Partial Transformation Of Austenite Research Articles

Effect of Cr, Mo and Al on Microstructure, Abrasive Wear and Corrosion Resistance of Ni-Mn-Cu Cast Iron.

Results of a study on influence of Cr, Mo and Al on the microstructure, abrasive wear and corrosion resistance of Ni-Mn-Cu cast iron in the as-cast and heat-treated conditions are presented. Because of the chilling effect of first two elements (tendency to create hard spots), graphitising Al was added to the alloys, with the highest concentration of Cr and Mo. All castings in the as-cast condition showed an austenitic matrix, guaranteeing good machinability. Heat treatment of raw castings, consisting in annealing at 500 °C for 4 h, resulted in partial transformation of austenite. As a result the carbon-supersaturated acicular ferrite, morphologically similar to bainitic ferrite was formed. The degree of this transformation increased with increasing concentrations of Cr and Mo, which successively decreased the thermodynamic stability of austenite. A change of matrix structure made it possible to significantly increase hardness and abrasive-wear resistance of castings. The largest increment of hardness and abrasion resistance was demonstrated by the castings with the highest total concentration of Cr and Mo with an addition of 0.4% Al. Introduction of Cr and Mo also resulted in an increase of corrosion resistance. In the heat-treated specimens, increasing the concentration of Cr and Mo resulted in a successive decrease of the depth of corrosion pits, with an increase in their number at the same time. This is very favourable from the viewpoint of corrosion resistance.

52nd Hatfield Memorial Lecture Large chunks of very strong steel

Most new materials are introduced by selectively comparing their properties against those of steels. Steels set this standard because iron and its alloys have so much potential that new concepts are discovered and implemented with notorious regularity. In this 52nd Hatfield Memorial Lecture, I describe a remarkably beautiful microstructure consisting of slender crystals of ferrite, whose controlling scale compares well with that of carbon nanotubes. The crystals are generated by the partial transformation of austenite, resulting in an extraordinary combination of strength, hardness and toughness. All this is in bulk steel without the use of expensive alloying elements. We now have a strong alloy of iron, which can be used for making items that are large in all three dimensions, which can be made without the need for mechanical processing or rapid cooling and is cheap to produce and apply.

Bulk nanocrystalline steel

Most new materials are introduced by selectively comparing their properties against those of steels. Steels set this standard because iron and its alloys have so much potential that new concepts are discovered and implemented with notorious regularity. In this 52nd Hatfield Memorial Lecture, a remarkably beautiful microstructure consisting of slender crystals of ferrite, whose controlling scale compares well with that of carbon nanotubes, is described. The crystals are generated by the partial transformation of austenite, resulting in an extraordinary combination of strength, hardness and toughness. All this in bulk steel without the use of expensive alloying elements. We now have a strong alloy of iron, which can be used for making items that are large in all three dimensions, which can be made without the need for mechanical processing or rapid cooling and which is cheap to produce and apply.

Formation of the structure and properties of Kh12M steel in partial bainitic decomposition of austenite

1. To improve the mechanical properties of Kh12M steel, a stepped heat treatment including partial transformation of austenite in the bainitic transformation range for the purpose of obtaining structures of primary and secondary bainite in the hardened structure is proposed. 2. As the result of stepped heat treatment using the optimum cycles an α-solid solution with a high degree of homogeneity is formed in the structure of Kh12M steel after tempering. 3. To evaluate the effectiveness of the use of partial transformation of austenite in hardening heat treatment of Kh12M steel it is desirable to use a structural criterion taking into consideration the degree of homogeneity of the α-solid solution.

Structure and properties of die steels of the 5Kh2MF type

1. The high heat resistance (600–620°) of die steels in combination with good strength (σ0.2=135–140 kg/mm2) and toughness (an=4–5 kg-m/cm2) throught the section of large forgings (500×500 mm) after heat treatment is ensured by combined alloying within the following limits: 0.4–0.5% C, 0.5–1.0% Mn, 0.2–0.5% Si, 1.5–2.0% Cr, 0.8–1.2% Mo, 1.5–2.5% Ni, and 0.3–0.5% V. 2. In its combination of basic properties (heat resistance, strength, and toughness of large forgings), steel of the 5Kh2N2MF type surpasses standard steels 5KhNM (5KhNV) and 4Kh5V2FS (4Kh5MFS), and can be recommended for large heavily loaded drop-forging and pressing dies for hot working. 3. The partial transformation of austenite in steels of the 5Kh2MF type in the intermediate range during continuous cooling is accompanied by substantial reduction of the secondary hardness and toughness, and the highest secondary hardening occurs at higher tempering temperatures (580–600°).