Comparison and Effect of Different Shot Peening Parameter on Steel Blades with 12%Cr

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1 ISSN (Online): , ISSN (Print): Volume 2 Issue 2 Feb 215 Comparison and Effect of Different Shot Peening Parameter on Steel Blades with 12%Cr S. Srilakshmi 1, Mohamed Abbas 2, P.Muniraja Chandra 3, R.Manikandan 4, Mohd.F.Shabir 5, B.Dilip Jerold Assistant Professor, Department of Mechanical Engineering, Aalim Muhammed Salegh College of Engineering,Chennai 56 Professor, Department of Mechanical Engineering, Aalim Muhammed Salegh College of Engineering, Chennai Abstract: 12% Cr steel is extensively used as blading material for LP turbine component. These steels undergo different damage processes like corrosion and fatigue. Fatigue is the main damage process for the failure of blades. To increase the fatigue life, compressive stresses are induced on surface using shot peening process. In this work, the residual stresses are measured on the surface with different parameters of shot peened samples. stress is measured using X-ray Diffraction (XRD) technique. The developed and used assessing the residual life of the 12%Cr steel blades for different shot peening parameters. Keywords: 12%Cr Blading steel,, XRD, Shot peening. 1. INTRODUCTION Thermal Power Plant materials play an important role. There are varieties of material which will give us power consumption in the thermal systems. The above materials are extensively used in generator; boiler feed pump shafts, steam turbine blades, control value steam etc. The material of the equipment will depend as a function of service life due to the damage mechanism such as creep, fatigue, erosion, wear etc on many operating conditions. Due to these operating conditions the components may prematurely fail such as fatigue, environment, improper material processing, residual stresses, error in design etc. To ensure the satisfactory performance of the components during the projected service life of the component their effectiveness and failure mechanism have to be understood so that we can prevent or control their manifestation [1]. Steam turbine blades components are susceptible to premature failure that has a serious economics and safety implication. Blading steel is a Martensitic stainless steel. These steels are used in LP turbine blades due to their good corrosion resistance and moderately high strength. Failure statistics of these steels occur in the last stage of the region because of the environmental conditions, loading patterns, vibrations, high temperatures, corrosion, erosion etc. residual life assessment plays a very important role in increasing the life of existing power plant [4]. Fatigue failure initiation takes place on the surface in the form of a crack and even tensile stress also takes place on the surface and which is the major responsible for this initiation to occur on the component. The presence of tensile stress in the component is the important fatigue failure on the surface which is unfavourable for the component. To measure their residual stress there are so many methods can be used. Among the various methods, X-Ray Diffraction method is the best method and gives accurate reading for measuring the residual stresses on the material[5]. 17

2 ISSN (Online): , ISSN (Print): Volume 2 Issue 2 Feb 215 Fatigue occurs when a material is subjected to a repeated loading and unloading. The shapes of the structure will significantly affect the fatigue life. For some materials there is a theoretical values for stress amplitude below which it will not fail for any number of cycles called fatigue limit or fatigue strength. To improve fatigue resistance we should try to avoid tensile means and have compressive means stresses. To enhance the fatigue resistance of the materials there are many methods of inducing residual stresses. In which they will increase the life of the material of various methods. The various methods are as follows: Mechanical Method, Thermal Method, Plating, Machining etc. For measuring the residual stresses on the material there are many methods such as Hole-drilling, ultrasonic, magnetic method, X-ray diffraction, electron diffraction etc [7]. X-Ray Diffraction method is chosen for measuring the residual stresses. The residual stresses on the material are measured with the instrument XSTRESS 3 equipment which is manufactured by -tech Group, Finland. This method works on the principle of Bragg s Law[18]. Shot peening has been chosen for improving the life of the component. Shot peening is carried out in the equipment MECSHOT; Pune. Shot Peening is a cold working process used to produce a compressive residual stresses layers and modified mechanical properties of metals. It entails impacting a surface with a shot with a force sufficient to create plastic deformation [12]. Peening a surface spreads it plastically, causing changes in the mechanical properties of the surface. The work done on the surface mainly depends on a number of factors. Size and material of the spherical shot is important, as is its velocity and the rate and angle at which the blast pattern sweeps across the surface. The relative work done to the surface is called the Peening intensity [16]. As there are many variables in the shot peening method such as shot size, nozzle diameter, velocity, intensity, flow rate, coverage etc. each parameter will have their importance. The shot size, short hardness, intensity and coverage are the four important variables in this process. The main advantage of this process is it will increase the resistance to fatigue, corrosion; hydrogen assisted cracking increased strength, increased durability. Depth of profile is measured by electro-polishing [19]. The fatigue resistance of the material is improved by inducing surface compressive stresses, and in this study the effect of variables on stress in terms of is investigated. 2.EXPERIMENTAL PROCEDURE The material and the experimental procedures used in the present work. Material Used: The material for this investigation was taken as 12%Cr Blading steel, widely used in low pressure of steam turbine blades. PROCEDURE: The experiment consists of basic steps sample preparation, calibration of the equipment and measurement. Sample Preparation: The material used was in the form of bar of size 8*2*1mm. The sample on which the residual stress measurement is carried out is measured by XSTRESS3. For e.g. Exposure Time (sec) 2 No. of inclinations 4/4 Inclinations (deg) - 4 to +4 Angles Auto Psi-oscillations ± Material: The material under this test is a shot peened hardened blading steel sample. Shot Peening: To induce the surface compressive stresses in the material block samples were shot peened in a peening set up using different combinations of shot sizes, nozzle diameter, shot flow parameters. Peening intensity is 18

3 Journal of Recent Research in Engineering and Technology ISSN (Online): , ISSN (Print): Volume 2 Issue 2 Feb 215 estimated by using Almen Strip, and therefore 1 the block samples were peened off. Measurement: It is carried out on the shot peened blade samples using the XSTRESS 3 machine. Measurement parameters were finalized. With the stress free samples calibration is carried out. Now stress measurement is carried out on all the shot peened samples including as received. The profile is also measured on the shot peened samples by using the equipment Movipal-3 machine for electropolishing at a time of 3sec with a current of 1A and the material is scooped out. A prototype electrolyte was used as media for electro-polishing the material. At the same location every sample up to.3 mm residual stresses was measured at a standard interval by scooping of the material by the same method. 3.RESULTS AND DISCUSSIONS Blading steel is a steam turbine blade component has a susceptible to premature failure that has a serious economic and safety implication. These steam turbine blades are used for different environment and for different processing conditions. In which there have a particular interest to power industry and have a more important in the present study. Shot penning has been chosen for improving the life of the component by enhancing the surface residual stresses. Shot peening is a cold working process used to produce a compressive residual stresses layers and modified mechanical properties of metals. In the present investigation, an attempt that has been made to understand the role of residual stresses on shot peened blading steel. The results obtained in this investigation at various stages when is.3 mm for shot size of 4mm at different air pressure and intensity are incorporated and listed below: Fig 1: stresses at a of.3 mm, for shot size 4 mm at air pressure 2.8 kg/sq.cm with an intensity of Fig 2: stresses at a of.3 mm, for shot size 4 mm at air pressure 2.5 kg/sq.cm with an intensity of Fig 3: stresses at a of.3 mm, shot size 4 mm at air pressure 2.2 kg/sq.cm with an intensity of

4 ISSN (Online): , ISSN (Print): Volume 2 Issue 2 Feb 215 Discussion: The present aim was to establish shot peening parameters, in this section an attempt has been made to bring out the role of residual stresses present on the surface of the material to enhance the resistance to fatigue failure. A uniform surface finish has been achieved on shot peened blade samples. Shot size and Air pressure have the most influence on the residual stresses. Air pressure appears to be the most influencing role on the of the residual stresses. Air pressure and Almen intensity are also significant factors in terms of surface compressive residual stresses and on to which the residual stresses can be imparted. This give a compressive residual stress of 3MPa or more at a of.3mm from the surface. To achieve this requirement without affecting the surface finish a number of experiments has to be performed. Based on the results tabulated all the shot peened samples compressive surface residual stresses were observed. Keeping the shot size as constant and the other two parameters like almen intensity and air pressure are variables, the increased trend of residual stress pattern was observed by increasing the air pressured and almen intensity. By keeping the nozzle diameter as constant and varying almen intensity and air pressure are as variables, the increasing trend of residual stress pattern was observed by decreased the air pressured and almen intensity. Shot flow was kept constant and the other two parameters almen intensity and air pressure are as variables, the increased trend of residual stress pattern observed by decreasing the air pressured and almen intensity. As shot size increases with respect to air pressure and Almen Intensity the compressive residual stresses are also increased. Shot size also plays a very important role in shot peening and found that shot size increases the compressive residual stresses. If air pressure is kept constant with respect to shot size the compressive residual stresses are increased in higher shot size range. 4. CONCLUSIONS o The results will be useful in design, enhancing, and understanding the material behavior. o The shot peening process, being versatile and economical, can be easily adapted for other application to introduce compressive residual stresses. o On all the shot peened samples compressive surface residual stresses were observed. o With shot peening compressive residual stresses can be introduced into the surface of the steel under investigation which enhances fatigue properties. o Fatigue life is found to increase during the process of shot peening due to the fact that the compressive residual stresses reduces the crack initiation as tensile mean stresses on the surface of the component are no longer operative. o The results of the study indicates that variation of shot sizes would probably have a major influence on the magnitude of compressive residual stresses introduced REFERENCES: 1. International conference on life of power plant equipment-prediction and Extension Jan 23-25, 1989, Hyderabad. 2. Speidel,M.O: Corrosion failure of steam turbine blade materials, work shop proceeding, palo Alto (Ed)21-24, Sep Bashu.S.A, Singh.K, Rawat.M.S; effect of heat treatment on mechanical properties and frature behaviour of 12crMoV steel, Material sceience &engg. A127,7-15, BHEL R&D Literature Resources The following major conclusions are draw on the above experimental results. 5. Cullity.B.D:Elements of X-ray diffraction; Addition-Wesley publishing Co.Inc;

5 ISSN (Online): , ISSN (Print): Volume 2 Issue 2 Feb Macherauch, E: stresses Conf proc: Application of fracture mechanics to materials and structures 7. Risch,K shot peenig to prevent stress corrosion cracking and corrosion fatigue failures of autenitic stainless steels, ICPS 3, Germany stresses:part1 measurement techniques by P.J.withers and H.K.D.H. bhadeshia http// Laser hardening of cutting tools by Miralles marc, Master of Science Programme, department of applied physics and Mechanical Engg Mechanical engg.tv 14. Risch,K shot peenig to prevent stress corrosion cracking and corrosion fatigue failures of autenitic stainless steels, ICPS 3, Germany stresses:part1 measurement techniques by P.J.withers and H.K.D.H. bhadeshia 16. Sharma, M.C.:shot peening and corrosion fatigue of structural steel with different surface condition under seawater, conference, fatigue9, Honolun, hawai15-2, July Operating Instructions and Instrumement Document for X 3 system with Floor Stand and X-Y unit 19. Measurement of measurement by X-Ray Diffraction by PDF 17. Hayashi, effect of preliminary surface working on fatigue strength of type 34 stainless steel in air 2 pure water at 288 C,journal of the society of material science, japan 45 (1), Oct