Turning Affected Layers of GH4169 with Worn Tools

To solve problems of surface integrity of GH4169 caused by tool wear during machining,residual stresses layers(RSL),deformation layers(DL),and surface roughness of machined surface were studied in this work.Jobs were done at the turning parameters of v_(c)=15 m/min and f_(z)=0.05 mm/r and ap=1 mm with6 different worn tools.Firstly,tool nose wear closes to minor flank face and how it influenced machined surface were discussed.Details were given by image processing and it concluded to 5 tool w ear states according to cutting time.Secondly,relationships between tool wear states and tensile residual stresses(RS)were built so the RS range is manageable by placing a cutting time limit.Thirdly,affected layers’depths were associated w ith tool wear and the consistency betw een RSL and DL was presented.At last,roughness values variation with cutting time were discussed.Results show that RS in peripheral direction is far larger than that in axial direction.The total cutting time of a tool should be controlled within 37 min and a time period 30-37 min before severely worn owns excellent cutting effects.Tensile RS of 400 M Pa can be set as a reference value for evaluating tool quality from angle of workpiece.

Impact toughness of a gradient hardened layer of Cr5Mo1V steel treated by laser shock peening

Laser shock peening（LSP） is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP process.A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer.Assuming a linearly gradient distribution of impact toughness,the parameters controlling the impact toughness of the gradient hardened layer were given.The influence of laser power densities and the number of laser shots on the impact toughness were investigated.The impact toughness of the laser peened layer improves compared with an untreated specimen,and the impact toughness increases with the laser power densities and decreases with the number of laser shots.Through the fracture morphology analysis by a scanning electron microscope,we established that the Cr5Mo1 V steel was fractured by the cleavage fracture mechanism combined with a few dimples.The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.