Wear 251 (2001) 1257–1264 Corrosion–erosion of nitrogen bearing martensitic stainless steels in seawater–quartz slurry A. Toro a,∗ , A. Sinatora b , D.K. Tanaka b , A.P. Tschiptschin a a Metallurgical and Materials Engineering Department, University of São Paulo, Av. Prof. Mello Moraes 2463, CEP 05508-900 São Paulo, Brazil b Mechanical Engineering Department, University of São Paulo, Av. Prof. Mello Moraes 2463, CEP 05508-900 São Paulo, Brazil Abstract AISI 410S stainless steel was nitrided at 1473 K in N 2 atmosphere, direct quenched and tempered at temperatures between 473 and 873 K. Martensitic cases with circa 0.52 wt.% N at the surface were obtained. Corrosion–erosion tests were carried out in slurries composed by quartz particles and tap or substitute ocean water. The concentration of solids, the impact angle and the pH of solution were fixed, while the temperature, surface changes and mass losses were monitored during the tests. Quenched and tempered AISI 410 and 420 stainless steels were used as comparison materials. The results showed that the erosion resistance and the corrosion–erosion resistance of the nitrided steel tempered at 473 K were higher than those of the AISI 410 and 420 steels tempered at the same temperature. This behavior was due to the higher hardness and better intergranular, pitting and generalized corrosion resistance of the nitrided alloy. The synergism between corrosion and wear was more important in the AISI 410 and 420 samples. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Slurry erosion; Corrosion–erosion resistance; Nitrogen in stainless steels 1. Introduction Martensitic stainless steels have been used in components operating under wear, corrosion and wear–corrosion condi- tions found in distillation towers, slurry pumps and mixers of chemical products [1,2]. These materials show high me- chanical properties and moderate corrosion resistance, but when under erosion action by the presence of hard particles in aqueous solutions their performance is reduced due to a synergistic effect between wear and corrosion mechanisms [3–5]. Much information concerning the relationship between surface properties and slurry erosion behavior is available in literature for a number of materials, including austenitic and martensitic stainless steels. These results have been acquired as a function of pH, solid content and temperature of solution [4,6–8], as well as hardness and morphology of abrasive particles [9,10]. Peterson et al. [11] and Zum Gahr [12] reported the erosion wear mechanisms in steels to the microstructure of the eroded surfaces, showing that the brittle or ductile nature of phases present can determine the wear behavior of the tribosystem. Wang–Xu [7] clas- sified a wide variety of alloys as a function of their mass ∗ Corresponding author. loss under erosion in silica–water slurry, establishing a con- sistent relationship between hardness and wear resistance. On the other hand, Aiming et al. [3] reported the existence of a ‘breakaway’ impingement velocity, which marks the transition from moderate to severe erosive wear conditions. Generally speaking, wear of ductile materials under slurry erosion can differ from that under dry erosion conditions [13]. Maximum wear rates of ductile metals submitted to solid particle impingement are commonly observed for im- pingement angles up to 30 ◦ . Conversely, under slurry wear conditions, the maximum erosion rate can be reached at normal incidence, even for ductile materials [3,14]. Spalling of second phase particles and the existence of passive lay- ers may explain this behavior in high-alloyed steels and, in particular, stainless steels [7,8]. Nitrogen can improve the surface properties of industrial steel components. Rogers et al. [15] showed that sub-critical nitriding of 2.25–1Mo steels increases the resistance to corrosion–erosion of heat exchanger tubing for bubbling fluidized bed combustors, and Berns et al. [16] improved the slurry erosion resistance of stainless steels used in petrochemical applications by solution nitriding of stainless steels at high temperature (1423 K). In addition, a number of laboratory tests and theoretical models have been proposed to explain the beneficial effects of nitrogen in corrosion 0043-1648/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0043-1648(01)00765-7