<p>International Scientific Conference PRO-TECH-MA ’16 PROGRESSIVE TECHNOLOGIES AND MATERIALS P ANALYSIS OF DUAL-PHASE STEEL WELDABILITY USED IN AUTOMOTIVE INDUSTRY</p><p>Ján VIŇÁŠ1, Ľuboš KAŠČÁK2</p><p>Production of cars is significantly increasing in recent years in the EU. The increas- ing of production lead to increasing of interest in the application of new advanced materials in the production in order to minimize production costs, produce automotive fuels - saving ecology products, enhance comfort and passengers' safety. The paper deals with the problems of weldability of high strength dual-phase steels used in the car body production. The properties of the joints made by resistance spot weld- ing (RSW) respectively laser welding were analysed. These welding technology are domin- ant in the production of the car body. The quality of welded joints was evaluated on two types of steel such as DP 600 and DP 800 (Tab.1 and Tab.2) of 0.8 mm thickness. The du- al-phase (DP) steels have been the subject of particular attention owing to their good com- bination of high strength and ductility. The term dual-phase steel refers to the predomin- ance of two phases, the body-centered-cubic a ferrite and the relatively harder body- centered-tetragonal martensite [1]. </p><p>Tab. 1 Chemical composition of welded materials [in wt. %] C Mn Si P S Al Cu Cr 0,111 1,963 0,279 0,026 < 0,002 0,031 0,019 0,206 DP 600 Mo Ni V Ti Nb Co W Fe < 0,002 < 0,002 0,012 < 0,002 0,020 0,017 0,005 Bal C Mn Si P S Al Cu Cr 0,062 1,623 0,036 0,022 < 0,002 0,086 0,119 0,247 DP 800 Mo Ni V Ti Nb Co W Fe 0,293 0,107 0,056 < 0,002 0,077 0,1 < 0,002 Bal</p><p>Tab. 2 Mechanical properties of welded sheets specified by producer Material Re [MPa] Rm [MPa] A5 [%] DP 600 300 - 470 580 - 670 26 DP 800 450 - 560 780 - 900 17</p><p>The joints were made by overlapping of two sheets in the method 21 EN ISO 4063 (RSW), and as butt weld without a gap by laser welding. The hard welding regime of RSW was used with various values of welding current. Laser welding parameters were chosen ac- 1 [email protected], Technical University of Košice, Letná 9, 042 00 Košice, Slovakia 2 [email protected], Technical University in Košice, Letná 9, 042 00 Košice, Slovakia International Scientific Conference PRO-TECH-MA ’16 PROGRESSIVE TECHNOLOGIES AND MATERIALS P cording to the recommendations of IIW. The quality of welded joints was evaluated by visual control according to EN ISO 17637, static tension test STN 05 1122, structural ana- lysis of the joints on the light microscopy according to EN ISO 17639 were used. Minimum average value in resistance spot welded joints were Rm = 614 MPa in ma- terial DP 600 and Rm = 736 MPa in material DP 800. The average value of Rm = 620 MPa was measured in laser welded joints. The macrostructures of spot welded joints with the cavities in the middle of the weld are shown in Fig. 1 4. No internal defects were observed in laser welded joints – Fig. 5. </p><p>Fig. 1 Macrostructure of sample A - DP 600 Fig. 2 Macrostructure of sample B - DP 600</p><p>Fig. 3 Macrostructure of sample C - DP 800 Fig. 4 Macrostructure of sample D - DP 600</p><p>Fig. 5 Laser weld of DP 600</p><p>Acknowledgement</p><p>This work was supported by the Slovak Research and Development Agency under the contract No. APVV-0273-12. </p><p>References</p><p>[1] Marya, M. – Gayden, X. Q.: Development of Requirements for Resistance Spot Weld- ing Dual-Phase (DP600) Steels. In. Welding Journal, Nov. 2005. p. 172-182 [2] Zhang, H. – Senkara, J.: Resistance Welding: Fundamentals and Applications. Taylor&Francis Group, New York, 2006.</p>