Naprezanje tečenja i plastičnost legiranih čelika

This paper deals the results of investigation the flow stress of several various steel alloys and deformability by torsion test in hot condition in the temperature range 800 °C - 1250 °C on alloyed structural steels for special application.U radu su predstavljeni rezultati istraživanja naprezanja plastičnog tečenja čelika i deformabilnost, metodom uvijanja u toplom u temperaturnom podrućju 800 °C - 1250 °C legiranih konstrukcijskih čelika za posebne namjene

Utjecaj brzine deformacije na mehanička i tehnološka svojstva čeličnih traka

The paper analyses the influence of strain rate on the behaviour of un-alloyed steels with Re (yield strength) in the range of 210 … 550 MPa in the deformation process. It analyses the results of the influence of strain rate ranging from 10-3 to 2,5•102s-1 on the yield strength, the ultimate tensile strength (Rm), the elongation (A) and the reduction of area (Z). Achieved results of strain rate in relationship on values of Erichsen number IE are also given. By increasing of strain rate ranging from 10-3 to 2,5•102s-1 the ratio Re/Rm is increased, whereas it was observed more intensively for steels with the lower value of Re. By increasing of strain rate up to 1 s-1 are IE values of tested steels increased, whereas the ratio Re/Rm was equal 0,82. After exceeding of this strain rate was the ratio Re/Rm increased and IE value is remarkable decreased.U članku se analizira utjecaj brzine deformacije na ponašanje nelegiranog čelika s Re (granica razvlačenja) 210 do 550 MPa tijekom deformacije. Motre se rezultati utjecaja brzine deformacije u rasponu 10-3 do 2,5•102s-1 na granicu razvlačenja, vlačnu čvrstoću (Rm) istezanja (A) i kontrakciju (Z). Dodatno se prikazuje utjecaj brzine deformacije na vrijednost Erichsenovog broja IE. Povećanjem brzine deformacije u intervalu 10-3 do 2,5•102s-1 povećava se odnos Re/Rm i to intenzivnije za čelik s nižom vrijednošću Re. Povećanjem brzine deformacije do cca 1 s-1 povećava se IE ispitivanog čelika pri čemu Re/Rm = 0,82. Iznad te brzine odnos Re/Rm se povećava, a IE izrazito se smanjuje

The Influence of the Loading Rate on the Mechanical Properties of Drawing Steel Sheet

The paper analyzes the influence of the loading rate in the interval from 1 to 1000 mm/min on the mechanical properties of drawing steel sheet H260LAD with the gauge of 1 mm, used for the manufacture of automotive parts, under tension and bending conditions. It describes the aspects of material characteristics under tension and bending conditions, while bending tests were made on notched specimens (a modified impact bending test). The paper presents knowledge that using a modified notch toughness test it is possible to achieve the pressability (formability) characteristics corresponding to dynamic strain rates even under the static loading

The influence of heat treatnemnt on the abrasive wear resistnace of a construction and a tool steel

The paper deals about the influence of heat and chemical-heat treatment of construction steel 100Cr6 and alloy steel X210Cr12, which were treated according to their corresponding norms. The steel X210Cr12 was also treated in an unconventional way. The influence of the material structures and hardness on the abrasion wear resistance was studied. The influence of nitridation was considered in a way how to increase the abrasion wear resistance and how the heat treatment affects the hardness and the quality of the nitrided layer. The nitridation with diffusion annealing of the tested materials caused a decrease and also an increase of the materials wear resistances

Svojstva zamora materijala galvaniziranih ojačanih čeličnih traka

The paper analyzes the fatigues properties of galvanized microalloyed steel sheets H220LAD and H380LAD. Under flat bending conditions and the symmetrical cycle, the fatigue limit of the H220LAD sheet is σCo = ± 152 MPa and that of the H380LAD sheet is σCo = ±188 MPa, and the fatigue limit to tensile strength ratio is 0,41 and 0,37, respectively. During fatigue tests with an increasing number of cycles or an increasing stress value, the degradation of the zinc coating increases (relief formation, damage of integrity). As a result, local corrosion, but also continuation of fatigue damage after 107 cycles, and hence corrosion fatigue, can take place during operation.Članak analizira svojstva zamora materijala galvaniziranih mikrolegiranih čeličnih traka H220LAD i H380LAD. Pod uvjetima plosnatog savijanja i simetričnog ciklusa, granica zamora materijala trake H220LAD je σCo = ± 152 MPa a trake H380LAD je σCo = ±188 MPa, a granica zamora materijala prema otporu na istezanje je 0,41 odnosno 0,37. Tijekom testova zamora materijala s rastućim brojem ciklusa ili rastućom vrijednosti pritiska, povećava se degradacija cinčane obloge (formiranje reljefa, oštećenje integriteta). Posljedično, tijekom rada može doći do lokalne korozije, ali i daljnjeg oštećenja uslijed zamora materijala nakon 107 ciklusa, a time i zamora materijala uslijed korozije

Utjecaj pjeskarenja na mehanička svojstva čeličnog lima

The paper analyses the influence of blasting conditions on the properties of steel sheet RSt 37-2 having the gauge of 3 mm. Due to blasting, the surface roughness increases by an order and the surface strain hardening takes place to the depth of ca 0.06 mm, which results in compressive stress on the sheet surface. The above-mentioned changes, among others, increase the yield point and decrease the fatigue life in the tension-zero cycle. The increase of the yield point and the decrease of the fatigue life are more significant if the diameter of the blasting medium (within the tested interval from 0,56 to 0,9 mm) and the impact angle (30 to 75°) are greater at the air pressure of 0,4 to 0,5 MPa.U radu se analizira utjecaj pjeskarenja na svojstva čeličnog lima RSt 37-2 debljine 3 mm. Zbog pjeskarenja hrapavost površine se povećava za neki red veličine, a hladno otvrdnjavanje površine se proteže do 0,06 mm dubine, posljedica toga je tlačno naprezanje na površini lima. Gore spomenute promjene, između ostalog, povećavaju granicu razvlačenja a smanjuju vrijeme umora materijala pri cikličkom naprezanju. Povećanje granice razvlačenja smanjenje vremena umora materijala su značajniji ako su promjer medija pjeskarenja (unutar ispitivanog intervala od 0,56 do 0,9 mm) i udarni kut (30 do 75°) veći pri zračnom tlaku od 0,4 do 0,5 MPa

Utjecaj brzine deformacije na mehanička i tehnološka svojstva čeličnih traka

The paper analyses the influence of strain rate on the behaviour of un-alloyed steels with Re (yield strength) in the range of 210 … 550 MPa in the deformation process. It analyses the results of the influence of strain rate ranging from 10-3 to 2,5•102s-1 on the yield strength, the ultimate tensile strength (Rm), the elongation (A) and the reduction of area (Z). Achieved results of strain rate in relationship on values of Erichsen number IE are also given. By increasing of strain rate ranging from 10-3 to 2,5•102s-1 the ratio Re/Rm is increased, whereas it was observed more intensively for steels with the lower value of Re. By increasing of strain rate up to 1 s-1 are IE values of tested steels increased, whereas the ratio Re/Rm was equal 0,82. After exceeding of this strain rate was the ratio Re/Rm increased and IE value is remarkable decreased.U članku se analizira utjecaj brzine deformacije na ponašanje nelegiranog čelika s Re (granica razvlačenja) 210 do 550 MPa tijekom deformacije. Motre se rezultati utjecaja brzine deformacije u rasponu 10-3 do 2,5•102s-1 na granicu razvlačenja, vlačnu čvrstoću (Rm) istezanja (A) i kontrakciju (Z). Dodatno se prikazuje utjecaj brzine deformacije na vrijednost Erichsenovog broja IE. Povećanjem brzine deformacije u intervalu 10-3 do 2,5•102s-1 povećava se odnos Re/Rm i to intenzivnije za čelik s nižom vrijednošću Re. Povećanjem brzine deformacije do cca 1 s-1 povećava se IE ispitivanog čelika pri čemu Re/Rm = 0,82. Iznad te brzine odnos Re/Rm se povećava, a IE izrazito se smanjuje

Utjecaj brzine zatezanja na žilavost tankog vučenog lima

The paper assesses a possibility of implementing the notch toughness test on drawing sheets with the gauge up to 1 mm, the influence of the loading rate on the results, as well as a possibility of using this test to evaluate formability. Experiments were made on drawing steel sheets with a yield point from 145 to 250 MPa; the notch toughness test was made with the loading rates v1 = 1.7•10-5 ms-1, v2 = 5•10-2 ms-1 and v3 = 4.8 ms-1. The tests have shown that reproducible results can be achieved on light-gauge drawing sheets under defined conditions. The notch toughness values, as well as the force and deformation characteristics obtained in the notch toughness test can be used to supplement and make more exact the traditional characteristics in evaluating formability at increased sheet processing speeds, which are demanded in practice.Rad procjenjuje mogućnost primjene testa žilavosti na vučene limove debljine do 1 mm, utjecaj brzine zatezanja na rezultate, kao i mogućnost uporabe tog testa za procjenu kovkosti. Vršeni su eksperimenti na čeličnim limovima s granicom razvlačenja od 145 do 250 MPa; test na žilavost napravljen je brzinom zatezanja v1 = 1,7•10-5 ms-1, v2 = 5•10-2 ms-1 i v3 = 4,8 ms-1. Testovi su pokazali da se mogu dobiti rezultati koji se mogu postići i u proizvodnji tankih vučenih limova pod nekim određenim okolnostima. Vrijednost žilavosti, kao i sila i karakteristike deformacije dobivene u testu žilavosti mogu se koristiti za nadopunu tradicionalnih karakteristika i njihov točniji prikaz u procijenjivanju kovkosti pri povećanim brzinama obrade koje se traže u praksi

Degradation of mechanical properties of CrMo creep resistant steel operating under conditions of creep

Mechanical properties of a steam tube made of CrMo creep resistant steel are analysed in this contribution after up to 2,6•10⁵ hours service life in creep conditions at temperature 530 °C and calculated stress level in the tube wall 46,5 MPa. During service life there were in the steel gradual micro structure changes, fi rst pearlite spheroidization, precipitation, coaugulation and precipitate coarsening. Nevertheless the strength and deformation properties of the steel (R_e, R_m, A₅, Z), and the resistance to brittle fracture and the creep strength limit, were near to unchanged after 2,1•10⁵ hours in service. The steam tube is now in service more than 2,6•10⁵ h

Degradacija mehaničkih svojstava na puzanje otpornog CrMo čelika rabljenog pri uvjetima puzanja

Mechanical properties of a steam tube made of CrMo creep resistant steel are analyzed in this contribution after up to 2,6•105 hours service life in creep conditions at temperature 530 °C and calculated stress level in the tube wall 46,5 MPa. During service life there were in the steel gradual micro structure changes, first pearlite spheroidization, precipitation, coaugulation and precipitate coarsening. Nevertheless the strength and deformation properties of the steel (Re, Rm, A5, Z), and the resistance to brittle fracture and the creep strength limit, were near to unchanged after 2,1•105 hours in service. The steam tube is now in service more than 2,6•105 h.Članak analizira mehanička svojstva paravode izrađenog iz CrMo vatrootpornog čelika poslije rabljenja do 2,6•105 sati pri uvjetima puzanja pri temperaturi 530 °C i praračunato naprezanje u stjenci cijevi 46,5 MPa. Tijekom rabljenja postupno je dolazilo u ispitivanom čeliku do strukturnih promjena prvenstveno sferoidizaciji perlita, precipitaciji, koagulaciji i okrupnjavanjem precipitata. Usprkos navedenim promjenama čvrstoća i deformacijska svojstva (Re, Rm, A5, Z) otpornost krhkom lomu i puzanju i pri rabljenju do 2,1•105 sati praktički se nisu izmjenili, a parovod je u upotrebi čak 2,6•105 sati