Alternative PWHT to Improve High- Temperature Mechanical Properties of Advanced 9Cr Steel Welds

A. BURGOS; ZUYAO ZHANG; H. G. SVOBODA; E. SURIAN

JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE

SPRINGER

Lugar: Berlin; Año: 2018 vol. 27 p. 6328 - 6338

1059-9495

Creep-resistant 9Cr steels are extremely important in thermal power generation industry due to theirmarked resistance to creep and corrosion. The weldability of these alloys is critical since they are used inwelded construction equipment. The required mechanical properties are achieved after post-weld heattreatment. This study examined the effect of different post-weld heat treatments on microstructure andmechanical properties of creep strength-enhanced 9Cr steel welding deposits. It was obtained with anexperimental flux-cored arc welding wire used under protective gas (Ar-20% CO2). The heat treatmentsused were: (1) tempering (760 C 3 2 h), (2) solubilizing (1050 C 3 1 h) + tempering (760 C 3 2 h) and(3) solubilizing (1150 C 3 1 h) + first tempering (660 C 3 3 h) + second tempering (660 C 3 3 h). Allweldmetal chemical composition was analyzed, and hot tensile tests were carried out at different temperatures.Charpy-V impact tests and Vickers microhardness measurements were also performed.Microstructures were studied using x-ray diffraction and optical and scanning electron microscopy. In allcases, a martensitic matrix with intergranular and intra-granular precipitates was detected. In the asweldedcondition, d-ferrite was also found. Microhardness dropped, and the impact energy increased withpost-weld heat treatments. The highest hot tensile strength result was achieved with samples submitted toaustenization at 1150 C and double tempering at 660 C.