Predicting Delta Ferrite Content in Stainless Steel Castings

Abstract

The distribution of delta ferrite fraction was measured with the magnetic method in specimens of different stainless steel compositions cast by the investment casting (lost wax) process. Ferrite fraction measurements published in the literature for stainless steel cast samples were added to the present work data, enabling an extensive analysis about practical methods to calculate delta ferrite fractions in stainless steel castings. Nineteen different versions of practical methods were formed using Schaeffler, DeLong, and Siewert diagrams and the nickel and chromium equivalent indexes suggested by several authors. These methods were evaluated by a detailed statistical analysis, showing that the Siewert diagram, including its equivalent indexes and iso-ferrite lines, gives the lowest relative errors between calculated and measured delta ferrite fractions. Although originally created for stainless steel welds, this diagram gives relative errors lower than those for the current ASTM standard method (800/A 800M-01), developed to predict ferrite fractions in stainless steel castings. Practical methods originated from a combination of different chromium/nickel equivalent indexes and the iso-ferrite lines from Schaeffler diagram give the lowest relative errors when compared with combinations using other iso-ferrite line diagrams. For the samples cast in the present work, an increase in cooling rate from 0.78 to 2.7 K/s caused a decrease in the delta ferrite fraction, but a statistical hypothesis test revealed that this effect is significant in only 50% of the samples that have ferrite in their microstructures.

Effects of Nitrogen Gas Pressure on the Solidification Parameters and As-cast Microstructure Revolution during Pressurized Electroslag Remelting AISI 304 Stainless Steel

“…Martorano et al proposed that an increase in cooling rate caused a decrease in the content of residual ferrite. 36) The increase of nitrogen gas pressure not only affects the cooling rate in ingots, but also affects the nitrogen content in ingots. The content of residual ferrite firstly decreased and then increased with the increase of nitrogen gas pressure from 0.1 to 1.2 MPa.…”

Determinação Da Quantidade De Austenita Revertida Em Aço Maraging 350 Envelhecido

“…Essa metodologia foi a mesma empregada por Pardal e coautores [18] para determinar a fração volumétrica para um aço maraging 300.Os resultados obtidos por ambos os métodos foram comparados. A ferritoscopia geralmente é usada para medir a quantidade de fase ferromagnética, especialmente em aços inoxidáveis austeníticos, duplex e superduplex [30,31]. As medidas de ferritoscopia são baseadas no método da indução magnética [31] e apresentam uma similaridade de funcionamento com o instrumento usado por Habiby e coautores [22] para a detecção da austenita em um aço maraging 350.…”

Kinetics modeling of delta-ferrite formation and retainment during casting of supermartensitic stainless steel

“…Addition of Ni can largely suppress the retainment of δferrite but it is expensive and it potentially shifts the martensite start (Ms) temperature below room temperature. Previous research demonstrated the influence of the chemical composition and cooling-rate on the retainment of δ-ferrite [20][21][22].…”

“…The phase distribution after solidification can be estimated by a variety of available models, such as the lever rule, the Scheil Model [23] and empirical models such as the Schaeffler diagram [21]. These models are easy to apply, but oversimplify the mechanisms during solidification and cooling to different degrees.…”