Abstract
This chapter is centered on the development of austenitic high strength cast CrMnNi steels with excellent strength-ductility combination by triggering TWIP and TRIP effects. Special attention is given to obtain a high yield strength and a good formability. For this purpose, three generations of steels were developed. The 1st generation is comprised of cast X3CrMnNi16-7-x steels. Their Ni concentration was varied in order to manipulate the stacking fault energy of austenite and change the operative deformation mechanisms. Based on the mechanical properties of the 1st generation steels, the 2nd generation steels were developed with a composition similar to the X3CrMnNi16-7-6 steel. Interstitial alloying elements were added to take advantage of solid solution strengthening and precipitation hardening effects. The substitutional alloy contents were carefully adjusted to ensure the occurrence of TRIP/TWIP effects during plastic deformation. For the 3rd generation, two steels from the 2nd generation, X16CrNiMnN15-3-3 and X16CrNiMnN19-4-3, were treated with tailored quenching and partitioning (Q&P) processing routines to further increase the strength, especially the yield strength. The developed Q&P cast steels exhibited an outstanding strength-ductility combination, e.g. a yield strength over 1000 MPa and a total elongation exceeding 20% for the steel X16CrNiMnN15-3-3 containing 0.12 wt% N.
Highlights
Conventional austenitic stainless steels such as AISI 304 have been widely accepted in industry due to their outstanding properties such as superior toughness and extraordinary formability [1]
This chapter focuses on the development of cast CrMnNi stainless steels exhibiting excellent strength-ductility combination with the aid of TRIP/TWIP effect
Interstitially-alloyed steels Cr15NC10.X and Cr19NC15.X were produced for the 2nd generation steels, aiming at solid solution strengthening, second phase strengthening by introducing as-quenched α -martensite, and precipitation hardening
Summary
Conventional austenitic stainless steels such as AISI 304 have been widely accepted in industry due to their outstanding properties such as superior toughness and extraordinary formability [1] They are usually used in the annealed state and exhibit relatively low strength. Efforts have been made to develop metastable austenitic steels with low stacking fault energy (SFE) to enhance the strength-ductility combination by introducing transformation-induced and twinning-induced plasticity (TRIP and TWIP) effects during deformation of the steels [2–4]. Deformation can proceed via martensitic transformation, twinning and other plasticity mechanisms. The twins have different crystal orientations with respect to the matrix and they reduce the effective glide distance of dislocations The latter leads to an enhanced strain hardening, especially in the presence of a high twin density. Efforts, including varying the Ni content, addition of different interstitial contents, and application of tailored quenching and partitioning (Q&P) processing routines, were made to achieve a high strength combined with a high ductility in the cast CrMnNi stainless steels
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