In this research, has been compared fatigue behavior of Mo 40 steel in ferrite-martensite dual phase condition and quenched-tempered microstructure. The ferrite-martensite dual phase samples were prepared from intercritical annealing heat treatment process for 40 minute at ( α + γ ) dual phase region. The quenched martensite samples after heating at 860 ° C and quenched in water, were tempering heat treatment at 600 ° C for 3 0 minute. The Hardness, tensile and fatigue tests have been supplemented with optical and electron microscopies. The result shown that hardness of ferrite-martensite dual phase is more than quenched tempered sample. Also, tensile strength of ferrite martensite dual phase samples is lower than quenched-tempered sample, while the fatigue strength of samples is more than quenched-tempered sample. These results are rationalized to strengthening un tempered martensite phase in ferrite martensite dual phase sample compared to tempered martensite in quenched tempered sample.

Near dry Electrical Discharge Machining (EDM) is one of the advanced methods for removing materials environmentally friendly. Combining the minimum quantity of lubricant (MQL) and vegetable oil not only reduces health hazarders and costs, but also improves the process. This research has been conducted on Mo40 steel and the mixture of vegetable oil and air has been used as dielectric. The effect of electric current variables, open circuit voltage, pulse on and off time and air pressure were studied on material removal rate (MRR), tool wear rate (TWR), and surface roughness (Ra), using the method of designing the central composition of the response surface. The results showed that the increase in ampere, pulse on time and open circuit voltage increase the MRR; also, increase of the pulse off time improves washing of the environment that prevent short-circuit and all had an effect on the MRR. Also, increasing the ampere and open circuit voltage leads to an increase in the TWR and increasing the pulse on time, as well as the increase in pulse off time, reduces the TWR. Increasing the air pressure reduced the dielectric density and increased the TWR. On the other hand, the increase in the ampere and the pulse on time as well as the open circuit voltage increased Ra and increase in the pulse off time and the air pressure reduced Ra. This method has led to an increase of 200% in MRR, 30% reduction in TWR, and 60% reduction in Ra compared to the kerosene immersion method.

Nowadays, steel hardening has received much attention from researchers due to its frequent use in industries, especially is widely used in energy equipment, aerospace, and petrochemical industries. Low capability in chip removal of hardened steel has always been a significant machining issue. Mounted point grinding is a machining method to improve surface finish and remove burrs on the workpiece walls and hard-to-reach areas. This process is usually used without preparing the grinding wheel before and during the grinding operation, which reduces the proper performance of the process. Environmental contamination, surface integrity, coolant-lubricant-related diseases that affect workers' health, and machining costs heavily depend on the appropriate dressing and proper coolant-lubricant usage. In this study, the effect of dressing conditions (depth of dressing and dressing feed) and the workpiece feed rate during the mounted point grinding of a Mo40 hardened steel in two traditional wet and Minimum Quantity Lubrication (MQL) environments has been investigated. Surface roughness and wheel loading are two significant outputs in every grinding operation. The experimental result of this study reveals an improvement in enhancing the surface roughness in a soft dressing condition. Moreover, this study aimed to achieve proper surface roughness by implementing MQL technique to significantly reduce total cutting fluid usage compared to traditional wet machining. This study observed a higher wheel loading in MQL technique than in the conventional wet grinding.

The purpose of this research is to investigate microstructural features and mechanical properties of Mo40 low alloy steel under dual-phase ferritic-bainitic in comparison with those of full bainitic conditions. To do so, various heat treatment cycles including Austenitizing the samples at 860° C for 50 minutes, step quenching in primary 620° C salt bath for different duration times of 1 to 10 minutes, quenching in secondary 350° C salt bath for 30 minutes and then water quenching to room temperature in order to develop dual-phase ferritic-bainitic microstructures in the samples. The isothermal heat treatment in primary 620° C salt bath for various duration times was used in order to develop different volume fractions of ferritic phase in the microstructures, then the secondary 350° C salt bath was used for subsequent transformation of remaining prior austenite to bainite. Tensile test, micro and macro hardness testers, optical metallography and FE-SEM equipped with EDS were used for investigation of variations of mechanical properties and microstructural features. The experimental results show that there is a non-linear and abnormal relationship between the mechanical properties of dual-phase ferritic-bainitic samples and variations of ferrite and bainite volume fractions. The mechanical properties of dual-phase ferritic-bainitic samples involving 8-12 vol% grain boundary ferrite in the vicinity of bainite is considerably higher than other dual phase ferritic-bainitic samples and even full bainitic ones. This improvement in mechanical properties of dual-phase ferritic-bainitic samples involving 8-12 vol% ferrite is originating from interaction of bainite crystals on grain boundary ferrite.

Compound casting refers to a process that is used to produce bimetals. This study investigates the interface of Mo40/C93200 that is produced by compound casting process. In this research, molten bronze is poured around the steel core, and interaction between liquid and solid creates a diffusion zone and is followed by a transition layer which leads to the creation of a diffused region between the interfaces of metal layers. The results of micro-hardness and macro hardness tests were used to complete the studies. The results of the hardness of the Mo40 alloy revealed that the alloy micro-hardness was almost 308 Vickers which confirms the ferrite-pearlite state of microstructures. The results of metallography revealed that the boundary between steel and bronze alloys due to the difference in electric potential during etching evolved a galvanic cell and one section was formed as the cathode and the other section as the anode. In this situation, steel was corroded and bronze was protected. Also, the results of SEM show that the boundaries between two alloys have an acceptable adhesion and the strength of interface is sufficient. The result of tensile test indicates that the final yield strength was about 800 MPa and the elongation increases by 2%, which is an acceptable value. It is also observed that the failure is a soft defect type and a sufficient connection between steel and bronze is formed.

Wire EDM (WireCut) is a machining process utilizing electric discharge to gradually cut a workpiece with a spark-generating thin wire. It offers benefits like non-contact cutting, versatility with materials, and precise dimensional accuracy. However, it is important to note that surfaces cut by WireCut process may exhibit tensile residual stresses with significant values in the surface layers. Ultrasonic Peening Treatment (UPT) can be employed as a new approach to modify the surface structure of wire EDMed workpieces. UPT, which induces compression in the surface layers of the workpiece, generates compressive residual stress and enhances mechanical properties including hardness. In this study, UPT was performed on wire EDMed workpieces made of alloy steel Mo40 (DIN 1.7225) using an ultrasonic vibrating tool on a lathe, at 3 levels: finishing, semi-finishing, and roughing. The impact of parameters such as the number of passes, feeding rate, and the type of wire EDM cut on the constant amplitude of vibration were studied to understand their effect on the residual stress generated. The experiments conducted using the Taguchi method revealed that in every case, this process resulted in the conversion of tensile residual stresses into substantial compressive residual stresses in wire EDMed workpieces. The compressive residual stress also reached 1654 MPa. More passes lead to higher compressive residual stress, while a higher feeding rate leads to a decrease. Surface hardness increased by 30%, 31%, and 48% for the semi-finishing, finishing, and roughing workpieces in the initial pass. This trend continued with each subsequent pass.Key words: Residual stress - Surface hardness -Wire Electric Discharge Machining (WEDM) - Ultrasonic Peening Treatment (UPT) - Mo40 alloy steel

Introduction: Stainless steel crowns (SSCs) are widely used in restoring severely damaged primary molar teeth. Since these crowns do not adapt ideally to tooth substance, they may lead to some changes in surrounding gingiva. This clinical study was performed to evaluate the effect of stainless steel crowns placed on primary molars on gingival structures. Materials & Methods: In this retrospective study, 117 crowns in eighty four 4-11 year old children attended to pediatric department of Zahedan dental school were evaluated. Convenience sampling method was done. Some clinical factors such as gingival index, tooth type, state of being either right or left molar, or upper or lower molar, time elapsed after cementation, crown marginal adaptation, excessive cementation around the margin of crown and the oral hygiene level were examined. Kruskal-Wallis and Mann-Whitney tests were used for data analysis through SPSS 15 software (P<0.05). Results: In our study only 11.1% of the evaluated crowns demonstrated clinically healthy gingiva, and there was a significant correlation between upper and lower molar, crown marginal adaptation and oral hygiene level with gingival index (P<0.05), while gingival index was not significantly affected by tooth type, tooth side, time elapsed after cementation and presence of excessive cement around the margin of crown and sex (P>0.05).Conclusion: Stainless steel crowns had no harmful effect on the gingiva provided performing standard preparation procedures especially in upper molars and stablishing proper marginal adaptation and good oral hygiene level.

Introduction: The bonding process of the brackets to enamel has been a critical issue in orthodontic research. The purpose of this study was to evaluate the shear bond strength of 3 lightcured adhesives (transbond XT, Z250, light bond).Materials & Methods: In this study sixty extracted human premolars were collected and randomly divided into 3 test groups. All teeth were etched by 37% phosphoric acid. In first group brackets were bonded by Transbond XT adhesive, in group two brackets were bonded by Light bond adhesive and in third group were bonded by filtek Z250 composite. All of them were cured with Ortholux xt for 40 seconds.24 hours after thermocycling, Shear Bond Strength (SBS) values of these brackets were recorded using a Universal Testing Machine. Adhesive Remnant Index (ARI) scores were determined after the failure of the brackets, using Stereo Microscope the data were analyzed using ANOVA and Chi-square tests.Results: Mean shear bond strength of Transbond XT, light bond and Z250 were 28.9±2.25 MPa, 25.06±1.98 MPa and 26.8±2.57 MPa, respectively. No significant difference was observed in the SBS among the groups and a clinically acceptable SBS was found for the three adhesives. ARI scores were not significantly different between the various groups (P>0.05).Conclusion: This study showed that the Z250 can be used as light bond and transbond xt to bond orthodontic brackets and ARI and SBS scores were not significantly different.

Progressive collapse studies generally assess the performance of the structure under gravity and blast loads, while earthquakes may also lead to the progressive collapse of a damaged structure. In this study, the progressive collapse response of concentrically braced dual systems with steel moment-resisting frames was assessed under seismic loads through pushover analysis using triangular and uniform lateral load patterns. Two different bracing types (X and inverted V braces) were considered, and their performances were compared under different lateral load patterns using the nonlinear static alternate path method recommended in the Unified Facilities Criteria (UFC) guideline. Eventually, the seismic progressive collapse resistance of models was compared to their progressive collapse response under gravity loads. These studies showed that models under the seismic progressive collapse loads satisfied UFC acceptance criteria and limited rehabilitation objective. The structures had better performance under seismic progressive collapse than models under gravity loads because of more resistance, ductility, suitable load redistribution, and more structural elements that participated in load redistribution. Furthermore, despite studies on progressive collapse under gravity loads, the dual system with X braces showed better progressive collapse performance (more resistance, residual reserve strength ratio and ductility) under seismic loads than the model with inverted V braces.