Daz Bones is built to counter hakiless swordsmen, people with strong blunt attacks would simply dent his head in with one attack. His steel is not special, it's not said anywhere that it is and it's constantly referred to as just steel
"is this the power to cut steel"
"I can hear the breathing of his steel"
"A sword that cuts nothing but steel"
"Unfortunately you're not going to see me cut steel"
Zoro is not only confirming that Daz Bones is just steel but that he hasn't cut steel before, Hachi's sword might have been iron or some other material because Zoro says he never cut steel before.
The only special steel mentioned at that point was actually Don Krieg's armor which was said to be wootz steel.
"But sharp attacks counter Luffy"
They also counter zoro and everyone other human, Crocodile was 10 times more lethal and 10 times more competent of a fighter than Daz Bones