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A potential online nondestructive method using a multifrequency electromagnetic (EM) sensor to measure the decarburization of steels has been proposed and tested. Online (hot) testing was simulated, using composite samples comprised of a 316 stainless steel (paramagnetic) core and a surrounding tube of ferritic steel (ferromagnetic), with thicknesses between 100 and 600 lm. The sensor can detect the decarburization and quantify the depth. Offline (cold) measurement of decarburized high-carbon steel rods was also carried out and compared with the online measurement. The relationship between the sensor output and the decarburized layer type/thickness has been modeled using finite element methods (FEMs).

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The influence of austenitization treatment of a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) on austenite formation during reheating and on the fraction of austenite retained after tempering treatment is measured and analyzed. The results show the formation of austenite in two stages. This is probably due to inhomogeneous distribution of the austenite-stabilizing elements Ni and Mn, resulting from their slow diffusion from martensite into austenite and carbide and nitride dissolution during the second, higher temperature, stage. A better homogenization of the material causes an increase in the transformation temperatures for the martensite-to-austenite transformation and a lower retained austenite fraction with less variability after tempering. Furthermore, the martensite-to-austenite transformation was found to be incomplete at the target temperature of 1223 K (950°C), which is influenced by the previous austenitization treatment and the heating rate. The activation energy for martensite-to-austenite transformation was determined by a modified Kissinger equation to be approximately 400 and 500 kJ/mol for the first and the second stages of transformation, respectively. Both values are much higher than the activation energy found during isothermal treatment in a previous study and are believed to be effective activation energies comprising the activation energies of both mechanisms involved, i.e., nucleation and growth.

As modern industrial processes are associated with large Technology Centre, Moorgate, Rotherham, UK, and Mr Bailey was amounts of data, empirical models are increasingly being with Corus Engineering Steels, Stocksbridge Works, Stocksbridge, used to describe an industrial process.1-3 A range of empirical

The drive to increase the efficiency of fossil fired power generation to reduce CO2 emissions and to conserve energy resources has led Tata Steel to design new 10Cr martensitic compositions for use at temperatures of 620°C and above with creep properties superior to steel 92 (9Cr, 0·5Mo, and 2W), which is the best currently available steel of this type. In the new alloys, the chromium content was set at 10 to ensure the required oxidation resistance. The long term creep performance of steels with this level of chromium has been limited by the precipitation of Z phase nitrogen rich particles. These form at the expense of vanadium rich MN precipitates that are vital for long term creep strength. Compositions have been designed with the aim of suppressing or delaying Z phase formation. The principles underlying the new steel chemistries are discussed, and a detailed explanation is given of the role of heat treatment in optimising creep rupture strength at temperatures in excess of 600°C. The new steel compositions are based on published work supplemented by thermodynamic calculations to optimise the heat treatment cycle, to produce a fully martensitic microstructure and to maximise the stable nanoprecipitates that are essential to maximise creep rupture life.