Optimization, by Means of a Design of Experiments, of Heat Processes to Increase the Erosive Wear Resistance of White Hypoeutectic Cast Irons Alloyed with Cr and Mo.

To identify the design parameters in heat treatments that have a significant effect on the erosive wear resistance of hypoeutectic high chromium white cast irons, a design of experiment was applied to a white cast iron with 18wt.% Cr and 2wt.% Mo. The analyzed factors were the destabilization heat treatment of austenite (1000 or 1100 °C, for 4 or 8 h), different quench cooling media (in air or oil), different tempering treatments (200 or 500 °C, for 3 or 6 h), and the application of an ionic nitriding treatment. Despite what was expected, the nitriding treatment was not found to have a significant effect on said wear resistance. However, it is concluded that the highest wear resistance is obtained with the shortest dwell time at the destabilization temperature (4 h), quenching in oil, and with the shortest tempering times (3 h). Among the nitrided samples, the highest nitrided layer thicknesses were obtained when the destabilization temperature of the austenite was 1000 °C and the tempering temperature was 200 °C.

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The Joint Effects of Nitriding and Parameters Related to the Destabilisation of Austenite on Wear Resistance in White Cast Iron with 25% Cr

Metals ◽

10.3390/met11010085 ◽

2021 ◽

Vol 11 (1) ◽

pp. 85

Author(s):

Alejandro González-Pociño ◽

Florentino Alvarez-Antolin ◽

Juan Asensio-Lozano

Keyword(s):

Wear Resistance ◽

Cast Iron ◽

White Cast Iron ◽

Nitrided Layer ◽

Erosive Wear ◽

Air Cooling ◽

Cast Irons ◽

Eutectic Carbides ◽

Noticeable Increase ◽

Ionic Nitriding

In this article, the effects of an ionic nitriding treatment are analysed, together with deliberate variation of different thermal parameters associated with the destabilisation of austenite, on erosive wear resistance of white cast irons with 25% Cr. The methodology followed in this research was an experimental design, where six factors were analyzed by performing eight experiments. The thickness of the nitrided layer is much smaller than in white cast iron with lower percentages in Cr, never reaching 20 microns. The nitriding treatment entails considerable softening of the material underneath the nitriding layer. This softening behaviour becomes partially inhibited when the destabilisation temperature of austenite is 1100 °C and dwell times at such temperature are prolonged. This temperature seems to play a significant role in the solubilization of non-equilibrium eutectic carbides, formed during industrial solidification. The nitriding treatment leads to additional hardening, which, in these cases, favours a second destabilisation of austenite, with additional precipitation of secondary carbides and the transformation of retained austenite into martensite. Despite softening of the material, the nitriding treatment, together with air-cooling after destabilisation of the austenite, allows a noticeable increase in resistance to erosive wear.

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Improvement of Adhesive Wear Behavior by Variable Heat Treatment of a Tool Steel for Sheet Metal Forming

Materials ◽

10.3390/ma12172831 ◽

2019 ◽

Vol 12 (17) ◽

pp. 2831 ◽

Cited By ~ 4

Author(s):

Alejandro Gonzalez-Pociño ◽

Florentino Alvarez-Antolin ◽

Juan Asensio-Lozano

Keyword(s):

Wear Resistance ◽

Tool Steel ◽

Significant Influence ◽

Sheet Metal Forming ◽

Metal Forming ◽

Adhesive Wear ◽

Wear Behavior ◽

Air Cooling ◽

Tempering Temperature ◽

Quench Cooling

Vanadis 10 steel is a powder metallurgy (PM) processed tool steel. It is a ledeburitic steel with 8% Cr and 10% V. By deliberately varying the process parameters related to the quenching, tempering, and nitriding of these steels, the aim of this study is to determine which of these parameters have a significant influence on its adhesive wear resistance. The research methodology employed was a Design of Experiments (DoE) with six factors and two levels for each factor. The tempering temperature, number of temperings, and carrying out of a thermochemical nitriding treatment were found to have a significant effect. To increase adhesive wear resistance, austenitization at 1100 °C with air cooling is recommended, followed by three temperings at 500 °C and a subsequent nitriding treatment. It should be noted that the quench cooling medium does not have a significant influence on wear resistance. Furthermore, (Fe,Cr)7C3 (M7C3 carbides) are transformed into carbonitrides during nitriding. However, (Fe,V)C (MC carbides) are not affected by this nitriding process.

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Improvement of Impact Toughness and Abrasion Resistance of a 3C-25Cr-0.5Mo Alloy Using a Design of Experiment Statistical Technique: Microstructural Correlations after Heat Treatments

Metals ◽

10.3390/met11040595 ◽

2021 ◽

Vol 11 (4) ◽

pp. 595

Author(s):

Alejandro González-Pociño ◽

Juan Asensio-Lozano ◽

Florentino Álvarez-Antolín ◽

Ana García-Diez

Keyword(s):

Wear Resistance ◽

Impact Toughness ◽

Abrasive Wear ◽

Design Of Experiment ◽

Retained Austenite ◽

Statistical Technique ◽

Cast Irons ◽

Slow Cooling ◽

Tempering Temperature ◽

The Matrix

Hypoeutectic high chromium white cast irons are commonly used in the mining and cement industries, where high resistance to abrasive wear is demanded. Through the application of a Design of Experiment technique (DoE), different factors related to thermal industrial treatments are analysed with regard to resistance to abrasive wear and impact response. Abrasion tests were carried out in accordance with the ASTM G065-16 standard. The provisional results show that to increase wear resistance, high destabilisation temperatures (1050 °C) followed by slow cooling to room temperature (RT) and subsequent tempering at 400 °C are most favourable. This is because these conditions are favourable to maintaining a certain tetragonality of the martensite after tempering and also, because of the presence of a high density of mixed carbides M7C3, through a secondary precipitation during cooling. Oil quenching and a high tempering temperature (550 °C) with long dwell times of 6 h were found to increase impact toughness. These conditions favour a lack of retained austenite. The presence of retained austenite was found unfavourable for both wear resistance and toughness, whereas tempering at 400 °C has been shown to be insufficient to transform martensite on tempering, which in turn seemed to increase the hardness of the matrix constituent.

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Influence of Thermal Parameters Related to Destabilization Treatments on Erosive Wear Resistance and Microstructural Variation of White Cast Iron Containing 18% Cr. Application of Design of Experiments and Rietveld Structural Analysis

Materials ◽

10.3390/ma12193252 ◽

2019 ◽

Vol 12 (19) ◽

pp. 3252 ◽

Cited By ~ 4

Author(s):

Alejandro Gonzalez-Pociño ◽

Florentino Alvarez-Antolin ◽

Juan Asensio-Lozano

Keyword(s):

Wear Resistance ◽

Design Of Experiments ◽

Retained Austenite ◽

Erosive Wear ◽

Structural Refinement ◽

Cast Irons ◽

Additional Increase ◽

Eutectic Carbides ◽

The Matrix ◽

Key Factor

High-Cr hypo-eutectic white cast irons are used in very demanding environments that require high resistance to erosive wear. The influence on the microstructural variation and erosive wear resistance of several fundamental factors related to the thermal treatments of these cast irons was analysed by means of a fractional Design of Experiments (DoE). These factors included the ones related to the destabilization of austenite. The precipitated phases were identified by X-ray diffraction (XRD), while the Rietveld structural refinement method was used to determine their percentages by weight. Erosion wear resistance was calculated using the test defined by ASTM G76. It was concluded that the quench cooling medium does not significantly influence either erosive wear resistance or the proportion of martensite or retained austenite. The destabilization temperature is a key factor with respect to the percentage of retained austenite. In order to increase the amount of martensite and decrease the amount of retained austenite, temperatures not exceeding 1000 °C are required. An increase of 100 °C in the destabilization temperature can lead to a 25% increase in retained austenite. Moreover, tempering temperatures of around 500 °C favour an additional increase in the percentage of martensite. Erosive wear commences on the matrix constituent without initially affecting the eutectic carbides. Once the deterioration of the matrix constituent surrounding these carbides occurs, they are released. High tempering times provide an increase in resistance to erosive wear due to a second destabilization of austenite during the said tempering.

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Influence of Thermal Processing Factors, Linked to the Destabilisation of Austenite, on the Microstructural Variation of a White Cast Iron Containing 25% Cr and 0.6% Mo

Metals ◽

10.3390/met10060832 ◽

2020 ◽

Vol 10 (6) ◽

pp. 832 ◽

Cited By ~ 1

Author(s):

Alejandro González-Pociño ◽

Florentino Alvarez-Antolin ◽

Juan Asensio-Lozano ◽

Hugo Alvarez-Perez

Keyword(s):

Cast Iron ◽

Thermal Processing ◽

White Cast Iron ◽

Erosive Wear ◽

Unit Cell ◽

Cast Irons ◽

Tempering Temperature ◽

Eutectic Carbides ◽

Processing Factors ◽

Non Equilibrium

Hypoeutectic white cast irons containing 25% Cr are used in ore-processing industries due to their high resistance to erosive wear. Applying a Design of Experiments (DoE), the aim of this study is to analyse the influence of thermal processing factors on the microstructural variation of a white cast iron containing 25% Cr and 0.6% Mo. The carbides present in the as-cast state are of the M7C3, M2C, and M3C types. M2C carbides precipitate on the eutectic M7C3 carbides favoured by heterogeneous nucleation conditions. Two kinetics compete during the destabilisation of austenite. One dissolves those eutectic carbides precipitated as a result of non-equilibrium solidification (M7C3 and M2C), while the other enables the precipitation of secondary M7C3 and M23C6 carbides. The M7C3 carbides begin to precipitate first. Low destabilisation temperatures and short dwell times are insufficient to dissolve the precipitated eutectic carbides from non-equilibrium conditions, thus favouring the presence of M2C carbides, which are associated with Mo. The factor that has the greatest influence on hardness is the tempering temperature. The optimal tempering temperature is found to be 500 °C. Short tempering times maintain the distortion of the ferrite unit cell. The precipitation of Cr carbides during tempering requires a temperature of 500 °C and the prior dissolution of the carbon precipitated during the initial stages of said tempering. With short tempering times, the Cr atoms still remain dissolved in the ferrite, distorting its unit cell and increasing the hardness of the matrix constituent of the alloy.

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Erosive Wear Resistance Regarding Different Destabilization Heat Treatments of Austenite in High Chromium White Cast Iron, Alloyed with Mo

Metals ◽

10.3390/met9050522 ◽

2019 ◽

Vol 9 (5) ◽

pp. 522 ◽

Cited By ~ 10

Author(s):

Alejandro Gonzalez-Pociño ◽

Florentino Alvarez-Antolin ◽

Juan Asensio-Lozano

Keyword(s):

Wear Resistance ◽

Retained Austenite ◽

Erosive Wear ◽

Sharp Decrease ◽

Heat Treatments ◽

Structural Refinement ◽

Cast Irons ◽

Eutectic Carbides ◽

Secondary Carbides ◽

The Matrix

With the aim of improving erosive wear resistance in hypoeutectic white cast irons with 18% Cr and 2% Mo, several samples of this grade were subjected to different heat treatments at 1000 °C to destabilize the austenite. The dwell times at this temperature varied from 4 to 24 h and the samples were cooled in air or oil. The existing phases were identified and quantified by applying the Rietveld structural refinement method. The results were correlated with the hardness of the material and with the microhardness of the matrix constituent. The greatest resistance to erosive wear was achieved in those samples that had a higher percentage of secondary carbides. The longer the dwell time at the destabilization temperature of austenite, the greater the amount of precipitated secondary carbides. However, the percentage of dissolved eutectic carbides is also higher. These eutectic carbides were formed as a result of non-equilibrium solidification. Low cooling rates (in still air) can offset this solution of eutectic carbides via the additional precipitation of secondary carbides in the 600–400 °C temperature range. A sharp decrease is observed in the percentage of retained austenite in those treatments with dwell times at 1000 °C equal to or greater than 12 h, reaching minimum values of around 2% volume. The percentage of retained austenite was always lower after oil quenching and the hardness of oil quenched samples was observed to be greater than those quenched in air. In these samples, the maximum hardness value obtained was 993 HV after a 12 h dwell, which result from the optimum balance between the percentages of retained austenite and of precipitated carbides.

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Optimization of Thermal Processes Applied to Hypoeutectic White Cast Iron containing 25% Cr Aimed at Increasing Erosive Wear Resistance

Metals ◽

10.3390/met10030359 ◽

2020 ◽

Vol 10 (3) ◽

pp. 359 ◽

Cited By ~ 3

Author(s):

Alejandro Gonzalez-Pociño ◽

Florentino Alvarez-Antolin ◽

Juan Asensio-Lozano

Keyword(s):

Wear Resistance ◽

Erosive Wear ◽

Decisive Role ◽

Standard Test ◽

Test Method ◽

Structural Refinement ◽

Cast Irons ◽

Eutectic Carbides ◽

The Matrix ◽

Tempering Treatment

Hypoeutectic white cast irons containing 25% Cr are used in very demanding environments that require high resistance to erosive wear, for instance, the crushing and processing of minerals or the manufacture of cement. This high percentage in Cr, in turn, favors corrosion resistance. The application of a Design of Experiments (DoE) allows the analysis of the effects of modifying certain factors related to the heat treatments applied to these alloys. Among these factors, the influence of prior softening treatment to facilitate the machining of these cast irons and the influence of the factors related to the destabilization of austenite, during both quenching and tempering, were analyzed. The precipitated phases were identified by X-ray diffraction (XRD), while the Rietveld structural refinement method was used to determine their percentages by weight. Erosive wear resistance was calculated using the ASTM G76 standard test method. It is concluded that the thermal softening treatment, consisting of 2 h at 1000 °C and 24 h at 700 °C, does not result in additional softening of the material compared to its as-cast state. Furthermore, it is observed that not only eutectic carbides influence wear resistance, but that the influence of the matrix constituent is also significant. It is also verified that the tempering treatment plays a decisive role in wear resistance. Temperatures of 500 °C and tempering times of 6 h increase the wear resistance and hardness of the aforementioned matrix constituent. Tempering temperatures of 200 °C lead to an increase in retained austenite content and the presence of M3C carbides versus mixed M7C3 and M23C6 carbides. The quench cooling medium is not found to have a significant influence on the hardness or wear resistance.

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