High Strength Stainless Austenitic CrMnCN Steels – Part I: Alloy Design and Properties

Abstract

Generally the strength of stainless austenitic steels does not live up to their good corrosion resistance. Solid solution hardening by interstitial elements is a means of raising the strength, but is used only moderately because of poor weldability, which, however, is not required in various applications. The solubility of nitrogen is high in stainless austenite of steels with 18 mass% of Cr and Mn each, but low in the melt. Carbon reveals the opposite behaviour. Instead of producing high nitrogen steels by pressure metallurgy, about 1 mass% of C+N is dissolved in the melt at ambient pressure. The new cost‐effective C+N steel reaches a yield strength of 600 MPa, a true fracture strength above 2500 MPa and an elongation above 70 %. Conduction electron spin resonance revealed a high concentration of free electrons. Thus, the ductile metallic character of the C+N steel is enhanced, explaining the high product of strength times toughness. The high interstitial content requires rapid quenching to avoid an embrittling precipitation and respective intercrystalline corrosion.

The influence of the nitrogen/nickel‐ratio on the cyclic behavior of austenitic high strength steels with twinning‐induced plasticity and transformation‐induced plasticity effects

“…It has been reported earlier that the classical chromium nickel-(carbon + nitrogen < 0.44; lowcarbon and up to 0.4 wt.% nitrogen) as well the austenitic high nitrogen steels (carbon + nitrogen > 0.42; low-carbon and up to 1 wt.% nitrogen) do not have such a high capacity for dissipating plastic work under tensile tests like the so-called austenitic high interstitial steels (carbon + nitrogen > 0.7 and carbon/nitrogen % 0.4), which are characterized by a higher density of free electrons on the sliding planes [12,14,31,32]. This was also attributed to the reason why the twinning induced plasticity-type austenitic high nitrogen steels as well as the austenitic high interstitial steels show a 10 to 100 times slower stable crack propagation in comparison to the chromium nickel-as well as the trans-formation induced plasticity-steels investigated [33].…”

“…In general such steels show a cyclic hardening behavior, while the CrMnCn steels always exhibit planar slip and cyclic softening [9]. Still recently developed CrMnCN steels also bring about a higher fatigue limit, which could even be further improved by 20 % cold-working [12][13][14][15]. With these so-called austenitic high interstitial steels both carbon and nitrogen are of similar importance for all properties depending on the sum of carbon + nitrogen and its ratio carbon/nitrogen [16].…”

Gas–Solid Interactions During Nonisothermal Heat Treatment of a High-Strength CrMnCN Austenitic Steel Powder: Influence of Atmospheric Conditions and Heating Rate on the Densification Behavior

“…[1][2][3][4][5] In an analogy to Hadfield steels, [6] these materials achieve their strength from their high interstitial content. Being alloyed with carbon and nitrogen, CrMnCN austenites reach yield strengths and true fracture strengths of up to 600 MPa and 2500 MPa, respectively.…”

“…Being alloyed with carbon and nitrogen, CrMnCN austenites reach yield strengths and true fracture strengths of up to 600 MPa and 2500 MPa, respectively. [4] Furthermore, as a consequence of the combined presence of C + N in the solid solution, the concentration of free electrons is considerably increased, leading to improved short-range atomic ordering, higher solubility of the interstitials in the melt, and an enhanced ductile metallic character of the interatomic bonding. [3,4,7,8] In their experimental investigations of C + N austenites, Berns et al [4] measured elongation values at fracture of up to 74 pct and a specific fracture energy of approximately 700 J/cm 3 .…”

“…[4] Furthermore, as a consequence of the combined presence of C + N in the solid solution, the concentration of free electrons is considerably increased, leading to improved short-range atomic ordering, higher solubility of the interstitials in the melt, and an enhanced ductile metallic character of the interatomic bonding. [3,4,7,8] In their experimental investigations of C + N austenites, Berns et al [4] measured elongation values at fracture of up to 74 pct and a specific fracture energy of approximately 700 J/cm 3 . With respect to the constitution, CrMnCN austenites are typically alloyed with 18 -20 mass-pct Cr and Mn each and with up to 1 mass-pct C + N. [1,2,5] In these steels, chromium is necessary not only for corrosion resistance but also in combination with a high amount of manganese to enhance nitrogen solubility in the melt.…”