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用金相、电子显微镜二级复型、萃取复型和选区电子衍射等技术研究了15 MnB 钢低碳马氏体的回火过程,特别是沉淀碳化物的形貌、尺寸、分布和结构,说明了回火温度对机械性能的影响。在水淬及回火样品中,随回火温度的不同,发现了两种不同形状的碳化物:一种是淬火时就已沉淀的(自回火)弥散细小的细针状碳化物,其宽度只有80～100埃,它在250℃时长大,而升温至450℃回火时又溶解,另一种是500℃以上回火时在晶界聚集的大颗粒状碳化物,颗粒度可达2000～3000埃。用电子衍射证实了这两种形状不同的碳化物都是渗碳体,具有正交结构。用萃取复型法发现,对于在250℃附近回火的样品,沿马氏体板条边界有一层极薄的渗碳体薄膜,它是造成15MnB 钢出现第一类回火脆性的原因。
The tempering process of low carbon martensite in 15 MnB steel, especially the morphology, size, distribution and structure of precipitated carbides, was investigated by means of metallography, secondary complexation with electron microscope, extraction complexation and selected area electron diffraction. Described the tempering temperature on the mechanical properties. In the water quenching and tempering samples, with the different tempering temperature, two different shapes of carbides were found: one is the finely precipitated (self-tempering) precipitated fine needle-like carbides that quench, the Its width is only 80-100 Å. It grows at 250 ◦ C and dissolves when it is tempered at 450 ◦ C. The other is a large granular carbide that is aggregated at the grain boundaries when tempered at above 500 ◦ C and has a particle size of up to 2000 ~ 3000 angstroms. It was confirmed by electron diffraction that these two carbides with different shapes are all cementite and have an orthorhombic structure. Using the extraction complex method, it was found that for samples tempered around 250 ℃, there was a very thin cementite film along the boundary of the martensite slab, which is responsible for the first temper brittleness of 15MnB steel.