Surface topography and corrosion resistance of AISI 630 stainless steel after finish turning under different cooling methods

Abstract

AISI 630 stainless steel (SS) is widely used for medical devices. This paper describes the effects of dry, flood and minimum quantity lubrication (MQL) machining conditions on the surface topography and corrosion resistance (CR) of AISI 630 SS after finish turning. Small areas of valleys and large areas of peaks were observed on the surfaces with minimum surface roughness (SRmin) after dry machining at the feed rate (f) of 0.1 mm/rev and at the f = 0.14 mm/rev using the MQL method. Only small areas of peaks were observed after flood machining at the f = 0.1 mm/rev. Regardless of cooling methods, regularly distributed deep valleys and high peaks were observed on the surfaces with maximum surface roughness (SRmax) machined at the f = 0.35 mm/rev. Surfaces of the samples with SRmin and SRmax under flood machining and with SRmax under MQL machining had high oxygen content in the range of ∼ (20−30) %wt. during 7–72 days of the sample storage in SBF. Such an oxygen content is observed on the machined surfaces for which maximum peak height Sp parameters were in the range of ∼ (10–16) μm and maximum valley height Sv – ∼ (8–10) μm. Compared to SRmin, high ion diffusion was observed on surfaces with SRmax. This means that surfaces with regular deep valleys and high peaks provide high ion mobility between them. In addition, compared to dry and MQL machining, higher resistivity was obtained for the samples under flood machining. Depending on the industrial application requirements, the passivity and CR of AISI 630 SS can be modulated by selecting machining conditions and surface topography. It has been established that in order to achieve favorable CR of the AISI 630 SS surface after finish turning, the flood method is recommended.