Microestrutura e propriedades mecânicas - parafusos de aço inoxidável duplex para âncora

Most buildings have been using anchor bolts

commonly for installing outdoor advertising structures. Anchor bolts

of common carbon steel are widely used and often installed

indiscriminately by inadequate installation standards. In the area

where strong winds frequently blow, falling accidents of outdoor

advertising structures can occur and cause a serious disaster, which is

very dangerous and to be prevented. In this regard, the development of

high-performance anchor bolts is urgently required. In the present

study, 25Cr-8Ni-1.5Si-1Mn-0.4C alloy was produced by traditional

vacuum induction melting (VIM) for the application of anchor bolt.

The alloy composition is revealed as a duplex microstructure from

thermodynamic phase analysis by FactSage® and confirmed by

metallographic experiment. Addition of Nitrogen to the alloy was

found to reduce the ferritic phase domain and significantly increase the

hardness and the tensile strength. Microstructure observation revealed

mixed structure of austenite and ferrite with fine carbide distributed

along the grain and phase boundaries.

Duplex stainless steels have a mixed structure of bcc ferrite

and fcc austenite. The exact amount of each phase is a function

of composition and heat treatment. Most alloys are designed to

contain about equal amounts of each phase in the annealed

condition. The principal alloying elements are chromium and

nickel, but nitrogen, molybdenum, copper, silicon, and tungsten

may be added to control structural balance and to impart certain

corrosion-resistance characteristics. The specific advantages

offered by duplex stainless steels over conventional 300-series

stainless steels are strength (about twice that of austenitic

stainless steels), chloride stress corrosion cracking (SCC)

resistance, and pitting corrosion resistance. [2] These materials

are used in the intermediate temperature range (about -60 to

300oC) where resistance to acids and aqueous chlorides is

required. Duplex stainless steels have found widespread use in a

range of industries, particularly the oil and gas, petrochemical,

pulp and paper, and pollution control industries