The effects of different sintering atmospheres (nitrogen and argon) on the densification, microstructure, and mechanical properties of HK30 stainless steel were studied. Compared with those of the samples sintered in Ar, sintered samples in N 2 had a lower density and higher N content. Some of the N atoms dissolved into the austenite matrix, and others were combined with metal atoms to be precipitated along the grain boundaries. Samples sintered in N 2 had a higher hardness than those in Ar. The hardness decreased with the distance from the edge to the center. The highest hardness was 360 HV 1.0 at the edge, the lowest one was 220 HV 1.0 at the center. The samples sintered in N 2 had a higher tensile strength than those sintered in Ar at testing temperatures from room temperature to 1000 °C.
The effects of forging and the cooling parameters on the microstructure of non-quenched and tempered 1538MV steel were studied using thermal simulation tests. With an increase of the deformation and a decrease of the deformation temperature, the austenite grains were refined, and the volume fraction of ferrite improved. With the increasing of the cooling rate, the austenite grain growth is significantly restrained, and the pearlite lamellar spacing is refined simultaneously. Therefore, the cooling process should be strictly controlled after forging. The cooling rate before the ferrite phase transition should be fast, while that during the phase transition should be slow. This is beneficial to the refinement of the microstructure and the full formation of ferrite, and the abnormal microstructures, such as bainite and martensite, are avoided. The numerical simulations show that the deformation of the finished forging process is very important for the filling of the die cavity and non-overloading of the equipment. The deformation of the finished forging should be reasonable, and the deformation temperature should not be too low. The above research results provide an important basis for the optimization of the forging and the cooling process for non-quenched and tempered 1538MV steel. Keywords: non-quenched and tempered steel, controlled forging, controlled cooling, microstructure, crankshafts Avtorji~lanka so s preizkusi na termi~nem simulatorju raziskovali vpliv tehnolo{kih parametrov kovanja in ohlajanja na mikrostrukturo nekaljenega in popu{~enega jekla 1538MV. Ugotovili so, da z nara{~ajo~o stopnjo deformacije in zni`evanjem temperature deformacije pride do udrobljenja austenitnih zrn in izbolj{anja volumskega dele`a ferita. Z nara{~ajo~o hitrostjo ohlajanja pa je znatno zavrta rast austenitnih zrn in isto~asno zmanj{ana razdalja med perlitnimi lamelami. Zato moramo proces ohlajevanja po kovanju absolutno kontrolirati. Ohlajevalna hitrost pred prehodom v feritno fazo mora biti velika, medtem ko mora biti fazni prehod po~asen. To je koristno za udrobljenje mikrostrukture in popolno tvorbo ferita in s tem se izognemo tvorbi v tem primeru ne`elenih mikrostruktur, kot sta bainit in martenzit. Numeri~na simulacija je pokazala, da je deformacija na koncu procesa kovanja zelo pomembna za zapolnjenje votline kova{kega orodja z materialom in nepretirano obremenitev opreme (kova{kega stroja in orodja). Deformacija na koncu kovanja mora biti ustrezna in temperatura deformacije ne sme biti prenizka. Predstavljeni rezultati raziskave predstavljajo pomembno osnovo za optimizacijo kovanja in procesa ohlajanja za nekaljeno in popu{~eno jeklo 1538MV. Klju~ne besede: nekaljeno in popu{~eno jeklo, kontrolirano kovanje, kontrolirano ohlajanje, mikrostruktura, ro~i~ne gredi
In order to investigate the development efficiency of China's logistics industry under the background of high-quality economy, the article constructs an evaluation index system based on the development of the logistics industry in 31 provinces of China from 2010 to 2019, and adopts the DEA-Malmquist index model to conduct static and dynamic analysis of the development efficiency of China's logistics industry. The study found that the regional development imbalance of China's logistics industry is more prominent. Finally, the article puts forward policy recommendations for the high-quality development of China's logistics industry in terms of the five development concepts and improving total factor productivity.
The temperature dependence of thermal conductivity (K),resistivity (ρ) and low field ac susceptibility (χ) of perovskite nick elates Nd_2-xSr_xNiO_4(x =0.33,1.35) have been measured at temperatures from 77 to 300 K. The thermal conductivity an omalies associated with charge_order (CO) and spin_order (SO) are observed simultaneously in Nd_1.67Sr0.33NiO_4 for the firs t time so far as we know. The thermal conductivity is enhanced belowT_CO , but is suppressed near T_SO. There is also response to CO and S O in the χ-Τ curve. Only CO is observed in the ρ-Τ curve. In contrast, th ere are no anomalies in K-Τ, ρ-Τ andχ-Τ of Nd_1.67Sr0.33NiO_4. The anomalous phonon thermal conductivi ty in Nd_1.67Sr0.33NiO_4 indicates that there are strong charg e_phonon interaction and the spin_phonon interaction in this compound.
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