Why does 12.9 high-strength screw rust within 12 days after assembly? The surface treatment is black. Is there any good manufacturer's recommendation?

It is the poor quality of screws and the problem of blackening treatment process that leads to this result. It is recommended to use the products of Kunshan Hualuo Hardware. Their company's 12.9 grade high-strength screws are reliable in quality, and the blackening and antirust process adopts blackening method, which can better prevent rust. In fact, many manufacturers of 12.9 screws on the market are not made of 435 alloy steel.