硅含量对9Cr-1.5W钢在550℃下蠕变性能的影响

在550℃下对硅质量分数分别为0.34%,0.60%,0.90%的9Cr-1.5W钢进行拉伸试验以及不同应力下的蠕变试验,研究了硅含量对试验钢高温拉伸性能和蠕变性能的影响。结果表明:随着硅含量的增加,试验钢在550℃下的屈服强度和抗拉强度均降低,但断后伸长率增大,应变硬化指数先升后降,含质量分数0.60%硅的试验钢具有最大的应变硬化指数;含质量分数0.60%硅的试验钢在不同应力下均具有较长的蠕变时间,表现出最佳的高温蠕变性能,应力指数最小,最小蠕变速率对外加应力敏感性最低;试验钢的蠕变行为均受位错攀移控制。

9Cr-1.5W-0.15Ta耐热钢搅拌摩擦焊焊缝组织和冲击性能分析

对9Cr-1.5W-0.15Ta耐热钢搅拌摩擦焊焊缝的微观组织演变和冲击性能进行了分析.结果表明,由于搅拌针剧烈的机械搅拌和焊接热循环的双重作用,搅拌摩擦焊缝区域内发生晶粒破碎、完全奥氏体化动态再结晶、晶界处M23C6相溶解和晶内M3C相析出,焊后较大的冷却速率抑制晶粒长大,促进了马氏体转变.在−100~20℃温度内进行了冲击试验,随着冲击试验温度的增加,母材和FSW焊缝的冲击吸收能量均表现为单调增大的特征,同时冲击断裂模式由脆性断裂逐渐转变为延性断裂.由于FSW焊缝中板条马氏体的形成、“针状”M3C碳化物的析出,FSW焊缝的硬度显著增大,并且在相同温度下FSW焊缝的冲击韧性发生降低,韧—脆转变温度由母材的−50℃升高至−40.2℃.

9Cr-1.5W-0.15Ta耐热钢电子束焊缝和搅拌摩擦焊缝组织性能比较

对9Cr-1.5W-0.15Ta耐热钢分别进行电子束焊和搅拌摩擦焊工艺试验,研究了不同焊接方法对焊缝微观组织及接头冲击韧性的影响规律.结果表明,电子束焊缝由粗大的树枝状板条马氏体组成,且原奥氏体晶界处和晶内的析出相发生完全溶解;搅拌摩擦焊缝由细小且均匀的板条马氏体组成,晶界处的M23C6碳化物发生溶解,晶内球状MX相无明显变化.由于形成大量的板条马氏体,电子束焊缝和搅拌摩擦焊缝硬度均显著高于母材.不同焊接方法对其焊缝的冲击吸收功有着显著影响,电子束焊缝冲击吸收能量仅为母材的12.2%,而搅拌摩擦焊缝则表现出较好地冲击韧性,其冲击吸收能量为母材的90%.

Formation of FeMo_2B_2 phase in boron containing 9Cr-1.5Mo ferritic steels

The segregation and diffusion of boron during heat treatments were studied. The influence of boron contents, aging time and applied stress on FeMo2B2 formation was also studied. Finally, the effects of boron contents and FeMo2B2 formation on the high temperature strength were studied. Boron atoms were segregated to prior austenite grain boundary during normalizing treatment. And these boron atoms were slowly diffused into the grain interior during tempering and aging at 700 ℃. The FeMo2B2 phase was only formed after 1,000 h aging at 700 ℃ in alloy containing 196 ppm boron. The formation of FeMo2B2 phase is accelerated by the applied stress. It was expected that the formation of FeMo2B2 is closely related to the redistribution of boron atoms. The tensile strengths at 700 ℃ are increased with the increase of boron contents. However, the formation of FeMo2B2 phase results in lower tensile strength.