MI Guofa
,
NAN Hongyan
,
LIU Yanlei
,
ZHANG Bin
,
ZHANG Hong
,
SONG Guoxiang
钢铁研究学报(英文版)
Speed increase and heavy-haul of the railway freight car are the effective measures to raise the transport ability of railway, and they have been the new trend for railway freight car development. The increase of speed and axle load will lead to the increase of wheel-rail contact stress, which will make a great change of stress distribution in the whole wheel rim. Goodier equation was employed to analyze the stress state around inclusion and cavity. In the operation of wheel-rail contact stress, stress concentration occurred in the pole of Al2O3 spherical inclusion, while it appeared on the equator of cavity. The critical inclusion sizes of 25t axle load freight car wheel at different velocities, a certain distance away from the tread, were calculated by Murakami equation. By contrast the inclusion state in cast-steel wheel and rolled-steel wheel, the inclusion character in cast-steel wheel determined that it has much more excellent crack resistance than that of rolled-steel wheel. In the meantime, in order to reduce the probability of rim crack, some suggestions were put forward.
关键词:
heavy-haul;contact stress;critical inclusion size;rim crack
HU Zheng-fei
,
WANG Qi-jiang
,
ZHANG Bin
钢铁研究学报(英文版)
Standardarized creep and rupture strength tests were conducted for commercial T91 martensitic heat-resistant steel at 650 ℃ and corresponding microstructure was characterized by BSED, TEM and EDS. The martensitic microstructure degenerated seriously during creep exposure, including martensitic substructure recovering, carbides coarsening, dissolving and precipitating. EDS analysis shows that the M23C6 carbides in different morphologies have dissimilar compositions. The rod/sheet like M23C6 particles within the matrix contain more additions, which might precipitate in situ while fine MX particles were re-solving. The high content of silicon in these rod/sheet like M23C6 carbides is probably related to self diffusion coefficient increasing for the exposed condition at 650 ℃ close to Curie temperature Tc. For those reasons, martensite substructure becomes unstable, and microstructure evolution is accelerated and leads to creep strength deteriorating severely.
关键词:
T91 steel
,
creep strength
,
microstructure
,
carbide
,
coarsening
,
self-diffusion
DONG Danyang
,
LIU Changsheng
,
ZHANG Bin
钢铁研究学报(英文版)
Based on the Miedema′s formation heat model for binary alloys and the Toop′s asymmetric model for ternary alloys, the formation heat, excess entropy, and activity coefficients of silicon ranging from 1 900 K to 4 100 K in the FeSiC melt formed during the laser cladding high silicon coatings process were calculated. The results indicated that all values of lnγ0Si, εCSi, ρSiSi and ρCSi are negative in the temperature range and these values increase as the temperature increases. And all values of εSiSi and ρSiCSi are positive and these values decrease with increasing temperature. The isoactivity lines of silicon are distributed axisymmetrically to the incident laser beam in the melt pool vertical to the laser scanning direction. And the isoactivity lines of silicon in the front of the melt pool along the laser scanning direction are more intensive than those in the back of the melt pool. The activity of silicon on the bottom of the melt pool is lower than that in the effecting center of laser beam on the top surface of the melt pool and it may be the important reason for the formation of the silicides and excellent metallurgical bonding between the laser cladding coating and the substrate.
关键词:
laser cladding;silicon steel;high silicon content coating;thermodynamic calculation;Miedema′s formation heat model
