A. Hernas

Contribution to mechanical metallurgy behaviour of steel during continuous casting

Abstract The paper is devoted to the study of the mechanical metallurgy characteristics of the mushy zone. The basic parameters of the brittle temperature range (TB), the zero strength (ZST), the zero ductility temperature (ZDT) and the liquid impenetrable temperature (LIT) are used for explaining the possibility of cracking. This temperature range was defined in the following form: ZDT

Microstructural degradation in boiler steels: materials developments, properties and assessment

Abstract: This chapter presents a brief description of types, properties and application of ferritic–bainitic (pearlitic), martensitic and austenitic steels designed for use in pressure elements of power boilers. It also describes assessment methodologies for material condition and residual life determination of the elements operated under creep conditions, as well as microstructural degradation processes and properties of creepresistant steels under the influence of long-term exposure to high temperature, with specific reference to the precipitation sequences of carbide phases in ferritic–bainitic and martensitic steels including the new types, e.g. VM12, and in austenitic steels.

Oxidation Resistance of Austenitic Steels under Thermal Shock Conditions in an Environment Containing Water Vapor

Abstract The oxidation behavior of Super 304 H, Sanicro 25, HR3C and HR6W steels, which are recommended for use in ultra-supercritical power plants, as well as corrosion resistant X2CrNiMo17-12-2 steel was studied in this work. Oxidation tests were carried out under thermal shock conditions in an oxygen-rich environment (containing 50 vol. % water vapor) at a temperature equal to 750 °C. The investigated steels (excluding X2CrNiMo17-12-2 steel) are characterized by good oxidation resistance under thermal shock conditions. A highly protective Cr2O3 layer was formed in the internal part of scales growing on the surfaces of investigated steels. The X2CrNiMo17-12-2 steel has worse oxidation resistant properties than the other grades of steels.

Characteristics of Fusion-Welded Joints Made Using Martensitic Steel after 100,000 Hours in Service

The paper presents the results of tests of mixed fusion-welded joints consisting of superheater pipes of grades T91 and HCM12A(T122) after 100,000 hours in service in a BB-1150 boiler welded to new pipes (in “as-delivered” condition) of grades T91 and VM12-SHC. The state of the microstructure and properties of the used tube material after long term service are characterized. The paper describes fusion welding conditions and parameters, and evaluates the quality of the created butt joints. The results of tests of the macro-and microstructure of the joints and their mechanical properties are presented. It was determined that the welding process intensifies further degradation of the tested materials to a small extent only. This work was performed under the Strategic Research Project No SP/E/1/67484/10 supported by the National Centre for Research and Development.

Microstructural characterization of second phases in X10CrMoVNb9–1 and 12CrMoWCuVNb steels after long steam exposure time at 550°C

Abstract Microstructural changes in high alloy (9–12% Cr) creep resistant martensitic X10CrMoVNb9–1 and 12CrMoW · CuVNb steels after 100 000 h of steam exposure at 550°C have been studied using scanning transmission electron microscopy. Precipitates were identified using electron diffraction patterns and energy dispersive X-ray spectroscopy analysis. After long time exposure, a significant coarsening of M23C6 carbides, and intensive precipitation of the coarse Laves phase were observed. Moreover, in the 12CrMoW · CuVNb steel, a low amount of the modified Z-phase particles was detected. The microstructures of the X10Cr · MoVNb9–1 and 12CrMoWCuVNb steels after 100 000 h of exposure differ in several aspects.

Scanning Transmission Electron Microscopy Studies of the Microstructure of High Chromium Steel after Long Time Exposure

The detailed microstructural analysis of HCM12 steel after long time (100 000 hours) exposure at service temperatures around 600°C was investigated by means of scanning transmission electron microscopy. The results show, that the recovery processes of the martensite lath structure and δ ferrite are significantly different. Moreover are differences in particles precipitating at the martensite and δ ferrite. The intensive process intragranular M23C6 and Laves particles precipitating is observed at the martensite/ δ ferrite interfaces.