Stornelli Giulia, Tselikova Anastasiya, Mirabile Gattia Daniele, Mortello Michelangelo, Schmidt Rolf, Sgambetterra Mirko, Testani Claudio, Zucca Guido, Di Schino Andrea
Dipartimento di Ingegneria, Università degli Studi di Perugia, Via G. Duranti 93, 06125 Perugia, Italy.
Vantage Alloys AG, 6300 Zug, Switzerland.
Materials (Basel). 2023 Apr 5;16(7):2897. doi: 10.3390/ma16072897.
The inter-critically reheated grain coarsened heat affected zone (IC GC HAZ) has been reported as one of the most brittle section of high-strength low-alloy (HSLA) steels welds. The presence of micro-alloying elements in HSLA steels induces the formation of microstructural constituents, capable to improve the mechanical performance of welded joints. Following double welding thermal cycle, with second peak temperature in the range between Ac1 and Ac3, the IC GC HAZ undergoes a strong loss of toughness and fatigue resistance, mainly caused by the formation of residual austenite (RA). The present study aims to investigate the behavior of IC GC HAZ of a S355 steel grade, with the addition of different vanadium contents. The influence of vanadium micro-alloying on the microstructural variation, RA fraction formation and precipitation state of samples subjected to thermal cycles experienced during double-pass welding was reported. Double-pass welding thermal cycles were reproduced by heat treatment using a dilatometer at five different maximum temperatures of the secondary peak in the inter-critical area, from 720 °C to 790 °C. Although after the heat treatment it appears that the addition of V favors the formation of residual austenite, the amount of residual austenite formed is not significant for inducing detrimental effects (from the EBSD analysis the values are always less than 0.6%). Moreover, the precipitation state for the variant with 0.1 wt.% of V (high content) showed the presence of vanadium rich precipitates with size smaller than 60 nm of which, more than 50% are smaller than 15 nm.
临界区间再加热晶粒粗化热影响区（IC GC HAZ）已被报道为高强度低合金（HSLA）钢焊缝中最脆的区域之一。HSLA钢中微合金元素的存在会促使微观结构成分的形成，从而能够改善焊接接头的力学性能。在双道焊接热循环过程中，当第二峰值温度处于Ac1和Ac3之间时，IC GC HAZ会出现韧性和抗疲劳性的大幅损失，这主要是由残余奥氏体（RA）的形成导致的。本研究旨在探究添加不同钒含量的S355钢级IC GC HAZ的行为。报道了钒微合金化对双道焊接过程中经历热循环的样品的微观结构变化、RA分数形成及析出状态的影响。通过使用膨胀仪在临界区间内五个不同的二次峰值最高温度（从720℃至790℃）下进行热处理，再现了双道焊接热循环。尽管热处理后似乎添加V有利于残余奥氏体的形成，但形成的残余奥氏体量对于产生有害影响并不显著（从电子背散射衍射分析来看，其值始终小于0.6%）。此外，含0.1 wt.% V（高含量）的变体的析出状态显示存在尺寸小于60 nm的富钒析出物，其中超过50%小于15 nm。
