Steels microstructure

The first case study shows how a knowledge of steel microstructures can help us trace the chain of events that led to a damaging engineering failure. 

R. W. K.. Honeycombe, Steels Microstructure and Properties (Metals Park, Ohio) ASM 1981.211-... 

Figure 1.10 Photo and details of a stainless steel microstructure cube generated bySLM method. Clearly, the single welding beads that have been generated layer by layer to form the walls are shown.

Figure 3.19. Relative phase stabilities of Ni-Cr steels. Reproduced with permission from Steels Microstructure and Properties, Honeycombe, R. W. K. Bhadeshia, H. K. D. H. 2nd ed., Wiley New York, 1995.

Honeycombe, R.W.K., Steels microstructure and properties, in Metallurgy and Materials Science, R.W.K. Honeycombe and P. Hancock, Eds., London Edward Arnold, 1981. 

Duplex stainless steels contain both ferrite and austenite in approximately equal amounts Alloy 2205 is an example. Figure 21.9 illustrates the microstructure of a duplex stainless steel microstructure in plate material. Typically, the duplex stainless steels contain 17 wt% or more chromium and <7% nickel. The more corrosion-resistant types contain at least 2% molybdenum. They are much stronger than the austenitic stainless steels, permitting a thinner section thickness. Thus, while they may cost more per pound, they may cost less per piece. 

X80 pipeline steel microstructure consisted of a polygonal ferrite and bainitic ferrite matrix with martensite/austenite (M/A) constituents distributed along grain boundaries (Fig. 8.13). The aUoy inclusions are Si, A1 oxide. Si-ferric carbide, and Al-Mg-Ca-O mixture. Hydrogen cracks are initiated even in the absence of external stress. Cracks are initiated in the presence of Si and A1 oxide-enriched inclusions [69]. 

Hor] Horovitz, M.B., Neto, F.B., Garbogini, A., Tschiptschin, A.P., Nitrogen Bearing Martensitic Stainless Steels - Microstructure and Properties , ISIJ Int., 36(7), 840-845 (1996) (Experimental, Meehan. Prop., Morphology, 14)... 

To overcome these medium- to long term substrate degradation issues, the surface of the structured material has to be properly prepared and protected during the phase of assembly and catalyst coating. This feature is so important that, as mentioned before, almost no relevant and detailed long-term studies have been reported yet on the corrosion effects on stainless-steel microstructured platelets. 

Figure 4J Experimental temperature profile measured for the steam reforming of methane in a stainless-steel microstructured reactor at 800°C...

Elevated tenperature damage to refinery furnace tubes may consist of corrosion-dependent failures and temperature-related defects connected with degradation of the steel microstructure and creep damage. At high temperatures, a steel tube may fail due to deformation and creep fracture even at a stress level well below the yield stress, whereas at low temperatures corrosion and microstmcture degradation processes prevail. These two ranges can be determined by yield strength and rupture stress vs temperature curves [8]. 

Fig. 9. Energy Dispersive X-ray Analysis and SEM of the rhodium containing alumina catalyst layer on top of the steel microstructure a) catalyst prepared by segregation of alumina during annealing on FeCrAlloy with subsequent incipaent wetness impregnation with rhodium precursor, b) sol-gel alumina layer with rhodium by incipient wetness impregnation on alloy 800.

De Las Heras E, Egidi DA, Corengia R Gonzalez-Santamaria D, Garcfa-Luis A, Brizuela M., Lopez GA, Flores Martinez M. (2008) Duplex surface treatment of an AISI 316L stainless steel Microstructure and tribological behaviour. Surf Coat Technol 202 2945-2954. 

Depending on the steel s composition, the process temperatures, and particularly the soaking times, layers of varying depths can be achieved. As the alloy content of the steels increases, the surface hardness achievable increases, and the layer thickness achievable declines. It helps to protect against deformation if the substrate is hard enough. Excessively intensive treatment can make the material brittle (nitride formation at the grain boundaries of the steel microstructure), leading to premature mold failure. 

Positron annihilation spectroscopy can provide essential information about the deterioration in the mechanical properties of RPV steels (microstructural defects and precipitates) during their irradiation, which is known as neutron embrittlement. Currently, there are three main techniques based on annihilation phenomena positron lifetime spectroscopy, Doppler-broadening spectroscopy and angular correlation measurements. 

Changes in steel microstructure due to a starting phase transition from bcc to fee were observed in all Western types of RPV steels using PAS at 725-750 °C. For Russian RPV steels, this phase transition was not observed up to 800 °C. The same phenomenon also appeared with MS, where the presence of paramagnetic austenite was clearly detected at 750 °C in Western batches of steels and at 800-850 °C in Russians steels. 

What roles do alloying elements play in the mlcrostructure of an RPV steel How can the analytical methods focused on steel microstructure be effectively... 

Honeycombe RWK (1981) Steels - microstructure and properties. Edward Arnold, London... 

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