Effect of Auxiliary Mechanical Vibrations on Mechanical and Metallurgical properties of Stainless Steel (AISI 202)

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1 IJME, Vol. 1, Issue 1 (Jan-Feb 2014) e-issn: p-issn: Effect of Auxiliary Mechanical Vibrations on Mechanical and Metallurgical properties of Stainless Steel (AISI 202) Vivek Kumar Sharma 1, Munish Kainth 2 1,2 Mechanical Engineering Department, Universal Institute of Engineering & Technology, Lalru, Punjab (India) 1 vivek3052@yahoo.com, 2 kmunishk@gmail.com Abstract-The aim of the work was to obtain a modification in mechanical properties and metallurgical properties of microstructure by auxiliary mechanical vibrations. The study was done to investigate the effect of auxiliary vibratory set up on the mechanical properties of 8 thick stainless steel (AISI 202) butt joint. Bad bead profile has a considerable effect on the performance of weld. One pass of a multi-pass welding has a bad bead profile it can cause incomplete fusion or slag inclusions, even though the subsequent weld assess will partially remelt the first pass. The auxiliary vibration produces disturbance in weld pool during solidification. After completion of nucleation the solidification process will continue with nucleus growth. The weld joint fabricated under vibratory condition was found to possess high tensile strength. Keywords- Manual Arc Welding (MAW), Heat Affected Zone(HAZ), Vibratory Weld Conditioning(VWC), Shielded Metal Arc Welding(SMAW), American Welding Society(AWS), American Iron and Steel Institute(AISI) I. INTRODUCTION Mechanical properties most required of weld metals are toughness and strength. Properties of weld metals are greatly influenced by type of microstructure and grain size. Fine grained materials normally have higher strength and are more ductile than similar coarse grained materials. In addition, the lack of segregation and/or second phases also contributes to higher strength and ductility of materials since there are fewer areas for localized yielding and stress raisers. It is often intended to achieve fine grain structure in the weld bead because such structure leads to:- 1) Reduced susceptibility of the weld metal to solidification cracking during welding. 2) Fine grain help improve mechanical properties like ductility and toughness of weld metal. II. LITERATURE REVIEW This chapter discusses the literature review carried out in order to identify the research gaps in the broader area of micro structural modifications for enhancing the mechanical properties, so that the problem could be identified and accordingly, the objectives be formulated to accomplish using a systematically devised methodology/approach. Many researchers have analyzed the effect of vibrations on microstructure and mechanical properties of welded joints and have reached a generic conclusion that vibrations are able to alter/enhance the microstructure thus improving the mechanical properties of welds and cast elements due to the fundamental reason that mechanical properties of welds are influenced by the microstructure and grain size of welds. Mechanism Of Solidification Of Weldments Under Vibratory Condition Watanabe and Nakamura (1990) [2] investigated the effect of electromagnetic stirring on microstructure of SVS 310 S. They examined the parameters to achieve grain refinement like magnetic field intensity, the frequency of alternating International Journal of Mechanical Engineering 1

2 stirring and the relative distance from electrode to magnetic field centre. Their work included laying bead on plate TIG welds under the condition that welding current was 60A and travel speed was 3 cm/min. A significant decrease in the grain size of weld metal could be achieved when the electrode was located 1-2 cm apart from the magnetic field centre in the welding direction and the stirring frequency was Hz. Their work concluded that grain size change/refinement might be due to fragmentation and the increase in constitutional super cooling ahead of solidification interface due to the molten metal stirring assisted by the weld metal in grain refining. Izdinska (1990, 1991) [3] studied the effect of ultrasonic treatment upon fatigue properties of welded joints. His finding was that due to ultrasonic reduction macroscopic residual stresses had a favourable effect on the fatigue properties. This finding was rather favourable when compared with annealing. Dvornak et al. (1991) [4] while studying the solidification under vibratory conditions concluded that the grain refinement so observed was due to the lower energy required for the nucleation of the solid phase. However, the rapid removal of latent heat of solidification from the solid-liquid interface played a minor part in the grain refinement under vibration. Wei (1992) [5] introduced longitudinal steady state sinusoidal vibrations into the unidirectional dendrite solidification process of Al-3 Mg alloy in first (470 Hz), second (1050 Hz) and third (1736 Hz) order resonant frequencies of solidification system to produce strong vibrations response out of less exciting energy. He observed that alloy mechanical properties are appreciably improved if the second and third order resonant frequencies are applied. Miclosi et al. (1993) [6] found good effect of electromagnetic oscillation upon the characteristics of weld. They found that the present of the electromagnetic axial pulsation of the electric arc led to smaller penetration and enlarged the width of the weld. This is favourable effect from the point of view of heat cracking because deep and narrow weld run a higher risk of heat cracking. Govindarao P. et al. (2012) [8] studied that small grain structure is attained due to the effect of vibration Increase in hardness leads to crack initiation along the weld bead, so it is not preferable. During manual butt weld joints uniform long dendrites which show that a uniform solidification process took place with uniform dendrites. Due to auxiliary mechanical vibrations long dendrites break and form a new nucleation sites. AIM OF THE OBJECTIVES Based upon the research gaps identified the following objectives were formulated:- 1) Design and development of a setup for inducing auxiliary mechanical vibrations into the weld pool during welding 2) To study the effect of auxiliary mechanical vibrations on the mechanical properties of butt welded joints using SMAW process on stainless steel combination III. EXPERIMENTAL SET UP An auxiliary mechanical vibration during welding is provided with the help of vibration table. It is designed to carry a load of 140 kg. The apparatus consists of a motor fitted with a variable pitch pulley housed in a cabinet. The vibrations are imparted by means of off-balance masses rotating on a shaft of a vibrator clamped to the underside of the table top. The table top is 50cm x 50cm. and has stops along its edges. The variable pitch pulley arrangement permits the frequency to be varied steplessly between a maximum of 3600 vibrations down to 1600 vibrations per minute. A speed regulation handle is provided for increasing or decreasing the frequency. A switch is provided for starting and stopping the motor. The motor is 3-phase and is suitable for operation on 440 volts, 50 cycles, A.C.supply. The set up has to be in direct contact so as to produce the vibrations under the weld pool. Qinghua, Lu et al. (2007) [7] studied that the microscopic structure has dramatically changed after V-SAW. Vibratory energy breaks up the growing dendrite grains in the weld and the HAZ. A Significantly higher weld pool velocity which leads to a faster the heat removal during solidification is produced in VWC. Thus, the higher the cooling rate, the more the nuclei coming into play and the smaller the grain size. And a finer grain size benefits the mechanical properties. International Journal of Mechanical Engineering 2

3 SELECTION OF ELECTRODE The selection of electrode for welding the stainless steels is based on the composition of the S.S being welded. It is possible to weld several different stainless steel grades with one filler metal. For shielded metal arc welding (SMAW) there are two types of electrode coatings as per AWS classification. These are E and E The prefix E indicates that it is an arc welding electrode followed by AISI s three digit number. This number indicates the type of stainless steel in the filler metal. To the right of AISI number, the AWS adds dash followed by suffix number. The number 15 is used to indicate that there is a lime based coating so DC is used. The number 16 is used to indicate that there is Titania type coating so AC & DC welding current can be used. The lime type electrodes are more crack resistant and are slightly better. So, that is why E welding electrode is used. Model AWS E Fig: Vibration Table SELECTION OF MATERIAL Stainless steel (SS 202) is selected for this experiment. The dimensions of the plates are 100*100 each and 8 thick. Stainless steel 202 is an Austenitic Standard Grade Stainless Steel. It is also called AISI 202 Chromium-Manganese-Nickel steel. Its chemical composition is composed in table no-1. Table 1: Chemical Composition of SS 202 Element Weight % C 0.10 Mn Si 1.00 Cr Ni P 0.06 S 0.03 N 0.25 Deposited metal chemical composition (%) Diameter 3.15 Type coating type coating character weld power source length use Introduction C 0.08 Mn0.5~2.5 Si 0.90 S P Cu 0.75 Ni9.0~11.0 Mo 0.75 Cr18.0~21.0 stainless steel Titanium calcium Acidity AC or DC 340 Used for welding 0 cr19ni9 and 0 cr19ni11ti stainless steel structure which work temperature below 300,corrosion resistance AWS E is lime-titania type medicine leather Cr19Ni10 stainless steel electrode. Deposited metal has good mechanical properties and resistance to intergranular corrosion resistance. Have good welding processing properties and resistance to cracking. Can be used on ac/dc. SELECTION OF TYPE OF JOINT & WELD TYPE The butt joint is used to join the ends or edges of two plates located approximately in the same plane with each other. Light gauge section requires 90 sheared edges with no International Journal of Mechanical Engineering 3

4 spacing between them. Materials ranging from 8 to 13 thick, which can be welded from one side, should be reduced either as a single-v or a single U joint. It is generally more expensive to prepare a U-shape rather than the straight edged V or bevel. So, single V- butt joint-with gap is selected as shown in fig. below. Fig: Groove Weld [1] IV. EXPERIMENTAL DESIGN & ANALYSIS Fig: Single Vee Butt With Gap [1] Now, Edge is prepared with the help of End mill cutter on milling machine such that the bevel angle becomes 32 and 1 is left at the bottom of plate to make root face. The plates are kept at a distance 1-2 apart from each other to accoodate root opening as the plates are >6 thick. First of all auxiliary vibrations are to be provided during welding and to solve this purpose vibration table is made available. This vibration table will provide the auxiliary vibration during welding. Now, an arrangement to hold the S.S plates (S.S 202) is to make which will hold the work piece during Vibration welding. For this purpose M.S plate of slightly bigger dimension is welded on the top of the table as shown below. Fig: Edge Preparation There are different types of welds. Some of these welds have many variations and also weld types can be combined together. Groove weld is the second most popular weld type (first one is Fillet weld). It is defined as, a weld made in groove between two members to be joined. The groove weld is regarded as being in the joint. There are different groove weld design based on type of edge preparation, and they can be used as single or double welds. Fig: Vibration Table Now, two S.S plates each of dimension 100*100 are held as shown in figure with the help of C-clamps. The plates are kept 1-2 apart from each other so that the weld pool fills completely between the two plates during welding. International Journal of Mechanical Engineering 4

5 these 4 passes are made with conventional SMAW process (i.e without auxiliary vibrations). After each pass slag is removed with the help of chipping haer to ensure that there should not be any cavity in the weld pool. These plates after SMAW welding are marked N-1 and are shown in Fig. Fig: SS Plates Clamped On Vibration Table Now, Shielded Metal Arc Welding is to be carried out in order to make butt joint on SS plates. First of all vibration table is earthed in order to have SS plate conducting. A current of 200 amperes is supplied then arc is created by striking in between the plates. There are 4 numbers of passes to make the butt joint. 3 of these passes are main passes which are made under auxiliary vibrations and 1 is root pass. In the root pass the auxiliary vibrations are not provided. Then after the root pass is made, the auxiliary vibrations of 60 Hz and of amplitude 4 are provided with the help of vibration table to make the main pass. After each pass slag is removed with the help of chipping haer. This is done to ensure that there should not be any cavity in the weld pool. Then another pass is made. These plates after SMAW welding are marked V-1 and are shown in Fig. Fig: Welded Plates Marked V1 (With Auxiliary Vibrations) Now, take another set of S.S plates which are too welded under conventional SMAW process. These plates are clamped as clamped previously with the help of C-clamps on the vibration table. The butt joint is made with shielded metal arc welding. There are 4 numbers of passes to make the butt joint. Three of these passes are main passes and 1 is root pass. All Fig: Welded Plates Marked N1 (Without Auxiliary Vibrations) V. RESULTS AND DISCUSSION To measure the mechanical properties that is considered vital to the satisfactory performance of the welded joint in service. These tests include tensile test, hardness test, impact test etc. Here tensile test are to be carried out to determine the ultimate tensile strength and yield point under static loading of base metal, weld metal and welded joint. Percentage elongation is also determined. For determining the tensile strength of weld metal alone or welded joint the samples are to be prepared from both the welded plates i.e. SMAW and vibratory SMAW. Different types of tensile test can be carried out to evaluate weldment like transverse butt weld test, transverse butt weld test with a notch test, longitudinal butt weld test. Here transverse butt weld test is done to determine the tensile strength of welded joint. This is the standard accepted test and is quite widely used. From the Tensile test of N-1 specimen: Gauge length=40 Final gauge length=44.22 Percentage elongation = Tensile strength = MPa From the Tensile test of V-1 specimen: = 10.55% Gauge length=40 Final gauge length=45.5 Percentage elongation = = 13.75% 40 Tensile strength= MPa International Journal of Mechanical Engineering 5

6 Comparison of Mechanical Properties S. N o. Table 2: Comparison Table of Mechanical Properties Mechanical N1 V1 Improvement Properties 1 Max. Force (Fm) 2 Displaceme nt at Fm 3 Max. Displaceme nt 4 Tensile strength (Rm) 5 Elongation (%) KN MPa % KN MPa % ( )/ = 3.64% ( )/16.9 =27.81% ( )/17.7=26.55 % ( )/ =4.28% ( )/10.55 =30.47 % [6] Miclosi, V.,et al., Research Regarding The Influence Of Axial Electromagnetic Pulsation Of Liquid Metal Bath Upon The Characteristics Of The Weld, Euromat 93, The Third European Conference on Advanced Materials and Processes, Vol. 1,(Proc. Conf.) Paris, France, [7] Qinghua, Lu, Improving Welded Valve Quality By Vibratory Weld Conditioning, Materials Science and Engineering, , 2007 [8] Govindarao, P., et al., Affect Of Vibratory Welding Process To Improve The Mechanical Properties Of Butt Welded Joints, International Journal of Modern Engineering Research, 2/4, CONCLUSIONS Tensile strength of the material SS202 during vibration welding is 4.28% more as compared to the tensile strength of same material during SMAW. Elongation of the specimen is 30.47% more during vibration welding than SMAW. V1 specimen can bear 3.64% more force as compared to N1. During tensile test V1 is less displaced as compared to N1. Microstructure of weld metal of the material is not affected during both types of welding REFRENCES [1] PARMAR, R.S., Welding Engineering And Technology, Kalyani BO Press, , 2010 [2] Watanabe, T. and Nakamura, H., Solidification Control Of Austenitic Stainless Steel Weld Metal By Electromagnetic Stirring, National Research Institute For Metals (Japan), 21/2 (1990), [3] IZDINSKA, Z., The Effect Of Ultrasonic Treatment Upon Fatigue Properties Of Welded Joints, Welding Research Institute (Bratislava), Zvaranic, 5/6 (1991), [4] Dvornak, M.J.,et al., Influence Of Solidification Kinetics On Aluminium Weld Grain Refinement, Welding Journal, 70/10, [5] Wei, B., Unidirectional Dendritic Solidification Under Longitudinal Resonant Vibration, Acta Metallurgica Materialia, 101, , 1992 International Journal of Mechanical Engineering 6