Why Stainless Steel Fasteners Seize (Galling) | Causes, Prevention and Solutions

A Note Before We Begin

Stainless steel fastener galling (seizing) is one of the most frustrating experiences for first-time users — and, frankly, for experienced fastener professionals too. The best way to address it is to explain it clearly, once and for all.

Content authorized for publication by FULLERKREG.

What Is Galling (Seizing)?

Galling (also called seizing or cold welding) refers to the phenomenon where a bolt and nut lock together irreversibly during tightening. It occurs most commonly between stainless steel bolts and stainless steel nuts — hence the term "stainless steel screw seizing." Once fully seized, the thread surfaces show a lumpy, eroded, or fused appearance. Forced removal or cutting is required, and the fastener is destroyed in the process.

Which Situations Are Most Prone to Galling?

1. Power Tool (Electric or Pneumatic) Installation

Even in a free-running, unloaded condition, installing uncoated 304 bolts with 304 nuts (or 316 with 316) using a power tool at high speed will inevitably cause galling. This is not an exaggeration — it is a near-certainty.

• The faster the tool speed, the higher the galling probability
• Repeated rapid in-and-out cycling with a power tool can reach 100% galling rate
• Installing locking nuts (nylon insert, metal locking, prevailing torque types) with a power tool on stainless bolts is extremely high risk
• Manual installation does not cause galling — this alone confirms the direct relationship between installation speed and galling

2. High-Force Tightening, Misalignment, and Eccentric Installation

Flange connections are a classic high-risk scenario:

• Operators often tighten "as hard as possible" without torque control
• Flange bolt patterns create uneven loading during sequential tightening
• Similar risks exist with: inclined installation, misaligned threads (non-concentric), and eccentric bolt patterns

Root Causes: Two Factors

Factor 1: Adhesiveness (Ductility / "Stickiness")

304 and 316 stainless steel have a characteristic high ductility that makes them inherently "sticky" compared to carbon steel. This is a measurable mechanical property:

304 stainless steel's ductility is dramatically higher than carbon steel. This is why stainless steel produces long, stringy, spring-like chips during CNC turning — while brass and carbon steel produce short, brittle chips. The same "stickiness" that makes stainless difficult to machine also makes it prone to galling.

For reference: SUS304 full material guide | 10B21 carbon steel guide

Factor 2: Poor Thermal Conductivity

Stainless steel is a poor conductor of heat. Friction during tightening generates heat that cannot dissipate quickly, concentrating at the thread contact points:

Stainless steel conducts heat at only 1/3 the rate of carbon steel and 1/24 the rate of copper. Heat generated by thread friction accumulates rapidly at contact points, accelerating the galling process.

The Galling Mechanism: Step by Step

When a stainless steel fastener is tightened:

1. Pressure and heat at thread contact points break down and wipe away the chromium oxide passive film that provides corrosion resistance
2. A thread contact point experiences direct metal-to-metal contact, blocking, and shearing
3. Adhesion begins at the exposed metal surfaces
4. Adhesion propagates (typically within less than one full thread revolution)
5. The fastener is completely seized — it can neither be tightened further nor removed

Solutions

For Suppliers / Manufacturers

1. Water-based wax coating (e.g., AK-366): Immerse fasteners in water-based wax and centrifuge-dry. Significantly reduces galling probability with no visible surface change. This is the preferred first-line solution.
2. Lubricating and heat-conducting oil on threads: Apply to 3+ thread starts (on either bolt or nut) and bake dry. This is the ultimate solution — 100% galling prevention. Drawback: oil residue on the production line is considered "too messy" for some applications.

For End Users / Installers

1. Reduce power tool speed: The single most practical intervention. Slower installation speed dramatically reduces galling probability. Simply: tighten more slowly.
2. Use a torque wrench: Avoid over-tightening. "Tighten until it won’t move" is the fastest way to cause galling. Simply: tighten more gently.
3. Apply anti-seize lubricant directly to threads: The definitive user-side solution, particularly for high-load applications such as flange connections. Accepts that thread surfaces will have lubricant residue.

Galling in Other Materials

Note on copper/brass: Higher-quality copper fasteners (higher Cu content) are more prone to galling than lower-quality ones (higher Pb content). Lead reduces ductility and acts as a lubricant — which is why C3604 free-cutting brass (with intentional Pb addition) has better anti-galling characteristics than pure copper.

Is High Ductility a Defect?

No. As a mechanical property, high ductility is an advantage. Stainless steel’s high elongation means it can sustain greater deformation before fracture, performs better in vibration environments, and has longer fatigue life. Galling is simply an unintended consequence of this property in threaded fastener applications — not a material defect.

What to Do If Galling Has Already Occurred

• If galling just started at the thread entry and has not progressed deeply: apply significant reverse torque — there is a chance of recovery
• If the fastener is fully seized after being threaded in: it cannot be removed intact. The only option is to cut or grind off the fastener

Prevention is the only reliable strategy.

Related Guides

• SUS304 Stainless Steel — Chemical Composition and Properties
• SUS316 Stainless Steel — Chemical Composition and Properties
• Why Are Stainless Steel Fasteners Magnetic?
• Hydrogen Embrittlement in Fasteners
• D2-80 Duplex Stainless Steel — Superior Anti-Galling Performance

Content authorized for publication by FULLERKREG.