On the development of a new pre-weld thermal treatment procedure for preventing heat-affected zone (HAZ) liquation cracking in nickel-base IN 738 superalloy
On the development of a new pre-weld thermal treatment procedure for preventing heat-affected zone (HAZ) liquation cracking in nickel-base IN 738 superalloy
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DOI：
10.1080/14786435.2014.956838
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发表时间：
2014-01-01
影响因子：
1.6
通讯作者：
Chaturvedi, M. C.
中科院分区：
文献类型：
--
作者：
Ola, O. T.;Ojo, O. A.;Chaturvedi, M. C.
在熔焊过程中，沉淀强化镍基高温合金（如IN 738）的热影响区（HAZ）中的热裂纹仍然是限制镍基燃气涡轮机部件可修复性的主要因素。热影响区晶间裂纹问题可以通过热处理改变焊前材料的微观结构来解决，这需要深入了解控制裂纹行为的关键因素。在合金中的Mo-Cr-W-和Cr-富硼化物的分解，除其他因素外，已被观察到显着贡献的非平衡晶间液化，因此，晶间液化裂纹在焊接过程中。热影响区微观结构的Gleeble物理模拟还表明，非平衡液化在合金中分解的硼化物附近更严重，并且可以在低至1，150摄氏度的温度下发生。尽管目前存在的IN 738高温合金的焊前热处理使包括硼化物的第二相的溶解对HAZ晶间液化的贡献最小化，但是由于工艺相关的困难，这些热处理在工业上是不可行的。因此，一种新的工业上可行的和有效的焊前热处理工艺，指定为FUMT，在本研究期间开发的控制硼化物的形成和硼的偏析在焊前热处理材料的晶界。观察到该热处理非常显著地减少焊接IN 738高温合金中的晶间HAZ裂纹。本文详细介绍了开发过程和开发程序。
Hot cracking in the heat-affected zone (HAZ) of precipitation strengthened nickel-base superalloys, such as IN 738, during fusion welding remains a major factor limiting reparability of nickel-base gas turbine components. The problem of HAZ intergranular cracking can be addressed by modifying the microstructure of the pre-weld material through thermal treatment, which requires significant understanding of the critical factors controlling cracking behaviour. The decomposition of Mo-Cr-W- and Cr-rich borides in the alloy, among other factors, has been observed to contribute significantly to non-equilibrium intergranular liquation and, hence, intergranular liquation cracking during welding. Gleeble physical simulation of HAZ microstructure has also shown that non-equilibrium liquation is more severe in the vicinity of decomposed borides in the alloy and can occur at temperatures as low as 1,150 degrees C. Although currently existing pre-weld heat treatments for IN 738 superalloy minimize the contributions of dissolution of second phases, including borides, to HAZ intergranular liquation, these heat treatments are not industrially feasible due to process-related difficulties. Therefore, a new industrially feasible and effective pre-weld thermal treatment process, designated as FUMT, was developed during the present research by controlling both the formation of borides and the segregation of boron at the grain boundaries in the pre-weld heat-treated material. This thermal treatment was observed to very significantly reduce intergranular HAZ cracking in welded IN 738 superalloy. The details of the development process and developed procedure are presented in this paper.