| 20CrMnTi steel is the most commonly used gear steel in our country,and GDL-1steel is a new kind of bainitic steel used as drill rod.The gears and drill rods produced in our country have prombles of short service life and poor reliability.Therefore,it is of great significance to improve the service life by surface modification.High pressure water jet peening(WJP),as a surface strengthening process instead of traditional shot peening,has a bright future.However,the research and application of WJP about carburizing steel is not go far enough.So,two kinds of carburizing steel are strengthened by post-mixed abrasive water jet peening(AWJP),and the change law of surface integrity and fatigue properties of 20 CrMnTi steel and GDL-1 steel under different parameters are studied.Besides,the thermal relaxation behavior of GDL-1steel is investigated too after AWJP.The following main conclusions are obtained:1.The flow rate of mixed-abrasive is smaller than glass abrasive under the same conditions,but the kinetic energy of erosion is larger,which easily leads to brittle removal of the material surface.Considering the effect of different density abrasives on workpiece strengthening,the abrasive density,flux and velocity should be taken into account.2.Compared with glass abrasive water jet peening,the surface damage of specimens are more serious and the roughness is bigger after mixed-abrasive water jet peening.At the same time,the surface plastic deformation degree is smaller than galss abrassive WJP,which can be verified by the change of hardness,residual austenite,residual stress,et al.Comprehensive description that the surface integrity is better after glass abrassive water jet peening.3.The contact fatigue life of 20 CrMnTi samples has been greatly improved after glass abrasive water jet peening,and the contact fatigue life of 300 MPa has increasedby 6.8 and 2.1 times compared with those unpeened and 200 MPa WJP respectively.Unpeened samples belong to pitting failure.200 MPa and 300 MPa water jet samples are basically belong to deep spalling,but the crack source location of 300 MPa specimen is deeper.4.After AWJP,the most decarburized layer of GDL-1 steel is removed,the hardness of the surface layer is markedly improved,the grain size and microstructure are refined,the residual austenite content is decreased,and about380?m residual compressive stress layer is formed.Besides,duing to the impact of abrasive,many pits and erosion grooves are formed on the surface of the specimens,and brittle delamination occurres in some places.At the same time,glass abrasive are founded embedded on the surface too.After AWJP,the fatigue limit of polishing specimen reache 526 MPa,increased by 19% compared with the unpeened,and all the fatigue sources are formed close to the 1/2R position from the surface.5.The thermal relaxation behavior of residual stress is mainly affected by holding time and holding temperature,and it is also proved that the Zener-Wert-Avrami equation is not suitable for describing the whole recovery process.To use the equation,proper modifications must be made. |
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