Alloys of Iron and Chromium

0
262

An alloy is a mixture having metallic qualities that contain two or more elements, at least one of which is a metal. Some alloys are actual compounds, whereas others are solid mixtures of two metals. Partial solutions produce two or more phases that, depending on the temperature history, may or may not have a homogenous distribution, whereas complete solid solution alloys produce a single solid phase microstructure.

The properties of alloys are typically distinct from those of their constituent elements. The majority of the time, alloy components are weighed. Depending on the atomic configuration that gives rise to the alloy, alloys are typically classified as substitutional or interstitial alloys. They can also be classified into three other categories: intermetallic, where there is no clear division between phases; heterogeneous, consisting of two or more phases; and homogeneous, consisting of a single phase.

Ferroalloys

One of the important components used in the production of alloys and special steels is a ferroalloy. Steel is given unique characteristics by ferroalloys. The alloy’s purpose is to improve hardness, tensile strength at high temperatures, and wear and abrasion resistance, with the inclusion of carbon to boost creep strength and other properties. Thus, the expansion of the iron and steel industries is correlated with the growth of the ferroalloys sector. Chromium, manganese and silicon are the main components of ferroalloys. Ferromanganese, silico-manganese, ferrosilicon and ferrochrome make up the bulk.

Ferroalloys are classified into two main categories: bulk ferroalloys and noble ferroalloys. Due to the high cost of power, the ferroalloys industry has not been able to utilise its full capacity. The ferroalloys industry spends 40 to 70% of production costs on power consumption. The power consumption per tonne of ferroalloys production in the country varied from 3,000 to 12,000 kWh. About 35 to 40% of the production of ferroalloys is exported. Ferro-manganese, silico-manganese, ferrosilicon and high-carbon ferrochrome are exported after meeting the domestic requirements.

An Alloy of Iron-Nickel and Chromium

Stainless steels are alloys of iron and chromium, with or without other added components. They are the most widely applied and versatile of the corrosion-resistant alloys formulated from the anodic passivating metals. Other alloys from within the nickel, chromium, iron and molybdenum system are specialist materials designed to meet specific difficult environments and are excluded from the general application of their high costs. This constraint does not apply to alloys in which iron and chromium predominate because chromium is available as an inexpensive iron-chromium master alloy, ferrochrome, suitable for alloying with iron. As a consequence, a wide range of corrosion-resistant alloys is available at a moderate cost; some of them are mass products manufactured in integrated steel plants.

For stainless steels, more than for any other group of alloys, structures, properties, corrosion resistance and costs are so closely related that none of these aspects can be properly appreciated without detailed reference to the others. The need to maintain or enhance the passivating characteristics restricts the most useful additional alloy components to nickel, molybdenum and carbon. Certain other elements may also be added: titanium or niobium to control the effects of carbon, manganese or nitrogen to economise on the use of nickel and copper to induce precipitation-hardening.