Development of Ultrahigh Strength Low Alloy Steel through Electroslag Refining Process

Abstract

In this investigation, attempts are made to develop special steel by electroslag refining (ESR) process. The base alloy is prepared with a chemical composition of 0.28 % C, 1.0 % Mn, 1.0 % Mo, 0.35 % V, 4.2 % Cr with trace amount of S and P. This alloy displays yield strength of about 1 450 MPa in quenched-and-tempered condition. It is further attempted to increase the strength and toughness of the base alloy by addition of 1 to 3 % of nickel. As a result there is a substantial improvement of mechanical properties. 3 % nickel steel displays tensile strength of 1 758 MPa and yield strength of 1 542 MPa. The austenite grains are marginally reduced in nickel alloys. With the chemical composition of nickel alloys when about 0.07 % titanium is inoculated during ESR process, there is a deterioration of the tensile properties. In 3 % nickel alloy the effect is more prominent, which displays yield strength of 1 455 MPa along with the lowest value of elongation. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) studies indicate that the microstructures of un-inoculated nickel steel predominantly consist of tempered lath martensites. In titanium inoculated alloys the microstructures are mixture of retain austenite, bainite and martensites. Strengths are deteriorated possibly due to the inhomogenous distribution of carbon because of the formation of different phases and depletion of nickel due to the precipitation of the corresponding intermetallics of (Ni, Ti).KEY WORDS: electroslag refining; effect of alloying; ultrahigh strength steel; mechanical properties; microstructures.

Effect of Slag Composition on the Oxidation Kinetics of Alloying Elements during Electroslag Remelting of Stainless Steel: Part-2 Control of Titanium and Aluminum Content

“…After the temperature reaches 1 950 K (over 13 cm height of remelted ingot), both the slag S1 and S2 have the decreasing trend of lg( tend to increase according to the Eq. (2).…”

“…(7) to obtain the smooth curve. If assuming that the approximate average depth of the cylinder h r in metal pool is 15 mm, the depth of the arc h e is 40 mm, and the radius of crystallizer R C is 67 mm, the area and volume of the molten metal pool can be calculated as 141.03 cm 2 and 399.57 cm 3 , respectively. Thus, the change of the molten metal pool volume (V Pool ) with time can be determined by ellipse Eq.…”

“…Hou 3,4) studied the effect of slag on titanium, silicon and aluminum content in superalloy based on slag-metal interaction experiment in a resistant furnace, and illustrated that the CaO has large effect on the activities of Al 2 O 3 , TiO 2 and SiO 2 based on thermodynamics. Cheng 6) investigated the relationship between titanium and aluminum…”

“…1,2) Not only the reactions among Al + Al 2 O 3 , Si + SiO 2 and Ti + TiO 2 systems but also the oxidation reactions caused by ferrous oxide, influence the alloying element content, which makes the active alloying element control difficultly. Therefore, it is particularly urgent to provide reliable active alloying element in ingot control technology based on thermodynamic and kinetic analysis during the ESR process.…”

Effect of Slag Composition on the Oxidation Kinetics of Alloying Elements during Electroslag Remelting of Stainless Steel: Part-1 Mass-transfer Model

“…Electroslag remelting (ESR) is employed for producing special steels and alloys in consideration of its exclusively outstanding advantages, 1,2) such as effective removal of non-metallic inclusions, homogeneous composition and excellent solidification structure of final products. With the requirement for homogeneity of chemical composition along the height of ingot becoming increasingly strict, the details of the processes controlling solute redistribution base on mass transfer model should be understood quantitatively to lower the cost of experiment.…”