Contrasting the mechanical and metallurgical properties of laser welded and gas tungsten arc welded S500MC steel

S500MC steel is a grade of high-strength low-alloy steel (HSLA) which is widely used in the automotive industry and for agricultural machinery and equipment. Considering properties of this alloy, selection of the welding process and parameters becomes essential to ensure that HSLA assemblies meet specific service requirements. In this work, mechanical and metallurgical properties of S500MC steel produced by autogenous laser beam welding (LBW) and automatic gas tungsten arc welding (GTAW) were compared. Tensile testing, metallography, hardness testing, and fractographic analysis were performed on the welded specimens, revealing that the heat input by these welding processes caused significant microstructural changes within the joints. In LBW samples, the heat input about 10 times lower than that in GTAW produced a finer microstructure, narrower fusion zone width, and smaller heat-affected zone. All fractures of the GTAW specimens occurred in the base metal, while all fractures of the LBW specimens occurred in the weld zone, both regardless of the heat input. GTAW joints exhibited higher mechanical properties (even higher than those obtained in the base metal) as compared to LBW joints

Welding and Corrosion Behavior of AISI H13 Welds: The Effect of Filler Metal on the Microstructural Evolutions

Welding of AISI H13 tool steel which is mainly used in mold making is difficult due to the some alloying elements and it high hardenability. The effect filler metal composition on the microstructural changes, phase evolutions, and hardness during gas tungsten arc welding of AISI H13 hot work tool steel was investigated. Corrosion resistance of each weld was studied. For this purpose, four filler metals i.e. ER 312, ER NiCrMo-3, ER 80S, and 18Ni maraging steel were supplied. Potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) were used to study the corrosion behavior of weldments. It was found the ER 80S weld showed the highest hardness owing to fully martensitic microstructure. The hardness in ER 312 and ER NiCrMo3 weld metals was noticeably lower than that of the other weld metals in which the microstructures mainly consisted of austenite phase. The results showed that the corrosion rate of ER 312 weld metal was lower than that other weld metals which is due to the high chromium content in this weld metal. The corrosion rate of ER NiCrMo-3 was lower than that of 18Ni maraging weld. The obtained results from EIS tests confirm the findings of potentiodynamic polarization tests

Microstructural Characteristics and Strengthening Mechanisms of Ferritic–Martensitic Dual-Phase Steels: A Review

Ferritic–martensitic dual-phase (DP) steels are prominent and advanced high-strength steels (AHSS) broadly employed in automotive industries. Hence, extensive study is conducted regarding the relationship between the microstructure and mechanical properties of DP steels due to the high importance of DP steels in these industries. In this respect, this paper was aimed at reviewing the microstructural characteristics and strengthening mechanisms of DP steels. This review article represents that the main microstructural characteristics of DP steels include the ferrite grain size (FGS), martensite volume fraction (MVF), and martensite morphology (MM), which play a key role in the strengthening mechanisms and mechanical properties. In other words, these can act as strengthening factors, which were separately considered in this paper. Thus, the properties of DP steels are intensely governed by focusing on these characteristics (i.e., FGS, MVF, and MM). This review article addressed the improvement techniques of strengthening mechanisms and the effects of hardening factors on mechanical properties. The relevant techniques were also made up of several processing routes, e.g., thermal cycling, cold rolling, hot rolling, etc., that could make a great strength–ductility balance. Lastly, this review paper could provide substantial assistance to researchers and automotive engineers for DP steel manufacturing with excellent properties. Hence, researchers and automotive engineers are also able to design automobiles using DP steels that possess the lowest fuel consumption and prevent accidents that result from premature mechanical failures

Microstructural Characteristics and Strengthening Mechanisms of Ferritic–Martensitic Dual-Phase Steels: A Review

Ferritic–martensitic dual-phase (DP) steels are prominent and advanced high-strength steels (AHSS) broadly employed in automotive industries. Hence, extensive study is conducted regarding the relationship between the microstructure and mechanical properties of DP steels due to the high importance of DP steels in these industries. In this respect, this paper was aimed at reviewing the microstructural characteristics and strengthening mechanisms of DP steels. This review article represents that the main microstructural characteristics of DP steels include the ferrite grain size (FGS), martensite volume fraction (MVF), and martensite morphology (MM), which play a key role in the strengthening mechanisms and mechanical properties. In other words, these can act as strengthening factors, which were separately considered in this paper. Thus, the properties of DP steels are intensely governed by focusing on these characteristics (i.e., FGS, MVF, and MM). This review article addressed the improvement techniques of strengthening mechanisms and the effects of hardening factors on mechanical properties. The relevant techniques were also made up of several processing routes, e.g., thermal cycling, cold rolling, hot rolling, etc., that could make a great strength–ductility balance. Lastly, this review paper could provide substantial assistance to researchers and automotive engineers for DP steel manufacturing with excellent properties. Hence, researchers and automotive engineers are also able to design automobiles using DP steels that possess the lowest fuel consumption and prevent accidents that result from premature mechanical failures

Friction stir welding/processing of mg-based alloys: A critical review on advancements and challenges

Friction stir welding (FSW) and friction stir processing (FSP) are two of the most widely used solid-state welding techniques for magnesium (Mg) and magnesium alloys. Mg-based alloys are widely used in the railway, aerospace, nuclear, and marine industries, among others. Their primary advantage is their high strength-to-weight ratio and usefulness as a structural material. Due to their properties, it is difficult to weld using traditional gas- or electric-based processes; however, FSW and FSP work very well for Mg and its alloys. Recently, extensive studies have been carried out on FSW and FSP of Mg-based alloys. This paper reviews the context of future areas and existing constraints for FSW/FSP. In addition, in this review article, in connection with the FSW and FSP of Mg alloys, research advancement; the influencing parameters and their influence on weld characteristics; applications; and evolution related to the microstructure, substructure, texture and phase formations as well as mechanical properties were considered. The mechanisms underlying the joining and grain refinement during FSW/FSP of Mg alloys-based alloys are discussed. Moreover, this review paper can provide valuable and vital information regarding the FSW and FSP of these alloys for different sectors of relevant industries

Additive manufacturing of biodegradable magnesium-based materials: Design strategies, properties, and biomedical applications

Magnesium (Mg)-based materials are a new generation of alloys with the exclusive ability to be biodegradable within the human/animal body. In addition to biodegradability, their inherent biocompatibility and similar-to-bone density make Mg-based alloys good candidates for fabricating surgical bioimplants for use in orthopedic and traumatology treatments. To this end, nowadays additive manufacturing (AM) along with three-dimensional (3D) printing represents a promising manufacturing technique as it allows for the integration of bioimplant design and manufacturing processes specific to given applications. Meanwhile, this technique also faces many new challenges associated with the properties of Mg-based alloys, including high chemical reactivity, potential for combustion, and low vaporization temperature. In this review article, various AM processes to fabricate biomedical implants from Mg-based alloys, along with their metallic microstructure, mechanical properties, biodegradability, biocompatibility, and antibacterial properties, as well as various post-AM treatments were critically reviewed. Also, the challenges and issues involved in AM processes from the perspectives of bioimplant design, properties, and applications were identified; the possibilities and potential scope of the Mg-based scaffolds/implants are discussed and highlighted

Relationship between the Expression of Matrix Metalloproteinase and Clinicopathologic Features in Oral Squamous Cell Carcinoma

Introduction: Squamous cell carcinoma of the oral cavity is one of the most important and common types of head and neck malignancy, with an estimated rate of 4% among all human malignancies. The aim of this study was to determine the association between expression of matrix metalloproteinase 2 and 9 and the clinicopathological features of oral squamous cell carcinoma (OSCC).   Materials and Methods: One hundred existing samples of formalin-fixed paraffin embedded specimens of OSCC were evaluated by immunohistochemistry staining for matrix metalloproteinase 2 and 9 antibodies. Samples were divided into four groups: negative, 50%. Patient records were assessed for demographic characteristics such as age and gender, smoking and family history of OSCC as well as tumor features including location, differentiation, stage and lymph node involvement.   Results: In this study, 58 patients (58%) were male and 42 (42%) female. The mean age of patients was 60.38±14.07 years. The average number of lymph nodes involved was 8.9±3.8. Tumoral grade, tumoral stage, lymphatic metastasis and history of smoking were significantly related to MMP2 and MMP9 expression.   Conclusion:  Our study demonstrated that MMP2 and MMP9 expression are important in the development of OSCC

Contrasting the mechanical and metallurgical properties of laser welded and gas tungsten arc welded S500MC steel

S500MC steel is a grade of high-strength low-alloy steel (HSLA) which is widely used in the automotive industry and for agricultural machinery and equipment. Considering properties of this alloy, selection of the welding process and parameters become essential to ensure that HSLA assemblies meet specific service requirements. In this work, mechanical and metallurgical properties of S500MC steel produced by autogenous laser beam welding (LBW) and automatic gas tungsten arc welding (GTAW) were compared. Tensile testing, metallography, hardness testing, and fractographic analysis were performed on the welded specimens, revealing that the heat input by these welding processes caused significant microstructural changes within the joints. In LBW samples, the heat input about 10-times lower than in GTAW produced a finer microstructure, narrower fusion zone width and smaller heat affected zone. All fractures of the GTAW specimens occurred in the base metal, while all fractures of the LBW specimens occurred in the weld zone, both regardless of the heat input. GTAW joints exhibited higher mechanical properties (even higher than those obtained in the base metal) as compared to LBW joints

Frequency of five Escherichia Coli pathotypes in Iranian adults and children with acute diarrhea.

BackgroundKnowledge about the distribution of Escherichia Coli (E. coli) pathotypes in Iran is limited. This nation-wide survey aims to provide a comprehensive description of the distribution of five pathogenic E. coli in Iran.MethodsStool samples were collected from 1,306 acute diarrhea cases from 15 provinces (2013-2014). E. coli-positive cultures underwent PCR testing for the detection of STEC, ETEC, EPEC, EAEC, and EIEC pathotypes. Pathotype frequency by province, age-group, and season was estimated.Results979 diarrhea samples (75.0%) were culture-positive for E. coli (95% CI: 72.6, 77.3%), and 659 (50.5%) were pathogenic E. coli (95% CI: 47.8, 53.2%). STEC was the most frequent pathotype (35.4%). ETEC (14.0%) and EPEC (13.1%) were the second and the third most frequent pathotypes, respectively. EAEC (4.3%) and EIEC (0.3%) were not highly prevalent. Fars (88.7%) and Khorasan-e-Razavi (34.8%) provinces had the highest and lowest frequencies, respectively. E. coli pathotypes were more frequent in warmer than cooler seasons, showed the highest frequency among children under five years of age (73%), and had no significant association with participants' gender.ConclusionsDiarrheagenic E. coli may be an important cause of acute diarrhea in adults and children in Iran. STEC and ETEC seem to be widespread in the country with a peak in warmer seasons, impacting the recommended use of seasonal STEC and ETEC vaccines, especially in high-risk groups. Monitoring the incidence of E. coli pathotypes, serotypes, and antibiotic resistance over time is highly recommended for evaluation of interventions