Abstract
This research studied the application of the response surface methodology (RSM) and central composite design (CCD) experiment in mathematical model and optimizes postweld heat treatment (PWHT). The material of study is a pressure vessel steel ASTM A516 grade 70 that is used for gas metal arc welding. PWHT parameters examined in this study included PWHT temperatures and time. The resulting materials were examined using CCD experiment and the RSM to determine the resulting material tensile strength test, observed with optical microscopy and scanning electron microscopy. The experimental results show that using a full quadratic model with the proposed mathematical model is Y TS = −285.521 + 15.706X 1 + 2.514X 2 − 0.004X 1 2 − 0.001X 2 2 − 0.029X 1 X 2. Tensile strength parameters of PWHT were optimized PWHT time of 5.00 hr and PWHT temperature of 645.75°C. The results show that the PWHT time is the dominant mechanism used to modify the tensile strength compared to the PWHT temperatures. This phenomenon could be explained by the fact that pearlite can contribute to higher tensile strength. Pearlite has an intensity, which results in increased material tensile strength. The research described here can be used as material data on PWHT parameters for an ASTM A516 grade 70 weld.
Highlights
Pressure vessel steel ASTM A516 Grade 70 is a boiler pressure vessel quality steel that has good weldability and excellent notch toughness and is perfect for moderate and lower temperature services
This research is the application of response surface methodology (RSM) to find the optimal parameters and the central composite design (CCD) experimental design for a mathematical model to predict the tensile strength [9, 10]
The second factor consisted of postweld heat treatment (PWHT) temperature examined at 470, 520, 570, and 620∘ C
Summary
Pressure vessel steel ASTM A516 Grade 70 is a boiler pressure vessel quality steel that has good weldability and excellent notch toughness and is perfect for moderate and lower temperature services. As the carbon content of the steel is increased, welding procedures must be designed to avoid the formation of large amount of hard martensite in the heat affected zone [1]. Mead and Pike [6] and Hill and Hunter [7] conducted earlier work on RSM This has been used in tool life modeling, surface roughness modeling, and other machining processes. This research is the application of response surface methodology (RSM) to find the optimal parameters and the central composite design (CCD) experimental design for a mathematical model to predict the tensile strength [9, 10].
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