{' '} {' '}
Limited time offer
SAVE % on your upgrade.

Page 22

S . P á l k a – J . H a s i l – P. D o l e ž a l

Z l e p š e n í v l a s t n o s t í l i t é Cr- N i o c e l i D I N 1. 4 8 65 p ř í s a d o u i n o ku l a nt ů

O D B O R N É R ECEN ZOVA N É ČL Á N K Y

Ghe  Gho f  

Obr. 1. Fig. 1.

Rozměry vzorku a vyhodnocované body Dimensions of the sample and points of evaluation

Vyhodnocení odolnost i vůči tepelné únavě Rozptyl dosažených výsledků při této zkoušce je obvykle celkem velký (tab. III), proto byl soubor výsledků statisticky otestován a došlo k vyřazení jedné hodnoty. Navzdory rozptylu zde bylo zaznamenáno viditelné zlepšení odolnosti vůči tepelné únavě u vzorků s EGR. Průměrná hodnota dosažených cyklů byla o 19 % vyšší (obr. 5).

(3)

There are several types of the inoculants known for Cr-Ni steels. The most common are niobium and Al/Ce inoculants which have a density very similar to the melt which causes slow floating of the particles from the melt. Also the addition of boron, zirconium or metallic oxides is being successfully used in laboratory conditions. Several studies worked with the addition of EGR (Elkem grain refiner) which is based on Al/Ce oxides. Principle of the EGR inoculation is the lowering of the pouring temperature working together with combined deoxidation via aluminium and EGR. Aluminium creates oxides which further react with cerium from EGR and there develop dense particles with the density very similar to the melt. Such inclusions slowly float out of the melt and they remain trapped in the base metal where they work as nuclei.

Z ávě r Úspěšné použití inokulantů v Cr-Ni austenitických ocelích vyžaduje užití a kontrolu správné výrobní technologie. Je poměrně snadné dosáhnout zjemnění struktury niobem, ale toto vede ke změně chemického složení materiálu. Použití

a)

c)

Obr. 3. Fig. 3.

164

Obr. 2. Fig. 2.

Zkouška odolnosti vůči tepelné únavě TFR test

b)

d)

Srovnání struktur a průměrného DAS: a) referenční vzorek, DAS 60,8 µm, b) inokulace 1,5 % FeNb, DAS 47,9 µm, c) inokulace 1 % EGR, DAS 41,9 µm, d) inokulace 0,7 % EGR, DAS 52,3 µm Comparison of structures and average DAS: a) reference DAS, 60.8 µm, b) refined by 1.5 % FeNb, DAS 47.9 µm, c) refined by 1 % EGR, DAS 41.9 µm, d) refined by 0.7 % EGR, DAS 52.3 µm

S l é vá re ns t v í . L X I V . k v ě te n – č e r v e n 2016 . 5 – 6

Experiment description The alloy DIN 1.4865 was melted in a 20 kg laboratory induction furnace. There were two kinds of castings produced. Cubes 50 × 50 × 100 mm were used for evaluation of the dendrite arm spacing (DAS). A keel block was parallel used for the production of machined samples for the mechanical testing. There were carried out 22 melts total and produced 44 samples with different combination of deoxidation and inoculation. Pouring temperature was the same in all cases, i.e. 1,480 °C. First of all the reference sample with no inoculation was produced and all further products were compared to it. The granularity of the refiners was 1 – 4 mm in all cases following the recommendation of the producer. The exact conditions of tests and results of average DAS is stated in tab. I. The microstructure was evaluated in 4 points (fig. 1). Hot tensile properties and thermal fatigue at 950 °C were evaluated on the samples produced by the technology

Profile for INA SPORT spol. s r.o.

Slevarenstvi 5-6 2016  

Slevarenstvi 5-6 2016  

Profile for inasport