Mates Steven, Stoudt Mark, Gangireddy Sindhura
Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland, USA 20899-8553.
JOM (1989). 2016 Jul;68(7):1832-1838. doi: 10.1007/s11837-016-1951-9. Epub 2016 May 13.
Carbon steels containing ferrite-pearlite microstructures weaken dramatically when pearlite dissolves into austenite on heating. The kinetics of this phase transformation, while fast, can play a role during dynamic, high temperature manufacturing processes, including high speed machining, when the time scale of this transformation is on the order of the manufacturing process itself. In such a regime, the mechanical strength of carbon steel can become time-dependent. The present work uses a rapidly-heated, high strain rate mechanical test to study the effect of temperature and time on the amount of pearlite dissolved and on the resulting transient effect on dynamic strength of a low and a high carbon (eutectoid) steel. Measurements indicate that the transient effect occurs for heating times less than about three seconds. The 1075 steel loses about twice the strength compared to the 1018 steel (85 MPa to 45 MPa) owing to its higher initial pearlite volume fraction. Pearlite dissolution is confirmed by metallographic examination of tested samples. Despite the different starting pearlite fractions, the kinetics of dissolution are comparable for the two steels, owing to the similarity in their initial pearlite morphology.
当含有铁素体-珠光体微观组织的碳钢在加热时珠光体溶解到奥氏体中时，其强度会大幅减弱。这种相变动力学虽然很快，但在动态高温制造过程中会起作用，包括高速加工，此时该相变的时间尺度与制造过程本身相当。在这种情况下，碳钢的机械强度会随时间变化。本研究采用快速加热、高应变速率的力学试验，研究温度和时间对珠光体溶解量的影响，以及由此对低碳和高碳（共析）钢动态强度产生的瞬态效应。测量结果表明，加热时间小于约三秒时会出现瞬态效应。由于1075钢初始珠光体体积分数较高，其强度损失约为1018钢的两倍（从85兆帕降至45兆帕）。通过对测试样品的金相检验证实了珠光体的溶解。尽管两种钢的初始珠光体分数不同，但由于它们初始珠光体形态相似，溶解动力学相当。
