Analysis The Heat Treatment Process And Structure Properties Of The Spiral Spike Used By Cold Heading Steel

The cold heading steel is used of metal plastic molding process at roomtemperature,due to tight of the material internal organization,good mechanicalproperties,high production efficiency,high dimensional accuracy and surface finish,soit is widely used in making of railway spiral spike.Spiral spike is a fastener connectionbetween the rail and sleepers,which resist the lateral stress and prevent tilt of rail.Theferrite microstructure dispersed improve the steel toughness aftersubcritical.quenching.Meanwhile,the heating temperature is lower than the generalquenching,reducing energy consumption,decreasing the heat treatment deformationand crack.After the SWCH35K obaining the ferrite and globular pearlite uniform,smallpearlite dispersion ofthedistribution around the ferrite matrix at760℃spheroidizedannealed18hours.Austenitizing temperature from810to880℃,quenching to thedifferent concentrations quenching medium of NaNO3,KR6680,KR7280,this Yu860,JinYu901,water indicate that the medium of NaNO3,KR7280,this JinYu901reach quenching grade requirements.The cooling rate of NaNO3is fastest,followed byJinYu901,and the the KR7280is lowest,it is not micro-cracks for the surface of thesample after quenching by fluorescent magnetic particle testing.But the samplesurface corrosion rate is fast by the nitrate quenching,and nitrate of equipment requirea higher.There are no microscopic cracks by the fluorescent magnetic particleafter.quenched and tempered,the specimens cold-formed15°testing,and the bestperformance by the organic quenching medium JinYu901after sub-temperaturequenching and tempering,while organic medium anti-higher tempering stability. theprocess performance after subcritical quenching was slightly lower than the completequenching, but achieve the spiral spike requirements. The spiral spike subject tovibration and shocks in the work environment, so the subcritical quenching improvethe toughness of the spike, which can effectively improve the useful life and costsavings of it.A large number of observation microstructure by OM, SEM testing.suggest thatthe specimens surface structure is mainly composed of martensite and a littleferrite,and heart structure is made of a large number of pearlite and ferrite and a littlemartensite after subcritical quenching; Tempering sorbite and ferrite after tempering.itcan improve the steel toughness significantly that the core part keep more of ferriteafter subcritical quenching and tempering,the macroscopic morphology of the fracture is typical of ductile fracture.there is non-existent residual austenite in steel afterquenching detected by XRD.Meanwhile,martensite morphology is the lath,whichwidth is about0.5um.Heating of quenching and tempering process isin the carbonthermal protective atmosphere furnace,there is no decarburization phenomenon,thesurface quality is better.