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Bearings are in the process of mechanical transmission fixed and reduced load coefficient of friction parts, in the work process to withstand high loads, high stress, high speed and alternating stress and impact stress, therefore bearings requiring high hardness, high abrasion resistance and high impact resistance, fatigue resistance and long service life. Bearings are often used in high frequency induction heating machine for induction hardening surface treatment to ensure the workpiece with high abrasion resistance and impact resistance, good fatigue resistance. Found in the production of bulk product cracks and fractures, loss. Today, small to analyse reasons for cracking of bearing and improvement process.
Check bearing quenching microstructure and hardness are in line with technical requirements. The surface hardness of 62.5HRC, Center for 35.5HRC, hardened layer depth of 1.98mm, all qualified. Inner ring of the bearing tests, arc-shaped cracks in the small rib, the fracture cracks exist, flange outside diameter 2.1-2.2mm crack extension, small rib shell. Because of the grinding cracks or crack was found forging crack feature, exclude the possibility of forged grinding crack and crack. From morphology and characteristic analysis of crack, the crack is an induction-hardening crack. Characterized by tapering near the crack tip and fracture patterns of crack formation and cracks.
Based on the foregoing analysis, process improvement measures proposed are as follows:
(1) heat using high frequency induction heating machine, induction hardening temperature decreased from 880 to 865, to reduce the quenching stress and quenching at 865 no coarse carbides and carbide defects.
(2) in order to reduce the quenching stress, quenched cooldown reduced from 5min to 1.5min. Workpiece temperature of approximately 120-150, than the original oil temperature of 50 ° c by 70-100 ℃, its role in tempering effect.
(3) after increase in induction hardening and tempering treatment. Found that after quenching crack after 72h, which is caused by quenching stress release. For this reason, if no secondary hardening treatment after quenching, an additional 200 ¡æ tempering treatment.
Many manufacturers use the above improvement measures, bearing flaws on the workpiece does not occur, product quality, reduces the production cost and technical economy significantly. Because crack is not saved, therefore, we at the time of heat treatment process to be very seriously and carefully.