Effect Of Surface Pretreatment On Plasma Nitriding Of Three Screw Pump Materials

As a basic component,screw pump plays an important role in the mechanical components and is one of the hydraulic components with high technical content.It is widely used in the heavy and high end equipment industry in oil,aerospace,offshore drilling platforms,marine engineering ships,submarines,environmental protection,electric power and other countries.The three screw pump is a positive displacement pump,in which the active screw is engaged with two driven screws,and the pump is sleeved outside the screw.These equipment are used to lubricate the liquid medium,and the friction wear,corrosion and leakage are easy to occur under the condition of high power transportation.Therefore,the main friction parts of the three screw pump must have excellent wear resistance and corrosion resistance.The traditional three screw pump surface treatment technology,such as chromium plating,surface quenching and nitriding,has been unable to meet the service conditions of active screw pump because of the lack of wear resistance,large thermal deformation of the workpiece and low bonding strength between the strengthening layer and the matrix.In this paper,the three screw pump screw was pretreated with laser transformation hardening and ultrasonic impact nanoscale technology,and then ion nitriding was carried out to obtain a compound nitriding layer with excellent thickness and excellent performance.After the laser transformation hardening treatment,the microhardness value of the laser transformation hardening layer shows a trend of slightly increasing and then dropping slightly from the surface,and finally maintaining the stability to the matrix,and the hardness of the subsurface layer is up to 861.4HV_0.2.The surface hardness and surface depth of the material were increased by about 0.85mm.The hardened layer of the sample consists of three kinds:complete hardened layer,transition zone and heat affected zone.There are fine needle like martensite structures in the fully quenched layer.The surface grain size is refined from 283nm to 124nm by ultrasonic impact nanoscale pretreatment,and the roughness is reduced by 50%.The surface microhardness of the specimen without ultrasonic shock is about 290HV_0.2,while the surface microhardness of the ultrasonic impact specimen is about 480HV_0.2,the hardness is about 62%,the plastic deformation zone thickness caused by the Hyper impact is about about It is within 400?m.At 470?and 530?8h,the plasma nitriding of the substrate,surface nanocrystallization and laser transformation hardening samples is carried out.The thickness of plasma nitriding nitriding layer is about 212?m under 530 temperature.The thickness of the nitriding layer of laser phase transformation hardening ion nitriding is about 268?m,and the thickness of the surface nanoscale nitriding layer is 247?m.The nitrided layer thickness of ion nitriding at 470C is about 127?m.The thickness of laser phase transformation hardening ion nitriding nitrided layer is about 228?m,and the thickness of the surface nanoscale nitriding layer is about 212?m.According to JB-T6956,the surface hardness of 40Cr is no less than 500HV,and the general depth range is 0.2-0.5/mm.Through surface nanocrystallization and laser transformation hardening pretreatment,nitriding layer with the national standard has been obtained at 470degree plasma nitriding.With the increase of temperature and pretreatment of laser transformation hardening,the wear form changed from abrasive wear to fretting wear and adhesive wear,and the wear degree gradually reduced.The wear volume decreased by 67%and the friction coefficient decreased by 44%under dry friction condition.The effect of laser transformation hardening,plasma nitriding layer refinement and a large number of dispersed nitrides on passivation of hardened layer can increase matrix toughness and transform martensite structure to further improve the abrasive wear resistance.With the increase of plasma nitriding temperature and surface nanocrystallization pretreatment,the abrasive wear,adhesive wear and plastic deformation of the sample surface become weaker under the 500g load and 0.334m/s rotation speed.We can see that,without the main performance of ion nitriding and ion nitriding wear under 470 DEG C for abrasive wear,the phenomenon is very serious.The matrix.When the temperature rises to 530 degrees,basically can not see the furrow phenomenon,and with the pretreatment of surface nanocrystallization,debris become finer,the third body lubrication role is more obvious,abrasive wear began to disappear,the type of adhesive wear transition.