Atmospheric steels

In atmospheric exposure 18% Ni maraging steel corrodes in a uniform manner , and becomes completely rust covered. Pit depths tend to be more shallow than for the low-alloy high-strength steels. Atmospheric corrosion rates in industrial (Bayonne, New Jersey) and marine (Kute Beach, North Carolina) atmospheres are compared with those for low-alloy steel in Figs. 3.29, 3.30 and 3.31. The corrosion rates drop substantially after the first year or two and in all cases the rates for maraging steel are about half the corrosion rate for HY80 and AISI 4340 steels. 

Edney, E. 0. Stiles, D. C. Spence, J. W. Haynie, F. H. Wilson, W. E. "Laboratory Investigations of the Impact of Dry Deposition of SO2 and Wet Deposition of Acidic Species on the Atmospheric Corrosion of Galvanized Steel" Atmospheric Environment, (in press). 

Table 2.39 Case Histories of Galvanized Steel Atmospheric Exposure in the United Kingdom More than 15 Years in Service...

Legault, R. A., and Pearson, V. P. (1978). Kinetics of the atmospheric corrosion of galvanized steels. Atmospheric Factors Affecting the Corrosion of Engineering Metals. ASTM STP 646. ASTM, Philadelphia, pp. 83-%. 

COREX France GENESTAII 80 Prevention (low-alloy steel, atmospheric) In use (EDF) ... 

In case hardening C and N are introduced into the iron by heating in a Nj —NH3 atmosphere or by immersing the steel in molten NaCN/Na2C03 at about 900"C. 

Stainless steel. A group of Cr or Cr —Ni steels showing an unusually high resistance to corrosion by the atmosphere and many chemical reagents. In order to achieve this resistance to corrosion > 12% Cr is necessary. 

The catalyst is carried on perforated shelves inside cylindrical steel vessels called converters. The gas enters these at 670-720 K at atmospheric pressure. 

Alcoholysis (ester interchange) is performed at atmospheric pressure near the boiling point of methanol in carbon steel equipment. Sodium methoxide [124-41 -4] CH ONa, the catalyst, can be prepared in the same reactor by reaction of methanol and metallic sodium, or it can be purchased in methanol solution. Usage is approximately 0.3—1.0 wt % of the triglyceride. 

P/M steels can be heat treated in the same manner as cast or wrought steels. They may be austenitized, quenched, and tempered. Surface hardening includes pack or gas carburization or nitriding, ie, heating in a nitrogen-containing atmosphere. Because of the greater amount of exposed surface area in the form of porosity, a protective atmosphere is needed (see Metal surface treatments). 

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