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1

Wieloetapowa zintegrowana obróbka cieplna wysokowytrzymałych stali konstrukcyjnych o mikrostrukturze wielofazowej

Garbarz B.

Stal, Metale & Nowe Technologie

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2017

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nr 3-4

76--83

PL

W artykule przedstawiono przegląd stanu badań i zastosowań wieloetapowych zintegrowanych obróbek cieplnych. Obróbki te umoż- liwiają wytworzenie w wyrobach stalowych drobnoziarnistej mikrostruktury wielofazowej. Jednym z często stosowanych etapów zintegrowanych obróbek cieplnych jest operacja Q&P (quenching and partitioning) – hartowanie częściowe i rozsegregowanie węgla (z powstałego martenzytu do nieprzemienionego austenitu). Mikrostruktura wielofazowa w stalach wysokowytrzymałych składają- ca się z drobnych ziaren ferrytu, bainitu, martenzytu i austenitu resztkowego w różnych kombinacjach i w różnych proporcjach umoż- liwia uzyskanie korzystnego połączenia wysokich właściwości mechanicznych i dobrej ciągliwości, przy ograniczeniu zawartości pierwiastków stopowych.

EN

The current state of the art in the areas of research and application of multi-step integrated heat treatments has been presented in the paper. These processes allow to produce fine-grained multi-phase microstructure in steel products. One of the frequently used steps of multi-step integrated heat treatments is a Q&P (quenching and partitioning) operation, forcing carbon to partition from the produced martensite to the un-transformed austenite. The multi-phase microstructure in high-strength steels comprising fine grains of ferrite, bainite, martensite and retained austenite – in various proportions and quantities – enables to obtain the attractive combination of high strength properties and good ductility, with the limited content of alloying elements.

2

Optimization of the Q-P Process Parameters for Low Alloyed Steels with 0.2% C

Jirková H., Kučerová L., Aišman D., Mašek B.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 3

1205--1210

EN

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.

PL

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%.

3

High-strength martensitic steels with low Ms temperature

Bublikova D., Masek B., Jirkova H., Jenicek S., Ibrahim K., Cubrova J.

Archives of Materials Science and Engineering

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2014

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Vol. 65, nr 2

53--57

EN

Purpose: Various novel heat treatments and thermomechanical treatment procedures have been developed recently in order to enhance mechanical properties of high-strength steels. Design/methodology/approach: The new heat treatment process was tested on newly designed low alloy AHSS steels alloyed with manganese, silicon, chromium and alternatively molybdenum and nickel. Two different cooling rates of 16°C/s and 1°C/s showed that over a wide interval of cooling rates a hardened structure based on martensite and retained austenite can be achieved with an average hardness from 538 to 716 HV10 and ultimate strength in the range between 1837 and 2354 MPa. Findings: The main aim of these steels was to decrease the temperature Mf to below 100°C by quenching in a water or oil bath and use common industrial techniques. Manganese alloying was used for the required decrease of temperatures Ms and Mf. Silicon and chromium were used to increase the ultimate strength, silicon was used to eliminate the carbide formation and to support sufficient oversaturation of martensite. Practical implications: The industrial application of this process is complicated by the need for quenching in the range between Ms and Mf. The Ms temperature normally lies in the 200-250 °C interval. This is why new steels with low Ms temperature were selected for the experimental programme. Thanks to this feature, the steels could be quenched in water or polymer-based baths. The primary alloying elements of these four selected steels were manganese, silicon, molybdenum and chromium. Originality/value: The experimental heat treatment led to microstructures of martensite with retained austenite in all steels. Their strengths were in the range of 1750-2400 MPa and their A5 mm elongation levels were up to 10%. The morphology and distribution of retained austenite dictate the resulting mechanical properties of the material.