The mechanical properties of shipbuilding steel at low temperatures

U radu su ispitana mehanička svojstva austenitnog čelika AISI 316L, koji se koristi za izradu tankova LNG brodova. Temperatura ukapljenog prirodnog plina pri prijevozu iznosi -165°C , pa se na brodove postavljaju visoki zahtjevi u pogledu mehaničkih svojstava materijala strukturnih skladišnih prostora, kao i nestrukturnih tankova pri niskim temperaturama. Mehanička svojstva materijala zauzimanju posebno mjesto među ostalim fizikalnim i kemijskim svojstvima, a u ovom radu su statičkim vlačnim pokusom provedena ispitivanja brodograđevnog čelika pri niskim temperaturama, koje su postignute u komorama za temperiranje uzoraka, prema normama i Pravilima Hrvatskog registra brodova. Ispitivanja mehaničkih svojstava provedena su na temperaturama 22°C, -40°C, -80°C i -165°C, te su određene iznosi modula elastičnosti E, konvencionalne granice razvlačenja Rp0,2, vlačne čvrstoće Rm, deformacija em i istezljivosti A za svaku definiranu temperaturu. U radu je dan kratki opis brodova za prijevoz ukapljenog prirodnog plina, opisan je statički vlačni pokus te rad kidalice i laserskog ekstenzometra.In this paper are examined mechanical properties of astenitic steel AISI 316L, which used for tanks of LNG ships. The temperature of liquified natural gas in transport is -165°C, and that is why high requirements, in terms of mechnanical properties of tank materials at low temperatures, must be set on ships. Mechanical properties of materials are especially rated among order physical and chemical material properties, and this paper discusses the mechanical properties of austenitic steel, which are examined by implementing static tensile tests, at low temperature that were reached in the temperes samples chambers, foloowing norms and rules of Croatian Register of Shipping. Testing of mechanical properties were performed at temperatures 22°C, -40°C, -80°C and -165°C, and values of elasticity modulus E, conventional strech border Rp0,2, yield strength Rm, deformation Em and elongation A for each defined temperatures were determined. It also shortly describes types of ships for liquified natural gas transport, tensile test, work testing machine for tensile test and laser speckle extensometers