Impact on properties of 316L from additional elements? 2

[mhiggins]

After reviewing a Material Certification from our 316L investment casting supplier, I'm concerned with what appears to be additional elements that are not listed in ASTM-A240 for 316L. The added non-standard elements and their respective concentrations are: Vanadium - .066%, Copper - .258%, Tungsten - .012%, Titanium - .005%, Cobalt - .136%, Aluminum - .006%, and Niobium - .003%.
At a minimum, these added elements are displacing the required elements for 316L. The question is, is there enough of the non-standard elements to affect the properties of 316L, and if so, what properties could one expect to change, i.e., corrosion resistance and strength? As an FYI, per the material certification, the other standard elements are within ASTM-A240 specs, but on the low end of the range. These are investment castings in the annealed state to be electropolished after machining.

 

[GRoberts]

At those levels, I would doubt that the supplier added those alloying elements, but instead were residual elements included in thier melt stock. Many suppliers have those elements in their stainless steel, but you would never know it because they only report the elements required by the specification.

 

[mcguire]

These levels are quite consistent with normal 316. These tramp elements cannot be removed from the scrap from which nearly all stainless is at least partly made. Their effect on any important property is not measurable.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[panduru]

Actually there are two ways of looking at it. When ASTM specifies a lower threshold of a constituent, it implies that (i) the rest of the constituents listed shall make up the difference OR (ii) the percentage shortfall accounts for trace materials which do not influence the properties.

If there is no such clarification in ASTM, we need to confirm the influence of each of the possible trace materials on the properties (an impossible task?).

Just my 2 cents.

 

[mcguire]

Some trace elements actually do affect properties of 316L. The producer probably added titanium to de-oxidize and boron for hot workability. That helps corrosion resistance. Sulfur is bad for resistance to corrosion and you should want less than 0.003%, unless you have to TIG weld it, which sulfur helps. Phosphorus is bad, but you cannot get rid of it. Some residual copper is good, same with tungsten. These questions were addressed when ASTM constructed the standard.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[panduru]

Many thanks, mcguire
.

 

[EdStainless]

The more redily oxidizable elements, Ti, Al, and to a lesser extent V, Nb, are deliberatly added for deoxidation in the melting process.
Cu, W, and Co are carried in the scrap. There is no way to seperate these in melting. At low levels they have no impact. Cu and Co are both austenite stabalizers. W promotes ferrite formation. At some level they can impact weldability and alloy stablity.
There is a lot of work that shows there are no negitive effects from S up to 0.020%.
P and B are maybe from slag/flux. Less is always better, they are the grain boundary trash. These along with Ca and O could have an impact on defects that you see in EP.

If any of these really impacted your application ( can think of reasons to limit may of the elements) then you could melt from pure metals and make a virgin heat. There are two problems. First, it costs a lot more. Secondly you don't have as good of chemistry control.

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