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1

Effect of Plastic Deformation on CCT-Diagram of Multi-Phase Forging Steel

Wojtach A., Opiela M.

Advances in Science and Technology. Research Journal

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2021

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Vol. 15, no 4

72--80

EN

The paper presents the results of research on the influence of plastic deformation and cooling conditions on microstructure, hardness and a shape of CCT-diagram (Continuous Cooling Transformations) of newly developed multi-phase steel assigned for die forgings, combining high strength, crack resistance and fatigue strength. The diagrams of undeformed and plastically deformed supercooled austenite transformations of steel, containing 0.175% C, 1.87% Mn, 1.0% Si, 0.22% Mo as well as Ti and V microadditions in concentration of 0.031% and 0.022%, respectively, were determined. Dilatometric tests were performed using a Bahr 805 A/D dilatometer. Specimens were austenitized at the temperature of 1000°C for 300 s and successively cooled to ambient temperature at a rate ranging from 60°C/s to 0.1°C/s. In order to determine the influence of plastic deformation on the shape of CCT-diagram, samples were deformed at the temperature of 1000°C, using a 50% degree of deformation, and then cooled in the same rate range as the samples which were not plastically deformed. The tests showed the following temperature results: Ac3 = 960°C, Ac1 = 832°C and a relatively low MS temperature equal 330°C. Plastic deformation of steel at the temperature of 1000°C, prior to the beginning of phase transformations, leads to significant increase in the ferritic transformation range, shifting the temperature of the beginning of this transformation to higher temperature in the entire range of cooling rates. It was also revealed that the specimens, plastically deformed at the austenitizing temperature, exhibit higher hardness compared to the specimens which were not plastically deformed, cooled with the same cooling rate. The elaborated CCT-diagrams of supercooled austenite transformations constitute the basis for correct development of the conditions of thermo-mechanical treatment of forgings from the tested steel.

2

Empirical Formulae for The Calculation of Austenite Supercooled Transformation Temperatures

Trzaska J.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 1

181--185

EN

The paper presents empirical formulae for the calculation of austenite supercooled transformation temperatures, basing on the chemical composition, austenitising temperature and cooling rate. The multiple regression method was used. Four equations were established allowing to calculate temperature of the start area of ferrite, perlite, bainite and martensite at the given cooling rate. The calculation results obtained do not allow to determine the cooling rate range of ferritic, pearlitic, bainitic and martensite transformations. Classifiers based on logistic regression or neural network were established to solve this problem.

PL

W pracy przedstawiono zależności empiryczne do obliczania temperatury przemian austenitu przechłodzonego na podstawie składu chemicznego, temperatury austenityzowania i szybkości chłodzenia. Zastosowano metodę regresji wielorakiej. Opracowano cztery równania, które umożliwiają obliczenie temperatury początku przemiany ferrytycznej, perlitycznej, baini-tycznej i martenzytycznej. Wyniki obliczeń nie pozwalają na wyznaczenie zakresu szybkości chłodzenia, dla których występują przemiany ferrytyczna, perlityczna, bainityczna i martenzytyczna. Do rozwiązania problemu opracowano klasyfikatory stosując regresję logistyczną lub sztuczne sieci neuronowe.

3

Designing and controlling the microstructure of 37MnNiMo6-4-3 hypoeutectoid steel after continuous cooling

Rożniata E.

Journal of Achievements in Materials and Manufacturing Engineering

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2013

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Vol. 58, nr 1

24--30

EN

Purpose: Present work corresponds to the research on the kinetic of phase transformation of undercooled austenite of 37MnNiMo6-4-3 hypoeutctoid steel. The kinetic of phase transformation of under cooled austenite of investigated alloy was presented on CCT diagram (continuous cooling transformation). Also the methodology of a dilatometric samples preparation and the method of the critical points determination were described. Design/methodology/approach: The austenitising temperature was defined in a standard way i. e. 30-50°C higher than Ac3 temperature for hypoeutectoid steels. The technology of full annealing was proposed for the iron based alloy. The CCT diagram was made on the grounds of dilatograms recorded for samples cooled with various rates. The microstructure of each dilatometric sample was photographed after its cooling to the room temperature and the sample hardness was measured. Also EDS analysis was performed using scanning microscope. Findings: The test material has been hypoeutectoid steel. These steels represent a groups of alloy steels for quenching and tempering. The microstructure of test 37MnNiMo6-4-3 hypoeutectoid steel on CCT diagram changes depending on the cooling rate. Research limitations/implications: The new hypoeutectoid steel and new CCT diagram. Practical implications: The paper contains a description of one from a group of iron based model alloys with 0.35-0.40% carbon content. According to PN-EN 10027 standard this steel should have a symbol 37MnNiMo6-4-3. Originality/value: The new hypoeutectoid steel (Mn-Ni-Mo iron based model alloy).

4

Calculation of the steel hardness after continuous cooling

Trzaska J.

Archives of Materials Science and Engineering

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2013

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Vol. 61, nr 2

87--92

EN

Purpose: The paper presents method in predicting hardness of steel cooled continuously from the austenitizing temperature, basing on the chemical composition, austenitizing temperature and cooling rate. Design/methodology/approach: In the paper it has ©been applied a hybrid approach that combined application of various mathematical tools including logistic regression and multiple regression to solve selected tasks from the area of materials science. Findings: Modelling make improvement of engineering materials properties possible, as well as prediction of their properties, even before the materials are fabricated, with the significant reduction of expenditures and time necessary for their investigation and application. Practical implications: The worked out relationships may be used in computer systems of steels’ designing for the heat-treated machine parts. Originality/value: The paper presents the method for calculating hardness of the structural steels, depending on their chemical composition, austenitizing temperature and cooling rate.

5

Application of neural networks for selection of steel with the assumed hardness after cooling from the austenitising temperature

Trzaska J., Dobrzański L. A.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 16, nr 1-2

145--150

PL

Purpose: The aim of the study is to establish a system that supports the choice of steel grade for quenching and tempering at a required hardness curve as function of cooling rate from the austenitising temperature. Design/methodology/approach: It has been assumed that the steel will meet the criterion provided that the hardness curve, defined by the user, is included within the range of hardness change that is characteristic of a certain steel grade. In order to determine the steel hardness ranges it has been necessary to work out a suitable calculation model. Therefore, a neural network has been designed and verified numerically to calculate the steel hardness on the basis of chemical content for the predetermined cooling rate. To develop the relationship between the chemical composition, austenitising temperature, cooling rate and hardness of the steels for quenching and tempering the artificial neural network was used. The obtained results were used for determination of neural classifier. The classifiers based on the neural networks carries out the task of selection of the steel grade. Findings: Artificial neural networks can be applied for selection of steel with the assumed hardness after cooling from the austenitising temperature. Practical implications:The system presented can be applied to selection of steel grade intended for machine parts of predetermined hardness in the section of a hardened or normalized element. Originality/value: The research presented in this paper offers a new strategy useful in selection of steel grade.