Comparative analysis on delta ferrite determination for austenitic stainless steels

ABSTRACT In the welding of austenitic stainless steels, the determination of delta ferrite (δ-ferrite) is very important to assess the susceptibility of weld metal to hot cracking, one of the major problems related to weldability, metallurgical and mechanical behavior of this type of steels. The determining δ-ferrite in the weld metal can be performed with predictive methods from the chemical composition of weld metal provided by the welding consumable (the diagram of Schaeffler, Delong, WRC 1988, WRC1992), by metallography and using nondestructive testing technique by magnetic determination of ferrite. This paper presents a comparative analysis of the predictive determination of δ-ferrite and the magnetic method using austenitic stainless electrodes for SMAW process using different classifications and diameters. The filler metals used correspond to different batches of such consumables and it has used a standardized methodology for magnetic determination. The correlation between the two methods seems to work best for NF values between 4 and 8. Errors and the correlation between the two methods applied to determine NF are not acceptable when the electrodes deposit solder metals with high NF values, greater than 18.摘要 在奥氏体不锈钢焊接过程中，δ铁素体（delta ferrite）的测定对评估焊缝金属的热裂纹敏感性至关重要，而热裂纹是这类钢材焊接性、冶金及力学性能相关的主要问题之一。焊缝金属中δ铁素体的测定可通过以下方式实现：基于焊接材料提供的焊缝金属化学成分的预测方法（如舍夫勒（Schaeffler）图、德龙（Delong）图、WRC 1988图、WRC 1992图）、金相分析法，以及采用铁素体磁测法的无损检测技术。本文针对采用不同牌号及直径的奥氏体不锈钢焊条进行焊条电弧焊（SMAW）的工况，开展了δ铁素体预测测定法与磁测法的对比分析。本次研究使用的填充金属取自该类焊材的不同批次，并采用了标准化的磁测方法。当NF值处于4至8区间时，两种方法的相关性表现最佳。当焊条熔敷的焊缝金属NF值高于18时，两种测定NF的方法的误差及相关性均无法满足要求。