Influence of heat input on the microhardness and microstructure of the welding interface between nickel-based alloy and low-alloy steel

The evolution of microstructure and local properties near the welding interface is essential for the service safety of dissimilar metal welded joints between nickel-based alloy(NA) and low-alloy steel(LA).In this work,NA filler metal was deposited on LA substrate under different heat inputs by tungsten inert gas(TIG) welding.Microstructural characterization and microhardness tests were carried out near the prepared cladding interfaces.Optical and scanning electron microscopes show the lack of evident hardening transition layer along the welding interface.As the heat input increases,the mean hardness of the deposited layer also increases remarkably due to the rising dilution rate.Microstructural characterization shows a significant composition gradient across the cladding interface,but the diffusion gradient is limited to a small range.Under high heat input,a planar grain zone is generated along the interface due to the large temperature gradient across the interface region.

Similarity evaluation model for the internal defect detection of strip steel

An internal defect meter is an instrument to detect the internal inclusion defects of cold-rolled strip steel.The detection accuracy of the equipment can be evaluated based on the similarity of the multiple detection data obtained for the same steel coil.Based on the cosine similarity model and eigenvalue matrix model,a comprehensive evaluation method to calculate the weighted average of similarity is proposed.Results show that the new method is consistent with and can even replace artificial evaluation to realize the automatic evaluation of strip defect detection results.

Research and development of 3PP coating steel pipes

The industrial application of an exterior three-layer anticorrosive polypropylene coating system(3PP)on large-diameter(larger than Φ600 mm)steel pipes was developed using an experimental process simulation study and the optimization of raw materials inspection,steel pipe surface pretreatments,and water cooling control on a coating application process.The coating properties meet ISO standard 21809 on buried or submerged 3PP pipelines used in the petroleum and natural gas industries.Differential scanning calorimetry and X-ray diffraction were used to analyze the crystallinities and grain sizes of polypropylene(PP)top coats with different cooling rates.Increasing the melt cooling rate reduces the crystallinity and grain size of the PP top coat and enhances its strength and toughness.

Influence of heat input on microhardness and microstructure across the welding interface between stainless steel and low alloy steel

The welding interface is crucial to the service safety of dissimilar metal weld(DMW)joints between stainless steel(SS)and low alloy(LA)steel.Different status of welding interfaces was prepared by cladding SS consumables to LA steel substrates with different heat inputs via tungsten inert gas arc welding(TIG),followed by a series of microstructural characterizations and hardness tests.Results showed that a hardening and transition layer(TL)would be generated along the welding interface,and the width and hardening degree of the TL would increase with the heat input.Meanwhile,heavy load hardness tests showed that highly severe inhomogeneous plastic deformation and the microcrack would be generated in the interfacial region and the welding interface respectively in the highest heat input sample(1.03 kJ/mm).These results indicate that the increase in heat input would deteriorate the bonding performance of DMW joints.Further microstructural observations showed that the higher hardening degree of the highest heat input sample was mainly attributed to the stronger grain boundary,solution,and dislocation strengthening effects.

Methods to prevent side marks from rusting on heavy steel plates

When a steel plate produced by a steel plant leaves the factory,its upper surface should be marked with the specification,variety,batch number,and other identifying information,and its side should be marked with a side marking.The side marking contains the plate number,specification,batch number,and other information,which are convenient for customers to accurately identify relevant information after stacking.However,because of the influence of weather,environment,and other factors,the side marking becomes unidentifiable when the steel plate is corroded,affecting the customer’s loading,unloading,and other operations.The development and application of side anticorrosion devices and cleaning of finished heavy steel plates with antirust agents will solve the problem of unrecognizable side marking due to corrosion.

Experimental study on the forming characteristics of 1.5 GPa ultrahigh-strength dual-phase steel

The DP1500 steel series successfully produced by Baosteel is a marked improvement over the cold-rolled hot-dip galvanized dual-phase steel series.Sufficient parameter data related to forming characteristics are needed for the successful application of dual-phase steel series in engineering structures.Therefore,differences in the mech-anical properties,forming limit,hole expansion ratio,and stretch bend limit of the 1.5 GPa ultrahigh-strength steel,including DP1500,QP1500,and MS1500,have been systematically studied.Results show that the DP1500 exhibits good plastic deformation performance and approximately 5% uniform elongation,and its true major strain minimum on the forming limit curve(FLC_(0)) value is approximately 0.083,which is higher and lower than the FLC_(0) values of MS1500 and QP1500 of the same strength grade,respectively.DP1500 also exhibits good flanging and pore expansion capabilities and superior performance to QP1500 and MS1500.The minimum radius-to-thickness(R/T) ratio(1.4) of DP1500 in the 90° bend tests transverse to the rolling direction is between the R/T ratios of MS1500 and the QP1500.Overall,the formability performance of DP1500 is between that of MS1500 and QP1500.Its excellent crash energy absorption and formability performance render it a suitable structural component,and it has been successfully tested and verified on a typical complex ultrahigh-strength steel skeleton structure.

Study on the high-temperature properties of heat-resistant steel 309S

The properties of heat-resistant steel 309S at elevated properties were investigated.The results revealed a rapid decrease in the short-time tensile strength at elevated temperatures.At 1 000 ℃,the yield strength and tensile strength are 14% and 7% of their respective values at room temperature,respectively.The creep rupture strength was inferred in terms of the relationship between stress and duration time at high temperatures.After 1 000 h,the creep rupture strength is 37.98 MPa at 800 ℃,12.63 MPa at 900 ℃,and 7.27 MPa at 1 000 ℃.The fractures occurring at these high temperatures were intergranular in nature.Under the experimental condition,the fatigue limit stress is 25 MPa.The number of fatigue cycles and crack growth time decrease with increasing stress.Fracture morphology analysis shows that the fatigue cracks initiate on the surface of the sample and propagate through transgranular expansion.

Creep property research of new martensite heat-resistant steel G115

G115 steel was jointly developed by China Iron & Steel Research Institute Group Co.,Ltd.and Baosteel for usage in 600-650 ℃ ultrasupercritical boiler tubes.Using a hot extruded G115 tube,creep tests were conducted under a constant stress of 130 MPa and temperatures of 625,650 and 675 ℃.Comparing creep curves under different temperatures,it is observed that the creep performance of a G115 tube is more sensitive to temperature than stress.Steady-state creep rates of creep specimens are significantly increased by enhancing the temperature.A micro-structural analysis of ruptured creep specimens under a stress of 130 MPa and temperatures of 650 ℃ and 675 ℃ was performed;the fracture mechanism of creep specimens under these two temperatures mainly included the appearance of creep holes on the grain boundary and a decrease in the martensite lath density.

ToF-SIMS characterization of a bare-spot defect in a hot-dip galvanized boron-added steel sheet

To determine the root cause of a bare-spot defect in a hot-dip galvanized boron-added steel sheet,we performed metallurgical characterizations using time-of-flight secondary ion mass spectrometry(ToF-SIMS)in addition to glow discharge optical emission spectrometry,field-emission scanning electron microscopy(FE-SEM),and energy dispersive spectroscopy.Mn and B enrichments on the steel surface in the bare-spot area were detected through various methods.FE-SEM revealed external oxide nodules and zinc droplets,which indicated poor wettability.ToF-SIMS further revealed considerably more detailed lateral and depth distributions of Mn,B,and Al.The formation of external Mn-B compound oxides on the steel surface prior to hot dipping,which substantially deteriorated the wettability and prevented the formation of a Fe_(2)Al_(5)inhibition layer,resulted in the formation of a bare-spot defect.ToF-SIMS mapping of Al ion proved that a slight reaction still occurred between the dissolved Al in the molten zinc bath and steel substrate,although no evident Fe_(2)Al_(5)inhibition layer formed in the bare-spot area.

Corrosion behavior of super 13Cr stainless steel in a H_(2)S and CO_(2) environment

The corrosion behavior of 95 ksi grade super 13Cr stainless steel in an environment consisting of H_(2)S and CO_(2)was investigated.The results reveal that for both loading methods(constant load and four-point bending),local corrosion occurred on the surface of the samples tested at ambient temperature but was absent from the samples tested at high temperatures.The local corrosion was caused by the formation of pits at nonmetal inclusions;the pits were formed under the action of stress in an acidic environment,which was due to an acid solution.Subsequently,the corrosion extended along the direction of stress.The sensitivity of stress corrosion cracking increased because of the local corrosion.

Self-cleaning performance of a self-cleaning pre-coated steel sheet in an industrial environment

A type of self-cleaning pre-coated steel sheet with excellent self-cleaning performance was developed using hydrophilic surface treatment technology. To understand the self-cleaning properties of this pre-coated steel sheet in an industrial environment, the Jiangjin natural environmental test station was chosen as the outdoor exposure test to be conducted, and the self-cleaning performance of the steel sheet was studied by measuring the water contact angle, stain resistance factor, color difference, and gloss of the steel sheet during the outdoor exposure test. The water contact angle of the self-cleaning steel sheet quickly decreased from 84° to 29° during the outdoor exposure test, and the steel sheet showed excellent hydrophilic properties, which were beneficial to the spread of rain drops and detrimental to the accumulation of the surface pollutants. After an outdoor exposure of 12 months,the self-cleaning steel sheet had a higher stain resistance and cleaner surface than the comparison sample sheet, demonstrating its excellent self-cleaning properties. Moreover, the color difference and gloss rate of the self-cleaning steel ＇sheet were similar to those of the pre-coated steel sheet without hydrophilic surface treatment. Therefore, the hydrophilic surface treatment technology used in this study did not affect the anti-aging property of the self-cleaning steel sheet.

Evaluation on the contribution of steel products to environmental improvement from LCA perspectives

High functionality given to steel products results in an increase of environmental loads in the steelmaking stage. However, at the stage of their utilization, the high-functional steel products prove to be more environmentally friendly than their conventional counterparts in many cases. In view of this contradiction, the evaluation on the contribution of steel products to environmental improvement requires a more integrated approach--Life Cycle Assessment （ LCA ）, which incorporates the effects over the products＇ entire life cycles. This paper discusses the relationship between the improvement of steel products＇ performance and the according environmental impact from the entire life cycle perspectives. How to evaluate and assess the contribution of high-functional steel products to environmental improvement using LCA method is explained in detail. Two case studies of Baosteel are given to substantiate the effectiveness of LCA as a scientific and systematic method for eco-material evaluation or eco-design： @ For a power transformer, by replacing silicon steel B30G130 with B30Pll0,the carbon dioxide emissions were reduced by 15.1% over the life cycle of the transformer. @ Tinplate steel of Baosteel used for two-piece steel cans experienced six reductions in thickness from 0.28 mm to 0.225 mm,which results in a 14.5% emission reduction over the life cycle of two-piece steel cans.

Comparative study of the thermal insulation performance of steel and aluminum battery packs in high-and low-temperature environments

As the only power source of pure electric vehicles,the performance of battery packs is easily affected by the temperature,and too high or too low temperature will make the performance of battery packs decline.In this study,the thermal analysis finite element modeling of a cast aluminum battery pack and steel battery pack of a pure electric vehicle is established to compare the thermal insulation performance of two kinds of battery packs under high-and low-temperature conditions.The simulation results show that the thermal insulation performance of the two kinds of battery packs meets the design requirements under high-and low-temperature conditions.The external environment of the cell and battery pack mainly transmits heat through heat conduction.Aiming at the problem that the uniform temperature performance of the steel battery pack is lower than that of the cast aluminum battery pack,several optimization solutions are put forward for the insulation design of the steel battery pack,and the optimal solution is obtained by comparing the simulation results.

Effect of nitrogen content on the microstructure and mechanical properties of titanium-bearing nonquenched and tempered steel after hot forging

The microstructure and mechanical properties of titanium(Ti)-bearing medium-carbon nonquenched and tempered steel with different nitrogen content before and after hot forging were investigated through smelting,forging,and laboratory tests.The results show that the grain size of nonquenched and tempered steel was gradually refined,and the ferrite content gradually increased with an increase in nitrogen content.The grain size of the material with low nitrogen content increased abnormally,and its impact properties significantly decreased after hot forging.The grain size of nonquenched and tempered steel with higher nitrogen content was slightly larger than that before forging,and the tensile and yield strength increased,but the impact toughness was not significantly reduced.The Ti-bearing nonquenched and tempered steel showed better strength and toughness after hot forging with the addition of 0.010%0.015%nitrogen.

Microstructure and mechanical properties of an Nb-microalloyed EH47 steel

The loading capacity of ultralarge container ships has reached 24000 TEUs so far,and to ensure the safe operation of these ships,the maxmium thickness of crack arrest steel used in the upper deck areas reaches 100 mm,and crack arrest toughness(K_(ca))needs to be>8000 N/mm^(3)/2.The EH47 steel was employed to study the effect of Nb on the phase transformation of supercooled austenite in the continuous cooling process after rolling and the effect of Nb on microstructure and mechanical properties of the crack arrest steel plate.It was found that the addition of 0.02%Nb can inhibit the ferrite transformation,improve the steel plate strength,and reduce the strength inhomogeneity in the thickness direction.Industrial production of 100 mm-thick EH47 was carried out based on the function of Nb in EH47 steel,and the test results reveal that high-strength EH47 shipbuilding plates with high toughness,excellent fracture and crack arrest toughness,and good welding properties can be produced using Nb-microalloyed composition design and the thermal mechanical control process(TMCP);furthermore,the value of the crack arrest toughness reached 9450.7 N/mm^(3/2) at-10℃.

Study on gas metal arc welding of two types of TMCP steels

Gas metal arc welding experiments were conducted on two types of steels with 0.41% carbon equivalent(Ceq) and 0.31% Cequsing WER70T wire and 20% CO_(2)and 80% Ar as shielding gas.The two types of steels show satisfactory weldability.The transition temperatures of 50% upper shelf energy(Tk0.5) for Charpy-V impact test of both the welded joints are below-40 ℃.However, the toughness of the fusion line zone and heat-affected zone(HAZ) of the two steel joints exhibits differences, with the toughness of 0.41% Ceqsteel being better than that of 0.31% Ceqsteel.The Tk0.5of the fusion line zone and the HAZ of 0.41% Ceqsteel is below-60℃,whereas that of 0.31% Ceqsteel is above-40℃.The welded joint of 0.41% Ceqsteel has low hardness fluctuation, while that of 0.31% Ceqsteel exhibits a narrow, softened zone, which has no obvious influence on the tested tensile strength.The coarse grain heat-affected zone(CGHAZ)microstructure of 0.41% Ceqsteel is bainite, while that of 0.31% Ceqsteel is bainite with ferrite and minor pearlite.

Precise control of bainite micro-morphology and the effects on the mechanical properties of ultrahigh-strength complex-phase sheet steel

Bainite, the main microstructure of ultrahigh-strength complex-phase(CP) sheet steel, usually exhibits various micro-morphologies when subjected to different austempering treatments.In the current study, conventional austempering treatment at the bainite nose temperature resulted in two bainite types with distinct micro-morphologies: polygonal blocky bainite and acicular bainite, which resulted in large fluctuations in the mechanical properties of CP steel, particularly yield strength and hole expansion ratio.Therefore, the precise control of bainite micro-morphology was studied and applied to separate the two bainite types through austempering optimization.The two bainite types of different micro-morphologies had different effects on the mechanical properties of CP steel: the acicular bainite favored hole expansion and flangeability but deteriorated ductility, while the polygonal blocky bainite favored ductility but deteriorated hole expansion and flangeability.Accordingly, two types of ultrahigh-strength CP steels of different mechanical properties can be stably manufactured through the precise control of bainitic micro-morphology to satisfy the specific demands of vehicle components in terms of the mechanical properties of CP steels.

Effect of low-temperature tempering on the mechanical properties of cold-rolled martensitic steel

Cold-rolled martensitic steel is an important type of advanced high-strength steel for automobile production.With martensite as its primary microstructure constituent, martensitic steel possesses exceptional high strength despite its low alloy content.As the strength of cold-rolled martensitic steel increases, the martensite and carbon content also increases, leading to a decrease in bending properties and toughness.In this paper, the effect of various tempering parameters on the bending property and impact toughness of a quenched cold-rolled martensitic steel sheet was studied.It is found that after quenching, the ductility and impact toughness of the experimental steel are improved using low-temperature heat treatment.The optimal tempering conditions for ductility and toughness are analyzed.

Influence of heat treatment processing on the microstructure and properties in medium manganese steel

For the purpose of developing a 1 500 MPa grade steel sheet with excellent strength and ductility, a 0.15C-10Mn-1.5Al steel was employed to study austenite stability and microstructural evolution based on a novel double annealing processing.After a conventional intercritical annealing process, the sample was heated again to a temperature higher than A_(c3) for a very short time to generate austenite grains with different manganese content;thus, the microstructure of martensite plus austenite can be obtained at room temperature.The experimental results show that with increasing annealing temperature, the tensile strength and yield strength increase.When the annealing temperature was higher than 820 ℃,the microstructure consisted of martensite plus austenite, and the tensile strength almost remained invariant with the annealing temperature.A tensile strength of 1 537 MPa and an elong-ation of 25.1% were achieved for the 820 ℃ condition.The volume fractions of austenite and martensite were identified by X-ray diffraction.It was found that with increasing annealing temperature, the volume fraction of the retained austenite decreased, and the ductility also had a gradual downward trend.The related austenite stability was discussed here as well.

Influence of two distinct quenching end-temperatures on phase development and mechanical properties in QP980 steel

Bainite microstructures have become increasingly attractive for the development of advanced high-strength steel owing to their balanced strength-plasticity properties.In this study, the final microstructure and mechanical properties of a quenching and partitioning(QP) steel sample after two distinct QP processes were analyzed.The results reveal that martensite transformation after quenching resulted in a lathed morphology with higher yield strength and hole expansion ratio.In contrast, bainite transformation after quenching resulted in the formation of a blocky microstructure composed of bainitic ferrite retained austenite and nanoscale precipitates during the subsequent phase transformation at a higher temperature.This kind of final microstructure is beneficial to the elongation of QP steel but detrimental to the hole expansion ratio.