Analysis of spot defects on the surface of a cold-rolled Fe-36%Ni alloy strip

Many spot defects were found on the surface of a cold-rolled Fe-36%Ni alloy strip produced in a factory,which seriously affected the surface quality of the product.Through metallographic microscopy and scanning electron microscopy analyses,it was found that the spot defects were caused by the residual oxide layer on the surface of the cold-rolled Fe-36%Ni alloy strip after hydrogen annealing.By properly increasing the grinding amount of the blank before cold rolling to remove the oxide layer,the spot defects on the surface of the cold-rolled strip were effectively eliminated,and the surface quality of the product was ensured.

Creep rupture properties and microstructure stability of the GH984G alloy tube

GH984G alloy is a significant candidate material for 650-700℃ ultra-supercritical coal-fired generating units.In this paper,creep rupture properties and microstructure stability of the GH984G alloy tube were studied,and the findings indicated excellent creep rupture properties at 700℃.Furthermore,the extrapolated strength for 100000 h was found to be 153.8 MPa,which satisfies the requirements for the long-term performance of high-temperature materials in power stations.Aging at 700℃ with the extension of time,the grain boundary carbides and the particle size of the γ′phase on the matrix gradually coarsen,but its spherical morphology remains uniformly distributed.However,no harmful phase precipitates were found even after aging at 700℃ for up to 19144 h.Excellent microstructure stability guarantees the 700℃ creep rupture properties of the GH984G alloy tube.

Metallurgy quality of GH4720Li alloy by VIM+PESR+VAR

Superalloy is developed to meet the stringent requirements of materials used in aeroengine hot-end parts.It has become an irreplaceable key material for military and civil engines.With the increasing contents of Al and Ti,the hot-working properties of superalloy materials are significantly reduced.The metallurgical technology and product quality of GH4720Li alloy produced by triple-melted process were introduced.The results showed that the PESR ingot structure was shrinkage-free,compact,and had high-degree purity,and the VAR process was obviously stable.The sulfur content of GH4720Li alloy was only several 10^(-6) by the triple-melted process,which was propitious for forging the alloy.The uniform heat treatment technology was also studied,and the results showed that the hot-working plasticity of GH4720Li alloy ingot was significantly improved after uniform heat treatment.The properties of GH4720Li alloy by the triple-melted process were good.

Effects of different helium cooling conditions on the structures of GH4169 alloy vacuum arc remelting ingots

The effects of different helium cooling conditions on the molten pool depth,dendrite structure,and microsegregation of GH4169 alloy ?508 mm vacuum arc remelting( VAR) ingots were studied using an optical microscope and an electron probe. The results show that under different helium cooling conditions,the growth of columnar crystals in the VAR ingot is the same with a certain angle running from the edge to the center and the dendrites at the edges are relatively small whereas the dendrites near the center are large. As the helium cooling increased,the molten pool depth decreased from 137 mm to 120 mm. Observations of the microstructure showed that as the helium cooling increased,the secondary dendrite arm spacing( SDAS) decreased at the center and R/2 region. Also,the Laves phase content markedly decreased. Under the same helium cooling conditions,the SDAS and Laves phase content at the center were higher than that at the R/2 region. Thus,more intense helium cooling effectively reduced segregation in VAR ingots and improved the metallurgical quality.

Effect of quenching and tempering processes on properties and microstructure of G115 steel

The novel martensitic heat-resistant steel G115 was designed for thick-section boiler components of ultra-supercritical(USC) power plants at 630-650 ℃.The impact of the quenching and tempering processes on the properties and microstructure of G115 steel was explored.The samples that were quenched and tempered twice had a higher tensile strength at room temperature and 650 ℃,and the impact energy was significantly improved.The strength and impact energy increased in proportion to the increase in the first quenching temperature.The microstructure differences between the single and double quenched and tempered samples were examined using metallographic microscopy and scanning electron microscopy.The grain size of the double quenched and tempered samples was finer than that of the single quenched and tempered samples, and the tempered martensite lath is more visible, as are the carbides and other precipitates, which are finer and more uniformly distributed.As the first quenching temperature increased, the grains became coarser but more uniform.

Practice and numerical simulation of ingot solidification for high-performance homogeneous steel

A 40 t EAF+LF+VD→mold casting 20 t ingot→hot forging and heating process is employed to produce high-performance homogeneous steel.The solidification process of the 20 t ingot for the high-performance homogeneous steel was simulated by ProCAST casting simulation software.The distribution area and degree of segregation or porosity defects in the longitudinal section of the ingot were analyzed.The reason for the defect formation in the large-scale ingot for forging material was determined, which can be used as a guide for production.The results show that controlling the superheat of die casting and adding a riser heating agent improve ingot quality for forging high-performance homogeneous steel and that flaw detection defects are effectively controlled after forging.

Property uniformity of thick nickel-based alloy plate for nuclear power steam-generator divider plate

This paper introduces a thick 690 nickel-based alloy plate produced by the former Baosteel Special Steel Co.,Ltd.used as the steam-generator divider plate in the pressurized water reactor nuclear power plant.According to the product characteristics and design requirements of the thick nickel-based alloy plate,multidimensional sampling and testing were conducted to investigate its microstructure and mechanical properties.The results show that all the property indexes of the thick hot-rolled nickel-based alloy plate meet the design requirements,and there is good uniformity in the microstructure and mechanical properties in different dimensions.These findings indicate that China has mastered the core manufacturing technology of thick nickel-based alloy plates for their use as divider plates in nuclear power steam generators.

Unravelling the competitive effect of microstructural features on the fracture toughness and tensile properties of near beta titanium alloys

The competitive effect of microstructural features including primaryα(α_(p)),secondaryα(α_(s)),grain boundaryα(α_(GB)) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes.The relative effect of β grain size and STA(solution treatment and ageing)processing parameters on mechanical properties were quantitatively explored by the application of Taguchi method.These results were further explained via correlating microstructure with the fracture toughness and tensile properties.It was found that large numbers of fine as precipitates and continuous α_(s) played greater roles than other features,resulting in a high strength and very low ductility(<2%)of STA process samples.The β grain size had a negative correlation with fracture toughness.In the samples prepared by BASCA( β anneal slow cooling and ageing)process,improved ductility and fracture toughness were obtained due to a lower density ofα;precipitates,a basket-weave structure and zigzag morphology of α_(GB).For this heat treatment,an increase in prior β grain size had an observable positive effect on fracture toughness.The contradictory effect of β grain size on fracture toughness found in literature was for the first time explained.It was shown that the microstructure obtained from different processes after β solution has complex effect on mechanical properties.This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties.A novel table was proposed to quasi-quantitatively unravel these competitive effects.

Unveiling the precipitation behavior and mechanical properties of Co-free Ni_(47-x)Fe_(30)Cr_(12)Mn_(8)Al_(x)Ti_(3) high-entropy alloys

Precipitate hardening is considered as an effective method to strengthen High-and medium-entropy alloys(HEAs and MEAs),especially the recently developed Co-free HEAs/MEAs,In this work,a systematic study on precipitation and mechanical behaviors of a Co-free HEAs with dilute amount of Al addition,Ni_(47-x)Fe_(30 C)r_(12)Mn_(8) Al_(x)Ti_(3)(x=2 at.%,5 at.% and 7 at.%),is presented.Results shown that the Ni_(45)Fe_(30)Cr_(12)Mn_(8) Al_(2) Ti_(3) has a face-centered cubic(FCC)+L1_(2)+η three-phased structure.With increasing Al content,the formation of η phase is inhibited,accompanying with an enhanced formation of B2 phase,and FCC+L1_(2)+B2 three-phased structure is thus observed in alloys with x=5 and 7.The constrained lattice mismatch between FCC matrix and L1_(2) precipitates is decreased with increasing Al content,leading to an enhanced precipitation behavior of L1_(2) phase.As a result of microstructural evolution,the mechanical properties of the aged HEAs changed:the Ni_(42)Fe_(30)Cr_(12)Mn_(8) Al_5 Ti_(3) alloy exhibits a better combination of a yield strength of 661 MPa and tensile ductility of 29.7% as compared to the 2 at.% Al alloyed HEA;and addition of Al beyond 5 at.% results in an increase of strength with a large expense of ductility.We believe that the present work is helpful for developing high-performance Co-free HEAs/MEAs strengthened by nanoprecipitates via composition optimizing.