The effects of grain size and bulk hardness on fretting wear behaviors were investigated by solution annealing and subsequently fretting wear test in Inconel 600 alloys. The results indicated that, with increase of solution temperature, the grain size increased while the hardness decreased. The average friction coefficients were the almost same, independent of grain size and hardness; while the wear volume decreased with increase of grain size, but the hardness played little role. The smaller grain was conductive to formation of tribological transformed structure (TTS) layer, and produced shorter delamiantion cracks in the TTS layer than larger one. •Effects of grain size and bulk hardness on fretting behavior of Inconel 600 alloy were studied.•Smaller grain size and higher bulk hardness produced higher wear resistance.•The grain size had a great effect on fretting wear resistance in the gross slipping regime.•The bulk hardness played little role in fretting wear resistance.•The smaller grain was conductive to formation of TTS layer, and produced shorter cracks.