Effect of Carbon and Titanium Variations in Fe‐Based Heat‐Resistant Superalloy A286 on TiC and η Phase Formation

Abstract

A286 super austenitic stainless steel is a kind of superalloy containing large amounts of Ni and Cr and small amounts of Ti (1-3%), C (0-0.06%), Al (0.1-0.3%), Mn (0.5-1.5%), and Co (0-0.5). [1] Similar to Ni-based superalloys in microstructure, this alloy is strengthened by age-hardening. As a heat-resistant superalloy, it has been designed for applications requiring sufficiently high creep fracture strength and excellent fatigue resistance at temperatures as high as 700 C. Typical areas of applications include aircraft engines, turbine wheels and blades, fasteners and springs, etc. [2][3][4][5][6] In this alloy, eta (η) Ni 3 Ti hcp phase is a stable phase which is formed from the dissolution of γ 0 phase [7][8][9] at aging temperatures in the range of 600 850 C. [10][11][12][13] Some researchers stated that during prolonged hotworking above 720 C, η phase can easily precipitate at grain boundaries from the fcc austenitic matrix, [14] which can have a direct influence on the creep behavior of the alloys. [15,16] Depending on the chemical composition and heat treatment conditions, η and carbide phases precipitate simultaneously or sequentially in this alloy system.Many efforts have been made by researchers to find a suitable composition which can enhance the strengthening mechanism by proper control of eta (η) phases up to some extent at high temperature by the addition of alloying elements. Finding a suitable ratio of constituent elements, especially Ti and Al, is required to give the highest strengthening effect at higher temperature works for a long time. [8][9][10][11][12][13][15][16][17][18] Moreover, it is well known that the addition of C is required in some alloys to enhance hardness, [19] but elemental C can cause brittleness during composition setting. If C and Ti are added in a certain ratio, they can combine with each other to form into TiC, which acts as a reinforcement ceramic particles and has a beneficial effect by enhancing the strengthening mechanism in alloys. [16,17] Strengthening mechanism by TiC reinforcement particles has been widely studied in different stainless steel alloys, especially 300 and 400 series, [20,21] but not well studied in A286 heatresistant alloys.To enhance the strengthening mechanism at sufficient high temperatures, TiC particles are widely used in the austenite matrix as a reinforcement, [16,17] which can limit the formation of chromium-rich M 23 C 6 -type carbide at grain boundaries, can prevent intergranular stress corrosion, and can increase the tensile and creep strength at both high and low temperatures.

Carbon and Titanium Effect on Tensile Behavior of Aged A286 Nickel-Iron Based Superalloy

“…% Cr austenitic alloy containing Ti, Al and other minor alloying additives [1,2]. This nickel-iron base superalloy is widely used in aviation industry as fasteners, gas turbine blades, shaft of jet engines and other similar applications due to their good thermal resistance, superior mechanical properties, and ease of fabrication [1][2][3][4]. Working at high temperature for long time and severe conditions of constant stresses can degrade microstructural and creep behavior of this alloy [5].…”