Behaviour of Iron and Steel Materials during Tensile Testing Aug28

Behaviour of Iron and Steel Materials during Tensile Testing...

Behaviour of Iron and Steel Materials during Tensile Testing The mechanical properties of iron and steels are often assessed through tensile testing. The testing technique is well standardized and can be conducted economically with a minimum of equipment. Since iron and steel materials are being utilized in structural applications, they are to have tensile properties which meet the requirements of the relevant codes and standards. These requirements in the code and standards are the minimum strength and ductility levels. Due to this, information available from tensile testing is often underutilized. However, direct examination of many of the metallurgical interactions which influence the results of tensile testing can considerably improve the usefulness of the testing data. Examination of these interactions, and correlation with metallurgical / material /application variables such as heat treatment, surface finish, test environment, stress state, and anticipated thermo-mechanical exposures, can lead to significant improvements in both the efficiency and the quality of utilization of iron and steel materials in the engineering applications. Tensile testing of iron and steel materials is done for many reasons. Tensile properties are normally included in material specification to ensure quality and are often used to predict the behaviour of these materials during different forms of loading other than uniaxial tension. The result of tensile testing is normally used in the selection of these materials for engineering uses. It provides a relatively easy and cheap technique for developing mechanical property data for the selection, qualification, and utilization of these materials in engineering applications. This data is generally used to establish the suitability of these materials for a particular application, and/or to provide a basis for comparison with other substitute materials. The elastic moduli of iron and steel materials are dependent on the rate at which the test sample...

Molybdenum in Steels

Molybdenum in Steels Molybdenum (Mo) (atomic number 42 and atomic weight 95.95) has a density of 10.22 gm/cc. Melting point of Mo is 2610 deg C and boiling point is 5560 deg C. The phase diagram of the iron molybdenum (Fe-Mo) binary system is at Fig 1. Fig 1 Iron molybdenum binary system Mo is normally referred in short as ‘moly’.  It has many important uses in alloy steels, stainless steels, alloy cast irons and super alloys. It is a powerful hardenability agent and is a constituent of many heat treatable alloy steels. Mo retards softening at higher temperatures. Hence it is used in boiler and pressure vessel steels, as well as several grades of high speed and other tool steels. Mo improves the corrosion resistance of stainless steels. In HSLA (high speed low alloy) steels, it produces acicular ferrite structures. Mo is the basis for many of the as-rolled DP (dual phase) steels used in automotive applications. While Mo may often be used interchangeably with chromium (Cr) and vanadium (V), in many cases the properties it imparts are unique. Due to it, the use of Mo has increased considerably over the past several decades. Available forms Mo is supplied as ferro-molybdenum (Fe-Mo) and as molybdic oxide (MoO3). Fe – Mo contains a minimum of 60 % Mo. Silicon (Si) and copper (Cu) may be present in quantities up to 1 % each. It is relatively expensive and is sparingly used for addition. Technical MoO3 has a minimum of 57 % Mo. SiO2 is the main impurity, but it may also contain small amounts of Cu, sulfur (S), and phosphorus (P). MoO3 is supplied either in cans or as briquettes. MoO3 briquettes may also contain some amount of carbon (C). Considerable quantity of Mo is recovered...

Sulphur in Steels

Sulphur in Steels  Sulphur (S) (atomic number 16 and atomic weight 32.066) has density of 2.05 gm/cc. Monoclinic S melts at 119.25 deg C and boils at 444.6 deg C. However, S and iron (Fe) are miscible, and Fe-S binary system at one atmosphere of pressure forms a liquid at temperatures as high as 1800 deg C, far above the boiling point of S alone. Fig 1 is the phase diagram of the Fe-S binary system at 1 atmosphere of pressure.  Fig 1 Fe-S phase diagram S is an element which is always present in steel in small quantities. S in steel is introduced through iron ore and fuel (coal and coke). The removal of S during steel making is a tedious and difficult process. S is normally regarded as an impurity in steel and is required to be reduced to the limits of practicality. However steels which are to be machined need a certain minimum S content for proper chip formation. Where machining constitutes a major fraction of the end products cost, many types of steel (carbon, alloy, and less often stainless) are intentionally resulphurized just for this reason. (refer http://ispatguru.com/free-cutting-steels/) Except in those cases where it is added for machinability, or where residual S content of around 0.040 % maximum is tolerable, the usual aim during iron and steel making is to reduce S to low levels, consistent with mechanical property requirements. For high strength (HS) steel plates and for some special bar quality (SBQ) steel products, this may mean removing the S to a level of 0.005 % maximum. There are several methods which are widely used for achieving this level of S. Further, efficient removal of S from liquid steel or iron depends on specific metallurgical and thermodynamic conditions. Though...

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...

Tool Steels

Tool Steels The term tool steel is a generic description for those steels which have been developed specifically for tooling applications. These steels are used for making tools, punches and dies etc. Tools used for working steels and other metals must be stronger and harder than the steels or the materials they cut or form. Normally tool steels are known for their distinctive toughness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures (red hardness). Some of the operations that tool steels are used for include drawing, blanking, mould inserts, stamping, metal slitting, forming and embossing, although their use is not limited to just these areas. The metallurgical characteristics of various compositions of tool steels are extremely complex. There are hundreds of different types of tool steels available and each may have a specific composition and end use. Tool steels are mainly medium to high carbon steels with specific alloying elements added in different amounts to provide it special characteristics. The carbon in the tool steel is provided to help harden the steel to greater hardness for cutting and wear resistance while alloying elements are added to the tool steel for providing it greater toughness or strength. In some cases, alloying elements are added to retain the size and shape of the tool during its heat treat hardening operation or to make the hardening operation safer and to provide red hardness to it so that the tool retains its hardness and strength when it becomes extremely hot. Various alloying elements in addition to carbon are chromium (Cr), cobalt (Co), manganese (Mn), molybdenum (Mo), nickel (Ni), tungsten (W), and vanadium (V). The effect of the alloying elements on the properties of tool steels is as follows. Chromium –...