Development and Microstructural Improvement of Spin Cast High-Speed Steel Rolls

A detailed microstructural analysis was conducted on a series of radial shell samples extracted from commercially produced centrifugally spin casted high-speed steel (HSS) work rolls for finishing hot strip mills (HSM). The systematic microstructural analysis was coupled with a numerical and experimental investigation to improve the life of HSS rolls. An integrated computational-experimental approach was developed to optimize the response of the HSS roll material that permitted the enhancement of the microstructure and properties of the HSS roll shell layer. Local continuous microstructural transformations through the thickness of the shell: carbide formation, precipitation, dissolution sequence and phase changes, were studied in great details. The analyses were conducted with the aid of advanced metallographic and experimental methods, finite-element (FE) analysis, and using commercial software systems to conduct thermodynamic-kinetics predictions. In order to analyze a response of the HSS roll to the hardening heat treatment (HT) and to control stress-strain evolution, a 3-D FE model was developed of the composite structure of the roll. The multilayered model considers nonlinear material properties of each individual layer as a function of temperature, based on measured chemical composition gradients through the HSS shell. Transient coupled thermal-stress analysis was performed, using actual measured surface temperatures as boundary conditions (BC) for the FE model. The allowable thermal stress-strain levels were established and compared with a) thermodynamically predicted high temperature mechanical properties and b) room temperature test results of the shear strengths for the shell, bonding and core. In addition, sub-structuring and image-based processing techniques were implemented to aid in the development of a meso-scale FE model to simulate the local response of a given microstructural constituents and matrix under particular thermal conditions. The fundamental interpretation of multilayered structure and multi-scale approach help to understand the kinetics phenomena associated with continuous local microstructural transformations due to nonlinear heat transfer. The results from the microstructural observations were in good agreement with the numerical predictions. The major impact of this work clearly indicated that a refined as-cast structure prior to the heat treatment promoted an increased precipitation of carbides during final hardening, which greatly improved strength and performance. A non-conventional HT was defined and implemented in order to provide an additional degree of microstructural pre-conditioning, which homogenized the matrix throughout the HSS shell. The new HT defined the austenitization temperatures and times to modify the morphology of brittle interdendritic eutectic carbide networks and, hence, facilitating the kinetics of dissolution of these carbides. This behavior caused an increase in the solute content of the matrix. As a result, the matrix hardness and strength were increased during subsequent hardening HT in comparison to the conventional HT routes used for as-cast HSS rolls. Reports about rolls with the new material that have been placed in service indicate that the rolls last 50-70% longer

Special Issue on Critical Metal Occurrence, Enrichment, and Application

Critical metals are a new resource concept introduced in recent years, referring to a category of metal elements that have essential and irreplaceable uses for emerging industries such as new energy, new materials, information technology, and defense industries [...

New zircon U-Pb and Hf isotopic constraints on the crustal evolution of the Skjoldungen region, South-East Greenland

We report new zircon U-Pb and Hf isotopic data from the Skjoldungen region between c. 62°30´ and 63°40´N in South-East Greenland. The work was carried out under the South-East Greenland Mineral Endowment Task (SEGMENT); a joint project between the Geological Survey of Denmark and Greenland (GEUS) and the Ministry of Mineral Resources (MMR) in Greenland to assess the mineral endowment and update the geological knowledge of the region using modern petrological, geochemical and geochronological tools. This paper presents new zircon U-Pb and Hf isotopic data from a range of different Archaean rocks in the Skjoldungen region, which greatly improve the understanding of the history of crustal growth

Mineralogy and titanite geochronology of the Caojiaba W deposit, Xiangzhong metallogenic province, southern China: implications for a distal reduced skarn W formation

The Caojiaba tungsten deposit (19.03 Mt@ 0.37 wt% WO3) is hosted by skarn along the contact between clastic and carbonate rocks in the Xiangzhong Metallogenic Province of southern China. The deposit is characterized by an early prograde skarn containing low andraditic garnet (Ad0.7–21.9) and hedenbergitic pyroxene (Hd52.9–77.3) overprinted by a retrograde biotite–chlorite assemblage and then by quartz–scheelite veins, similar to well-studied reduced tungsten skarns worldwide. Scheelite has low MoO3 (0.01–0.16 wt%), and ore commonly contains up to 1.5 ppm Au and up to 0.33 wt% Sb. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb analyses of hydrothermal titanite coexisting with scheelite in three skarn ore samples provide ages between 206 ± 5 Ma and 196 ± 3 Ma (2σ). Our new ages demonstrate that the tungsten mineralization took place at Caojiaba between 206 and 196 Ma, overlapping the 228–201 Ma emplacement age of granitic rocks in the Xiangzhong Metallogenic Province. Mineralogical and geochronological evidence collectively indicates that Caojiaba is a distal reduced W skarn deposit. The 226–196 Ma granite-related W mineralization recognized throughout the province has a possible link with the widespread Sb–Au mineralization in the region.This work was supported by the National Basic Research Program of China (2014CB440902) and the National Science Foundation of China (41573042, 41430314 and 41372090)

Mineralisation associated with the fractionated Cretaceous Baoshan Monzogranite: Tectonic implications for South China

Jurassic and Late Cretaceous granites are spatially and temporally associated with mineralisation in the Paleozoic Dayaoshan Terrane in South China (also known as South China Block). The porphyritic Baoshan Monzogranite of Late Cretaceous is an example that is petrographically studied in this contribution. Sensitive High-Resolution Ion-Microprobe (SHRIMP) zircon U-Pb ages, in-situ zircon O-Hf isotopic analyses, and whole-rock geochemistry are here used to better constrain the genesis of the monzogranite, which is porphyritic, and located in the Baoshan Cu mining area. SHRIMP zircon dating yields a weighted mean 206Pb/238U age of 89 ± 1 Ma, interpreted to be the crystallisation age of the porphyritic monzogranite. Its geochemical data indicates it is derived from partial melting of the lower to crust, followed by fractionation, and emplacement in secondary faults related to the major Bobai-Cenxi Fault. The monzogranite has a Paleo- to Mesoproterozoic source in the crust, which was metasomatised during Neoproterozoic subduction. The rotation of Izanagi Plate’s subduction from NW to NE resulted into the reactivation of NW and NE-trending thrust faults as transpressional or extensional ones. It was during this period that Late Cretaceous intrusions such as the Baoshan porphyritic monzogranite were emplaced in the terrane near the NW-trending faults and other intrusions at the edges of basins such as Yangchun, Luoding and Bobai basins near NE-trending faults.This research was financially supported by the National Natural Science Foundation of China (Projects 41572072) and the National Key Basic Research Program of China (Project 2014CB440902)

Cretaceous–Cenozoic tectonic history of the Jiaojia Fault and gold mineralization in the Jiaodong Peninsula, China: constraints from zircon U–Pb, illite K–Ar, and apatite fission track thermochronometry

The Jiaojia Fault (JJF) in the Jiaodong area of eastern China is an important NNE-trending structure that is subsidiary to the regional Tancheng–Lujiang (Tan-Lu) Fault Zone, and hosts >1200 t of gold reserves contained in disseminated and stockwork ore, dominantly in the footwall of the fault. We present new zircon U–Pb, apatite fission track, and illite K–Ar data along the JJF and have delineated its tectonic history focusing on its formation and reactivation. Zircon U–Pb dating shows that the Shangzhuang granite is a composite body with ages between 132 ± 1 and 127 ± 1 Ma. Illite K–Ar ages for the fault's gouge range from 83 ± 2 to 68 ± 2 Ma, and the measured apatite fission track ages for ores are between 55 and 21 Ma. Previous zircon U–Pb geochronology and structural studies suggest that the JJF was originally activated in the Jurassic during 160–150 Ma as a sinistral fault. The JJF was a normal fault in the Early Cretaceous due to NW–SE orientated tension and NE–SW compression, which lasted from 135 to 120 Ma. This was followed by sinistral strike–slip faulting due to NW–SE compression and NE–SW tension during 120–110 Ma, and it changed to normal displacement at ca. 110 Ma. Our apatite fission track data analysis and thermal modeling of representative samples suggest that there was a subsequent dextral reactivation of the fault at ca. 55 Ma. Previous age data of ca. 130–110 Ma for gold mineralization along the JJF coincides with the Early Cretaceous magmatism and is coeval with the transition from normal faulting to sinistral strike–slip faulting of the JJF in Early Cretaceous, which is interpreted to be due to changing direction of the subducting Pacific Plate