Abel Co Ltd (Yao City, Osaka Prefecture) showed the "Abel Black," which is a black stainless steel material whose corrosion resistance was improved by forming a thick passive film.
The material was exhibited at Monozukuri Partner Forum 2017, which Nikkei Monozukuri had Nov 20 and 21, 2017, at Shinagawa Intercity Hall in Tokyo.
While the thickness of the passive film of a normal colored stainless steel material is 0.2-0.3μm, the thickness of the Abel Black's passive film is 0.4μm. Abel increased the thickness by using both a chemical treatment and electrolytic corrosion to grow the film. As a result, even when the base material is SUS304, it is possible to realize a corrosion resistance eight times higher than that of SUS316, which is said to have a high corrosion resistance.
On the other hand, unlike plating and coating whose thickness is several micrometers or more, the irregularities of the base material's surface are not lost, making it possible to utilize the textures of mirror- and hairline-finished base materials as they are.
The passive film is not peeled by sheet-metal processing or laser processing. And the pre-surface-treated Abel Black material can be machine-processed as it is and does not require post-processing. In addition to mechanical parts, the Abel Black is used as a material for high-grade design building materials because it keeps a beautiful black color. As for base materials, it supports SUS304/316. Abel is also developing an austenite-based stainless steel.
The thickness of the passive films of normal stainless steel materials is several nanometers. On the other hand, in the case of colored stainless steel materials, the passive film is grown by chemical treatment (using chemicals), and the interference of light reflected from each of the passive film's surface and interface is used to produce color. Because the Abel Black has an even thicker passive film, its durability is also higher than those of colored stainless materials, Abel said.