@Md-Martin:
Remember though, Luffy only had 2 years of training. While he learned in in a year and a half, Rayleigh said it'd still be rushing it. Luffy most likely has to concentrate harder/put more effort into hardening. Especially during the middle of a fight like this, it would be hard to use hardening to protect against Hody's bites or something of the sort, compared to using a regular Armament.
The times Luffy was smacking hody around with haki,it only took like,a second to turn his body parts black.And he switched pretty quickly from arm to leg then back to arm,so I think he has the activation thing down.And Luffy did say,it's very strong for blunt attacks(punches,kicks) but it's still too weak to defend against blades and sharp things(bites).Sonmaybe the vulcanization can be cut by a very strong blade,even though it's hard….
Gaah,the only problem is that's it's inconsistent,that sometimes he turns black,sometimes not...
just discovered-Red hawk is actually Jet Bullet+CoA vulcanization and NOT Jetpistol+CoA vulcanization
And i was looking at the panels where Luffy attacked the pacaifista and when he attacked Hody,and the two major difference were:
Against the pacaifista,only his forearm and fist were gear seconded.When he stretches,steam is only coming from the top part .
While against Hody to activate Red Hawk,you see it starts of around his forearm and fist,but the haki(blackness) and steam gradually reach up to his shoulder.So he gear seconded and haki'ed his entire outstretched arm,instead of a small part.