Marine grade stainless is a stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

 preferred for use in marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 environments to avoid pitting corrosion

Pitting corrosion

Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading...

. The AISI number grade

AISI steel grades

The Society of Automotive Engineers designates SAE steel grades. These are four digit numbers which represent chemical composition standards for steel specifications. The American Iron and Steel Institute originally started a very similar system...

 is 316 and refers to the chromium

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

 content.

The salinity contained with the oceans acts as a catalyst to the rusting process, therefore a higher quality stainless steel is used on marine vessels.

While the steel is not completely rust-proof, the alloy is more resistant than household stainless steels, and hence more expensive. Fire trucks manufactured in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

are made with Marine Grade stainless steel.