Abstract: An experimental investigation of chip morphologies in high-speed dry milling of 32Cr3NiMoVA steel was conducted over a variety of different cutting parameters.The free surface and the back surface of the chip were investigated through VHX-500F optical microscope.The experimental results showed that，with 0.2 mm/r feed per tooth,0.5mm cutting depth and 200 to 1 000 m/min cutting speed，a suitable cutting chip of helical chip was formed;and with the cutting speed increased，the diameter of the helical chip reduced at first but eventually stabilized at a relatively constant value.The degree of chip serration was more pronounced and evident with the increase in cutting speed，feed per tooth and cutting depth.The variation in chip serration should be attributed to the reinforcement of coupled thermo-mechanical behavior in the cutting process with the increase in machining parameters.

Key words: ultra-high-strength steel, 32cr3niMoVa, high-speed milling, cutting parameters, helical chip