D train says 20 kg. max. weight, what if the bag is 30 kg. what then? They refuse it or charge more?

I plan to take a "D" train from Nanchang to Hangzhou, I think it's about 4.5 hours? My first time on a China fast train so I worry that my large international luggage (from Canada) will not be allowed on the train because thy say 20 kg. maximum and i have 2 bags, about 30 KG and 15 kg., will they accept it but just charge more...or refuse big bags? Do they have a place to keep these large bags on the D train, a storage place, because cannot keep them on my seat!