factors affecting bearing life and control industry 双列角接触球轴承|3056轴承-pg电子官方网站

1 , the material factors that affect bearing life
early failure in the form of rolling bearings , mainly broken , plastic deformation, wear, corrosion and fatigue , under normal conditions, mainly contact fatigue . in addition to the failure of the bearing parts of the service conditions , mainly by the steel hardness , strength, toughness, wear resistance , corrosion resistance and stress state constraints . the main internal factors affecting these properties and there are several states .
1.1 quenched martensite steel
carbon chromium steel raw tissue granular pearlite in quenching and tempering state quenched martensite carbon content, significantly affect the mechanical properties of steel. strength and toughness at around 0.5% , contact fatigue life of about 0.55% , compressive crushing capacity of about 0.42% , while gcr15 steel quenched martensite carbon content of 0.5% to 0.56 %, the strongest available anti- lapse mechanical properties .
it should be noted , in this case the martensite is implicit martensite obtained , the carbon content was measured by the average carbon content . in fact , the amount of carbon in the martensite region is slightly uneven , the carbon concentration is higher than away from the close surrounding carbide carbide in ferrite portion , so that they start the martensite transformation temperature is different, thus inhibiting the grain growth and microstructure of martensite morphology display becomes hidden martensite . it is easy to form high -carbon steel can be avoided quenching microcracking , and its sub- structure high strength and toughness of the strip plate martensite dislocation . therefore, access to anti- bearing parts may fail to get the best capability matrix carbon martensite hidden only when high-carbon steel quenching.
1.2 , the residual austenite in hardened steel
normal high carbon chromium steel after quenching, may contain 8% ~ 20% ar ( residual austenite ) . bearing parts of ar advantages and disadvantages , in order to better bring , ar content should be appropriate. due to the amount of principal and ar quenching austenite conditions, and how much it would affect the number of carbon quenched martensite and undissolved carbides , difficult to accurately reflect the amount of influence on the mechanical properties of ar . for this purpose, fixed albright conditions, using body heat of austenite stabilization process in order to obtain different amount of ar , in this study the effects of ar content on gcr15 steel hardness and contact fatigue life after quenching and tempering . with the increase in the content of austenite , both hardness and consequent contact fatigue life increases, reaches a peak and then subsequently decreased, but the peak of the ar content of different hardness peak at about 17% ar , and the contact fatigue life peak at about 9% . when the test load is reduced, the amount of the increase due to the impact of ar contact fatigue life decreases.
this is because when the time is not more than the amount of ar to reduce the impact strength , while toughening effect is more obvious. the reason is that when the load is small , ar small amount of deformation occurs , both reduced the stress peaks , and so ar process has strengthened and the occurrence of deformation stress and strain induced martensite transformation and strengthening. however, if the load is large , ar large plastic deformation and stress concentration matrix of the partial rupture , so that life expectancy is reduced. should be noted that the beneficial effects of ar must be stable under ar , if spontaneously into martensite , will drastically reduce the toughness of the steel brittle .
1.3 , hardened steel undissolved carbides
hardened steel undissolved carbides number , morphology , size distribution , chemical composition of both the affected and hardened steel before the original organization , but also affected the austenitic condition , the relevant undissolved carbides on bearing life less impact studies . carbide phase is hard and brittle , in addition to abrasion than beneficial , because the carrier will ( especially non-spherical carbide ) with the substrate and cracks caused by stress concentration , which decrease the toughness and fatigue resistance. quenching undissolved carbides in addition to its impact on the performance of steel , but also affect the carbon content and the content and distribution of ar quenched martensite , resulting in an additional impact on the performance of the steel.
in order to reveal the impact on performance of undissolved carbides , using different carbon content of the steel , the carbon content of martensite after quenching it and ar content of dissolved carbon content the same without different state , after 150 ℃ tempering , due to the same carbon content of martensite , and high hardness , and therefore a small amount of undissolved carbides little higher hardness values increased , reflecting the strength and toughness of crushing load is decreased, stress concentration is sensitive contact fatigue life significantly reduced. so much undissolved carbides hardening mechanical properties of steel and failure resistance is harmful. appropriate to reduce the carbon content of bearing steel is one of the ways to improve the service life of parts .
in addition to the number of undissolved carbides hardening of the material properties outside influence , size, morphology, distribution also have an impact on the material properties . in order to avoid bearing steel undissolved carbides hazards , requiring less undissolved carbides ( small number ) , small ( small size ) , uniform ( size each other by small and evenly distributed ) , round (each carbides were highly spherical ) . it should be noted , after a small amount of hardened bearing steel undissolved carbides is necessary, not only to maintain sufficient abrasion resistance, but also a prerequisite to obtain fine-grained cryptocrystalline martensite .
1.4 , the residual stress after quenching and tempering
bearing parts after quenching and tempering , still has a large internal stress. advantages and disadvantages of the two states part of the residual stress . after the heat treatment of steel , with the increase of the surface residual compressive stress , the fatigue strength of steel along with it , whereas the inner surface of the residual stress is tensile stress , the fatigue strength of the steel is reduced.
this is due to fatigue failure in bear parts is too large tensile stress , and when there is a large surface residual compressive stress , it will offset the tensile stress equal value , leaving the actual steel tensile stress value decreases, the fatigue strength limit increased, when the surface of a larger residual tensile stress when exposed to tensile stress with the superimposed load leaving the actual steel to withstand tensile stress significantly increases the fatigue strength even if the lower limit value .
therefore, the bearing parts quenching and tempering larger surface residual stress after , but also one of the measures to improve the life (of course, too much residual stress may cause cracking or deformation of parts should be given enough attention ) .
impurity content of 1.5 , steel
impurities in steel and non-metallic inclusions include harmful elements ( acid soluble ) content , they endanger performance of steel is often fueled each other , such as the oxygen content is higher , the more oxide inclusions . types of impurities on the mechanical properties of steel and parts failures ability of anti- impurity , nature , number, size and shape of the related, but often have reduced the role of toughness , ductility and fatigue life.
as the size of the inclusions is increased , reducing the fatigue strength of the attendant , and the higher the tensile strength of steel , reduced tendency to increase . increased oxygen content in steel ( oxide inclusions increase ) , bending fatigue and contact fatigue life under high stress decreases. therefore, for the work under high stress bearing parts , lower manufacturing steel oxygen is necessary. some studies suggest that the mns inclusions in steel , because of the shape was ellipsoidal , but also against the larger parcel oxide inclusions , therefore reducing its impact on the fatigue life may be even less useful , they can be lenient control .
2 , control the impact of material factors bearing life
in order to make the above material factors affecting bearing life at its best , you first need to control the original organization before quenching of steel, technical measures that can be taken include: high temperature (1050 ℃) austenitizing rapid cooling to 630 ℃ to obtain a pseudo- isothermal normalizing eutectoid fine pearlite or cooling to 420 ℃ isothermal treatment , obtain bainite . wrought heat can also be used rapid thermal annealing , to obtain fine granular pearlite , carbide steel to ensure small and evenly distributed. original organization in this state at the time of quenching austenite , carbide besides dissolved in austenite , the undissolved carbides will gather into small granules .
when the steel in the original tissue is fixed, quenched martensite carbon content ( ie, the carbon content of austenite after quenching ) , the amount of retained austenite and undissolved carbides depends on the amount of quenching temperature and holding time , with the quenching temperature increases ( time constant) , the number of undissolved carbides in the steel to reduce ( increase the carbon content of the martensitic quenching ) , the number of residual austenite increases , the hardness increases as the quenching temperature be increased , reaches a peak and then decreases with increasing temperature .
when the quenching temperature is constant, with the extension of the austenitizing time , reduce the number of undissolved carbides , increased the number of retained austenite , the hardness increases , a longer period of time, this trend is slowing . when the original tissue carbide fine , because the carbide is easy dissolved in austenite , the hardness after quenching peak toward lower temperatures and in shorter austenitizing time .
in summary , gcrl5 steel undissolved carbides after quenching at about 7 %, residual austenite at around 9% ( average carbon content of martensite hidden around 0.55% ) composed of the best organizations . moreover, when the original tissue carbide fine , uniform distribution , while reliably controlling the microstructure level composition conducive to high mechanical properties , which have high life. it should be noted , has a fine dispersed carbides original organization , quenching heat insulation , small undissolved carbides will grow up together , so coarsening. therefore, the original organization bearing parts quenching time with this should not be too long , the use of rapid heating austenitizing quenching process , will receive higher mechanical properties. to make the bearing parts after quenching and tempering larger surface residual compressive stress in the quenching can pass into the atmosphere carburizing or nitriding , carburizing or nitriding surface a short time . because of this steel quenching austenite actual carbon content is not high , far below the equilibrium concentration phase diagram shown , so you can suck carbon ( or nitrogen ) . after the austenite -containing high carbon or nitrogen , which ms lower than the surface of the martensite transformation and the inner central portion of the quenched , resulting in a larger residual stress . gcrl5 steel to carburizing atmosphere and non- carburizing atmosphere heating quenching (both by low-temperature tempering ) after treatment , after contact fatigue tests can be seen, the surface of life than non- carburizing carburizing increased 1.5 times. the reason for this is that parts of the surface carburizing has a large residual stress .
3 , conclusion
impact of high carbon chromium steel bearing parts life factors and the degree of control the main material for :
( 1 ) in the original organization carbide steel before quenching the requirements of small , dispersed . austenitizing temperature can be 630 ℃, or 420 ℃ high temperature , wrought heat can also be used to achieve rapid thermal annealing process .
( 2 ) for gcr15 steel after quenching, the requirements to obtain the average carbon content of about 0.55% of the hidden martensite , about 9% ar and 7% were uniform , round state undissolved carbides microstructure . quenching can be used to control the temperature and time to get this microstructure .
( 3 ) parts after quenching and tempering requires a larger surface residual compressive stress , which helps to improve the fatigue resistance . can be subjected to a surface treatment process short carburizing or nitriding during quenching , so that a larger surface residual compressive stress .
( 4 ) manufacturing steel bearing parts , requires a high purity, mainly to reduce the content of o2, n2, p, oxides and phosphides . can be remelting , vacuum smelting technology measures the oxygen content of the material ≤ 15ppm appropriate.