形变和冷却对B1500HS硼钢马氏体相变的影响

Effect of Deformation and Cooling on the Phase Transformation of Martensite for B1500HS Boron Steel

利用Gleeble-1500D热模拟试验机,以恒定的应变速率将在900℃奥氏体化的B1500HS硼钢试样分别压缩10%、20%、30%、40%,然后分别以50℃/s、40℃/s、25℃/s的速度对试样进行冷却。研究形变量及冷却速度对B1500HS硼钢的马氏体相变温度、微观组织、显微硬度和残余奥氏体等方面的影响规律。结果表明:相同冷却速度下,马氏体相变开始温度和相变终止温度均随着形变量的增加逐渐升高。随着形变量的增加,马氏体组织越来越细小,而且薄片状马氏体越来越少,板条状马氏体越来越多。形变量和冷却速度的增大,均使B1500HS试样中的残余奥氏体量减小。形变导致B1500HS硼钢的连续冷却转变图左移,避免未变形B1500HS钢试样生成贝氏体组织的临界冷却速度约为25℃/s。当冷却速度为25℃/s时,试样的变形程度达到30%时,微观组织中开始出现贝氏体。

Some samples of B1500 HS boron steel austenizing at 900 are compressed about 10%, 20%, 30% and 40% at a constant ℃strain rate by Gleeble 1500 D thermo-mechanical simulator. The deformed samples are cooled at the rate of 50 ℃/s, 40 ℃/s and 25 ℃/s, the effects of deformation and cooling rate on the phase-transformation temperature, micro-structure, micro-hardness and retained austenite are researched. The results show that, the start and finish temperatures of martensite phase-transformation rise with increasing the deformation degree at the same cooling rate. The size of martensite microstructure becomes smaller, less twin martensite and more lath martensite are produced in the microstructure with increasing the deformation degree. The increase of deformation and cooling rate are both helpful to reduce the volume fraction of retained austenite in the samples of B1500 HS steel. The continuous cooling transformation diagrams of B1500 HS steel moves to left due to the deformation. The critical cooling rate for the undeformed austenite of B1500 HS steel not transformed into bainite is approximately 25 ℃/s. If the deformation degree of B1500 HS steel specimen is more than 30 %, bainite can be produced in the microstructure at the cooling rate of 25 ℃/s.