Structure and Mechanical and Corrosion Properties of New High-Nitrogen Cr-Mn Steels Containing Molybdenum

The structure, mechanical properties, and pitting corrosion of nickel-free high-nitrogen (0.8% N) austenitic 06Kh18AG19M2 and 07Kh16AG13M3 steels have been studied in various structural states obtained after hot deformation, quenching, and tempering at 300 and 500 degrees C. Both steels are shown to be resistant to the gamma -> alpha and gamma -> epsilon martensite transformations irrespective of the decomposition of a gamma solid solution (06Kh18AG19M2 steel). Austenite of the steel with 19 wt % Mn shows lower resistance to recrystallization, which provides its higher plasticity (delta(5)) and fracture toughness at a lower strength as compared to the steel with 13 wt % Mn. Electrochemical studies of the steels tempered at 300 and 500 degrees C show that they are in a stable passive state during tests in a 3.5% NaCl solution and have high pitting resistance up to a potential E-pf = 1.3-1.4 V, which is higher than that in 12Kh18N10T steel. In the quenched state, the passive state is instable but pitting formation potentials E-pf retain their values. In all steels under study, pitting is shown to form predominantly along the grain boundaries of nonrecrystallized austenite. The lowest pitting resistance is demonstrated by the structure with a double grain boundary network that results from incomplete recrystallization at 1100 degrees C and from the existence of initial and recrystallized austenite in the 07Kh16AG13M3 steel. To obtain a set of high mechanical and corrosion properties under given rolling conditions (1200-1150 degrees C), annealing of the steels at temperatures no less than 1150 degrees C (for 1 h) with water quenching and tempering at 500 degrees C for 2 h are recommended.