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Abstract

The phenomenon of “soft zone” is occurring in the heat affected zone (HAZ) of high strength low alloy (HSLA) steels. Therefore, the process of weld metal solidification and phase transformation in HAZ is essential to understand the behaviour of the material, especially in the case where welded joints are debilitating part of the construction. The simulation program SYSWELD is powerful tool to predict solidification and phase transformation of welding joint, what correspond to the mechanical properties of the joints. To achieve relevant results of the simulation, it is necessary to use right mathematic-material model of the investigated material. Dilatometric test is the important methods to gather necessary input values for material database. In this paper is investigated physical and metallurgical properties of S960MC steel. The dilatometric curves were carried out on the laboratory machine dilatometer DIL 805L. In addition to determination of the phase transformation temperatures at eight levels of the cooling rate, the microstructure and hardness of the material are further analysed. The hardness of the samples reflects the achieved microstructure. Depending on the cooling rate, several austenitic transformation products were observed such as pearlite, bainite, martensite and many different ferritic microstructures. The differences between the transformation temperature results using the first derivation method and the three tangent method are up to 2%. The limit cooling rate was set at value 30°C/s. The microstructure consists only of bainite and martensite and the hardness reaches a value of 348HV and higher.
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Authors and Affiliations

M. Málek
1
M. Mičian
1
ORCID: ORCID
J. Moravec
1

  1. Faculty of Mechanical Engineering, Technical University of Liberec, Studentská 1402/2, 461 17 Liberec I, Czech Republic
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Abstract

This research is focused on the analysis of heat-affected sub-zones in 2 mm thick steel S960MC samples, with the aim of observing and evaluating the mechanical properties after exposure to temperatures corresponding to individual heat-affected sub-zones. Test samples were prepared using a Gleeble 3500 thermo-mechanical simulator. The samples were heated in the range from 550°C to 1350°C and were subsequently quickly cooled. The specimens, together with the base material, were then subjected to tensile testing, impact testing, and micro-hardness measurements in the sample cross-section, as well as evaluation of their microstructure. Fracture surfaces are investigated in samples after impact testing. The heat-affected sub-zones studied indicate high sensitivity to the thermal input of welding. There is a significant decrease in tensile strength and yield strength at temperatures around 550°C.

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Authors and Affiliations

M. Mičian
ORCID: ORCID
J. Winczek
D. Harmaniak
R. Koňár
M. Gucwa
J. Moravec
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Abstract

The work is focused on welding of fine-grained ultra-high-strength steel S960MC by laser beam welding and electron beam welding technologies. For a given type of steel, when the heat input is exceeded, the mechanical properties of welded joints will deteriorate. As a result, using beam welding technologies to limit the amount of heat input is recommended. Several butt welds were made, and mechanical tests and macroscopic analyses were performed to determine the impact of welding parameters on mechanical properties. Using beam welding technologies, the value of heat input was reduced by up to 73% compared to gas metal arc welding. When compared to a gas metal arc welded joint, the width of the soft zone was reduced by 69 to 79%. This resulted in a considerable reduction in the width of the soft zone, which was reflected in a 24% increase in yield strength and a 23% increase in tensile strength compared to gas metal arc welding.
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Authors and Affiliations

M. Mičian
1
ORCID: ORCID
M. Frátrik
1
ORCID: ORCID
J. Bárta
2
ORCID: ORCID

  1. University of Žilina, Faculty of Mechanical Engineering, Univerzitná 8215/1, 010 26 Žilina, Slovak Republic
  2. Slovak University of Technology, Faculty of Materials Science and Technology in Trnava, J. Bottu 2781/25, 917 24 Trnava, Slovak Republic

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