Metallographic diagram of granular bainite 18Cr2Ni4WA (furnace cooled at 950°C)

18Cr2Ni4WA is a cast austenitic heat-resistant steel with good metallurgical properties and reasonable mechanical properties. This steel is commonly used for components operating at temperatures up to 950°C in the aerospace, power generation and nuclear industries.

The microstructure of this steel can be analysed using a quantitative analysis of grains and possible growth structures. Qualitatively, the analysis consists primarily of determining the composition, abundance, size and shape of individual grains and their components.

Grain size of 18Cr2Ni4WA can be determined by taking a standard metallographic sample and etching it in a suitable etchant. The etched sample is then observed under a microscope and image analysis is performed to determine grain size, shape, orientation and boundary distributions.

The amount of impurities present in the steel can be quantified by preparing a polished sample and viewing it under a scanning electron microscope. This analysis can reveal the type and concentration of inclusions present.

To determine the grain boundaries and the amount of segregation present in the sample, an optical microscope can be used. This microscope is capable of magnifying the sample up to 500X, allowing for a more detailed view of grain boundaries and other structural defects.

A closer look at the microstructure can be obtained using X-ray diffraction (XRD) techniques. XRD techniques detect light reflected from crystal planes, allowing for the determination of crystal plane orientation and the presence of any impurities or segregations.

Similarly, transmission electron microscopy (TEM) can be used to analyse the microstructure of 18Cr2Ni4WA. TEM is capable of providing detailed information on the existence of defects, impurities, segregation and grain boundaries.

In summary, analysis of the metal structure of 18Cr2Ni4WA can be completed using a variety of techniques. These techniques allow for a more detailed understanding of the metal’s properties and its suitability for different applications.

The 18Cr2Ni4WA (950℃ furnace-cooled) granular Bainite microstructure has a combination of ferrite and retained austenite.The ferrite is arranged in acicular or lath broad plates.The ferrite consists of needle-like crystals with a very fine lamellar structure within it.The retained austenite is usually found in scattered patches,located in the boundaries of the ferrite grains or in small pockets or areas of much less grain refinement.The surface of the Bainite reveals a very fine gray,matte finish indicating that the heat treatment was successful in refining and toughening the material.The micrograph also shows the presence of very small carbides distributed throughout the ferrite,although this may not be the case for all Bainite structures depending on the starting material,heat treatment and cooling rate.It is interesting to note that,in this case,the Austenite retension is found to be quite low.Overall,the micrograph displays a typical Bainite structure.

The Bainite method of heat treatment is most common for materials such as low-carbon,alloy tool steels,as well as some plain-carbon steels.The Bainite structure not only provides dynamic strength,but also good wear and fatigue resistance.This structure further allows for a low-cost manufacturing process,as it does not require intricate tooling and machinery.The Bainite structure is also very stable due to the combination of the ferrite and austenite,which ensures that it can sustain the effects of environmental or oxidation.

Therefore, 18Cr2Ni4WA (950℃ furnace-cooled) granular Bainite heat treatment is seen as a reliable,cost-effective solution for certain steels and other materials, as it offers a combination of mechanical properties such as strength and wear resistance for a wide range of applications.