The relation between the composition of MnS inclusions and crevice corrosion behavior of 18-8 stainless steel has been investigated metallographically in chloride media by an electrochemical method. It was found that in highly corrosive environments the tendency to crevice corrosion depends on the amount of MnS, while in mildly corrosive environments it depends on the amount of MnS and the Mn/S ratio. The tendency to the cessation of crevice corrosion, however, depends on the amount of MnS and the Mn/S ratio, in both environments. The morphology of corrosion near the entrance of crevices in steels in which the Mn/S ratio is large was pitting caused by preferential dissolution of the MnS inclusions. In the inner parts of the crevices, however, the matrix is dissolved preferentially independent of the Mn/S ratio. It was also determined metallographically that the corrosion potential in the inner parts of crevices is less noble than that near the entrances.

View full abstract

The author has previously reported on the boronizing and siliconizing of a WC -Co cemented carbide system. The aluminizing and chromizing of the same alloy were successively tested.
Research results are summarized as follows:
(1) The mass and hardness of the alloy increased after aluminizing for a short period but decreased after a long period. The optimum time for the high frequency heating of this alloy was therefore concluded to be less than five or six minutes.
(2) The effectiveness of double coated pastes in chromizing was confirmed. The greater the Co content of the alloy, the greater the mass gain after chromizing.
(3) In aluminizing, the temperature and time of heat treatment remarkably influenced the hardness and transverse rupture strength of the alloy. In chromizing, paste thickness was also confirmed to be an important factor.
(4) After high frequency heating of the paste, intermetallic compounds were observed to form at the surface of the alloy within a very short time.
(5) Alloys low in Co content could be hardened to the some extent as well as iron and steel, but toughness was decreased by aluminizing. It is recommended that Co content be increased to obtain alloys with greater toughness.

View full abstract

With a duplication method using a micro-pipette, a technique for the colorimetric determination of the principal components and impurities in various plating solutions has been developed. A pair of vessels (2cmW×2cmL×15cmH) were used in a visual comparison of color intensity (one for the sample and the other for the referent). The sample solution was introduced into vessel I, mixed with suitable color-producing reagents, and made up to 20ml with water. The same color-producing reagents were introduced into vessel II and similarly made up to 20ml, and to this mixture a standard solution of analyte was added dropwise (5 or 10μl at a drop) with the micro-pipette, until the color of the sample solution was duplicated in the referent. Chromium (VI) was identified in a chromium plating solution using cobalt (II) and EDTA as the color-producing reagents, and 1000μg/ml of chromium standard solution for the duplication. Copper in copper sulfate plating solution and nickel in nickel plating solution were identified using EDTA as the color-producing reagent, and 20mg/ml of copper and 100mg/ml of nickel standard solution respectively for the duplication. For iron in chromium and copper sulfate plating solution, sulfosalicylic acid was used as the color-producing reagent, and the duplication was made by adding 1.0mg/ml of iron (III) standard solution. The precision of this method was within ±7%.

View full abstract