Li Y J, Ponge D, Choi P, Raabe D
Max-Planck Institut für Eisenforschung, Max-Planck-Str. 1, D-40237 Düsseldorf, Germany.
Max-Planck Institut für Eisenforschung, Max-Planck-Str. 1, D-40237 Düsseldorf, Germany.
Ultramicroscopy. 2015 Dec;159 Pt 2:240-7. doi: 10.1016/j.ultramic.2015.03.009. Epub 2015 Mar 14.
B-added low carbon steels exhibit excellent hardenability. The reason has been frequently attributed to B segregation at prior austenite grain boundaries, which prevents the austenite to ferrite transformation and favors the formation of martensite. The segregation behavior of B at prior austenite grain boundaries is strongly influenced by processing conditions such as austenitization temperatures and cooling rates and by alloying elements such as Mo, Cr, and Nb. Here an local electrode atom probe was employed to investigate the segregation behavior of B and other alloying elements (C, Mn, Si, and Cr) in a Cr-added Mo-free martensitic steel. Similar to our previous results on a Mo-added steel, we found that in both steels B is segregated at prior austenite grain boundaries with similar excess values, whereas B is neither detected in the martensitic matrix nor at martensite-martensite boundaries at the given cooling rate of 30K/s. These results are in agreement with the literature reporting that Cr has the same effect on hardenability of steels as Mo in the case of high cooling rates. The absence of B at martensite-martensite boundaries suggests that B segregates to prior austenite grain boundaries via a non-equilibrium mechanism. Segregation of C at all boundaries such as prior austenite grain boundaries and martensite-martensite boundaries may occur by an equilibrium mechanism.
添加硼的低碳钢具有优异的淬透性。其原因通常归因于硼在原奥氏体晶界处的偏聚，这会阻止奥氏体向铁素体的转变，并有利于马氏体的形成。硼在原奥氏体晶界处的偏聚行为受到诸如奥氏体化温度和冷却速率等加工条件以及诸如钼、铬和铌等合金元素的强烈影响。在此，采用局部电极原子探针来研究硼和其他合金元素（碳、锰、硅和铬）在一种添加铬但不含钼的马氏体钢中的偏聚行为。与我们之前对添加钼的钢的研究结果类似，我们发现，在这两种钢中，硼都以相似的过量值偏聚在原奥氏体晶界处，而在给定的30K/s冷却速率下，在马氏体基体中以及马氏体 - 马氏体边界处均未检测到硼。这些结果与文献报道一致，即在高冷却速率的情况下，铬对钢淬透性的影响与钼相同。在马氏体 - 马氏体边界处未检测到硼表明硼是通过非平衡机制偏聚到原奥氏体晶界处的。碳在所有边界（如原奥氏体晶界和马氏体 - 马氏体边界）处的偏聚可能是通过平衡机制发生的。
