'Black spots' genesis analysis - bearing ring surface bearing knowledge

Raw materials for 1 test material and method of china. greases GCr15 bearing steel production. Technology: EBT electric furnace smelting - 100 t LF refining - VD vacuum - processing Send CCM300 billet temperature ( Or into the slow cooling pit) - - - - - - Rolling - Cutting to length Finishing - Products inspection. Interception of sample in produce 'black spots' place, use JMS - 5600 Louis vuitton scanning electron microscopy (sem) and NORAN spectrometer for observation and correspondence analysis. 2 test results of specimens is observed by scan electron microscope after anhydrous alcohol cleaning found 'black spots' for large and small and corrosion pitting corrosion pit, parallel stripes for grinding cutting stripes. After enlargement observation of corrosion pit with corrosion products, energy spectrum analysis is used to inspect to the higher concentration of oxygen, sulfur, chlorine, sodium, potassium and other elements, inclusions, judgement is not steel itself problems, may be caused during processing. Because of acid liquid chlorine, and used in grinding coolant in sodium, potassium and other elements. To pitting corrosion at high magnification, covered with a layer of corrosion products inkstone, its morphology of cracked mud shape pattern. Small white ying for carbide in steel, this is because the carbide residue on the surface is not easy to corrode. 3 'black spots' discussion and analysis with literature defects for the inclusion of gather, by scanning electron microscope and energy spectrum analysis, the 'black spots' on the surface of the bearing is mainly caused by chlorine and sodium, potassium ion corrosion, found no aggregation of inclusions. Chloride ion is tubes in the pickling solution by into, as part of the oxide film on the surface of the metal (for some reason May be scratches or dent) Destroyed, then cause the Cl - in the residual acid Invasion, and on the surface of the metal as the anode reaction, while the rest of the cathode, the formation of micro batteries. Is the metal surface corrosion as many corrosion pits, while containing Cr carbide is not easy to corrode preserved ( As shown in figure 3) 。 Corrosion pit around generated by the cathode reaction of alkali promoted the passivation, thereby inhibiting the corrosion. Sodium, potassium ion is bearing tube by the cooling fluid into when turning processing, its invasion of accelerated corrosion. To prevent similar phenomenon, in the process of manufacturing process must be strictly prevent the workpiece and chlorine, sodium, potassium plasma medium contact, pickling surface scale when need to wash the residual acid, and turning to clean the surface of the cooling fluid. By this measure, after the production of a similar situation never happened. 4 conclusion by electron microscopy and energy spectrum analysis, found that 'black spots' defect for acid liquid cleaning not clean in the manufacturing process of local produce corrosion, and then the cooling fluid in the promotion of Na, K cation.