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Thermodynamic Analysis of Precipitation Process of Complex Carbonitride TixV1-xCyN1-y in HSLA-Type Steel

Wojtacha Anna, Opiela Marek

Advances in Science and Technology. Research Journal

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2022

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Vol. 16, no 4

64--73

EN

The paper presents a detailed analysis of the MX-type interstitial phase precipitation process and a thermodynamic analysis of the TixV1-xCyN1-y carbonitride precipitation in austenite. The subject of research analysis was the newly developed HSLA-type steel containing 0.175% C, 1.02% Si, 1.87% Mn, 0.0064% N, 0.22% Mo, and microadditions 0.022% V and 0.031% Ti. Analysis of the process of precipitation of MX interstitial phases under thermodynamic equilibrium conditions proved that the first phase that precipitates in the austenite of the tested steel is TiN-type nitride. The onset temperature of this phase was 1450°C. Subsequently, carbides of the TiC-type, VN-type nitrides and VC-type carbides, for which the precipitation onset temperatures were 1180°C, 870°C and 775°C will be released, respectively. The analysis of the precipitation process of the complex carbonitride in austenite under thermodynamic equilibrium conditions was based on the Hillert and Staffansson model, developed by Adrian, with the use of the CarbNit computer program. The beginning of carbonitride precipitation with the stoichiometric composition Ti0.985V0.015C0.073N0.927 occurred at the temperature of 1394°C. At 850°C practically all of the Ti is bound in the carbonitride of the stoichiometric composition Ti0.883V0.117C0.378N0.622. At the same temperature, a significant part of microaddition V will be dissolved in austenite, which means that vanadium will have a lesser effect on the formation of a fine-grained austenite structure, but more strongly on the precipitation hardening of steel by the dispersion VN and V particles (C,N) released during the cooling of the products.

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Thermodynamic Analysis of Precipitation Process of MX-type Phases in High Strength Low Alloy Steels

Opiela Marek

Advances in Science and Technology. Research Journal

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2021

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Vol. 15, no 2

90--100

EN

The paper presents the results of thermodynamic analysis of precipitation process of MX-type interstitial phases in austenite. The subject of the investigation were two newly developed high strength low alloy microalloyed steels with similar concentration of C and N and with diversified amount of Nb, Ti and V microadditions. Thermodynamic analysis of the state of phase equilibrium of structural constituents, taking into consideration the austenite of investigated microalloyed steels, was mainly focused on analytic calculations of chemical composition of austenite and the content and chemical composition of potential MX-type interstitial phases (M – metal, X – metalloid) as a function of heating or cooling temperature. The analysis of precipitation process of complex carbonitrides in austenite under thermodynamic equilibrium conditions has allowed to define stoichiometric compositions of carbonitrides as a function of temperature along with determination of their volume portion. This study was based on the model proposed by Hillert and Staffanson, which was subsequently developed by Adrian. The results of performed investigation can be used to develop the appropriate parameters of thermomechanical treatment of metallurgical products from the tested HSLA-type steels.

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Effect of boron microaddition on hardenability of new-developed HSLA-type steels

Opiela M.

Archives of Materials Science and Engineering

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2019

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Vol. 99, nr 1/2

13--23

EN

Purpose: The paper presents the results of investigations on the effect of 0.003% boron microaddition on the hardenability of new-developed HSLA-type steels. In order to prevent the binding of the boron microaddition with nitrogen in BN nitrides, Ti microaddition at concentrations of 0.033% and 0.028% was also added into the tested steels. Design/methodology/approach: Evaluation of hardenability of the investigated steels was carried out on the basis of the Jominy test and the analytical method, according to the ASTM 255-89 standard, taking into account the effect of the boron microaddition. Additionally, developed of the CCT-diagram of investigated steel. A DIL 805A/D dilatometer with a LVDT-type measuring head was used to carry out the dilatometric test. Findings: Microaddition of boron, introduced into steel in a concentration of 0.003% along with Ti microaddition shielding (in concentration of 0.033% in steel A and 0.028% in steel B), advantageously improves hardenability. This is reflected in calculated ideal critical diameter DIB, which is equal 163 mm for steel A and 155 mm for steel B. The form of curves of phase transformations of supercooled austenite is typical for steels with microaddition of boron, with similar chemical composition. Research limitations/implications: Due to similar chemical composition of investigated steels, the kinetics of phase transformations of austenite, supercooled under continuous cooling, was determined for steel B containing 0.28% C, 1.4% Mn, 0.3% Si, 0.26% Cr, 0.22% Mo and Nb, Ti, V and B microadditions at 0.027%, 0.028%, 0.019% and 0.003% respectively. Practical implications: Tested steels have high hardenability and show the full usability for production of forged parts with the method of thermomechanical treatment, i.e., hotdeformed in the temperature range adjusted to the type of microadditions added to steel, with direct quenching of forgings from finishing forging temperature. The results of the tests may be useful for developing the parameters of heat treatment and thermomechanical treatment of investigated steels. Originality/value: The hardenability of new-developed HSLA-type steels was determined.

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Rozwój mikrostruktury austenitu stali typu HSLA podczas obróbki plastycznej na gorąco

Opiela M.

Hutnik, Wiadomości Hutnicze

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2018

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Vol. 85, nr 5

156--160

PL

W pracy zbadano wpływ parametrów obróbki plastycznej na gorąco na przebieg dynamicznych i statycznych procesów aktywowanych cieplnie w stali konstrukcyjnej typu HSLA (High Strength Low Alloy) zawierającej 0,17% C, 1,37% Mn oraz mikrododatki Nb, Ti, V o stężeniu – odpowiednio – 0,025%, 0,004% i 0,019%. Do wyznaczenia krzywych σ–ε oraz kinetyki rekrystalizacji austenitu odkształconego plastycznie wykorzystano symulator termomechaniczny Gleeble 3800. Próbki badano w zakresie temperatury od 900 do 1000°C z prędkością odkształcenia 3 s-1. Ujawniono strukturę austenitu pierwotnego próbek po dwuetapowym ściskaniu z wytrzymaniem izotermicznym przez czas od 0,2 do 120 s oraz wyznaczono energię aktywacji procesu odkształcenia plastycznego na gorąco badanej stali. Uzyskane wyniki badań pozwolą na opracowanie technologii blach grubych ze stali mikrostopowej typu HSLA metodą obróbki cieplno-plastycznej – walcowania ze sterowaną rekrystalizacją.

EN

The paper investigates the influence of hot-working parameters on the progression of thermally activated dynamic and static processes in HSLA (High Strength Low Alloy) constructional steel, containing 0.17% C, 1.37% Mn and microadditions of Nb, Ti, V in the amounts of 0.025 %, 0.004% and 0.019%, respectively. In order to determine the σ–ε curves and the kinetics of recrystallization of plastically deformed austenite, the Gleeble 3800 thermomechanical simulator was used. Specimens were tested in the temperature range from 900 to 1000°C, at the deformation rate of 3 s-1. Microstructure of primary austenite was revealed after two-stage compression of samples, with isothermal holding for the period of 0.2 to 120 s; the activation energy for hot working of the examined steel was determined. Obtained research results will allow to develop the technology of HSLA type microalloyed steel plates with the method of thermomechanical treatment – recrystallization controlled rolling.