申論題

(c) A BCT unit cell in martensitic steel is simply a body-centered cube that has been elongated along the c-axis. Due to the reduced symmetry from BCC, the martensite (002) and (200) peaks spit in X-ray diffraction pattern may be observed. Today a martensitic steel sampie with unknown carbon concentration is detected to have 2θ = 5.7° difference between (002) and (200) planes while using X-ray diffraction with Cr-Ka radiation (wavelength = 0.22897 nm). From a linear relationship between carbon content and cla ratio: , and lattice parameter a = 0.2868 nm, evaluate the carbon concentration of this martensitic steel. (4%)