Recrystallization of "Х18Н10Т" austenitic steel under fractional hot deformation

The recrystallization of 12Х18Н10Т steel of the austenitic class is investigated under conditions of fractional hot deformation during technological testing simulating the process of manufacturing stepped billets. The kinetics of recrystallization stages is determined. Recommendations are given for the modes of hot fractional deformation during forging of billets. Keywords: austenitic steel, recrystallization, fractional hot deformation, unevenness of the deformed state, metallographic analysis, grain size. [email protected]

STUDY OF CHANGE IN WEAR RESISTANCE OF STAINLESS STEEL SURFACE OBTAINED BY LASER PULSE ALLOYING IN THE COATING LAYER

The paper describes an experimental study of laser pulsed modification of the surface of stainless chromium-nickel steel of the austenitic class 12Cr18Ni10T with a graphite coating previously applied to it. The microhardness of the treated surface and its dependence on the modes of laser radiation were determined. The abrasion method was used to study the change in the wear resistance of the modified layer and the possibility of its increase. For a quantitative assessment of the surface resistance to wear, a gravimetric analysis of samples subjected to ball abrasion was carried out, the results of which are fully consistent with the calculation of the dimensionless wear resistance index. It was found that the value of the microhardness is largely influenced by the voltage of the pulses. Thus, the highest microhardness indicators were observed during processing by laser pulses in the voltage ranges of 250-280 V and 340-440 V and take values of 5-6 GPa and 4-5 GPa, respectively. A comprehensive study of abrasion resistance, including the calculation of a dimensionless wear resistance index and an analysis of the weight loss of steel samples as a result of the test, showed that, to the greatest extent, the surface hardening effect is characteristic of samples subjected to treatment with laser pulses focused into a spot 1 mm in diameter at a pulse voltage of range 300-400 V.

COMPARATIVE ANALYSIS OF THE INFLUENCE OF THE COMPOSITION OF THE ALLOYING COVERING ON THE CHANGE IN THE STRUCTURE AND MICROHARDNESS OF STAINLESS STEEL 12KH18N10T

The article is devoted to the experimental analysis of the influence of the process of laser pulsed alloying in a layer of alloying mixture on the qualitative and physical and mechanical characteristics of the modified surface of stainless chromium-nickel steel of the austenitic class 12Cr18Ni10T. It was found that the use of graphite paste as an alloying compound leads to a significant increase in microhardness, a change in micromorphology, and the formation of a heat hardening zone in the near-surface layer of steel. The smoothing of the boundaries of structural changes is revealed and the effect of surface hardening is determined when a finely dispersed powder of titanium dioxide (anatase) is added to the alloying coating. According to the data obtained, a comparative analysis of the dependence of the microhardness of the modified surface on the voltage of the pump lamp and the diameter of the laser pulse spot is carried out. The maximum microhardness value, equal to 9,56 GPa, was achieved as a result of laser processing of a series of samples, where graphite paste was applied as a preliminary surface preparation. Rational technological modes of laser modification of the surface of 12Cr18Ni10T steel that have previously undergone abrasive blasting, modes of laser pulsed alloying in a layer of graphite coating and laser pulsed alloying of steel in a layer of coating consisting of graphite paste and anatase powder in a ratio of 4:1, respectively, are recommended.

Effect of Cavitation Erosion Wear, Vibration Tumbling, and Heat Treatment on Additively Manufactured Surface Quality and Properties

The paper is devoted to researching various post-processing methods that affect surface quality, physical properties, and mechanical properties of laser additively manufactured steel parts. The samples made of two types of anticorrosion steels—20kH13 (DIN 1.4021, X20Cr13, AISI 420) and 12kH18N9T (DIN 1.4541, X10CrNiTi18-10, AISI 321) steels—of martensitic and austenitic class were subjected to cavitation abrasive finishing and vibration tumbling. The roughness parameter Ra was reduced by 4.2 times for the 20kH13 (X20Cr13) sample by cavitation-abrasive finishing when the roughness parameter Ra for 12kH18N9T (X10CrNiTi18-10) sample was reduced by 2.8 times by vibratory tumbling. The factors of cavitation-abrasive finishing were quantitatively evaluated and mathematically supported. The samples after low tempering at 240 °C in air, at 680 °C in oil, and annealing at 760 °C in air were compared with cast samples after quenching at 1030 °C and tempering at 240 °C in air, 680 °C in oil. It was shown that the strength characteristics increased by ~15% for 20kH13 (X20Cr13) steel and ~20% for 12kH18N9T (X10CrNiTi18-10) steel than for traditionally heat-treated cast samples. The wear resistance of 20kH13 (X20Cr13) steel during abrasive wear correlated with measured hardness and decreased with an increase in tempering temperatures.

Cold resistance of new casting Cr – Mn – Ni – Mo – N steel with 0.5 % of N. Part. 1

The authors have studied cold resistance of thelaboratorymetal of a new austenitic grade of nitrogen-containing casting steel (21 – 22) Cr – 15Mn – 8Ni – 1.5Mo – V (Russian grade 5Kh21АG15N8МFL) with nitrogen content of 0.5 % and yield strength of ~400 MPa. The temperature dependence of impact toughness was constructed in the range +20 ... –160 °C and it was shown that the steel is characterized by a wide temperature range of the viscous-brittle transition with T DBT = –75 °C, at which KCV = 120 ± 10 J/cm2. Comparison material – industrial, centrifugally cast 18Cr – 10Ni steel (grade 12Kh18N10-CC) has such a KCV level at +20 °C. It is not prone to viscous-brittle transition, its impact strength decreases more gently and at temperatures lower than –80 °C and its KCV level is higher than that of nitrous steel. However, in the entire range of climatic temperatures, nitrous casting steel with 0.5 % of N exceeds its impact strength. The studied steels have residual δ-ferrite in the cast structure in an amount of up to ~10 % in Cr– Ni industrial steel and a smaller amount in laboratory nitrous steel. It is enriched by chromium, up to 26 and 34 wt. % respectively, and contains ~14 % of Mn in nitrogen steel. Presence of Mn does not affect the nature of fractures at climatic temperatures. However, δ-ferrite of nitrous steel at –160 °C is beyond the cold brittle threshold. Therefore, its fracture obtained at this temperature contains numerous cracks in δ-ferrite crystals. The critical fragility temperature below which this material is not recommended for use is Тк ≈ –110 °С; it was determined by the criterion method. It corresponds to a level of KCV of 68 – 83 J/cm2, higher than the level of KCU at +20 °C, allowed by the standard of the Russian Federation for castings from austenitic class of steels (up to 59 J/cm2 ). Based on a comparison of literature and our own data, it was concluded that it is impossible to ensure high cold resistance and, at the same time, high strength, due to alloying of economically alloyed nickel (up to 4 %) corrosion-resistant steels by 0.5 – 0.6 % of N.

Features of Processing of Corrosion Resistant Steels

The information about the applications and features of mechanical treatment of corrosion resistant steels which refer to the ferritic-austenitic class is provided in the paper. It is shown that increasing of alloying elements’ content, in comparison to austenitic steels, improves the strength characteristics while improving corrosion resistance and resulting in a dramatic reduction in machinability. The paper defines the directions of efficiency increase for machining of duplex steels by determining the processing conditions appropriate to reduce the tool wear intensity.