Steels and Cast irons and their Essential and Incidental Elements...

Steels and Cast irons and their Essential and Incidental Elements Steels and cast irons are basically alloys of iron and different other elements in the periodic table. The vast majority of steels and all cast irons contain carbon as a principal alloying element. As a general definition, steel is an alloy of iron, carbon (less than 2 % C), and other alloying elements which is capable of being hot and/or cold deformed into various shapes. On the other hand, cast iron is an alloy of iron, carbon (higher than 2 % C), and other alloying elements and is not generally capable of being hot and/or cold deformed. A cast iron is used in its cast form. Steels and cast irons are the most widely used and least expensive metallic materials. There are several thousands of different steel compositions presently available. A vast variety of terminology is used to differentiate different types of steels. In fact, the way the steels are classified sometimes is quite confusing even to the regular user of steels. However, in many cases, the steels fall into a limited number of well-defined classes. Generally, the carbon and low alloy steels come under a classification system based on composition. The high alloy steels (the stainless, heat resistant, and wear resistant steels, etc.) are being classified according to many different systems, including composition, microstructure, application, or specification. The easiest way to classify steels is by their chemical composition. Different alloying elements are normally added to iron for the purpose of attaining certain specific properties and characteristics. These elements include, but are not limited to, carbon, manganese, silicon, nickel, chromium, molybdenum, vanadium, niobium, copper, aluminum, titanium, tungsten, and cobalt. The general category of carbon and low alloy steels encompasses plain carbon steels, alloy steels,...

Fasteners and Their Types...

Fasteners and Their Types Steel plants are associated with the fasteners in two ways. Firstly they supply steels of various qualities used in the manufacture of fasteners and secondly, they use various types of fasteners of different varieties, sizes and qualities in the equipments used in the steel plant. A fastener is a hardware device that mechanically joins or affixes two or more objects together. It is defined as a hardware which can be easily installed and removed with hand tool or power tool. Common fasteners include screws, bolts, nuts and rivets. The terms bolts and screws do not refer to specific types of fasteners, but rather how they are used (i.e. the application). Thus the same fastener may be termed a bolt or a screw. Bolts are defined as headed fasteners having external threads that meet an exacting, uniform thread specification such that they can accept a non-tapered nut. Screws are defined as headed, externally-threaded fasteners that do not mate with a non-tapered nut and are instead threaded into the material they hold. Principal purposes of the fasteners are (i) dis-assembly for inspection and repair, (ii) modular design, where a product consists of a number of sub-assemblies. The fastener types are (i) removable which permits the parts to be readily disconnected without damaging the fastener, e.g. nut and bolt, (ii) semi-permanent type where the parts can be disconnected, but some damage usually occurs to the fastener, e.g. cotter pin, and (iii) permanent type where the parts are never be disassembled e.g. rivets and welding of fasteners The most common types of male fasteners used in industry are hex head, slotted head, flat (or countersunk) head, round head, socket (or ‘allen’) head, button head and socket set screw. The most common types of female fasteners (i.e. nuts)...

Nickel in Steels

Nickel in Steels  Nickel (Ni) (atomic number 28 and atomic weight 58.69) has density of 8.902 gm/cc. Melting point of Ni is 1455 deg C and boiling point is 2910 deg C. The phase diagram of the Fe-Ni binary system is at Fig 1. Ni has a face centered cubic (f.c.c.) crystal structure. It is ferromagnetic up to 353 deg C, its curie point.   Fig 1 Fe-Ni phase diagram Ni is an important and widely used constituent of alloy steels. It is best known as a solid solution strengthener, a mild hardenability agent and, most important, as a means of promoting high toughness, especially at low temperatures. Ni is an important ingredient in stainless steel, helping it to prevent rust, scratches and resist heat. Around 65 % of global Ni production goes into the production of stainless steel. Ni alloyed steels contain as little as fraction of a percent to almost 30 % Ni. As may be expected, properties of these alloy steels range from strengths similar to plain carbon steel to some of the strongest metallic materials known. On the lower side of the Ni percentage in the steels are the alloy and HSLA (high strength and low alloy) structural steels. Hot rolled steels with yield strengths of 345 MPa may contain 0.50 % to 2.00 % Ni for toughness and added corrosion resistance. Age hardening steels contain 1.3 % to 1.5 % Ni plus copper (Cu) and niobium (Nb). Quenched and tempered or normalized and tempered structural steels contain nickel (Ni) up to 2.25 %, as well as a variety of other constituents including chromium (Cr), molybdenum (Mo) or boron (B). Nickel bearing addition agents Ni bearing addition agents are ferro- nickel (Fe- Ni) ferroalloy, Ni containing steel scrap, Nickel oxide...

Carburizing Process and Carburizing Steels...

Carburizing Process and Carburizing Steels  Carburizing is one of the most widely used surface hardening processes. It has been in use for a long time. The process involves diffusing carbon into a low carbon steel to form a high carbon steel surface. Carburizing process is also referred to as case hardening or case carburizing process. It is a heat treatment process that produces a surface which is resistant to wear, while maintaining toughness and strength of the core. The carburizing process has evolved with advancements in heat treatment techniques that have improved the hardness and durability of products like carbon steel wire springs and carbon steel forgings. Carburizing is a heat treatment process in which steel absorbs carbon liberated when the steel is heated between 850 deg C to 950 deg C in the presence of a carbon bearing material, such as charcoal or carbon monoxide, with the intent of making the steel harder. The heated steel at this temperature has austenitic structure which has got high solubility for carbon and which is a stable structure. Depending on the amount of time and temperature, the affected area can vary in carbon content. Longer carburizing times and higher temperatures typically increase the depth of carbon diffusion. When the steel is cooled rapidly by quenching, the higher carbon content on the outer surface becomes hard via the transformation from austenite to martensite while the core remains soft and tough as a ferritic and/or pearlitic microstructure. The typical carburizing process cycle including the quenching and tempering steps is shown in Fig 1. Fig 1 Typical carburizing cycle including the quenching and tempering step  Carburized steel consists of a composite material, where the carburized surface is hard but the unaffected core is softer and ductile. Compressive residual stresses are formed in...