Cr Segregation and Impact Fracture in a Martensitic Stainless Steel

Abstract

The fracture surfaces of a 10.5 wt.% Cr martensitic stainless steel broken in Charpy tests have been investigated through X-ray photoelectron spectroscopy (XPS). The specimens have been examined in two different conditions: as-quenched and heat treated for 10 h at 700 °C. The trends of Fe/Cr ratio vs. test temperature are similar to the sigmoidal curves of absorbed energy and, after both ductile and quasi-cleavage brittle fractures, such ratio is always significantly lower than the nominal value of the steel chemical composition. Cr segregation does not occur on a macroscopic scale but takes place in microscopic zones which represent weaker spots in the steel matrix and a preferred path for moving cracks. Small area (diameter 300 µm) XPS measurements evidenced a higher density of such microscopic zones in the inner part of probes; this is explained by the different diffusion length of Cr atoms in the external and inner parts during quenching from austenitic field which has been calculated through FEM simulations. No significant differences of Cr concentration were observed in fracture surfaces of probes with and without heat treatment. The results highlight how Cr segregation plays a role not only in the intergranular mode of fracture but also in the quasi-cleavage and ductile ones.

ESCA as a Tool for Exploration of Metals’ Surface

“…Various phenomena on the metallic surfaces were revealed: the formation of impurity defects on collection coins, the microchemical composition and corrosion of stainless steel coated by Cr and Ti nitrides, modifications of microchemical composition in biphasic Ni-based superalloys, carbon diffusion at high temperature in the interface of Ti6Al4V/SiCf composite, microchemical inhomogeneity of liquid PbBi alloy, surface modification of austenitic steels by plasma carburizing, and nitrogen migration at high temperature, with an influence of polycrystalline metal substrates (Cu, Ni, and NiCu alloy) on the growth of graphene. One more recent example of an advantageous ESCA application for the study of Cr segregation in martensitic stainless steel is reported in the present issue of this journal [48].…”

Review on Dynamic Recrystallization of Martensitic Stainless Steels during Hot Deformation: Part I—Experimental Study

“…Grain elongation and thinning increase the grain boundary area dramatically [90][91][92][93]. The grain boundaries become serrated as a result of LAGB (sub-grain) formation [94]. This behavior compresses grains serrations on The cDRX directly changes the orientation of sub-grains and forms new grains [87,88].…”

Intergranular Corrosion and Ductile-Brittle Transition Behaviour in Martensitic Stainless Steel

“…Martensitic stainless steel is always in tempered conditions due to the precipitation of chromium-rich carbides. The precipitation precedes austenitic grain boundaries and at the martensitic lath borders [6,[13][14][15][16]. Chromium will decrease in the metal matrix around the carbide, resulting in chromium depletion at the carbide-matrix interface.…”

“…6. The impact energy as a function of temperature The Cr content in martensite stainless steel significantly affects mechanical properties such as creep strength, corrosion resistance, oxidation resistance, and the ductile-brittle transition temperature (DBTT) [14,[23][24][25]. In terms of fabrication methods like hot rolling, the direction of crack propagation substantially impacts DBTT, which is influenced by crystallographic texture and microstructural morphology; the DBTT is extremely low in the case of fracture with delamination [26].…”