PSI - Issue 22

L. Sena, R. C. Reis, A. A. Monteiro , C. Oliveira, C. Reis , P. L. Silva, Analysis of iron FC 250 microstructure under the effect of phosphoric acid corrosion ,2019

L. Sena et al. / Procedia Structural Integrity 22 (2019) 171–180

176

5.0

Temperatura 298 K

4.5

323 K 373 K

4.0

3.5

2.0 Perda Mássica (x10 -3 kg) 2.5 3.0

1.5

1.0

0

50 100 150 200 250 300 350 400

Tempo de Imersão (x10 3 segundos)

Fig. 3. Mass loss values, as a function of immersion time for different temperatures, in percentage of 3% acid.

Costa (2015) compared the corrosion resistance in cast irons with different microstructures, one of perlite and one bainitic, both in solution that simulated the condensate obtained through the flue gases. It may be seen that iron microstructure is an important factor in determining the corrosion rate. Although no material is free of corrosion in the test medium, the perlitic microstructure exhibits less corrosion product formation than the bainitic material. This result is due to the phosphorous eutectic phase in the perlitic microstructure, which has enormous resistance to the solution attack and remains on the surface together with the matrix corrosion products (COSTA, 2016). Thus, it was possible to identify by means of an optical microscope, the iron structure used in the tests, as perlite matrix and the existence of the phosphorous eutectic phase (Figure 4).

Fig. 4. Optical microscope photomicrograph, of the Gray Cast Iron microstructure, with perlite matrix, after chemical attack with 2% Nital (100x magnification).