Cold heading quality steels and cold heading process...

Cold heading quality steels and cold heading process Cold heading quality (CHQ) Steel is the raw material which is used for the production of fasteners such as bolts, screws, nuts, rivets, nails, and other similar complex parts.  Traditionally fasteners have been manufactured using the thread cutting or by hot working method. But now the trend is moving towards using the cold working process to enhance productivity and to keep the cost down. It also provides good surface finish and dimensional accuracies to the fasteners. Cold heading process Cold heading process revolves around the concept of altering initial steel “blank” through force, using a series of tools and dies to change the blank into a finished product. The actual volume of steel remains unchanged, but the process maintains or improves its overall tensile strength. Cold heading is a high speed manufacturing process that relies on metal flow due to applied pressure as opposed to traditional metal cutting. It is a type of forging operation which is carried without the application of any heat. During the process material in the form of a wire is fed into the cold heading machine, cropped to length and then formed in a single heading station or progressively in each subsequent heading station. During cold heading load should be below the tensile strength, but above the yield strength of the material to cause plastic flow. The cold heading process uses high speed automated “cold-headers” or “part formers.” This equipment has the ability of transforming a wire into an intricately shaped part with tight and repetitive tolerances using a tooling progression at speeds up to 400 pieces per minute. The cold heading process is volume specific and the process uses dies and punches to convert a specific “slug” or blank of...

Combined blowing process in converter steel making Apr30

Combined blowing process in converter steel making...

  Combined blowing process in converter steel making Inhomogeneities in chemical composition and temperature are created in the melt during the oxygen blow in the top blown converters due to the lack of the mixing in the metal bath. There is a relatively dead zone directly under the jet cavity in the converter. The necessity to improve the steel making process in the top blown converter has led to the development of the combined blowing process. The first combined blowing practice to be commercially accepted was the LBE (Lance Bubbling Equilibrium) process developed by ARBE-IRSID. This process is much more closely related to the BOF process in that all the oxygen is supplied from the top lance. The combined blowing aspect is achieved by a set of porous elements installed in the bottom of the converter through which argon or nitrogen is blown. In LBE process the nitrogen gas is typically used almost exclusively for the majority of the blow in the range of 3 -11 N Cum/min. However in the later part of the blow when nitrogen absorption can create a problem, argon gas is used for stirring. In addition, argon is used almost exclusively as the inert gas for post blow stirring, at this time the rate is increased to 10-17 N Cum/min. The process is shown in Fig.1. Fig 1 Combined blowing processes The profile of a porous element is shown in Fig 2   Fig 2 Profile of a porous element for the LBE process The bottom buildup and the subsequent loss of the porous element is the major problem associated with this process. The difficulties in maintaining the LBE elements operational have led to pursue the application of the non cooled tuyeres. Here also the oxygen is delivered through...

Weathering Steels

Weathering Steels All low alloy steels have a tendency to rust in the presence of moisture and air. This rust is a porous oxide layer which can hold moisture and oxygen and promote further corrosion. The rate of rust formation depends on the access of oxygen, moisture and atmospheric contaminants to the metal surface. As the rusting process progresses, the rust layer forms a barrier to the ingress of oxygen, moisture and contaminants, and the rate of rusting slows down. The rust layers formed on most conventional structural steels detach from the metal surface after a certain time and in the process exposes the surface once again to rusting and thus commencing the corrosion cycle again. The rate of rust formation progresses as a series of incremental curves approximating to a straight line. The slope of this straight depends on the aggressiveness of the environment. Weathering steels are weather resistant steels which work by controlling the rate at which oxygen in the atmosphere can react with the surface of the metal. These steels are high strength low alloy steels which can provide corrosion protection without additional coating. Increase in alloying elements, mainly copper, provides an arresting mechanism to atmospheric corrosion in the steel itself. The alloying elements in the steel produce a stable and durable rust layer that adheres to the base metal. This rust ‘patina’ develops under conditions of alternate wetting and drying to produce a protective barrier, which impedes further access of oxygen and moisture. This patina acts as a skin to protect the steel substrate. Section loss on the order of 100 mils (2.54 mm) may be expected before the patina sets up, but this is negligible to the structural performance. Comparison of rate of rusting in low alloy steel and...

Use of Nut Coke in a blast furnace Apr27

Use of Nut Coke in a blast furnace...

Use of Nut Coke in a blast furnace Metallurgical coke is produced during the carbonization of coking coal blend in a coke oven battery. This coke is produced normally in three size fractions namely coke breeze (size – 10 mm), nut coke (size +10 mm to – 25 mm) and blast furnace (BF) coke (+ 25 mm to – 80 mm).  BF coke is one of the most important factors which affect the economic efficiency of a blast furnace. It also constitutes a great portion of the production costs of the hot metal. The use of nut coke in blast furnace is the essential factor to reduce the costs of iron making. The consumption of the BF coke is strongly related to the CO2 emissions. History Earlier there was no use of nut coke in an integrated steel plant and it was sold to other users. Prof. V. I. Loginov suggested in 1960s to charge nut coke into the blast furnace in mixture with sinter.  Though this idea was successfully tested, yet there was initial resistance to use nut coke in blast furnace. In mid 90s Visakhapatnam Steel Plant started using nut coke in their blast furnaces and soon achieved a monthly specific consumption level of over 50 Kg/tHM. The blast furnace of Neelachal Ispat Nigam Limited which was commissioned in February 2002 achieved by 2004-05 a monthly average specific consumption level of over 100 Kg/tHM. Presently the use of nut coke in blast furnace as a substitute of a part of BF coke is considered as a proven technology and nut coke is being used extensively in blast furnaces all over the world. Modern blast furnaces use nut coke in different amount (10-140 Kg/tHM) and in different size of nut coke (10-40 mm)....

Electrical steels

Electrical steels Electrical steel is kind of special steel which is tailored to exhibit certain specific magnetic properties such as small hysteresis area (small energy dissipation per cycle or low core loss) and high permeability. It is also called lamination steel, silicon (Si) steel, silicon electrical steel or transformer steel. The steel contains specific percentage of silicon in it which is responsible for its unique property.  In mild steel there is much loss in electrical energy due to hysteresis and eddy current and hence use of mild steel is uneconomical when it is used in the electrical devices. The hysteresis loss is shown in Fig.1.  The hysteresis loss is proportional to the area of the respective loops shown in the figure.                             Fig 1 Comparison of hysteresis loss in electrical steel (left) and mild steel (right) Electrical steel is an iron alloy of iron which may have from zero to 6.5 % silicon but usually has silicon content up to 3.2 % (higher concentrations usually provoke brittleness during cold rolling). Manganese and aluminum can be added up to 0.5 %. Silicon significantly increases the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop of the material, thus lowering the core loss. However due to the silicon the grain structure hardens and embrittles the steel, which adversely affects the workability of the steel, especially during rolling. When alloying, the concentration levels of carbon, sulphur, oxygen and nitrogen should be kept low since these elements indicate the presence of carbides, sulphides, oxides and nitrides in the steel. These compounds, even in particles sizes as small as one micrometer in diameter, increase hysteresis losses and decrease magnetic permeability. The...