316 Stainless Spring Wire - Molybdenum Content and Pitting Resistance

Product Introduction

TOPONE supplies 316 stainless steel spring wire in 0.15-12 mm diameters for springs that work in chloride-bearing environments. The difference between 316 and ordinary 304 wire is molybdenum: a deliberate 2.0-3.0 percent addition that raises the pitting corrosion threshold of the passive film. Coil weight, tensile class, and surface (soap coated or bright annealed) are arranged per order.

Product Specifications

Why Molybdenum Matters

Molybdenum stabilises the passive film at the weak points where chloride ions start their attack. In coastal air, de-icing salt, brine, or chemical process streams, 304 wire can develop pitting that later becomes a fatigue crack origin. 316 wire resists the same exposure, which is why marine, pharmaceutical, and food-processing springs are specified in 316 by default.

Pitting Resistance Equivalent Number (PREN)

Pitting resistance is ranked with the PREN formula:

PREN = %Cr + 3.3 x %Mo + 16 x %N

A typical 316 heat (17 % Cr, 2.5 % Mo, 0.06 % N) gives PREN of about 25-26, against roughly 18-20 for 304. Nitrogen-bearing 316LN lifts PREN further without losing cold formability. The mill test certificate reports the actual molybdenum analysis, so the PREN of every coil can be verified before spring production starts.

Choosing Between 304, 316 and 316L

• 304: indoor, fresh water and mild atmosphere service at the lowest cost.
• 316: chloride exposure, humidity and elevated temperature - marine and chemical service.
• 316L: welded parts or heating after forming - intergranular corrosion resistance.

Applications

• Marine and offshore spring components
• Chemical and pharmaceutical processing springs
• Food equipment springs exposed to brine cleaning
• Coastal architectural and fastener wire

Product Advantages

• Certified 2.0-3.0 % molybdenum chemistry on every heat
• Tight diameter tolerance and cast control for automatic coiling
• Soap-coated surface for high-speed spring forming
• ASTM A580 / EN 10270-3 conformity with 3.1 MTC

Quality Control

Chemistry (including molybdenum), diameter, tensile strength and surface condition are checked coil by coil. The test certificate states the molybdenum value so buyers can confirm PREN before production.

Selection and Ordering Notes

1. Describe the chloride level, humidity and temperature of the service environment.
2. Select 316L for welded parts or heating after forming.
3. Specify diameter, tensile class and surface finish.
4. Request the 3.1 MTC to verify molybdenum content.
5. Confirm coil weight and packaging (coil, spool or reel).