Experimental Study on Thermomechanical Properties of New-Generation ODS Alloys

By using a combination of new technologies together with an unconventional use of different types of materials, specific mechanical properties and structures of the material can be achieved. Some possibilities are enabled by a combination of powder metallurgy in the preparation of a metal matrix with dispersed stable particles achieved by mechanical alloying and hot consolidation. This paper explains the thermomechanical properties of new generation of Oxide Dispersion Strengthened alloys (ODS) within three ranges of temperature with specified deformation profiles. The results show that the mechanical properties of new ODS alloys are significantly affected by the thermomechanical treatment

SEMI-SOLID PROCESSING OF METAL-OXIDE COMPOSITE

One of the available routes to developing a new material resistant to high-temperature creep is to create a microstructure consisting of a metal matrix and dispersed stable particles. For making intricately shaped components from such materials, new processes must be found to allow near net shape products to be manufactured in a simple and rapid manner. A semi-solid processing chain relying on mini-thixoforming could become one such process. For this purpose, an unconventional technology chain was designed in the present experiment. The chain comprises mechanical alloying, powder metallurgy techniques and thermomechanical treatment with transition through the semi-solid state. In this chain, thanks to the intensive deformation at the thixo-forming stage, the desired shape is achieved effectively. The second requirement was the good creep resistance of the material. To this purpose, two different powder materials consisting of metals and oxides were proposed. In both cases, the metal constituent contained iron and aluminium. The primary difference between the materials denoted as A and B was the nature of the oxides acting as strengthening particles. The powder mixture was prepared by mechanical alloying and compacted using various techniques. The powder mixture for the A material was compacted using high-pressure torsion (HPT). The B material was compacted by heating the mechanically alloyed powder enclosed in a steel container in a furnace and by subsequent intensive compressive deformation in a press. From the resulting products, cylindrical specimens for semi-solid processing were cut. The rate of heating to the semi-solid processing region was high. In the first stage, appropriate temperatures and heating rates were sought and optimized. These are crucial in obtaining the desired fine and adequately uniform dispersion of particles providing the strengthening effect

VÝZKUM VLIVU DEFORMACE NA CHOVÁNÍ CHROMOVÝCH KARBIDŮ V NÁSTROJOVÉ OCELI POMOCÍ TECHNOLOGIE TVÁŘENÍ S PŘECHODEM PŘES SEMI-SOLID STAV

Klasické zpracování nástrojových ocelí je již v průmyslové praxi běžně využíváno, přesto se však stále hledají cesty, jak odstranit ze struktury problematické ostrohranné primární karbidy chromu, které zhoršují houževnatost nástrojových ocelí. Díky dalšímu výzkumu jiných metod tváření byla objevena nové dosud nevyužívané metody pro modifikaci výsledných struktur. Díky tomuto zpracování lze dosáhnout lepších mechanických vlastností. Hlavním problémem u vysocepecných ocelí ledeburitického typu je tvorba ostrohranných karbidů. Tyto karbidy jsou obtížně rozpustitelné a v mikrostruktuře díky jejich velikosti a tvaru nežádoucí. Zvyšují sice odolnost materiálu vůči opotřebení, ale současně snižují houževnatost a mohou být koncentrátory napětí. Tento příspěvek je věnován využití jedné z těchto technologií. V tomto případě se jedná o využití technologii semi-solid zpracování. V přechozích letech bylo při zpracování nástrojové oceli pomocí tixoformingu dosaženo nekonvenční struktury a mechanických vlastností. Toto zjištění se následně stalo podnětem k dalším experimentům. Struktura získaná kombinací semi-solid zpracování a následným tvářením měla oproti standardně dosahovaným strukturám po semi-solid zpracování odlišný charakter. Karbidické síťoví bylo redistribuováno v celém objemu materiálu, tím vytvářelo zpevňující prvek a nezpůsobovalo křehkost oceli, kterou trpí materiály s výrazným karbidickým síťovím. Tímto způsobem byla navržena a sestavena nová technologie, umožňující zásadní modifikaci struktury a tím i zlepšení mechanických vlastností. Tento postup zpracování byl dále aplikován na polotovary větších rozměrů a byl zjišťován i vliv jednotlivých stupňů deformace i směr tváření na vývoj struktury.Induction hardening technology is mainly used for processing parts where high hardness, although conventional treatment of tool steels is ordinarily used in industrial practice, engineers continue to seek new procedures to rid tool steels of objectionable primary sharp-edged chromium carbides, which impair toughness. Fortunately, research into metal forming yielded new methods of modifying the microstructure of hypereutectoid steels. Using these methods, mechanical properties can be improved by virtue of eliminating objectionable sharp-edged carbides. These carbides resist dissolution and their size and shape make them undesirable microstructural constituents. Although they do improve wear resistance of the matrix, they also impair toughness and may act as stress concentrators. The microstructures produced by a sequence involving semi-solid processing and subsequent forming operations were different from conventional semi-solid-processed microstructures. In the former microstructures, the prior carbide network was broken up, dispersed, and became a strengthening constituent. Brittleness which plagues materials with prominent carbide networks was thus removed. The experimental material used in this study was X210Cr12 tool steel. Two semi-solid processing temperatures were used: 1240°C and 1260°C. There were two holding times: 30 minutes and 60 minutes. Another variable was the number of reductions. The resulting microstructures were examined with respect to individual sequences and reductions applied. Detailed microstructure analysis was carried out using a scanning electron microscope (SEM). Chemical compositions of carbides were determined by means of EDS (Energy Dispersive X-ray Spectroscopy). Microhardness was measured in order to gather comprehensive materials data. The purpose of the study was to identify trends, if any, in microstructural property evolution in response to the above-described processing sequence

The Effect of Alloying on Mechanical Properties of Advanced High Strength Steels

Quenching and partitioning process with incorporated incremental deformation was optimized for six high strength steels with various contents of carbon (0.4-0.6%), manganese (0.6-1.2), silicon (2-2.6%) and chromium (0.8-1.3%). The optimization was gradually done for each steel with respect to the final microstructures and properties. The effect of cooling rate, quenching and partitioning temperature on microstructure development was further investigated. Interesting combinations of mechanical properties were obtained, with tensile strength in the region of 1600-2400 MPa and ductility of 6-20%

High Versatility of Niobium Alloyed AHSS

The effect of processing parameters on the final microstructure and properties of advanced high strength CMnSiNb steel was investigated. Several processing strategies with various numbers of deformation steps and various cooling schedules were carried out, namely heat treatment without deformation, conventional quenching and TRIP steel processing with bainitic hold or continuous cooling. Obtained multiphase microstructures consisted of the mixture of ferrite, bainite, retained austenite and M-A constituent. They possessed ultimate tensile strength in the range of 780-970 MPa with high ductility A5 mm above 30%. Volume fraction of retained austenite was for all the samples around 13%. The only exception was reference quenched sample with the highest strength 1186 MPa, lowest ductility A5 mm = 20% and only 4% of retained austenite

Obróbka Q-P dla stali o zawartości 0.2% C

In steels which are treated by the quenching and partitioning (Q&P) process, carbon content is one of the crucial parameters because carbon contributes greatly to stabilization of retained austenite and strengthens the material. In the present study, the Q&P process was gradually optimised for two low-alloyed steels with 0.2 % carbon content and with and without Cr addition. The results show that the cooling rate, as well as the austenitizing temperature, has a pronounced effect on microstructure evolution. The strength and elongation in the Mn, Si and Cr-alloyed steel was approx. 900 MPa and more than 30 %, respectively.W stalach poddanych obróbce hartowania i partycjonowania (Quenching and Partitioning – Q&P), zawartość węgla jest jednym z kluczowych parametrów, ponieważ węgiel znacząco wpływa na stabilizacje austenitu szczątkowego i umacnia materiał. W niniejszych badaniach obróbka Q&P była stopniowo optymalizowana dla dwóch niskostopniowych stali o zawartości węgla 0, 2% zawierających dodatek chromu oraz bez tego dodatku. Wyniki pokazują wyraźny wpływ szybkości chłodzeniaoraz temperatury austenityzacji na ewolucje mikrostruktury. Wytrzymałość na rozciąganie oraz wydłużenie do zerwania w manganowo-krzemowo-chromowej stali wyniosły odpowiednio ok.900 MPa oraz ponad 30%

High Versatility of Niobium Alloyed AHSS

The effect of processing parameters on the final microstructure and properties of advanced high strength CMnSiNb steel was investigated. Several processing strategies with various numbers of deformation steps and various cooling schedules were carried out, namely heat treatment without deformation, conventional quenching and TRIP steel processing with bainitic hold or continuous cooling. Obtained multiphase microstructures consisted of the mixture of ferrite, bainite, retained austenite and M-A constituent. They possessed ultimate tensile strength in the range of 780-970 MPa with high ductility A5mm above 30%. Volume fraction of retained austenite was for all the samples around 13%. The only exception was reference quenched sample with the highest strength 1186 MPa, lowest ductility A5mm = 20% and only 4% of retained austenite

Díly z vysokopevných ocelí vyrobených tvářením vnitřním přetlakem plynu za tepla

Moderní vysokopevné oceli se stále častěji prosazují jako velmi perspektivní materiál. Tyto materiály se využívají v automobilovém průmyslu, protože umožňují snižovat hmotnost karoserie aut, a tím snižovat spotřebu paliva. Vysoké meze pevnosti jsou dosahovány u martenzitických ocelí, které se zpracovávají tzv. Q-P procesem. Jednou z reálné možnosti výroby tvarových dílů je tváření vnitřním přetlakem za vyšších teplot. Byly odzkoušeny různé parametry tepelného zpracování. Nejprve bylo odzkoušeno pouze kalení dílů v nástroji na různou teplotu pod teplotou Ms. Poté byl zjišťován vliv procesu kalení a přerozdělení. Na oceli s obsahem uhlíku 0,42% byla dosažena mez pevnosti přes 1800 MPa s tažností přes 15%.Advanced high strength steels are promising materials for a variety of applications. They can be used in the automotive industry to reduce the car body weight, and thus the fuel consumption as well. Very good mechanical properties can be obtained in martensitic steels by the quenching and partitioning process. Making complex-shaped parts using a single forming step is now possible with hot metal gas forming. Several heat treatment sequences were designed. One involved plain hardening to a temperature below the martensite start temperature. Another sequence was intended to explore the influence of the quenching and partitioning process. In this steel with a carbon content of 0.42%, tensile strengths in excess of 1800 MPa with elongations above 15% can be achieved