Abstract For the heat resistance steel weld metal, special post-weld heat treatments need to be performed to maintain the creep resistance, improve the impact toughness, and relieve the welding residual stress. In this paper, firstly, the three factors affecting variability and lower values of toughness were revealed. Secondly, two different post-weld heat treatment (PWHT) methods have been used to improve the impact toughness of a heat resistance steel weld metal. Two PWHT methods include post-weld direct tempering (PWDT) process at 690 °C/26 h/air cooling and post-weld normalized tempering (PWNT) process with re-austenitization at 960 °C/1.5 h/air cooling + tempering at 690 °C/26 h/air cooling. For three type specimens with as-welded (AW), PWDT, PWNT processes, the impact toughness and the hardness were measured, and the fracture surface, microstructures were observed and analyzed by scanning electron microscope (SEM). Results indicated that PWDT heat treatment can improve the impact toughness of the weld metals from the original 79 J - 169 J to 82 J–290 J because the microstructure is changed from granular bainite to block ferrite and granular bainite. PWNT heat treatment can remarkably improve the impact toughness of the weld metals from the original 79 J- 169 J to 148 J–325 J. It is attributed to that PWNT heat treatment process can remove the boundaries of the columnar grain zone and reheated zone, make the difference of the microstructure between the columnar grain zone and reheated zone decrease, and improve the homogeneity of the microstructure.

中文翻译：

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低 Cr-Mo 钢焊缝金属的冲击韧性变化和改进的来源

摘要 对于耐热钢焊缝金属，需要进行特殊的焊后热处理，以保持抗蠕变性，提高冲击韧性，消除焊接残余应力。在本文中，首先揭示了影响可变性和较低韧性值的三个因素。其次，已使用两种不同的焊后热处理 (PWHT) 方法来提高耐热钢焊缝金属的冲击韧性。两种 PWHT 方法包括 690 °C/26 小时/空冷的焊后直接回火 (PWDT) 工艺和 960 °C/1.5 小时/空冷再奥氏体化的焊后正火 (PWNT) 工艺690 °C/26 小时/风冷。对于采用焊态 (AW)、PWDT、PWNT 工艺的三种类型试样，测量了冲击韧性和硬度，以及断裂表面，通过扫描电子显微镜（SEM）观察和分析微观结构。结果表明，PWDT热处理可使焊缝金属的冲击韧性由原来的79 J～169 J提高到82 J～290 J，这是因为组织由粒状贝氏体转变为块状铁素体和粒状贝氏体。PWNT热处理可以显着提高焊缝金属的冲击韧性，由原来的79 J-169 J提高到148 J-325 J。这归因于PWNT热处理工艺可以去除柱状晶区和再加热区的边界，使柱状晶区与再加热区的显微组织差异减小，提高显微组织的均匀性。结果表明，PWDT热处理可使焊缝金属的冲击韧性由原来的79 J～169 J提高到82 J～290 J，这是因为组织由粒状贝氏体转变为块状铁素体和粒状贝氏体。PWNT热处理可以显着提高焊缝金属的冲击韧性，由原来的79 J-169 J提高到148 J-325 J。这归因于PWNT热处理工艺可以去除柱状晶区和再加热区的边界，使柱状晶区与再加热区的显微组织差异减小，提高显微组织的均匀性。结果表明，PWDT热处理可使焊缝金属的冲击韧性由原来的79 J～169 J提高到82 J～290 J，这是因为组织由粒状贝氏体转变为块状铁素体和粒状贝氏体。PWNT热处理可以显着提高焊缝金属的冲击韧性，由原来的79 J-169 J提高到148 J-325 J。这归因于PWNT热处理工艺可以去除柱状晶区和再加热区的边界，使柱状晶区与再加热区的显微组织差异减小，提高显微组织的均匀性。