Purpose

The purpose of this paper is to present the results of a metallurgical, mechanical and tribological characterization of the weld and heat-affected zone (HAZ) of aluminothermic welding of premium rails used in heavy haul, looking into the origins of the squat defects associated with rail wear.

Design/methodology/approach

A full factorial design of experiment was carried out for 24 welds of premium and super premium rails. The factors studied were chemical composition, welding gap and preheating time. The welds were inspected visually and by ultrasound to detect superficial and internal defects and characterized by macrographic analysis, hardness profile, tensile tests and microstructural characterization in scanning electronic microscopy. Pin-on-disk test were carried out to compare the tribological behavior of the different regions of the weld rail.

Findings

Squat formation was shown to be associated with spheroidized pearlite regions formed on the HAZ of the welds, presenting near half the hardness of the weld metal. Thermal analysis showed that spheroidized pearlite is a result of partial austenitization at these positions. Tribological tests showed that low hardness regions presented smaller wear resistance than both the weld metal and the parent rail. Tensile test of the whole region resulted in brittle fracture along the weld metal.

Originality/value

The results showed that it is essential to reduce the dimensions of the HAZ and the width of the hardness drop area to mitigate squat formation in the HAZ edges.

Peer review

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0020/

中文翻译：

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铝热焊接钢轨热影响区（HAZ）边缘的铝和铝焊接的深部冶金学和摩擦学方面

目的

本文的目的是介绍重型运输中使用的优质钢轨的铝热焊接的焊接和热影响区（HAZ）的冶金，机械和摩擦学特性的结果，并探讨与之相关的下蹲缺陷的成因轨道磨损。

设计/方法/方法

对24条优质和超优质钢轨焊缝进行了全因子设计实验。研究的因素是化学成分，焊接间隙和预热时间。对焊缝进行目视检查和超声波检查，以检测表面和内部缺陷，并在扫描电子显微镜下通过宏观分析，硬度分布，拉伸试验和微观结构表征对其进行表征。进行了销钉在盘上的测试，以比较焊轨不同区域的摩擦学行为。

发现

已表明，深蹲形成与焊缝热影响区上形成的球形珠光体区域有关，呈现出焊缝金属硬度的近一半。热分析表明，球形珠光体是这些位置上部分奥氏体化的结果。摩擦学测试表明，低硬度区域的耐磨性低于焊接金属和母轨。整个区域的拉伸试验导致沿焊接金属的脆性断裂。

创意/价值

结果表明，必须减小HAZ的尺寸和硬度下降区域的宽度，以减轻HAZ边缘的下蹲现象。

同行评审

本文的同行评审历史记录可在以下网址获得：https://publons.com/publon/10.1108/ILT-01-2020-0020/