Bearing rings surface shading cause analysis

1 test materials and methods
Raw materials for the XingCheng steel production GCr15 bearing steel.
The process route: electric smelting - EBT 100t LF refining - CCM300 DVD vacuum processing - billet temperature send (or into slow cold pit) - rolling - cutting scale - finishing - inspection into the Treasury.
In dark spots "in produce" JSM - with samples, interception 5600LV scanning electron microscopy (sem) and energy dispersive spectrometer NORAN carries on the observation and correspondence phase analysis.
2 test results   Sliding Bearing Angular Contact Spherical Plain Bearing Ball Joint Rod End
Sample without water after washing by alcohol with scanning electron microscopy (sem) found that "black" as greatly small corrosive pit and corrosion pitted, 1horizontal stripes for grinding cutting stripes.
Corrosion pit after enlargement observation including corrosion products with energy spectrum analysis detected, higher concentration of oxygen, sulfur, chloride, sodium, potassium, without inclusion, can determine not steel itself, may be a point of caused in machining process. Because the acid liquid chlorine, grinding in the coolant used when there are sodium, potassium and other elements.

Will corrosion hemp point a layer at high magnification, exemplifies the corrosion products covered, its morphology (for cracking mud pattern. White small clever grain for steel, this is because carbide carbide not easily by corrosion and remain in the surface.
3 discussion and analysis
A dark spots "paper" defects arising for gathered by the inclusion is caused, scanning electron microscopy (sem) and energy spectrum analysis shows that the "black" bearing surface is mainly due to chlorine and sodium, potassium ion cause point corrosion, did not find the inclusions gathered. Chlorine ion is drought tubes in the pickling by acid liquid into when the metal surface, when the partial oxidation film for some reason (probably bruises or bruising) destroyed, it causes the Cl - residual acid, and surface of metal invasion, and the rest became anodic reactions to the cathode, form micro battery.
Causes the metal surface corrosion into a lot of corrosion pit, and will not be containing Cr carbon corrosion is preserved (figure 3). By the cathode corrosion pit generated in the reaction around the alkali promoted the passivation, thereby inhibiting the corrosion. Sodium, potassium ion is bearing tube at turning processing by cooling fluid into, its invasion of accelerated corrosion. To prevent similar phenomena occurred in manufacturing process, must strictly prevent workpiece and chloride, sodium, potassium plasma medium surface oxidation skin contact, pickling must wash residual acid, and turning processing to wash surface after cooling fluid. By this measure, the production after a similar situation did not happen again.
4 conclusion
By electron microscopy, energy spectrum analysis, found "shading" defect process of acid liquid for cleaning sordid locally generated by pitting erosion, and later in the cooling liquid making, K caused by the cation promote.