表面温度波动对微合金钢连铸板坯热塑性的影响

Influence of surface temperature fluctuations on the hot ductility of microalloyed steel slabs during continuous casting

由于铸坯表面与二冷辊列夹持辊发生的间断式接触传热,其表面温度存在一定程度的上下波动.基于J55微合金钢,考虑温度波动的影响,研究了钢在不同热状态下的热塑性.结果表明,高于850℃时温度波动制度下测得的断面收缩率低于常规恒温制度下的测量值,而等于或低于850℃时情况相反.分析了两种不同温度制度下测试结果的差异,认为对于微合金钢,存在着略高于所测钢种Ae3温度的某一分界温度,高于该温度时恒温制度下测得的塑性值相比波动制度下塑性值偏高,而低于该温度时则偏低.这一认识有助于更加合理地制定实际连铸过程的矫直温度.

Temperature fluctuations exist on the slab surface due to unstable heat flux during repeated contact and departure between the hot slab surface and the relatively cold supporting rollers in the secondary cooling zone. Considering thermal oscillations,hot ductility test under different thermal conditions was carried out on J55 microalloyed steel. The results show that at a temperature higher than 850 ℃,the hot ductility under the oscillating condition is lower than that under the isothermal condition,but it is on the contrary when the temperature equals or falls below 850 ℃. By analyzing results from experiment and from literature comprehensively,for the microalloyed steel,it is inferred that there exists a critical temperature a bit higher than the Ae3 temperature. Above this critical temperature the hot ductility under the isothermal condition is higher than that measured by the more accurate oscillating way,while below it the result is opposite. This conclusion is meaningful to determine the straightening temperature for microalloyed steel production during continuous casting.