Effect of Cu on the Precipitation of Deleterious Phases and the Mechanical Properties of 27Cr–7Ni Hyper Duplex Stainless Steels

Abstract

Cu addition to the base alloy reduces the total amount of deleterious phases such as chromium nitride and sigma and chi phases. In particular, Cu addition to the base alloy results in pronounced suppression of the amount of sigma phase whereas it slightly facilitates the precipitation of chromium nitride and chi phase along the phase boundaries and within ferrite grains. During the initial stage of aging, the preferential precipitation of chromium nitride and chi phase seems to be closely associated with the retardation of the precipitation of the sigma phase. The preferential precipitation of chromium nitride and the chi phase inhibits the nucleation and growth of the sigma phase by depleting the Cr adjacent to the chromium nitride particles and depleting the Mo and W adjacent to the chi phase. Thus, the addition of Cu to the base alloy reduces its embrittlement owing to the delayed precipitation of these deleterious phases.

Hyper Duplex Stainless Steels and Their Weldability

“…Artan alaşım içeriği ile birlikte SDSS'ler, sıcak işlem, ısıl işlem ve kaynak sırasında istenmeyen ikincil fazların (σ fazı, χ fazı ve Cr2N gibi) çökelmesine karşı daha duyarlı hale gelmişlerdir [14][15][16]. Bu ikincil fazlar, mekanik özelliklerin yanı sıra korozyon direncini de önemli ölçüde bozmaktadır [17,18]. Özellikle 850-900 o C'de çok kısa sürede oluşan σ fazı ve 830 o C'de oluşmaya başlayan χ fazı, malzemenin mekanik ve korozif dayanımını düşürmektedir [19].…”

Using kinetics to avoid sigma phase formation on hyper duplex stainless weld cladding

“…HDSS material was developed for tubing used in severely corrosive environments, such as heat exchangers. Therefore, studies have focused on evaluating the material's performance due to potential sigma phase formation [13][14][15]. Most research focused on base material artificially aged to induce intermetallic formation.…”

Modelling of Sigma Phase Dissolution by Solution Treatment in Super Duplex Stainless Steel

“…In later years, super duplex stainless steels, improved the corrosion resistance by increasing the amount of chromium, molybdenum, tungsten and nitrogen, have been developed. [1][2][3][4][5][6][7][8][9][10] However, the increase in the amount of these elements promotes the harmful intermetallic such as sigma phase. Therefore the prevention of this phase formation is an important subject in the welding, fabrication, and manufacturing process for practical use.…”