Duran Mercedes Andrea, Peitsch Pablo, Svoboda Hernán Gabriel
Facultad de Ingeniería, Universidad de Buenos Aires, GTSyCM3, Buenos Aires C1053ABH, Argentina.
Laboratorio de Investigación Aplicada a la Producción y el Trabajo, Universidad Nacional de Hurlingham (UNAHUR), Hurlingham B1688AXC, Argentina.
Materials (Basel). 2025 Jun 16;18(12):2820. doi: 10.3390/ma18122820.
Welding of maraging steels leads to a microstructural gradient from base material (BM) to weld metal (WM). During post-weld heat treatment (PWHT) the precipitation and reverted austenite (γ) reactions will occur defining the mechanical properties. These reactions are affected by the microstructure and local chemical composition of each zone in the "as welded" (AW) condition. This effect has not been clearly described yet nor the evolution of the microstructure. The objective of this work was to analyse the phase transformations at the different zones of the welded joint during the PWHT to explain the microstructure obtained at each zone. Samples of C250 maraging steel were butt-welded by GTAW-P (Gas Tungsten Arc Welding-Pulsed) process without filler material. The AW condition showed an inhomogeneous microhardness profile, associated with a partial precipitation hardening in the subcritical heat affected zone (SC-HAZ) followed by a softening in the intercritical (IC-HAZ) and recrystallized heat affected zone (R-HAZ). A loop-shaped phase was observed between low temperature IC-HAZ and SC-HAZ, associated with γ, as well as microsegregation at the weld metal (WM). The microstructural evolution during PWHT (480 °C) was evaluated on samples treated to different times (1-360 min). Microhardness profile along the welded joint was mostly homogeneous after 5 min of PWHT due to precipitation reaction. The microhardness in the WM was lower than in the rest of the joint due to the depletion of Ni, Ti and Mo in the martensite matrix related with the γ formation. The isothermal kinetics of precipitation reaction at 480 °C was studied using Differential Scanning Calorimetry (DSC), obtaining a JMAK expression. The average microhardness for each weld zone was proposed for monitoring the precipitation during PWHT, showing a different behaviour for the WM. γ in the WM was also quantified and modelled, while in the IC-HAZ tends to increase with PWHT time, affecting the microhardness.
马氏体时效钢的焊接会导致从母材（BM）到焊缝金属（WM）的微观结构梯度。在焊后热处理（PWHT）期间，会发生析出和逆转变奥氏体（γ）反应，从而决定机械性能。这些反应受“焊态”（AW）条件下每个区域的微观结构和局部化学成分的影响。这种影响尚未得到清晰描述，微观结构的演变情况也未明确。这项工作的目的是分析PWHT期间焊接接头不同区域的相变，以解释每个区域获得的微观结构。采用GTAW-P（钨极气体保护电弧焊-脉冲）工艺在无填充材料的情况下对C250马氏体时效钢进行对接焊接。AW状态显示出不均匀的显微硬度分布，这与亚临界热影响区（SC-HAZ）中的部分析出硬化有关，随后在临界区（IC-HAZ）和再结晶热影响区（R-HAZ）出现软化。在低温IC-HAZ和SC-HAZ之间观察到一个与γ相关的环形相，以及焊缝金属（WM）中的微观偏析。对在不同时间（1 - 360分钟）处理的样品评估了PWHT（480°C）期间的微观结构演变。由于析出反应，PWHT 5分钟后沿焊接接头的显微硬度分布大多变得均匀。由于与γ形成相关的马氏体基体中Ni、Ti和Mo的贫化，WM中的显微硬度低于接头的其他部分。使用差示扫描量热法（DSC）研究了480°C下析出反应的等温动力学，得到了一个JMAK表达式。提出了每个焊接区域的平均显微硬度用于监测PWHT期间的析出情况，结果显示WM表现出不同的行为。对WM中的γ也进行了定量和建模，而在IC-HAZ中，γ倾向于随PWHT时间增加，从而影响显微硬度。
