High Temperature Creep Rupture Strength Research Articles

Research on Remaining Life Evaluation Method of T92 Steel for Superheater Tube Based on Oxide Layer Growth

T92 steel is widely used in high-temperature superheater of supercritical power station boiler, and the researches on its remaining life have always been the hot spot of scholars around the world. In this paper, based on the analysis of high-temperature creep rupture strength data, the optimum C value of Larson–Miller parameter formula for T92 steel is obtained by using isothermal extrapolation method. On this basis, combining the relationship between the thickness of the oxide layer and the operating time, the relationship between the thickness of the oxide layer and the temperature of the tube wall and the relationship between the thickness of the oxide layer and the stress of the tube wall, a new remaining life evaluation formula is deduced. Finally, based on the cumulative creep damage life evaluation method, the service life of superheater tube is divided into three stages, which provides a new reference for the service life evaluation of superheater tube of ultra-supercritical boiler.

Effect of Holding Time on Microstructure and Properties of Transient Liquid-Phase-Bonded Joints of a Single Crystal Alloy

Experimental investigations have been done to verify the effects of hold time during transient liquid-phase bonding on joint microstructure and mechanical properties of a nickel-based single crystal superalloy. The superalloy was bonded at 1473-1513 K for 0.25-12 h in vacuum environment. A set of parameters, 1513 K for 10 h, was determined as the optimum bonding condition. SEM results revealed that the joint without the completion of isothermal solidification is comprised of four different distinct regions, namely, rapid solidification zone (RSZ), isothermal solidification zone (ISZ), diffusion zone, and base metal. EBSD data indicated that the ISZ across the centerline of the bond has an undifferentiated crystallographic orientation being the same as the base metal. At increasing hold times at 1513 K, RSZ and also borides would disappear and result in an improvement of mechanical properties. Mechanical property tests at elevated temperatures have been done to determine the joints’ quality. High-temperature creep rupture strength (for 100 h at 1373 K) and tensile strength (at 1273 K) of the joints could both attain 90% of those of the base metal.

Microstructure Stability of V and Ta Microalloyed 12%Cr Reduced Activation Ferrite/Martensite Steel during Long-term Aging at 650 °C

In view of developing novel alloys for applications in supercritical water-cooled reactor fuel cladding and in-core components, a 12%Cr reduced activation ferrite/martensite (RAFM) steel with good corrosion resistance and irradiation performance was developed. V and Ta were added to form fine MX type carbonitrides and enhance the high temperature creep rupture strength. Microstructure stability of the steel during long-term aging at 650 °C was studied experimentally combined with the simulation of Thermo-Calc and DICTRA software. The results show that the precipitates in the steel during long-term aging contain M23C6, MX and Laves phase. M23C6 carbides play a major role in the stabilization of the tempered martensite lath structure by exerting a large Zener pinning force as compared with MX and Laves phase. Adding V and Ta in the steel can not only promote MX precipitation, but also refine M23C6 carbides and thus improve the thermal stability of lath/subgrains, which is beneficial to the improvement of high temperature microstructure stability of the 12%Cr RAFM steel.

The problem of preparation of creep rupture strength data during the formulation of regulatory documents for metal-intensive power equipment

The paper addresses the problem of compiling and updating the high-temperature creep rupture strength data for steels and alloys used in heat-and-power engineering, and various aspects of tackling the problem are discussed. Special attention is given to the necessity of processing the available creep rupture strength data by the base diagram method, the generalized and detailed representation of such data for the widest possible temperature–time ranges, and subsequent system analysis.

Alloy Design of Ni-based Single Crystal Superalloys for the Combination of Strength and Surface Stability at Elevated Temperatures

Following the findings regarding the surface stability of superalloys recently obtained by the authors, three Ni-based single crystal (SC) superalloys containing Re are designed with the aid of d-electrons concept. Creep-rupture, hot-corrosion and oxidation tests are conducted with the designed alloys in order to investigate experimentally their high temperature properties. The superalloy containing 5.4 mass% Re and 3.8 mass% Cr (A-1) shows an excellent combination of high temperature creep strength and hot corrosion resistance in comparison with a commercial second generation SC superalloy containing 3 mass% Re. The A1 alloy exhibits better creep rupture strength than the 3 mass% Re alloy under all the test conditions of 1313 K/137 MPa, 1 193 K/314 MPa, 248 MPa, 206 MPa and 1 123 K/441 MPa. Performance of the A-1 alloy is well comparable to the second generation alloy in the isothermal oxidation test but poor in the cyclic oxidation test. Another alloy (A-3) exhibits an excellent resistance to the cyclic oxidation test but its creep strength is not a level comparable to the second generation superalloy. Alloying balance is discussed for the excellent combination of high temperature creep rupture strength and good surface stability of superalloys.

Manufacture of alloy steel tube by high frequency electric resistance welding.

The quality of chromium, chromium-molybdenum and austenitic stainless steel tubes manufactured by an electric resistance welding (ERW) is highly dependent on the sophisticated technologies of non-oxidizing welding, precise control of welding energy and smooth cutting of inside flush. In this report a newly developed manufacturing technology for ERW alloy steel tubes is described on the following items; oxygen content in the welding atmosphere for a non-oxidizing welding and its control equipment, appropriate welding energy and its control system and a high performance impeder.Furthermore, the quality of the mass-produced ERW alloy steel tubes by the new technology is investigated focusing on their corrosion resistance, high temperature creep rupture strength and fatigue strength.

ＷＣ‐Ｃｏ超硬合金のクリープ破壊強度に及ぼすＷＣ粒度および結合相粒度の影響

Bending creep-rupture strength of WC-(6-20)%Co high carbon alloys was investigated at 700-900°C for the rupture time up to 2 hr in relation to the carbide grain size (1.3-3.8 μm) and domain size of binder phase (60-500 gm).The results obtained were as follows; (1) As the test temperature increased, the creep-rupture strength of each alloy having a given domain size tended to show a maximum with increasing carbide grain size. On the other hand, the strength of the alloys having a given carbide grain size increased with increasing domain size. (2) In each alloy, it was generally observed that microcracks were first formed at WC/WC interfaces and then connected each other to yield a main stable crack. The growth rate of main stable crack, therefore, appeared to correlate with the formation rate of microcracks. (3) The high temperature creeprupture strength of WC-Co cemented carbides would be controlled by the WC/WC interfaces.

IN-738

Abstract IN-738 is a vacuum cast, precipitation hardened, nickel-base alloy possessing excellent high temperature creep-rupture strength combined with hot corrosion resistance superior to that of many present day high-strength superalloys of lower chromium content. This datasheet provides information on composition, physical properties, and tensile properties as well as creep and fatigue. It also includes information on high temperature performance and corrosion resistance as well as casting, heat treating, machining, and joining. Filing Code: Ni-172. Producer or source: Licensees of International Nickel.

Creep Rupture Strength of Incoloy (32Ni-20Cr Steel)

It is a well known fact that austenitic stainless steels such as 18 Cr-8 Ni type or high Ni base alloys Inconel (70 Ni-15 Cr alloy). They are quite useful materials as the chemical plant fabricated materials used in a high temperature or corrosion atmosphere service.Incoloy (32 Ni-15 Cr-45 Fe) is also a useful material as intermediate between the two above mentioned materials. But its high temperature properties, especially creep rupture data are not accurately defined as yet.We have made high temperature creep rupture tests on domestic Incoloy mother plates and weld joints, and attempted to clarify their high temperature characteristics which has so far been left ambiguous.The results can be summarized as follows.1) The high temperature creep rupture strength on the mother plates increases as the grain size grows to the grain number 3-4 by the solution heat treatment.2) The creep rupture strength on the weld joints {mother plate: coarse-grained material, welding rod: Inco weld-A rod (70 Ni-15 Cr)} is more or less superior to that of the coarse grained mother plate.3) We dwelt upon the relation which exists among the optional temperature, stress and creep rate. The results are formal that a fine-grained material behavior is superior to a coarse-grained one below 720°C and vice versa above 720°C, and generally speaking any fine-grained material tends to decrease its strength in comparison to any coarse-grained materials as the temperature increases.4) The high temperature creep rupture strength level of Incoloy is almost identical with those of AISI 304, 310, 330 type or Inconel, which are generally considered to be heat resistant alloys.

高圧窒素中における高Cr鋼の熔製ならびに316L型鋼の耐熱特性について

An experimental study was made on the fundamental phenomena occuring in melting and casting of various high-chromium steels in high-pressure nitrogen atmosphere and on the influence of nitrogen content on heat-resisting properties of type 316L steels. It was confirmed that the solubility of nitrogen in the type 316L steel melted at about 1550°C in nitrogen atmosphere up to 10 atm obeys the Sieverts' law, and was represented by the following equation:%N=0.183 (PN2) 1/2The high-pressure melting was also c1arried out for such steels as 10-25%Cr-20%Ni-Fe alloys, 17-4PH type stainless steels containing 0.5% or 3% of Si, 18%Cr-4%Ni stainless steels, 18%Cr-8%Mn stainless steels, 22%Cr stainless steels containing O or 2% of Ni and LCN-155 alloys, and the effects on ingot soundness of nitrogen contents, melting conditions, casting conditions and of the sort of the phase formed in process of solidification, were discussed in detail. Further, it was confirmed that the nitrogen contained in these ingots did not diffuse out from the steel unless it was heated to high temperatures in high vacuum.It was observed also that the nitrogen raised the strength of type 316L steels at both room and high-temperatures, the ductility at high temperatures dropped considerably and high temperature creep-rupture strength of the steels showed the maximum at a nitrogen content of about 0.33%.