Effect Of Heat Treatment Process On Strength And Toughness Of 2Cr13 Valve Parts

Under the traditional heat treatment process,it is difficult for 2Cr13 steel to meet the contradictory indexes of high strength and good toughness.In order to improve the material toughness,meet the Chinese heavy sail precision casting co.,LTD.,valve parts performance requirements,by optimizing heat treatment of annealing,quenching and tempering parameters such as heating temperature,holding time,cooling mode and under different process for 2 cr13 material mechanical performance test,microstructure analysis,impact fracture surface morphology observed by SEM,EDAX energy spectrum analysis and XRD phase analysis,studied the phase transition mechanism of different heat treatment process parameters,obtained meet the performance requirements of 2cr13 high toughness valve parts.The specific results are as follows:(1)The final quenching process is 940? quenching and heat preservation for 1h.After 1000?,the crystal nucleus began to be bulky,and obvious tissue coarsening occurred.The hardness value at 840? suddenly increased,and began to slow down at about 950?.Under the condition of tempering temperature at 600? and holding temperature unchanged for 3h,quenching at 940? can obtain the maximum iMPact toughness at 30.5512j after holding temperature for 1h,and various indexes such as tensile strength and hardness are at the same level with about 1000?.At 940? tempering,the shape of tempered soxhlet was better,the carbides dispersed,the martensite orientation maintained,and there were fine undissolved ferrite.The SEM fracture surface at 940? was quasi cleavage plane,with obvious river pattern and the least intergranular fracture.After quenching at 940? and changing the heat preservation time,there was no significant difference in hardness,iMPact toughness was the highest at 1h and the worst at 2h.The iMPact toughness of Sample 22 was 26.3312J.A small amount of spherical oxide inclusion was found at the break of 0.5h heat preservation.(2)The final tempering process is 700? tempering,holding heat for 3h.The average hardness of tempering at 720? was only 205HBW.The tensile strength and yield strength decreased with the increase of tempering temperature,and the elongation reached a maximum of 27%at 720?.The iMPact toughness(Akv/J)showed an upward trend,which increased slowly when the temperature was below 660?,and increased rapidly in the range of 680? to 720?,with a growth rate of 141.5%and up to 154.533J at 720?.Organization metallographic microstructure increased with the temperature of the second phase is less,organization,the single,to maintain the whole lath martensite bearing tempered sorbite,640? when the most uneven and carbide precipitation on the grain boundary,had a tendency to mesh,700? and 720? similar organization form,grain size,grain fine and dispersion is good,uniform organization.700? when the SEM photo shows toughening nest form,fracture for a large number of toughening nest group,have different toughening litter size,large size toughening nest about 20 microns in diameter and deep,dense around small size toughening,crystal skull cleavage plane appear,for a typical ductile fracture morphology,720?,is the best temperature iMPact toughness,coMPared to 700? has a greater density of toughening nest group,and toughening litter size is more uniform.(3)At 700? tempering,there were a large number of dimples on the fracture at each holding time of 2h,3h,4h and 5h,all of which were typical ductile fracture.The iMPact toughness at 4h was the lowest but it could reach 80J.XRD diffraction characteristic peak phase,under the analysis of each heat preservation time,20°to 100°map in this interval appear only alpha Fe peak,the crystal lattice parameters for the(110),(200),(211),(220),all for ferrite peak,the distribution of cementite is scattered,content is low,XRD characteristic peak is not apparent,but with the increase of holding time,the original quenching organization sorbite more fully,and carbide precipitation increase,you can see the Cr7C3 diffraction peak period of a certain increase trend.(4)2Cr13 alloy steel with high chromium shall be cooled quickly after quenching.It shall be kept at 940? for 1h+ tempered at 700? for 3h with brine cooling.After tempering,all the workpieces will crack.Therefore,940? quenching is finally used for 1h+700? tempering for 3h.The three-point average Brinell hardness was 221HBW,iMPact toughness was 120.2145J,tensile strength and yield were 660MPa and 482MPa respectively,elongation rate was 23%.