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Precast elements

Production of precast elements is done in casting yard. Moulds of adequate stiffness have been used and installed as per issued GFC drawings. The sequence of activities involved in the production of precast elements is as follows:

1. Mould cleaning and preparation

2. Shuttering/assembling the mould components

3. Fixing of rebars / cast-in-fittings

4. Pre-concrete check

5. Concreting

6. Curing

7. Demoulding

8. Final inspection

9. Stacking

Stacking of Precast Elements. Lifting and handling of precast elements have been done using gantry cranes and other approved lifting devices. Number and location of lifting points have been decided such that the ‘handling stresses’ were always within allowable limits. For members having unsymmetrical geometry or projecting sections required supplementary lifting point. Precast elements such as precast slabs, beams, spandrels and staircase landing elements were stacked horizontally and supported with strips of wood or batten across the full width of the bearing points. Precast walls, column-beam-wall panels shall be stacked in vertical position supporting their self-weight using racks. Precast elements were transported to the site on a flatbed or low bed trailers. The delivery of precast elements was planned according to the erection sequence to avoid or minimize unnecessary handling or storage at the site. The precast elements are being loaded using gantry crane of 10 to 15 ton of varying capacity and delivered to the site with proper supports, frames and cushioning to prevent transit damages. The elements were delivered in a manner in which they can be lifted directly and erected without much change in the orientation or Sequence. Average 136 numbers of elements were to be transported per day to the site with the help of around 10 numbers of trailers.

Before the erection of precast elements, the following preparatory works shall be carried out to achieve efficient and quality installation.

1. Site accessibility shall be checked for the delivery of precast elements.

2. Check whether the right element is dispatched or not.

3. Visual inspection shall be done to check the concrete finishes and damages if any.

4. Crane shall be checked for its working clearance for hoisting the precast element.

5. The elements shall be stored using “First In First Out” principle according to the erection sequence

During the erection of vertical members, the reference line and offset line was set out to determine the position of the element to be installed. Then shim plates or level pads were provided for setting the level of the elements. For external wall or column elements, a compressible form of the backer rod was fixed on the outer perimeter of the wall. The element was placed in the designated location and secured with diagonal props (push-pull jacks) and then check for the alignment. After installing the element, grouting work was carried out. Approved grouting material was prepared as per specifications and applied to seal the gaps along the bottom edge of the inner side of the element. This is a technique of post-tensioning; where elements are placed first and then by inserting the grout material, tension is imparted in the element to achieve the highest strength. Erection of horizontal element is similar to that of the vertical element; but the difference is, props were kept ready before bringing the horizontal element to the location, and levelling is done. Screed concrete of 60mm thickness was placed over the slab as specified in the drawings.

Weldability of Steel

The term weldability is the ability to obtain economic welds, which are good, crack-free and would meet all the requirements. What is of great importance is the chemistry and the structure of the base metal and the weld metal. The effects of heating and cooling associated with welding are experienced by the weld metal and the Heat Affected Zone (HAZ) of the core metal. The base metal surrounding the weld metal and the weld itself have unduly varying hardness distribution across a weld. The hardness in steel depends upon the rate at which steel is cooled near the fusion zone; the hardness is maximum due to the higher temperature at that location and also have the maximum rate of cooling. A higher value of hardness leads to cracks in HAZ or in the weld. There are chances of Cracks that might be formed during or after the welding process. Good design and standard welding procedure help minimise the cracking problem.

The main features that affect weld cracking during the welding processes are

Joint restraint that builds up high stress in the weld (convex or concave)

Carbon and alloy content

Cooling rate

Hydrogen and nitrogen absorption

The cracks in HAZ are mainly caused by high carbon content, hydrogen embrittlement and rate of cooling. In most of the steels, weld cracks become a problem as the thickness of the plate increases. Types of joints and welds By means of welding, it is possible to make continuous, load-bearing joints between the members of a structure.

A variety of joints is used in structural steelwork and they can be classified into four basic configurations are

  1. Lap joint

  2. Tee joint

  3. Butt joint

  4. Corner joint.

The weld defects detected during inspection are acceptable for structures. • For joints welded from both the surfaces, incomplete perception with thickness up to 5% of the parent metal thickness, but not surpassing 2 mm and the expansion, more than 500 mm can be accepted. The aggregate expansion of stain shall not be more than 200 mm per meter length of the joint. Incomplete perception and cracks are not permitted at or near the end or beginning of a joint.

For joints united from one side without backing strip, incomplete penetration with thickness up to 15% of parent metal thickness but not exceeding 3 mm at the root is permitted.

Slag inclusion located along the weld as a chain or unbroken line is allowed if their whole length does not exceed 200 mm per meter of the weld length. Size of the slag may also be considered.

Total of isolated gas pores and slag inclusion shall not exceed 5 in number per square centimetre of the weld.

The incomplete penetration, slag inclusion on pores located separately or as a chain shall not exceed 10% of metal thickness but not greater than 2 mm when welding is done from both the sides and 15% of metal thickness, but not vaster than 3 mm when welding is done from one side.

Structural steel

Structural steel has superior characteristics when compared with competing materials. In order to replace an area of steel in tension, an equivalent plain concrete area of about 200 units would be required. To compete with Structural Steel in construction, Reinforcing Steel needs to be added to it. The cracking of concrete in tension still cannot be avoided, which often encourages corrosion of reinforcement. In compression, one unit area of steel is the equivalent of 15-20 units of M20 concrete. A comparison shows that steel is at least 3.5 times more effective than concrete. In a compressive loading, there would be 8 times shortening of steel in concrete. Reinforcing steel has to prop up the plain concrete. In structures built of Structural Steel, accidental overloading does not usually lead to great havoc, as there are a considerable reserve strength and ductility. Steel may thus be regarded as a forgiving material whereas concrete structures under accidental overload may well suffer the catastrophic collapse of the whole structure. Repair and retrofit of steel members and their strengthening at a future date (for example, to take account of enhanced loading) are a lot easier than that of strengthened concrete members. The quality of steel-intensive construction is invariably superior when compared with all other competing systems (including concrete structures) thus ensuring enhanced durability. The quality control in construction at the site in India is poor. Structural Steel is recyclable and environment-friendly. Over 400 million tonnes of steel infrastructure and technology for the recycling of steel is very well organised. Steel is a material that can be easily recycled. The recycled, steel can change from one product to another without losing its quality. Steel can as easily turn up in precision blades for turbines or super strong suspension cables. Recycling of steel leads to protection of energy and primary resources and reduces waste. A steel building can be easily designed to allow disassembly or deconstruction at the end of their useful lives leading to many environmental and economic benefits; it can mean that steel components can be re-used in later buildings without the need for recycling, and the lack of proper usage of the energy used and the by-products from the steel production processes. Steel-intensive construction results in the least disturbance to the community in which the structure is located. The latest construction techniques developed in recent years with the help of steel-intensive solutions have been brought to effect that leads to the least disruption to traffic and minimises financial losses to the community and business. As such the initial cost of a concrete intensive structure may sometimes appear to be cheaper, in comparison to the equivalent steel-intensive structure, but it is a known fact that the total lifetime cost of gold is significantly higher. The usual belief that the concrete-intensive structure is cheaper is not based on verifiable facts! There is, therefore, no real cost advantage either.

Composite Beams

Continuous steel-concrete composite beams are largely used in building and bridge construction but are characterized by a very complex behaviour even for low-stress levels. In fact, composite action depends on the interaction between three main components: the reinforced concrete slab, the steel profile, and the shear connection ( Mechanical properties and arrangement of common composite cross sections ensure a good response to positive bending, but a reduced bearing capacity when negative bending is considered. Therefore, redistribution of the internal forces at the ultimate limit state is a key factor in the design process, as it allows a reduction of bending moments at the internal support and the exploitation of the positive bending resistance. A reliable assessment of available rotation capacity is required in order to define design criteria and simplified code provisions. Experimental and theoretical analyses have focused mainly on the steel component affected by the buckling phenomena, which reduce the rotation capacity. Nevertheless, many experimental results on joints and semi-continuous beams shows that the collapse is often due to fracture of reinforcement placed in the slab and pointed out that properties and arrangement of reinforcement can influence the structural response of such beams.
Furthermore relative displacements between slab and profile due to mechanical connecting devices that are not completely rigid increase the deformability of the system and affect the global behaviour of members. The solution of a continuous composite beam can be performed using a unified approach to the modelling of the cross-section. In fact, each slip and the related interaction phenomenon are described by a static parameter that can change between an upper limit and a lower limit depending on the properties of the materials. Furthermore, when the cross section is subjected to negative bending, the moment-curvature relationship is defined assuming a given value of Tct and changing the interaction force F. In particular, if the results of tensile stresses on the effective area is zero, tensile stresses cannot arise in the slab, and the cross section is cracked. As a result, from a static point of view, the equilibrium conditions for the concrete slab are not strictly related to the assumed kinematic model. Thus the moment-curvature relationship for composite sections under positive bending belongs to the family of curves generated in compliance with the assumptions for a composite section under negative bending. This remark allows a unified approach to modelling of composite beams since the proposed generalized moment-curvature relationship is able to fully describe the flexural response of the section and can be used as a powerful tool to perform refined structural analyses.

Structural Design

Conventional structural design was based on satisfying two requirements, namely safety and serviceability. Safety relates to extreme loadings, which have a very low probability of occurrence, on the order of 2 %, during a structure’s life, and is concerned with the collapse of the structure, major damage to the structure, its contents, and loss of life. The major priority is on ensuring sufficient structural integrity so that the sudden collapse can be avoided. Serviceability pertains to medium to large loadings, which may occur during the structure’s lifetime. For loading, the structure must be designed well, must suffer minimal damage, and the motion experienced by the structure should not exceed specified comfort levels for humans and motion-sensitive apparatus mounted on the structure. Typical occurrence probabilities for service loads range from 10 to 50 % Safety concerns are satisfied by requiring the resistance, i.e., the strength of the individual structural elements must always be greater than the demand associated with the extreme loading. Once the structure is dimensioned, the stiffness properties are achieved and used to check the various serviceability constraints such as elastic behaviour. The same process is necessary for convergence to an acceptable structural design. This approach is referred to as strength-based design since the components are dimensioned initially according to strength specifications. Application of strength-based preliminary design is appropriate when strength is the dominant design requirement. Earlier, most of the structural design problems came under this category. However, certain developments have occurred in the recent past that limits the effectiveness of the strength-based approach. The requirement of a structure that is flexible like a tall building and long-span horizontal structures has resulted in more structural motion under service loading, thus shifting the emphasis toward serviceability.

Secondly, some new types of conveniences such as microdevice manufacturing centres and hospital operating centres have more severe design confinements on motion than the typical civil structure. For example, the environment for microdevice manufacturing must be essentially motion free. Thirdly, recent advances in material science and engineering have resulted in major increases in the power of conventional civil engineering materials. However, the material stiffness has not increased at the same rate. The lag in material stiffness vs. material strength has led to a problem that satisfies the requirements of the various motion parameters. Thus it can be said that, for very high strength materials, the motion requirements control the design. Fourthly, experience with recent earthquakes has shown that the cost of repairing structural loss due to inelastic deformation was considerably greater than envisioned. This finding has resulted in a trend toward decreasing the reliance on inelastic deformation to dissipate energy and shifting to another type of energy dissipating and energy absorption mechanisms. Performance-based design is an alternate design paradigm that addresses such issues. The manoeuvring takes as its principal aim the success of motion related design elements such as conditions on displacement and acceleration and has the optimal deployment of element stiffness and motion control devices to achieve these design purposes as well as satisfy the constraints on strength and elastic behaviour. Limit state design can be described as a form of performance-based design where the structure is allowed to experience a specific amount of inelastic deformation under extreme loading.

How is Ductility and toughness important in structures?

Ductility and toughness are the structural properties that show the ability of a structural element to sustain damage when overloaded while continuing to carry the load without failure. These are extremely important for structures designed to sustain damage without collapse. Most structural elements are designed to provide sufficient strength to support anticipated loads without failure and enough stiffness so that they will not deflect excessively under these loads. If such an element is subjected to a load substantially larger than it was designed to carry, it may fail in an abrupt manner, losing load-carrying capacity and allowing the structure to collapse. Masonry and concrete, for example, will crash when overloaded in compression and will crack and pull apart when placed in tension or shear. Wood will crush when overloaded in compression, will split when overloaded in shear, and will break when overloaded in tension. Steel will buckle if overloaded in compression and will twist when loaded in bending if not accurately braced but will yield when overloaded in stress. The property of the steel to stretch a great deal while continuing to carry the load, allows it to be used in structures of all types to provide them with ductility and toughness. The buildings, that have no steel reinforcement, are not very ductile or tough and frequently collapse in earthquakes. In concrete structures, steel is used in the form of reinforcing bars that are placed integrally with the masonry and concrete. When reinforced masonry and concrete elements are loaded in bending or shear, the steel reinforcing bars will yield in tension and continue to carry the load, thus protecting the masonry and concrete from failure. Inwood structures, steel fasteners (typically nails, bolts, and straps) bind the pieces of wood together. On loading the wood in shear or bending, these steel connectors yield and shield the wood from breaking and crushing. In steel structures, ductility is achieved by proportioning the structural members with sufficient thickness to prevent local buckling, by bracing the members to prevent them from twisting, and by joining the members together using connections that are stronger than the members themselves so the structure does not pull apart. In all structures, ductility and toughness are achieved by proportioning the structure so that some members can yield to protect the rest of the structure from damage. The measures applied to obtain ductility and toughness in structural components are individual to each building material and to each type of structural system. The building codes specify the measures to use to provide ductility and toughness to steel structures.

Building Information Modeling

The essence of the BIM involves the fact that a design is treated as an integral part of the building life cycle. The work between the design parts and members is replaced by the adjusted process. This is achieved by changing the design technology substantially, switching from the development of a set of 2D drawings to the development of a 3D computer-aided model of a building, that consists of all the parts of the design, such as architectural, structural, mechanical, technological, construction process management and estimates. In the design stage, these goals are brought into effect by the technology of a Building continuum model, which focuses on the finally completed and fully equipped 3D building model comprising all the design parts. The base of this technology consists of the 3D graphical-information model covering the following: building a geometrical model; its physical properties (materials, etc.); functional peculiarities of its components. One of the fundamental innovations of this technology includes component modelling. The component modelling technology allows working in parallel with all design data at the level of data components covering the entire design cycle on the scale of a users group. Engineering components are graphical models of real objects. These models characterize geometry, properties, links, and attributes of the real objects. It is assumed that a building consists of elements and parts different by their functions, properties, and manufacture technology. Each part may consist of a simple structural component or a complex structure.


All elements or parts have a specific 3D shape with the properties of the elements of real structures (physical properties, class or standard). They are parametrically controlled and intellectual, i.e. each object “knows” about itself both quantitative information (length, area, volume, and etc.) and qualitative information (material, contents). All this provide unlimited possibilities not only to develop objects, to change and edit the shape of objects rapidly and effectively, but also to preserve and manage their attributive information, using the 3D building model. In the meanwhile 2D information, i.e. different drawings (plans, sections, facades, details, and nodes) and other design documentation (list of materials, specifications, reports, and estimates) are generated from the 3D model. Quantity and price of the specified components may be calculated by the measurement units required taking into account volume, area, length, or just by the parameter entered. Since these reports are linked to the model, new editions of the model update design data automatically. If necessary, external databases may be connected and used. Thus, accuracy, coordination, and synchronization of changes in the whole project documentation are ensured. BIM consists of discipline-specific solutions, working together. By applying information and model-based technology solutions to allow the automatic generation of drawings and reports, design analysis, cost estimating, schedule simulation, facilities management, and more – ultimately enabling the building team to focus on the information and their decisions, rather than the documentation tools and process. The result is a better way for building teams to work – with time saved, improved quality, and better buildings because of the informed decisions made along the way. Using BIM the entire lifecycle of the building is considered (design/build/operations). All information about the building and its lifecycle are included defining and simulating the building, its delivery, and operation using integrated tools. BIM integrates work, processes, and information for the following: multiple disciplines, multiple companies; multiple project phases.

What is Bracing?

Bracing is considered as an efficient and economical method to laterally stiffen the frame structures against the wind loads. A braced bent includes the columns and girders with the primary purpose of supporting the gravity loading, and diagonal bracing members that are connected so that total set of members form a vertical cantilever truss to resist the horizontal forces. Bracing is considered efficient as the diagonals tend to work in axial stress and therefore need minimum member sizes in providing the stiffness and strength against horizontal shear.With the increase in trend of constructing tall buildings,there must be a cost effective structural form of bracing system that needs be used in tall buildings against the lateral loads.A regular shape tall building can be analyzed for wind loads acting along the minor axis of bending of column and acting along the major axis of bending of column.


Similarly,when wind loads along the minor axis the building is braced in minor direction of bending and when the wind loads along the major axis the building is braced in minor direction of bending. Moreover, various options of bracing provision in different bays of the building at same level have also been identified.
Bracing can be categorized into the following types;


Diagonal bracing


This type of bracing isgenerally used when the availability of the opening spaces in a bay of frame are required. Diagonal bracing is usually obstructive in nature because it blocks the location of opening which ultimately affects the esthetic of the building elevation. It also sometimes hinders the passage for use. Diagonal bracing can be either single or double diagonal . If there is no architectural limitation, diagonal bracings are considered to be the most efficient in resisting the lateral forces due to wind as these form a fully triangular vertical truss. The beams and columns are actually designed to take up the gravity loads only.


K-bracing

The full diagonal bracing is not preferably used in areas where a passage is required. In such cases, k – bracings are used over diagonal bracing because there is a room to provide opening for doors and windows.

Eccentric bracing

Besides K-bracing, there is another type of bracing in which door and window openings can be allowed which is known as eccentric bracing . Such type of bracing arrangement cause the bending of the horizontal members of the web of braced bent.

Generally these types of braced bents tend to resist the lateral forces due to the bending action of beams and columns. These provide less lateral stiffness hence less efficient as compared to diagonal bracingUnder the action of gravity loads, columns shorten axially due to the compressive loads. As a result the diagonals are subjected to compression and beam will undergo axial tension due to the tying action . In situations where diagonals are not connected at the end of the beam, the diagonal members will not carry any force because no restraint is provided by the beams to develop force. Therefore, such bracing will not take part in resisting the gravity loads.

Beam-to-column connections

These styles of connections are common as they need the ability to supply for minor changes while using un torqued bolts in a pair of millimetre clearance holes. Un-remarkably the cleats are utilized in pairs. Any easy equilibrium analysis is appropriate for the look of this kind of connection. The bolt cluster connecting the cleats to the beam net should be designed for the shear force and therefore the moment made by the merchandise of the top shear and therefore the eccentricity of the bolt cluster from the face of the column. The bolts connecting the cleats to the face of the column ought to be designed for the applied shear solely.The cleats to the column are seldom vital and therefore the style is sort of forever ruled by the bolts pertaining to to the net of the beam. The move capability of this affiliation is ruled mostly by the deformation capability of the angles and therefore the slip between the connected elements. Most of the rotation of the connections comes from the deformation of the angles whereas fastener deformation is extremely little. To minimise move resistance (and increase move capacity) the thickness of the angle ought to be unbroken to a minimum and therefore the bolt cross-centres ought to be as giant as is much potential. Once connecting to the axis of a column it’s going to be necessary to trim the flanges of the beam however this doesn’t amendment the shear capability of the beam. throughout erection the beam with the cleats hooked up is lowered down the column between the column flanges.
Single angle net cleats :Single angle net cleats are un remarkably solely used for little connections or wherever access precludes the employment of double angle or end-plate connections. This kind of affiliation isn’t fascinating from Associate in Nursing erector’s purpose due to the tendency of the beam to twist throughout erection. Care ought to be taken once victimisation this kind of affiliation in areas wherever axial tension is high. The bolts connecting the cleat to the column should even be checked for the instant made by the merchandise of the top shear force and therefore the distance between the bolts and therefore the centre line of the beam. Flexible end-plates :These connections encompass one plate fillet welded to the top of the beam and web site fastened to either a supporting column or beam. This affiliation is comparatively cheap however has the disadvantage that there’s no area for website adjustment. Overall beam lengths got to be unreal at intervals tight limits though packs are often accustomed make amends for fabrication and erection tolerances. The end-plate is usually elaborated to increase to the total depth of the beam however there’s no got to weld the end-plate to the flanges of the beam. typically the end-plate is welded to the beam flanges to boost the steadiness of the frame throughout erection and avoid the necessity for temporary bracing. this kind of affiliation derives its flexibility from the employment of comparatively skinny end-plates combined with giant bolt cross-centres. Associate in Nursing eight millimeter thick end-plate combined with ninety millimeter cross-centres is typically used for beams up to or so 450 millimeter deep. For beams 533 millimeter deep and over a ten millimeter thick end-plate combined with a hundred and forty millimeter cross-centres is usually recommended. The native shear capability of the net of the beam should be checked and, owing to their lack of plasticity, the welds between the end-plate and beam net should not be the weakest link. Fin plates: The introduction of the fin plate is primarily to transfer beam finish reactions and is economical to fabricate and easy to erect. There’s clearance between the ends of the supported beam and therefore the supporting beam or column therefore making certain a simple work. These connections comprise one plate with either pre-punched or pre-drilled holes that’s search welded to the supporting column projection or net. considerable effort has been invested with in making an attempt to spot the acceptable line of action for the shear. There are 2 prospects, either the shear acts at the face of the column or it acts on the centre of the bolt cluster connecting the fin plate to the beam net. For this reason all vital sections ought to be checked for a minimum moment taken because the product of the vertical shear and therefore the distance between the face of the column and therefore the centre of the bolt cluster. The vital sections are then checked for the ensuing moment combined with the vertical shear. The validation of this and different style assumptions were checked against a series of tests on fin plate connections. The results of those tests ended that the look approach was conservative and gave adequate predictions of strength. The tests conjointly showed that fin plates with long projections had a bent to twist and fail by lateral torsional buckling. Fin plate connections derive their in-plane move capability from the bolt deformation in shear, from the distortion of the bolt holes in bearing and from the out-of-plane bending of the fin plate. tekla design

Types of Steel

Steel is outlined as an alloy of iron and carbon, although alternative alloying components also are found in several steels.The foremost dramatic property of steel is that some alloys may be reinforced by quench hardening. Hot metal is speedily cooled by plunging it into a liquid. These alloys will therefore be ductile for fabrication and far stronger as a finished product. Steels are loosely sorted by carbon content into low carbon steels (< zero.35% carbon by weight, approximately), medium carbon steels (0.35%–0.5% carbon by weight, approximately), and high carbon steels (0.5%–1.5% carbon by weight, approximately). These numbers could appear to be little, however they replicate the very fact that carbon may be a little, light-weight component, whereas iron may be a abundant larger, heavier atom. once metallurgists check out the elaborated structure of steels, they’re involved concerning the presence, and notably the form, of the inorganic compound Fe3C. This compound is twenty fifth carbon by atom fraction, but only 6.7% carbon by weight. There square measure 2 principal disadvantages with victimisation steels. Among metals, steel is comparatively significant. they will conjointly deteriorate by corrosion. However, the expectation is that, if steel can work, it’ll in all probability be the smallest amount high-ticket metal alternative. Low Carbon Steels This class contains far and away the most important tunnage of steel created, because it includes the structural steels of bridges and buildings. These steels typically have little amounts of alternative alloying components. they’re not quench hardened, as plasticity within the final product is desired. Low carbon steels are generally observed as delicate steels. In some cases, these steels could also be surface treated to get the most effective of each worlds – a ductile, impact-resistant interior with a tough, abrasive-resistant surface. Common surface treatments for hardness embrace carburizing, nitriding, and cyaniding. Low carbon steels might also be surface treated for corrosion resistance, victimisation processes of galvanising, electroplating, yet as simply plain painting. Medium Carbon Steels Steels during this class also are medium alloy steels. Up to concerning third-dimensional by weight can be comprised of varied proportions of metal, nickel, chromium, molybdenum, or generally alternative components. Medium alloy steels may be quench hardened, and therefore the supplemental alloying components square measure primarily to boost hardenability. Hardenability can be loosely represented because the simple getting hardness. To harden steel, its temperature should be modified speedily to avoid the formation of softer equilibrium phases, and to provide the required arduous, robust section known as primary solid solution. Upon ending, the surface cools 1st, whereas the inside cools additional slowly. These temperature gradients produce stresses that, within the worst case, will crack the half. Also, the inside might not cool quickly enough to harden. Steels of high hardenability square measure advantageous in 2 aspects:  For a given quench medium, larger components may be totally hardened.  For a given half, a milder, less speedy quench may be accustomed minimize cracking. The atoms of a metal square measure positioned in symmetrical geometrical arrays known as crystal lattices. a selected array of Associate in Nursing alloy is named a section. High Carbon Steels These also are the high alloy steels, with some 5%–10% by weight consisting of alloying components apart from carbon. tho’high carbon steels square measure employed in the littlest amounts, these square measure specialty steels, usually observed as tool steels. they’re the steels used for hammers, pick-axes, and cutting tools like knives and chisels. they’re the steels used at the best temperatures. The tool steels square measure usually heat treated. The Quench Hardening method There square measure 3 stages to the quench hardening of steels: answer heat treat, quench, and heat (temper). The Quench Hardening method – answer Heat Treat The steel is command at a warm temperature to dissolve the alloying components into a standardized, primary solid solution beginning section. The time needed depends totally on the dimensions of the half. The Quench Hardening method – Quench The hardening (strengthening) happens here. speedy quenches promote hardening however risk cracking. Slower quenches forestall cracking, however might not sufficiently harden. the subsequent media square measure ordered from severe quench (rapid) to delicate quench (slow) The Quench Hardening method – heat (Temper) instantly once ending, steel is simply too brittle to be serviceable. Tempering is holding the half at an intermediate temperature between the initial answer temperature and therefore the quench temperature. The aim of tempering is to revive impact strength to the hardened half.