difference between 304, 321, 302, stainless steel. whats best?

Im looking to purchase headers and dont know what the differnce between 304, 321, 302, stainless steel. Whats best for headers?

Stainless steel Grades

• 200 Series—austenitic chromium-nickel-manganese alloys
  
• 300 Series—austenitic chromium-nickel alloys
  • Type 301—highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and fatigue strength than 304.
    
  • Type 302—same corrosion resistance as 304, with slightly higher strength due to additional carbon.
    
  • Type 303—easier machining version of 304 via addition of sulfur and phosphorus. Also referred to as "A1" in accordance with International Organization for Standardization ISO 3506.[6]
    
  • Type 304—the most common grade; the classic 18/8 stainless steel. Also referred to as "A2" in accordance with International Organization for Standardization ISO 3506.[7]
    
  • Type 309— better temperature resistance than 304
    
  • Type 316—the second most common grade (after 304); for food and surgical stainless steel uses; Alloy addition of molybdenum prevents specific forms of corrosion. 316 steel is used in the manufacture and handling of food and pharmaceutical products where it is often required in order to minimize metallic contamination. It is also known as "marine grade" stainless steel due to its increased resistance to chloride corrosion compared to type 304. SS316 is often used for building nuclear reprocessing plants. Most watches that are made of stainless steel are made of Type 316L; Rolex is an exception in that they use Type 904L. Also referred to as "A4" in accordance with International Organization for Standardization ISO 3506.[8]
    
  • Type 321— similar to 304 but lower risk of weld decay due to addition of titanium. See also 347 with addition of niobium for desensitization during welding.

  [*]400 Series—ferritic and martensitic chromium alloys

  • Type 408—heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel.
    
  • Type 409—cheapest type; used for automobile exhausts; ferritic (iron/chromium only).
    
  • Type 410—martensitic (high-strength iron/chromium). Wear resistant, but less corrosion resistant.
    
  • Type 416— easy to machine due to additional sulfur
    
  • Type 420—"Cutlery Grade" martensitic; similar to the Brearley's original "rustless steel". Also known as "surgical steel". Excellent polishability.
    
  • Type 430—decorative, e.g., for automotive trim; ferritic. Good formability, but with reduced temperature and corrosion resistance.
    
  • Type 440—a higher grade of cutlery steel, with more carbon in it, which allows for much better edge retention when the steel is heat treated properly. It can be hardened to Rockwell 58 hardness, making it one of the hardest stainless steels. Due to its toughness and relatively low cost, most display-only and replica swords or knives are made of 440 stainless. Also known as "razor blade steel". Available in four grades 440A, 440B, 440C (more common) and 440F (free machinable).

  [*]500 Series—heat resisting chromium alloys

  [*]600 Series—martensitic precipitation hardening alloys

  • Type 630—most common PH stainless, better known as 17-4; 17% chromium, 4% nickel

you might want to add in "L" nomenclature to these specifications? (regarding carbon levels)

O thats perfect! thanks so much!

next question is heat how each grade of stainless steel handles it

321 is supposed to be a little more tolerant of heat than 304. that being said, if you are overheating 304, you might have other things to worry about....

Which one of these is so-called "mild" steel?

Which one of these is so-called "mild" steel?

 

None of them. All the above listed steels are stainless. Mild steel is not stainless. The term mild steel is usually in reference to a low carbon steel.

None of them. All the above listed steels are stainless. Mild steel is not stainless. The term mild steel is usually in reference to a low carbon steel.

 

Ah, reading comprehension.... Thx.

Generally, headers are made from 304L ("L" stands for low carbon to help with welding), a slight step up is 321 which adds a little titanium. The best austenitic (300 series) for exhaust manifolds is 309S which I believe has even more chromium and a few other things to give it the highest strength at temperature. The problem with austenitics is that they expand much faster then mild steels and ferritics (400 series). This expansion leads to longer runner growth and adds stress the critical areas which likely results in yielding the material (i.e. strain) when the manifold gets up to temperature.

 

In recent years, steels makers have developed some pretty good ferritics due to the ridicules cost of austenitic stainless steels. These high grade ferritics can actually result in a more durable manifold if designed properly. They cannot handle the extreme temps (~1800F skin), but have there advantages since they expand at half the rate of 300 series.

 

To answer your question: 321 is the best on your list. As an example... LS2, LS6, and Dodge Viper OEM headers are made from 321. Pretty good stuff.

To answer your question: 321 is the best on your list. As an example... LS2, LS6, and Dodge Viper OEM headers are made from 321. Pretty good stuff.

 

And APS headers for the LGT

yeah not even many of the expensive headers are made from 321 but great info thanks for all the help everyone