Influence of heat input on microstructure and mechanical properties of gas tungsten arc welded HSLA S500MC steel joints

High-strength low alloy (HSLA) S500MC steel is widely used for chassis components, structural parts, and pressure vessels. In this study, the effects of heat input during automatic gas tungsten arc welding (GTAW) on microstructure and mechanical properties of thermomechanically controlled processed (TMP) S500MC steel were investigated. A butt joint configuration was used, and welding was performed in autogenous mode. Six different levels of heat input namely 1.764 kJ/mm, 1.995 kJ/mm, 2.035 kJ/mm, 2.132 kJ/mm, 2.229 kJ/mm, and 2.33 kJ/mm were considered. Microstructural investigations revealed a different microstructure than base metal in the fusion zone (FZ) of all welded joints which was most likely due to a lath martensitic microstructure surrounded by retained austenite. With increased heat input, the amount of retained austenite and the size of packets increased. In the heat-affected zone (HAZ), two distinct regions of coarse grain (CG-HAZ) and fine grain (FG-HAZ) were observed. Due to the presence of carbides in the HAZ, mostly a martensitic microstructure with smaller packets, compared to FZ, was formed. By increasing the heat input and through the dissolution of carbides, the dimension of packets increased. Due to microstructural changes and grain growth, in both the FZ and the HAZ, the mechanical properties produced by TMP were lost in these regions. However, failure occurred in the base metal of all samples with a maximum tensile strength of 690 MPa. Thus, tensile strength in the weld zone and HAZ were higher than the base metal even for the highest heat input indicating the formation of a good joint between S500MC plates with GTAW, regardless of heat input

Prediction and Optimization of Magnetic Properties of Laser Welded AISI 430 Stainless Steels

The AISI 430 stainless steel with ferritic structure is a low cost material for replacing austenitic stainless steel because of its higher yield strength, higher ductility and also better polarisation resistance in harsh environments. The applications of AISI 430 stainless steel are limited due to insignificant ductility and some undesirable changes of magnetic properties of its weld area with different microstructures. In this research, a study has been done to explore the effects of parameters of laser welding process, namely, welding speed, laser lamping current, and pulse duration, on the coercivity of laser welded AISI 430 stainless steel. Vibrating sample magnetometery has been used used to measure the values of magnetic properties. Observation of microstructural changes and also texture analysis were implemented in order to elucidate the change mechanism of magnetic properties in the welded sections. The results indicated that the laser welded samples undergo a considerable change in magnetic properties. These changes were attributed to the significant grain growth which these grains are ideally oriented in the easiest direction of magnetization and also formation of some non-magnetic phases. The main effects of the above-mentioned factors and the interaction effects with other factors were evaluated quantitatively. The analysis considered the effect of lamping current (175-200 A), pulse duration (10-20 ms) and travel speed (2-10 mm/min) on the coercivity of laser welded samples

The Effect of Filler Metal on Properties of AISI 4130 to AISI 316L Dissimilar Joint

In this research, dissimilar welding between 4130 low alloy steel and austenitic stainless steel 316L has been investigated using Gas Tungsten Arc Welding (GTAW). Two types of filler metals, including ERNiCr-3 and ER309L, were used for this purpose. Moreover, the joint microstructures including the weld metals, heat affected zones and interfaces were characterized by optical and Scanning Electron Microscopy (SEM). The mechanical behavior of the joint was tested by impact and tension tests. Observations by SEM showed that in impact test, the fracture is soft. In the tensile test, the welded sample by ER309L filler metal was fractured from 316L base metal, but welded specimen with ERNiCr-3 was fractured from welded zone. Also, the results showed a dendritic structure in the nickel-based weld metal. No crack was found in the cellular-dendritic microstructure of ER309L weld metal due to the existance of delta ferrite between them. &nbsp

The study of accuracy of color Doppler ultrasonography in detecting the grade of stenosis of cervical carotid arteries in comparison to angiography

This is retrospective double-blind research, which was carried out in Imam Khomeini hospital in order to study the accuracy of color Doppler ultrasonography for detecting the site and grade of stenosis in cervical carotid artery. 40 patients with mean age of 62 years studied with color Doppler before DSA angiography. The most common sites of stenosis were left internal carotid (39.5%) and right internal carotid arteries (38.4%). We measured peak systolic and end-diastolic velocities (PSA and EDV) and ratios of PSA and EDV at stenosis sites to CCA (PSV ratio and EDV ratio). Results showed that PSA has the highest sensitivity and accuracy in all grades of stenosis: Mild to moderate stenosis: Sensitivity (90.5%), accuracy (89.5%); Severe stenosis: Sensitivity (82.1%), accuracy (92.8%); Total occlusion: Sensitivity (93.8%), accuracy (96.5%). There is no difference between accuracy of Doppler parameters for detection of total occlusion (96.5%) but in other grades after PSV, EDV (Mild-moderate 86%, severe 87.2%). EDV ratio and PSV ratio (Mild-moderate both 84.8%, severe both 86%) have the highest accuracies. We concluded that color Doppler sonography can reliability detect stenosis in carotid arteries & PSV has the highest accuracy