Effects of Austenitizing Temperature on Tensile and Impact Properties of a Martensitic Stainless Steel Containing Metastable Retained Austenite

Abstract

Austenitizing temperature is one decisive factor for the mechanical properties of medium carbon martensitic stainless steels (MCMSSs). In the present work, the effects of austenitizing temperature (1000, 1020, 1040 and 1060 °C) on the microstructure and mechanical properties of MCMSSs containing metastable retained austenite (RA) were investigated by means of electron microscopy, X-ray diffraction (XRD), as well as tensile and impact toughness tests. Results suggest that the microstructure including an area fraction of undissolved M23C6, carbon and chromium content in matrix, prior austenite grain size (PAGS), fraction and composition of RA in studied MCMSSs varies with employed austenitizing temperature. By optimizing austenitizing temperature (1060 °C for 40 min) and tempering (250 °C for 30 min) heat treatments, the MCMSS demonstrates excellent mechanical properties with the ultimate tensile strength of 1740 ± 8 MPa, a yield strength of 1237 ± 19 MPa, total elongation (ductility) of 10.3 ± 0.7% and impact toughness of 94.6 ± 8.0 Jcm−2 at room temperature. The increased ductility of alloys is mainly attributed to the RA with a suitable stability via a transformation-induced plasticity (TRIP) effect, and a matrix containing reduced carbon and chromium content. However, the impact toughness of MCMSSs largely depends on M23C6 carbides.

Influence of Partitioning Effects on the Retained Austenite Content and Properties of Martensitic Stainless Steel

“…According to, [ 18 ] based on the example of the medium carbon martensitic stainless steels, the influence of the carbides on the impact toughness is stronger than that of the amount and stability of the RA. X40Cr14 has a calculated carbide content at T Aust of 2.1% and “X25CrN13”; the N–alloyed steel has all carbides dissolved and only 0.1% nitrides left at 1020 °C (see Table 2).…”

“…[21] but may also be affected by the carbide content, as indicated in ref. [18] In the case of X40Cr14 at T Aust ¼ 1050 °C (Figure 5c), the toughness maximum of 15.8 J cm À2 is the lowest, despite the RA content being higher than at the lower T Aust . This great difference in toughness between the X40Cr14 at T Aust ¼ 1050 °C and the "X25CrN13" at T Aust ¼ 1020 °C, despite similar RA values, shows clearly that not only the amount but also the stability of the RA, influenced by nitrogen, strongly influences toughness.…”

“…[13] Especially, in martensitic stainless steels, partitioning effects have been proved. [14][15][16][17][18][19] However, in these steels, no pure partitioning happens, but a combination of tempering and partitioning. [14,17] In contrast, martensite-toaustenite reversion is claimed in ref.…”

Recent Progress of Low and Medium-Carbon Advanced Martensitic Steels

“…Differing from the IT process (Figure 4a), the MA phase and carbide are hardly formed because the process is not cooled to temperatures below Mf, similar to TBF, Q&P, and CFB steels with a BF/M matrix structure [29][30][31][32]34,[42][43][44]47]. In addition, such a microstructure without carbide in the soft lath-martensite resembles that of 0.23%C-2.3%Mn-1.5%Si-12.5%Cr-0.03%Ti-0.05%Nb martensitic stainless steel containing retained austenite [87].…”

Prediction of Deformation-Induced Martensite Start Temperature by Convolutional Neural Network with Dual Mode Features

“…Metastable austenite tailoring is a long-standing hot topic in the field of steel materials [ 1 , 2 , 3 , 4 , 5 , 6 ]. By transformation-induced plasticity (TRIP) in metastable austenite, different kinds of advanced steels [ 7 , 8 , 9 ], including 3rd generation ultra-high strength automobile steel, high Co-Ni secondary hardening steels [ 10 , 11 ], cryogenic steels [ 12 , 13 ], etc., obtained excellent comprehensive mechanical properties.…”