165 15 th International Research/Expert Conference ”Trends in the Development of Machinery and Associated Technology” TMT 2011, Prague, Czech Republic, 12-18 September 2011 CONTRIBUTION TO THE DEVELOPMENT OF HIGH-STRENGTH STEEL THROUGH RESEARCH OF THE RELATIONSHIP BETWEEN MICROSTRUCTURE AND PROPERTIES Milenko Rimac Mirsada Oruč Omer Beganović Univerzity of Zenica – Institute of Metalurgy „Kemal Kapetanović“ Zenica Travnička cesta 7, Zenica Bosnia and Herzegovina Sulejman Muhamedagić Univerzity of Zenica – Faculty of Metallurgy and Materials Science Zenica Travnička cesta 1, Zenica Bosnia and Herzegovina ABSTRACT In this paper some results of the research related to high-strength Maraging steel 18Ni (250) and precipitation-hardening stainless steel 17-7 PH are presented. The research identified some mechanisms that take place in the microstructure depending on the heat treatment, which have direct affect on mechanical properties and exploitation characteristic. Particularly it was analyzed the reduction of ductility in Maraging steel 18Ni (250). The research has performed on experimental heats produced on pilot plants of the Institute. The static and dynamic mechanical properties were tested. Microstructural characteristics were investigated on the light, and on scanning and transmission electronic microscope. Keywords: high-strenght steels, stainless steels, mechanical properties, microstructure 1. INTRODUCTION Aviation and automotive industry requiring high-strength materials with sufficient ductility initiated development of Maraging and precipitation-hardening stainless steel. These steels have certain advantages in making structural components such as hardening without quenching, and the absence of distortion and decarburization. Generally, the tensile strength of these steels is satisfactory, but it can not be said for the ductile properties. Therefore, the improvement of their ductility is still the subject of very extensive research. In this paper the microstructural factors having affects on ductile properties at Maraging and precipitation-hardening stainless steels are analyzed. 2. HIHG-STRENGTH STEELS Maraging steels are high-strength steels in which relatively soft martensite are strengthened in the process of aging by the formation of fine precipitates of high density. The precipitates are intermetallic compounds of nickel with molybdenum, titanium and aluminum, which are formed depending on the type of steel. Precipitation-hardening stainless steels are high-alloyed steels that are strengthened by controlled transformation austenite in matrensite and by subsequent precipitation of intermetallic compounds NiAl. Maraging steel 18Ni (250) and precipitation-hardening stainless steels 17-7 PH (UNS S17700) have the widest commercial application. The chemical compositions and mechanical properties of these steels produced for research purposes are given in Table 1 [1].