EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

High Silicon Strengthened Ductile Irons (HSiSDI) with 3.5, 4.2 and 4.5 % wt. silicon contents were produced in Y-blocks with different geometries to investigate the effects of silicon and solidification rate on microstructure integrity and tensile mechanical properties. With increasing silicon the strength of the HSiSDs increased, while the ductility decreased progressively, with an abrupt...

Fatigue properties of tool steels and ductile irons are a concern in many of its applications, and the two materials may in some applications be competitor selections. In many cases are long life endurance a requirement, and it may even be as high life lengths as ranging up in the Very High Cycle Fatigue (VHCF) regime, i.e. above 107 load cycles. Tool steels are mostly used with a martensitic...

High-chromium cast irons are typically used in high demanding applications, where low production costs and wear performance are key factors. The excellent resistance of these alloys to both abrasion and erosion results from the overall microstructural features, i.e. type, morphology and distribution of hard primary and secondary carbides, along with the matrix constituents. More specifically,...

Nitriding of cast iron can improve mechanical surface properties. The non-nitridable graphite, however, causes heterogeneities in the nitride layer which limit improvements in corrosion resistance usually achievable upon nitriding of other Fe-based alloys. A strategy to overcome this problem for cast iron is surface remelting to form a white-solidified surface layer and subsequent nitriding....

The complex metallurgical interrelationships in the production of ductile cast iron can lead to enormous differences in graphite formation and the local microstructure by small variations during production. Artificial intelligence algorithms were used to describe graphite formation, which is influenced by a variety of parameters. By predicting the local graphite formation, measures to stabilize...

Cracks in components are subjected to crack-closure-mechanisms that affect the build-up of the relevant stress intensity range threshold during cyclic loading. These mechanisms are essential for crack propagation under service loads in mechanical engineering applications. Such varying load ratios enforce an appropriate change of the long crack threshold value, thus leading to stress ratio...

Reheating of steel slabs for further processing such as hot rolling usually takes place in gas-fired pusher furnaces. Temperatures well above 1000 °C, combined with an atmosphere containing H₂O, CO₂, and O₂, lead to substantial oxidation of most steel grades. Newly developed advanced steels often contain significant amounts of Si. This element plays a dominant...

Tempering of nanostructured bainite has proven to be an excellent choice for components where requirements for enhance service properties at elevated temperatures are needed. Supporting secondary hardening by alloying Mo and V enables the possibilities to combine both effects: nanostructured matrix and secondary precipitation. Detailed characterization by dilatometry and phase analysis using...

In this study, the thermal stability of bainitic ferrite and carbon-enriched retained austenite has been studied in in two steels containing 0.6 C (wt %) and microallowed with V and Mo. For this goal, a nanobaintic microstructure was developed in both steels by a thermal treatment consisting of austinitization at 1150°C for 180 s and a bainitic transformation at 250°C for 14h. High resolution...

Tempering of martensitic steels is commonly employed to improve their ductility and increase their strength by secondary precipitation. The different phenomena which occur during tempering were intensively studied and are well established in such steels. Nano-bainitic steels represent a new class of alloys, whose microstructure consists of nano-structured bainite formed at low temperature with...

In the aviation industry the commercial PH15-5 steel is predominantly applied in structural parts which are subjected to strict requirements for toughness properties. Its microstructure consists of a soft martensitic matrix exhibiting a hierarchical structure consisting of so-called laths, blocks and packets. Previous work of the authors suggested that a small martensitic block size increases...

Compared to other types of steels, maraging steels show an excellent combination of high strength and good toughness. This is achieved by precipitation of intermetallic compounds during ageing of a martensitic matrix. However, delta ferrite might be formed during processing due to non-equilibrium solidification. The present work investigates the influence of delta ferrite on the impact...

Duplex stainless steels (SS) comprise of both ferrite and austenite phases. The combined properties of the individual phases in austenitic-ferritic stainless steel result in excellent combination of corrosion resistance and mechanical properties, and thus they are fast replacing the conventional single-phase austenitic or ferritic stainless steels. The strength of the duplex SS can be further...

Oxide Dispersion Strengthened (ODS) ferritic steels are promising candidates as cladding material for 4th Generation Sodium-cooled Fast nuclear Reactors. Conventional reinforcement is achieved by introducing titanium and yttrium oxide Y2O3 during mechanical milling with matrix steel powder. The strengthening particles are dissolved or reduced as sub-nanometric clusters during this step, before...

Changes in the martensite structure of 0.1%C-2%Si-5% Mn steel with decrease in the prior austenite grain size have been investigated. While prior austenite grain size in the range of 150 to 24 micro-meter led to the formation of martensite with a multi-packet and multi-block structure, a single packet and multi-block martensite structure formed from the prior austenite grain size of about 7...

The cooling rate during the martensitic transformation has been shown to have a strong impact on the fatigue performance of case-hardened steels with differences of up to 20 % [1]. The mechanism for this increase is not fully understood. To clarify the underlying mechanism, the impact of cooling rates on the martensitic transformation in two high carbon steels (0.54 and 0.74 w% C) was studied....

Nanostructurization by bainitic phase transformation is a revolutionary method of improving mechanical properties of the wide range of steels. It can be applied as a single process or as a part of the innovative multistage heat treatment, named B-Q&P, which combines, in one route, two processes: Bainitization and Quenching & Partitioning. While implementing to high carbon low-alloy steels it...

Heat treatment with an electric current has gained interest in the last few years. However, the physical phenomena occurring in these type of treatments are not always fully understood. Thus, to study the influence of the electric current on the interstitial diffusion of carbon, an ARMCO iron sample is placed between the two graphite punches of a Spark Plasma Sintering facility. The current...

The concept of lean medium Mn Quenching and Partitioning (Q&P) steels is supposed to be one of the promising candidates to fulfil the sophisticated requirements for third generation advanced high strength steels (AHSS). The microstructure of Q&P steels consists of a carbon-depleted martensitic matrix with a substantial volume fraction of retained austenite (RA), which undergoes the...

The concept of quenching and partitioning steels, with a high product of strength and strain, as well as good local formability, has arrived in the high-end commercial steel production and has found promising applications in the automotive industry. To this day, the research has focused on the development of uncoated Q&P grades. By using inline galvannealing lines, which includes beside the...

The quenching and partitioning (Q&P) heat treatment is a promising way to produce third generation advanced high strength sheet steels consisting of martensite and retained austenite. To extend the range of the mechanical properties, especially to increase the formability, ferrite can be introduced into the Q&P microstructure. This can be done by annealing in the intercritical temperature...

A novel processing route of thermomechanical rolling followed by direct quenching and partitioning (DQ&P) developed at the University of Oulu has shown good potential for the development of tough ductile ultra-high strength steels both for structural and abrasion-resistant purposes. In this study, fresh attempts have been made to conduct DQ&P processing on medium carbon steels with different...

The increasing demand for lightweight and energetically sustainable automobile materials has brought the application of the Quenching and Partitioning (Q&P) process into consideration for the development of martensitic stainless steels with improved combinations of strength and ductility. The resulting microstructures are formed by a matrix of carbon depleted martensite and films of retained...

The mechanisms governing variant selection phenomena in bainitic microstructures formed during ausforming treatments are not fully understood yet. Previous results cannot be explained by the same rule, which suggests that variant selection is controlled by different mechanisms depending on the steel. In this work, we aim to understand the mechanisms governing variant selection in a medium...

Evaluation of microstructural evolution is often essential for comprehension of aspects of locally occurring physicochemical based phenomena. Often this evaluation is restricted by external limitations such as high temperature phases and therefore impossible to put into execution or too complex to be performed excessively. Simulations have been used widely to model material behavior or...

As the steel industry is tending to the autonomous line control and to improve the control of the products properties by predicting them as a function of the process variables, a model that could estimate the mechanical properties of low-carbon martensitic steels after tempering is required. Modifications to a physical-based model previously developed [1] were applied to simulate industrial...

A new model has been extended to predict austenite $\leftrightarrow$ ferrite transformation kinetics for complex thermal cycles with the cementite dissolution on a wide range of Fe-C-Mn steels. For each alloying element, the concentration profile is computed solving a unique diffusion equation (including the 2 phases and the interface). The interface is described assuming linear variation of...

Quenching and Partitioning (Q&P) is not a typical heat treatment for martensitic stainless steels, but variation of the interception temperature and subsequent holding at low “tempering” temperatures (<500°C) has a significant impact on these steels due to partitioning effects.

With the help of physical models, the microstructure after Q&P heat treatment can be predicted. In comparison to...

Introduction/Purpose

The need for steels with high strength, increased toughness and good weldability led to the development of high - strength low - alloy (HSLA) steels. In this steels a combination of microalloying elements and thermomechanical processing leads to the required properties. An understanding of the precipitation behavior of the nanometer - sized precipitates is essential...

Thermochemical surface treatments, such as carburizing are widely used methods for case hardening in order to improve wear resistance, impact strength, and fatigue properties in gear applications. Alternatives to carburizing are nitriding or carbonitriding by diffusing nitrogen into the surface of metals. Previous works have shown that the nitrogen enrichment in austenite has drastic...

High-strength low-carbon steels are of considerable technological importance in engineering applications such as automotive, shipbuilding, and energy industries. Precipitation strengthening is an effective method for strengthening low-carbon steels. Among various potential precipitates used for precipitation strengthening, NiAl is one of the most effective phases to achieve high...

Phase transformations and the partitioning of carbon play a key role for the evolution of the microstructures of high speed steels. In particular the microstructural contributions to the hot properties of high-speed steels (matrix strengthening and strengthening due to secondary hardening carbides) have to be revealed. The quenching process after austenitization of high speed steels is a key...

Low alloyed, creep resistant CrMoV alloys such as 2.25Cr-1Mo-0.25V are often used for high pressure vessels like hydrocracking reactors in the petrochemical industry. Therefore, they are usually joined via submerged-arc welding. For this purpose, the material and especially the weld seams have to withstand high temperatures in combination with high pressures. Fine V and Nb containing...

Austenite-to-ferrite phase transformation in steels has been largely investigated during the last decades as it plays an important role in controlling the mechanical properties of steels. Despite tremendous efforts in understanding the mechanisms controlling ferrite formation, the role of substitutional elements during ferrite

Validation of the developed models requires an experimental...

Advance High Strength Steels (AHSS) have been widely used in the automobile industry during the last decades due to their excellent combination of strength, ductility and weldability at a competitive cost. In this context, low carbon bainitic steels have proved to be interesting alloys to obtain high strength and toughness microstructures with good formability. However, the final mechanical...

Nowadays steel research is devoted to improve mechanical properties in order to produce lightweight products, in particular for automotive industry. 3rd generation of advanced high strength steel (AHSS) represent a significant step in the reduction of fuel consumption and the production of light and safe car bodies. In particular, carbide free bainitic TRIP (TRansformation Induced Plasticity)...

K340 steel thanks to the high value of alloying elements and high mechanical properties is used for dies and punches in mint industry. In this work we tried to increase its properties via different heat treatments. A series of simulations and dylatometric measurements was made to determine optimal parameters of heat treatment. Then properties such as hardness, crack resistance, tensile...

Heat treatments containing interrupted quenching and bainitizing below the primal Ms temperature were investigated for EN X38CrMoV5-1 steel. Via complex treatment triple-phase microstructures including martensite, bainitic ferrite and austenite were obtained. Prior martensite provided additional surfaces for bainite heterogenous nucleation. In this way, bainitic transformation was supported by...

The desired microstructure of advanced high strength steels is often multiphase in nature, combining softer (ferrite, retained austenite) and harder (martensite, bainite) phase constituents in order to achieve high strength-ductility combinations. The thermomechanical processing of these steels may involve isothermal heat treatments around the Ms temperature. The presence of pre-existing...

The development of Very High Bypass Ratio (VHBR) aero-engines can contribute to fulfilling the goals of the Sustainable and Green Engines (SAGE) programme. The potential environmental benefits of the new
aero-engine concept require increased speed and loading capabilities as compared to today’s solutions.

This paper describes the development of an advanced temperature resistant, corrosion...

Driven by the demands for energy efficiency and weight savings, the improvement of Advanced High Strength Steels (AHSS) is of high industrial interest. Despite the high strength and ductility of AHSS, the Zinc (Zn) coating typically applied to increase its corrosion resistance can be the origin of significant mechanical property degradation if, for example, joined with spot welding. This...

Zn-coated advanced high strength steels (AHSS) of the 3rd generation are an important part of modern car body lightweight constructions with excellent corrosion properties. However, liquid metal embrittlement (LME) during manufacturing processes such as resistance spot welding of AHSS is still a major concern that has attracted a great attention of industries and academic researchers. Despite...

The present study focuses on the effect of heating rate on ferrite to austenite transformation and carbide dissolution in a chromium-molybdenum low alloyed steel. Scope is to shed light in the mechanisms that lead to mixed microstructures with the coexistence of martensite, lower bainite and small amounts of retained austenite. For this purpose a conventional heating rate (10oC/s) was examined...