V-N微合金化Q420B大规格角钢连铸坯高温热塑性的研究

Study on High-temperature Thermal Plasticity of V-N Microalloying Q420B Large Width Angle Steel Continuous Cast Slab

通过Gleeble-3500热模拟试验机研究了不同应变速率下V-N微合金化Q420B钢连铸坯的高温热塑性,利用扫描电镜观察高塑性区和第Ⅲ脆性温度区拉伸试样的断口形貌及断口处组织形貌,分析了试验钢在高温下的强度和塑性随温度变化的关系,动态再结晶、相变和析出物对高温热塑性的影响。结果表明在应变速率为ε=5×10^-3/s时,存在第Ⅲ脆性区（700～900℃）,在1000℃时断面收缩率（RA）达到最大值92.16%;当应变速率为ε=5×10^-2/s时,存在第Ⅲ脆性区（600～862℃）,在1100℃时RA达到最大值90.39%;当应变速率为ε=5×10^-1/s时,不存在塑性凹槽;3个应变速率下均没有出现第Ⅱ脆性区;在第Ⅲ脆性区,随着应变速率的增大,断面收缩率提高;在1000～1200℃出现高塑性的主要原因是发生了动态再结晶;第Ⅲ脆性区塑性低主要是由于晶界处有析出物和夹杂物,同时也是由于沿奥氏体晶界析出的铁素体抗拉强度低。

The high-temperature thermal plasticity of V-N microalloying Q420B steel continuous cast slab at different strain rate was investigated on Gleeble-3500 thermal simulator. The morphology characteristics and microstructure of fracture surface of tensile specimens at high plasticity zone and brittle temperature zone Ⅲ was observed. The relationship between strength and ductility of test steel at high temperature changes with temperature, the influences of dynamic recrystallization, phase change and precipitate on high-temperature thermal plasticity were analyzed. The results show that there is brittle zone Ⅲ（700-900℃） at the ε=5×10^-3/s strain rate, the area reduction（RA） reaches 92.16% at 1000 ℃; at the ε=5×10^-2/s strain rate, there is brittle zone Ⅲ（600-862℃）, with a maximum RA of 90.39% at 1100℃;there is no plastic groove at a higher strain rate of the ε=5×10^-1/s; the brittle zone Ⅱ does not exist under three strain rate; the area reduction improved with the increase of strain rate in brittle zone Ⅲ;the main reason for high plasticity between 1000-1200 ℃ is the appearance of dynamic recrystallization;the existence of precipitates and inclusions at grain boundaries is the main reason for low ductility in brittle zone Ⅲ, at the same time, the ferrite precipitates out along austenite grain boundaries is also the reason for low ultimate tensile strength.