高Cr铸造镍基高温合金K4648的母合金净度研究

对两炉冲击韧性存在明显差异的高Cr铸造镍基高温合金K4648进行了对比研究,通过分析两炉母合金的主量元素和气体含量,采用电子束纽扣锭(EB锭)实验观察合金内夹杂物和对母合金用原材料金属Cr的显微组织分析等方法研究了K4648母合金净度。结果表明:1#与2#炉批母合金主量元素无明显差别。1#母合金由于气体元素O含量高达(20.5±7.5)×10-6,远高于2#合金的6×10-6,造成其室温冲击韧性(aku)不及2#合金的一半,低于技术条件要求的19.6J/cm2。电子束纽扣锭(EB锭)实验可有效地将K4648中的夹杂物汇聚,经分析主要是富Y,Ce的氧化物和富Al氧化物。证明高Cr铸造镍基高温合金K4648中添加稀土元素Y,Ce可有效攫取合金中自由态的O和S,生成稳定的稀土氧化物或硫化物,起到净化合金的作用。K4648母合金原材料中金属Cr基体中固溶有15%(质量分数)的元素O,还分布有富Cr氧化物和Cr,Al,Si的复合氧化物。此外,还存在含N、贫O区域,该区域的维氏显微硬度可达8.2GPa,是Cr基体1.3GPa的6倍,证明N使金属Cr的硬度明显升高。

Investigation of the Master Alloy Cleanliness of High Cr Content Cast Ni-base Superalloy K4648

Two heats of high Cr content cast Ni-base superalloy K4648,which possess significant differences on impact ductility,were investigated comparatively.The cleanliness of K4648 master alloy was studied by chemical analysis on the alloy composition and gas content,electron beam button(EB button) technique evaluation on inclusions and microstructure observation of chromium metal used in raw materials.The results indicate that the two heats of K4648 master alloy have no obvious difference in major constituent.However,1# master alloy possesses a high oxygen level of(20.5±7.5)×10-6,which is much higher than 6×10-6 of 2# alloy.The impact ductility of 1# alloy is less than half that of 2# alloy and lower than the K4648 specification requirement of 19.6J/cm2.The electron beam button(EB button) experiment could effectively aggregate the inclusions in specific region.The inclusions were identified as(Y,Ce)-rich oxide and Al-rich oxide.It is evident that the addition of rare earth(RE) element such as yttrium and cerium in high Cr content cast Ni-base superalloy K4648 can snatch the free oxygen or sulfur,and form stable RE oxides or sulfides to purify the master alloy.About 15%(atom fraction) element O is solusionized in the chromium metal matrix which is used in raw materials for K4648 master alloy.Some Cr-rich oxides and(Cr,Al,Si)-rich oxides distributes in the Cr matrix.In addition,a N-bearing and O-depletion zone exists in the Cr matrix.The Vickers microhardness of this region can reach 8.2GPa,which is 6 times harder than 1.3GPa of Cr matrix,indicate that the element N can harden and embrittle the chromium metal.