Abstracts Book - IMRC 2018

• SE4-P031
THERMAL FATIGUE EFFECT ON THE CORROSION RESISTANCE OF
THE MARTENSITIC STAINLESS STEEL HARDFACING
Luis Bejar 1 , Engelbert Huape Padilla 1 , Ariosto Medina 2 , Hector Carreón 2 , Jose G. Chacon Nava 3 ,
Manuel Alejandro Paniagua 1
1 Universidad Michoacana de San Nicolás de Hidalgo, Facultad de Ingeniería Mecánica, Mexico.
2 Universidad Michoacana de San Nicolás de Hidalgo, Instituto de Investigación en Metalurgia y
Materiales, Mexico. 3 Centro de Investigación en Materiales Avanzados, S.C., Laboratorio de
Deterioro de Materiales y Recubrimientos, Mexico.
Continuous casting rolls are subjected to extreme temperature fluctuations and
harsh environmental conditions during service. Fluctuating thermal stresses
develop due to changes in the temperature of the roll surface as it contacts the
hot slab followed by water spraying as the roll revolves. In the present work, the
termal fatigue effect on the corrosion resistance of martensitic stainless steel in
synthetic seawater deposited as hardfacing was studied, weldment have been
obtained using an automatic flux-cored arc welding process (FCAW). The rolls
were surfaced with a 414N tubular wire. The welding parameters were: Arc
voltage 26 V, Welding speed 2.0 mm/s, Stick-out 28 mm and Welding current
300A; the samples were subjected to thermal cycles as follows: samples were
initially heated to 600°C and cooled to 550°C to comply a thermal cycle, in this
sense the samples were subjected to 100 cycles (M1, 1.38 hr), 1000 cycles (M2,
13.8 hr) and 2000 cycles (M3, 27.7 hr). Due to thermal cycles, samples
microstructures consist to tempered martensite. According to the results, all
samples show preferential corrosion sites, where corrosion products inside
pitting were found. SEM-EDS results show corrosion products rich in O and Fe,
indicating that iron oxide is formed, also Cr presence. On the other hand, the
electrochemical results exhibit an resistive behavior in low frequencies to 12 and
24 hours, at high frequencies all samples exhibit a Warburg impedance due to
diffusion of Cr and Fe to 12 hours. While to 24 hours, at high frequencies only
M1 and M3 exhibit Warburg impedance. M2 shows a charge transfer resistance,
indicating more corrosion resistance in seawater. This behavior can be
attributed to the interaction of the carbides present, steel 414 as hardfacing
presents a martensitic microstructure with M23C6 (rich to Cr) carbides in limits
grain due to low rate cooling according to literature. After 100 thermal cycles
M23C6 transform to M6C (rich to Mo) favored by N addition, N decreases with
the increase of the cycles. Then, after 1000 thermal cycles M6C transforms to a
complex M23C6 (M = Mo0.16, Cr0.16, Fe0.68) where Cr returns to the matrix.