Corrosion and microstructural characterization of martensitic stainless steels submitted to industrial thermal processes for use in surgical tools

Abstract

Introduction: The mechanical properties and corrosion resistance of a material are dependent on its microstructure and can be modifi ed by phase transformation. When a phase transformation occurs in a material it usually forms at least one new phase, with physical-chemical characteristics that differ from the original phase. Moreover, most phase transformations do not occur instantly. This paper presents an evaluation of the phase transformation of martensitic stainless steels ASTM 420A and ASTM 440C when submitted to different thermal processes. Methods: Dilatometry tests were performed with several continuous heating and cooling rates in order to obtain the profi les of the continuous heating transformation (CHT) and continuous cooling transformation (CCT) diagrams for these two types of steel. Also, the temperature ranges for the formation of the different phases (ferrite and carbides; ferrite; austenite and carbides; non-homogeneous and homogeneous austenite phases) were identifi ed. Rockwell hardness (HRC) tests were performed on all thermally treated steels. Anodic and cathodic potential dynamic polarization measurements were carried out through immersion in enzymatic detergent as an electrolyte for different samples submitted to the thermal processes in order to select the best routes for the heat treatment and to recommend steels for the manufacture of surgical tools. Results: The martensitic transformation temperature tends to increase with increasing temperature for the initiation of cooling. The 440C steel had a higher hardness value than the 420A steel at the austenitizing temperature of 1100 °C. Above the austenitizing temperature of 1100 °C, the material does not form martensite at the cooling rate used, which explains the sharp decline in the hardness values. Conclusion: The study reported herein achieved its proposed objectives, successfully investigating the issues and indicating solutions to the industrial problems addressed, which are frequently encountered in the manufacture of surgical instruments.

Influence of Chemical Inhomogeneities on Local Phase Stabilities and Material Properties in Cast Martensitic Stainless Steel

“…After cooling from 1150 °C, however, the strain/temperature curve appears differently showing an anomaly in the curve slope at 367 ± 10 °C. This phenomena has been detected in several MSS grades such as X20–45Cr13 and X40–60CrMoV14 and is described by Garcia de Andres et al as a successive transformation of austenite within different stages that are limited by different points for M s (M s,I , M s,II ). While M s,I is used to represent the temperature at which a massive transformation of austenite into martensite occurs, M s,II represents the splitting point above M s,I .…”

Effect of Pulsed Laser Ablation in Water on the Corrosion Behaviour and Surface Hardness of Stainless Steels

“…The surface microhardness (196.94 Hv) of lasertreated sample was slightly improved by 8.7% from the as-received sample (181.2 Hv). This finding can be attributed to the martensite formation on the surface, and the hardness was significantly higher than the core original material due to the rapid cooling effect of the PLAL treatment [28]. This gradual enhancement was only apparent at <400 µm depth from the surface.…”

Microstructural Changes During Short-Term Heat Treatment of Martensitic Stainless Steel—Simulation and Experimental Verification

“…In the literature different possibilities of evaluation are described and evaluated. [8][9][10][11][12] When looking at the change in length during cooling after austenitizing for 5 minutes with different evaluation methods something is noticeable which cannot be explained directly. With a few of the usual evaluation methods, incorrect martensite start temperatures would be determined.…”