A dilatometric study of the phase transformations in 300 and 350 maraging steels during continuous heating rates

Abstract

The influences of the chemical composition and heating rate have been studied in 300 and 350 maraging steels using dilatometry. For these tests, heating was carried out with heating rates of 1, 10 and 28 °C/s. The results have shown that the precipitation mechanism for both materials in the studied range is by lattice diffusion. Furthermore, Co and Ti contents influence strongly the precipitation. The lattice diffusion mechanism in the martensite reversion is influenced by Ni and Co contents and heating rate. For small heating rates ( ~1 °C/s) this mechanism prevails in the 300 maraging steel while for the 350 maraging steel has a minor importance. The mechanism of martensite reversion for 350 maraging steel in the studied range is mainly by shear mechanism. For higher heating rates (~28 ºC/s) the shear mechanism prevails in both maraging steels.

Microstructural Analysis of Co-Free Maraging Steel Aged

“…Steel with martensitic structure, when subjected to a heat treatment at a constant temperature, suffers a growth of intermetallic precipitates uniformly in the matrix (Carvalho et al, 2013). The precipitate size is a contributing factor to the increased mechanical resistance of maraging steels.…”

“…The alloying elements of maraging steel, such as molybdenum, titanium, nickel, cobalt, aluminum, and others, have a great influence on the mechanical properties of this alloy, in other words, they are responsible by precipitates hardeners (Carvalho et al, 2013). However, recent studies (Hu et al, 2008;Leitner et al, 2011;Mahmoudi et al, 2011;Mahmudi et al, 2011;Nili-Ahmadabadi, 2008;Schnitzer et al, 2010;Sha et al, 2013) are being conducted in maraging steels without cobalt addition, in order to reduce the production costs of this alloy.…”

“…Maraging steels are being investigated because of the possibility of replacing the commercial alloy steels, 300M and 4340 for example, widely used in aeronautical industry (Carvalho et al, 2013). Thus, this study aims to examine the effect of aging heat treatment in non-commercial maraging steel (Co-free), in order to compare it to the 300M and 4340 steels.…”

Short-term Creep Properties and Fracture Surface of 18 Ni (300) Maraging Steel Plasma Nitrided

“…The literature reports an A s (Austenite formation start) of 623 ºC and A f (Austenite formation finish) of 801 ºC, but exposure at temperatures even below A s can produces different amount of reverted austenite. The reason is that the martensite that is formed during solution treatment is metastable and the system decomposes to the equilibrium austenite and ferrite structures via diffusioncontrolled reactions 18,[20][21][22] . Specialized applications of the steel occasionally demand short-time exposures to high temperatures and it is desirable to have data on the creep behavior of the material during such service conditions.…”

Um estudo cinético da precipitação de compostos intermetálicos e da reversão da martensita em aços maraging 300 e 350.

“…A figura 38 mostra também que o comportamento da variação do tamanho da amostra na dilatometria, com relação ao seu tamanho durante o ciclo de aquecimento e resfriamento, permite a identificação de três transformações de fase: a precipitação de compostos intermetálicos, reversão da martensita e a transformação martensítica (CARVALHO et al, 2013). Além da obtenção das temperaturas de início e de fim das transformações por desvio da linearidade da variação do comprimento da amostra com a temperatura, a dilatometria permite também outras informações da precipitação de compostos intermetálicos e da reversão da martensita por meio da derivada da variação do comprimento da amostra em função da temperatura, como apresentado na figura 39.…”