How is austenitic stainless steel made?

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Discussion Overview

The discussion revolves around the production and properties of austenitic stainless steel, including the phase transformations that occur during heating and cooling, the role of alloying elements, and comparisons with other types of stainless steel. The scope includes theoretical aspects of metallurgy and practical implications for material properties.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about the cooling process of austenitic stainless steel to maintain its austenitic phase, noting the transformations to cementite and martensite under different cooling conditions.
  • Another participant explains that alloying components, particularly high chromium and nickel content, inhibit the transformation from austenite to other phases, suggesting that these elements are crucial in maintaining the austenitic structure.
  • A follow-up question arises regarding whether all austenitic stainless steels are in a solution annealed condition and why they are not normalized, indicating uncertainty about the manufacturing processes.
  • The same participant questions the role of nickel in preventing the transformation of austenitic stainless steel into pearlite and seeks clarification on how ferritic stainless steels are produced, given their different alloying compositions.
  • Another participant provides links to articles that may offer additional insights into alloy steels and the effects of alloying elements on phase formation.
  • It is noted that steels are often discussed in their annealed condition, but they can also undergo forging or working processes that affect their strength.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the production processes and properties of austenitic and ferritic stainless steels, with some questions remaining unanswered and no consensus reached on certain aspects of the discussion.

Contextual Notes

There are limitations in the discussion regarding the specific conditions under which different phases form, the definitions of terms like "solution annealed," and the absence of detailed information on creep temperature ranges as per ASME standards.

Ask1122
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Hi all, just wanted to find out how is austenitic stainless steel made? Because when you heat the steel above certain temperature, your cementite starts to diffuse out and austenite starts to form, but the thing is this: if you allow the austenite to cool down, it reverts back to cementite and ferrite, and if you quench it you will get martensite, but then how do you cool down the austenitic stainless steel to keep the austenite?

Thanks!
 
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A variety of alloying components inhibit the transformation from austenite to other phases. A typical 300 series stainless will have high chromium content and usually ~10% nickel, which prevents the transformation. Other additives are often used to reduce nickel content, keeping costs down.
 
Thx Timmay, that make much more sense to me now. But then does it mean that all austenitic stainless steel comes in a solution annealed condition, I saw somewhere that austenitic stainless steel are not normalised, but i am not sure why?

And if the nickel and chromium prevent the transformation of austenitic stainless steel into pearlites, then how are ferritic stainless steel (e.g. gr 430) made? I see that there are only chromium in the martensitic and ferritic stainless steel, does it mean that Nickel is the only elements that prevents the transformation?

And my last question is if you by any chance know where the creep temperature range for the materials are in ASME?

Thank you for all your help!
 
These articles might be of interest:

Alloy steels
Index - http://steel.keytometals.com/default.aspx?ID=Articles#p5
Alloy steels - http://steel.keytometals.com/default.aspx?ID=CheckArticle&NM=4

Characteristic of alloying elements
http://steel.keytometals.com/default.aspx?ID=CheckArticle&NM=10

Effects on the martensite, pearlite and bainite formation
http://steel.keytometals.com/default.aspx?ID=CheckArticle&NM=51


Steels and their properties are often given in the annealed condition, but they can be forged or hot/cold worked, which does effect strength.
 
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