LOW ALLOY STEEL

Particles of impurities (usually oxides, sulfides, silicates, etc) that are held mechanically or are formed during the solidification or by subsequent reaction within the solid metal.

Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical.

Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing and quenching. Although the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

Hardness is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. Some materials (e.g. metals) are harder than others (e.g. plastics, wood). Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness.

Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity.

A medium or high carbon quality steel strip which has been subjected to the sequence of heating, quenching and tempering. The two major processes of hardening and tempering can be broken down into four major steps. First, a strip of carbon steel is heated gradually until it reaches a temperature above the alloy’s critical temperature. The steel is then quenched, usually in water or oil (though other quenches, such as brine or sodium hydroxide solutions, are sometimes used to achieve a particular result). The steel is now at that given alloy’s maximum hardness, but as stated above, also brittle. At this point, tempering is usually performed to achieve a more useful balance of hardness and toughness. The steel is gradually heated until the desired temper colours are drawn, generally at a temperature significantly lower than the alloy’s critical temperature. Different colours in the temper spectrum reflect different balances of hardness to toughness, so different temper levels are appropriate for different applications. The steel is then re-quenched to ‘fix’ the temper at the desired level. A talented smith or metalworker can fine-tune the performance of a steel tool or item to precisely what is required based solely on careful observation of temper colours. A visual representation of this process may make the concept easier to understand.

The hardenability of a metal alloy is the depth to which a material is hardened after putting it through a heat treatment process. It should not be confused with hardness, which is a measure of a sample’s resistance to indentation or scratching.^[1] It is an important property for welding, since it is inversely proportional to weldability, that is, the ease of welding a material.

An increase in metallic crystal size as annealing temperature is raised; growth occurs by invasion of crystal areas by other crystals.

Average diameter of grains in the metal under consideration, or alternatively, the number of grains per unit area. Since increase in grain size is paralleled by lower ductility and impact resistance, the question of general grain size is of great significance. The addition of certain metals set up a grain size standard for steels, and the McQuaid – Ehn Test has been developed as a method of measurement.

Grain, in metallurgy, any of the crystallites (small crystals or grains) of varying, randomly distributed, small sizes that compose a solid metal. Randomly oriented, the grains contact each other at surfaces called grain boundaries. The structure and size of the grains determine important physical properties of the solid metal. Grains of a metal ingot can be elongated and locked together by rolling to improve the mechanical properties in the direction of grain length. Internal stresses at grain boundaries may be relieved by annealing to restore exhausted ductility in certain alloys or to harden other alloys.

It is the stress level below which an infinite number of loading cycles can be applied to a material without causing fatigue failure.

Elongation to failure is a measure of the ductility of a materials, in other words it is the amount of strain it can experience before failure in tensile testing. A ductile material (most metals and polymers) will record a high elongation.

Decarburization is the process opposite to carburization, namely the reduction of carbon content. The term is typically used in metallurgy, describing the reduction of the content of carbon in metals.

Cold rolling is a process by which the sheet metal or strip stock is introduced between rollers and then compressed and squeezed. The amount of strain introduced determines the hardness and other material properties of the finished product.

Carbides are compounds composed of carbon and less electronegative elements and they are distinguished by their chemical bonding (ionic, covalent). They are generally prepared from metals or metal oxides at high temperatures (1500 °C or higher) by combining the metal with carbon.

Edgewise curvature, a lateral deviation of an edge from a straight line. Lateral departure of the edge of the material from straight line forming a chord.

A concave surface departing from a straight line edge to edge. Indicates transverse or across the width.

Metal strip, made from hot – rolled strip, by rolling on cold – reduciton mills.

• Coil Breaks are creases that appear as lines transverse to the rolling direction and generally extend across the width of the steel.
• If a coil is sheeted and used in flat form the condition is considered unsightly.
• Coil Breaks are purely cosmetic.They are non-injurious and will not affect formability.Coil Breaks will not affect the integrity of formed parts.The presence of Coil Breaks is a clear indication of very formable and ductile material.

A lengthwise curve or set found in coiled strip metals following its coil pattern. A departure from longitudinal flatness. Can be removed by roller or stretcher leveling from metals in the softer temper ranges.

(Chemical symbol Cr) Element No.24 of the periodic system; atomic weight 52.01. It is of bright silvery color, relatively hard. It is strongly resistant to atmospheric and other oxidation. It is of great value in the manufacture of Stainless Steel as an iron – base alloy. Chromium plating has also become a large outlet for the metal. Its principal functions as an alloy in steel making;
1 increases resistance to corrosion and oxidation
2 increases hardenability
3 adds some strength at high temperatures
4 resists abrasion and wear (with high carbon)

Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure, it is a hard, brittle material, normally classified as a ceramic in its pure form, and is a frequently found and important constituent in ferrous metallurgy. While cementite is present in most steels and cast irons,[2] it is produced as a raw material in the iron carbide process, which belongs to the family of alternative ironmaking technologies.

Carburization is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-bearing material, such as charcoal or carbon monoxide. The intent is to make the metal harder. 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 iron or steel is cooled rapidly by quenching, the higher carbon content on the outer surface becomes hard due to the transformation from austenite to martensite, while the core remains soft and tough as a ferritic and/or pearlite microstructure.

(Chemical symbol c) Element No.6 of the periodic system; atomic weight 12.01; has three allotropic modifications, all non-metallic, Carbon is present in practically all ferrous alloys, and has tremendous effect on the properties of the resultant metal. Carbon is also an essential component of the cemented carbides. Its metallurgical use, in the form of coke, for reduction of oxides, is very extensive.

Bonderizing is a method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of a chemical phosphate conversion coating.

The bend test is a simple and inexpensive qualitative test that can be used to evaluate both the ductility and soundness of a material. It is often used as a quality control test for butt-welded joints, having the advantage of simplicity of both test piece and equipment.

Bainite is a plate-like microstructure that forms in steels at temperatures of 125–550 °C (depending on alloy content). it is one of the products that may form when austenite (the face-centered cubic crystal structure of iron) is cooled past a temperature where it no longer is thermodynamically stable with respect to ferrite, cementite, or ferrite and cementite.

A burr is a raised edge or small piece of material that remains attached to a workpiece after a modification process.[1]
It is usually an unwanted piece of material and is removed with a deburring tool in a process called ‘deburring’. Burrs are most commonly created by machining operations, such as grinding, drilling, milling, engraving or turning.

Brittleness describes the property of a material that fractures when subjected to stress but has a little tendency to deform before rupture. Brittle materials are characterized by little deformation, poor capacity to resist impact and vibration of load, high compressive strength, and low tensile strength. Most of inorganic non-metallic materials are brittle materials.

The Brinell hardness test method as used to determine Brinell hardness, is defined in ASTM E10. Most commonly it is used to test materials that have a structure that is too coarse or that have a surface that is too rough to be tested using another test method, e.g., castings and forgings. Brinell testing often use a very high test load (3000 kgf) and a 10mm diameter indenter so that the resulting indentation averages out most surface and sub-surface inconsistencies.

The Brinell method applies a predetermined test load (F) to a carbide ball of fixed diameter (D) which is held for a predetermined time period and then removed. The resulting impression is measured with a specially designed Brinell microscope or optical system across at least two diameters – usually at right angles to each other and these results are averaged (d). Although the calculation below can be used to generate the Brinell number, most often a chart is then used to convert the averaged diameter measurement to a Brinell hardness number.

Common test forces range from 500kgf often used for non-ferrous materials to 3000kgf usually used for steels and cast iron. There are other Brinell scales with load as low as 1kgf and 1mm diameter indenters but these are infrequently used.

(For tempered steel.) A method of testing hardened and tempered high carbon spring steel strip wherein the specimen is held and best across the grain in a vice-like calibrated testing machine. Pressure is applied until the metal fractures at which point a reading is taken and compared with a standard chart of brake limitations for various thickness ranges.

(WOOD) – A hardened tempered bright polished high carbon cold rolled spring steel strip produced especially for use in the manufacture of band saws for sawing wood, non ferrous metals, and plastics. Usually carries some nickel and with a Rockwell value of approximately C40/45.

Austempering is heat treatment that is applied to ferrous metals, most notably steel and ductile iron. In steel it produces a bainite microstructure whereas in cast irons it produces a structure of acicular ferrite and high carbon, stabilized austenite known as ausferrite. It is primarily used to improve mechanical properties or reduce / eliminate distortion. Austempering is defined by both the process and the resultant microstructure. Typical austempering process parameters applied to an unsuitable material will not result in the formation of bainite or ausferrite and thus the final product will not be called austempered. Both microstructures may also be produced via other methods. For example, they may be produced as-cast or air cooled with the proper alloy content.

Austenitic stainless steels possess austenite as their primary crystalline structure (face-centered cubic). This austenite crystalline structure is achieved by sufficient additions of the austenite stabilizing elements nickel, manganese and nitrogen. Due to their crystalline structure, austenitic steels are not hardenable by heat treatment and are essentially non-magnetic

Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron, with an alloying element.[1] In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (727 °C); other alloys of steel have different eutectoid temperatures.

Annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for an appropriate amount of time and then cooling.

In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to a change in ductility and hardness. As the material cools it recrystallizes. For many alloys, including carbon steel, the crystal grain size and phase composition, which ultimately determine the material properties, are dependent on the heating rate and cooling rate. Hot working or cold working after the annealing process alters the metal structure, so further heat treatments may be used to achieve the properties required. With knowledge of the composition and phase diagram, heat treatment can be used to adjust from harder and more brittle to softer and more ductile.

In the case of ferrous metals, such as steel, annealing is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air. Copper, silver and brass can be either cooled slowly in air, or quickly by quenching in water.^[1] In this fashion, the metal is softened and prepared for further work such as shaping, stamping, or forming.

To make a killed steel, aluminum (which has a stronger affinity for oxygen than carbon, manganese, or silicon) is added to the molten steel before it is poured. The aluminum locks up the oxygen, in the form of aluminum oxide, so that it cannot form gas bubbles during welding.

Acid embrittlement is a process in which brittleness is induced in metals, especially steel, when immersed in acidic solutions. Acids contain hydrogen, and when these metals are immersed in acids, they absorb hydrogen, becoming brittle, and can readily fracture when subjected to stress.

Hydrogen embrittlement (HE) also known as hydrogen assisted cracking (HAC) and hydrogen-induced cracking (HIC), describes the embrittling of metal after being exposed to hydrogen.

Mechanisms that have been proposed to explain embrittlement include the formation of brittle hydrides, the creation of voids that can lead to bubbles and pressure build-up within a material and enhanced decohesion or localised plasticity that assist in the propagation of cracks.^[2]

For hydrogen embrittlement to occur, a combination of three conditions are required:

1. the presence and diffusion of hydrogen
2. a susceptible material
3. stress

Hardened and Tempered to meet the most exacting requirements; Polished, Edged and then chemically blued for appropriate usage.

Spring steel is a name given to a wide range of steels^[1] used in the manufacture of springs, prominently in automotive and industrial suspension applications. These steels are generally low-alloy manganese, medium-carbon steel or high-carbon steel with a very high yield strength. This allows objects made of spring steel to return to their original shape despite significant deflection or twisting.

Cold rolled strip is a steel product that is produced from a hot rolled strip that has been pickled. The coil is then reduced by a single stand cold roll steel mill straight away or reversing mill or in a tandem mill consisting of several single stands in a series. The strip is reduced to approximately final thickness by cold-rolling directly, or with the inclusion of an annealing operation at some intermediate thickness to facilitate further cold reduction or to obtain mechanical properties desired in the finished product. High carbon strip steel^[3] requires additional annealing and cold reduction operations.^[4] The coil is then slit to the desired width through the process of roll slitting.

The final product typically consists of cold rolled steel that has been cut into strips of a specific widths and coiled or oscillate coiled for delivery, frequently interleaved with paper or another material which protects the surface finish of the material and assists in retaining oil or some other rust prevention solution. This product is often later stamped to form a part from the strip steel.