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Evaluation of resistance of duplex steels to sulfide stress cracking at various load modes

Jonsta P., Sojka J., Matocha K., Jonsta Z., Konecna K.

Hutnik, Wiadomości Hutnicze

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2012

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Vol. 79, nr 9

708--713

EN

The paper deals with influence of various load modes and microstructural characteristics on evaluation of resistance of duplex steels 22Cr05Ni to sulfide stress cracking (SSC). Two heats of duplex steel were used. Each of these heats was evaluated both in as-supplied state after rolling and after homogenisation annealing, and also in the state after laboratory annealing by the mode 800 oC/5h/air. Microstructure of steel in the as-supplied state was ferritic-austenitic, in the state after annealing it was ferritic-austenitic with occurrence of the phase σ at the majority phases interface. Testing of resistance of duplex steels was performed in accordance with the standard NACE TM 0177 by tensile test and by four-point bending test. The obtained results have confirmed influence of the used metallurgy of testing on final evaluation of resistance of duplex steels to SSC, as well as influence of microstructural characteristics, which manifested themselves namely by scope of corrosion attack of the samples and by different manner of crack propagation in the matrix.

PL

Artykuł dotyczy wpływu różnych rodzajów obciążeń i zmian mikrostrukturalnych na ocenę odporności stali duplex 22Cr05Ni na siarczkową korozję naprężeniową (SSC). Użyto stali duplex z dwóch wytopów. Każdy z wytopów był oceniany zarówno w stanie bezpośrednio po procesie walcowania i wyżarzania ujednorodniającego, jak i wyżarzonych w warunkach laboratoryjnych (800 oC/5h/powietrze). Mikrostruktura stali w stanie wyjściowym była ferrytyczno-austenityczna, natomiast po wyżarzaniu ferrytyczno-austenityczna z obecnością fazy σ na powierzchni rozdziału faz. Badanie odporności stali duplex przeprowadzono zgodnie z normą NACE TM 0177 wykonując próbę rozciągania oraz próbę zginania 4-punktowego. Uzyskane wyniki potwierdziły zarówno wpływ zastosowanej metody wytwarzania badanego materiału na końcową ocenę odporności stali duplex na siarczkową korozję naprężeniową (SSC), jak również wpływ zmian strukturalnych, co przejawiało się w zasięgu oddziaływań korodujących w badanych próbkach oraz odmiennym sposobie propagacji pęknięć w osnowie.

2

Structural characteristics of nickel super alloy INCONEL 713LC after heat treatment

Jonsta P., Jonsta Z., Sojka J., Cizek L., Hernas A.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 21, nr 2

29-32

EN

Purpose: Aircraft industry often uses nickel super-alloys for blades of jet engine turbines. This paper summarises analysis of infuence of heat treatment on structural characteristics of nickel super-alloy INCONEL 713C. Design/methodology/approach: Experimental investigation castings made of commercially produced nickel super-alloy INCONEL 713LC. Material was after heat treatment subjected to detailed structural analysis with use of methods of light microscopy (LM), or scanning electron microscopy (SEM) on microscopes OLYMPUS IX71 and JEOLJSM 50A. Findings: Mode of optimum heat treatment was proposed. On this basis of obtained results it is possible to recommend a heat treatment, which would consist of heating and dwell at the temperature exceeding 1240 degrees centigrade (min. 1260 degrees centigrade), so that precipitates at the grain boundaries dissolve completly, with subsequent slow cooling down to the temperature of approx. 940-950 degrees centigrade, so that there occurs intesive intra-granular precipitation of inter-metallic phase gamma'. Research limitations/implications: The experiment was limited by occurence a void in cast alloys. Practical implications: Aircraft industry often uses nickel super-alloys for blades of jet engine turbines. Originality/value: On the basis of obtained results it is possible to recommend the most suitable heat treatment, which produce intensive intra-granular precipitation of intermetallic phase gamma'. It was received a new know-how in this field.

3

Comparison of microfractographic behaviour of acicular ferrite and bainite and hydrogen cracking resistance

Mazancova E., Jonsta Z., Mazanec K.

Archives of Materials Science

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2007

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Vol. 28, nr 1-4

90-94

EN

Materials characterized as TRIPLEX having decreased density are constituted on the following chemical composition usually: Fe-26/30Al-0.9/1.2C. Alloy microstructure is preferentially based on the FCC arrangement. Further, microstructure consists of nano-size carbides regularly dispersed in the FCC matrix and of low ferritic particle content (8% approximately). The strength level of this material is immediately connected with the solid solution strengthening forming the matrix basis. Besides this effect, it is useful to take into consideration process of its strengthening due to precipitated fine carbides (above mentioned nano-size k-carbides). The preferential effect of this material is connected with its high absorption capacity (double capacity in comparison with the conventional deep drawing steels applied in automotive industry). The formation of uniformly arranged shear bands (SIP effect) has very important influence on the realized deformation process of discussed material and the achieved beneficial technical response. This process is also influenced due to regular distribution of nano-size k-carbides being coherent to the FCC matrix. Owing to the density decrease up to 10-12%, attained strength level (1000 MPa), excellent formability and high resistance to dynamic loading (high absorption and achieved dynamic capacity) the presented high manganese material can be held for perspective type for many applications in automotive industry. Further, this material finds a perspective application in cryogenic technique (transport and storage of liquid gases) and in rotating machine elements, too.

4

Contribution to the physical metallurgy analysis of transverse cracking in continuously cast steel

Jonsta Z., Hernas A., Mazanec K.

Metallurgy and Foundry Engineering

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1998

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T. 24, no. 4

269--274

EN

The paper is devoted to the study of the physical metallurgy principles of transverse cracking in continuously cast (CC) products. The transversen cracking is connected with the straightening process carried out when the cast steel is solidified throughout the cross section at temperature between 700-11OO°C. The study was performed on commercial low-carbon steel CC at comparable speed 1.6-1.8 m/min. and at different cooling rate intensity of CC billets (180 x 180 mm) and of CC slabs (150 x 700 mm). The microstructure of CC billets consists of a higher amount of ferrite forming a large, soft zone at the grain boundaries of prior austenite. The microstructure of CC slabs consists of a very narrow ferrite films surrounding the prior austenitc grains. The bainite microstructure was found in the matrix. The interaction of the localized plastic deformation in the ferrite zones with the particles precipitated at the austenite grain boundaries contributes to void initiation and subscequently to fracture formation. The occurring of transverse cracking was not observed in the case of billets. The localized stresses and concentrated deformation in a very narrow ferrite film in CC slabs attain the critical values resulting in crack initiation in ferrite.

XX

W pracy przeanalizowano metaloznawcze uwarunkowania powstawania poprzecznych pęknięć w półwyrobach, wykonanych technologią ciągłego odlewania stali. Badania przeprowadzono na przemysłowych wlewkach kwadratowych - o wymiarach poprzecznych 180 x 180 mm, oraz płaskich - o wymiarach 150 x 700 mm, wykonanych z niskowęglowej stali przy porównywalnej prędkości krystalizacji 1,6- l ,8 m/min. i różnej intensywności chłodzenia. W strukturze kwadratowych wlewków stwierdza się znaczny udział ferrytu, tworzącego szerokie strefy wzdłuż-granic pierwotnego austenitu. Natomiast w płaskich wlewkach ferryt tworzy bardzo wąskie strefy na pierwotnych granicach ziarn austenitu. Bainit tworzy osnowę. Generowanie mikropęknięć, a w konsekwencji pękanie wlewków, zachodzi wskutek lokalizacji odkształceń plastycznych w miękkich strefach ferrytycznych i oddziaływania z procesem wydzieleniowym na granicach ziarn austenitu. We wlewkach kwadratowych nie stwierdzono przypadków poprzecznego pękania. Natomiast w płaskich wlewkach inicjowanie oraz rozwój pęknięć powodowane jest obecnością w strukturze bardzo wąskich stref ferrytu.