OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
A working mixture was consisting of 25 to 35 percent fresh carburizer and 65 to 75 percent used material. Work
pieces were cleaned of dirt, scale, and rust for solid carburizing. They were then placed in a box. Welded boxes
of cast heat resistant alloys were used.
Packing the work was accomplished by first covering the bottom of the box with a 40mm to 45 mm layer of
carburizer. The work pieces to be carburized were placed on this layer with spaces 20mm to 25 mm between
them and the box walls. Then they were covered with a dense layer of carburizer, 20 to 25 mm thick, which was
rammed before laying the next row of work pieces. The upper row was covered with a layer of carburizer 40mm
to 50 mm thick. The box was closed with a cover. The packed box was placed in the furnace for different time
periods.
3. Results and Discussion
3.1. Surface hardness
The surface hardness of different specimens was measured by Vicker hardness tester. The hardness was checked
three times at different positions and mean of them is shown in table 4. It was seen that for a solid case
carburized component, hardness depends on holding time. It is clear from the table 4 that solid case carburizing
softens the austenitic stainless steel. The surface hardness is found to be increased with shot peening and
nitriding of welded joint.
The surface hardness of the welded joint was enhanced after shot peening due to closing of crests and valleys on
the surface. The average surface hardness of welded joint before shot peening was 235VHN. It is enhanced to
351VHN after shot peening at 5A
S. No.
Table 4: Surface hardness of un-treated, shot peened, nitride carburized specimens and.
Un-treated
specimen
(VHN)
Shot peened
at 5A
(VHN)
Liquid
nitrided
specimen
(VHN)
Carburized specimen
Holding Surface
Time Hardness
(hrs) (VHN)
1 238 352 691 6 210
2 229 347 659 8 219
3 242 362 678 10 225
4 230 341 682 12 228
Average 235 351 678 - 221
The surface hardness of the un-treated, shot peened, nitrided and carburized specimens are listed in Table 4. For
an easy comparison Fig. 3 shows the surface hardness of the different specimens of welded 304L austenitic
stainless steel. It is evident that nitriding causes a high increase in the surface hardness as compared to shot
peening and carburizing process (table 4 and fig 3). The percentage increase in surface hardness with nitiding is
approximately 188%.
Fig 3. Hardness variation for un-treated, shot peened, nitride and carburized specimens.
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