Abstract
Austempered ductile iron (ADI) with ausferrite structure is now of great interest for its low production cost, good recycling capacity, excellent castability and a wide range of mechanical properties . However, for more design flexibility and more use of low-cost potential material as well as for repairing the casting defects in producing ADI, the importance of welding DI which could be later converted to ADI, cannot be overridden. In the present work, coated electrode was first developed for grade I ADI without and with cerium using nano-CeO2 and weld procedure was established as per AWS (D11) using preheat at 300 °C for 1 h followed by post-weld heat treatment (PWHT ) for 300 °C for 1 h immediate after welding. DI weldments were then austenitized at 900 °C for 2 h holding time followed by austempering at 300 and 350 °C for three different holding times (1.5, 2 and 2.5 h) at each austempering temperature. Results show that both the weld metals responded austempering heat treatment ; but more refined bainitic ferrite and increase volume percentage of retained austenite were obtained in Ce containing weld metal compared to without Ce containing weld metal. Though 100% joint efficiency was observed in both the welded joints (with and without Ce), fatigue strength and charpy impact toughness of ADI weld metals enhanced with the addition of Ce.
Keywords
Introduction
Austempered ductile iron (ADI) is a new and very promising engineering material with duplex matrix microstructure of bainitic ferrite matrix and retained austenite [1]. The material is now of great interest for its low production cost, good recycling capacity, excellent castability and a wide range of mechanical properties such as high yield and tensile strengths, good ductility, good fatigue strength , excellent wear resistance and high fracture toughness [1,2,3,4,5].
The chemical composition of ADI is similar to conventional DI. However, some alloying elements such as Ni, Cu and Mo are usually added to increase the austemperability and to delay the austenite decomposition [6] to pearlite and ferrite upon cooling. DI converts to ADI with the help of two steps isothermal heat treatment process. At first, austenitization is done at 850–910 °C for 30 min–2 h holding time followed by austempering at 250–450 °C for 5 min–4 h holding time and finally cooled to room temperature in the open air [7]. At lower austempering temperature the microstructure formed in needle-like (acicular) bainitic ferrite with high carbon untransformed austenite, i.e. called retained austenite [7]. By increasing austempering temperature the shape of the bainitic ferrite (acicular) changed and transformed to plate-like (feathery) shape along with retained austenite . If the austempering time is too long, a second stage reaction will start and high carbon austenite transforms into carbide (ɛ carbide) and makes the material hard and brittle.
The excellent castability and good mechanical properties along with lower cost of ADI have attracted its use as castings in automotive, rail, structural and heavy engineering applications [6, 7]. However, due to the desired and completed shape of the castings sometimes it is required to be fabricated and joining between the castings parts. Also many a times, DI casting is required to be repaired, which demands welding consumables compatible with DI. Although different coated electrodes such as pure nickel (90–97%) [8], stainless steel and iron nickel [9] are available commercially for welding DI, these electrodes show negligible respond to austempering heat treatment as the alloying elements present in the electrode belong to poor austemperability. As a result, weld metals produced by these electrodes cannot be converted into ADI structure. Thus, there is an urgent need to develop a coated electrode consisting of elements having good austemperability as well as compatible with DI.
It is well known that the attractive properties of ADI are derived from the fine microstructural constituents consisting of retained austenite , carbon content of retained austenite , morphology of ferrite, precipitated carbide if any, the number, size, distribution and nodularity of graphite [10]. Several investigators [11,12,13] have shown that rare earth metal such as cerium has a beneficial effect on the microstructure and properties of DI. In addition to the beneficial effect of Ce in DI and other cast iron, a few investigators have reported refined microstructure and improved properties of the welds while Ce was added in the weld metals through flux coating of the coated electrode. While systematically varying cerium oxide content in the flux formulation of basic coated austenitic stainless steel electrode, Srinivasan et al. [14] expressed that an optimum amount of 0.4% Ce improved mechanical properties of the weld deposits mainly through decrease in oxygen and sulphur content, inclusion size and no. of inclusions. In another investigation, Samanta et al. [15] introduced cerium (Ce) in the form of mischmetal (50% Ce) and Nb in the form of FeNb (50% Nb) into the weld pool as powder form (200 mesh size) through the tubes of 316L stainless steel foil as the filler wire. Refinement of weld microstructure , improvement of oxidation resistance as well as oxide scale adherence of 316L weld was reported.
The above review of the literature indicates that Ce has a significant beneficial effect on microstructure and properties of DI and other types of cast iron. Also, microstructure modification and improved properties of weld metals particularly for austenitic stainless steel have been reported with the addition of Ce. The recently beneficial effect of nanomaterials substituting micro size materials in SMAW electrode has been observed. However, there is no published literature available on the modification of DI weld metal using Ce and the influence of Ce on the performance of ADI weld metals produced after austempering heat treatment . The present work thus aims at developing the coated electrode further with the addition of nanosize CeO2 in the flux ingredient as coating and subsequently to study the performance of ADI weld metal after austempering DI joints using without and with Ce content of developed electrodes. The microstructural study was done using OM, SEM and TEM . Phase analysis was performed utilizing XRD and EDX. Mechanical properties of the ADI welded joints such as microhardness , transverse tensile, room temperature Charpy impact and high cycle fatigue have been evaluated to study and compare the performance of Ce and without Ce containing ADI welded joints.
Experimental Procedure
Base Metal
The as-cast DI (base metal) was collected from M/S Cresmac Foundry Pvt. Ltd., Kolkata. The chemical composition of the base metal is consisted of 3.60% C, 2.6% Si, 0.22% Mn, 0.028% Cr, 0.041% Mg, 0.019% S and 0.01% P.
Chemical Composition of Weld Deposits
Chemical analysis of the weld deposits using two selected developed coated electrodes (without and with Ce content) were carried out from the eight layers of the deposit on DI base plate by spectral analysis. The detailed chemical compositions of the two developed coated electrodes are given in Table 1.
Establishment of Weld Procedure
Single-pass bead-on-plate welds were deposited on DI base plate in flat position using two selected electrodes (without and with Ce content) at the same welding parameters in shielded metal arc welding (SMAW) process. Three different levels of preheating, that is, 200, 300, and 400 °C for 1 h and post-weld heat treatment (PWHT ) maintaining at same preheat temperatures for 1 h holding time were tried. The quality of the welds as per standard (AWS) D11 [16] were obtained for both the electrodes only at preheat of 300 °C for 1 h and PWHT immediately after welding at 300 °C for 1 h. The details welding parameters for the establishment of a weld procedure are given in Table 2.
After successfully establishment of weld procedure the groove welding was done on 20 mm-thick DI base plate of size 6 × 120 × 20 mm using selected electrodes for extracting the metallographic, transverse tensile, charpy impact test and high cycle fatigue test specimens. The groove design for DI plate welding and typical groove weld joint and test specimen extraction after welding is shown schematically in Fig. 1a, b.
Isothermal Heat Treatment
After successfully completion of groove welding, isothermal heat treatments of the DI welded plates were done to study the comparative response of both the weld metals along with the performance of the joints. Heat treatment was performed in two steps process, i.e. austenitization and austempering. Austenitization was done at 900 °C for 2 h holding time at box type furnace and austempering were done at 300 and 350 °C for 1.5, 2 and 2.5 h holding time at salt bath furnace and finally those were air cooled to room temperature. The typical heat treatment cycle for both the DI welded plates is given in Fig. 2.
Metallography
For metallographic experiments, the samples were cut from the DI welded joints (before and after austempering) and grounded flat for removing the carburised skins and finally mounted at room temperature. Then the samples were polished in silicon carbide papers very smoothly followed by cloth polishing using fine 0.05 μm alumina solutions. After polishing the samples were etched with 5% nital solution and examined under the optical microscope made of Carl Zeiss (AXIO Imager A1 m) and photomicrographs were taken at different magnifications. For better clarity, samples were studied under scanning electron microscopy (SEM) (JEOL JSM-5510 with INKA software EDS system using an ultra-thin window detector) and photographs were taken at different magnifications.
EDX analysis was also done on the matrix phase and graphite nodules of the weld metals after austempering at 350 °C for 2 h holding time in order to understand the presence of Ce content in ADI weld metals.
XRD Analysis
X-ray diffraction (XRD) analysis was performed to estimate the volume fraction of retained austenite and its carbon content using anode Co–Kα radiation in 1.79026 targets with 24 kV and tube current was 40 mA. The specified 2θ range was varied from 30° to 110° with a step size of 0.2°/min. Detailed XRD analysis was performed using integrated intensities of the positions and the integrated intensities for the {1 1 1}, {2 2 0} and {3 1 1} planes of FCC austenite as well as the {1 1 0} and {2 1 1} planes of BCC ferrite. The volume fraction of retained austenite was calculated using the following empirical formula [17]:
The carbon concentration of the austenite was determined using the equation [17].
Microhardness
Vickers microhardness values were taken at six different positions of the weld metals in as-weld conditions and after austempering at 300 and 350 °C for 1.5, 2, 2.5 h holding time using Leco microhardness tester (Model LM 248 SAT) at 100 gf load for 10 s holding time. The average of the six values was considered as representative one.
Transverse Tensile Test
Tensile properties such as ultimate tensile strength (UTS), yield strength (YS) and percentage of elongation (% El) of both the ADI welded joints were evaluated using transverse tensile specimen keeping the weld metal at the centre of the gauge length. The tests were performed under uniaxial loading at a crosshead speed of 5 mm/min in universal tensile testing m/c (Instron 8862) at room temperature. Three samples were tested at each austempering conditions (300 and 350 °C for 2 h holding time) and the average of three values have been reported.
Charpy Impact Test
Sub-size (55 × 10 × 3.3 mm) without notch transverse Charpy impact test specimens for both the ADI welded joints were tested at room temperature according to ASTM E-23. Four samples were tested at each austempering conditions (300 and 350 °C for 2 h holding time) and the average of four values have been reported.
High Cycle Fatigue Performance
High cycle fatigue (HCF ) test of the transverse welded specimen was performed using a Rumul resonant testing machine to determine the S–N curve. The tests were run to failure and up to 107 cycles at constant stress control mode and the number of cycles to failure was recorded with keeping the load ratio R = 0.1. The fracture surface of the failed samples was studied under SEM.
Results and Discussion
Base Metal Microstructure
The optical microstructure of the as-received DI as shown in Fig. 3 consists of graphite nodules surrounded by ferrite matrix. The average graphite nodularity is approximately 90%. There are 130 nodules per unit area (mm2) and the average nodule size (r) = 18.43 µm.
As-Welded Microstructure
The optical microstructures of the as-welded weld metals using without and with Ce containing developed electrodes are shown in Fig. 4. Both the as-weld microstructures show ledeburitic carbide with alloyed pearlite and graphite nodules (Fig. 4a, b). However, a close look into the microstructure reveals the difference in grain size and volume percentage of ledeburitic carbide and alloyed pearlite. The presence of Ce in weld metal has caused the structure finer (finer the dendritic structure), lesser ledeburitic carbide, higher amount of alloyed pearlite and increasing the volume percentage and nodularity of graphite .
A number of experimental studies on the addition of rare earth elements in cast iron and steel have been made. It has been shown that cerium reduces both primary [18] and secondary [19] dendritic arm spacing as well as inhibit the development of columnar crystal. Also, the degree of supercooling for rare earth treated steel has been reported to be smaller than rare earth free steel [20]. The refined microstructure (Fig. 4b) that has been observed for Ce-treated weld metal, is presumably due to the fine primary austenite dendrite and suppression of columnar grain growth during solidification of the weld pool. Furthermore, it is believed that a smaller degree of supercooling associated with Ce-treated weld metal has caused a reduction in ledeburitic carbide. When the small liquid weld pool undergoes the eutectic reaction at the end of solidification , small undercooling will attribute reduced rate of eutectic reaction resulting in the lesser formation of ledeburitic. It is not unusual for ledeburite to be separated completely, with the eutectic austenite added to the primary austenite dendrites, leaving behind the free carbide. Consequently, because of smaller interdendritic spacing the concentration of solutes having a lower partition coefficient such as oxygen, carbon, sulphur, manganese, etc., will be enriched more in the interdendritic region. Thus, it is more likely that austenite will be more enriched with C and Mn for Ce-treated weld metal. When such austenite is cooled through the eutectoid temperature, alloyed pearlite will form simultaneously during the transformation. Also, due to strong deoxidation and desulfuration effect of Ce [21], Ce-rich oxides, Ce-rich sulphide or Ce-rich oxide-sulphides will form and they will act as a more effective substrate for graphite formation due to their higher melting temperatures and favourable lattice misfit [22].
Austempered Microstructure
The microstructures of weld metals after austempering heat treatment , show bainitic ferrite, retained austenite and graphite nodules (Fig. 5). The structure varied in morphology, amount, graphite nodule size and nodularity with changing the austempering temperature, holding time and type of electrode used (without and with Ce content).
At 300 °C austempering temperature microstructures Fig. 5a, c of both the weld metals show needle shape bainitic ferrite with retained austenite content and graphite nodules. Whereas at 350 °C the structures Fig. 5b, d shows lath type (feathery shape) bainitic ferrite with retained austenite and graphite nodules. However, at 350 °C more amount of retained austenite and lesser amount of bainitic ferrite is observed (Table 3); but the opposite trend in microstructural constituents has been revealed at 300 °C, that is, lower amount of retained austenite and higher amount bainitic ferrite.
The microstructural constituents also varied with changing the austempering holding time at a given temperature. However, for both the austempering temperatures variation of the microstructural constituent is similar, that is, with changing holding time from 1.5 to 2 h the amount of retained austenite increased and amount of bainitic ferrite decreased also refine the bainitic ferrite shape and size. Further increasing the austempering holding time from 2 to 2.5 h the amount of retained austenite decreased and the amount of bainitic ferrite increased. Interestingly, at both 300 and 350 °C austempering temperature for 2 h holding time the carbon enrichment in austenite is maximum which has caused to stabilize more amount of retained austenite in both the austempering temperatures after cooling to room temperature. However, with further increasing holding time (2.5 h) untransformed austenite transformed to carbides (ε carbide) and bainitic ferrite leading to decrease the amount of retained austenite content.
The observed finer and homogeneous structure along with the increased amount of retained austenite content (Fig. 5c, d) with the presence of Ce content in ADI weld metal at both 300 and 350 °C can be attributed to as-welded fine structures, carbon enriched austenite, segregation of Ce. The carbon enrichment of austenite will be faster in Ce-treated weld metal due to lesser diffusion distance for carbon which diffuses from fine cementite lamellae of pearlite. Also, smaller graphite nodule size having more surface area to volume ratio will favour carbon diffusion from graphite . Thus with an increase of carbon content of initial austenite the driving force for stage I austempering decreases [1]. Furthermore, the bainitic transformation is delayed due to the drag effect induced by the segregation of Ce at the ferrite interface and the retardation of Ce on carbon diffusion [23].
The results of the EDX analysis of both the weld metals (without and with Ce content) austempered at 350 °C for 2 h holding time are shown in Fig. 6a, b. Figure 6a shows graphite and matrix of weld metal without Ce content and Fig. 6b shows graphite and matrix of weld metal with Ce content. The results show the presence of Ce along with other elements like Si, S, O, C, Mg, Cr and trace amount of Ca in the graphite nodules of weld metal containing Ce. This indicates that graphite nucleated from Ce2O2S and Ce2S3 after reacting Ce with O & S and also Mg facilitated to nucleate the graphite nodules as well. However, the matrix of both the welds is composed of Al, Si, Ca, Cr and C except the presence of Ce in weld metal containing Ce.
Volume Percentage of Retained Austenite and Its Carbon Content
The volume percentage of retained austenite and its carbon content of both the weld metals (without and with Ce content) after austempering at 300–350 °C for different holding times have been calculated from X-ray diffraction analysis. The calculated results of the volume percentage of retained austenite are given in Table 3. From the Table 3 it is seen that at two austempering temperatures (300–350 °C) the amount of retained austenite increased in both the weld metals and base metal with increasing the holding time from 1.5 to 2 h. With further increasing holding time from 2 to 2.5 h the amount of retained austenite however decreased. Although the nature of variation of retained austenite content with changing holding time at both the austempering temperatures is same, austempering at 350 °C shows a higher amount of retained austenite content at each holding time studied than 300 °C. This could be due to higher diffusion of carbon during bainitic ferrite transformation at a higher austempering temperature resulting in the higher amount of retained austenite .
The austenitic carbon content also varied with varying the austempering temperature and its holding time. The trend in variation of carbon content in retained austenite with changing in holding time at 300–350 °C is similar to the variation of retained austenite content. At 350 °C, the carbon content increased with increasing the amount of retained austenite . Also, the maximum carbon content in retained austenite was achieved for 2 h holding time irrespective of austempering temperature of ADI weldment. However, weld metal containing Ce attributed highest carbon content in retained austenite and base metal shows lowest carbon content. During austempering process, bainitic ferrite needles are nucleated out of austenite to refusing the carbon content. The remaining austenite absorbs the carbon and amount of austenite thus increased and stabilized. Thus maximum stability of retained austenite should possess at 2 h holding time irrespective of austempering temperature for both the weld metals. Therefore, it can be postulated that the change of carbon content in retained austenite is proportional to changing in the amount of retained austenite content at different austempering temperatures and holding time. Hence, the stability of retained austenite should be higher at 2 h holding time irrespective of weld metal composition and austempering temperature in the present investigation. Furthermore, weld metal containing Ce shows higher carbon content in retained austenite due higher transformation rate of bainitic ferrite.
Microhardness
The microhardness of both the weld metals (with and without Ce containing) after austempering at 300–350 °C for 1.5, 2 and 2.5 h holding time were taken at six different positions of the weld metal and the average of six considered final value. The average microhardness of the weld metals at both 300–350 °C austempering temperature are plotted in Fig. 7 with respect to the holding time. Figure 7 demonstrates that at 300 °C both the weld metal shows higher hardness value than 350 °C due to the variation of the amount of carbon enriched austenite. However, the hardness values varied with changing the austempering holding time. In both the weld metals at both 300–350 °C holding time changed from 1.5 to 2 h, the hardness values decreased with increasing the amount of retained austenite . With increasing holding time from 2 to 2.5 h the hardness values increased, with decreasing the amount of carbon enriched retained austenite in weld metals (Table 3). At higher holding time the stage II reaction probably started and the carbon-enriched retained transformed to bainitic ferrite and carbide, as a result the amount of retained austenite was decreased and the hardness increased [24]. At both the austempering temperatures, both weld metals at 2 h holding time attributed lower hardness due to the presence of higher amount of retained austenite (Table 3).
Further, at each austempering conditions, Ce containing weld metal shows lower hardness value due to higher amount of carbon enriched retained austenite in weld metal and attributed minimum hardness (273 Hv) at 350 °C for 2 h holding time due to presence of higher amount of retained austenite (46.7%) compared to without Ce containing weld metal.
Transverse Tensile
The transverse tensile tests of the ADI welded joints (without and with Ce content) were carried out after austempered at 300–350 °C for 2 h holding time. For confirmation of the test results, three samples at each condition were tested and an average of the three test results was considered as representative one. The failure of all the tensile test specimens took place from base metals (Fig. 8) indicating 100% joint efficiency and the weld metal and even HAZ is much stronger than base metal.
The tensile properties of ADI is strongly depended on the amount of retained austenite and its carbon content, the shape and size of bainitic ferrite and the numbers of graphite nodules presence [25, 26]. At each austempering condition both the weld metals attributed more amount of retained austenite and finer bainic ferrite and smaller size of graphite nodules compare to base metal and HAZ . During tensile testing, weld metal is possibly more strain hardened compare to base metal and HAZ due to the presence of higher amount of retained austenite [27]. It is well known that austenite having FCC structure posses higher strain hardening rate than BCC ferrite (bainitic ferrite) and the strain hardening rate of austenite also increases with carbon content [27]. However, with increasing tensile load, the strain hardening effect becomes saturated, which facilitates the transmission of load to the adjacent base metal. Since the base metal cannot bear the load, failure takes place at the base metal.
Charpy Impact
The average sub-size Charpy impact values of weld metals with and without Ce content after austempering at 300–350 °C for 2 h holding time are given in Table 4. The results show that the Charpy impact toughness improves with the addition of Ce in weld metal and increased with increasing the austempering temperature form 300 to 350 °C.
The Charpy impact values are directly related to austempered microstructures of the weld metals. The impact toughness of weld metals strongly depends on the amount of retained austenite , austenitic carbon content, nodularity, nodule size and shape of the bainitic ferrite. Presence of higher carbon content in austenite the strain hardening rate of austenite is high and consequently more energy is being absorbed leading to an increase in impact toughness [27]. The higher nodularity could suppress the crack initiation due to lower stress concentration and increase in the amount of graphite nodules could act as crack arrester during impact testing.
The fracture surfaces of the freshly broken Charpy impact test specimens of both without and with Ce containing after austempering at 300–350 °C for 2 h holding time were examined under SEM in order to relate impact properties to operative fracture mechanism and are given in Fig. 9. At 300 °C, both the weld metal (Fig. 9a, c) fracture surface exhibits quasi-cleavage along with dimple types fracture. However, at 350 °C (Fig. 9b, d) the fracture surface shows predominantly finer dimple type exhibiting ductile fracture of both the weld metals. Presence of Ce content in weld metal makes the sizes of the dimple finer indicating higher impact toughness .
High Cycle Fatigue Performance
High cycle fatigue test was performed under different stress amplitudes that is 30–70% YS to predict fatigue life and the fatigue test was continued to failure or to 107 cycles at which specimen was considered to be stopped. It is to be noted that during fatigue testing of ADI joints, in case of stress amplitude above 50% YS the fatigue crack initiated at weld metal irrespective of with and without Ce content and after certain no. of cycles loading the crack propagation is stopped automatically. Whereas in case of stress amplitude at and below 50% YS failure of ADI joints took place from the base metal. Typical stress amplitude versus number of cycles to failure plots of different ADI joints is shown in Fig. 10. The S–N curve is drawn through the data point as best fit line and the arrows indicate that the samples did not fail even after 107 cycles (endurance limit) [28]. The highest stress at which specimens endured 107 cycles is taken as the fatigue strength given in Table 4. It is clearly apparent that maximum fatigue strength is obtained in ADI joint austempered at 350 °C. Interestingly same austempering condition attributed maximum toughness as well. However, Ce containing weld metal also shows higher fatigue strength than weld metal without Ce content. For example, in case of stress amplitude of about 190.33 MPa (70% YS), fatigue life of Ce containing weld metal is almost three times more (433,240 cycles) than that of weld metal without Ce content (154,727 cycles).
The fracture surfaces of the fatigue tested specimens of ADI joints have been examined by SEM in order to understand operative fracture mechanism (s). The fracture surfaces exhibit predominantly quasi cleavage (Fig. 11a). Zones of brittle fracture by transgranular cleavage and intergranular decohesion are also visible (Fig. 11b). The combination of ductile striation and cleavage plane whose river patterns (Fig. 11c) go into tear rivers is named as quasi-cleavage [29]. Other typical and frequent morphologies are steps between different cleavage level (Fig. 11d).
Conclusions
Based on the above studies, the following conclusions can be drawn.
-
1.
The quality of DI groove welded joints as per AWS (D11) has been established using developed coated electrode without and with the addition of nano-CeO2 with preheating at 300 °C for 1 h and PWHT for 1 h immediate after welding.
-
2.
As-welded microstructures of both the weld metals show ledeburitic carbide with alloyed pearlite and a small amount of graphite nodules. However, the microstructure of Ce containing weld metal attributed finer structure with the lower amount of ledeburitic carbide and higher amount of alloyed pearlite.
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3.
Austempering at 300 °C microstructures shows needle shape bainitic ferrite with lower amount of retained austenite and graphite nodules. Whereas, at 350 °C shows feathery shape bainitic ferrite with a higher amount of retained austenite . However, the presence of Ce in weld metal exhibits similar microstructural appearance like without Ce content except the structure becomes finer along with the higher amount of retained austenite .
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4.
The microhardness of weld metal shows a lower value at 350 °C than 300 °C austempering temperature. With changing the austempering holding time the hardness values changed and show lower hardness value at 2 h holding time irrespective of austempering temperature. However, Ce in weld metal decreased the hardness value at both the temperature. Transverse tensile testing of all the welded ADI specimens after different austempering conditions shows failure from the base metals indicating 100% joint efficiency and weld metal and even HAZ are stronger than base metal. The Charpy impact toughness of Ce-treated weld metal improved significantly compared to without Ce at both the austempering conditions. However, the highest impact toughness was obtained at 350 °C for 2 h holding time.
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5.
Fatigue strength of both ADI weld joint improved with improving the austempering temperature. At 350 °C feathery shaped bainitic ferrite with a higher amount of retained austenite shows higher fatigue strength than needle-shaped bainitic ferrite with a small amount of retained austenite at 300 °C. Ce containing weld metal shows higher fatigue strength than without Ce content at both the austempering temperatures.
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Pal, T.K., Sarkar, T. (2019). Comparative Austempering Response Between Weld Metals of ADI Weldments With and Without Cerium Addition. In: TMS 2019 148th Annual Meeting & Exhibition Supplemental Proceedings. The Minerals, Metals & Materials Series. Springer, Cham. https://doi.org/10.1007/978-3-030-05861-6_20
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