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Steel | Steel Composition, Types, Property, Stress-strain Curve

Hello today Civil Experience going to discuss the different material properties of steel because we are going to use steel as a structural material So before going to use that we must know what is the behaviour of the steel using that means using as a structural material like steel

Everything About Steel

We should know the composition of the steel then how the composition is going to vary along with the structural properties then what are the structural properties are there in the case of steel material, What are the advantages of steel and disadvantages of the steel so that we can wisely use the steel as a structural material So these aspects will be discussed

Also, we will see we know the (structure) steel is a to some extent ductile So how it behaves under stress-strain curve means there stress-strain curve of steel we will see how the strain is going to vary with stress those aspects will be discussed in today in Civil Experience article

    Chemical Composition of The Steel

    Chemical composition of the steel basically steel is an alloy which maintains mainly contains iron and carbon apart from the carbon a small percentage of manganese, silicon, phosphorus, nickel and copper are also added to modify the specific properties of steel

    Here in IS 2062-1992 and IS 8500 the chemical composition of structural steel have been given So some of the chemical composition of the different structural grade of steel has been reported in this table like Fe410 of grade A, B, C the percentage of carbon might be shown (refer below Image) So different percentage of carbon, manganese then Sulpher, phosphorus, silicon and carbon equivalent has been given it

    Chemical Composition of The Steel
    Chemical Composition of The Steel

    So with the different ratio of this, we can achieve a particular grade of steel that means a particular weight of steel means a particular strength we will be able to achieve

    Here carbon equivalent means basically the carbon plus manganese by 6 then chromium plus molybdenum plus vanadium by 5 and nickel plus copper by 15 So this summation is called Carbon Equivalent

    This is given here right and the terms in the bracket denote the maximum limit of the flat products. It is giving it for it is for flat product So if we want to produce means if we want to know in a particular weight of steel what is the composition that can be found from this table

    Types of Structural Steel

    Now coming to types of structural steel we can see that one is carbon basically different steel have been produced based on  necessity by changing the chemical composition and manufacturing process 

    So in the case of carbon steel, the structural steel carbon and manganese are used as extra element and another type of steel is high strength carbon steel (HSCS) By increasing the carbon content

    This type of steel can be manufactured which basically produces steel with a comparatively higher strength but less ductility for this type of steel you will get high strength but less ductile

    This is high strength carbon steel another steel is stainless steel in this type of steel mainly foreign materials like nickel and chromium are used along with a small percentage of carbon

    Carbon Steel

    In this type of structural steel carbon and manganese are used as extra elements

    High Strength Carbon Steel

    By increasing the carbon content this type of steel can be manufactured which basically produces steel with a comparatively higher strength but less ductility

    Stainless Steel

    In this type of steel mainly foreign material like nickel and chromium are used along with the small percentage of carbon

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    What is The Property of Structural Steel

    The structural engineer will try to see what is the property of structural steel. Now properties mean a different type of properties structural steel have but being a structural engineer or a steel designer we will be focusing on ultimate strength, yield stress and the ductility

    1. Ultimate Strength
    2. Yield Stress
    3. Ductility

    These three things are very important. These are mechanical properties. this is the ultimate strength what will be the ultimate strength and what will yield stress and then ductility whether it is ductile or not

    These are very important for using the steel and also weldability, toughness, corrosion resistance and machinability are also some of the properties mechanical properties and in these last four properties are important for the durability of the material and often associate with the fabrication of steel members So for durability consideration these last four properties are very important

    We have to keep in mind and mechanical properties of the steel largely depends on these five  things one is the chemical composition

    Chemical Composition of Steel

    Chemical composition So we have to know what is a carbon percentage is given and other different elements what is the percentage of that are present So depending on that the mechanical properties of the steel will vary and that the heat treatment

    Property of Structural steel
    Property of Structural steel

    How the treatment going to be made for producing steel then stress history, rolling methods and rolling thickness So these are the few things few parameters which we have to keep in mind  for getting the structural property of the steel because these structural properties of steel largely depend on this 

    Now the structural steel whatever we are using should conform to the IS 2062-2011 is hot rolled medium and high tensile structural steel So it should conform to this code and we use mostly the Fe 410 grade of steel Most commonly used weight

    Structural Steel
    Structural Steel

    In general, we can see that it is Fe 410 and few physical properties of structural steel which are given in IS 800-2007 in clause 2.2.4.1 because this is also these properties also will be required for some times like unit mass of steel rho the density of the mass density of steel is 7850 Kg/m3 

    This is required because when we are going find out the self-weight of the structure self-weight of the steel structure then we have to find out (the) what is the weight of the steel, in that case, we have to know the mass density of the steel unless we know that we will not be able to get the proper load  self-weight what is coming due to the steel member

    Modulus of Elasticity of Steel

    Modulus of elasticity this is also important to find out the thickness of the steel member and we consider that E = 2.0 x 10N/mm2

    Poisons ration also is important which we consider in general 0.3 and modulus of rigidity G we considered as G = 0.769 x 10N/mm2 and co-efficient of thermal expansion for heat related problem (we will) we have to consider this thermal expansion that is α = 12 x 10-6 /°C because steel 

    We can expand or contract because the stress may develop so that thermal stress whatever is going to be developed that has to be calculated and that traditional forces have to be calculated while analyzing their structure So in that case thermal expansion coefficient is important

    Mechanical properties

    Now coming to mechanical properties as I told the three things are very important is one is yield stress what is the yield stress of the steel, What are the ultimate stress and the minimum percentage elongation

    Mechanical properties
    Mechanical properties

    Minimum percentage of elongation so these we can find out in table 1 of IS 800-2007 mechanical properties of structural steel like we use Fe 410 grade of steel So in that case the yield stress is put as a 250 and ultimate stress is 410 in MPa and elongation percentage is 23

    Here you see another yield stress is given for thickness from 20 mm to 40 mm for this 250 we can achieve if the thickness is less than 20 mm but t if t is 20 to 40 then 240 and if t is this thickness is more than 40 mm then the yield stress is going to be considered as 230 MPa So for Fe 410 grade of steel what we use 

    We use yield stress either 250, 240 or 230 and ultimate stress as 410 and elongation percentage as 23 Similarly Fe 440 grade of steel we can find out yield stress as 300 and ultimate tensile stress as 440 and elongation is  22 So in this way we can find out the important properties like yield stress  ultimate stress and percentage elongation from the grade of steel if a particular grade of steel is given then we can find out what is the yields stress ultimate tensile stress and  grade of steel right

    Ductility

    Now coming to ductility a very important parameter in the case of steel design is ductility So I will discuss a little more about ductility

    It is the ability to deform under tensile force. Ductility is basically the ability to deform under tensile force and  it undergoes large emulatic deformation in in case of ductility

    Ductile material deformation happens and emulates deformation means permanent deformation without loss of strength under the application algorithm So if we see something like this the stress-strain diagram of the material if this is strain and this is stress then  this portion is basically the ductility portion where stress is not developing as such but the strain is going to increase and if we release the load it will be coming to its earlier position of course of in not in the same path because it is inelastic but it will come to its earlier position with deformation

    This ductility means if the material is ductile that means it will be much more seismic-resistant So we prefer ductile material so that deformations are allowed without failure

    Then another property we also come across which is called hardness

    Hardness

    Hardness is one of the mechanical properties of steel by virtue of which it offers resistance to and scratching So hardness can be measure by a different test like the Rock well hardness test. well hardness test Another test we make is called the Vickers hardness test and then another test through which the hardness is measure is called the Brinell hardness test So through this one can test the hardness of the material and another property also

    We come across is called toughness So I am discussing some property such as mechanical properties and other properties of steel which is important to know for designing the structure and when we are going to design a member we must know what is a behaviour of the member under load say for example if we make a stress-strain diagram of material say stress and strain so brittle material means it will be like this and suddenly it will fail brittle material and ductile material means it will not fail it will undergo strain So this is a ductile material

    Toughness is the ability to absorb energy up to fracture

    Toughness

    Toughness is called the ability to absorb energy up to fracture and this toughness is measure by the area under the stress-strain curve So stress-strain curve of this material and stress-strain curve of this material the area we can find out and we can measure the toughness So 

    The ability to absorb the energy up to facture is called toughness 

    It is one type of mechanical property of steel So basically, it offers resistance to fracture under the action of the impact load So this is one property another is fatigue

    Fatigue

    Fatigue means the repeated loading.

    It is means damage is caused due to repeated loading repeated fluctuation of stress and which leads to productive cracking of the structural element and due to cyclic loading damage and failure of the material may happen which is called fatigue

    Resistance Against Corrosion

    Resistance against corrosion means what is a resistance property against corrosion that also we have to keep in mind In presence of moisture corrosion of steel is means corrosion of steel happens So to avoid that what we can do

    We can go for painting or metallic coating So either of these two can be made to take care of the corrosion So this is one property which we have to keep in mind and then another property is residual stress

    Residual stress

    Residual stress comes into the picture because of unable heating and cooling because of unable heating and cooling the residual stress is in the member develop 

    So how the material has been produced depending on that what is the residual stress there that we can calculate we can found and accordingly the design of the member can be done

    Then another is stress concentration when certain changes of  geometry properties are there say stress concentration concentration 

    Stress Concentration

    It is basically a highly localized state of stress where at particular location stress is concentrated and because of the abrupt change of the shape in the vicinity of the notch where say suppose a member is like this so sudden change at the vicinity of the notch can make the development of stress concentration

    Also during near the hole, the stress also generated several times greater than the actual stress and for that, we have to take care that means when we are going to design there may be chances of failure at a certain localized point because of concentration of stress

    So we have to make the section in such a way their stress concentration can be avoided

    Also ReadSegregation of Concrete Causes & Prevention of Segregation

    Stress-strain Curve

    Strain curve of the mild steel now we will come to the stress-strain curve So stress-strain curve of the mild steel we will see first say this is a strain which is called epsilon and this is stress which is called sigma

    Now in the case of mild steel, an ideal curve looks like the below image So this is the origin from where stress-strain

    ideal stress-strain curve
    ideal stress-strain curve

    Curve develops and this is point A this point A up to point A that means up to O means from point O to point A is called the limit of proportionality

    This portion is called the limit of proportionality that means proportionality right that means up to this it is linear and it obeys the hooks law So OA is basically called the limit of proportionality

    ideal stress strain curve
    ideal stress strain curve

    Then from A to B actually after reaching point A change in strain is rapid compared to that of stress but still the material behaves elastically up to an elastic limit of B It behaves elastically but a change of strain is rapid compared to stress up to point B means part AB right So this up to point B is the elastic limit then point C' is the upper yield point means 

    If we go on increasing the force then we will observe that yield point means it reaches yield point upper yield point So after upper yield point again it will come down to say C is the lower yield point 

    This observation of C' and C point depends on the rate of loading it means depending on the rate of loading we can observe the point C and C dash

    Then CD part so beyond yield point the material start flowing plastically without any significant increase in the stress and material goes large deformation So CD part is basically plastic

    Plastic part So it means it flows like plastic and without any increase of the stress the strain increases then up to point E

    DE means after reaching point D strain hardening occurs in the material and who is here the requirement of higher load to continue the deformation. This phenomenon is called strain hardening that means it resists deformation and needs more load to deform So after CD means where the load was not increasing but after that point it starts resisting deformation So strain hardening occurs so with the increase of stress-strain also is going to increase up to a certain level which is highest point E 

    E represent the fu the ultimate stress and after that, the stress going to be reduced and at a certain point it breaks So f is a breaking stress right f is the breaking stress so this is how the material behaves So what we need to know that when we are going to design a steel member we have to know what is a property of steel under load that means stress-strain diagram how it varies in case of mild steel it varies in a way in case of torque steel it varies another way so we have to know and accordingly 

    We have to find out what is the fu value and what is fy value and what will be the strain at fu and strain at fy right that means how much ductile

    This material is depending on that means we can think of designing the member properly So when we go to the design procedure member when a member is going to be designed under certain procedure like working stress method or limit state method or ultimate stress-strain design method 

    We have to know the stress-strain diagram, stress-strain behaviour of the material so that we can understand that up to what level we are going to allow the deformation and then how we are going to find out the maximum allowable stress and then according to that design criteria would be decided So this is all about the day's lecture Civil Experience article about the steel as a structural material

    Also Read: Civil Excel Sheet
    FAQ 1: What are Types of Structural Steel?

    1. Carbon Steel In this type of structural steel carbon and manganese are used as extra elements 2. High Strength Carbon Steel By increasing the carbon content this type of steel can be manufactured which basically produces steel with a comparatively higher strength but less ductility 3. Stainless Steel In this type of steel mainly foreign material like nickel and chromium are used along with the small percentage of carbon

    FAQ 2: What is The main Property of Structural Steel

    The structural engineer will try to see what is the property of structural steel. Now properties mean a different type of properties structural steel have but being a structural engineer or a steel designer we will be focusing on ultimate strength, yield stress and the ductility

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