Grain size of a 304 austenitic stainless steel was tuned via deformation-induced martensite transformation and austenite reversion annealing, and the significant effects of grain size on mechanical ...properties, strain hardening behavior, deformation mechanisms were studied. The results showed that grain refinement strengthening significantly increased the yield strength from 235 MPa (~20 μm) to 1030 MPa (~200 nm), meanwhile, the interaction of Lüders deformation and deformation-induced martensite transformation realized the stable propagation of Lüders bands, leading to a considerable total elongation (above 30%). It was inferred that martensitic transformation was enhanced with a decrease in grain size. The underlying reasons were attributed to the formation of carbide precipitation (M23C6) and the change of martensite nucleation sites depending on grain size. In coarse grains, α'-martensite formed at shear bands with or without the aid of ɛ-martensite, whereas α'-martensite mainly nucleated at grain boundaries and deformation twins in ultrafine austenite grains. Besides TRIP effect and dislocation glide, TWIP effect also became one of the dominate deformation mechanism with the decrease in austenite grain size.
•Nano/ultrafine-grained (NG/UFG) 304 stainless steels with high strength and good tensile plasticity are achieved.•Deformation-induced martensite transformation is enhanced as austenite grain sizes decrease.•The enhanced strain-hardening caused by martensitic transformation supports the propagation of Lüders bands.•The dominant strain hardening mechanisms change from TRIP effect in CG steels to TRIP and TWIP effects in NG/UFG steels.
The present study focuses on the significant effect of grain size on mechanical property and corrosion behavior of a 304 stainless steel. Three initial structures with average grain sizes of 360 nm ...(UFG), 910 nm (FG), and 3.6 μm (CG) are obtained via cryogenic rolling (80% thickness reduction) and subsequent reversion/recrystallization annealing. Results indicate that both mechanical property and corrosion resistance could be simultaneously optimized as grain size decreases from several micrometers down to a few hundred nanometers. The UFG steel exhibits a good combination of high strength (yield strength of 780 MPa, and tensile strength of 950 MPa) and good ductility (elongation-to-fracture of ∼38%) with considerable strain hardening ability. Meanwhile, it is found that grain refinement also enhances the corrosion resistance of the experimental steel in the 3.5 wt% NaCl solution. With the decrease in austenite grain size, the semiconductive type of passive film has not been changed, and bi-layer structured passive films are formed on all samples. The thicker passive film with higher stability and lower chemical activity are supposed to be responsible for the superior corrosion resistance of UFG steel.
•304 stainless steel with different average grain sizes was obtained via cryogenic rolling and reversion annealing.•Both mechanical property and corrosion resistance could be simultaneously optimized as grain refinement.•The thickness and stability of the passive film were improved by grain refinement.
We studied newly found high Nb-Ta alkaline rhyolites in the northern volcanic belt of the Great Xing'an Range, China. The LA-ICP-MS U-Pb weighted mean age is 114.07 ± 0.55 Ma, indicating that the ...rocks formed during the late Early Cretaceous and were the product of the late eruption of a Mesozoic volcano. The major element contents are characterized by high Si, rich K, low Fe, and poor Ca and Mg. In the total alkaline-silicon diagram, the sample points are in the alkaline rhyolite region. Meanwhile, rare earth elements show obvious Ce/Ce* positive anomalies and Eu/Eu* negative anomalies. In addition, trace elements are characterized by high Nb, Ta, and Yb, and low Sr. The two-stage Nd isotopic model age T2DM of the depleted mantle is between 799-813 Ma, indicating that the diagenetic material originated from the depleted mantle or partial melting of newly formed young crustal materials. The source rocks melted at a relative shallow depth (<30 km), under lower pressure (<0.5 Gpa) and high oxygen fugacity; moreover, the residues in the source region were Ca-rich mafic plagioclase + amphibole + orthopyroxene. In the Nb-Y-3Ga and Nb-Y-Ce diagrams, the sample points are in the A1 type region. It can be concluded that the mantle-derived basaltic magma underplated and supplied the heat sources for partial melting of the metamorphic crustal rocks in an intraplate extensional tectonic environment related to a rift, mantle plume, and hot spot.
The outliers of the statistical population are usually far from most samples in the observation space. Therefore, the total distance from a sample to all remaining samples in the population can be ...used to quantitatively represent the anomaly level of the sample. The greater the total distance between the sample and all the remaining samples, the more likely the sample is to be an outlier. Accordingly, the total distance of each sample in the population can be used to define a distance anomaly factor for each sample for outlier detection. The spatial distance between each pair of samples in the population can be measured by different distance measures, such as the Mahalanobis distance, Manhattan distance, Euclidean distance, and kernel Euclidean distance. According to different distances, different distance anomaly factors can be defined for each sample in outlier detection. These distance anomaly factors are potentially useful in geoscientific data procession. For demonstration purposes, the distance anomaly factors were used to detect multivariate geochemical anomalies associated with gold deposits from the stream sediment survey data in the Jinchanggouliang district, Inner Mongolia, China. Receiver operating characteristic curve and area under the curve were used to evaluate the performance of distance anomaly factors for geochemical anomaly detection. The results show that the distance anomaly factors perform better than continuous restricted Boltzmann machine and one-class support vector machine in the detection of multivariate geochemical anomalies associated with gold deposits. The Youden index was used to determine the optimal threshold to separate geochemical anomalies from geochemical background. The geochemical anomalies detected by the distance anomaly factors occupy 6.2–14.4% of the study area while contain 70–91% of the known gold deposits. The geochemical anomalies detected by the continuous restricted Boltzmann machine occupy respectively 3.1% of the study area while contain 52% of the known gold deposits. The geochemical anomalies detected by the one-class support vector machine occupy respectively 8.5% of the study area while contain 70% of the known gold deposits. Therefore, the distance anomaly factors are potentially useful techniques for geochemical anomaly detection.
•Propose distance anomaly factors (DAFs) for anomaly detection.•DAFs are used to detect geochemical anomalies associated with gold deposits.•Performance of DAFs, one-class SVM and CRBM are compared using ROC curves.•AUC values and correlation coefficients are used to select indicator elements.
Isolation forest and elliptic envelope are used to detect geochemical anomalies, and the bat algorithm was adopted to optimize the parameters of the two models. The two bat-optimized models and their ...default-parameter counterparts were used to detect multivariate geochemical anomalies from the stream sediment survey data of 1:50 000 scale collected from the Helong district, Jilin Province, China. Based on the data modeling results, the receiver operating characteristic (ROC) curve analysis was performed to evaluate the performance of the two bat-optimized models and their default-parameter counterparts. The results show that the bat algorithm can improve the performance of the two models by optimizing their parameters in geochemical anomaly detection. The optimal threshold determined by the Youden index was used to identify geochemical anomalies from the geochemical data points. Compared with the anomalies detected by the elliptic envelope models, the anomalies detected by the isolation forest models have higher spatial relationship with the mineral occurrences discovered in the study area. According to the results of this study and previous work, it can be inferred that the background population of the study area is complex, which is not suitable for the establishment of elliptic envelope model.
The conventional 4340 steel was used after quenching and tempering, strengthened by the classical pearlitic structure where cementite particles are dispersed through the ferrite matrix. In the ...present study, a heterostructure microstructure consisting of micro-sized residual ferrite zones and pearlitic zones was introduced by an optimized process of intercritical quenching and tempering, resulting in a steel with higher strength and better toughness. The pearlite steel has a tensile strength of 1233 MPa, yield strength of 1156 MPa, and toughness of 121.5 MJ/m3. Compared with the pearlite steel, the tensile strength and yield strength of the heterostructure steel have been improved by 67 MPa and 74 MPa, respectively, while the toughness has been increased by 52.5 MJ/m3. In this heterostructure, the micro-sized ferrite bulks serve as the soft zones surrounded by the hard zones of the pearlite structure to achieve a remarkable work-hardening capacity. Statistical analysis shows that the heterostructure has the best hetero-deformation-induced (HDI) hardening capability when the residual ferrite bulk contributes ~31% by volume fraction, and the quenching temperature is around 780 °C. This study opens new ways of thinking about the strengthening and toughening mechanism of heat treatment of medium carbon steels.
There continues to be debate regarding the timing of the collision between the Indian and Eurasian Plates and the uplift of the Tibetan Plateau. This study presents zircon U-Pb geochronology, ...whole-rock geochemistry, and Lu-Hf isotopic data for the Saiduopugangri granite of the Qiangtang Terrane, located within the core of the Tibetan Plateau. These data provide the basis for the geodynamic setting, petrogenesis, and characteristics of its magma source. Zircons from the Saiduopugangri granite yield a weighted-mean 206Pb/238U age of 62.72 ± 0.06 Ma, indicating that these rocks formed during the early Palaeocene. The rocks are members of the highly calc-alkaline to shoshonitic series, with weak peraluminous characteristics. Trace elements are characterized by high Sr (483-616 ppm), and low Y (6-10 ppm) and Yb (1 ppm) content, typical of a high Sr and low Yb granite. The εHf(t) of zircon ranges from -2.14 to 2.35, with two-stage Hf model ages (TDM2) ranging from 1182 to 895 Ma. These data suggest that the Saiduopugangri granite magma was derived from the melting of lower-crustal clastic meta-sedimentary rocks and mantle-derived basalts. The high Sr and low Yb granite characteristics and experimental results indicate that melting occurred at >1.2 GPa and >750 °C, consistent with a crustal thickness greater than 50 km. Magmatism occurred from the Late Cretaceous to the early Paleogene and is broadly synchronous with the collision timing between the Indian and Eurasian Plates. The Saiduopugangri granite provides evidence of crustal thickening of the Tibetan Plateau and its age and petrogenesis constrain the timing of the initial uplift.
Distance anomaly factors (DAFs) were defined for each cell of the unit cell population in a study area to represent mineral potential of the cell. A DAF of a cell is a formula for the total distance ...from the cell to all other cells in the study area. The distance between two cells can be expressed as the Manhattan distance, Canberra distance, Euclidean distance, and kernel Euclidean distance. The kernels in the kernel Euclidean distance can be radial basis function (RBF) kernel, chi-squared kernel, sigmoid kernel, Laplacian kernel, and polynomial kernel. Accordingly, eight DAFs were defined to map gold potential of the Jinchanggouliang area, Inner Mongolia, China. The receiver operating characteristic (ROC) curve analysis was used to evaluate the effectiveness of the eight DAFs. The results show that these DAFs are comparable to one-class support vector machine (OCSVM) in gold potential mapping. The optimal threshold for distinguishing gold potential cells from all the cells was determined by maximizing the Youden index. The gold potential targets predicted by the eight DAFs occupy 7.4% – 16.5% of the study area, while containing 78% - 91% of the discovered gold deposits. The gold potential targets predicted by the default parameter OCSVM and by the bat-optimized OCSVM occupy 9.4% and 16.4% of the study area, respectively, while containing 78% and 87% of the discovered gold deposits. Therefore, the eight DAFs are feasible approaches for gold potential mapping. Their effectiveness needs to be further tested in mineral potential mapping in other areas.
Impact fracture behavior at low temperatures was investigated in medium manganese steel with bcc-fcc duplex microstructures. The impact energy was above 150 J (−80~20 °C) and the fractography showed ...dimples for inter-critical annealing at 630 °C (QHA) because of the high retained austenite stability and low martensite dislocation density. The impact energy was from 180 J (20 °C) to 60 J (−80 °C) and the fractography was intergranular for inter-critical annealing at 610 °C (QLA) because of the low stability of RA and carbides precipitated at the prior austenite grain boundaries. The impact energy was below 60 J (−80~20 °C) and the fractography showed cleavage for direct quenching (DQ) because of the high dislocation density of martensite.
This paper presents zircon U-Pb-Hf isotopic compositions and whole-rock geochemical data for monzogranites and mafic-ultramafic complexes of the Maxingdawannan area in the western end of the east ...Kunlun orogenic belt, western China. The data are used to determine the ages, petrogenesis, magma sources, and geodynamic setting of the studied rocks. U-Pb zircon dating indicates that monzogranites and gabbros of the complexes were emplaced at 399 and 397 Ma, respectively. The monzogranites are shoshonitic, with high SiO
2
, Al
2
O
3
and total-alkali contents, and low TFeO, MgO, TiO
2
and P
2
O
5
contents. The mafic-ultramafic complexes are characterized by low SiO
2
contents. The monzogranites display enrichment in light rare-earth elements (LREE) and large-ion lithophile elements (LILE), depletion in heavy REEs (HREE) and high-field-strength elements (HFSE), and negative Eu anomalies (Eu/Eu*=0.36–0.48). The mafic-ultramafic complexes are also enriched in LREEs and LILEs, and depleted in HREEs and HFSEs, with weak Eu anomalies (Eu/Eu*=0.84–1.16). Zircon
ε
Hf
(
t
) values for the monzogranites and mafic-ultramafic complexes range from −6.68 to 1.11 and −1.81 to 6.29, with zircon model ages of 1 812–1 319 Ma (
T
DM2
) and 1 087–769 Ma (
T
DM1
), respectively. Hf isotopic data indicate that primary magmas of the monzogranites are originated from partial melting of ancient lower crust during the Paleo-Mesoproterozoic, with a juvenile-crust component. Primitive magmas of the mafic-ultramafic complexes are likely originated from a depleted-mantle source modified by slab-derived fluids and contaminated by crustal components. Geochemical data and the geological setting indicate that Devonian intrusions in the Maxingdawannan area are related to northward subduction of the Proto-Tethys oceanic lithosphere.
