Stainless - less low-temp fatigue resistance?

[Zak Smith]

This old UseNet thread contains some claims that stainless steel has poor fatigue resistance at very temperatures:

Several arms companies have recently offered hunting rifles with a stainless steel barrel. Here's some cautionary information about stainless steel barrels.

When the temperature goes down, stainless steel has less fatigue resistance. Its physical properties drop off with temperature. There have been instances of stainless barrels in hunting rifles bursting when the ambient temperature is around zero degrees, or less.

Some custom barrel makers specifically caution against using their stainless barrels in hunting rifles. One (Krieger) doesn't even make sporting/hunting barrels in stainless steel. In a conversation with B.J. Obermeyer some years ago, he told me that some of his stainless barrels were installed in hunting rifles and used in Alaska winter-time hunts. Some of these barrels burst when fired.

Chrome-moly (i.e., type 4140 or 4150) barrels maintain their fatigue resistance very well in really cold temperatures. Stainless steel (i.e, type 416R), typically used for rifle barrels, is the really cold-weather culprit.

I'm wondering if anyone who has bought a new rifle with a stainless steel barrel has noticed any cautions in printed material supplied with the rifle. Even more so, I'm wondering if rifle makers even concern themselves with this issue.

Has anyone here heard of this issue? Do any rifle manufacturers mention it? I've never heard of it before.

If it is true, it would give me pause when considering buying a rifle with a stainless barrel. Last winter I did some shooting in -10F weather.

As an aside, http://yarchive.net/gun/ contains many posts by Gale and Rock McMillan from 1997 and prior.

-z

 

[Johan762]

I cannot see why SS would be more brittle than....

....chrome moly steel. I will include some metallurgical factors to support my opinion.

First of all, there are two classes of terminologies getting mixed up: (1)fatigue endurance / fatigue limit and (2)ductile to brittle transition temperature. The earlier term refer to the numbers of cycles when steel and titanium will undergo fracture at a certain stress amplitude. Fatigue limit is the maximum stress amplitude steel or titanium at which they can be subjected to infinite numbers of stress without experiencing failure. Then there is ductile to brittle transition temperature, which refer to the temperature in which a normally ductile steel (and other metals with Body Center Cubic crystal structure) will exhibit catastrophic brittle frature, i.e, rapid crack propagation with very little or no plastic deformation.

It is the ductile to brittle transition nature of BCC metals that must be considered in low temperature uses, not the fatigue resistance. Lower cycle fatigues are observed at higher temperature usage, such as in boilers and pressure vessels. In my opinion, it was a mistake that the term "fatigure resistance" was even used. The author of that article should have chose the words "ductile to brittle transition" instead.

What metallurgical factors affect transition temperature? Chemistry wise, oxygen, silicon (>0.25%), carbon and manganese ratio (Mn:C should be 3:1), nitrogen, sulfur, and Molybdenum (principle ingredient in the chrome-moly steel) will raise the transition temperature. Chromium, the main alloying element of 416 stainless steel, do not have any effect on steel's DBT temperature. Physically, grain size also plays extremely important role in ductile to brittle transition temperature.

So, what made this gentleman to content that stainless steel is prone to burs more in lower temperature than chrome moly steel? What metallurgical evidence did he provide? Did he take a look at the microstructure of the burst barrels? Was the barrel of the tempered martensitic microstructure with fine grain size to lower the DBT temperature? Did he check the burst barrel's metal chemical composition? Was the steel completely deoxidized? Was there higher amount of sulphur and silicone present?

I just cannot think as to why stainless steel would be more prone to failure at lower temperature than the average chrome moly steel. After all, 416 stainless steel have similar chemical composition to 4140 chrome moly steel, except for the much higher chromium content of the earlier.

Johannes

 

[slo_dog]

Have used my ss .270 @ 15 below & it worked just fine . No temp. warnings came with gun when I purchased it new . Never heard of failures due to low temps. before this . Me I'll use it when I need it no matter what the temp.