Effect of Heat Treatment on Microstructure and Mechanical Properties of API X90 Pipeline Steel Welded Joints

In this work, X90 pipeline steel was welded by shielded metal arc welding with root and submerged arc welding with calk and cap. After that, the joint was tempered at 550 °C and 600 °C. Subsequently, the microstructure and mechanical properties were investigated by optical microscope, scanning electron microscope (SEM) and Vickers hardness tester. The fracture surface of welded joint was analyzed by SEM. The experiments show that: After high-temperature tempering treatment, the Widmanstatten structure disappears in coarse-grained region. The number of lath martensite in the original structure of the welded joint decreases, and the quantity of granular bainite increases. The acicular ferrite disappears gradually and the polygonal ferrite grains increase, and the M/A island components decompose into fine grains with the increase in tempering temperature. The mechanical properties of the joints also change and the hardness rises because of the disappearance of Widmanstatten structure improves after heat treatment, and yield strength and tensile strength of the specimens have the lowest values after tempering at 550 °C. After tempering at 600 °C, the hardness decreases and strength–ductility reaches 11,571 MPa%. The tensile fracture of 600 °C sample presents delamination and ductile fracture. Through comparative analysis, it can be concluded that the plasticity and toughness of multilayer welded joints after tempering at 600 °C is improved, and they have better comprehensive mechanical properties.

     

Type IV Creep Damage Behavior in Gr.91 Steel Welded Joints

Modified 9Cr-1Mo steel (ASME Grade 91 steel) is used as a key structural material for boiler components in ultra-supercritical (USC) thermal power plants at approximately 873 K (600 °C). The creep strength of welded joints of this steel decreases as a result of Type IV creep cracking that forms in the heat-affected zone (HAZ) under long-term use at high temperatures. The current article aims to elucidate the damage processes and microstructural degradations that take place in the HAZ of these welded joints. Long-term creep tests for base metal, simulated HAZ, and welded joints were conducted at 823 K, 873 K, and 923 K (550 °C, 600 °C, and 650 °C). Furthermore, creep tests of thick welded joint specimens were interrupted at several time steps at 873 K (600 °C) and 90 MPa, after which the distribution and evolution of creep damage inside the plates were measured quantitatively. It was found that creep voids are initiated in the early stages (0.2 of life) of creep rupture life, which coalesce to form a crack at a later stage (0.8 of life). In a fine-grained HAZ, creep damage is concentrated chiefly in an area approximately 20 pct below the surface of the plate. The experimental creep damage distributions coincide closely with the computed results obtained by damage mechanics analysis using the creep properties of a simulated fine-grained HAZ. Both the concentration of creep strain and the high multiaxial stress conditions in the fine-grained HAZ influence the distribution of Type IV creep damage.     

Kinetic Modeling of the Reaction Rate for Quartz and Carbon Pellet

Metallurgical and Materials Transactions B - Kinetic modeling of quartz and carbon pellet at temperatures of 1898 K, 1923 K, and 1948 K (1625 °C,...     

The Effect of Nb Addition on the Microstructure and the High-Temperature Strength of Fe3Al Aluminide

Metallurgical and Materials Transactions A - The microstructural and high-temperature mechanical properties of Fe–26Al–xNb (x = 3 and 5 at. pct) are...     

Phase Equilibria in the TiO2-Rich Part of the TiO2-CaO-SiO2-10 Wt Pct Al2O3-5 Wt Pct MgO System at 1773 K

Metallurgical and Materials Transactions B - The phase equilibria of the TiO2-CaO-SiO2-10 wt pct Al2O3-5 wt pct MgO system in the TiO2-rich part were...     

Ab Initio Molecular Dynamics Studies of Pb m Sb n (m + n ≤ 9) Alloy Clusters

Metallurgical and Materials Transactions A - Structure, stability, and dynamics of Pb m Sb n (m + n ≤ 9) clusters were investigated using ab initio...     

Relationship of Coke Reactivity and Critical Coke Properties

Metallurgical and Materials Transactions B - The gasification reactions of five metallurgical cokes were studied using a thermogravimetric analyzer at 1273 K and 1673 K in...     

Direct Observation of Pure Cu and Cu-Ag Anode Passivation in H2SO4-CuSO4 Aqueous Solution by Channel Flow Double Electrode and Optical Microscopy

Metallurgical and Materials Transactions B - The dissolution and passivation of pure Cu and Cu-5 wt pct Ag anodes in H2SO4-CuSO4 electrolyte were investigated by a direct...     

Effects of Heat Treatment and Plating Sequence on Microstructure Evolution and Corrosion Properties of Mechanically Plated Zinc-Tin Coatings

Metallurgical and Materials Transactions A - Steel fasteners were mechanically plated with different deposition sequence of Zn and Sn and heat treated at 340 °C for 30 min....     

Microstructure-Fracture Behavior Relationships of Slot-Welded Rail Steels

Microstructural analyses of the parent pearlitic and bainitic rail steels were performed, and the results were compared with the microstructure of the welded pearlitic and bainitic steels. An increase in the ASTM grain size number of the heat-affected zone (HAZ) for both pearlitic and bainitic slot welds was observed. The microstructural features that were identified in the weldment of both slot-welded steels were very similar. This was expected since the same welding wire was used to weld both rail steels. The weld consisted of mainly ferrite and had similar grain size. The fusion zones of the welded pearlitic and bainitic rail steels were examined after flexural tests to determine if there were any cracks present due to improper or weak fusion. Examination of the entire fusion zone under high optical magnification revealed no cracks, indicating that a perfect fusion was achieved. The three-point flexural behavior of the parent pearlitic and bainitic steels was evaluated and compared with that of the slot-welded steels. It was found that that the welded pearlitic steel has superior fracture resistance properties when compared to the parent pearlitic steel. The average fracture resistance of the parent pearlitic steel was 79 MPa√m compared to 119 MPa√m for the welded pearlitic steel. The slot-welded bainitic steel, however, showed similar fracture resistance properties to the parent bainitic steel with average values of 121 and 128 MPa√m, respectively. The failure mechanism of the welded and parent pearlitic and bainitic steels was also identified. Microvoid coalescence was observed in both welded rail steel samples. This was manifested by dimpled features, which are associated with ductile failure.     

Flow Behavior and Microstructural Evolution of 7A85 High-Strength Aluminum Alloy During Hot Deformation

Metallurgical and Materials Transactions A - Hot deformation behavior of 7A85 high-strength aluminum alloy was investigated at 593 K to 713 K (320 °C to...     

Effect of Chlorine on the Viscosities and Structures of CaO-SiO2-CaCl2 Slags

Metallurgical and Materials Transactions B - The viscosities of CaO-SiO2-CaCl2 (CaO/SiO2 = 1.12) slags were measured to elucidate the effect of chlorine with CaCl2 content from 0...     

Influence of Growth Rate on Eutectic Spacing,Microhardness, and Ultimate Tensile Strength in the Directionally Solidified Al-Cu-Ni Eutectic Alloy

Metallurgical and Materials Transactions B - In this work, the mechanical properties of the Al-Cu-Ni eutectic alloy, Al-32.5 wt pct Cu-1 wt pct Ni, were investigated in terms of...     

The Effect of Cooling Rate on High-Temperature Precipitation in a Powder-Metallurgy,Gamma/Gamma-Prime Nickel-Base Superalloy

Metallurgical and Materials Transactions A - The effect of cooling rate in the range of 10 K/s to 250 K/s (10 °C/s to 250 °C/s) on the precipitation of...     

Quantitative Analysis of Microstructural Constituents in Welded Transformation-Induced-Plasticity Steels

A quantitative analysis of retained austenite and nonmetallic inclusions in gas tungsten arc (GTA)–welded aluminum-containing transformation-induced-plasticity (TRIP) steels is presented. The amount of retained austenite in the heat-affected and fusion zones of welded aluminum-containing TRIP steel with different base metal austenite fractions has been measured by magnetic saturation measurements, to study the effect of weld thermal cycles on the stabilization of austenite. It is found that for base metals containing 3 to 14 pct of austenite, 4 to 13 pct of austenite is found in the heat-affected zones and 6 to 10 pct in the fusion zones. The decomposition kinetics of retained austenite in the base metal and welded samples was also studied by thermomagnetic measurements. The decomposition kinetics of the austenite in the fusion zone is found to be slower compared to that in the base metal. Thermomagnetic measurements indicated the formation of ferromagnetic ε carbides above 290 °C and paramagnetic η(ε′) transient iron carbides at approximately 400 °C due to the decomposition of austenite during heating.     

Phase Transformations in Mn–Al and Mn–Bi Magnets by Repeated Heat Treatment

Transactions of the Indian Institute of Metals - A stepped heating cycle in a tube furnace at 1000 °C for 1 h followed by holding at 400 °C for 1 h...     

Experimental Study on the Activities of Al and Ca in Ferrosilicon

Metallurgical and Materials Transactions B - Experiments were carried out to determine the activities of Al and Ca in liquid ferrosilicon (with about 50 wt pct Si) at...     

Thermodynamics and Structure of CaO-Al2O3-3 Mass Pct B2O3 Slag at 1773 K (1500 °C)

Metallurgical and Materials Transactions B - Activity values of Al2O3 in CaO-Al2O3-B2O3 systems at 1773 K (1500 °C) were determined experimentally using a...     

Preparation of TiB2-20 Wt Pct MoSi2 Composite Material by Mechanochemical Synthesis and Spark Plasma Sintering

Metallurgical and Materials Transactions A - The mechanosynthesis process of composite powders for the preparation of a TiB2-20 wt pct MoSi2 composite material from...