Microstructure and Mechanical Properties of Weld Fusion Zones in Modified 9Cr-1Mo Steel
01 Jun 2001-Journal of Materials Engineering and Performance (Springer US)-Vol. 10, Iss: 3, pp 320-330
TL;DR: In this article, a plate of modified 9Cr-1Mo steel was welded with three different filler materials: standard 9Cr 1Mo, modified 9 Cr 1Mo and nickel-base alloy Inconel 182 post-weld heat treatment (PWHT) for periods of 2 and 6 hours.
Abstract: Modified 9Cr-1Mo steel finds increasing application in power plant construction because of its excellent high-temperature properties While it has been shown to be weldable and resistant to all types of cracking in the weld metal and heat-affected zone (HAZ), the achievement of optimum weld metal properties has often caused concern The design of appropriate welding consumables is important in this regard In the present work, plates of modified 9Cr-1Mo steel were welded with three different filler materials: standard 9Cr-1Mo steel, modified 9Cr-1Mo, and nickel-base alloy Inconel 182 Post-weld heat treatment (PWHT) was carried out at 730 and 760 °C for periods of 2 and 6 h The joints were characterized in detail by metallography Hardness, tensile properties, and Charpy toughness were evaluated Among the three filler materials used, although Inconel 182 resulted in high weld metal toughness, the strength properties were too low Between modified and standard 9Cr-1Mo, the former led to superior hardness and strength in all conditions However, with modified 9Cr-1Mo, fusion zone toughness was low and an acceptable value could be obtained only after PWHT for 6 h at 760 °C The relatively poor toughness was correlated to the occurrence of local regions of untransformed ferrite in the microstructure
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10 May 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions.
Abstract: To achieve high thermal efficiency, modern day thermal power plants operate at higher operating temperature and pressure which necessitates use of steels with high creep rupture strength such as modified 9Cr-1Mo steels. In the present study, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions. The main focus has been to study the effect of heat treatment temperature ranging from 623 K to 1033 K (350–760 °C) on P91 steel. Further, the effect of furnace cooling, water quenching, tempering at 1273 K (1000 °C) and austenitizing on the mechanical properties and microstructure has been studied. The techniques used for material characterization were scanning electron microscopy (SEM), optical microscopy (OM) and X-ray diffraction. For low tempering temperature, i.e. 623 K (350 °C), M 23 C 6 , M 3 C, M 7 C 3, and MX precipitates have been observed with high yield strength (YS), tensile strength (UTS), hardness and low toughness. In the high temperature range, 923–1033 K (650–760 °C), fine MX, M 7 C 3 , M 23 C 6 , M 2 X, and M 3 C precipitates have been observed with low YS, UTS, hardness and high toughness. The steel tempered at 1033 K (760 °C) was observed to be having best combination of YS, UTS, hardness, toughness and ductility.
122 citations
TL;DR: In this article, microstructure evolution in P91 steel and their weldments are reviewed in as-virgin and heat treatment and creep exposure condition, and the role of grain coarsening, Cr/Fe ratio, lath widening and dislocation density on creep rupture life of base metal and weldments is discussed.
Abstract: In present research article, microstructure evolution in P91 steel and their weldments are reviewed in as-virgin and heat treatment and creep exposure condition. The thermal stability of P91 steel is derived from solid solution strengthening, sub-grain hardening and precipitation hardening. The initial microstructure plays an important role in deciding the mechanical properties of P91 steel and their weldment in long-term ageing and creep exposure condition. Effects of various alloying elements present in P91 steel and their related phase have also been discussed in details. The role of grain coarsening, Cr/Fe ratio, lath widening and dislocation density on creep rupture life of base metal and weldments are discussed. The combined effects of lath martensitic microstructure, residual stress and diffusible hydrogen content on performance of P91 steel material are also discussed.
100 citations
07 Mar 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel has been investigated using optical metallography and scanning electron microscopy (SEM).
Abstract: Mechanical properties of creep enhanced ferritic (CSEF) steels is affected by various parameters, the solutionizing temperature is one of them. The present work demonstrates the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel. Optical metallography (OM) and Scanning electron microscopy (SEM) were carried out to study the microstructure of P91 steel in different heat treatment conditions. In order to determine the precipitates present in microstructure; X-ray analysis was performed. Moreover, the influence of solutionizing temperature on the mechanical properties (strength, hardness and impact toughness) has also been studied.
86 citations
TL;DR: In this article, the effect of postwelding heat treatment (PWHT) and weld groove designs on the overall microstructure and mechanical properties of P91 steel pipe welds produced by the gas tungsten arc welding process was studied.
Abstract: The martensitic creep-resistant steel designated as ASTM A335 for plate and as P91 for pipe is primarily used for high-temperature and high-pressure applications in steam power plants due to its excellent high-temperature properties such as high creep strength, high thermal conductivity, low thermal expansion, and so on. However, in the case of welded joints of such steels, the presence of an inter-critical heat-affected zone (IC-HAZ) can cause the joint to have lower creep strength than the base metal. In the present study, the effect of post-welding heat treatment (PWHT) and weld groove designs on the overall microstructure and mechanical properties of P91 steel pipe welds produced by the gas tungsten arc welding process was studied. Various regions of welded joints were characterized in detail for hardness and metallographic and tensile properties. Sub-size tensile samples were also tested to evaluate the mechanical properties of the weld metal and heat-affected zone (HAZ) with respect to PWHT. After PWHT, a homogenous microstructure was observed in the HAZ and tensile test fracture samples revealed shifting of the fracture location from the IC-HAZ to the fine-grained heat-affected zone. Before PWHT, the conventional V-grooved welded joints exhibited higher tensile strength compared to the narrow-grooved joints. However, after PWHT, both narrow- and V-grooved joints exhibited similar strength. Fractography of the samples indicates the presence of carbide precipitates such as Cr23C6, VC, and NbC on the fracture surface.
74 citations
TL;DR: In this paper, the effect of high service temperature on impact toughness of P91 (X10CrMoVNb 9-1) base material, weld fusion zone, and HAZ was investigated.
Abstract: The new generation super critical thermal power plants are required to operate at enhanced thermal efficiency of over 50% to reduce the fuel consumption and environmental pollution. Creep strength-enhanced ferritic steels, commonly known as Cr-Mo alloys such as P91 (X10CrMoVNb 9-1) are such material of choice for the next generation power plants. The operating requirement of these next generation power plants is that steam temperature of around 650 °C is maintained. For such high-temperature application, creep strength of material is the primary consideration together with adequate weld heat-affected zone (HAZ) toughness. Present work deals with the effect of high service temperature on impact toughness of P91 (X10CrMoVNb 9-1) base material, weld fusion zone, and HAZ. The impact toughness of HAZ for conventional weld groove design and narrow weld groove design has been evaluated experimentally in as-welded and at different post-weld heat treatment conditions. Fractography of the impact toughness specimens of base metal, weld fusion zone, and HAZ was carried out using scanning electron microscope. The effects of heat treatment schemes on the percentage of element present at the fracture surface were also studied.
63 citations
References
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TL;DR: In this article, the authors investigated the influence of trace amounts of V and Nb on the sequence of precipitation processes and identified the basis for the enhanced high-temperature strength compared to the standard 9Cr-lMo composition.
Abstract: The tempering and subsequent annealing of modified 9Cr-lMo steel have been investigated to determine the influence of trace amounts of V and Nb on the sequence of precipitation processes and to identify the basis for the enhanced high-temperature strength compared to the standard 9Cr-lMo composition. Air cooling (normalizing) from 1045 °C results in the precipitation of fine (Fe, Cr)3C particles within the martensite laths. Additional carbide precipitation and changes in the dislocation structure occur during the tempering of martensite at 700 °C and 760 °C after normalizing. The precipitation of M23C6 carbides occurs preferentially at lath interfaces and dislocations. The formation of Cr2C was detected during the first hour of tempering over the range of 650 °C to 760 °C but was replaced by V4C3 within 1 hour at 760 °C. During prolonged annealing at 550 °C to 650 °C, following tempering, the lath morphology remains relatively stable; partitioning of the laths into subgrains and some carbide coarsening are evident after 400 hours of annealing at 650 °C, but the lath morphology persists. The enhanced martensite lath stability is attributed primarily to the V4C3 precipitates distributed along the lath interfaces and is suggested as the basis for the improved performance of the modified 9Cr-lMo alloy under elevated temperature tensile and creep conditions.
155 citations
TL;DR: In this paper, a ternary system composed of a pure iron substrate and a 70Ni-30Cu filler metal was used to determine the nature and evolution of boundaries and structure in dissimilar metal welds.
Abstract: Cracking, or disbonding, along the fusion boundary in dissimilar metal welds has been a persistent problem, particularly in applications where austenitic alloys are clad on to structural steels for corrosion protection. Many failures in dissimilar metal welds occur as a result of cracking along a boundary that runs parallel to the fusion boundary in the adjacent weld metal. A preliminary investigation was undertaken to determine the nature and evolution of boundaries and structure in dissimilar metal welds using a simple ternary system composed of a pure iron substrate and a 70Ni–30Cu (Monel) filler metal. Changes in base metal dilution were found to alter the evolution of boundaries and structures near the fusion boundary dramatically. Optical metallography and electron microanalysis reveal that the resulting weld microstructures and boundaries are similar to those observed in engineering materials used for cladding and corrosion resistant overlay. Transmission electron diffraction analysis revea...
55 citations
TL;DR: In this paper, the authors describe an investigation of the creep rupture strength (CRS) of 9Cr•1Mo•V•Nb•N steel welded joints by welding thermal cycle simulation.
Abstract: Summary This paper describes an investigation of the creep rupture strength (CRS) of 9Cr‐1Mo‐V‐Nb‐N steel welded joints by welding thermal cycle simulation. The reduction in the CRS of the welded joints is successfully reproduced, and the reasons for this reduction are discussed from the perspective of fine precipitates in the matrix. The CRS of the simulated HAZ (heat affected zone) varies with the peak temperature of welding thermal cycle simulation (PT). It falls sharply beyond the Ac1 temperature, gradually reaching the minimum at the Ac3 temperature of 925 °C. At any higher temperature than Ac3, it rises steadily, showing almost the same CRS as the base metal at 1100°C. The weakest CRS of the simulated HAZ lies at the lowest limit of the CRS data band of various welded joints prepared by GTA (TIG), MMA, and submerged‐arc (SA) welding with the same base metal. The simulated HAZ is useful for evaluation and analysis of the CRS reduction of welded joints. Heating to the Ac3 temperature by welding change...
26 citations
TL;DR: In this paper, the authors describe the Weldability of 9Cr•1Mo•Nb, V P91 steel intended for service in the power industry and show that it can be used in a number of applications.
Abstract: (1996). Weldability of 9Cr‐1Mo‐Nb, V P91 steel intended for service in the power industry. Welding International: Vol. 10, No. 5, pp. 370-380.
13 citations