I used to work in welding and fabrication. Imported Steel varies in quality globally, from products that meet all the quality specs the manufacturer codes and is traceable back to the works, to for instance Chinese or Indian products that meet no standards or have fraudulent standards. Chinese steel was rated as " abysmal" quality maybe a decade ago, though now they have a programme to improve it, I don't think they even use their own steel for bridges ect. Major Civil engineering projects like bridges, tall buildings, and ship building don't use unidentified imported steel as its not safe. Poor quality means less dense, inclusions, and delaminations, which also mean corrosion problems, you rely on good quality steel for the big long term investment you put into buying your boat.
As for the welding , its an insane situation that there are no standards for inland waterways craft and anyone can build and sell one , in fact I know of one boatyard where they do overplating and stretching where the "welder" has no qualifications, and would fail a city and guilds part time 2 week course in basic welding practice, he doesnt even know how to set the correct sheilding gas flow. Surveyors regularly pass his work because he uses a trick called ' manual pulse' MIG welding which produces a nice looking weld but with no penetration or strength. Proves these surveyors know nothing about welding. This person also built a hull which is basically a demo piece of bad welding, I'm sure one day it will be sold and there's nothing anyone can do about it, the new owner will end up with £1000 of scrap minus cutting up charges, ie he will have to pay them to take it away.
I also saw a survey from a well known boat yard on the Thames on a nb which declared the hull 5 / 6 mm thick, the new owner was happy, bought it and dry docked it and the pressure washer went straight through the bottom, the owner faced maybe 4/5 years in litigation, no legal aid, and the boat on hard standing with more surveyors and lawyers arguing about who was right for years, they chose to sell it at a £15,000 loss and move on . Some surveyors carefully word their reports so that they're not legally binding.
Two years ago i saw up close on hard standing a 60 / 70 ft nb that was condemned here the hull welds were just put in without any edge preparation on closed butted plates, say 2 mm of penetration on 10 mm plate only on the top, joins where the distortion had got the better of them were just left unwelded. And this boat was sold and fitted out and the owners were left to fight it out in court.
I wouldn't buy any steel hull without proven steel origin certificates, and the qualifications of the welders on the job. Not much to ask for tens of thousands payment ?