Heterogeneous precipitation and mechanical property change by heat treatments for the laser weldments of V-4Cr-4Ti alloy
Heterogeneous precipitation and mechanical property change by heat treatments for the laser weldments of V-4Cr-4Ti alloy
复制标题
DOI：
10.1585/pfr.10.1405092
复制
发表时间：
2015
影响因子：
0.8
通讯作者：
T. Muroga;N. Heo;T. Nagasaka;Hideo Watanabe;A. Nishimura;K. Shinozaki
中科院分区：
文献类型：
--
作者：
T. Muroga;N. Heo;T. Nagasaka;Hideo Watanabe;A. Nishimura;K. Shinozaki
采用2.0kW的激光对4 mm厚的V-4Cr-4Ti合金(NiS-HEAT-2)进行了堆焊。在不同条件下进行焊后热处理(PWHT)。对焊缝金属进行了PWHT处理，获得了显微组织、维氏硬度和冲击性能。热处理1h后，硬度随温度升高而升高，峰值后随温度升高而下降。873K时，随着热处理时间的延长，硬度逐渐升高，峰值后逐渐下降。显微组织观察表明，随着硬度的提高，高密度的细小析出物均匀形成，但析出物的分布转变为由发达的析出物集合体组成的非均匀孤岛，这与硬度的降低和冲击性能的恢复相一致。光学显微镜观察表明，PWHT形成了析出聚集区的胞状结构。显微化学分析表明，钛在析出聚集区有明显的富集区。因此，焊接过程中钛浓度的区域振荡和熔化再结晶形成的胞状结构导致了后续的PWHT非均匀析出。富钛区的析出净化了焊缝金属的基质，导致了硬化的恢复和冲击性能的退化。根据实验结果讨论了最佳的热处理工艺条件。
Bead-on-plate welds were produced on the 4 mm-thick V-4Cr-4Ti alloy (NIFS-HEAT-2), using a 2.0 kW YAG laser. The post-weld heat treatments (PWHT) were carried out in various conditions. Microstructures, Vickers hardness and Charpy impact properties were obtained for the weld metal after the PWHT. After PWHT for one hour, the hardness increased and after the peak declined with temperature. At 873 K, the hardness increased and after the peak declined with the time of PWHT. Microstructural observation showed that high density of fine precipitates formed homogeneously when the hardness increased, but the precipitate distribution changed into heterogeneous forming islands of developed precipitate aggregates, coincident with decrease in hardness and recovery of impact properties. Optical microscope observations suggested that a cellular structure of precipitate aggregate region was formed by PWHT. Microchemical analysis showed that Ti was enriched in the precipitate aggregate region. Therefore the areal oscillation of Ti concentration with cellular structures formed by melting and resolidification during the welding resulted in the heterogeneous precipitation by the following PWHT. The precipitation in the Ti-rich area purified the matrix of the weld metal and induced the recovery of hardening and impact property degradation. Optimum PWHT conditions were discussed according to the present results.