Nb对高碳钢珠光体球化的影响

摘要：设计了2种不同Nb含量的高碳珠光体钢（0.025Nb和Free -Nb），采用光学显微镜、扫描显微镜、透射电镜和硬度测试仪对两种试验钢珠光体球化前后的显微组织进行了观察和球化后的硬度进行了测量。结果表明：Nb元素可以细化高碳珠光体钢的片层间距，相同条件下具有更多的铁素体 渗碳体界面，在球化退火的第一阶段提供大量的位错和亚晶界使片状珠光体快速熔断，同时也给第二阶段碳的扩散提供高速扩散通道；细小的片层间距缩短了碳和合金元素的扩散距离，使球化转变速度加快，促进了高碳珠光体的球化。Nb元素的添加获得了细小片层间距以及更多的合金碳化物使试验钢的初始硬度偏高，球化退火前4h硬度值下降幅度较大，球化退火4h后对试验钢硬度的影响不大。

Effect of Nb on spheroidization of pearlitic for high carbon steel

Two kinds of high carbon pearlitic steel(0.025Nb and free-Nb) with different Nb contents were designed.The microstructures of the pearlite before and after spheroidization were observed by optical microscope, scanning microscope, transmission electron microscope and the hardness of test steel after spheroidization was measured by hardness tester. The results show that Nb can refine the interlamellar spacing of high carbon pearlitic steel, and have more ferrite cementite interfaces under the same conditions. In the first stage of spheroidal annealing, a large number of dislocations and sub boundaries are provided to make the lamellat pearlite broken up rapidly, and meanwhile, high speed diffusion channel is provided for the carbon diffusion in the second stage of spheroidal annealing. The fine interlamellar spacing shortens the diffusion distance of carbon and alloy elements, the spheroidization transformation of pearlite was accelerated by the separation. With the addition of Nb element, the initial hardness of the test steel was relatively high due to the fine interlamellar spacing and more alloy carbide. Nb microalloying makes the hardness of test steel decrease rapidly 4 hours before spheroidizing annealing, but has little effect on hardness after 4 hours.