Influence of chromium, molybdenum and cobalt on the corrosion behaviour of high carbon steels in dependence of heat treatment

Abstract

High chromium martensitic steels are designed to provide high corrosion resistance in combination with high strength. Some of these steel grades contain primary carbides for improving the wear resistance, e.g. the steel 440C. The present paper mainly deals with the effect of chemical composition and microstructure on the corrosion properties. Different experimental alloys were produced in the shape of small ingots. The influence of the alloying elements chromium, molybdenum, cobalt, and carbon on the corrosion properties was studied. The results can be summarized as follows: Chromium and molybdenum improve the corrosion resistance, however, only the content of these elements in solid solution in the steel matrix is effective. In case of cobalt the corrosion resistance decreases.The reason is the interaction between cobalt and carbon and its effect on the chromium content in the steel matrix. The calculated pitting resistant equivalent number of high chromium martensitic steels is only limited valid, because there is a major effect of carbide precipitation on the corrosion behaviour. Further investigations were focused on the heat treatment. Especially the effect of the tempering temperature of these steels was studied. The tempering temperature is most relevant for secondary hardening carbide precipitation, which lowers the chromium content of the matrix with detrimental influence on the corrosion properties. The carbide precipitation and chromium distribution was characterized by means of energy filtered transmission electron microscopy (EFTEM).

Corrosion properties of a complex multi‐phase martensitic stainless steel depending on the tempering temperature

“…According to , tempering at low temperatures should improve the corrosion resistance because it decreases internal stresses. However, in the present study, the corrosion resistance is slightly lower in the range of T temp = 100–400 °C, which is in accordance with . In contrast to the as‐quenched condition the retained austenite is deleterious for the corrosion resistance after tempering because it is more prone to precipitation .…”

“…in . However, the detailed behaviour has rarely been described so far and is thus the focus of this paper. Electrochemical polarisation tests are performed in sulphuric acid and NaCl solution.…”

Influence of Heat Treatment on the Performance Characteristics of a Plastic Mold Steel

“…On the other hand the transformation of retained austenite is accompanied by the precipitation of chromium‐rich carbides. This increases the amount of local elements and the matrix is locally depleted in chromium which in fact is responsible for the increased current density in the high tempered state 21–23.…”

Investigation of the Properties of Molybdenum Nanocube Crystals Deposited by Dc Sputtering

“…This characteristic makes it attractive for applications that require good stiffness (greater than that of steel) along with low weight. When it is alloyed with steel, improves the corrosion resistance [7]. Molybdenum has good electrical conductivity [8].…”