A R C H I V E S o f

F O U N D R Y E N G I N E E R I N G

Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences

ISSN (1897-3310)Volume 15

Issue 4/2015

75 – 80

15/4

A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 5 , I s s u e 4 / 2 0 1 5 , 7 5 - 8 0 75

Primary Crystallization Studies and

Abrasion Analysis of Cr-Ni-Mo Cast Steel

A. Studnicki *, M. Gromczyk, M. Kondracki, J. Suchoń, J. Szajnar

Department of Foundry Engineering, Silesian University of Technology, Towarowa 7, 44-100 Gliwice, Poland

* Corresponding author. E-mail address: andrzej.studnicki@polsl.pl

Received 30.06.2015; accepted in revised form 15.07.2015

Abstract The article shows results of studies of primary crystallization and wear resistance of Cr-Ni-Mo cast steel intended for work in corrosive and abrasive conditions. The studies of primary crystallization were conducted with use of TDA method and modified tester allowing measurement casting cooling time influence on the cooling and crystallization curves of studied alloys. After heat treatment of examined cast steel wear tests of the samples were conducted on pin-on-disc type device. Keywords: Chromium cast steel, Primary crystallization, Wear, Abrasion, Pin-on-disc

1. Introduction In mining and mineral processing industries the elements of

machines are exposed to influence of particles causing wear (such as sand) and corrosive environment (such as highly salted water). Materials for such elements besides having high mechanical properties need to have high wear and corrosion resistance [1-4].

Among cast alloys high wear resistance and high corrosion is presented by ferrous alloys with high Cr content. Wear resistance remarkably increases with the presence of chromium carbides which are harder than most common wearing materials such as quartz sand. Content of chromium higher than 12 % in ferrous alloys grants enhanced corrosion resistance which is strictly connected with the durability of the passive layer made by alloying elements with high affinity for oxygen such as Cr. Nickel as the second basic alloying element in examined cast steel besides having positive influence on corrosion resistance visibly increases plasticity, impact strength and technological properties of cast steel [4]. Molybdenum in corrosion resistant cast steels

highly increases resistance for pitting due to modification of passive layer [4].

While choosing corrosion and wear resistant material we have to make a compromise and decide which one is more important for us in examined case. The excess of carbon in corrosion resistant cast steels is unfavourable, but in wear resistant cast steels it is very favourable as it allows formation of carbides. In the Department of Foundry Engineering of Silesian University of Technology while analysing different groups of cast steels the focus was on tool cast steels, especially chromium cast steels. Adding Ni and Mo to those cast steels resulted in creation of new Cr-Ni-Mo cast steel having changeable wear and corrosion resistance due to its working conditions.

In presented article the results of primary crystallization and wear studies of the new Cr-Ni-Mo cast steel obtained in industrial conditions were shown.

76 A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 5 , I s s u e 4 / 2 0 1 5 , 7 5 - 8 0

2. Materials and methodology of the research

The primary crystallization and wear resistance of two Cr-Ni-Mo cast steels with 12 % and 18 % Cr wt. were examined. Table 1 shows chemical compositions of examined cast steels.

Cr-Ni-Mo cast steel was melted in industrial conditions using electrical arc furnace with the capacity of 0,5 ton from the commonly used materials (steel scrap, ferrochromium, ferromolybdenum, nickel). Prepared alloy was used for mechanical coal miner parts and specimen castings poured according to scheme in Fig. 1.

Table 1. Chemical composition of examined Cr-Ni-Mo cast steel % wt.

No. melt C Mn Si P S Cr Ni Mo V Cu Al Ti 1 Cr18 0,60 0,47 0,64 0,029 0,013 17,20 3,07 0,66 0,043 0,12 0,070 0,033 2 Cr12 0,52 0,68 0,57 0,026 0,014 12,30 1,54 0,67 0,043 0,17 0,072 0,020 3 C8 0,24 1,16 0,71 0,008 0,003 0,65 0,26 0,30 0,009 0,15 0,036 0,044

Fig. 1. Test stand

Crystallization process was examined with use of TDA method [5-7, 9]. On the test stand three cooling curves of three castings with different solidification modules were obtained. Specimen casting with the lowest module (M=0,75) was recorded in ATD-C probe, moderate module (M=0,90) in ATD-Is probe and the highest module (M=2,50) in ATD-Is100 probe.

The solidification time of the casting in ATD-Is100 probe is 10 times longer than the solidification time in ATD-C probe. ATD-Is100 probe is commonly used for examination of the thermal gradient in cooling castings. In the studies only the cooling curve registered in the thermal centre of the examined casting was used.

Wear tests were conducted with the modified pin-on-disc method using the Tribotester 3-POD device [9]. In this method the reference sample made of low alloyed wear resistant steel is used (table 1). Figure 2 shows scheme of the device, its photo and the sample. The samples for wear tests were extracted from overflow part of the measuring casting and heat treated using air quenching (950oC/15 min/air). Hardness of examined samples is shown is table 2.

Table 2. Hardness of examined samples

No. melt Heat treatment Hardness HRC

1 Cr18h 950oC/15 min/air 51 2 Cr12h 950oC/15 min/air 52 3 C8

(reference) As delivered

(Creusabro 8000) 42

In conducted studies the parameters of the work of Tribotester 3-POD device were: − grinding wheel: abrasive paper C120, silicon carbide, − rotational speed of the grinding wheel: 100 rpm, − rotational speed of sample holder: 400 rpm, − load of single sample: 220 G, − total time of wear test: 60 min, − dry grinding.

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