Quantitative Description of the Microstructure of Duplex Stainless Steels Using Selective Etching

: The properties of duplex stainless steels (DSSs) depend on the ferrite–austenite ratio and on the contents of secondary phases. Therefore, it is necessary to control the volume fractions, morphologies, and distribution patterns of all phases. The phases in the samples were identified using thermodynamic modeling and scanning electron microscopy. Investigated specimens were obtained after different heat treatments, such as solution annealing and quenching from 1050 to 1250 °C to obtain different amounts of ferrite and annealing at 850 °C to precipitate the σ-phase. Therefore, a metallographic technique for assessing the phases in DSSs based on selective etching and subsequent analysis according to ASTM E 1245 was developed. It was shown that the developed method of quantitative analysis based on selective etching and metallographic assessment according to ASTM E 1245 allows obtaining much more accurate results compared to the proposed ASTM E 562 method, which correlates well with the XRD quantitative phase analysis.

Identification of Carbides in Tool Steel by Selective Etching

This paper describes simple metallographic technique for selective etching of individual types of carbides (MC, M2C and M6C and M7C3) in tool steel. Electrolytic etching in chromic acid was used in order to reveal the MC carbides. Chemical etching in permanganate solution revealed the M2C and M6C carbides, while the electrolytic etching in the latter solution enabled to observe M7C3, M2C and M6C carbides. These techniques were demonstrated on an experimental niobium-containing tool steel prepared by powder metallurgy. The results confirm that the MC carbides are highly thermally stable, while the M2C carbides decompose during austenitizing at the temperature of 1050 °C and higher. The M7C3 carbides dissolve in the austenite significantly. This exact and simple observation of the carbides behaviour enables to describe the role of particular carbides on heat treatment behaviour and also to save the carbide-forming elements, where the important ones (tungsten, vanadium) are listed as critical raw materials and the others (chromium and molybdenum) are also strategic.

Characterization and Fracture Toughness on AISI 8620 with Hard Coatings

The present studies characterize and evaluate the fracture toughness at the surface AISI 8620 with hard coating. The hard coatings FeB and Fe2B were formed using the boriding dehydrated paste at temperatures 1223 and 1273 K with 6 and 8 h exposure time, respectively. The presence of hard coatings formed on the surface AISI 8620 were confirmed by the classical metallographic technique combined with X-ray diffraction analysis. The distribution of alloying elements was determined by Energy Dispersive Spectroscopy (EDS). The fracture toughness of the hard coatings on AISI 8620 was estimated using a Vicker microindentation induced fracture testing of 15 and 35 μm from the surface, applying four load (0.49, 0.98,1.96 and N). The microcrack generated at the corner of the microindentation was considered as an experimental parameter and the tree model Palmqvist crack model was employed to determine the fracture toughness. The adherence of the hard coatings/substrate was evaluate in qualitative form though the VDI 3198 by testing Rockwell C and observed by Scanning Electron Microscopy (SEM). The formation of hard layers was obtained in the range of 100-130 μm, results of XRD present phases FeB, Fe2B, CrB and MnB, the values obtained of Kc are in the range of 2.3 to 4.1 MPam1⁄2 and results of acceptable adhesion HF4 patterns for conditions 6 h of treatment

Metallographic Characterization of a Ti-Containing Low-Density Fe-Mn-Al-C Steel in As-Cast Condition

ABSTRACTLow-density steels, with an excellent combination of outstanding mechanical properties, ultimate tensile strength and specific weight reduction, have been attracting great attention as a new group of materials in many industrial applications, particularly in the automotive industry. The aim of this work was to characterize the microstructure of a Ti-containing low-density Fe-Mn-Al-C steel in the as-cast condition. For this purpose, Ti-containing low-density steel was melted in an induction furnace using high purity raw materials and cast into a metal ingot mold. Chemical composition of the studied steel was Fe-32Mn-7.0Al-2.2C-0.5Ti (wt%). Samples were prepared by standard metallographic technique (grinding and polishing) and chemically etched with 2% nital solution, in order to reveal the dendritic microstructure. Microstructure observations were performed by scanning electron microscopy and the chemical nature of the present phases was determined by energy-dispersive X-ray. X-ray diffraction was performed at room temperature using a diffractometer with Cu Kα radiation. Phase equilibria by thermodynamic calculations for the studied steel were performed using JMatPro® software package. In general, results revealed a finer dendritic microstructure composed of ferritic matrix and austenite islands. The presence of ferrite and austenite in the steel was also confirmed by X-ray diffraction.

Color Metallographic Technique for Microstructure Analysis of Aluminum Alloy Weld

Through traditional corrosion method of aluminum alloy weld could only get a black-and-white metallographic structure. Color metallographic structure could be got by using color metallographic technique, which could improve discrimination of metallographic structure. The welding test pieces were got by using A7N01 and A6N01 aluminum sheets as base metal and E5356 and E4043 as welding wire. Through sampling, mounting, grinding and polishing process, metallographic specimens were obtained. Contrast test of aluminum alloy specimens was investigated. Conventional Keller’s reagent corrosion results showed the grain outline was not very clear and the grain boundary was fuzzy. Color metallographic corrosion results showed both the grain outline and boundary were very clear. Grains of different orientation and composition segregation presented different color. So color can be used to distinguish orientation and composition segregation. Color metallographic technique was better than black-and-white metallographic technique to observe the metallographic structure.