ZHANG Chi
,
et al
钢铁研究学报(英文版)
Abstract Effects of prior austenite deformation and non-metallic inclusions on the ferrite nucleation and grain refinement of two kinds of low carbon steels have been studied. The ferrites nucleation on MnS and V(C,N) is observed. The combination of thermal-mechanical processes with adequate amounts of non-metallic inclusions formed in low carbon steels could effectively refine the grain size and the microstructure. Ferrite nucleated on the single MnS or V(C,N) inclusions and complex MnS+V(C,N) inclusion. The proper addition of elements S and V could effectively promote the formation of ferrite and further refinement of ferrite grains.
关键词:
austenite deformation;Non-metallic inclusions;Ferrite nucleation;low carbon steel;
XIA Zhi-xin
,
ZHANG Chi
,
HUANG Qun-ying
,
LIU Shao-jun
,
LI Zhao-dong
,
YANG Zhi-gang
钢铁研究学报(英文版)
The effect of TaC on grains and packets coarsening in the reduced activation ferritic/martensitic (RAFM) steels was investigated. It was found that the combined effect of the austenitizing temperature and heating rate resulted in the heterogeneous austenite grain growth. When the austenitizing temperature was raised above 1423 K, the TaC particles disappeared, and the homogenous grains abruptly increased. The thermodynamic model for dissolution of TaC particles during austenitizing was applied to interpret the results.
关键词:
reduced activation steel
,
TaC precipitation
,
diffusion
,
thermodynamic model
WANG Xiao-nan
,
DI Hong-shuang
,
ZHANG Chi
,
DU Lin-xiu
,
DONG Xue-xin
钢铁研究学报(英文版)
CO2-shielded welding experiments of newly developed, 780 MPa super-high strength heavy-duty truck crossbeam steel were conducted, and the microstructure, microhardness, mechanical properties, and impact toughness of the welded joint were studied. The evolution of the microstructure of the welded joint occurred as follows: welding seam (acicular ferrite+proeutectoid ferrite)→fusion zone (granular bainite-long strip M/A island)→coarse grain zone (granular bainite-long strip or short bar M/A island)→fine grain zone (ferrite+pearlite+blocky M/A island)→mixed grained zone (ferrite+granular bainite+blocky M/A island)→base metal (proeutectoid ferrite+granular bainite-blocky or granular M/A island). Increasing the density of the grain boundaries can effectively improve the impact toughness, and the blocky M/A island hindered crack propagation more effectively than the long strip M/A island. The new hot-rolled 780 MPa super-high strength steel had excellent weldability. The welding technology was applied under the following conditions: welding voltage was 20 to 21 V, welding current was 200 to 210 A, and the gas flow rate was 25 L/min.
关键词:
super-high strength steel
,
crossbeam steel
,
weldability
,
M/A island
,
impact toughness
TAO Peng
,
ZHANG Chi
,
YANG Zhi-gang
,
et al
钢铁研究学报(英文版)
Transformation and coarsening of carbides in 2.25Cr-1Mo steel weld metal during tempering at 700 oC for different time intervals ranging from 1 to 150 h has been examined by transmission electron microscopy and scanning electron microscopy. M3C carbides were observed in the as-welded specimens and when tempered the precipitates were mainly composed of M3C, M7C3 and M23C6 carbides. A sequence for corresponding carbide transformation during tempering with initial precipitation of M3C and followed by M7C3 and M23C6 has been proposed. The precipitation of M7C3 with higher Cr content is the main factor contributing to the decrease of coarsening rate of precipitates after prolonged tempering. The decrease of hardness in the tempered specimens agreed well with the prediction of the weakening of precipitation strengthening due to the coarsening of carbides.
关键词:
weld metal;carbide;tempering;coarsening
