WANG Qingfeng
,
CHAI Feng
,
CAI Jianwei
,
PAN Tao
,
SU Hang
钢铁研究学报(英文版)
The kinetics of εCu particle dissolution in the matrix of heat affected zone (HAZ) during welding of a coppercontaining steel was determined by assembling the welding temperaturetime program into a modified Whelan′s solution. The particle dissolution dependence on the degree of “superheating” above the equilibrium transformation is demonstrated from the model. In terms of volume fraction of particle dissolution, the HAZ may be classified into three zones, including the undissolving zone, the partially dissolving zone, and the completely dissolving zone, respectively. The numerical solution was in good agreement with the experimental examination finding. The results of model can be used to quantitatively map the εCu dissolution zone dependence on the peak temperature of welding thermal cycles and understand the evolution of this transformation during welding.
关键词:
εCu;particle dissolution;kinetics;welding;steel
PAN Tao
,
YANG Cai-fu
钢铁研究学报(英文版)
Chemistry and process optimization of N80 seamless tube was studied by thermo-mechanical simulation tester Gleeble 1500D. Several heats of V-microalloyed steel with different N contents were firstly made at lab in order to simulate N80 seamless tube steel. The results showed that N addition increased strength under condition that toughness was kept at a high level compared with low-N steel. In this study N content with 120-200 ppm enhanced combination performance of strength and toughness whether in-line normalizing process was adopted or not. In-line normalizing process was helpful to improve the toughness though it lowered strength by some degree. However, direct final rolling after tandem rolling (without in-line normalizing) helped increase strength while the toughness remained somehow poor. The above phenomena concerning N80 seamless tube was closely associated with dissolution and precipitation behavior of V(CN). V(CN) precipitation was optimized when N content was increased. When in-line normalizing process was adopted, V(CN) precipitation in austenite increased due to low temperature history during intermediate (in-line) normalizing process. V(CN) particles existing in austenite contributed to grain refinement for VN induced intergranular ferrite, while they weakened precipitation strengthening effect since V precipitating in ferrite wais reduced.
关键词:
seamless tube;in-line normalizing;V-N microalloying;reheating;mechanical properties;Gleeble simulation
SU Hang
,
PAN Tao
,
LI Li
,
YANG Caifu
,
CUI Yinhui
,
JI Huaizhong
钢铁研究学报(英文版)
By combining thermomechanical coupling finite element analysis with the characteristics of phase transformation [continuous cooling transformation (CCT) curve], the thermal fatigue behavior of train wheel steel under high speed and heavy load conditions was analyzed. The influence of different materials on the formation of the phase transformation zone of the wheel tread was discussed. The result showed that the peak temperature of wheel/track friction zone could be higher than the austenitizing temperature for braking. The depth of the austenitized region could reach a point of 09 mm beneath the wheel tread surface. The supercooled austenite is transformed to a hard and brittle martensite layer during the following rapid cooling process, which may lead to cracking and then spalling on the wheel tread surface. The decrease in carbon contents of the train wheel steel helps inhibit the formation of martensite by increasing the austenitizing temperature of the train wheel steel. When the carbon contents decrease from 07% to 04%, the Ac3 of the wheel steel is increased by 45 ℃, and the thickness of the martensite layer is decreased by 30%, which is helpful in reducing the thermal cycling fatigue of the train wheel tread such as spalling.
关键词:
train wheel steel;thermal cycling fatigue;friction;martensite transformation;thermomechanical coupling
ZHAO Xiqing
,
PAN Tao
,
WANG Qingfeng
,
SU Hang
,
YANG Caifu
,
YANG Qingxiang
钢铁研究学报(英文版)
Mechanical properties of quenching, intercritical quenching and tempering (QLT) treated steel containing Ni of 9% were evaluated from specimens subject to various tempering temperatures. The detailed microstructures of steel containing Ni of 9% at different tempering temperatures were observed by optical microscope (OM) and transmission electron microscope (TEM). The volume fraction of austenite was estimated by XRD. The results show that high strength and cryogenic toughness of steel containing Ni of 9% are obtained when the tempering temperature are between 540 and 580 ℃. The microstructure keeps the dual phase lamellar structure after the intercritical quenching and there is cementite created in the Nirich constituents when tempering temperature is 540 ℃. When tempering temperatures are between 560 and 580 ℃, the reversed austenites (γ′) grow up and the dual phase lamellar structure is not clear. The γ′ becomes instable at 600 ℃. When tempered at temperature ranging from 500 to 520 ℃, the increase of dislocation density in the lamellar matrix makes both tensile strength and yield strength decrease. When tempered at 540 ℃ and higher temperature, the yield strength decreases continuously because the C and alloying elements in the matrix are absorbed by the cementite and the γ′, so the yield ratio is decreased by the γ′. There are two toughness mechanisms at different tempering temperatures. One is that the precipitation of cementite absorbs the carbon in the steel which plays a major role in improving cryogenic toughness at lower temperature. Another is that the γ′ and the purified matrix become major role at higher tempering temperature. When the tempering temperature is 600 ℃, the stability of γ′ is decreased quickly, even the transformation takes place at room temperature, which results in a sharp decrease of CharpyV impact energy at 77 K. The tempering temperature range is enlarged by the special distribution of cementite and the lamellar structure.
关键词:
steel containing Ni of 9%
,
tempering temperature
,
cementite
,
reversed austenite
,
cryogenic toughness
