本文应用薄膜透射电镜方法对经不同温度一段及二段氮化后的18Cr2Ni4WA钢的内氮化层显微组织及其强化本质进行了研究.结果表明,该钢内氮化层形成过程可分为二个阶段:1.合金元素及氮原子在铁素体基体{100}α面上形成有序化的混合偏聚区;2.由偏聚区转变成平衡沉淀相CrN,它与基体的位相关系符合Baker-Nutting关系:(001)_(CrN)∥(001)α;[110]CrN∥[100]α在较低温度氮化时,CrN还可由碳化物转变而成.造成内氮化层高硬度的主要原因是铁素体基体内形成弥散的有序化混合偏聚区.在420—500℃氮化的条件下,内氮化层强度达最高值.随氮化温度升高,其硬度逐渐下降.采用低温+高温二段氮化时,由于低温形成的有序化偏聚区相当稳定,从而使氮化层的高硬度能保持到较高的温度,所以二段氮化在保持内氮化层高硬度的同时可以加速氮化过程,缩短氮化时间.
The microstructure and strengthening behaviour of the internal nitrided layerin 18Cr2Ni4WA steel after one-and two-step nitriding at various temperatureshave been studied by observation under TEM.Results showed that the formationof the internal nitrided layer proceeds as two stages:(1)a mixed clustering-order-ing zone of alloying elements and nitrogen atoms is formed on{100}_α basal planeof matrix;(2)the clustering zone transforms into equilibrium precipitate CrN.Theorientation relationship between the precipitate and parent phase accords withBaker-Nutting relation,i.e.,(001)_(CrN)∥(001)_α;[110]_(CrN)∥[100]_α.The CrN may alsobe formed from alloyed carbide at lower nitriding temperatures.The main causefor the very high hardness of internal nitrided layer is considered to be the for-mation of such mixed clustering-ordering zones within ferritic matrix.For one-step nitriding,the hardness of internal nitrided layer achieved maximum value at420—500℃ and decreased as the increase of nitriding temperature.For two-stepnitriding,owing to the mixed clustering-ordering zone which first formed at lowertemperature is remarkably stable,the nitrided layer remains its higher hardness tillhigh temperatures.Therfore,the two-step nitriding may provide a way to accele-rate the nitriding process and to shorten the nitriding time,but the hardness ofinternal nitriding layer keeps in high extent.
参考文献
| [1] | |
| [2] | |
| [3] | |
| [4] | |
| [5] | |
| [6] | |
| [7] | |
| [8] |
- 下载量()
- 访问量()
- 您的评分：
-
10%
-
20%
-
30%
-
40%
-
50%