How To Study The Tensile Properties Of Stainless Steel

Transcription

1 A Coparative Study of Tensile Properties of Two Different es of Stainless Steel at Different Teperatures Haza Zafar Physics Faculty National University of Coputer and Eerging Sciences (FAST) Lahore, Pakistan Syed Karrar Haider Physics Faculty National University of Coputer and Eerging Sciences (FAST) Lahore, Pakistan Abstract Two grades of stainless steel: 316 and 201 were annealed at constant teperature for suitable duration of tie. The annealed speciens were first tested at 300K, up to fracture. Afterwards, the test teperature was increased to 500K, with an interval of 50K.The stress-strain curves were obtained with the help of software operated Universal Testing Machine (UTM).The study was carried out to draw a coparison between the tensile paraeters like Yield stress, Tensile stress and Ultiate tensile stress of the chosen grades of stainless steel at various teperatures. Introduction Stainless steel is a solitary versatile aterial. Stainless steel is used by people in food, edical instruents, transportation, restaurants, kitchens, toasters, vacuu cleaners, new vehicles and continues to influence their lives every day. Stainless steel is itself fully recyclable according to our requireents. Stainless steel being failiar etal of 21 st century.introductory and invention credentials of Stainless steel goes to Harry Braerley, son of steel elter.in 1908, proper working on stainless steel was started in Brown Firth Laboratories, Sheffield, England [1]. Stainless steels are defined as iron based alloys containing at least 10.5% chroiu and a axiu of 1.2% carbon[2].stainless steel have drawn wide attention as versatile aterial for ultiple applications due to their excellent Corrosion Resistance. Corrosion resistance is not an intrinsic property of a aterial, but the behavior of that aterial that stes fro the interaction with the surrounding ediu and the aterial s surface. The corrosion resistance in stainless steel is provided by a passive surface fil which acts as a barrier between the alloy and surrounding ediu [3].Chroiu plays an essential role in the foration and the stabilization of the passive aterial. A iniu of 10.5% chroiu is required for the foration of a protective layer of chroiu oxide on the sheet surface. The stability of the passive fils depends upon the chroiu content, by increasing the chroiu content fro 10.5% to 18% provides ore stability of passive fils. Aerican Research Institute for Policy Developent 23

2 Every Metal has its disadvantages and stainless steel is no exception. Soe of the priary disadvantages include: its fabrication without using the proper techniques, the difficulty in welding due to its fast dissipation of heat which can also produce ruined pieces. Stainless steels are generally classified according to their icrostructure as a) Ferritic b) Austenitic c) Duplex d) Martensitic The relationship between coposition, structure and properties of different grades of stainless steels is suarized in Fig.1. Fig.1 Coposition, Structure and Property Relationship of Stainless Steels [4] Fig.2 Stainless Steels classification [5] In our current research, we study the echanical properties of Stainless Steel; tensile strength, yield strength, elongation and hardening. The tensile properties were studied with the help of Japanese Universal testing achine. The tensile properties of a stainless steel are generally deterined fro tension tests on sall speciens in accordance with standard procedures. The behavior is closely related to the behavior of structural-steel ebers under static loads. Because, for structural stainless steels, the yield points and oduli of elasticity deterined in tension and copression are nearly the sae, copression tests are seldo necessary. Aerican Research Institute for Policy Developent 24

3 In studying the tensile properties, Hooke s law deterined the liit of proportionality. Alost every aterial obeys Hooke's Law, which states that if a load is applied to a aterial, it will defor in a proportional anner to the aount of applied load. The odulus of elasticity is siply the ratio of stress to corresponding strain below the proportional liit of the specien. It is also referred to as Young s odulus; it has units of psi or N/ 2.Yield point is that point where a tensile test piece begins to extend peranently. If the load is reduced to zero, the test piece will not return to its original length. The yield point arks the end of elastic behavior and the beginning of plastic behavior. Fig 3: Stress Strain Graph[6] For any aterials that do not have a well-defined yield point, a quantity called yield strength is substituted. Yield Strength is the stress at which a aterial has undergone soe arbitrary chosen aount of peranent deforation, often 0.2 percent. The resistance of a aterial to a force tending to tear it apart, easured as the axiu tension the aterial can withstand without tearing. This is the point at which the axiu stress the specien and aterial is capable of withstanding is reached.this is the point at which the saple finally breaks. It should be noted that the Breaking point and the Ultiate point are, ore often than not, two separate, distinct points on the stress / strain curve. Experiental Work: Step(a) Selection of aterials and setting its diensions: The aterial involved in our current study is Stainless Steel es 316 and 201.The grade 201 and 316 stainless steel specien cut into the desired length. Step(b) Grinding and Polishing of Speciens: In our research study, Grinding and polishing of speciens is very iportant for reoving the dirt layers on the surface of specien and regain its original shine. The speciens were polished with silicon carbide paper.silicon carbide no.120 and 320 were used for polishing the specien. The grinding and polishing were carried on both sides of speciens. Step (c) Setting the specien in Universal Testing Machine: For our research purpose i.e Tensile tests, were carried out using the Trapeziu software operated achine called Universal Testing Machine. A UTM has ability and efficiency to perfor standard tensile and copression tests on speciens, coponents, and structures. Aerican Research Institute for Policy Developent 25

4 The ain coponents of Universal testing achine used to carry out experiental results are; a)load cell (Overload protect High accuracy force transducer). b) Manual wedge tensile grip ( tensile Grip, firly holds the specien). c) Cross head displaceent restricts. d)software operated (Trapeziu). The speciens were ounted in the cross heads of achine, cross heads firly hold the specien in the jaws. After ounting the specien the tension was subjected, the cross heads oved with a speed of 1 per second. The tensile force was recorded as a function of the increase in gauge length, as shown in the graph (a).the speciens were first tested at roo teperature. The teperature was then increased with an interval of 50K and finally the speciens were tested at 500K. Graphs a)stress Strain graph(e 201) Aerican Research Institute for Policy Developent 26

5 b)stress Strain Graph(e316) Speci en e 316 e 316 e 201 e 201 Gau ge leng th 5.6c 5.6c Results: Dia ete r 0.56c 0.56c 3c 0.39c 3c 0.39c Cross head speed 1/in 1/in 1/in 1/in Specien Tept Tensile Strength Proof Stress %age elongation e 316 At roo 495 MPa 20% teperature 185MPa e K 510 MPa 201MPa 26% e 201 At roo 1800 MPa 1490MPa 33% Teperature e K 1880MPa 1570MPa 39% Aerican Research Institute for Policy Developent 27

6 The above table displays the results of Stainless Steel grades: 316 and 201 at roo teperature and 500K.The percentage elongation was easured to be 20% at roo teperature and 26% at 500K in case of e 316.While the elongation was found out to be equal to 33% and 39% at roo teperature and 500K respectively. This was the observation ade in case of e 201.The effect of increasing test teperature on the tensile properties shows the increase in unifor elongation while the yield stress increases as the test teperature is raised.the response of echanical properties shows that the ductility of specien increases as the yield stress increases. The rise of teperature results increase in yield stress, tensile stress and ultiate tensile strength of the speciens. This happens as plastic deforation, registers an increase with the rise of deforation teperature. Conclusion The research work has been taken up to study the effects of different teperatures on the Stainless Steel es:316 and 201. Tensile properties of the speciens were deterined fro the autographic records by using the Universal Testing Machine of 50 KN in teperature ranging up to 500K. Fro the different graphs axiu stress and strain points were observed and the %age elongation was easured through these curves. The percentage elongation increases with the increase of test teperature increase of test teperatur References Page 01-02(2011) European standard EN :Stainless Steels-Part 1:List of Stainless Steels vol.01;03-04(2012) Stainless Steel, Mechanical properties vol 01; 4(2001) J. E. Castle and J. H. Qiu, Corrosion Science, Vol.30, No.4; (1990). Stainless Steels-when health coes first;6(2010) Aerican Research Institute for Policy Developent 28