Temperature Depending Influence of the Martensite Formation on the Mechanical Properties of High‐Alloyed Cr‐Mn‐Ni As‐Cast Steels

Abstract

The temperature dependence of the martensite formation and the mechanical properties of three high alloyed Cr‐Mn‐Ni as‐cast steels with varying Ni contents were studied. The results showed that the Ms and Md temperatures of the steels decrease with increasing nickel contents. Therefore the strain‐induced martensite formation, the TRIP effect and the temperature anomaly of the elongations occurs at lower temperatures. The steel alloyed with 3% nickel shows a stress induced formation of martensite and a dynamic strain aging. Depending on the nickel content and the temperature a TWIP effect occurs additionally to the TRIP effect in the investigated steels. The study was performed by using static tensile tests, dilatometer tests, optical microscopy and the magnetic scale for the detection of ferromagnetic phase fractions.

Considerations in the Design of Formable Austenitic Stainless Steels Based on Deformation-Induced Processes

“…To secure a high formability at room temperature, the M d γ → α′ temperature must be close to room temperature as is the case with commercial austenitic stainless steels such as the AISI 304-grade (Fe-18Cr-10Ni) stainless steel. The development of the AISI 200 series (FeCrNiMn) austenitic stainless steels in which Ni is partially replaced with Mn is also in accord with the preceding design principle [39].…”

“…The schematic in Figure 9 generalizes the temperature dependence of tensile elongation in austenitic stainless steels [10,15,[38][39][40][41][42][43]. The schematic elongation curve consists of three regions marked I-III.…”

“…Although the proximity of M d γ → α′ temperature and the temperature associated with maximum tensile elongation has been documented in many researches involving tensile tests at various temperatures followed by the quantification of bulk α′-martensite fractions in the uniformly strained regions of tensile specimens [14,17,[36][37][38][39], there also exist experimental results in support of the ductility-enhancing effect of α′-martensite formation [10,14]. Figure 11 shows such an instance where the tensile elongation increases concurrently with the formation of α′ at temperatures…”

“…Therefore, the M d γ → α′ temperature may be used to predict the influence of alloying elements on the elongation curve. Tensile tests at various temperatures of austenitic stainless steels with varied amounts of Ni [39,42], Mn [43], Al [15], Cr [23,25,27], C [23,24], and N [25] have confirmed that they shift the peak elongation temperature to lower temperatures. All of the preceding alloying elements except Al are unanimously known to decrease both M d γ → α′ and M s temperatures [54,55].…”

Segregation-Induced Enhancement of Low-Temperature Tensile Ductility in a Cast High-Nitrogen Austenitic Stainless Steel Exhibiting Deformation-Induced α′ Martensite Formation

“…The observed behavior was explained by the presence of microstructural regions with different stabilities with respect to deformationinduced a¢ martensite formation caused by the segregation of alloying elements. Tensile elongation near room temperature of low stacking fault energy (SFE) austenitic steels including stainless, [1][2][3][4][5][6][7][8][9] high Mn, [10][11][12][13] and high Ni [14] steels varies in three temperature regimes as follows. At the highest temperature range (regime I), tensile elongation remains more or less constant or exhibits a weak temperature dependence.…”