Improvement of the corrosion behavior of AISI 304L stainless steel by deep rolling treatment under cryogenic cooling

Abstract

The effects of deep rolling parameters; particularly, work speed and cooling conditions (dry and cryogenic) on the surface integrity of AISI 304L machined samples and their further impact on uniform and localized corrosion behavior in chloride environment were experimentally investigated in this work. The electrochemical behavior of machined and deep rolled samples was assessed using cyclic potentiodynamic polarization tests in synthetic seawater. Findings of this study exhibit that grain refinement generated in the surface layers leads to improved corrosion behavior of deep rolled specimens with regard to machining state. In addition, machined samples deep rolled at a speed of 25 m/min, without cooling, showed better corrosion resistance than those processed under cryogenic cooling. However, the application of cryogenic deep rolling at speeds of 75 m/min and 120 m/min significantly enhanced the electrochemical behavior of mechanically treated specimens. It was found that the corrosion behavior of AISI 304L deep rolled components is related to combined factors (surface roughness, strain-induced martensite, microhardness, residual stress). Despite of high amounts of strain-induced martensite that can deteriorate the electrochemical behavior, it was shown that deep rolled specimens under cryogenic cooling with low surface roughness depict better uniform and localized corrosion resistances.

Influence of the hydrostatic ball burnishing on surface quality and ultra-microhardness

“…On Figure 7a the mean Ra values and their respective standard deviation are presented, for some levels of n an increase on burnishing speed tends to reduce the Ra values. For a single burnishing pass, an increase on burnishing speed, from 10 2 to 10 3 and from 10 3 to 10 4 mm/min, induces a decrease on Ra values, respectively to 0.15; 0.13 and 0.12 µm, this behavior is like the one observed by Gharbi et al [13]. The roughness profile however did not change significant as indicated by Figure 7b.…”

“…These authors also observed a grain refinement on a layer of 50 60 µm, which presented micro-sized grains. Grain refinement was also detected by Gharbi et al [13] that observed ultra-refined grains at the deep rolled AISI 304L surface, the altered layer presented a region with indistinct grain boundaries. Surface hardening and microstructural change on stainless steel after deep rolling was also observed by Muoz-Cubillos et al [14], these authors noticed strain hardening up to 340 µm of depth on AISI 304 steel, with the surface hardness increase reaching 157 HV 200g for the highest deep rolling force used (492 N).…”

“…The increase on AISI 304 hardness detected by Akkurt [11] after burnishing the internal surfaces of holes reached depths of almost 1 mm, with a surface with values 40 HV 0.05 higher than the ones obtained by the machining process. Gharbi et al [13] detected a hardened layer of 800 µm with surface hardness of approximately 500 HV 0.1 after deep rolling of AISI 304, the machined condition presented a hardened layer of 400 µm and surface hardness of 380 HV 0.1 . Also considering the treatment of AISI 304 Kongthep et al [16] detected an increase on surface hardness reaching a depth of approximately 0.4 mm.…”

“…The roughness reduction after burnishing was also observed by Shiou et al [20] after treating AISI 420 stainless steel, the roughness could be improved from Ra = 1.1 µm to Ra = 0.025 µm, when higher forces (650 N) and number of passes (3), and lower feeds (0.05) where used. Considering the treatment of AISI 304 Maximov et al [10] and Gharbi et al [13] studied its effect on roughness. The first ones observed that the roughness changed from Ra = 0.6 µm from the machined part, to 0.1 µm after burnishing.…”

Improvement in Fatigue Strength of Chromium–Nickel Austenitic Stainless Steels via Diamond Burnishing and Subsequent Low-Temperature Gas Nitriding

“…In recent years, many studies have been devoted to improving the surface integrity (SI) and operating behavior (wear, corrosion and fatigue resistance) of CNASS components by means of static SCW methods: ball burnishing [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], roller burnishing [6,[22][23][24][25] and DB [2][3][4][26][27][28][29][30][31][32][33][34][35]. There are relatively few studies devoted to improvement in the fatigue behavior of CNASS components by means of SCW [2][3][4][8][9][10][11][12][13]18,23].…”