A. Yu. Kaletin

Enhancement of impact toughness of structural steels upon formation of carbide-free bainite

Mechanical properties of chromium-nickel-molybdenum steels with the carbon contents of 0.1 to 0.4% after slow continuous cooling in the bainitic range have been determined, and the structure has been investigated. It has been shown that, at a carbon content of about 0.10–0.15% and upon additional alloying with silicon and aluminum after such a heat treatment, in steels, the structure of carbide-free bainite is formed and a substantial enhancement in the impact toughness is observed compared to bainite containing carbide precipitates. The enhancement in the level of toughness is related to the presence in carbide-free bainite of an appreciable amount of retained austenite enriched with carbon.

Phase transformations and structure of Ni–Mn–In alloys with varying ratio Ni/Mn

The fine structure of Ni–Mn–In alloys has been studied when manganese atoms are substituted for nickel atoms in an annealing state. The concentration dependence of the critical temperatures and the structures of the alloys have been discussed. It has been found that, as manganese atoms replace nickel atoms, the structure after annealing is changed from a two-phase (L21 + martensite) to single-phase L21 structure. The martensitic transformation in Ni47Mn42In11 alloy is accompanied by the formation of modulated 14M martensite.

Evolution of the structure and properties of silicon steels in the austenite-bainite phase transition

The specific features of the structure of low-alloy silicon steels have been studied after the phase transition in the temperature range of the bainite transformation. It has been shown that the bainite transformation exhibits a pronounced two-stage character. At the first stage, the completely carbide-free bainite is formed, which contains up to 45% of residual austenite that is stable during deep cooling. The mechanical properties are studied as functions of the morphology and the carbon inhomogeneity of phases formed during the isothermal transformation in the bainite region.

Effect of thermal cycling on structure and properties of Ni–Mn–In-based alloys

The results of investigations of the structure and properties of ternary alloys Ni47–xMn42 + xIn11 (0 ≤ x ≤ 2) after thermal cycling are presented. It has been shown that multiple cycles of heating and deep cooling result in a change in the shape of grain boundaries and an increase in microhardness. Thermal cycling does not cause any significant changes in the magnetic susceptibility of the investigated alloys.

On the role of retained austenite in the structure of alloyed steels and the effect of external factors

We present a review of the results of the effect of external factors on the amount of austenite retained in steels and alloys. Possible methods of reducing the amount of retained austenite via the action of cold treatment, magnetic field, and plastic deformation, as well as the question of the effect of retained austenite on the mechanical properties of commercial and model steels and alloys, — have been discussed and analyzed.

Effect of cooling rate on the amount of retained austenite upon bainitic transformations

We have presented a review of the results of investigating the effect of the cooling conditions and heat treatment on the amount of retained austenite and mechanical properties of commercial steels. Possible methods of obtaining enhanced amount of retained austenite due to the stabilization effect, bainitic transformation, and quenching from the intercritical temperature range have been discussed and analyzed.

Phase transitions and thermal expansion in Ni 51– x Mn 36 + x Sn 13 alloys

Thermal expansion and structural and magnetic phase transitions in alloys of the Ni–Mn–Sn system have been investigated. The spontaneous martensitic transformation in Ni51–xMn36 + xSn13 (0 ≤ x ≤ 3) alloys is found to be accompanied by high jumps in the temperature dependences of the linear thermal expansion. The relative change in the linear sizes of these alloys at the martensitic transformation is ~1.5 × 10–3. There are no anomalies in the magnetic-ordering temperature range in the temperature dependences of the coefficient of linear thermal expansion. The differences in the behavior of linear thermal expansion at the martensitic transformation in Ni51–xMn36 + xSn13 (0 ≤ x ≤ 3) and Ni47Mn40Sn13(x = 4) alloys have been established.

Crystallographic specific features of the martensitic structure of Ni 47 Mn 42 In 11 alloy

The structure of Ni47Mn42In11 alloy after annealing has been investigated. It is shown that the martensitic transformation in Ni47Mn42In11 alloy upon cooling is accompanied by the formation of 14M modulated martensite. Crystallographic analysis of the martensite structure has been performed. The orientation relationships between the high-temperature austenitic phase and martensite and habit planes of the martensite plates have been determined.

Formation of Structure of Lower Carbide-Free Bainite Due to Isothermal Treatment of Steels of Types Kh3G3MFS and KhN3MFS

The principal possibility of formation of a structure of lower carbide-free bainite under long-term holds is shown for steels of two alloying systems Kh3G3MFS and KhN3MFS containing 0.25 – 0.30 and 0.40 – 0.45% carbon. Dilatometric analysis of the phase transformations is performed and the bainitic range of the diagrams of decomposition of supercooled austenite is plotted. The structure is studied by the methods of light, scanning electron, and transmission microscopy.

Alloying and heat treatment of steels with bainitic structure

Conclusions1.To ensure a good complex of mechanical properties, the alloying of bainitic steels has to be carried out in such a way that isothermal hardening is accopanied by the formation of carbidefree (lower) bainite with stable residual austen2.Alloying steels with silicon and aluminum, and also reducing the carbon content extends the time up to the onset of carbide formation in the bainite reaction and provides the possibility of obtaining carbidefree bainite with carbon enriched stable residual austenite.3.Hardened steels whose structure contains carbidefree bainite of different morphology and martensite have to be tempered at 300°C for 1–3 h. Such tempering entails additional disintegration of residual austenite with out carbide segregation and its enrichment with carbon; this enhances the impact toughness of the steel.