Properties Of Heat-resistant Steel Research Articles

Mechanical properties of heat resistant steel serviced for 30 months

Grade 91 steel pipe was replaced after about 30 months of service. In this paper, the tensile properties, microhardness and chemical composition of the pipeline steel are systematically tested and analyzed. The results show that the properties of the steel still meet the requirements of relevant standards.

Influence of the activation of the nicarbing process on mechanical properties of heat-resistant steel

The results of evaluating the microhardness, durability, and back-to-back endurance of heat-resistant VKS-7 and VKS-10 steels after the nicarbing process have been presented. The evaluation consisted of two stages, i.e., prior plastic deformation by the warm sinking strain method and nicarbing. Supplementary reserves for improving serviceability of critical parts made of heat-resistant steel were shown.

Microstructure Evolution and Nitridation in an As-Cast 25Cr-35Ni-1Mo Radiant Tube After Long-Term Service

The microstructure evolution of 25Cr-35Ni-1Mo radiant tubes was investigated after approx- imately two years of service in a continuous annealing furnace. The inner and outer tube walls were exposed to N2-containing combustion environment and protective atmosphere, respec- tively. The decarburization feature analysis indicated that carbon content decreased toward the tube surface. However, precipitates at the inner and outer walls were coarser, their content increased and the microhardness value also increased compared to that in the central area. X-ray diffraction illustrated that M2(C,N) and M6(C,N) were the dominant carbide at the inner and outer walls, and precipitates in the central area were mainly M23C6 and M6(C,N) phases. The results were assumed to be associated with the nitridation phenomenon that occurred in the N2-containing environment at elevated temperatures. IN the manufacturing process for the cold-rolled sheet of steels, steel strips are submitted to an annealing furnace section after cold rolling in order to obtain required mechanical properties. The continuous anneal- ing furnace is now commonly used as reheating equip- ment, in which the annealing process involves passing steel strips continuously through a heating furnace filled with classical N2-H2 protective atmosphere. In the continuous annealing process, radiant tubes are used as indirect heating equipment. Heat is transferred from combustion gas to the radiant tube, and then it radiates energy to the load, without any direct flame or com- bustion exhaust coming in contact with the load. Centrifugally cast Fe-Ni-Cr based heat-resistant steels (1) are widely used in heat treatment applications, such as radiant tubes, for their good exhibition of mechanical property and corrosion resistance at high temperatures. The microstructure of these centrifugally cast tubular materials consists of austenite dendrites delineated by a network of eutectic carbides. (2-4) As a consequence of the high Cr content in this class of steels, various types of those carbides can be precipitated. For example, precipitation of Cr-rich carbide M7C3 and M23C6 is very common, and the addition of stabilizing elements such as Ti, Nb, and V usually results in MC type carbides, (5,6) and so on. Detailed mechanical properties of these heat-resistant steels are dependent on the stability of the microstructure, particularly the formation, coarsening, and transformation of these precipitates. However, precip- itates initially formed in as-cast microstructures undergo morphological and chemical changes under service condi- tions such as high-temperature aging, corrosion, and creep. Then coarsening and phase transformation of these pre- cipitates occur. Those changes, with few exceptions, are undesirable and they can be detrimental to the corrosion resistance and mechanical properties of heat-resistant steels. Precipitation behaviors in austenitic stainless steels were studied extensively, and detailed information of such phases can be followed in the literature of other

Effects of Laser Multiple Processing on Properties of Heat-Resistant Steel

The heat-resistant steel after aluminized was treated by laser shock processing (LSP) with high power Nd:YAG laser, and then was tensile tested at 400°C. The effects of the high-temperature behavior after LSP were analyzed from residual stress and fracture organization. The results showed that the yield strength and tensile strength of heat-resistant steel after aluminized were improved obviously during the tensile testing at high temperature, and the High-temperature fatigue life of 00Cr12 with composite processing was enhanced vastly. Compared with the LSP, the High-temperature fatigue life of 00Cr12 heat-resistant steel by aluminizing and LSP had a larger increase.

Influence of Aging on Creep Rupture Properties of Heat Resistant Steels for Steam Turbine Rotors of Thermal Power Plants

Influences of aging on the creep rupture properties of super-clean 9%CrMoV steel and 1%CrMoV steel, the heat resistant steels for steam turbine rotors of thermal power plants, are investigated. Using the as-received and the aging-treated materials of the two steels, creep rupture tests are carried out at 566°C. Creep rupture lives, creep fracture modes as well as the microstructural changes of the specimens are examined. It is made clear that the creep strength and the microstructural stability of super-clean 9%CrMoV steel are superior to those of 1%CrMoV steel in long-term services.

Elastic properties of heat resistant steels after long-term creep exposure

In order to clarify the effect of microstructural change during ageing and creep on elastic modulus, the elastic moduli of aged, crept and serviced (service-exposed) materials were investigated. In ferritic steels, the elastic modulus obtained by ultrasonic pulse does not change after long-term ageing and creep although the formation of creep voids slightly decreases the elastic modulus. In SUS304 and SUS316, the elastic modulus evaluated by ultrasonic pulse increases during ageing due to precipitation of M23C6 carbides, Laves phase and σ phase though the elastic modulus decreases during creep because of the formation of creep voids on grain boundaries. The increased elastic modulus of aged material with a large amount of σ phase was regarded as that of composite consists of matrix and σ phase. For STBA24, the elastic modulus obtained by a high temperature tensile test decreases after long-term service. The tensile test at a higher strain rate was proposed to avoid underestimation of elastic modulus of serviced materials at high temperatures.

Elastic properties of heat resistant steels after long-term creep exposure

AbstractIn order to clarify the effect of microstructural change during ageing and creep on elastic modulus, the elastic moduli of aged, crept and serviced (service-exposed) materials were investigated. In ferritic steels, the elastic modulus obtained by ultrasonic pulse does not change after long-term ageing and creep although the formation of creep voids slightly decreases the elastic modulus. In SUS304 and SUS316, the elastic modulus evaluated by ultrasonic pulse increases during ageing due to precipitation of M23C6 carbides, Laves phase and σ phase though the elastic modulus decreases during creep because of the formation of creep voids on grain boundaries. The increased elastic modulus of aged material with a large amount of σ phase was regarded as that of composite consists of matrix and σ phase. For STBA24, the elastic modulus obtained by a high temperature tensile test decreases after long-term service. The tensile test at a higher strain rate was proposed to avoid underestimation of elastic modul...

Structure and Properties of Heat-Resistant Steels Obtained from Powders after Mechanical Activation

The effect of mechanical activation of heat-resistant steel 55Kh20N4AG9 powders on the structure and properties of high-density material obtained by dynamic hot pressing with extrusion elements was investigated. Mechanical activation improves the chemical homogeneity of the highly alloyed material, decreases the particle size of the strengthening carbonitride phase, promotes its interaction with dislocation tangles and increases their thermal stability. Mechanical activation of powders with intermediate anneals promotes the accumulation of thermally stable defects in the crystal structure and leads to the accelerated formation of a cellular fragmented structure in the austenite, characterized by a high dislocation density in block walls. The developed cellular fragmented substructure is retained after dynamic hot pressing and subsequent heat treatment, and elevates the mechanical properties of the high-density heat-resistant powder metallurgy steels.

Mutual determination of the solutions of problems of the description and analysis of special features of high-temperature creep of metallic materials

The article analyzes the problem of the necessity of systematizing the known data on the mechanical properties of heat-resistant steels and alloys with the object of improving the effectiveness of checking the possibilities of the constructed equations of state. It substantiates one of the variants of describing the regularities of instantaneous and short-term strain, creeps, stress relaxation, and creep limit from the same positions.

Properties of heat-resistant steels after vacuum heat treatment

1. Heating in vacuum (10−2 and 10−3 mm Hg) does not change the microrelief on the surface and produces the required surface finish of Δ7. 2. Heating and cooling in vacuum (10−2 and 10−3 mm Hg) in treatments 3, 4, 5, 6, 9, 13, and 17 produce a bright surface. 3. After heating for quenching the depth of the surface layer depleted of alloying elements was ≤50–60 μ (determined from the microhardness, metallographic analysis, and microanalysis). 4. Heating at a pressure of 1·10−3 mm Hg for tempering and aging does not cause additional changes in the condition of the surface or the formation of a depleted surface layer. 5. The change in the average chemical composition by layers (C, Cr, Mo, W, Ti, Al), determined by sectioning and chemical analysis, does not exceed the limits established by GOST 5632-61 for steels 2Kh13 and 1Kh11MF or for EI893 (ChMTU/TsNIIChM 138-66). 6. Cooling in inert gases (argon A, GOST 10157-62; nitrogen, GOST 9293-69) at pressures of 400 and 700 mm Hg does not change the chemical composition as compared with cooling in vacuum. 7. The mechanical properties of samples heat treated in vacuum (quenching and tempering) indicate that the vacuum treatment, ensuring degassing of the steels, increases the ductility and does not lower the strength.

The effect of sigma phase on the mechanical properties of heat resistant steels

1. A study of the fracture mechanism of a two-phase 18-8 type steel containing sigma phase and deformed in vacuum at 650–800 °C showed that the sigma phase possesses a rather good plasticity at high temperatures so that the cracks in the specimens under investigation appeared inside the austenite grain junctions. 2. The ordinarily brittle sigma phase does not impair the overall plasticity of the steel when deformed at high temperature during short- as well as long-time tests.