Effect of stainless-steel substrate grain boundaries on surface graphene morphology and nano-friction behavior

•Substrate grain boundaries cause graphene to bulge and the friction in the bulge region increases.•A two-stage rise in friction occurs when the tip comes into contact with bulged graphene.•The first stage has a fast rise in friction and the mechanism of action is the fold theory.•The second stage has a slow rise in friction and the mechanism of action is the quality evolution theory.