Sensitivity to Mn content mechanical properties of phase composition of ADI

The effect of manganese content on the phase composition and mechanical properties was studied on ADI materials that are isothermally quenchеd at different temperatures. ADI samples with Mn content of 0.78% and 0.24% were analyzed. The final structure of the cast iron was created by austenitizing heating at 900 ° C for 30 minutes. and subsequent isothermal quenching in liquid tin at temperatures of 310, 330, 350, 380 ° C for samples with high manganese content and at 350, 370 ° C for samples with low content. It is shown that increasing the manganese content increases the amount of residual austenite under the same quenching conditions. This enhances the positive role of the TRIP effect on the hardening processes. In particular, ADI with a high content of Mn show a higher rate of strengthening at the initial region of loading diagram, higher hardness and increased damping capacity. Instead, due to the embrittlement action of manganese, such materials have lower mechanical characteristics, which determined fracture moment. It was found that for the same quenching conditions, deformation to fracture and toughness are reduced by half on samples with higher manganese content. The negative effect of manganese on the fatigue is less significant, because the embrittlement action is compensated by phase transformations in the crack head, which inhibits its spread under cyclic loading. Due to the fact that manganese enhances the positive role of the TRIP effect but decrease fracture résistance, it is proposed to use ADI materials with high Mn content in products that operate in conditions of wear but are not subject to extreme stress. Keywords: ADI materials, manganese alloying, isothermal hardening, TRIP effect, retained austenite, strengthening, hardness. damping capacity.

Effect of Hot Working Processes on Microstructure and Mechanical Properties of Pipeline Steel

The microstructure and microhardness of X70 pipeline steel were investigated after conducting different processing routes. The microstructure was characterized using optical and electron microscopy. Scanning electron microscopy equipped with electron backscattered diffraction (EBSD) and transmission electron microscopy techniques were applied for investigation of different thermal processing treatment conditions. Mechanical properties were characterized by a microhardness tester. The results show that the microstructure mainly consists of granular bainite, acicular ferrite and a small amount of M/A constituents under hot rolling states. There are many dislocations inside the acicular ferrite. The thermal simulation experiments show that the microstructure becomes homogeneous with the increase in cooling rate. The acicular ferrite morphology becomes fine and uniform, and the content of M/A constituents increases at the same compression amount. The compression gives rise to the accumulated strain and stored energy, which accelerate the transformation of acicular ferrite and refine the microstructure of the pipeline steel. The microhardness rises with the increase in deformation ratio and cooling rate. The microstructure of the pipeline steel subjected to the isothermal quenching process is ultrafine ferrite and M/A islands. When the isothermal quenching temperature reaches 550 °C, a small amount of upper bainite appears in the microstructure. With the increase in isothermal quenching temperature, the microhardness decreases. Acicular ferrite is a better candidate microstructure than ultrafine ferrite for the pipeline steels.

Influence of modes of thermal hardening and the subsequent cryogenic processing on structure and properties of steel 38Ni3CrMoV

For the production of various machine-building products - rolling rolls, parts of power equipment, piercing mandrels - complex alloy steels containing chromium and a significant number of other deficient alloying elements (nickel, vanadium, molybdenum) type 38Ni3CrMoV are used. The paper presents the results of research on the influence of modes of hardening and subsequent cryogenic treatment on the parameters of the structure, hardness and wear resistance of this steel. Visible changes in the microstructure of thermally improved steel samples during cryogenic treatment were not found, which can be explained by the high thermodynamic stability of the sorbitol structure and the practical absence of residual austenite due to its decomposition during high tempering. It is shown that cryogenic treatment of thermally improved 38Ni3CrMoV steel contributes to an increase in the hardness, toughness and wear resistance this steel (~3.8 %). In this case, there is a slight increase in the parameter and magnitude of microstresses of the crystal lattice, an increase in the density of dislocations due to the removal of thermal stresses. To obtain a multiphase structure of 38Ni3CrMoV steel with retained austenite, isothermal quenching from the γ - α region has been proposed. The use of cryogenic treatment for the experimental mode of hardening of 38Ni3CrMoV steel samples promotes the transformation of retained austenite in the final structure of the samples into martensite with a significant increase in the microhardness of its structural components at the 22.3 %. The experimental hardening mode + cryogenic treatment provides a significant increase in the hardness and wear resistance of 38Ni3CrMoV steel at the 21.6 % while ensuring a certain level of its impact toughness (more than 4 J/cm2) and can be recommended for the implementation of the technology of differentiated hardening of large-sized products made of 38Ni3CrMoV steel. Keywords: steel, structure, hardness, wear resistance, isothermal hardening, cryogenic treatment.

Structure and properties forming in ductile iron during isothermal hardening using ultrasound

The paper considers the possibility of intensifying isothermal holding processes during quenching of high-strength cast irons by using an external source of physical impact in the form of ultrasonic waves. For experimental evaluation of this effect in the laboratory of MiAM of the Physical-Technical Institute of the National Academy of Sciences of Belarus, prototypes of highstrength cast irons were cast in an ISV 0.004 crucible induction furnace. A mixture of NaNO2 and KNO3 salts in a 1:1 ratio was used as a liquid cooling medium during quenching. Ultrasonic treatment of the salt melt during the cooling of the samples was carried out using an UZG-20–15 generator in cooperation with the ITA of NAS of Belarus. The mechanical properties and structure of the treated cast irons were determined both in the cast state and after isothermal quenching.To study the effect of ultrasonic treatment of the quenching bath on the formation of the structure and properties of highstrength cast irons during isothermal quenching, a number of comparative experiments were carried out, consisting in cooling the samples from 910 °C to 350 °C with and without the use of dynamic waves to the bath. With the help of metallographic analysis, measurements of hardness and friction coefficient, the beneficial effect of ultrasonic treatment of the cooling medium on the structure and properties is shown, which is reflected in an increase in the uniformity of the distribution of hardness over the cross section of cast iron and in its wear resistance, as well as a reduction in the isothermal holding time by up to two times.