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...

Austenitic Manganese Steel...

Austenitic Manganese Steel The first austenitic manganese steel was developed in 1882 by Robert Abbott Hadfield. Hadfield had done a series of test with adding ferro-manganese containing 80 % manganese and 7 % carbon to decarbonised iron. Increasing manganese and carbon contents led to increasing brittleness up to 7.5 % manganese. At manganese contents above 10 % however, the steel became remarkably tough. The toughness increased by heating the steel to 1000 deg C followed by water quenching, a treatment that would render carbon steel very brittle. The alloy introduced commercially contained 1.2 % carbon (C) and 12 % manganese (Mn) in a ratio of 1:10. This composition is used even today, and the austenitic manganese steel is still known as Hadfield steel. The steel was unique since it exhibited high toughness, high ductility, high work hardening ability and excellent wear resistance. Because of these properties Hadfield’s austenitic manganese steel (AMS) gained rapid acceptance as a useful engineering material. Austenitic manganese steels have a proven high resistance to abrasive wear including blows and metal-to-metal wear, even though they have a low initial hardness. These steels are supposed to work harden under use and thus give a hard wear resistant surface, but it has been reported that these steels have a good wear resistance in components even without heavy mechanical deformation. Hadfield`s austenitic manganese steel is still used extensively, with minor modifications in composition and heat treatment, primarily in the fields of earthmoving, mining, quarrying, oil well drilling, steelmaking, railroading, dredging, lumbering, and in the manufacture of cement and clay products. Austenitic manganese steel is used in equipment for handling and processing earthen materials (such as rock crushers, grinding mills, dredge buckets, power shovel buckets and teeth, and pumps for handling gravel and rocks). Other...