Research On Microstructure And Properties Of High Performance Bearing Steel

A new type of low carbon martensite Fe- Co- Cr- Ni- Mo high performance bearing steel was designed by the method of martensitic phase transformation strengthening and precipitation strengthening on the basis of a traditional bearing steel. The effects of quenching temperature, tempering temperature and cryogenic treatment cycles on the micro structure and properties of this steel were studied by the means of OPM, SEM, XRD, TEM and mechanical performance testing. The relationship between processes, micro structure and properties was discussed in this article.The main microstructure of the tested steel after quenching at 1020?1050? was lath martensite and about 16% retained austenite. The austenite grain size increased and the beams of martensite lath were rough with the increasing of quenching temperature. After quenching at 1050?, the ?-Fe was distributed at the original austenite grain boundaries since the quenching temperature is too high. The growing of original austenite grain and the existence of 8-Fe leads to the decrease of HRC with the increase of quenching temperature.By studying the retained austenite content of different cryogenic treatment cycles, The result shows that the first cryogenic treatment after quenching at -75? for 2h can greatly promote the transformation of retained austenite, the retained austenite volume fraction declined about 75.4%; for the second cryogenic treatment, the transformation of retained austenite content doesn't decrease obviously. There is still a small amount of retained austenite after the second cryongenic treatment, which is showed that cryogenic treatment cannot make retained austenite transformate completely.The microstructure of the test steel was lath martensite and a small amount of retained austenite after specimens were treated as the following processes:1040? (Q)?-75?(QC) ?510?(QCT)?-75?(QCTC)?510?(QCTCT). The decrease of retained austenite content made the increase of HRC and the decrease of impact energy.The microstructure was fine tempered martensite after secondary tempering at 485? 525?,and the content of retained austenite is about 2%. With the increase of tempering temperature, the martensite matrix solid solution strengthening decreased and the precipitation strengthening enhanced, which makes the tensile strength of the tested steel (Rm), yield strength (R0.2) and rockwell hardness (HRC) increased, while elongation (?) and impact energy values (Ak) declined slightly.The tested steel displayed an favorable comprehensive mechanics performance when tempered at 525?, Rm=1848.0 MPa; R0.2= 1505.0MPa; ?=16.75%; the product of strength and elongation is 30.95 GPa·%; the yiel ratio is 0.80.