Acta Metallurgica Slovaca

Abstract
The paper presents the experimental results obtained in structural hardening of the welded safety locks for the railway containers, made from G20Mn6 cast steel, in accordance with SEW 520 standard. Safety locks for the railway containers are placed on the wagon platform. These components are made from cast alloyed steels or cast and welded alloyed steels.
These steels are subjected to normalizing after the casting, to homogenize the dendritic structure of the cast product. If it is necessary, the cast products can be subjected to secondary heat treatments. In the delivery state, I, cast and normalized (C + N), the steel structure is ferrite and perlite with short dendrites, without micro-cracks. In the delivery state, II, quenched and tempered (Q + T), the steel structure is sorbite with small zones of acicular ferrite and perlite.
No heat treatments defects were observed.
The welded safety locks must have good structural and mechanical characteristics for long time. The base metal and the welded joints were subjected to different heat treatments. The aim of the structural hardening heat treatments applied on the mechanical strong stressed base components is to improve the mechanical characteristics, especially the toughness.
The structural examinations and mechanical testing for short time had the aim to choose the optimum structural hardening treatment. Also, a post-welding stress relief heat treatment was performed. The cast products are subjected to volume quenching and high tempering (Q + T) in the next conditions: quenching temperature, 880? C…900? C; cooling medium at quenching: water; maintaining time at quenching, 30 min.; tempering temperature, 520? C…570? C; maintaining time at tempering, 120 min.; cooling medium at tempering, open air.
Also, the cast welded products are subjected to stress relief heat treatments: PWHT1 at 650? C…680? C; PWHT2 at 600? C…650? C; PWHT3 at 520? C…570? C.
During the heat treatments, heating rate, vh, and cooling rate, vc were approximately 100? C / h. The maintaining time at maximum temperature was 120 min. The accuracy of the electric oven for heat treatments was ± 10 %, at maximum temperature of 1000? C.
Metallographic examinations made in accordance with EN 1321 evidenced the structures in the investigated zones. So, in the weld zone of the steel in Q + T + PWHT state, the ferrite and pearlite with acicular ferrite placed in small areas were observed. Also, in the heat affected zone, ferrite and pearlite with sorbite zones and acicular ferrite, non-uniform placed in the matrix were observed. But, no chemical segregations or micro-cracks were observed.
After the structural hardening, the welded safety locks had the mechanical characteristics almost the same with the base metal, in accordance with SEW 520 standard. The maximum hardness values were around 245 HV5 and the tensile stress was 750 – 790 N/mm2.
Impact bending test was performed at - 20? C and + 20? C, in accordance with SR EN 875 – 97 and SR EN 10045/1 – 93, on the samples ISO – V.
The optimum variant for the welded joints was stress relieving heat treatment, made at 520? C…570? C, which led to impact energy values of 59 J, at - 20? C, and 81 J, at + 20? C, much more than the imposed value, 27 J.

No 1 (2007), p. 109-116

mag13.pdf (1 MB)

mag13_eng.txt (3 kB)

Lejček P., Janovec J., Konečná R.

NANOSEGREGATION PHENOMENA AT GRAIN BOUNDARIES OF METALLIC MATERIALS

No 1 (2007), p. 117-130

mag14.pdf (1 MB)

mag14_eng.txt (3 kB)