AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 - 391 - EFFECT OF DOUBLE QUENCHING ON WEAR BEHAVIOR FOR LOW CARBON DUAL PHASE STEEL By Khamaal Muhsen Kseer University of Technology/ Department of Applied science ABSTRACT: In this paper the effect of double quenching heat treatment on microstructure and dry sliding wear behavior of low carbon dual phase steel with carbon concentration (0.0977% C) was investigated. The specimens were intercritically heat treated at different temperatures and then water-quenched. The martensite volume fraction in the double quenched specimens was higher than that of the single quenched specimens. Hardness test was conducted on low carbon steel specimens using Brinell hardness test. Optical microscopy was employed to examine the microstructure of the specimens. Wear test were carried out on the single and double quenched specimens under dry sliding wear condition using a pin-on-disk machine at different loads with constant sliding time and speed, and at different sliding time with constant loads and speed. The experimental results showed that the wear rate effectively decreased in the double quenched specimen. KEY WORDS: dual phase steel, low carbon steel, wear test, double quenching, intercritical heat treatment. ورتاثير االخماد الثنائي على سلوك البلى للصلب واطيء الكربون ثنائي الط خمائل محسن كسير الجامعة التكنلوجية / قسم العلوم التطبيقية الخالصة تم دراسة تاثير االخماد الثنائي على البنية المجهرية والبلى االنزالقي الجاف للصلب واطيء في هذا البحث مادها بالماء . لقد وجد ( .تم معاملة العينات بدرجات حرارة مختلفة واخ%0.0977كربون )تركيز ذو ثنائي الطور الكربون رتنسايت اكبر في العينات التي اجري لها اخماد ثنائي من العينات التي اجري لها اخماد مرة اان مقدار الكسر الحجمي للم ان اختبار البنية المجهرية تم باستخدام ل لعينات الصلب الواطيء الكربون . يواحدة . كما تم اجراء اختبار صالدة برن . المجهر الضوئي AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 المسمار على تقنيةاجري اختبار البلى االنزالقي للعينات االخماد الثنائي والعينات المخمدة مرة واحدة باستخدام تحت ازمان انزالق مختلفة مع تثبيت كل كما تم االختبار احمال مختلفة و زمن انزالق وسرعة ثابتين , باستعمالالقرص نت ان معدل البلى قد قل بشكل واضح في العينات التي تم اجراءاالخماد الثنائي لها من الحمل والسرعة . النتائج العملية بي . INTRODUCTION In most cases, failures of material initiate from the surface, and are sensitive to microstructure and properties of the surface [1]. Wear is one of the important mechanical properties expected from steels in actual service condition for some of the aerospace and automobile parts [2], the best opportunities of the application for different elements of cars have the steels with a ferritic – martensitic structure. The DP-type (Dual Phase) steels have a structure of a ferritic matrix with islands of martensite [3]; the amount of martensite present in ferrite-martensite steel will depend on the intercritical annealing temperature in the ferrite plus austenite region. Further increasing the volume fraction of martensite increases the strength of the dual phase material. Unfortunately, increasing the martensite content might reduce ductility and toughness [4]; hence wear resistance increase with increasing ductility so the excess in martensite phase raises wear rate [5]. Adamczyk and Grajcar [3] investigated various routes of a heat treatment by using double quenching in order to obtain a DP-type structure with required fractions of ferrite and martensite and optimum mechanical properties of the investigated low-carbon steel and they concluded that various initial structure influences morphology of martensite in a final DP-type structure of the heat-treated steel. Also Güral et al. [5] studied the effect of double quenching on wear properties of atomized iron powder mixed with 0.3 % graphite and 1 % Ni powders, the mixed powders were cold pressed and sintered at 1200°C for 30 min under pure Ar gas atmosphere. They found that martensite volume fraction in the double quenched specimens was higher than that of the single quenched specimen and wear coefficient effectively decreased in the double quenched specimen. Tekeli et al. [2] studied dry sliding wear behavior of Fe + 0.3% graphite powder metallurgy processed (PM) steels. After wear tests it was seen that the wear rate of the intercritically annealed specimens was very low in comparison to as-sintered specimen. The specimen intercritically annealed at 728 °C showed the lowest wear rate, despite its lower martensite volume fraction. Wang et al. [1] observed that the friction coefficient decreases and the wear resistance increases with the nanocrystalline (nc) surface layer. The improvement in friction and wear properties may be attributed to the harder nc surface layer which reduces the degree of plowing and micro-cutting under the lower load and the degree of plastic removal and surface fatigue fracture under the higher load, respectively. The aim of this paper is to use double quenching heat treatment in order to obtain a DP-type structure with required fractions of martensite and optimum wear properties of the investigated low-carbon steel. EXPERIMENTAL PROCEDURE 1. Material and Heat Treatment The chemical composition of the investigated low-carbon steel was carried out at Alnaser Company for Mechanical Industry / Ministry of Industry and Minerals by using spectroscopy method (Table 1). AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 - 391 - The established heat treatment conditions are schematically shown in (Table 2), respectively all samples are tempered at temperature 200°C for one hour after heat treatment. 2. Microscopy Characteristics The microstructure of the surface layer on the investigated low-carbon steel characterized by optical microscope, the specimens were grinded by using Aluminum oxide paper lubricated with water (600, 800, 1000, and 1200) grit, the samples polished by alumina suspension then etched with the 2% Nital solution. Mean linear intercept method was used for the calculation of martensite volume fraction according to the ASTM E562 [6]. 3. Hardness Test Hardness test was achieved by using Brinell hardness test. The specimens were grinded by using Aluminum oxide paper lubricated with water, ball diameter of the tester was 2.5 mm, and the applied load was 187.5 kgf. Hardness values were calculated using Brinell hardness equation [7]. 4. Wear Test Unlubricated wear experiment were performed under ambient laboratory conditions using a pin -on- disc wear tester, where the pin is loaded normally. The variables which are used for wear test can be presented by: 1- Study the effect of normal load on wear rate by using load (10, 20 and 30) N at both constant sliding time 20 min and constant speed. 2- Study the effect of the sliding time on wear rate by using times (10, 20 and 30) min at constant normal load 2N and constant speed .Wear rate can be calculating by using the followed equation: )1( 2 tnr w rw    Where: w = weight difference of the sample (gm) , 21 www  . rnt2 = sliding distance (cm). r = radius from sample centre to the disc centre (cm) . n = disc rotational speed = 500 r.p.m. t = test time (min). AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 RESULTES & DISCUSSION 1. Microstructure Characteristics The specimens have a ferritic matrix and the martensite is located on boundaries of α phase as a network (Figs.3 & 4) or as islands (Figs. 1, 2, 5&6). The location of martensite is strongly dependent on a distribution of the austenite formed due to a carbon enrichment of the boundary-zones of ferrite connected with a decomposition of pearlite grains [3]. During the heat treatment of the investigated steel the privileged diffusion of carbon on the boundaries of the α phase is occurred, an increasing in heat treatment temperature leads to the increase of martensite volume fraction, keeping the distribution of this phase on grain boundaries of the α phase [3]. The diversity in morphology of the structure was the specimens quenched twice. In this case, during heating the steel the nucleation of austenite mainly occurs on the boundaries of martensite laths formed after primary quenching of the investigated steel from a temperature of 900°C [3]. The predominated martensite fraction occurs mainly as islands located in surroundings of grain boundaries of ferrite grains (Figs. 1, 2,5and 6). Moreover, in surroundings of martensite, especially at a boundary zone of large grains of the α phase, small grains of the recrystallized ferrite can be identified. They are a result of plastic deformation connected with volume changes accompanying the martensite transformation [3]. Apart from the morphology differences after the heat treatment of steel according to the route 1 the difference in a grain size of ferrite is observed. The more fine-grained structure has steel heat-treated according to the route 1. This is due to the increased number of places convenient for the nucleation of ferrite and also a partially course of the recrystallization of the specimens with an initial structure of martensite [3]. Optical micrographs reveal that the coarse martensite was obtained with further increase in Martensite volume fraction for specimens of the investigated steel. The increasing in temperature of heat treatment leads in increasing of volume fraction of the martensite (MVF) [2, 3, and 8] as shown in (Table 3) . 2. Hardness Test It appears from (Table 4) that hardness of the samples is increased as the temperature of heat treatment increase except the samples A1 and A2. An increase of the heat treatment temperature increases a fraction of martensite [2,3,8], the increase of martensite volume fraction increases the hardenability of steel[3]. But further increase in the MVF was to decrease the hardness; this result is agreed with the results obtained by Bello et.al. (2007)[4]. That is why hardness values of samples A1, A2 was less than the values of other samples. Martensite enriched in carbon increases the hardenability of steel, when the quenching temperature increase the fraction of martensite increase [2,3,8], but at the lower carbon enrichment. It causes lowering the hardenability of steel (austenite depleted in carbon) and can lead to a transformation of the part of austenite to undesirable bainite [3] . Clearly we can see that double quenching raises hardness values (Fig.7). This is reported to be attributed to the fine grains of the recrystallized ferrite. They are a result of plastic deformation connected with volume changes accompanying the martensite transformation [3], Microstructural refinement is expected to enhance hardness [1, 9]. Beside that the increase of martensite volume fraction increases the hardenability of steel. AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 - 391 - 3. Wear Test From (Fig.8) it has been noticed that wear rate is increased as sliding time increases until it reached highest sliding time. Increasing sliding time tends to raise surface temperature which causes cover of oxide on the surface of the sample. During sliding more and more oxide is produced, the metal–metal contact is reduced, thus lowering the wear rate, and leading to transition from severe to mild wear [10, 11]. In (Fig.9) when the load is lower than 20 N, wear loss mainly results from plowing and micro-cutting under the action of the abrasive particles and oxides fallen from the sample surface. When the load increases the abrasive particles indents more deeply into the surface; so the repetitive work-hardening in the surface layer will be severer under the repetitive sliding action. Eventually cracks propagating and growing induce spalling of the material in the surface layer. The dominant wear mechanism changes are plastic removal and surface fatigue fracture of the deformed layer when the load increases [1]. At the same time, wear rate caused by plowing and micro-cutting is less than that of the original sample under the lower load. As the load increases, the repetitive work-hardening caused by the reciprocated sliding action in the harder layer is smaller. Consequently the spalling loss of the treated sample is less than that of the original one too. In the harder surface layer of the treated samples, the depth that the abrasive particles indents is smaller, so that the force needed in the plastic deformation is diminished that the plastic removal in the harder surface layer is smaller, wear volume loss of the treated samples is less than that of the original sample under the higher load [1]. (Figs 8 and 9) show that double quenching process enhanced wear properties; this result is agreed with the results obtained by Gural et.al. (2007) [5], it is attributed to the higher hardness values are significantly associated with the finer distribution of martensite and ferrite composite microstructure gained from double quenching [4]. Microstructural refinement is expected to enhance hardness and then to result in an improvement in the adhesive wear resistance [1,2]. The higher hardness the lower wear rate [12], so the much enhanced wear resistance was of sample B1. (Figs 1, 3 and 5) of the microstructure test reveal that the microstructures of the samples of route (1) consist from fine ferrite and martensite phases. Coarse martensite was obtained with further increase in volume fraction [4].In the case of specimen A1; further increasing in volume fraction of martensite increases the strength of the dual phase material. Unfortunately, increasing the martensite content might reduce ductility and toughness [4]. Wear resistance of dual phase steels affect their ductility. If dual phase steels have high ductility, they have high wear resistance as well, generally, dual phase steels having lower MVF have high ductility [2]. Therefore, as the samples had lower MVF, it can be expected to have higher ductility and thus high wear resistance [2]. Beside that an increasing of the quenching temperature increases the fraction of martensite, but at the lower carbon enrichment. During this process, martensite volume fraction increases while its hardness decreases as mentioned before, which results in a decrease in wear resistance of dual phase steels [2,3]. Martensite phase in a microstructure is easily cracked under loads and thus the weight loss from the surface is increased [2] therefore the wear rates of the samples being sever at high load as shown in (Fig. 9). AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 CONCLUSION 1- Wear rate for the heat treated samples of low carbon dual phase steel shows improvement in comparison with the original one. 2- Double quenching showed enhancement in wear properties more than the single quenched samples. 3- Specimen double quenched from the temperature of 900°C and 850°C showed best wear resistance than the other samples. REFRENCESES 1. Wang Z.B., Tao N.R., Li S., Wang W., Liu G., Lu J., Lu K." Effect of surface nanocrystallization on friction and wear properties in low carbon steel", Journal of Materials Science and Engineering A, Vol. 352, pp. 144 -/149, (2003). 2. Tekeli S., Gural A., Ozyurek D.," Dry sliding wear behavior of low carbon dual phase powder metallurgy steels" Materials and Design , Vol. 28, Issue 5, pp. 1685-1688,( 2007). 3. Adamczyk J. , Grajcar A." Heat treatment and mechanical properties of low-carbon steel with dual-phase microstructure", Journal of Achievements in Materials and Manufacturing Engineering, Vol. 22 ,Issue 1, pp. 13-20 ,May (2007). 4. Bello K.A. , Hassan S.B., Abdulwahab M. , Shehu U. , Umoru L.E. , Oyetunji A. , Suleiman I.Y." Effect of Ferrite-Martensite Microstructural Evolution on hardness and Impact Toughness Behavior of High Martensite Dual Phase Steel" Australian Journal of Basic and Applied Sciences, 1(4): 407-414, (2007). 5. Gural A. ,Tekeli S. ,Ozyurek D. ,Gural M." Effect of Repeated Quenching Heat Treatment on Microstructure and Dry Sliding Wear Behavior of Low Carbon PM Steel" Journal of Materials Science Forum, Vol. 534, pp. 673-676, January, (2007). 6. George E. Totten,"Steel Heat Treatment Hand Book "second edition, Taylor and Francis group, 2007. 7. ASM HANDBOOK "Mechanical Testing and Evaluation" Vol.8, ASM International, 2000. http://www.scientific.net/MSF AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 - 399 - الراوي عويد, اسماعيل عبد الرزاق "المعامالت الحرارية للمعادن الحديدية والالحديدية ", قسم هندسة االنتاج .8 . 9191الجامعة التكنلوجية, /والمعادن 9. Wang Z.B., Lu J., Lu K." Wear and corrosion properties of a low carbon steel processed by means of SMAT followed by lower temperature chromizing treatment" Journal of Surface & Coatings Technology, Vol. 201 ,pp 2796 -2801,(2006). 10. Gupta V.K., Ray S., Pandey O.P." Dry sliding wear characteristics of 0.13 wt. % carbon steel" Materials Science-Poland, Vol. 26, No. 3, pp. 617-631 , (2008). 11. John H. Dumbleton , Joseph A. Donthett, "The Unlubricated Adhesive Wear Resistance of Metastable Austenitic Stainless Steel Containing Silicon ", Wear, Vol.42, pp .305-306,(1977). 12. Bressan J.D., Daros D.P., Sokolowski A., Mesquita R.A., Barbosa C.A. "Influence of hardness on the wear resistance of 17- 4 PH stainless steel evaluated by the pin-on-disc testing" journal of materials processing technology, Vol. 205, pp. 353–359, (2008). C Si S P Mn Ni Cr Elements % 0.097796 0.01275 0.28942 0.06166 1.27698 0.13058 0.16994 Mo V Cu W Ti Sn Co Elements % 0.02835 0.00508 0.14820 0.00738 0.00079 0.02097 0.01732 Al Pb Nb Zr Ca Zn Fe Elements % 0.00035 0.00894 0.00142 0.0027 0.00002 0.00268 97.7174 Table (1) Composition of the investigated low-carbon steel. AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 Martensite volume fraction % sample 36.71 A1 28.9 A2 31.24 B1 25 B2 21.09 C1 15.09 C2 sample Heat treatment R o u t 1 (d o u b le q u e n c h e d ) A1 First quenched from temperature 900°C, second quenched from 870°C (booth quenched in water). B1 First quenched from temperature 900°C, second quenched from 850°C (booth quenched in water). C1 First quenched from temperature 900°C, second quenched from 810°C (booth quenched in water). R o u t 2 (s in g le s q u e n c h e d ) A2 quenched from temperature 870°C in water B2 quenched from temperature 850°C in water C2 quenched from temperature 810°C in water D Metal as received Table (2): Heat treatment of steel according to routes 1 and 2. Table (3) Martensite volume fraction %. AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 - 103 - Hardness kg/mm 2 Sample 168 A1 166 A2 179 B1 173 B2 170 C1 161 C2 159 D Table (4) hardness values. Fig.1: sample (A1) Ferritic – martensitic structure of steel double quenched from the temperature of 900°C and 870°C, (80X) (F: Ferrite, M: Martensite). M F M F Fig.2: sample (A2) Ferritic – martensitic structure of steel quenched from the temperature of 870°C, (80X) (F: Ferrite, M: Martensite). M F Fig.3: sample (B1) Ferritic – martensitic structure of steel double quenched from the temperature of 900°C and 850°C, (80X) (F: Ferrite, M: Martensite). M F Fig.4: sample (B2) Ferritic – martensitic structure of steel quenched from the temperature of 850°C, (80X) (F: Ferrite, M: Martensite). AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 M F Fig.5: sample (C1) Ferritic – martensitic structure of steel double quenched from the temperature of 900°C and 810°C, (80X) (F: Ferrite, M: Martensite). Fig .7: Relationship between quenching temperature and Brinell hardness. AL-Qadisiya Journal For Engineering Sciences ,Vol. 6.No 2 Year 2013 - 101 - Fig.(8):Relationship between sliding time and wear rate. Fig. (9): Relationship between applied load and wear rate.