4340 Sulfer Content

[Thrasher1]

Good Afternoon! Can anyone tell me the affect of going from a Sulfer content of .025 to .038 on the part life. Is this an issue?? Government part? May be over engineered, not sure....

 

[salmon2]

Usually sulfur content should be kept as low as possible because it will impart your properties, especially impact toughness at transverse direction. Also it is a potensial problem for corrosion, if corrosion is concerned. So it is a no-no to me.

 

[Thrasher1]

Thanks for the reply!!

 

[metengr]

In addition to reduced notch toughness with elevated sulfur content, the fatigue properties of the steel will also be reduced.

 

[dbooker630]

For bar products I would not expect 0.038 to be a problem typical specs are 0.040 max. Yes it is true that lower sulfur is favorable, especially for cold or warm forming applications but at the expense of machinability. Sometimes a minimum sulfur is also added, say 0.025 to minimize variation in machinability.

 

[salmon2]

I thought spec callsout for S is .025 max, then Thrasher1 posted the question.

.025 is a common S limit for a lot of applications such as oil and gas industry vs. .040 for standard 4340. You are right on machinability. I agree discretion should depend on application.

 

[blacksmith37]

The application can make a difference; for high strength sour (oil) service OCTG, S levels are <0.005 % for T-95, "C-110" from the better mills.

 

[Wrenchbender]

Increasing the S limits as you stated will decrease fracture toughness. How much depends on the type steel, temperature, and tensile strength. There are curves published by the ASTM and in textbooks such as in Broek or Hertzberg comparing different amounts of S. Charpy V-Notch and fatigue strength are linked to fx toughness.

Typically Less S = More $. Vacuum arc remelted steel goes about <.001%. Also have seen ladle refined steel that low. Aircraft Quality is <.025. A level of .038 is probably okay for most applications; but as always it depends...