An EGR valve assembly for use in an EGR valve body having a chamber with an inlet and outlet, comprising: (a) a stemmed reciprocable valve controlling flow into said chamber, the stem of said valve being constituted of an iron-based core material (i.e., 300 seeries stainless steel) impregnated at its outer surface with an ingredient (i.e., electroless nickel, ion implanted or chemically deposited nitrides, and electrolytic chromium) that is compatible in sliding contact with ceramic and provides said stem with a hardness at room temperature of at least 60 R.sub.c and a lubricating oxidized passivation layer at a temperatures in excess of 600.degree. C., and (b) a ceramic-based bushing (SiC, Si.sub.3 N.sub.4, Al.sub.2 O.sub.3, ceramic/metal composite) for sealingly guiding the reciprocal movement of said stem.