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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TL;DR: In this paper, the pulsed current gas metal arc welding with appropriate welding conditions can provide acceptable bead profile and mechanical properties in welds of modified 9Cr-1Mo steels.
Abstract: Modified 9Cr-1Mo steels are commonly welded using gas tungsten arc welding process for its superior control over the rate of heat input and vaporization loss of the key alloying elements although the rate electrode deposition remains restricted. Recent developments in pulsed current gas metal arc welding have significantly improved its ability to enhance the rate of electrode deposition with a controlled heat input rate while its application for welding of modified 9Cr-1Mo steels is scarce. The present work reports a detailed experimental study on the pulsed current gas metal arc welding of modified 9Cr-1Mo steels. The effect of the shielding gas, welding current, and speed on the weld bead profile, microstructure and mechanical properties are examined. The results show that the pulsed current gas metal arc welding with appropriate welding conditions can provide acceptable bead profile and mechanical properties in welds of modified 9Cr-1Mo steels.
11 citations
TL;DR: In this article, the authors used GTA filler wire having low Nickel content (Mn+Ni of 0.58 wt% including nickel content 0.09 wt%) for P91 steel tempered welds at room temperature.
Abstract: Modified 9Cr-1Mo (P91) steel is widely used as a high temperature structural material in the fabrication of power plant components. Alloying elements significantly influences the microstructure and mechanical properties of P91 steel weldments. The alloying elements manganese and nickel significantly influence the lower critical phase transformation temperature (AC1) as well as tempering response of welds. In the existing published information there was wide spread use of high Mn+Ni filler wire. In the present study, weldment preparation was completed using GTA filler wire having low Nickel content (Mn+Ni of 0.58 wt% including nickel content of 0.09 wt%). Microstructure and mechanical properties characterization was done. There is a requirement on minimum toughness of 47 Joules for P91 steel tempered welds at room temperature. Microstructural observation revealed that the GTA welds have low δ-ferrite content (<0.5%) in the martensite matrix. In the as-weld condition, the toughness was 28 Joules whereas after PWHT at 760 °C-2 h it was 115 Joules. In the present study, toughness of low nickel weld was higher due to low δ-ferrite content (<0.5%), multipass grain refinement and weld metal deposition of single pass per layer of weldment.
11 citations
TL;DR: In this article, a straight P91 (9Cr-1Mo) martensitic stainless steel steam pipe subjected to a 24-hour daily sequence of start-up and shutdown cycles under a typical operating temperature of 550 °C and pressure of 18 MPa was investigated using finite element analysis code, Abaqus CAE/2019 in conjunction with fe-safe/Turbolife software.
11 citations
TL;DR: In this paper, the microstructural changes during creep of 9Cr-1Mo steel were characterized using ultrasonic and hardness measurements, showing that regardless of the stresses, the ultrasonic attenuation experiences a peak at about 20% of the creep rupture time and a minimum value at about 50%.
Abstract: In this work, microstructural changes during creep of 9Cr-1Mo steel were characterized using ultrasonic and hardness measurements. The creep testing of this steel was firstly performed at 873 K under the initial stresses of 160 and 175 MPa, respectively. Then, eight specimens under each stress level were prepared by the interrupted tests to simulate various creep states. Subsequently, two parameters of ultrasonic attenuation and velocity were introduced by the ultrasonic testing. Experiment results showed that regardless of the stresses, the ultrasonic attenuation experiences a peak at about 20% of the creep rupture time and a minimum value at about 50%, showing a strong correlation between ultrasonic attenuation and the creep life fraction. In addition to a slight increase during the primary creep, the ultrasonic velocity exhibits a significant change during the tertiary creep. Based on the analysis of microstructure changes, it indicated that the ultrasonic attenuation is significantly sensitive to the dynamic changes of the dislocation. In contrast, the velocity is mainly related to the evolution of precipitates. The Vickers hardness decreases monotonously during the creep process and presents a linear relation with the inverse of average diameter of M23C6 carbides during the secondary and tertiary creep. Accordingly, it suggested that the present ultrasonic and hardness measurements provided a convenient tool to evaluate the microstructure evolution during creep degradation of heat-resistant steels.
10 citations
TL;DR: A literature review of previous important articles on post weld heat treatment of pressure vessel steels and its effect on mechanical properties of material is also summarized in this paper, where critical observations, statistics and overall summary related to various materials and heat treatment methods are provided.
10 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.
166 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...
63 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...
30 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.
14 citations