KOYO import bearing parts after heat treatment of the common quality defects - bearing knowledge
KOYO import bearing parts after heat treatment of the common quality defects are: quenching microstructure overheating, less heat, quenching crack, hardness is not enough, heat treatment deformation, surface decarburization, soft point.
Overheating imports from KOYO bearing parts on the rough can observe the microstructure after quenching overheat.
But to correctly judge the degree of overheating must observe the microstructure.
If appear in gcr15 steel quenching organization coarse acicular martensite, organization for quenching overheating.
Reasons may be quenching heating temperature is too high or heating temperature time is too long cause comprehensive overheating;
Also may be due to the original organization banded carbide, low carbon zone between two belts forming local martensite acicular bulky, cause local overheating.
Overheating in the organization retained austenite increase, dimension stability.
Overheating due to quenching organization, steel crystal bulky, to cause a decline in the toughness of the parts, the fight against performance degradation, KOYO import bearing's life also reduced.
Serious overheating may even cause the quenching crack.
Owe the quenching temperature on the low side or cooling bad but will generate more than standard stipulated in the microstructure of austenite organization, called owe hot organization, it decreased the hardness, wear resistance reduced sharply, KOYO import bearing life.
Quenching crack KOYO import bearing parts in the process of hardening cooling by internal stress of the crack is called quenching crack.
Of the cause of the crack are: due to quenching heating temperature is too high or cooling.
The thermal stress and quality of metal volume change of the organization stress is greater than the fracture strength of steel;
The original defects on the surface of the work (
Such as micro cracks or scratches on the surface of the)
Or steel internal defects (
The non-metallic inclusions such as slag, serious, white spots, shrinkage residual, etc. )
When quenching form stress concentration;
Serious surface decarbonization and carbide segregation;
Parts fire or inadequate timely after quenching tempering;
The previous process caused by salt stress, cold forging folding, deep oil turning tool and hook sharp edges, etc.
KOYO import bearing parts during heat treatment, heat treatment deformation are the thermal stress and organization stress, the internal stress can overlay or partially offset each other, is complex and changeable, because it can as the heating temperature, heating rate, cooling methods, cooling speed, parts of the change of the shape and size changes, so the heat treatment deformation is inevitable.
Can make the change rule of understanding and mastering KOYO import deformation of bearing parts (
Such as sets of elliptic, large size up, etc. )
In the scope of the controllable, be helpful for production.
, of course, in the process of heat treatment, mechanical collision also can make parts deformation, but the deformation can be used to improve operations to reduce and avoid.
Surface decarburization KOYO import bearing parts in the process of heat treatment, if they are in oxidizing medium heat, surface oxidation happens reduce parts surface carbon mass fraction, causing surface decarburization.
The depth of the surface decarburization layer over the last machining allowance can make the parts scrap.
The determination of surface decarburization layer depth is available in the metallographic examination metallography and microhardness method.
Published by curve surface microhardness measurements that accurate, can be used as criterion of arbitration.
Soft spot caused by a lack of heating, cooling, quenching causes such as improper operation of KOYO import bearing parts surface local hardness insufficient phenomenon called the quenching soft point.
It like surface decarburization can cause a serious loss of surface wear resistance and fatigue.