本文利用S4-10型Stereoscan扫描电镜拉伸试验装置,对阴极充氢的Johnson-Matthey纯铁的形变和断裂微观过程进行了动态观察。主要结果如下: 1.随着氢含量的增加(从5.4cm~3/100g增到31.0cm~3/100g),屈服应力略有增加,流变应力和断裂强度显著增加,而断裂应变明显降低。在氢含量高于18.7cm~3/100g以上时,下屈服点和Lüders带消失。 2.氢含量低于10cm~3/100g的试样,裂纹优先在晶内滑移面上萌生形核,沿着亚晶界向前扩展,断裂途径大都是与拉伸轴呈45°方向断开。而氢含量大于16cm~3/100g的试样,裂纹易在晶界上开裂,在晶内呈锯齿形向前扩展,与拉伸轴正交方向断开。 3.纯铁氢脆的主要特征是:(1)试样表面上滑移线的明显减少,(2)脆性微观断裂形态的形成和增多。这是由于固溶的氢原子降低塑性形变所致。
The effect of hydrogen on the deformation and fracture microprocess in pure iron has been studied by means of the tensile test and observation in S4-10 SEM using cathodic charged specimens. The main results are as following:1. With the increase of hydrogen content, namely, from 5.4 up to 31.0 cm~3/100g, the yield strength increases slightly, the flow stress and the fracture strength increase obviously, but the fracture strain decreases remarkably. The lower yield point and Luders band disappear when the hydrogen content exceeds 18.7cm~3/100g.2. The nucleation of a microcrack is predominately on the slip plane and the microcrack propagates along subboundaries when hydrogen content is below 10 cm~3/100g. The nucleation of a microcrack is on the grain boundaries and the microcrack propagates in a zigzag way when hydrogen content exceeds 16 cm~3/100 g, The former is transgranular fracture and the latter is a mixed fracture of transgranular and intergranular.3. The characteristics of the hydrogen embrittlement in pure iron are: (1)the slip lines on the specimen surface decrease obviously, and (2) the microfracture of brittle feature is formed and increased. This seems due to that the dissolved hydrogen in pure iron decreases the plasitc deformation.
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