Utjecaj mikrostrukture brzoreznog čelika na tribološka svojstva reznih alata

U okviru ovog doktorskog rada ispitan je utjecaj mikrostrukture na tribološka svojstva brzoreznog čelika te reznih alata izrađenih od brzoreznog čelika prevučenih TiAlN prevlakom. Ispitivani brzorezni čelik dobiven je metalurgijom praha oznake Böhler PM S390 MC. Različita mikrostrukturna stanja ovog čelika dobivena su toplinskom obradom na dva načina: konvencionalno (kaljenje u vakuumu, tri visoko temperaturna popuštanja) i dubokim hlađenjem (kaljenje u vakuumu, duboko hlađenje u tekućem dušiku, visoko temperaturno popuštanje). Kod pojedinih stanja provedeno je i nitriranje u plazmi ionizirajućih plinova. Na tako pripremljenu podlogu nanesena je TiAN prevlaka PVD postupkom. Detaljna karakterizacija mikrostrukture provedena je "field emmission" skenirajućim elektronskim mikroskopom (FE SEM), transmisijskim elektronskim mikroskopom (TEM), rendgenskom difrakcijom (XRD). Mikro analiza kemijskog sastava pojedinih faza ispitana je EDS metodom te je EBSD metodom provedena mikrostrukturno - kristalografska analiza faza. TiAlN prevlaka je uz prethodno navedene metode ispitana još i fokusiranim snopom iona (FIB). Ispitana je otpornost na adhezijsko trošenje određivanjem kritičnih sila metodom rastućeg opterećenja, otpornost na suho klizno trošenje metodom "kuglica na ploči", otpornost na mikroabraziju metodom utiskivanja kuglice. Prionjivost prevlake ispitana je brazdanjem, metodom utiskivanja kuglice , Rockwellovom metodom utiskivanja indentora te određivanjem sile probijanja prevlake metodom "kuglica na ploči". Provedeno je i ispitivanje obradivosti jednoreznim alatom (alatom s jednom glavnom oštricom) tzv. "machinability test". Provedeno je pet serija kontinuiranog ispitivanja trošenja tokarenjem te su snimljene krivulje trošenja prekidanjem obrade svake 2min. Promatrani parametar trošenja alata bio je trošenje stražnje površine, VB, mm , a istrošena površina analizirana je na SEM-u. Provedena ispitivanja pokazala su da su mikrostrukture dobivene dubokim hlađenjem i nitriranjem utjecale na povećanje otpornosti na trošenje brzoreznog čelika PM S390 MC. Utvrđen je i njihov utjecaj na prionjivost TiAlN prevlake što je rezultiralo povećanjem otpornosti na trošenje uzoraka pri laboratorijskim ispitivanjima, kao i povećanje otpornosti na trošenje reznih pločica pri ispitivanju tokarenjem

Cutting performance of deep cryogenic treated and nitrided HSS cutting tool inserts

High speed steel (HSS) is a very important industrial tool material and has been constantly improved for different wear resistance applications and cutting tools, i.e. drills, milling cutters, hobs and for the cutting tools in which the economical cutting speed is too low for choosing the carbide tools. The properties of HSS depend significantly on the parameters of the conducted heat treatment. In this paper, the influence of deep cryogenic treatment in combination with nitriding of metallurgical powder metallurgy HSS on the wear resistance was measured. Additionally, the cutting performance in a single point cutting tool machinability test at the configuration of the dry low-speed turning of steel was investigated. The results showed that deep cryogenic treatment itself, and in combination with nitriding, resulted in the reduction of the wear rate. The results of the single point cutting tool machinability test showed that deep cryogenic treated and nitrided HSS inserts performed worse than the classically heat-treated inserts and deep cryogenic treated HSS inserts exhibited approximately the same flank wear as the nitrided ones

Microstructural changes in heat treatment of PM high-speed steels

Properly performed heat treatment can significantly affect final properties of high-speed steels, so the heat treatment parameters are chosen depending on the specific properties of the particular tool. Deep cryogenic treatment is carried out at a temperature of -196 °C (liquid nitrogen). By combining deep cryogenic treatments and various austenitization temperatures, which affects the volume of retained austenite, it is possible to affect the hardness and fracture toughness of tools and other steel parts. However, it may also affect the increase in wear resistance regardless of the increase in hardness. In addition, dimensional stability is achieved by transformation of residual austenite into martensite, eliminating the change in volume by 4%. This paper investigated the effect of deep cryogenic treatment on microstructures in high-speed steel produced by powder metallurgy in comparison to vacuum heat treatment

Influence of the LPBF Process Parameters on the Porosity of the AlSi10Mg Alloy

Laser powder bed fusion (LPBF) process has a great ability to produce complex AlSi10Mg 3D components with uncommon degrees of freedom for broad span of applications in different industries. Presence of the microstructural imperfections such as porosity, dependent on the parameters of the process can be detrimental to the printed products for different engineering applications. Parameters of the process and different post-processing heat and surface treatments are recognized for decrease of the occurrence of microstructural defects and for the improvement of the mechanical properties. The influence of laser power by applying four different laser speeds at one layer thickness with a constant hatch distance, on the microstructure and microhardness of the AlSi10Mg alloy was examined in this paper. The goal of the research was to determine whether increasing the laser speed will have a significant impact on the change in microstructure and the appearance of porosity in the tested samples

Utjecaj parametara toplinske obrade na svojstva brzoreznog čelika PM S390 MC

Svojstva konkretnog brzoreznog čelika bitno ovise o primijenjenim parametrima toplinske obrade. U radu su provedena ispitivanja na brzoreznom čeliku proizvedenim metalurgijom praha PM S390 MC koji je toplinski obrađen sa dvije temperature austenitizacije, a za svaku temperaturu austenitizacije varirana su tri različita ciklusa popuštanja. Utjecaj promatranih čimbenika na svojstva čelika procijenjen je na osnovi ispitivanja: mikrostrukture, tvrdoće, lomne žilavosti, tlačne i zarezne čvrstoće. Dobiveni rezultati upućuju da parametri toplinske obrade značajno utječu na ispitivana svojstva brzoreznog čelika te da će njihov odabir ovisiti o traženim svojstvima konkretnog alata

The knowledge of oral hygiene and oral hygiene habits during pregnancy and puerperium

Aim. We wanted to explore the knowledge and attitudes of pregnant women and women after giving birth to oral health. Likewise, we wanted to determine whether there was any awareness of oral hygiene during pregnancy in the population. Our aim was to establish the correlation between oral hygiene habits in relation to age, level of education and place of residence (urban / rural) and to determine the importance of the role of experts in further education of the patient. Study design. A cross-sectional study. Patients and methods. The subjects were patients admitted to the Maternal and Puerperal Ward of the General Hospital Zabok in the period from December 1st 2016 till February 15th 2017. Data for statistical analysis were obtained based on an anonymous questionnaire of 15 questions. Results. Nearly half of pregnant women and women after delivery (49%) believe that oral hygiene does not affect the outcome of pregnancy. In Planned Parenthood pregnancy 70% of women with the lowest levels of education are not going to control dental examinations. Over 90% of highly educated respondents used additional oral hygiene products, while only 20% of women with low levels of education used additional products. The results showed that 71% of women thought they had not received enough oral health information from their doctor. Also, in 60% of respondents, primary data on oral hygiene and health were not received by health professionals but from other sources. Conclusion. The obtained data show that almost half of the respondents did not develop the habit of awareness of the need for oral hygiene. The prevalence of monitoring the level of education but are weaker indicators correlate with low skill levels. The emphasis of the modern approach to the prevention of and given that over half of the surveyed women does not the necessary knowledge oral health opens space for continuing education and the promotion of information programs by the health system