Zirconium in Steels

Zirconium in Steels  Zirconium (Zr) (atomic number 40 and atomic weight 91.22) has density of 6.52 gm/cc. Melting point of Zr is 1855 deg C and boiling point is 4377 deg C. Zr  has a hexagonal close pack crystal structure. The phase diagram of the Fe-Zr binary system is given at Fig 1. Fig 1 Fe-Zr binary phase diagram Zr is being used as a alloying element in steels since the early 1920s, but has never been universally employed, as have niobium (Nb), titanium(Ti), and vanadium (V). Historically, the main use of additions of Zr to steel was for combination preferentially with sulphur, to avoid the formation of manganese sulphide (MnS), known to have a deleterious influence of the impact toughness of wrought and welded steel. These days there has been a renewed interest in the addition of Zr to the micro alloyed steels. Zr is highly reactive and has a strong affinity, in decreasing order, for oxygen (O), nitrogen (N), sulphur (S), and carbon (C). Its affinity for O, S, and N is the primary reason for its use in steelmaking. Due to this property it controls  the nonmetallic inclusions of sulphides and oxy-sulphides. it is also used for the fixation of N mainly in boron (B) steels. Zr also inhibits grain growth and prevents strain aging but its use for either of these reasons is limited. Because of its relatively high price and also due to the availability of cheaper replacements, general acceptance of Zr for use as an alloying element in steels is limited. Addition agents Te Zr addition agents in the liquid steel are iron-silicon-zirconium (FeSiZr) alloy, ferrozirconium (Fe-Zr) alloy, Zr alloy scrap and pure Zr sponge. Out of these the most popular addition agent is FeSiZr since it is...

Iron Nuggets

Iron Nuggets  The process of production of iron nuggets is capable of directly producing solid, high density, highly metalized iron nuggets from dry green balls. These green balls are made out of iron ore fines, pulverized coal, fluxes and binders. The pulverized coal is reductant which is added to the system to supply the carbon required for the reduction and carburization. Binder (bentonite) in conjunction with the finely ground iron ore particles serves to improve the properties of green balls in wet and dried conditions. The flux is limestone, which fluidizes the slag and also prevents excessive iron losses in the slag. The iron nuggets are produced using a direct reduction process. The reduction process is carried out in a rotary hearth furnace, using coal as the reductant and energy source. The direct reduction of iron by this process is more energy efficient and more environmentally friendly than traditional iron making processes. The process for producing iron nuggets by ITmk3 is described in the article having link http://ispatguru.com/itmk-3-process-of-making-iron-nuggets/ Iron nuggets are an ideal feed material for steelmaking and iron casting. This material consists of essentially all iron and carbon, with practically no gangue (slag) and low levels of metal residuals. Fig 1 shows sample of iron nuggets. Fig 1 Iron nuggets  Iron nuggets are a premium grade iron product with superior shipping and handling characteristics. They can be shipped in bulk either inland in railway wagons or trucks or in the ocean going vessels. Iron nuggets can be stored outside with no special precautions. They can be handled as a bulk commodity using conventional magnets, conveyors, bucket loaders, clams, and shovels. The physical properties of iron nuggets are as follows. Colour – Gray Shape and appearance – Pebble shaped elliptical structure Size – 5...

Interstitial Free Steels...

Interstitial Free Steels  The term ‘Interstitial Free steel or IF steel’ refers to the fact, that there are no interstitial solute atoms to strain the solid iron lattice, resulting in very soft steel. IF steels have interstitial free body centered cubic (bcc) ferrite matrix. These steels normally have low yield strength, high plastic strain ratio (r-value), high strain rate sensitivity and good formability. Conventional IF steels which were developed commercially in Japan during 1970s following the introduction of vacuum degassing technology contained carbon (C) in the range of 40 – 70 ppm and nitrogen (N) in the range of 30 -50 ppm. Later, niobium (Nb) and/or titanium (Ti) were added to these steels to stabilize the interstitial C and N atoms. IF steel is termed as ‘clean steel’ as the total volume fraction of precipitates is very less. In spite of this, the precipitates appear to have a very significant effect on the properties of IF steels. Liquid steel is processed to reduce C and N to levels low enough that the remainder can be ‘stabilized’ by small additions of Ti and Nb. Ti and Nb are strong carbide/nitride formers, taking the remaining C and N out of solution in liquid iron, after which these latter two elements are no longer available to reside in the interstices between solidified iron atoms. IF steel has ultra low carbon content, achieved by removing carbon monoxide, hydrogen, nitrogen, and other gasses during steelmaking through a vacuum degassing process. Interstitial elements like nitrogen or carbon are also in the form of nitrides and carbides due to the alloying elements such as Nb and/or Ti used for the stabilization of the residual interstitials. Therefore, IF steels posses typically non aging properties. Because of their non ageing properties, IF steels...

White Cast Iron

White Cast Iron The term cast iron refers to those iron carbon silicon alloys which contain 1.8 % – 4 carbon (C) and usually 0.5 % – 3 % silicon (Si). Cast iron is an important engineering material with a number of advantages, mainly good castability and machinability and moderate mechanical properties. White cast iron contains 1.8 % -3.6 % C, 0.5 % -1.9 % Si and 1 % – 2 % manganese (Mn). White cast irons are so called because when broken, the fracture surface is white. This is unlike the grey fracture surface normally associated with other cast irons which contain graphite. White cast iron is a cast iron without any alloy addition and with low C and Si content such that the structure is hard brittle iron carbide (Fe?C, also called cementite) with no free graphite. A fast cooling rate prevents the precipitation of C as graphite. Instead the C, which is in solution in the melt, forms iron carbide. The structure of white cast iron consists of pearlite and ledeburite, a eutectic mixture of pearlite (converted from austenite) and cementite. Cementite is hard and brittle and dominates the microstructure of white cast iron. Thus, white cast iron is hard and brittle and has a white crystalline fracture because it is essentially free of graphite. Typical micro structure of white cast iron is shown in Fig 1. Fig 1 Typical micro structure of white cast iron White cast iron does not have the easy castability of other cast irons because its solidification temperature is generally higher, and it solidifies with C in its combined form as iron carbide. White cast iron has a high compressive strength and excellent wear resistance, and it retains its hardness for limited periods even up to a red...

The Iron-Carbon Phase Diagram Mar11

The Iron-Carbon Phase Diagram...

The Iron-Carbon Phase Diagram In their simplest form, steels are alloys of Iron (Fe) and Carbon (C). The study of the constitution and structure of iron and steel start with the iron-carbon phase diagram. It is also the basis understanding of the heat treatment of steels. The Iron Carbon diagram is shown in Fig. 1. Fig 1 Iron Carbon phase diagram The diagram shown in Fig 1 actually shows two diagrams i) the stable iron-graphite diagram (dashed lines) and the metastable Fe-Fe3C diagram. The stable condition usually takes a very long time to develop specially in the low temperature and low carbon range hence the metastable diagram is of more interest. Many of the basic features of this irpn carbon system also influence the behavior of alloy steels. For example, the phases available in the simple binary Fe-C system are also available in the alloy steels, but it is essential to examine the effects of the alloying elements on the formation and properties of these phases. The iron-carbon diagram provides a solid base on which to build the knowledge of both plain carbon and alloy steels. There are some important metallurgical phases and micro constituents in thr iron carbon system. At the low-carbon end is the ferrite (?-iron) and austenite (?-iron). Ferrite can at most dissolve 0.028 wt% C at 727 deg C and austenite (?-iron) can dissolve 2.11 wt% C at 1148 deg C. At the carbon-rich side there is cementite (Fe3C). Between the single-phase fields are found regions with mixtures of two phases, such as ferrite & cementite, austenite & cementite, and ferrite & austenite. At the highest temperatures, the liquid phase field can be found and below this are the two phase fields liquid & austenite, liquid & cementite, and liquid...