Effects of Electromagnetic Stirring on the Cast Austenitic Stainless Steel Weldments by Gas Tungsten Arc Welding

Cast austenitic stainless steel (CASS) often contains high contents of silicon, phosphorus, and sulfur to prompt low melting phases to form in the welds. As a result, welding defects can be induced to degrade the welds. This study’s purpose was to investigate the effects of electromagnetic stirring (EMS) on the CASS weldments. The results showed that the ferrites in the heat affected zone (HAZ) had tortuous grain boundaries, while those that were close to the fusion lines had transformed austenites. EMS could reduce the influence of the welding heat to make the grain boundaries less tortuous and the transformed austenites smaller. Although their temperature profiles were almost the same, the gas-tungsten-arc-welding (GTAW) weld had smaller grains with massive ferrite colonies and more precipitates, while the GTAW+EMS weld had denser ferrite colonies with multi-orientations, but fewer precipitates. The hardness of the base metals and HAZs were typically higher than that of the welds. For both of the welds, the root was the region with the highest hardness. The hardness decreased from the root to the cap regions along the thickness direction. The GTAW weld had a higher hardness than the GTAW+EMS weld. At room temperature, the GTAW+EMS weld had a higher notched tensile strength and elongation than the GTAW weld. This could be attributed to the observation that the GTAW+EMS weld had dense and intersecting dendrites and that more austenites were deformed during tensile testing.

Mechanical Behavior of Aged Ti-15V-3Cr-3Sn-3Al Alloy

The effect of aging treatments on the mechanical behavior of Ti-15V-3Cr-3Sn-3Al (Ti153) alloy was evaluated in the present study. Properties of the two-step aged specimens were also compared with those of the one-step aged specimens. The second aging treatment, which was performed at 426o°C for 24 h, apparently raised the tensile strength at the expense of the notched tensile strength for the specimens previously aged at 426°C or below. On the other hand, the second-step aging had a minor effect on further hardening of the specimens prior to aging at 538°C and 593°C. In general, theJ-integral value (fracture toughness) had the same trend as that of the notch brittleness of the specimens. Overall, the specimens subjected to the two-step aging treatment did not show any advantage over the specimens subject to one-step aging treatment.

Studies of Ti-15V-3Cr-3Al-3Sn after Thermohydrogen Processing

Ti-15V-3Cr-3Al-3Sn, β-phase titanium alloy, is subjected to study the microstructure and mechanical behavior after thermohydrogen processing. It aims to study the relationship between microstructure modification and notched tensile test at room temperature. Meanwhile, the notched tensile test and fracture features of Ti-15-3 alloy without THP is also discussed. It follows that the hardness of Ti-15V-3Cr-3Al-3Sn would be clearly enhaced up to Hv 499 after thermohydrogen processing due to grain refinement. Besides, the notched tensile strength of the as-received specimen is about 904 MPa, and is increased to 959 MPa after THP, that is, Ti-15-3 alloy after THP shows higher hardness and notched tensile strength than as-received alloy. The enhanced high hardness does not induce a significant notched embrittlement effect.

Effect of the microstructure on the notched tensile strength of as-cast and austempered ductile cast irons

In this study, the effect of microstructure on the mechanical properties of four types of ductile cast irons with different morphologies was investigated using circumferentially notched cylindrical specimens with different notch root radii. These cast irons were also austempered using the same austempering heat treatment to make a comparison with the as-cast samples. Characterization of the specimens has been carried out by means of microstructure, hardness, tensile properties, notch tensile strength, notch sensitivity, fracture toughness, and fractography. A mixture of ferrite and pearlite in the microstructure of cast irons gives rise to a material of the highest tensile strength, notch tensile strength, and fracture toughness properties with the intermediate ductility and notch sensitivity. A higher pearlite in the matrix of cast irons gives very important mechanical properties such as hardness and strength, but brittleness of the matrix andnotch sensitivity are greatly increased. Austempering significantly increased the mechanical properties and also reduced the difference between the mechanical properties of the cast irons. Austempered ferritic ductile irons exhibited the highest notch tensile strength and fracture toughness, and the high tensile strength and the intermediate ductility properties with the lowest notch sensitivity, whereas austempered pearlitic ductile irons had the lowest tensile strength, ductility, notch tensile strength, fracture toughness, and the intermediate notch sensitivity properties. The mechanical properties of the as-cast and austempered ductile irons have increased almost linearly with increase in the notch root radius.

Dissimilar Laser Welding of Ti-6Al-4V to Ti-6Al-6V-2Sn

Notched tensile strength (NTS) of the Ti-6Al-4V (Ti-6-4) to Ti-6A16V-2Sn (Ti-6-6-2) dissimilar laser welds were determined, which had been subjected to post-weld heat treatment (PWHT) over the temperature range of 482-704°C. The results indicated for the weld with the PWHT at 482°C the fusion zone (FZ) and heat-affected zone (HAZ) showed a peak hardness, as compared with other welds at the counterpart regions, whereas, the weld with the PWHT at 704°C had the lowest hardness among the welds. In all the welds, the FZ of the weld subjected to PWHT at 482°C possessed the lowest NTS, while the as-welded and the weld with PWHT at 704°C had superior NTS to others. The presence of grain boundary α, which promoted grain boundary shear, accounted for the typical features of mainly transgranular fracture with intergranular dimples of the welds.

Temperature Effect on Microstructure and Mechanical Behavior of Ti-15V-3Cr-3Al-3Sn

Ti-15V-3Cr-3Al-3Sn, β-phase titanium alloy, is subjected to study the temperature effects on microstructure and mechanical behavior by using different aging temperature (426 ∼ 600 oC) and high temperature (450oC) notched tensile test. It follows that the highest hardness of Ti-15V-3Cr-3Al-3Sn would be got up to 420 Hv after 426 oC aging. Afterward, the hardness is decreasing with increasing aging temperature. By means of microstructure analyses, it reveals that the narrow and intragranular α-phase precipitates with lamella-shape in the grains at 426 oC aging treatment caused the age hardening of the titanium alloy. Subsequently, the α-phase precipitates were coarsening with increasing the aging temperature and showed the thick morphologies distributed along grain boundaries, which results in overaging. In the notched tensile test at 450oC, the highest notched tensile strength (1160 MPa) is also obtained after 426oC aging treatment, and then decreasing with increasing aging temperature. Its mechanical behavior is different from the room temperature notched tensile test, which demonstrates the lowest notched tensile strength (813 MPa) after 426 oC aging treatment due to the notched embrittlement effect. According to microstructure study, it suggests that the environment temperature effect enhanced the toughness of the alloy and terminated the notched embrittlement effect resulted from the 426oC aging treatment.

Fracture Behavior of Long Glass Fiber Reinforced PP Sheets With Hole

Recently, owning to the increasing concerns on the environment, lightweight materials representative by composite are being considered to be used in primary structure components in particular in vehicle instead of metal. In order to enhance the mechanical property in particularly tensile property, at current study, stampable sheets (glass mat which were fabricated by punch knitted technology) were adopt to make glass mat reinforced thermoplastic PP (GMT). In the paper, three kinds of specimens including two GMT which have glass fiber weight percent 40 and 20 wt% respectively and a LFT (normal long fiber reinforced thermoplastics PP) which has glass fiber 40wt% were fabricated and tensile tested. The mean fiber length of GMT and LFT were 6.67 and 1.37 mm, respectively. For tensile test, it was observed that the modulus of 40GMT and 40LFT were similar. However, it was found that 40GMT specimens have better tensile strength than 40LFT specimens. In the case of different glass fiber content, 40GMT had more than two times higher value than 20GMT in both tensile modulus and tensile strength. Referring to the effect of hole on the tensile property of GMT and LFT, it was found that the notched tensile strength of both GMT and LFT decrease when W/d equal to 2.0. On the other hand, for W/d equal to 2.5 and 3.0 have no effect to tensile strength.