving the actual steel tensile stress value decreases, so that the fatigue strength

limit higher superimposed leaving steel withstand the tensile stress increased significantly when the surface has a large residual tensile stress, will withstand the tensile

stress load, even if the limit fatigue strength reduced. Therefore, the larger bearing parts quenched and tempered surface residual compressive stress, but also to improve the

life of one of the measures (of course, too large residual stress may cause cracking or deformation of the parts should be given enough attention).

Impurity content of 1.5 Steel

The impurities in the steel, including acid) content of the non-metallic inclusions and harmful elements (steel performance hazards are often mutually reinforcing, such as the

oxygen content is higher, the more oxide inclusions. Anti-failure capacity of steel impurities on the mechani cal properties and parts of the type of impurities, the nature,

number, size and shape, but usually have lower toughness, ductility and fatigue life.

Fatigue strength along with the increase in the size of the inclusions is reduced, and the higher the tensile strength of the steel, to reduce the tendency to increase. Oxygen

content in steel increased (oxide inclusions increase), bending fatigue and contact fatigue life decreases under high stress. Therefore, working under high stress bearing parts,

it is necessary to reduce the oxygen content of the steel manufacturing. Some studies suggest that MnS inclusions in steel, ellipsoidal shape, but also against the larger parcel

oxide inclusions, and reduce the impact on the fatigue life may be even less useful, they can be lenient control.

Second, increase the bearing life:
(A) the material factors affect bearing life control method:

To make mat erial factors affecting bearing life at its best:
1, you first need to control before hardening steel original organization, the technical measures that can be taken include: high temperature (1050 ℃) austenitizing rapid

cooling to 630 ° C isothermal normalizing the pseudo-eutectoid fine pearlite or cooling to 420 ° C The isothermal treatment bainite. Rapid thermal annealing, fine granular

pearlite unwrought waste heat can be used to ensure that small and evenly distributed carbides. Austenitizing original organization in this state quenching, in addition to the

integration into the carbide in austenite and undissolved carbides will gather into a fine granular.

When the steel in the original tissue is constant, the amount of quenched martensite carbonaceous (i.e. quenching heated austenite carbon content), the amount of retained

austenite and the amount of undissolved carbides depends primarily on the quenching temperature and holding time With the quenching temperature increased (a certain time),

reduce the number of undissolved carbides in the steel (quenched martensite carbon content increased), increased number of retained austenite, hardness first increases with

increasing quenching temperature, reached a peak and then decreases as the temperature rises. When the quenching temperature is constant, with the extension of austenitizing

time, the number of undissolved carbides reduce the number of retained austenite increased hardness increased, long time, this trend slowed. When the small original tissue

carbide, carbide Ease into austenite, so that the hardness after quenching of the peak towards lower temperature and appears in the austenitizing time shorter.

Summary, GCrl5 steel quenched the undissolved carbides at about 7% residual austenite at around 9% (cryptocrystalline martensite average carbon content o f about 0.55%) is the

best organization. Moreover, when the original tissue carbide small, uniform distribution, composition reliably control the level of the microstructure is conducive to obtain

high mechanical properties, which have a high life. It should be noted that the fine dispersion of carbides original organization, quenching insulation, fine carbides

undissolved gathering grew to coarsening. Therefore, should not be too long to have this original organization bearing parts quenching time, the use of rapid heating

austenitizing quenching process, will receive higher mechanical properties.

In order to make the bearing parts greater compressive stress remaining on the surface after quenching and tempering, is heated in the hardening pass into the carburizing or

nitriding atmosphere, for a short period of surface carburization or nitriding. Austenitic not actual carbon content of this steel quenchi ng, well below the equilibrium

concentration phase diagram shows, so you can suck carbon (or nitrogen). Austenite with high carbon or nitrogen, reduce the Ms quenching surface compared to the inner and center

martensitic transformation occurs, resulting in a larger residual compressive stress. The Hardening GCrl5 steel carburizing atmosphere and carburizing atmosphere (both by the

low-temperature tempering) after the treatment, the contact fatigue test can be seen, surface carburization life than not carburization increased 1.5 times. The reason is that

the surface of the carburized parts having a large residual compressive stress.


(B) the main material factors affecting the service life of high carbon chrome steel bearing parts and the degree of control:

(1) steel carbide in the original organization before quenching requires small, dispersed. Austenitizing 630 ℃, can be high temperature or high t emperature of 420 ℃, unwrought

waste heat to achieve rapid annealing process.

(2) For the GCr15 steel after quenching, the requirement to obtain the average carbon content of about 0.55% cryptocrystalline martensite, about 9% Ar and 7 percent were

uniform, round state undissolved carbides microstructure. Quenching temperature and time to control this microstructure.

(3) low temperature parts quenching after tempering requires larger surface residual compressive stress, which helps to improve fatigue resistance. Quenching may be used the

surface short carburizing or nitriding treatment process, making the large compressive residual stress on the surface.

(4) manufacturing steel bearing parts, and requires a high level of purity, is to reduce the content of O2, N2, P, oxides and phosphides. The electroslag remelting can be used

to vacuum smelting technology measures the material oxygen content & le; 15PPM appropriate.