Use nano-indentation meters to determine the effect of corrosion on the hardness of steel screws

As the most common failure mechanism in industry, corrosion of materials costs the U.S. economy hundreds of billions of dollars a year. Optimal corrosion control experiments are required to improve the life cycle of materials and asset management. Compared with corrosion tests conducted in natural environments, artificial acceleration tests can greatly accelerate the test speed. Laboratory corrosion tests can simulate very closely the effects of atmospheric environments on the corrosion of materials, and this laboratory corrosion test can significantly improve quality control levels and the development of new materials as well as protective coatings for challenging environments.
mechanical properties of the material can be reduced by corrosion. Carbon steel, for example, corrodes in atmospheric environments to form
γ-hydroxy-iron oxide (γ-FeOOH) and α-hydroxy-iron oxide (α-FeOOH). the loose and porous properties of γ-hydroxy-iron oxide (γ-FeOOH) and α-hydroxy-iron oxide (α-FeOOH) make them easy to absorb moisture, which in turn accelerates the corrosion process. β-hydroxy iron oxide (β-FeOOH), another iron oxide that is produced on the surface of steel when it is exposed to chloride-containing environments. Nano-indentation meters can control the depth of indentation to microns or even nanoscales, making it possible to quantify the hardness and Yang's mod of corrosion products produced on metal surfaces (see Figure 1). In the corrosion process, it provides a physicochemical field of view, which greatly facilitates our selection of the best alternative material for the target application.
this experiment, we showed the
Nanovea's mechanical tester, in nano-indentation mode, tested the effects of rust on the mechanical properties of two types of steel screws in corrosive media.
Test Environment
In this article, nano-indentation meters experiment mainly on screws made of two types of steel: stainless steel
316 (SS316) and alloy steel with a black oxide surface. The screws were immersed in a 3.5% (weight percentage) NaCl solution for 7 and 14 days, respectively, and then thoroughly cleaned with isopropylol and acetone solutions before being tested with nano-indentation meters. Use non-corrosive screws as a standard sample. The environmental parameters for nano-indentation determination are detailed in Table 1. At least 10 tests have been conducted in each test environment to ensure the repeatability of the test results.
results and discussion of
nano-indentation meters in stainless steel
SS316 and alloy steel after different corrosion times are detailed in Figure 2. Hardness is recorded in Figure 3 as a parameter representing corrosion time. The SS316 stainless steel screws are consistent in mechanical properties during 14 days of immersion in a 3.5% NaCl solution. Based on the controlled load-displacement curve, it has a constant nano-indentation hardness of about 4.5GPa. Due to the strengthening of the mechanical properties of the black iron oxide layer on its surface, alloy steel screws showed a higher surface hardness of -6.7GPa, but after 7 days of impregnation in 3.5% NaCl solution, the surface hardness of the alloy steel screws was rapidly reduced to about 4.6GPa.
in order to study the reasons for the decrease in the hardness of alloy steel screws, alloy steel screws impregnated in
The evolution of corrosion after 7 and 14 days in NaCl solutions is shown in Figures 4 and 5, respectively. We can observe that in Figure 4, red corrosion products gradually accumulate on the surface of alloy steel screws, and in Figure 5, these red corrosion
products are dispersed into the
NaCl solution. The formation of this porous and loose red rust leads to the degradation of the properties of the super-hard black iron oxide layer on the alloy surface. Finally, its surface hardness was reduced from 6.7GPa to 4.6GPa.
-accelerated corrosion tests in corrosive media simulate the metal effects of the natural environment and are strategically important for quality control and research and development of new materials and heavy anti-corrosion coatings for severely corrosive environments. Nano-indentation meters allow us to quantify the effects of corrosion on the mechanical properties of various metals or coatings for specific applications. The evaluation and study of the mechanical properties of metal surfaces can give us a deeper understanding of the degradation mechanism hidden in the formation of corrosion products. Metal degradation is very serious in various industrial applications such as petroleum industry and marine industry. As an upgraded version of carbon steel, stainless steel enhances and enhances the durability and reliability of mechanical components exposed to harsh environments.
conclusion
nano-indentation tests were carried out using the
Nanovea mechanical tester on two sets of screws made of SS316 stainless steel and alloy steel, respectively. Artificial accelerated corrosion tests in salt solutions result faster results than those obtained from natural climates, which can significantly assist in the development of new alloys and coatings. Corrosion reactions have a negative effect on the mechanical properties of metal surfaces, e.g. alloy steel has a surface hardness reduced from 6.7GPa to 4.6GPa after the first 7 days of 3.5% NaCl solution impregnation. This hardness value remains unchanged in the next 7-day impregnation corrosion experiment. Correspondingly, the stainless steel SS316 shows constant hardness throughout the corrosion test, demonstrating the importance of corrosion resistance to reliable mechanical properties.
testers offer versatile nano, micron and larger test modules on the same platform. Both modules are available in scratch testing, hardness testing and friction testing to provide a wider and friendlier testing experience.
referenceles /Publ ications /ccsupp.pdf.。 Almeida, E.; Morcillo, M.; Rosales, B.; Marrocos, M. Atmospheric orrosion of Mild Steel Part I − Rural and Urban Atmospheres," Materisals and Corrosion, vol. 51, no. 12, pp.859-864, 2000.。 Kamimura, T.; Hara, S.; Miyuki, H.; Yamashita, M.; Uchida,H. Composition and Protective Ability of Rust Layer Formedon Weathering Steel Exposed to Various Environments, Corrosion Science, vol. 48, no. 9, pp. 2799-2812, 2006.
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