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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.

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Influence of plastic deformation on CCT-diagrams of new-developed microalloyed steel

Opiela M., Zalecki W., Grajcar A.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 51, nr 2

78--89

EN

Purpose: The aim of the paper is to investigate the influence of plastic deformation and cooling conditions on a structure and a shape of CCT-diagrams of new-developed Nb-Ti-V microalloyed steel. Design/methodology/approach: The diagrams of undeformed and plastically-deformed supercooled austenite transformations for Nb-Ti-V microalloyed steel were determined. A part of the specimens were austenitized at a temperature of 885°C and next cooled to ambient temperature with a various rate from 234°C/s to 1°C/min. To investigate the influence of plastic deformation on a shape of CCT (Continuous Cooling Transformations) diagrams, another part of the specimens were 50% deformed at 885°C or 1100°C and cooled to ambient temperature with a rate from 95°C/s to 1°C/min. The DIL 805A/D dilatometer, with a LVDT-type measuring head, was used to carry out dilatometric test. Findings: Performed dilatometric research revealed that the steel is characterized with Ac3=843°C, Ac1=707°C and a relatively low Ms temperature equal 370°C. Plastic deformation of steel at the temperature of 885°C prior to the start of phase transformations results in distinct acceleration of pearlitic transformation and slight translation of bainitic transformation towards shorter times. Research limitations/implications: Elaborated curves of supercooled austenite transformations of studied steel fully predispose it to production of forgings quenched directly from forging finish temperature and successively subjected to high temperature tempering. Practical implications: The obtained CCT diagrams of supercooled plastically-deformed austenite transformations can be useful in determination of cooling condition of the thermo-mechanical processing for high strength forged machine parts obtained from microalloyed steels. Originality/value: The diagrams of the plastically-deformed supercooled austenite for a new-developed microalloyed steel were obtained.

3

Influence of plastic deformation on CCT-diagrams of low-carbon and medium-carbon TRIP-steels

Grajcar A., Opiela M.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 29, nr 1

71-78

EN

Purpose: The aim of the paper is to investigate the influence of plastic deformation and cooling conditions on a structure and a shape of CCT-diagrams of new-developed TRIP-aided microalloyed steels. Design/methodology/approach: The diagrams of undeformed and plastically-deformed supercooled austenite transformations for low-carbon and medium-carbon microalloyed steels were determined. A part of the specimens were austenitized at a temperature of 1100*C, then slowly cooled to 900*C and next cooled to ambient temperature with a various rate from 1 to 300*C/s. To investigate the influence of plastic deformation on a shape of CCT (Continuous Cooling Transformations) diagrams, another part of the specimens were 50% deformed at 900*C and cooled to ambient temperature with a rate from 88 to 1*C/s. The DIL805A/D dilatometer, with a LVDT-type measuring head, was used to carry out dilatometric tests. Findings: It was found that a shape of CCT diagrams of elaborated steels predisposes them for multiphase sheets manufacturing. The new-developed steels possess ferritic and bainitic bays put forward to short times and pearlitic regions put aside. However, cooling the steel with a constant rate from austenitizing temperature doesn't lead to obtaining proper participation of ferrite. Plastic deformation of steel has a profitable influence on the shape of supercooled austenite curves. The region of γ-α transformation is translated to the left at simultaneous raise of start temperature of austenite into ferrite transformation resulting in definitely higher ferrite fraction. Moreover, significant refinement of microstructure in a whole range of cooling rate was also obtained. Research limitations/implications: To increase the ferrite fraction, modification of the cooling after hot-working finishing should be applied. In the fist stage, steel should be rapidly cooled in order to enter the range of γ-α transformation and successively slowly cooled in a range of γ-α transformation. Practical implications: The obtained CCT diagrams of supercooled plastically-deformed austenite transformations can be useful in a determination of cooling in the thermo-mechanical processing for TRIP-type steel sheets. Originality/value: The diagrams of the plastically-deformed supercooled austenite for TRIP-type microalloyed steels were obtained.

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Diagrams of supercooled austenite transformations of low-carbon and medium-carbon TRIP-steels

Grajcar A., Opiela M.

Archives of Materials Science and Engineering

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2008

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Vol. 32, nr 1

13-16

EN

Purpose: The aim of the paper is to determine the influence of cooling conditions on a structure and a shape of CCT-diagrams of TRIP-aided steels. Design/methodology/approach: The diagrams of undeformed supercooled austenite transformations for low-carbon and medium-carbon steels were determined. The specimens were austenitized at a temperature of 1100°C and cooled from a temperature of 900°C with a rate in a range from 1 to 300°Cs-1. The dilatometric tests were carried out by the use of the DIL805A/D dilatometer with a LVDT-type measuring head. Findings: It was found that obtained CCT-diagrams of low-carbon and medium-carbon steels are favourable for manufacturing TRIP-type steels with multiphase structures. The steels are characterized by large ferritic and bainitic fields and a right-displaced pearlitic range. However, a ferrite fraction obtained after cooling with an optimum rate from a temperature of 900°C is low. Increasing the fraction of the α phase requires two-stage cooling after austenitizing. Research limitations/implications: To obtain the optimum ferrite fraction, it is necessary to modify a cooling course in a range of γ→α transformation. It should result in an effective utilization of the time for the transformation of austenite into the fine-grained ferrite. Practical implications: The obtained diagrams of supercooled austenite transformations can be useful in a determination of a cooling course from a finishing rolling temperature for sheets with a multiphase structure. Originality/value: The diagrams of the undeformed supercooled austenite for the low-carbon and medium-carbon steels containing Nb and Ti microadditions were obtained.

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Effect of plastic deformation on the supercooled austenite transformations of the Cr-Mo steel with Nb, Ti and B microadditions.

Adamczyk J., Opiela M.

Inżynieria Materiałowa

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1998

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R. XIX, nr 3

360-363

EN

Effect of plastic deformation of austenitizing temperature was investigated on phase transformations, structure and hardness of the supercooled austenite transformation products of the Cr-Mo constructional steel with Nb, Ti, and B microadditions. Basing on the analysis of the phase transformation plots of the supercooled undeformed austenite and of the supercooled and plastically deformed one, it was found out that direct cooling of specimens after completing their plastic deformation in the abovementioned conditions, results in a significant acceleration of the alpha -> beta, and ferritic and pearlitic transformations, and in the decrease of the transformation products hardness. These phenomena are of great importance for working out of the thermo-mechanical treatment of products made from the heat-treatable microalloyed steels.