| Summary: | temperature and
Boiler superheated installation of power plant requires the materials which
have stable mechanical properties at high pressure, typically of
17.90 MPa and temperature of about 490oC. Cr-Mo alloy steel, according to
ASME standards, can be used for that purpose. Cr-Mo alloy steel has high
hardenability, therefore, a high cooling rate should be avoided on welding
process. The effort to solve these problems is to provide preheating before
welding.
are to study the effect of preheat on the The objectives of this research
changes in microstructure and mechanical properties such as hardness, toughness
and tensile strength. The superheater material is in the form of 12Cr1MoV alloy
steel pipes with a diameter of 2.5 inch and a thickness of 9.1 mm. Welding was
using GTAW welding, filler ER80SG, 110A current and 15V voltage. Preheating
temperature used was 150oC, 200oC, 250oC and without preheat. Mechanical
testing performed was tensile, micro hardness, impact, and microstructure
analysis.
The results of microstructure analysis show that the preheat affects the size
and the phase of microstructure especially on the weld metal and HAZ coarse.
Preheat also increase the toughness and strength and decrease hardness of the
weld. Mechanical testing results show: the tensile strength of 524 MPa without
preheat increased to 531 MPa at 250oC preheat, impact value on weld metal
without preheat for 1.09 J/mm2 increased to 1.22 J/mm2 at 250oC preheat, while
the average value of hardness in the weld metal without preheat at 268, 68kg/mm2
kg/mm2 reduced to 267.13 at 250oC preheat. Stress rupture test results at
temperatures of 600oC show: the value of the strain without preheat reduced by
7.43% to 6.17% at 250oC preheat, no preheat while LMP by 16.93 to 17.59 at
250oC preheat. Based on the weighted properties method shows that the best preheat parameter is preheat 250oC with performance index 98.49
|
|---|