[TowerTalk] Stainless Steel Galling (Larry McDavid)

[Larry McDavid]

> weaker in what respect?

Common 300-series stainless steels have lower tensile strength than 
common alloy steels. Stainless steel fasteners are more prone to 
shearing off when torqued if you are not aware of this.

Note that if you want a high-strength fastener, you look for a Grade 5 
or a Grade 8 fastener. These will be plated, typically today with zinc, 
  because they rust otherwise; they are not "stainless."

Granted, there are high-strength chromium/nickel steels but they are 
generally 400-series or 4000-series alloys. And, many of them rust. 
"Stainless" does not always mean rust-free.

When you hear, "stainless steel" it usually is referring to a 300-series 
alloy, what is sometimes called "18-8" stainless steel. But, "18-8" is a 
very generic term and does not identify the specific alloy. You often 
see knives advertised as "18-8" but you really don't know what alloy is 
used. What you can count on, though, is that a "18-8" knife will not 
hold a sharp edge so well as a carbon steel knife. That is an indication 
of the lower tensile strength of stainless steel.

And, yes, we may be beating this horse to death! Stainless steel galling 
is a serious problem in loaded fasteners that must be removed 
repeatedly. But keep in mind that galling is a problem when both 
fasteners are stainless steel. If you are screwing a stainless steel 
bolt into brass or aluminum, don't expect galling.

I once worked with fine-pitch large stainless steel threaded parts that 
were extraordinarily clean for an aerospace application. It was simply 
impossible to get them to screw together even once as galling was 
immediate. The solution was to use a lubricant: silver plating. Some 
MIL-spec fasteners are silver plated for lubrication; it works extremely 
well. Silver flakes would certainly work in an anti-galling grease. No, 
I'm not proposing this for amateur radio use!

Larry W6FUB


Dayle Johnson wrote:
>> From: Larry McDavid <lmcdavid at lmceng.com>
>> Subject: Re: [TowerTalk] Stainless Steel Galling

>> Stainless steel material inherently galls; it is a characteristic of the 
>> soft material. Most stainless steels have a softer surface than steel 
>> screws that rust; most stainless steels don't rust but are generally 
>> weaker than steel screws.
> 
>  
> 
> weaker in what respect?
...
-- 
Best wishes,

Larry McDavid W6FUB
Anaheim, CA  (20 miles southeast of Los Angeles, near Disneyland)