(Microsoft Word - \343\321\346\307\344 \346 \314\343\307\34145- 50) Al-Khwarizmi Engineering Journal Al-Khwarizmi Engineering Journal, Vol. 15, No. 3, September, (2019) P.P. 45- 50 Effect of Shot Peening on Fatigue Properties for Corroded and Uncorroded (CK35) Steel Marwan N. Arbilei* Jamal Mohammed Hamed** *,** Department of Biomedical Engineering/ University of Technology/ Baghdad/ Iraq *Email: engmna@gmail.com **Email: jamal_hamed2001@yahoo.com (Received 13 November 2018; accepted 27 March 2019) https://doi.org/10.22153/kej.2019.03.002 Abstract The traction property is one of the important mechanical properties, especially the rotary parts which are subjected to constant and variable loads There are many methods used to improve this property, and the shoot peening by metal balls is considered the most critical one. the study focuses on this characteristic of steel CK35 used in many engineering applications as the rotating shafts and railway This study shows that the fatigue strength is improved by14% after shoot peening with metal balls. The study includs the rehabilitation of damaged samples as a result of fatigue corrosion. The standard solution adopted was 36% MgCl2 with a 30 days immersion period. These samples has been improved by 6% after it decreased by18% due to immersion in the alkaline solution. Keywords: Crevice corrosion, CK 35, fatigue strength, shot pining. 1. Introduction There are many methods for surface hardening; the-chemical methods, such as carburizing and nitriding. Physical methods showed a better interest with changing the chemical composition of treated alloys. One of these methods is shot peening with metal balls. The theory depends on the resist of nucleation and growth of cracks. Cracks and growth are with time working. This is required by many alloys subjected to continuous vibration and forces especially those used in bone fixation [1]. All the above listed methods increase surface hardness by producing compressive residual stresses. The surface plays a key role in the life of the metal parts, especially the fatigue age which is related to the formation and growth of cracks on the surface [2]. The shoot peening process depends on many variables, such as the speed of balls, the time spent on the process of solidification, and the dimensions of the balls used in the process of molding and shape [3]. In this study, used alloy steel (CK35) is used which resist vibration the presence of an auxiliary medium on corrosion leading to the acceleration of the process of the emergence of the crack and progress., The resistance of metal to the fatigue in the corrosion medium is less than in the non- helping to corrosion [4] in that the number of cycles necessary to break the corrosive medium which is less than the number of cycles required to obtain the fracture in the other medium when the same voltage value is applied to the alloy. [5,6]. The selection of shoot metal balls is as a method of surface hardening to obtain better properties of metal is to satisfy their requirements and efficiency. The shoot method of balls is applied to treat the damage caused by corrosion when the metal is exposed to hard corrosive media. The shoot of the balls leads to the closure of the pressure and some short cracks and impedes its progress, which improves the surface properties of the metal especially fatigue resistance. The Marwan N. Arbilei Al-Khwarizmi Engineering Journal, Vol. 15, No. 3, P.P. 45- 50 (2019) 46 objective of this research is to raise the efficiency of the metal chosen for studying as a common metal used in the engineering parts and improve its properties by increasing the hardness of the surface and to maintain a strong heart to withstand shocks 2. Experimental Work 2.1 Material The alloy was in the form of rods with various lengths and diameters, which were machined by CNC to obtain accurate dimensions. Then, the samples surfaces were grinding and polished to avoid stress concentration areas. Fig 1 has showed the standard dimensions of the sample supplied with testing device used in rotational bending tests. The chemical composition and mechanical properties of CK35 illustrated in Tables 1 and 2, according to AISI1035. Fig. 1. standard fatigue sample (ISO 1143:2010 en) Table 1, chemical composition Fe Other Mn Si C Element Rem <1% ≤0.65 ≤0.40 0.35 Standard Rem 0.7% 0.6 0.33 0.34 investigated Table 2, Mechanical Properties according to AISI 1035 2.2 Machines and Instruments 2.2.1 Testing Machine The HI-TECH Rotating Bending Fatigue Testing machine tester is used. The rotating speed of 5600 RPM where 1/3 million stress reversals occur per hour. Fig. 2. Testing machine. 2.2.2 Shoot Peening Device The shooting is performed using a shoot device where a ball bearing cast steel balls and the parameters as illustrated in table 3. Fig. 3. Shoot Device. Hardness(HB) Є% σult. (MPa) σ yield (MPa) 190 21 480-670 300 sample switch motor Control system Balls Marwan N. Arbilei Al-Khwarizmi Engineering Journal, Vol. 15, No. 3, P.P. 45- 50 (2019) 47 Table 3, Parameters of shot peening 2.2.3 Optical Microscope Optical microscopic imaging has been used to investigate the fracture section surface fir both types of samples (Shoot Peening and Corrosion). The magnification for all samples was 500x) 2.2.4 High Precision Electronic Balance Accuracy (10-5 gm) 2.3 Corrosion Test Medium A standard corrosion test was selected to test for the resistance of fatigue, magnesium chloride at a concentration of 36% MgCl2 (ASTM G36). This test solution was prepared by dissolving 360 g of high purity magnesium chloride per liter of distilled water. The PH of the solution daily was measured to keep the solution stable during testing time by adding more salt and water to corrosion cell. 2.4 Test Groups Test groups were classified into four groups according to the type of mechanical and chemical treatment. Where 24 samples for each group have been machines by using Indexed turning machine. According to the standard specimen shown in Fig. 1. Table 4, Group of samples Coding Type of test Group As Received AS After Shot Peening SP After Corrosion CR After Corrosion and Shot peening CRSP 3. Results and Discussion To draw the S – N curve which is illustrated in Fig (4), the titration test is performed on eight groups of samples. Each group consisted of three samples by casting a constant value of stress for each group and calculating the value of the number of cycles Failures for each sample to give more accuracy to the obtained results and to eliminate the random behavior of the samples. The same tests are repeated for the same number of samples with metal balls. The same tests is performed after the samples are immersed in salt solution. Then, the samples is cast with metal balls and the tests is carried out as shown in Fig (4) Age-adjusted equations for the results is obtained in Fig (4) using a best curve fitting method and are as in Table (5) Table 5, Equation and fatigue limit Enhance ment % Fatigue limit Fatigue equation Samples Group 14% 320 σf = 1184Nf -0.093 SP 280 σf = 1216Nf -0.102 AS 6% 265 σf = 1259Nf -0.112 CRSP 250 σf = 11446Nf -0.11 CR The fig (4) and table (5) show the increased fatigue limit and fatigue resistance of the alloy with the shooting of the metal balls compared with the test performed without shooting. This increase value is due to the exposure of the sample to a surface hardening process. The hardening of the surface leads to obstruction and even in the case the emergence of such cracks. The increase with shooting is about 14%. When test in solution (36% MgCl2) according to ASTM G36, the sample – typically U-bend – is immersed in a boiling MgCl2-solution. The time to cracking is an indication of the resistance to stress corrosion cracking. This test causes a decrease in the weight of the alloy comparing to the test conducted under dry conditions. This decrease is due to the immersion of these samples in the salt solution which influenced efficiency on the samples. Clicking on the surface and thus cracks develop faster because of the combined effect of stress and corrosion. The continued effect of this medium causes more pits and the formation of many cracks and makes these cracks faster [8]. The decrease in the value of the threshold was about 18%. The shooting of the specimens led to the termination and closure of the pits caused by the salt solution and the creation of compressive stresses on the surface hardening the progress of the crevices. The increase in properties unreturned samples to their original state due to the corrosive Parameter value Diameter ball 0.6 mm Hardness(HRC) 50 Pressure 12 bars Speed 40 m/s Distance between ball and machine 10 mm Speed of lathe machine 20 rpm Marwan N. Arbilei Al-Khwarizmi Engineering Journal, Vol. 15, No. 3, P.P. 45- 50 (2019) 48 effect of the salt solution, the value of the increase was 6%. The corrosion rates of the tested samples are presented in Table (6). Fig. 4. (S – N) curve for test specimens. Table 6, Corrosion rates of samples Type of test AS SP CR CRSP Weight loss (g) 0.0530 0.0355 0.0815 0.0670 It is noted that the weight loss due to corrosion decreased with shoot metal balls while this rate increased when immersed in salt solution and decreased again when the cast of metal balls has been shoot. This is in line with the results of the tests presented previously. The fracture sections as shown in Fig 5 has reveled a finer cracking in the shot samples, in addition to stress cracking has been avoided in the shot samples after corrosion. 4. Conclusions Shot peening increases the fatigue resistance for the un corroded samples with 6% meanwhile the fatigue resistance has a better enhancement with the uncorroded samples with 14%. The weight loss due to corrosion of shot samples overcomes the cervices corrosion. The fatigue resistance can be enhanced and maintained perfectly even after corrosion. Acknowledgment Special thanks are forwarded to The Department of Biomedical Engineering University of Technology - Baghdad-Iraq A: without shoot (200x) B: with shoot (200x) Hard cracking Fine cracking Marwan N. Arbilei Al-Khwarizmi Engineering Journal, Vol. 15, No. 3, P.P. 45- 50 (2019) 49 C: corrosion (200x) D: corrosion + shoot (200x) Fig. 5. Fracture surface of four cases. 5. References [1] A. Stoic, J. Kopac, “Turning condition of CK35 steel with alternate hardness zones” Journal of achievements in materials and manufacturing engineering, vol 34, ISSUE 1 ,2009. [2] F. Abadie, L. Barrlier, “Ceramic shot enhancement of high strength steel endurance application to springs and gears”, Icspa shot peening, 2015. [3] T. Saeid, S. yazdani, “Shot peening as an alternative to fatigue life improvement of CK35 steel coated with an electroless Ni-Cu-P”, International journal of ISSI, vol2, 2015. [4] Aleksander, Grzegorz, waraw, “Effect of shot peening on the fatigue strength of spring steel after exposure to corrosion”, Poland, 2005. [5] yoshiki, james, “Effect of shot peening on fatigue damaged high strength aluminum alloy applicability of rejuvenation on fatigue damaged compopents” university, Syracuse, New York, 2012 [6] Hill.S, Gregson and Hara, “Effect of shot peening on fatigue performance of advanced aluminum alloys and aluminum based metal matrix composites” Engineering materials, University of Southampton, UK. 2010 [7] Alkawi. H. J, Awsi. M. Q, “Influence of shot peening on 70/30 brass residual stresses using plasticity theory” engineering and technology , ISSN: 16816900 24120758 Year: 2009 Volume: 27 Issue: 16 Pages: 3064-3075 Iraq , 2009. [8] W. 6TH Street Mishawaka, “Shot peening overview” J. ChaMPaigne, Electronics Inc 1428, In 46544, USA 2000. [9] S. Romero, E. Rios, “Optimization of the shot peening process in terms of fatigue resistance” presented at seventh international conference on shot peening, ICSP-7 Warsaw, Poland, 1999. [10] Zuhal abd alzahra, "Shot Peening Time Effect on Corrosion Behaviors of Al Alloy 2024-T3" Khwarzmi Engineering Journal, V12,No1,page 110-116, 2016 [11] Zainab Azeez Betti, Amer Hameed Maajeed, Alalkawi H.J.M." Interaction of Corrosion- Cumulative Fatigue and Shot Peening of 1100-H12 Aluminum Alloy" Al-Khwarzmi Engineering Journal, V11,No1,page 65-72, 2005. Less Stress corrosion cracks Stress corrosion cracks )2019( 45- 50، صفحة 3، العدد15دجلة الخوارزمي الهندسية المجلم مروان نافع علي 50 CK35تأثير القذف بالكرات على خواص الكالل لعينات متآكلة وغير متآكلة للفوالذ **جمال محمد حمد *مروان نافع علي العراق/ بغداد /قسم هندسة الطب الحياتي/ الجامعة التكنولوجية*،** engmna@gmail.com :البريد االلكتروني* jamal_hamed2001@yahoo.com :البريد االلكتروني ** الخالصة ). حيث تضمن البحث دراسة اربع حاالت من خالل اختبار الكالل. الحالة االولى للعينات CK35تم في هذا البحث دراسة تحسين خواص الكالل للفوالذ ( ينات مغمورة في محلو كما أستلمت. والحالة الثانية تم فبها اختبار الكالل بعد اجراء بسمرة بالقذف بكرات حديدية. والحالة الثالثة كانت بأختبار الكالل لع 2MgCl و الحالة الرابعة واالخيرة كانت باختبار العينات المغمورة بعد اجراء بسمرة القذف بكرات الحديد. حيث تحسنت مقاومة يوما. ٣٠لمدة %٣٦بتركيز . و بعد أجراء البسمرة بالقذف طرأ تحسن %١٨. بينما انخفضت خواص الكالل بالنسبة للعينات المغمورة بنسبة %١١الكالل للعينات بعد بسمرة القذف بنسبة . وعليه نجد ان القذف بالبسمرة من العوامل التي تعيد تأهيل العينات من ناحية مقاومة الكالل حتى بعد تعرضها %١٤الكالل لتلك العينات بنسبة على خواص للتآكل.