Heat treatment can be performed on ductile iron to increase strength, wear resistance, ductility, toughness, and/or improve machinability by controlling the matrix microstructure. In ferrous alloys, an intercritical heat treatment starts with partial austenitization in the intercritical region where ferrite and austenite are present. The amount of austenite depends on the chemistry of the alloy and the temperature. Continue reading
Electro-Slag Welding (ESW) of Titanium Alloys: Part Two
Due to its well-known superior strength to weight ratios, titanium has become a more and more critical material choice in aerospace applications which require heavy loading.
Due to titanium’s high chemical activity welding can be a real challenge but to overcome this, new technologies are being developed which uses the slag pool and argon to shield the weld site from interstitial element contamination. Continue reading
High Entropy Alloys: Part One
As technology increases to become more advanced and complex it puts an ever increasing demand on materials and their performance to keep pace.
Currently the application of high entropy alloys is restricted currently to protective coatings for high temperature components however it is a rapidly developing field which will soon diverge to cover materials which have high loading conditions coupled with extremely high temperatures. Continue reading
High Chromium Cast Iron: Part Two
High chromium cast irons (HCCI’s) exhibit very good mechanical properties and offer benefits for a range of manufacturing applications.
One of the main flexibilities exhibited is the possibility of HCCI’s to have different matrix structures in different treatment states whether it be austenite in casting state, pearlite in annealing state, martensite in quenching state, and tempered martensite in tempering state.
Brazing of Titanium and Titanium Alloys: Part One
Titanium and its alloys are well known for their high-strength and corrosion resistant properties but one distinct disadvantage is the challenges associated with bonding them with other materials. Brazing could provide a solution to these challenges since only the filler material is melted in the process therefore aiding dissimilar material bonding due to little or no effect on the two main subject materials. Continue reading
Low Phosphorus Partition Ratio Models
Phosphorus is a key impurity which affects predominantly the ductility of the finished product and so it is essential that methods are employed to keep the levels of phosphorus in a controlled and desirable range.
General control of phosphorus content is carried out by a plant specific dephosphorization process which is a model that is honed by continuous monitoring and adjustment.
A real steelmaking process involves many complex physical and chemical coupled phenomena such as oxidation, decarburization, dephosphorization, and slag formation.
Phosphorus is an element of representative impurities that should be kept as low as possible in conventional steel grades. Low phosphorus content steels are essential for steel applications where high ductility is required, such as thin sheets, deep drawn structures, pipelines, and automobile exteriors. Phosphorus’ ability to strengthen and embrittle ferrite imposes restrictions on the maximum phosphorus content for the aforementioned applications. The main source of phosphorus in steel is from the raw materials; thus, raw material selection is a way to maintain the phosphorus content within the desirable range.
In (BOF) oxygen steelmaking it is difficult to predict the distribution of phosphorus between slag and metal by direct application of models (listed in Table 1), even though a pseudo-steady state is usually attained between slag and metal towards the end of the blow. This is because under practical (shop-floor) conditions, besides the slag composition and temperature, the phosphorus distribution is found to depend also upon other parameters, such as slag mass, turndown carbon, initial phosphorus content of metal, intensity of bottom stirring, lance height, oxygen flow rate, addition scheme and timing of addition of fluxes and iron ore.
Therefore, each plant usually develops its own blowing practice and, on the basis of analysis of plant data, adapts a suitable model for control and prediction of phosphorus at tap. The selection of a control model is not a simple task. It is to be noted that the models listed in Table I do not explicitly take into account the effect of precipitation and/or dissolution of C2S on phosphorus distribution.
Table 1: Phosphorus Distribution log Lp Equations
The phosphorus [P] removal in BOS steelmaking is generally described by the ionic reaction shown in equation (1). From (1) it can be seen that a high [P] activity, high oxygen potential [O] and high basicity O2- all promote phosphorus removal. Also, [P] removal may also be represented by the simple molecular reaction, given in equation (2), allowing a Gibbs free energy to be calculated using equation (3).
1. Hassan A.I, Kotelnikov G. I, Semin A. E, Megahed G. M: Phosphorous behavior in Electric Arc Furnace steelmaking with the melting of high phosphorous content direct reduced iron, METAL 2015, Jun 3rd – 5th 2015, Brno, Czech Republic, EU;
2. D. Y. Shin, C. H. Wee, M. S. Kim, B. D. You, J. W. Han, S. O. Choi, D. J. Yun: Distribution Behavior of Vanadium and Phosphorus between Slag and Molten Steel, Metals and Materials International, Vol. 13, No. 2 (2007), p. 171-176;
3. A. N. Assis, M. A. Tayeb, S. Sridhar, R. J. Fruehan: Phosphorus Equilibrium Between Liquid Iron and CaO-SiO2-MgO-Al2O3-FeO-P2O5 Slag Part 1: Literature Review, Methodology, and BOF Slags, Metallurgical and Materials Transactions B, 2015, DOI: 10.1007/s11663-015-0408-9;
4. Deo. B, Halder. J, Snoijer. B, Overbosch. A, Boom. R.: Effect of MgO and Al2O3 variations in oxygen steelmaking (BOF) slag on slag morphology and phosphorus distribution, VII International Conference on Molten Slags Fluxes and Salts, The South African Institute of Mining and Metallurgy, 2004;
5. C.P.Manning, R.J.Fruehan: The rate of the phosphorus reaction between liquid iron and slag, Metallurgical and Materials Transactions B, Vol.44B, February 2013, p.37-44;
6. K. Kunisada, H. Iwai: Effects of CaO, MnO, and Al2O3, on Phosphorus Distribution between liquid iron and Na2O-MgO-FeO—SiO2 slags, Transactions ISIJ, Vol. 27, 1987, p.332-339;
7. P.B. Drain, B. J. Monaghan, G. Zhang, R. J. Longbottom, I. Murgas, M.W. Chapman: Development of a New Phosphorus Partition Relation for Australian Steelmakers, Paper no. 3397176, Chemeca 2016, 25 – 28 September 2016, Adelaide, Australia;
Date Published: Aug-2017
The Microforming Process: Part One
Micro parts are increasingly common where the requirement is to manufacture miniaturized and sometimes complex geometries in the submillimeter range. Some of the parts which can be fabricated using these processes include among others connector pins, miniature screws, microgears, microshafts. Continue reading
High Chromium Cast Iron: Part One
High chromium cast irons (HCCI’s) exhibit very good mechanical properties and offer benefits for a range of manufacturing applications. With carefully controlled heat treatment the cast iron properties can be further influenced to yield higher strength and ductility depending on the desired application. Continue reading
Biodegradable Magnesium Alloys: Part One
Biodegradable metals have an extremely important part to play in healthcare since they are designed to dissolve in vivo, and without eliciting a negative response in the host. Magnesium is a very useful candidates for such applications since it is already an essential trace element and has a very low thrombogenicity and well-known biocompatibility. Continue reading
Inert Gas Soldering
Inert gas soldering can be classified as a system which uses a controlled nitrogen blanket atmosphere and an entry vacuum oxygen/nitrogen exchange chamber. Some of the main benefits of using inert gas soldering include very low oxide formation, flexibility around flux selection and elimination of post cleaning requirements. Continue reading