700-1000℃间含Nb钢铸坯的延塑性降低与Nb(C,N)析出

DUCTILITY LOSS AND Nb(C,N) PRECIPITATION IN Nb-CONTAINING STEEL SLAB IN THE TEMPERATURE RANGE FROM 700 TO 1000℃

在1×10-3／s应变速率下对含Nb钢连铸坯试样的高温延塑性进行了测定.在温度降至1100℃以下的变形试样中Nb（C，N）开始由γ晶中析出，1000-950℃之间析出的Nb（C，N）较粗大并在钢中零散分布;温度降至900℃左右时，大量微细的Nb（C，N）在γ晶界和晶粒内析出，尺寸平均为5-8nm，间距在30nm左右，造成了γ相区低温域合Nb钢延塑性的急剧减少;温度降至800℃时，先共折铁素体开始在γ晶界析出，钢的延塑性继续降低.由于含Nb钢试样共折转变的推迟，与不含Nb钢相比，其第Ⅲ脆性温度域向低温延伸.

Hot ductility of the continuously casted Nb-containing steel slab was measured under the strain rate of 1×10-3 /s. It was found that in the fractured specimens,Nb(C,N) precipitation took place when temperature decreased to below 1100℃. The Nb(C,N) particles precipitated in the temperature range from 1000 to 950℃ were coarse and rondomly distributed in the specimens. When the temperature was lowered to 900℃, the precipitation content of Nb(C,N) reached maximum and fine Nb(C,N) precipitates were found both along γ grain boundaries and inside the grains with mean particle size of 5-8 nm and interparticle spacing of about 30 nm. As the result of Nb(C,N) precipitation, the hot ductility of the steel was significantly reduced in the lower temperature region of γ single phase. As the temperature decreased to below 800℃, film-like proeutectoid ferrites formed aIong the γ grain boundaries that further reduced the steel ductility. The eutectoid transformation of the Nb-containing steel was delayed compared to the steel without Nb. This leads to the extension of the low ductility of the steel to the lower temperature.