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The dependence of fracture appearance transition temperature (FATT) on phosphorus grain boundary segregation, yield strength, and grain size is experimentally evaluated for a 2.25Cr–1Mo low‐alloy steel. Both the phosphorus boundary segregation and yield strength are directly correlated to the FATT of the steel. However, the prior austenite grain size is not directly linked to the FATT although it influences phosphorus boundary segregation and yield strength. The FATT exhibits linear relations to phosphorus segregation concentration and yield strength, but there is no synergistic effect between these two entities. Based on the measurements, an embrittlement equation is established, which is expressed as FATT(°C) = 0.25σs + 2.64CP–270, where σs is the yield strength in MPa and CP is the phosphorus boundary concentration in at%. The calculated FATTs have a good agreement with the measured ones. [ABSTRACT FROM AUTHOR]

The fracture appearance transition temperatures (FATTs) are evaluated for the samples of a Nb-stabilized and P-strengthened interstitial free (IF) steel. Based on the measurements, the combined effect of hardening and phosphorus grain boundary segregation on the embrittlement of the steel is investigated. Both hardening and P boundary segregation can raise the FATT of the steel, causing hardening embrittlement and non-hardening embrittlement, respectively. Meanwhile, the grain size influences both kinds of embrittlement, i.e., there is a synergistic effect between grain size and hardening or P boundary segregation on the FATT of the steel. With the aid of the Taylor expansion along with the experimental data, a combined hardening and non-hardening embrittlement equation is established, being expressed as FATT  = 2.1 C p + 3.48 σ s − 22.36 d −1⁄2 + 0.64( C p − 14)( d −1⁄2 − 3.06) + 0.896( σ s − 14)( d −1⁄2 − 3.06) − 13.7, where FATT is the fracture appearance transition temperature in °C, C p is the phosphorus boundary concentration in at%, σ s is the yield strength in 10 MPa, and d is the grain size in mm. A comparison of the calculated and measured FATTs is made, demonstrating that the calculated FATTs are well consistent with the measured ones. [ABSTRACT FROM AUTHOR]

The samples of SA508-III reactor pressure vessel steel, undoped, doped with Sn, and doped with Sn + Ce, are heated at 1300 °C and then cooled down to different temperatures between 650 and 1050 °C, followed by tensile deformation until fracture using a Gleeble machine. The steel hot ductility evaluated by the reduction of area (RA) is determined at each test temperature. The tested samples are characterized using scanning electron microscopy, optical microscopy, and field emission gun scanning transmission electron microscopy. The steel exhibits a hot ductility trough and Sn substantially deteriorates the hot ductility of the steel by deepening and widening the ductility trough. However, Ce can well suppress this Sn-induced hot ductility deterioration. Grain boundary segregation of Sn or Sn + Ce occurs in the Sn-doped or Sn + Ce-doped samples. The segregation of Sn is primarily responsible for the hot ductility deterioration as it weakens grain boundary, thereby enhancing grain boundary sliding and deteriorating hot ductility. The segregation of Ce is mainly responsible for the suppression of the deterioration as it strengthens grain boundary, thereby restraining grain boundary sliding and suppressing Sn-induced hot ductility deterioration. [ABSTRACT FROM AUTHOR]

The creep properties of 2.25Cr-1Mo steel samples, undoped and doped with Sb (0.05 wt%), are examined under different applied engineering stresses (150–400 MPa) and temperatures (773–873 K). The creep behavior follows a unified Monkman-Grant relation ε ̇ m × t r 1.04 = 0.046 for both the undoped and Sb-doped steels, where ε ̇ m is the minimum creep rate in h−1 and t r is the rupture time in h. Under the same experimental conditions, the rupture time of the undoped steel is much longer than that of the Sb-doped steel, and meanwhile the minimum creep rate of the former is apparently smaller. Moreover, the threshold stress for creep is much lower for the Sb-doped steel than for the undoped one. This indicates that the impurity element Sb severely lowers the high temperature creep resistance of 2.25Cr-1Mo steel. As shown by boundary microanalysis, there is apparent grain or subgrain boundary segregation of Sb, which could promote the boundary sliding and the nucleation of cavities or microcracks, thereby leading to the creep property deterioration of the steel. [ABSTRACT FROM AUTHOR]

The embrittlement of heat affected zones (HAZs) resulting from the welding of a P-doped 2.25Cr-1Mo steel was studied by the analysis of the fracture appearance transition temperatures (FATTs) of the HAZs simulated under a heat input of 45 kJ/cm with different peak temperatures. The FATTs of the HAZs both with and without tempering increased with the rise of the peak temperature. However, the FATTs were apparently lower for the tempered HAZs. For the as-welded (untempered) HAZs, the FATTs were mainly affected by residual stress, martensite/austenite (M/A) islands, and bainite morphology. The observed embrittlement is a hardening embrittlement. On the other hand, the FATTs of the tempered HAZs were mainly affected by phosphorus grain boundary segregation, thereby causing a non-hardening embrittlement. The results demonstrate that the hardening embrittlement of the as-welded HAZs was more severe than the non-hardening embrittlement of the tempered HAZs. Consequently, a post-weld heat treatment should be carried out if possible so as to eliminate the hardening embrittlement. [ABSTRACT FROM AUTHOR]

Grain boundary (GB) segregation of P in 2.25Cr1Mo steel induced by elastic stress shows that the P equilibrium concentration, after reaching the non-equilibrium concentration maximum at critical time, returns to its initial thermal equilibrium level. This finding confirms the interesting phenomenon that the effect of elastic stress on GB segregation of P is significant in kinetics while slight in thermodynamics. Through extending the “pressure” in classical theory of chemical potential to the “elastic stress”, the thermodynamic effect of elastic stress on GB segregation is studied, and the relationship between elastic stress and segregation Gibbs energy is formulated. The formulas reveal that the difference in the segregation Gibbs energy between the elastically-stressed and non-stressed states depends on the excess molar volume of GB segregation and the magnitude of elastic stress. Model calculations in segregation Gibbs energy confirm that the effect of elastic stress on the thermodynamics of equilibrium GB segregation is slight, and the theoretical analyses considerably agree with the experimental results. The confirmation indicates that the nature of the thermodynamic effect is well captured. [ABSTRACT FROM AUTHOR]

The effect of phosphorous on the hot-ductility of SA508Gr.4N reactor pressure vessel (RPV) steel has been studied. The investigation is done with the use of a Gleeble machine in conjunction with optical metallography, scanning electron microscopy, and transmission electron microscopy. It is observed that both the undoped and P-doped steels exhibit hot-ductility troughs between 750 and 900 °C. However, the trough for the P-doped steel is much shallower than that for the undoped steel. At around 850 °C, the reduction of area (RA) of the undoped steel is quite low (~50%), in comparison to the P-doped steel (~75%). Since there is no grain-boundary precipitation of ferrite and carbides in both undoped and P-doped samples over this temperature range, it can be inferred that the enhancement in hot-ductility for the P-doped steel is independent of these two factors. Grain-boundary microanalysis shows the presence of grain-boundary segregation of P in the tested P-doped samples, implying that the P-induced hot-ductility improvement of this RPV steel may arise from the suppression of grain-boundary sliding by P grain-boundary segregation. Undoubtedly, the present effect of P is unusual and the underlying mechanism for this effect has been briefly discussed. It needs to be underlined that a minor addition of P can play a positive role in the hot-ductility improvement of SA508Gr.4N RPV steel. [ABSTRACT FROM AUTHOR]