🔩 How to choose the material of fasteners? Difference between Carbon Steel/304/316 Stainless Steel Core

The selection of commonly used materials for fasteners mainly depends on three factors: stress requirements (strength), usage environment (corrosion/humidity), and budget. Below are the most direct comparison and selection suggestions for you.

1、 Comparison Table of Common Materials

Typical material grades, strength, anti-corrosion ability, characteristics, applicable scenarios

Carbon steel+surface treatment Q235/35 #/45 #/40Cr medium to high (can be quenched and tempered up to 8.8~12.9 levels) ★★★★ (by galvanizing and other treatments) cheap, high strength, easy to rust indoor drying equipment, mechanical structures, general steel structures

304 stainless steel A2-70 (commonly used standard method) medium (≈ 700MPa tensile strength, not quenched and tempered) ★★★★ (resistant to atmosphere/humidity) good rust prevention, cannot be used in strong acid and alkali/seaside kitchens and bathrooms, outdoor general, electrical cabinets, general humid environments

316 stainless steel A4-70/A4-80 medium (slightly higher than 304) ★★★★★ (salt spray/weak acid resistance) Mo containing anti pitting corrosion, suitable for coastal/port, chemical, pharmaceutical, marine engineering

Alloy steel (quenched and tempered) 40Cr/35CrMo/42CrMo very high (10.9/12.9 grade) ★★★★ (by surface treatment) high temperature and high strength, not corrosion-resistant for engines, heavy machinery, wind power, bridges

💡 A2-70=304 stainless steel, σb≈700MPa； A4-70=316 stainless steel, σb≈700MPa

Stainless steel fasteners generally do not meet the 8.8 grade strength standard and rely on cold processing to achieve A2-70/A4-80

2、 How to choose between different environments?

Indoor dryness and stress requirements (most important structure)

Carbon steel grade 8.8/10.9+galvanized/Dacromet (sufficient strength, economical)

Indoor humidity/general outdoor (urban environment)

→ 304 stainless steel (A2-70), or carbon steel+hot-dip galvanized/Dacromet

• Seaside, salt spray, chemical plants, long-term exposure to rain and sun

316 stainless steel (A4-70/A4-80), it is not recommended to use 304 (prone to rust and pitting)

-High temperature (>300 ℃) or ultra-high strength
Alloy steel quenched and tempered bolts+heat-resistant surface treatment (stainless steel’s high-temperature strength actually decreases)

3、 Special attention should be paid to stainless steel fasteners ⚠️

1. Thread biting (cold welding)
Stainless steel has a high coefficient of friction, and stainless steel bolts and nuts are prone to “biting”. It is recommended to:
Apply anti bite paste/molybdenum disulfide grease

• Or paired with nuts of different materials (such as 304 bolts+brass/carbon steel nuts, depending on anti-corrosion requirements)

2. Magnetic issues
Weak magnetism after cold processing of 304/316 is a normal phenomenon and does not affect its anti-corrosion performance

3. Strength ≠ Carbon steel of the same grade
Stainless steel is usually equivalent to carbon steel 4.6-5.8 or A2-70 (some A4-80), and cannot replace high-strength load-bearing nodes

4. It is not recommended to mix with carbon steel without isolation
Long term moisture on the contact surface can cause galvanic corrosion (accelerating carbon steel rust)

4、 Quick selection mnemonic ✅

-Strength required → Carbon steel/alloy steel quenched and tempered (starting from 8.8)

-Rust prevention is generally required → 304 stainless steel or carbon steel galvanized

-To withstand salt spray/seaside → 316 stainless steel

-Key stress+outdoor → high-strength carbon steel+Dacromet/hot-dip galvanizing