Bolt grade refers to the strength of the steel and is an important consideration when selecting fasteners, while coatings can provide additional protection, especially against corrosion.
There are a variety of coatings that are applied to steel, the most common being zinc-plated (BZP) and black oxide.
For general-purpose bolts and fasteners, coating steel with zinc is a popular choice. Zinc plating prevents corrosion and creates a shiny finish, making it ideal for decorative applications.
However, the main difference between regular stainless steel bolts and zinc-plated bolts is the degree of corrosion protection they provide, which makes stainless steel more expensive than BZP.
What is black oxide?
Another form of steel passivation is black oxide or black passivation, which is a chemical coating process that is often applied to stainless steel to prevent corrosion and give it a black surface. It also makes objects, such as black oxide bolts, harder and more wear-resistant, and is often used in engineering applications.
It is an ingenious process that immerses the steel in a high-temperature chemical solution, then rinses the steel bolts and applies oil to provide a strong finish.
It is a common practice to apply a supplemental post-treatment after the black oxide coating is applied, which is designed to enhance the black oxide coating’s corrosion protection capabilities. In its standalone form, black oxide provides modest corrosion protection.
However, with the careful application of a suitable post-treatment, the best results can be achieved by thoroughly absorbing the supplemental coating into the pores of the black oxide coating.
This not only improves the corrosion resistance of the metal, but also imparts a deeper and more durable black appearance. In addition, judicious choice of post-treatment helps improve wear resistance in situations involving part fit, thereby improving the overall life and functionality of the black oxide coated component.
What are 316 and 304 stainless steel?
The difference between 316 and 304 stainless steel lies in the level of corrosion resistance of each grade. 316 stainless steel is a higher grade of stainless steel, commonly referred to as marine grade (A4) stainless steel. 304 grade steel (A2) is more commonly used in everyday items and is referred to as stainless steel because of its blend of 18% chromium and 8% nickel.
Conclusion: DIN933 DIN934 Hexagon Bolts
Black coating: provides additional corrosion protection, especially in wet or harsh environments, while improving the wear resistance of the bolts, suitable for industrial and outdoor use.
Stainless steel material: has excellent corrosion resistance and strong durability, suitable for applications exposed to harsh conditions for a long time, such as marine or chemical environments, and stainless steel also has an aesthetic appearance.