Ferritic matrix

On tempering or annealing martensite, bainite or even pearlite at even higher temperatures (about 970K) a structure consisting of coarse cementite spheroids (readily visible in a light microscope) in a ferrite matrix is obtained. This is the most stable of all ferrite/cementite aggregates, and it is also one of the softest. 

Table II. Size Reported as Means and Standard Deviations for Spheroidal Carbides In Ferrite Matrix (left) and for Atomized and Sponge Iron Powders (right).

C = ferritic matrix with carbide and austenite precipitates. 

Carbide particles (M23C6), formed during quenching, in the ferritic matrix as in fig 5 at C. Electron micrograph of thin foil (TEM). 

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]. 

The samples of FesC examined in the present investigation were in the form of second-phase particles in the Fe-1.83 wt.% C alloy. A micrograph of FesC in the ferrite matrix is shown in Fig. la. A "graphitized" Fe target was prepared from a Fe—1.83% C alloy by first... 

Photograph 1-3 Unusually large belite in UPC in Aspdin paste. Note prominent lamellar extensions into ferrite matrix. Probably an effect of CaO resorption during slow cooling. (S A6608)... 

Photograph 7-50 Dense, coarsely crystalline clinker showing large, blue belite crystals (center right) with numerous exsolved dotlike inclusions tan areas (upper left) of apparently nonlamellar belite secondary belite dots in ferrite matrix (center left). Coal-fired, wet-process kiln with temperature known to be approximately 1650°C. (S A6670)... 

Photograph 7-58 Belite striations in light blue alite. Multicolored, round belite showing typical lamellae, but somewhat scalloped cross section. Small secondary belite in brightly reflecting ferrite matrix. Clinker sample contains remnants of chrome-magnesia refractory brick. (S A6678)... 

Photograph 9-3 Microcracks (from etching ) in alite crystals in ferrite matrix. (S A6730)... 

Par] studied steels containing 1.65 mass% V with 0.26 mass% C that were isothermally transformed in the temperature range of 600 to 750°C using TEM and selected electron microdiffraction. On the contrary to the previous reports ferrite matrix and carbide precipitates possessed the Baker s-Nutting orientation relationship with no difference of carbide morphology. 

Bainite, a plate- or spearhead-shaped product consisting of a ferrite matrix in which carbide particles are dispersed. The bainitic transformation mechanism depends sensitively on alloy composition and the temperature of transformation, yielding essentially two microstructural variants. A somewhat coarser transformation product formed at about 450 is called upper bainite and a finer transformation product formed at about 350 °C is termed lower bainite. 

Figure 10.36 Microstructures of (A) composition 3 (see Table 10.4) after sintering for 0.5 h at 1550"C, showing rounded grains in a silicate matrix (B) composition 3 after sintering for 8 h at 1550 C (c) composition 2 after sintering for 8 h at 1550T (D) a composition of 85 wt% CaO(15 wt% Ca2Fe205> after firing for 8 h at 1550°C, showing rounded grains in a ferrite matrix. (The very dark areas are pores, some of which contain Araldite.) (From Ref. 2.)...

Traditional alloys, such as S32900, contain about 15-20 % austenite in a ferritic matrix. Modem duplex stainless steels (e.g., S32950, S32550, S32205) are alloyed with nitrogen to increase the austenite volume fraction to about 30-50 %. Because of their ferrite content, duplex stainless steels are magnetic. 

The resistance of the matrix and carbides to wear is a complex phenomenon due to hardness of the individual components. Ferrite matrix has a mere hardness of 150-250 HV. Austenite, as found in many stainless steels, has a hardness of 300-500 HV. Martensite, which is sometimes obtained by very fast solidification or chilling of the casting, has a hardness of 500-1000 HV. The iron carbides FejC have a hardness in the range of 850-1000 HV, Chromium carbide (FeCr)7C3 has a hardness of 1400-1600 HVas primary carbides and a hardness of 1200-1400 as eutectics (Huggett and Walker, 1992). 

During electron microscope investigation Fig. 17.1 it was founded that the fine material stmcture of springs produced by SSTMT method was tmiform with characteristic increased density of dislocations, subbotmdaries, disperse equally distributed carbide particles. Average ferrite matrix substmcture elements constituted 20. .. 40 nm at the dispersion of up to 100 nm. 

MoPlus stainless steel is a trademark of Carpenter Technology. It is a two-phase (duplex) alloy with approximately 45% austenite distributed within a ferrite matrix. Alloy S32950 displays good resistance to chloride SCC, pitting corrosion, and general corrosion in many severe environments. The chemical composition is shown in Table 12.2. 

The chemical composition of Ferralium 255 is shown in Table 12.4. This is a duplex alloy with austenite distributed within a ferrite matrix. This alloy has a maximum service temperature of 500°F (260°C). 

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