Enhanced mechanical properties induced by refined heat treatment for 9Cr–0.5Mo–1.8W martensitic heat resistant steel

Low cycle fatigue and creep fatigue interaction behavior of 9Cr-0.5Mo-1.8W-V-Nb heat-resistant steel at high temperature

A physically-based model has been proposed in a previous study to predict the creep-fatigue lifetime of P91 steel which is of the 9-12%Cr steels family (Fournier et al., 2008) [1]. The present study applies this model to three other different 9-12%Cr martensitic steels P92, Ti1, and VY2. All these materials were tested under pure fatigue conditions. Whereas for a P92 steel, the experimental lifetimes are very close to those of the P91 steel, the two other steels present a significantly shorter fatigue and creep-fatigue lifetime. First the damage mechanisms were observed on these three materials and compared to those identified on P91. Taking into account the increased cracks density and the grain size effect on crack initiation, the model is able to account quite accurately for these different fatigue and creep-fatigue lifetimes.

Lifetime prediction of 9-12%Cr martensitic steels subjected to creep-fatigue at high temperature

Evolution of microstructure and mechanical properties of 9Cr ferrite/martensite steels with different Si content after long-term aging at 550 °C

Influence of prior low cycle fatigue on microstructure evolution and subsequent creep behavior

The centrifugally cast 20Cr32Ni1Nb stainless steel aged at 950 ℃ from 200 h up to 5000 h was investigated on the mechanical properties and microstructural evolution using post-aged tensile tests, post-aged Charpy impact tests, Optical microscopy (OM) observations, and field emission-scanning electron microscopy (FE-SEM) examinations. Experimental results indicate that the as-cast microstructure of the steel typically consists of a supersaturated solid solution of austenite matrix with a network of interdendritic primary carbides (NbC and M23C6). During aging process, the growth and coarsening of NbC carbides and M23C6 carbides as well as the transformation of NbC carbide into G phase take place. Meanwhile, the transformation of NbC into G phase releases C into the matrix during aging exposure. This released C tends to combine with Cr, and forms M23C6 at the dendrite boundaries. Compared with a continuous reduction of the elongation in the whole aging period, the strength parameters (σult and σys) exhibit an initial increase followed by a continuous decrease with the aging time prolonged from 1000 h to 5000 h. Additionally, the variation of Charpy impact absorbed energy is relatively complex during aging process. The microstructural evolution during long-term aging process is consistent with the variation of mechanical properties.

Effect of long-term aging on microstructural stabilization and mechanical properties of 20Cr32Ni1Nb steel

A series of tensile tests, Charpy impact tests, optical microscopy observations, and field emission-scanning electron microscopy examinations, were carried out to investigate the mechanical properties and microstructural evolution of 20Cr32Ni1Nb steel. Experimental results indicate that the as-cast microstructure of the steel typically consists of a supersaturated solid solution of austenite matrix with a network of interdendritic primary carbides (NbC and M
 23C6). In the ex-service samples, large amounts of secondary carbides precipitate within austenite matrix. Besides the growth and coarsening of NbC and M
 23C6 carbides during service condition, the Ni-Nb silicides known as G-phase (Ni16Nb6Si7) are formed at the interdendritic boundaries. The microstructural evolution results in the degradation of the mechanical properties of the ex-service steel. In addition, the precipitate rate of G-phase, depending in part on Si content, varies greatly for the 20Cr32Ni1Nb steel, which plays a key role in the long-term microstructural stability of the steel. Based on the X-ray diffraction data, time–temperature–transformation curve for the steel is obtained from the aged specimens.

Formation of G-phase in 20Cr32Ni1Nb Stainless Steel and its Effect on Mechanical Properties

Abstract A series of uniaxial tensile tests were carried out at different strain rate and different temperatures to investigate the effects of temperature and strain rate on tensile deformation behavior of P92 steel. In the temperature range of 30–700 °C, the variations of flow stress, average work-hardening rate, tensile strength and ductility with temperature all show three temperature regimes. At intermediate temperature, the material exhibited the serrated flow behavior, the peak in flow stress, the maximum in average work-hardening rate, and the abnormal variations in tensile strength and ductility indicates the occurrence of DSA, whereas the sharp decrease in flow stress, average work-hardening rate as well as strength values, and the remarkable increase in ductility values with increasing temperature from 450 to 700 °C imply that dynamic recovery plays a dominant role in this regime. Additionally, for the temperature ranging from 550 to 650 °C, a significant decrease in flow stress values is observed with decreasing in strain rate. This phenomenon suggests the strain rate has a strong influence on flow stress. Based on the experimental results above, an Arrhenius-type constitutive equation is proposed to predict the flow stress.

Effects of Temperature and Strain Rate on Tensile Deformation Behavior of 9Cr-0.5Mo-1.8W-VNb Ferritic Heat-Resistant Steel

On the creep behaviour of HP40Nb alloy with high-temperature carburisation damage

Creep damage mechanism of 20Cr32Ni1Nb steel at high temperatures

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