Atom probe investigations on temper embrittlement and reversible temper embrittlement in S 690 steel weld metal

Severe embrittlement was observed in weld material of a brand new penstock of a huge hydro power plant. Temper embrittlement (TE) was found as root case of embrittlement. Reversible temper embrittlement (RTE) treatment characterised by a short-time heating at about 600°C, by which the toughness of embrittled weld material can significantly be recovered, was qualified and successfully applied in the plant. Basic investigations were performed to explain the embrittlement as well as the de-embrittlement effect. By the application of high resolution analytics as Atom Probe Tomography (APT) applied on TE as well as on the RTE-treated material, revealed phosphorus segregation in the grain boundaries as root cause of embrittlement. By application of RTE treatment the APT results revealed, that the phosphorus segregation in the grain boundaries disappeared. The mechanism of this behaviour can be explained by referring the McLean [Grain boundaries in metals. Oxford: Clarendon Press; 1957] based grain boundary equilibrium segregation of phosphorous. During RTE treatment, which occur at higher temperatures (600°C) that segregation (which starts during cooling at about 550°C), desegregation occurs. During this higher temperature, the diffusion is much faster than segregation producing the fast recovery of toughness.     

On the nature of embrittlement occurring while tempering a Ni-Cr alloy steel

Data are presented to show that embrittlement in a Ni-Cr alloy steel proceeds by one mechanism at 925°F and by a different mechanism at 1250°F. The embrittlement occurring at 925°F may be removed completely by reheating to higher temperatures for very short times and has no influence upon further embrittlement at 1250°F. The embrittlement occurring at 1250°F appears related to a permanent structural change which has a significant retarding influence upon subsequent development of embrittlement at 925°F. It is suggested that retrogression phenomena are not necessary to explain embrittlement; on the other hand, segregation of solute atoms to prior austenite and ferrite grain boundaries may provide a better explanation of the occurrence of the two modes of embrittlement.     

A quantitative measure of temper embrittlement

From the theories of flow and fracture it is shown that the difference in reciprocals of the transition temperatures (°K) is a quantitative measure of temper embrittlement. Experimental data are given which support this conclusion.     

Bruscato factor in temper embrittlement of welds

Abstract

Published experimental data on the tendency for 2.25Cr–1Mo to undergo impurity induced temper embrittlement have been analysed quantitatively. The results indicate strong effects owing to phosphorus, silicon, manganese, and molybdenum concentrations, but the influence of tin, antimony, and arsenic cannot be perceived because of the overwhelming effects of the other elements. A computer model for the calculations is obtainable freely over the World Wide Web.     

Evaluation of temper embrittlement by ultrasonic attenuation

Research conducted up to the present time indicates the possibility of predicting the toughness of a material by utilizing ultrasonic attenuation characteristics. However, practically all of the cases concerned involve the investigation of changes in toughness brought about by making large changes in the microstructure of the material. However, the temper embrittlement encountered in Cr---Mo steels and the like are accompanied by large degradations in toughness with virtually no changes in microstructure and tensile strength. For this reason, it has been considered difficult to evaluate temper embrittlement based on ultrasonic attenuation characteristics. In the research reported here, sensitivity was enhanced by increasing the ultrasonic frequency (to 50 MHz) and the correlation between ultrasonic attenuation characteristics and temper embrittlement characteristics has been experimentally clarified.     

Segregation of impurities,temper brittleness,and hydrogen embrittlement of steel 30KhNMA with different concentrations of molybdenum

In recent years practical and scientific interest in investigating segregation processes to assess the mechanism of steel embrittlement by impurity elements has grown. This interest was noticeably stimulated by industrial use of new metallurgical technologies that ensure higher purity of steel with respect to impurity elements. It has become possible to decrease the content of expensive molybdenum due to the higher purity of steels without substantial change in their properties. In the present work the structure and properties of steel 30KhNMA with conventional and elevated purities, standard and reduced concentrations of molybdenum, and microadditions of V, Ti, and Nb are investigated.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 21–24, May, 1995.     

Irreversible temper brittleness of cast steel

Conclusion The dendritic heterogeneity affects the irreversible temper brittleness of cast steel occurring after tempering at moderate temperatures.Altai Tractor Factory. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 62–63, November, 1971.     

Temper embrittlement of 5140 steel

Isothermal temper-embrittlement studies were conducted on a 5140 steel at various temperatures for times as long as 3000 hr. Specimens from the embrittled steel were subjected to impact tests, metallographic examination, microhardness, and lattice-parameter measurements.     

Hydrogen embrittlement of a Ti-strengthened 250 grade maraging steel

Constant extension-rate tensile tests are performed to investigate the effects of strain rate and environmental hydrogen concentration on the tensile properties of various aged T-250 specimens. The 426 °C (800 °F) underaged specimens are very sensitive to strain rate; the 482 °C (900 °F) peak-aged specimens exhibit a reduced ductility under low strain rates; and the 593 °C (1100 °F) overaged specimens are insensitive to strain rate when tested in air. The excellent resistance to embrittlement of the overaged specimens in gaseous hydrogen could be associated with the extensive formation of reverted austenite and the incoherent Ni₃Ti precipitates. The tensile-fractured surfaces of such specimens reveal a ductile dimple fracture. However, the peak-aged specimens are susceptible to gaseous hydrogen embrittlement, and the embrittled region shows a primary fracture mode of quasi-cleavage. The least resistant to hydrogen embrittlement of the underaged specimens is characterized by a more brittle fracture appearance, that is, intergranular fracture, under a low strain rate or in the gaseous hydrogen environment.     

Susceptibility of a X80 steel to hydrogen embrittlement

The susceptibility to hydrogen of a X80 grade steel produced by a thermo‐mechanical control process (TMCP) has been investigated by keeping straining notched specimens under continuous charging conditions. Hydrogen charging was carried out either in synthetic seawater under potentiostatic control at ? 1000 mV vs. SCE or in sulphuric acid with an absorption promoter under galvanostatic control at ? 5 mA/cm². Results reported in terms of hydrogen effect on the ductility of the steel as a function of both cross head speed and root radius of the notch indicate that under the combined effect of cathodic charging, notch severity and very low strain rates the ductility of the TMCP X80 steel can be greatly affected by the presence of hydrogen. With notched specimens strained in air increasing loss of ductility in terms of reduction in area is observed as the notch severity increases. Notched specimens are fairly “more brittle” than smooth ones. As notched specimens are strained under cathodic charging at ? 1000 mV vs. SCE in the synthetic seawater, considerable decrease of reduction in area (RA) is observed. The same trend is observed for displacement and load at fracture both being connected with ductility even if a definite tendency is not always obtained. As the notched specimens are strained under cathodic charging in seawater the fracture morphology shows regions of mixed ductile and brittle fracture and zones where intergranular and/or transgranular fracture path are prevailing. Area of intergranular and transgranular fracture path, that can be more strictly associated with the presence of hydrogen, tends to increase as the strain rate decreases, which suggests a fracture behaviour influenced by hydrogen diffusion. Several mechanisms were involved in the rupture process in sulphuric acid depending on the notch geometry and, especially, on the cross head speed. Apparently, transgranular (quasi‐cleavage) rupture tends to prevail as the displacement becomes lower and lower. No evidence of intergranular fracture was observed.     

Tempered martensite embrittlement in a 32NiCrMoV125 steel

This study focused on tempered martensite embrittlement in a 32NiCrMoV125 steel through examination of the effects of austenite grain size and tempering temperature on the mechanical properties and fracture morphology of this material. Two different austenite grain sizes were obtained by austenitizing at 870 and 950 °C. After quenching, the specimens were tempered in the temperature range of 200–650 °C. The results obtained in this research indicate that by increasing the tempering temperature, the strength and hardness decrease, but ductility increases. However, impact testing indicated that tempered martensite embrittlement occurred when samples were tempered in the range of 250–400 °C. Fractography revealed intergranular and quasi-cleavage fracture. In summary, increasing the austenite grain size decreased strength, but increased impact toughness, except for samples tempered between 200 and 350 °C.     

Ni-Cr钢中P的非平衡晶界偏聚现象

采用Auger电子能谱仪分析了经过1000℃淬火后600℃时效过程的Ni-Cr钢中元素磷的晶界偏聚浓度,得到晶界P的偏聚浓度随时效时间变化的动力学曲线。结果表明,Ni-Cr钢在600℃时效60 min时,P的晶界偏聚浓度出现极大峰值,与平衡晶界偏聚模型不符。利用溶质的非平衡晶界偏聚模型进行分析,证实这是由于钢中P的非平衡偏聚临界时间现象引起的。     

Liquid zinc embrittlement of twinning-induced plasticity steel

The susceptibility of a Fe22Mn0.6C twinning-induced plasticity steel to liquid zinc embrittlement has been investigated by performing hot tensile tests on bare and electrogalvanized specimens using a Gleeble thermomechanical simulator. Tensile tests were carried out at different temperatures and strain rates. The studied steel can be severely embrittled by liquid zinc (drastic reductions in elongation at rupture and fracture strength) given particular conditions of temperature and strain rate.