Investigation of physically simulated weld HAZ and CCT diagram of HSLA armour steel

• Published in: Welding in the world 2018, Vol.62 (1), p.47-54
• Main Authors: Falkenreck, Thora, Kromm, Arne, Böllinghaus, Thomas
• Format: Article
• Language: English
• Subjects: Arc welding; Armor; Chemistry and Materials Science; Coarsening; Cooling; Cooling rate; Dilatometry; Heat affected zone; Heat treating; High strength low alloy steels; Laser beam welding; Martensitic stainless steels; Martensitic transformations; Materials Science; Metallic Materials; Microstructure; Phase transitions; Research Paper; Simulation; Solid Mechanics; Stretching; Theoretical and Applied Mechanics; Welded joints
• ISSN: 0043-2288; 1878-6669
• DOI: 10.1007/s40194-017-0511-4

The phase transformation under various cooling rates and in different HAZ regions for high-strength armour steel was analysed by dilatometry. To develop a continuous cooling transformation (CCT) diagram, the samples were heated up to a peak temperature of 1250 °C to achieve a coarse-grained microstructure and then cooled down with a cooling time t 8/5 varying from 3 to 240 s. Analysis of dilatation curves revealed the austenite decomposition process, during which transformation temperatures were determined. The results showed martensitic transformations for all welding-relevant cooling times. Furthermore, to analyse different heat-affected subzones of the weld, the peak temperature was varied between 550 and 1250 °C at a constant cooling time t 8/5 of 6 s. The simulated coarse-grained heat-affected zone (CGHAZ) and fine-grained-heat affected zone (FGHAZ) showed only martensitic transformations with transformation temperatures below 400 °C. The steel exhibited an inhomogeneous hardness with hardening in the CGHAZ and FGHAZ and softening in the intercritical and subcritical HAZ. The physically simulated microstructure was validated by a real hybrid laser-arc weld microstructure.