HEAT treatment, HOT rolling, SPECIFIC gravity, TENSILE strength, MARTENSITE, and STRUCTURAL steel
Abstract
The paper presents the possibilities of heat treatment of low-density structural steels usable for springs. Heats have been prepared with chemical compositions 0.7 wt% C and 1 wt% C, as well as 7 wt% Al and 5 wt% Al. Samples were prepared from ingots weighing approximately 50 kg. These ingots were homogenised, then forged, and hot rolled. Primary transformation temperatures and specific gravity values were determined for these alloys. For low-density steels, there usually needs to be a solution to achieve the required ductility values. At cooling rates of 50 °C/s and 100 °C/s, the kappa phase is not present. A SEM analysed the fracture surfaces for the presence of transit carbides during tempering. The martensite start temperatures ranged from 55–131 °C, depending on the chemical composition. The densities of the measured alloys were 7.08 g/cm3 and 7.18 g/cm3, respectively. Therefore, heat treatment variation was carried out to achieve a tensile strength of over 2500 MPa, with ductility of almost 4%. Hardnesses above 60 HRC were achieved for 1 wt% C heats using the appropriate heat treatment. [ABSTRACT FROM AUTHOR]
Bricín, David, Ackermann, Michal, Jansa, Zdeněk, Kubátová, Dana, Kříž, Antonín, Špirit, Zbyněk, and Štafka, Jiří
Subjects
WC-Co, slinuté karbidy, SLM, HIP, pórovitost, hrubnutí zrna, éta fáze, hustota, struktura SK, cemented carbides, porosity, grain coarsening, eta phase, density, and CC structures
Abstract
Předložená studie se zabývá vývojem struktury práškové směsi WC-Co a to při jejím postupném zpracování SLM a HIP technologií. Použitá prášková směs obsahovala 13±0.6% hmotnostní podíl pojiva Co a WC frakci o průměrné velikosti zrna(3.0±1.9) μm.Jejím zpracováním SLM technologií došlo, v důsledku aplikace různé hustoty energie (VED), k vývoji různého stupně hustoty vytvářených vzorků. Při vysokých hodnotách VED bylo dosaženo hustoty až 88 %. Aplikovaná hodnota VED ovlivnila kromě hustoty pórů, které se ve struktuře vzorků vytvářely, typy strukturních fází a hrubost WC fáze. Při vysokých hodnotách VED se ve struktuře vzorků začaly utvářet trhliny, které vznikaly v důsledku zkřehnutí struktury vzorků a to z několika důvodů, mezi které patřilo hrubnutí α-fáze (WC), vypařování β-fáze (pojiva Co) a precipitace η-fáze. Při nízkých hodnotách VED byla oproti tomu struktura pórů tvořena převážně tvarově nesymetrickými póry, i o velikosti vyšší jak 500 μm. Následným zpracováním vybraných vzorků technologií HIP bylo dosaženo zvýšení jejich hustoty až na hodnotu 96 % kompaktního materiálu. Na tomto zvýšení hustoty se podílely strukturní přeměny zejména pak opětovné hrubnutí α-fáze až o 1300 % oproti původní velikosti zrna práškové směsi a vývoj η-fáze ve struktuře analyzovaných vzorků. Na základě získaných výsledků pak bylo možné rozhodnout o dalším směřování experimentálního programu, který se do větší hloubky bude zabývat zpracováním vybraných práškových směsí WC-Co technologiemi SLM a HIP za doposud nerealizovaných parametrů jejich zpracování. The study focuses on microstructural evolution in a WC-Co powder mixture during Selective Laser Melting (SLM) and hot isostatic pressing (HIP) processing. This powder mixture contained a 13 plus/minus 0.6 % weight fraction of Co binder and WC particles of mean size of 3.0 plus/minus 1.9 μm. SLM of the mixture produced samples of various densities, depending on the volumetric energy density (VED) applied. High VED levels led to densities of up to 88%. The aspects affected by changes in VED included the pore density as well as the resulting types of phases and the size of WC phase particles. At high VED, the material began to develop cracks due to embrittlement. This had multiple causes: coarsening of a-phase (WC), evaporation of b-phase (Co binder), and precipitation of h-phase. At low VED levels, pores formed, typically of nonsymmetric shapes, with sizes larger than 500 μm. Subsequent HIP processing led to an increased density, up to 96 % of solid material. Contributions to this increased density were provided by structure transformations, namely, coarsening of a-phase by up to 1300 % when compared to the powder grain size, and formation of h-phase. The results provided a basis for steering further research to explore to a greater depth the SLM and HIP processing of selected WC-Co powder mixtures with as yet unused ranges of process parameters.
Náplní této práce je studium struktutry niklem dopovaného SrTiO3 pomocí rentgenové difrakce. Všechny vzorky byly připravené pomocí magnetronového naprašování na Si a SiO2 subrstrát. Hlavním cílem práce bylo monitorování krystalizace deponovaných vrstev SrTiO3 dopovaných niklem. RTG měření bylo provedeno na vzorcích v původnímdeponovaném stavu a ve stavu po vyžíhání ve vakuu při teplotě 900 °C. Rentgenová analýza byla provedena pomocí obou geometrií (symetrické i asymetrické). Tato měření poskytla informace o vlivu niklu na finální strukturu, velikost krystalitů, mikronapětí a deformaci mřížky. Zejména je demonstrován vliv niklu na krystalizaci SrTiO3 v porovnání s nedopovaným SrTiO3. The aim of this work is to study the structure of Ni-doped SrTiO3 thin films by X-ray diffraction (XRD). All samples were prepared by magnetron sputtering on Si and SiO2 substrates. The main objective of this work is to monitor the crystallization of the deposited thin layer of Ni-doped SrTiO3. The X-ray diffraction measurements were done on the films as deposited and after annealing in vacuum up to 900°C. The x-ray analysis was used with both geometries (symmetric and asymmetric). Those measurements allow us to get information about the influence of Ni on the final structure, the size of crystallites, the micro-strains and the deformation of the lattice. In particular, here we demonstrate that Ni doping lead to the unique stabilisation of crystall growth of SrTiO3 as compared to the undoped SrTiO3.
Průcha, Vojtěch, Bricín, David, Kříž, Antonín, and Jansa, Zdeněk
Diffusion and Defect Data Part A: Defect and Diffusion Forum; September 2020, Vol. 403 Issue: 1 p75-89, 15p
Abstract
The present paper explores the effects of deep cryogenic treatment (DCT) on the properties of WC-Co cemented carbides. The investigation involved four different cemented carbide (CC) grades. Two of them were coarse-grained WC with grain sizes larger than 6 μm and binder fractions of 10 and 15 wt. %. The other two were fine-grained with WC grains of 0.5-0.8 μm and the same binder fractions of 10 and 15 wt. %. Their specimens were ground and polished to prepare them for DCT. In each specimen, one half of this polished surface was used for testing the properties of the CC before cryogenic treatment. The post-DCT properties were then determined on the other half. Properties of the cemented carbides prior to and after DCT were studied using optical and scanning electron microscopy, X-ray diffraction, hardness testing according to Vickers scale followed by calculation of fracture toughness KIC and a ball-on-disk test of the wear resistance of the surface. One of the findings was that cryogenic treatment led to a decrease in residual stresses and to lower fracture toughness KIC in the CC.
Průcha, Vojtěch, Jansa, Zdeněk, Šimeček, Jiří, Žďánský, Ondřej, and Kříž, Antonín
Diffusion and Defect Data Part B: Solid State Phenomena; November 2017, Vol. 270 Issue: 1 p265-270, 6p
Abstract
In this contribution, the preparation of metallographic sections and characterization of the microstructure of manganese Hadfield steels are discussed. The purpose of this paper is to provide information relevant to microstructural characterization of these steels. This type of steel is characterized by high resistance to abrasive wear, which is provided by surface strengthening through strain-induced martensitic transformation. Strengthening complicates the preparation of metallographic sections because the final microstructure can be influenced by the process and it can be eventually misinterpreted. Great attention must be paid to the choice of the etchant and the etching procedure. This contribution describes the entire metallographic characterization procedure, including the evaluation of grain size, micro-cleanness and presence of carbides on grain boundaries. It provides information for manufacturers and those, whose process and examine Hadfield steels with respect to their processing routes, wear resistance, non-magnetic properties and other aspects.
ISOSTATIC pressing, HOT pressing, CARBIDES, ENERGY density, GRAIN size, and EMBRITTLEMENT
Abstract
The study focuses on microstructural evolution in a WC-Co powder mixture during Selective Laser Melting (SLM) and hot isostatic pressing (HIP) processing. This powder mixture contained a 13 ± 0.6% weight fraction of Co binder and WC particles of mean size of 3.0 ± 1.9 μ m. SLM of the mixture produced samples of various densities, depending on the volumetric energy density (VED) applied. High VED levels led to densities of up to 88%. The aspects affected by changes in VED included the pore density as well as the resulting types of phases and the size of WC phase particles. At high VED, the material began to develop cracks due to embrittlement. This had multiple causes: coarsening of α -phase (WC), evaporation of β -phase (Co binder), and precipitation of η -phase. At low VED levels, pores formed, typically of nonsymmetric shapes, with sizes larger than 500 μ m. Subsequent HIP processing led to an increased density, up to 96% of solid material. Contributions to this increased density were provided by structure transformations, namely, coarsening of α -phase by up to 1300% when compared to the powder grain size, and formation of η -phase. The results provided a basis for steering further research to explore to a greater depth the SLM and HIP processing of selected WC-Co powder mixtures with as yet unused ranges of process parameters. [ABSTRACT FROM AUTHOR]
Hájek J, Nový Z, Kučerová L, Jirková H, Donik Č, and Jansa Z
Materials (Basel, Switzerland) [Materials (Basel)] 2023 May 19; Vol. 16 (10). Date of Electronic Publication: 2023 May 19.
Abstract
The paper presents the possibilities of heat treatment of low-density structural steels usable for springs. Heats have been prepared with chemical compositions 0.7 wt% C and 1 wt% C, as well as 7 wt% Al and 5 wt% Al. Samples were prepared from ingots weighing approximately 50 kg. These ingots were homogenised, then forged, and hot rolled. Primary transformation temperatures and specific gravity values were determined for these alloys. For low-density steels, there usually needs to be a solution to achieve the required ductility values. At cooling rates of 50 °C/s and 100 °C/s, the kappa phase is not present. A SEM analysed the fracture surfaces for the presence of transit carbides during tempering. The martensite start temperatures ranged from 55-131 °C, depending on the chemical composition. The densities of the measured alloys were 7.08 g/cm 3 and 7.18 g/cm 3 , respectively. Therefore, heat treatment variation was carried out to achieve a tensile strength of over 2500 MPa, with ductility of almost 4%. Hardnesses above 60 HRC were achieved for 1 wt% C heats using the appropriate heat treatment.
Salvetr P, Školáková A, Kotous J, Drahokoupil J, Melzer D, Jansa Z, Donik Č, Gokhman A, and Nový Z
Materials (Basel, Switzerland) [Materials (Basel)] 2023 Mar 06; Vol. 16 (5). Date of Electronic Publication: 2023 Mar 06.
Abstract
The present work aimed to study the properties of medium-carbon steel during tempering treatment and to present the strength increase of medium-carbon spring steels by strain-assisted tempering (SAT). The effect of double-step tempering and double-step tempering with rotary swaging, also known as SAT, on the mechanical properties and microstructure was investigated. The main goal was to achieve a further enhancement of the strength of medium-carbon steels using SAT treatment. The microstructure consists of tempered martensite with transition carbides in both cases. The yield strength of the DT sample is 1656 MPa, while that of the SAT sample is about 400 MPa higher. On the contrary, plastic properties such as the elongation and reduction in area have lower values after SAT processing, about 3% and 7%, respectively, compared to the DT treatment. Grain boundary strengthening from low-angle grain boundaries can be attributed to the increase in strength. Based on X-ray diffraction analysis, a lower dislocation strengthening contribution was determined for the SAT sample compared to the double-step tempered sample.
