1.What is the essential difference between galvanized steel and stainless steel?
Galvanized Steel: Base material: Ordinary carbon steel (easy to rust).
Rust-proof layer: The surface is covered with a layer of zinc metal (via hot-dip galvanizing, electroplating, etc.).
Principle: Zinc acts as a "sacrificial anode" that corrodes preferentially, protecting the steel substrate underneath. Even if there are small breaks in the coating, the zinc will continue to sacrifice itself to protect the exposed steel. But when the zinc layer is exhausted or a large area is broken, the base steel will begin to rust.
Stainless steel: Essence: A type of alloy steel.
Composition: The main component is iron, but it must contain at least 10.5% chromium. Common types (such as 304, 316) also contain elements such as nickel and molybdenum.
Principle: Chromium reacts with oxygen to form an extremely thin, dense, stable and self-healing chromium oxide passivation film on the surface of the steel. This film isolates oxygen and moisture from the internal iron, thereby preventing rust. After the passivation film is damaged, it can be quickly re-formed in the presence of oxygen.
2.What is the difference in corrosion resistance between galvanized steel and stainless steel?
Advantages of galvanized steel: Good protection in dry atmosphere and mildly corrosive environment (such as indoors, in the countryside), cost-effective.
Disadvantages: The zinc layer will gradually consume (the corrosion rate depends on the environment). In humid, acidic, alkaline, salt spray (seaside, deicing salt) environment, the zinc layer will consume quickly and have a limited life.
The steel below the damaged zinc layer will rust first, forming red rust, which may spread.
High temperature will accelerate the consumption of the zinc layer and even fall off.
Welding will damage the zinc layer, and the weld needs additional protection.
Stainless steel advantages: Overall corrosion resistance is much better than galvanized steel, especially in harsh environments such as humidity, salt spray, acidity, alkalinity, etc.
The passivation film has self-healing ability, and small scratches usually do not cause large-scale corrosion.
High temperature resistance is usually better (high chromium and nickel content models).
There are many alloy grades (such as 304, 316, 430, 2205, etc.), and more corrosion-resistant models can be selected according to the specific corrosion environment (such as 316 contains molybdenum, which has stronger resistance to pitting and crevice corrosion).
Disadvantages: Not completely stainless: Pitting, crevice corrosion or stress corrosion cracking may also occur under certain conditions (such as extremely high chloride ion concentration, oxygen-deficient environment, contact with carbon steel, surface contamination, improper welding, etc.).
Some low-end stainless steels (such as some 430) may not be as corrosion-resistant as high-end models or perform poorly in high-salt environments.
3.What is the difference between the mechanical properties of galvanized steel and stainless steel?
Galvanized steel: Mechanical properties depend mainly on the base carbon steel. There is a wide range of properties such as strength, hardness, and toughness, and different grades of carbon steel can be selected as needed. The zinc coating has little effect on the mechanical properties of the base.
Stainless steel: Mechanical properties depend on the specific alloy composition and heat treatment status. ◦ Austenitic stainless steels (such as 304, 316) generally have excellent toughness, ductility, and medium strength, and are non-magnetic.
Ferritic stainless steels (such as 430) have medium strength, poor toughness, and are magnetic.
Martensitic stainless steels (such as 410, 420) can be heat treated to obtain high strength and hardness, but have low toughness and are magnetic.
Duplex stainless steels (such as 2205) have both high strength and high corrosion resistance.
In general, stainless steels are usually more expensive than ordinary carbon steels (galvanized steel base) with the same strength requirements.
4.What is the difference between galvanized steel and stainless steel?
Galvanized steel: Typical silver-gray, with zinc flowers (hot-dip galvanizing) or uniform gray (electrogalvanizing) appearance. After a period of use, the zinc layer will oxidize and darken, white rust (basic zinc carbonate) will appear, and eventually it will be consumed and red rust will be exposed.
Stainless steel: Usually metallic silver-white, it can have a variety of surface treatments (such as 2B, BA, brushed, mirror, etc.), with a more beautiful and modern appearance, and can maintain its luster for a long time (under suitable conditions).
5.What is the difference in cost between galvanized steel and stainless steel?
Galvanized steel: Initial cost is significantly lower than stainless steel. An economical choice for rust protection.
Stainless steel: Initial material cost is much higher than galvanized steel (often several times the price). Alloying elements (especially nickel and molybdenum) are the main reason for the high cost.