Heat treatment is one of the most important manufacturing process for piping products(steel pipes,pipe fittings and flanges),we know overheating and underheating in heat treatment can alter the mechanical and physical properties of metals.Quenching crack,surface decarburization,soft point are also the common problems in heat treatment.
Heat Treatment For A420 WPL6 Fitting Material
Quenching crack:
High or cooling is too fast,the microstructure stress when the thermal stress and metal mass volume change is greater than the fracture strength of the steel;the original defects of the working surface(such as surface cracks or scratches) or the internal defects of the steel(such as slag inclusion,serious non-metallic inclusions,white spots, shrinkage pores,etc.) form stress concentration during quenching;severe surface decarburization and carbide segregation;insufficient tempering or quenching in time after quenching of parts;cold shock stress caused by previous processes oversized,forged folding,deep turning tool marks,sharp edges and corners of oil grooves.
In short,the cause of quenching crack may be one or more of the above factors,and the existence of internal stress is the main reason for the formation of quenching cracks.The quenching crack is deep and slender,the fracture is straight,and the fractured surface has no oxidation color.It is often a longitudinal straight crack or annular crack on the bearing ring;the shape on the bearing steel ball is S-shaped,T-shaped or ring-shaped.The microstructure of the quenching crack is that there is no decarburization on both sides of the crack,and the difference is obvious with forging cracks and material cracks.
Heat treatment of A105N steel flange
Surface decarburization:
During the heat treatment process of the bearing parts,if it is heated in an oxidizing medium,the surface will be oxidized to reduce the mass fraction of carbon on the surface of the part,resulting in surface decarburization.The depth of the surface decarburization layer exceeds the final processing allowance and the part is scrapped. Determining the depth of the surface decarburization layer.The metallographic method and the microhardness method can be used in the metallographic examination.The surface layer microhardness distribution curve measurement method shall prevail and the arbitration criterion may be used.
Soft point:
The phenomenon that the surface hardness of the roller bearing parts is insufficient due to insufficient heating,poor cooling,improper quenching operation,etc.is called quenching soft point.It can cause a serious drop in surface wear resistance and fatigue strength like surface decarburization.
Haihao Group supply piping products more than 30 years,our main products are butt welding/forged 45°/90°/180° elbow,equal/reducing/lateral/barred tee,concentric/eccentric reducer,3D/5D/7D bend,cap,semeless/welded/casing/ERW/SAW/SSAW steel pipe,weld neck/blind/slip on/lap joint/socket weld/threaded/flat/orifice flange,etc.We supply those products according to international standards such as ANSI/ASME,API,BS,DIN,EN,JIS,GOST,MSS,UNI,etc.If you want to know more about our piping products,please email us:sales@haihaogroup.com
