One common question among car modifiers or those restoring old cars is whether to choose steel or stainless steel bolts for automobiles? Many mistakenly believe that stainless steel bolts (usually 304 stainless steel) are always better because they are shiny, beautiful, and never rust. However, the widespread use of stainless steel bolts and screws in Ho Chi Minh City is a serious technical mistake.
Material Decision: The choice between steel and stainless steel bolts depends entirely on the specific application and the required tightening torque. High-strength galvanized steel bolts (such as 10.9) are the mandatory choice for major load-bearing structures such as suspension systems and engines. Conversely, stainless steel bolts (A2 or A4) should be used for areas requiring absolute corrosion resistance such as exhaust pipes or exterior parts.
The Truth About Strength Grades: 304 Stainless Steel Is Much Softer Than Steel
Steel Bolts Used in Cars: These are high-strength bolts (steel alloy), strength grades 8.8, 10.9, 12.9. They are extremely hard and withstand very high tightening torque. The only drawback is that they must be plated (zinc, phosphate) to prevent rust.
304/316 Stainless Steel Bolts: This is an excellent corrosion-resistant (rust-resistant) material. However, in terms of mechanical properties, they are VERY SOFT. The strength grade of 304 stainless steel bolts is usually only equivalent to 4.8 or 5.8.
Mistake 1: Using Stainless Steel Bolts for Wheels and Suspension Systems
This is suicidal, similar to using regular bolts.
- Consequences: 304 stainless steel bolts are not hard enough and cannot withstand the tightening torque. When tightening, the threads can strip. During operation, the bolt may bend, deform, or break, causing accidents.
Mistake 2: The "Galling" Disaster
A "deadly" characteristic of stainless steel is the phenomenon of "galling" or "cold welding."
- Consequences: When tightening bolts and nuts made of stainless steel at high speed, friction and pressure will cause the two thread surfaces to "stick" together as if welded. At this point, you can no longer unscrew them. The only way is to cut them off, destroying both the bolt and the machine part.
So When Should You Use Stainless Steel for Cars?
Stainless steel bolts have their place, but not in load-bearing areas.
Recommended for: Body parts and decorative elements. For example: Fenders, license plates, decorative trim in the engine compartment, interior screws...
Absolutely not for: Any parts related to safety and load bearing: Wheels, suspension, brakes, chassis, engine.
