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Effect of the Heating Temperature of a Nickel-Chromium Steel Charge Material on the Stability of the Forging Process and the Durability of the Die

Hawryluk Marek R., Lachowicz Marzena, Janik Marta, Gronostajski Zbigniew, Stachowicz Mateusz

Archives of Metallurgy and Materials

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2023

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Vol. 68, iss. 2

711--722

EN

The study discusses the issues of low durability of dies used in the first operation of producing a valve type forging from high nickel steel assigned for the application in motor truck engines. The analyzed process of manufacturing the exhaust valve forgings is realized in the coextrusion technology, followed by forging in closed dies. This process is difficult to master, mainly due to elevated adhesion of the charge material (high nickel steel - NCF3015) to the tool substrate as well as very high abrasive wear of the tool, most probably caused by the dissolution of hard carbide precipitates during the charge heating. A big temperature scatter of the charge during the heating and its short presence in the inductor prevents microstructure homogenization of the bearing roller and dissolution of hard precipitates. In effect, this causes an increase of the forging force and the pressures in the contact, which, in extreme cases, is the cause of the blocking of the forging already at the beginning of the process. In order to analyze this issue, complex investigations were conducted, which included: numerical modelling, dilatometric tests and hardness measurements. The microstructure examinations after the heating process pointed to lack of structure repeatability; the dilatometric tests determined the phase transformations, and the FEM results enabled an analysis of the process for different charge hardness values. On the basis of the conducted analyzes, it was found that the batch material heating process was not repeatable, because the collected samples showed a different amount of dissolved carbides in the microstructure, which translated into different hardnesses (from over 300 HV to 192 HV). Also, the results of numerical modeling showed that lower charge temperature translates into greater forces (by about 100 kN) and normal stresses (1000 MPa for the nominal process and 1500 MPa for a harder charge) and equivalent stresses in the tools (respectively: 1300 MPa and over 1800 MPa), as well as abrasive wear (3000 MPa mm; 4500 MPa mm). The obtained results determined the directions of further studies aiming at improvement of the production process and thus increase of tool durability.

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Influence of the nitrided layer thickness of dies made of two types of tool steel used in hot extrusion of valve forgings made of nickel–chromium steel on the durability of these tools

Hawryluk Marek, Lachowicz Marzena, Janik Marta, Ziemba Jacek, Gronostajski Zbigniew

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 4

277--293

EN

The study constitutes an analysis of the durability of dies used in the first operation of producing valve forgings from chromium–nickel steel (NCF 3015) for motor trucks. The average durability of the dies (subjected to standard thermal treatment and nitriding) in this operation equals about 800 forgings. To perform an in-depth analysis of the effect of the nitrided layer thickness (0.1 mm and 0.2 mm) and the tool material (W360 and QRO90) on the possibilities of increasing the die durability, complex studies were carried out, which included: a macroscopic analysis combined with 3D scanning, microstructural examinations using a scanning microscope and a metallographic microscope, as well as hardness measurements. A minimum of three tools were tested for different variants, and for each of them, one representative die was selected for detailed examinations. The research showed the presence of abrasive wear, thermo-mechanical fatigue and traces of adhesive wear as well as plastic deformation on the surface of the working impressions. Also observed was the effect of the extruded material sticking to the tools (high friction and the presence of intermetallic phases in the extruded material) and the forging being blocked in the smallest section of the die, which is a critical factor causing a production shutdown and the necessity of tool replacement. The highest mean durability equalling 2600 forgings was obtained for the dies with a lower carbon content and a higher content of vanadium and the nitrided layer thickness at the level of 0.2 mm. The lowest mean durability (after one forging item) was recorded for the dies made of steel with a higher carbon content and a higher chromium content, forming less stable compound carbides and the thickness layer at the level of 0.1 mm.

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Zastosowanie wyników symulacji numerycznej do analizy i poprawy przemysłowego procesu wytwarzania odkuwki zaworu

Hawryluk Marek, Krawczyk Jakub, Zwierzchowski Maciej, Janik Marta, Jaruzel Jerzy

Obróbka Plastyczna Metali

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2019

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T. 30, nr 4

291--306

PL

Artykuł dotyczy wykorzystania wyników modelowania numerycznego do wielowariantowej symulacji procesu wytwarzania odkuwki zaworu ze stali chromowo-niklowej przeznaczonej dla silników samochodów ciężarowych. Odkuwka tego typu wytwarza-na jest w dwóch operacjach: wyciskania współbieżnego długiego trzonka, a następnie kucia wykańczającego głowy zaworu. Głównym problemem w tym procesie jest stosunkowo niska trwałość narzędzi; w pierwszej operacji wyciskania obserwowane jest przedwczesne zużycie matrycy, a w drugiej operacji niska trwałość stempla, co związane jest z intensywnym zużyciem ściernym oraz adhezją materiału odkuwki do narzędzi. Modelowanie numeryczne przeprowadzono przy użyciu pakietu obliczeniowego Forge 2.0, w celu analizy wpływu zmian warunków temperaturowych oraz tarcia. Szczegółowej analizie poddano drugą operację kształtowania – kucie na gorąco głowy zaworu, gdyż w przemysłowym procesie, ze względu na niewystarczającą kontrolę kluczowych parametrów technologicznych, mogą wystąpić niewielkie zmiany warunków tribologicznych, co wpływa na poprawność całego procesu. Przeprowadzona wielowariantowa analiza procesu kucia z wykorzystaniem modelowania numerycznego do-starczyła wielu cennych informacji dotyczących zmian kluczowych parametrów trudnych do uzyskania podczas analizy procesu przemysłowego oraz ich wzajemnego wpływu na siebie, takich jak: rozkłady pól temperatury, nacisków oraz parametrów określających zużycie, a także przebiegów sił kucia. Na tej podstawie możliwe jest wprowadzenie bez większych obaw istotnych zmian w procesie przemysłowym, w celu uzyskania jego stabilności i powtarzalności oraz zwiększeniu trwałości oprzyrządowania kuźniczego.

EN

The article discusses the application of the results of numerical modelling for a multi-variant simulation of the process of producing a chromium-nickel steel valve forging designed for truck engines. A forging of this type is manufactured in two operations: coextrusion of a long shaft, followed by finishing forging of the valve head. The main problem in this process is a relatively low tool durability; in the first extrusion operation, we observe premature wear of the die, whereas in the second operation, a low durability of the punch can be noticed, which is connected with the intense abrasive wear as well as adhesion of the material of the forging to the tools. The numerical modelling was carried out with the use of the Forge 2.0 calculation packet in order to analyze the effect of the temperature conditions and friction. A detailed analysis was performed on the second forming operation – hot forging of a head valve, as, in the industrial process, due to insufficient control of the key technological parameters, slight changes of the tribological conditions might occur, which affect the properness of the whole process. The multi-variant analysis of the forging process with the use of numerical modeling provided a lot of valuable information regarding changes in key parameters difficult to obtain during the analysis of the industrial process and their mutual influence on each other, such as: distribution of tem-perature fields, pressures and parameters determining wear, as well as forging force courses. On this basis, it is possible to introduce without major worry significant changes in the in-dustrial process in order to obtain its stability and repeatability, and increase the durability of forging equipment.