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208 TRƯỜNG ĐẠI HỌC SƯ PHẠM KỸ THUẬT - ĐẠI HỌC ĐÀ NẴNG

temperature of electric arc. But choosing right filler Table 3 show selected welding parameters,
metal is very important matter because welding zone applied for each welding procedure with specific steel
has to be processed after that and immersion between grades with welding speed 60 - 70 mm/min
metal of mold cavity and metal of filler rod. This Table 3. Welding current, seleted to apply for welding
issue would be solved in the following section. procedures in experiments with weld bead are made
2. METHODOLOGY on the metal plates
By conducting welding procedures and checking Steel grade Welding current
matching between metal of tool die and metal of filler ER304L ER308L ER309L ER316L
rod, results of these experimental research are SKD11 150 140 130 140
evaluated via showing microstructure of weld beads.
Die steels SKD6, SKD11, K105, P20, S50C are K105 140 130 130 140
selected and they are welded by using filler rod SKD61 140 130 130 140
ER304L, ER308L, ER309L, ER316L with diameter P20 140 130 130 140
3.2mm, low carbon content. Steel plates are used in
welding experiments, represent for mold cavities (see S50C 140 140 130 140
Fig. 3) and need to be preheated due to their high In addition, all welding processes have been
content of alloy elements in composition. All steel conducted under protection of Argon with gas flow 6
plates are grinded to remove oxides for welding - 10 liter/minute at welding position.
surfaces. 3. RESULTS

In case of die cavity, made of SKD11 and filler
rod ER304L shows it is best choice for repair welding
when heat effected zone is narrow and solid liquid
boundary is very thin. These two most dangerous
zones can cause reduction of mechanical properties if
they are so wide.

Fig. 3. Weld beads created
on steel plate in the experiment.
Preheat temperature can be calculated by
definition carbon equivalent CE at first. Fig. 4. Microstructure of weld bead in which SKD11
+
Mn + Cr Mo V Ni + Cu is welded and filled with ER304L
= C + C + +
E For mold cavity, made of SKD61, welded with
6 5 15
filler rod 316L can be considered as the best solution
With chemical composition of steel, used as base in repair welding because evaluation of
metal, is identified by referencing material data sheet, microstructure assumes that grain sizes within weld
in which SKD11 steel has C210Cr12W12, SKD61 bead are small and the solid liquid boundary is very
steel has 40CrMoV5, P20 steel has 0.33C, 0.8Mn, thin (see Fig. 5). These features are evaluated
0.65Si, Chromium 1.75 and 0.4Molipdenum. optically due to limitation of experiments devices
Then preheat temperature can be defined via For mold cavity, made of P20, welded with filler
following formula: rod ER304L shows best result because grains in
microstructure within weld bead and HAZ are unique
T = P 350 C − 0.25 ( ) in size and the solid liquid boundary is also thin (see
E
Fig. 6)
Preheat temperatures are calculated and shown in
following table by using formula, described above.
Table 2. Preheat temperature calculated via CE (%)
Steel grade CE (%) Preheat Temperature Tp
SKD11 4.1 686
SKD61 1.94 455
P20 1.07 317
S50C 0.68 230 Fig. 5. Microstructure of weld bead in which SKD61
is welded and filled with ER316L
ISBN: 978-604-80-9779-0