The knowledge of the martensite start (Ms) temperature of steels is sometimes important during parts and structures fabrication, and it can not be always properly estimated using conventional empirical methods. The additions in newly developed steels of alloying elements not considered in the empirical relationships, or with compositions out of the bounds used to formulate the equations, are common problems to be solved by experimental trial and error. If the trial process was minimised, cost and time might be saved. This work outlines the use of an artificial neural network to model the calculation of Ms temperature in engineering steels from their chemical composition. Moreover, a physical interpretation of the results is presented.

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Determination of Ms Temperature in Steels: A Bayesian Neural Network Model

High-temperature low cycle fatigue, creep–fatigue and thermomechanical fatigue of steels and their welds

The precipitation reactions in two ferritic steels, 9Cr-1Mo-V-Nb and 12Cr-1Mo-V-W, were studied. Analytical electron microscopy, optical microscopy, electrolytic extractions, and hardness measurements were used to determine the types, amounts, and effects of precipitates formed as a function of the heat treatment. The effect of variations in the austenitizing treatment was ascertained. In addition to variations in the austenitizing time and temperature, different cooling rates after austenitization were also used. Air cooling after austenitization (normalization) resulted in little precipitation in both alloys. Precipitation in the 12Cr-1Mo-V-W alloy after furnace cooling was found in all cases examined. Under certain conditions precipitation was also found after furnace cooling the 9Cr-1Mo-V-Nb alloy. However, when compared to the amount of precipitate in the fully tempered state, the 9Cr-1Mo-V-Nb showed a much greater variation in the degree of precipitation following furnace cooling. In addition, the matrix microstructure of the 9Cr-1Mo-V-Nb alloy was very sensitive to cooling rate. The precipitation reactions during tempering after a normalizing treatment were followed as a function of tempering treatment. Tempering temperatures were varied from 400 to 780 °C. The carbide precipitation was essentially complete after one hour at 650 °C for both alloys. Analytical microscopy was used to identify the precipitates. In the 9Cr-1Mo-V-Nb alloy, a combination of chromium-rich M23C6 and vanadium-niobium-rich MC carbides was found. The carbides in the 12Cr-1Mo-V-W alloy were identified as chromium-rich M23C6 and vanadium-rich MC. The results give an indication of the sensitivity of these alloys to heat treatment variations.

Precipitation reactions during the heat treatment of ferritic steels

Ferritic-martensitic steels for fission and fusion applications

Steels 9-12% Cr, having the high creep rupture strength are advocated for the modern low polluting thermal power plants. In the present investigation, the P91 pipe weldments have been characterized for microstructural responses in as-welded, post-weld heat treatment (PWHT) and ageing conditions. The PWHT of welded samples were carried out at 760 °C for time of 2 h and ageing at 760 °C for 720 h and 1440 h, respectively. The effect of time has been studied on precipitates size, distribution of precipitates and grain sizes present in various zones of P91 steel weldments. The impact toughness and hardness variation of heat affected zone (HAZ) have also been studied in as-welded condition as well as at different heat treatment condition. A significant change was observed in grain size and precipitates size after each heat treatment condition. The maximum impact toughness of HAZ was obtained after PWHT at 760 °C for 2 h. The main phase observed in weld fusion zone in as-welded, PWHT and ageing conditions were M23C6, MX, M7C3, Fe-rich M3C and M2C. The unwanted Z-phase (NbCrN) was also noticed in weld fusion zone after ageing of 1440 h.

Characterization of microstructure of HAZs in as-welded and service condition of P91 pipe weldments

Ferritic steels for high-temperature applications : proceedings of an ASM International Conference on Production, Fabrication, Properties, and Application of Ferritic Steels for High-Temperature Applications, Warren, Pennsylvania, 6-8 October 1981

Ashok K. Khare

Papers

Ferritic steels for high-temperature applications : proceedings of an ASM International Conference on Production, Fabrication, Properties, and Application of Ferritic Steels for High-Temperature Applications, Warren, Pennsylvania, 6-8 October 1981