This experiment assesses the suitability of square-welding high strength steel using the deep penetration welding method, RapidWeld. The aim of this method suitability assessment was to compare the final material properties of three welds, welded accordingly to identical welding procedures. High strength, ultra-fine-grain steel S1100QL (XABO 1100) was used as a parent metal. The suitability confirmation was based on the achievement of requested mechanical properties of ISO 15614-1 and mobile crane manufactures standards. The hardness, strength properties and impact energy measurement and evaluatioon of the joint was performed during the experiment. The joint was welded repeatedly with the use of the same welding parameters for the confirmation of process stability. The achieved mechanical properties fulfill all the requirements. The hardness value deviation is caused by different properties in the heat affected zone. The root cause of the impact energy deviaton was not fully investigated, but the minimal measured values are above requirement. The deviation of the strength characteristics is mininal. The performed experiment has confirmed that the selected welding method is suitable to ensure that the requested material properties of welded high strength, ultra-fine-grained steel are achieved.

The experiment aimed on influence of shielding gas flow rate on properties of single V groove butt weld of high strength ultra-fine grained steel S960QL (XABO 960) and filler material G 89 6 M21 Mn4Ni2CrMo (X90) is described in this article. The steel S960QL is sensitive to presence of hydrogen in material structure, in exceed of maximal recommended content (<5ml/100g) the cold cracking may take place. During the experiment specimen 1 with reduced flow rate 5l.min-1 and specimen 2 with recommended flow rate 14l.min-1 was welded. The active shielding gas Corgon with the 82% Ar and 18% CO2 ratio was used. Flow rate of shielding gas has a noticeable influence on properties of welded joint. Because of specimen 1 reduced flow rate the full penetration was not achieved, chemical composition evaluation of weld metal shows fewer deoxidizing elements (Si, Mn, Ti) and increased hydrogen contents (≈18 ml/100g) as a result of chemical reaction between weld metal and air during welding. The increased hydrogen content, type of base metal and lack of penetration were the reasons of fracture of the specimen 1. Cold cracking was confirmed by hydrogen content measurement and by fracture surface evaluation by optical and electron microscopy. The porosity, fish eyes and cleavage facets typical for brittle fracture was found by microscopy. The high-quality weld with low content of hydrogen can be obtained with the recommended shielding gas flow rate, the flow rate adjustment is one of method how to avoid cold cracking of welds.