Edge defect analysis of high-strength corrosion-resistant steel

In this study, a 600 MPa hot-rolled corrosion-resistant steel plate produced by a specific company is investigated. Edge jagged defects and edge surface defects generated on both sides of the strip during production are characterized and analyzed. The results indicate that the distribution of reoxidation granules is located underneath the surface peel and that copper-containing granules diffuse along austenite grain boundaries. This phenomenon combined with the chemical composition and production parameters of a strip indicate that copper brittleness leads to edge jagged defects. However,the surface defects should be attributed to inherent defects on the surface of the strip. Measures that prevent surface oxidation and copper segregation at grain boundaries would likely eliminate these two types of edge defects.

Effects of chromium on the corrosion and electrochemical behaviors of ultra high strength steels

The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.

Effect of microstructure on corrosion behavior of high strength martensite steel-A literature review

The high strength martensite steels are widely used in aerospace,ocean engineering,etc.,due to their high strength,good ductility and acceptable corrosion resistance.This paper provides a review for the influence of microstructure on corrosion behavior of high strength martensite steels.Pitting is the most common corrosion type of high strength stainless steels,which always occurs at weak area of passive film such as inclusions,carbide/intermetallic interfaces.Meanwhile,the chromium carbide precipitations in the martensitic lath/prior austenite boundaries always result in intergranular corrosion.The precipitation,dislocation and grain/lath boundary are also used as crack nucleation and hydrogen traps,leading to hydrogen embrittlement and stress corrosion cracking for high strength martensite steels.Yet,the retained/reversed austenite has beneficial effects on the corrosion resistance and could reduce the sensitivity of stress corrosion cracking for high strength martensite steels.Finally,the corrosion mechanisms of additive manufacturing high strength steels and the ideas for designing new high strength martensite steel are explored.

Corrosion behavior of high-strength spring steel for high-speed railway

The corrosion resistance and evolution of corrosion products in medium-carbon high-strength spring steels were investigated in a neutral salt spray(5 wt% Na Cl solution). A formation model of γ-Fe OOH and a transformation model describing the conversion of γ-Fe OOH to α-Fe OOH were constructed. The results indicated that, at the initial corrosion stage, the corrosion resistance was gradually improved with the addition of Cr; however, with the addition of alloying element V, the corrosion resistance decreased. These results were attributed mainly to the initial corrosion stage being closely related to the matrix microstructure parameters such as grain-boundary character and dislocation density. After the rust layer was formed at a later corrosion stage, the corrosion resistance was reinforced with the addition of Cr and V because Cr strongly influenced the composition, structure, and morphology of the corrosion products. The results presented herein show that Cr was conducive to the transformation of γ-Fe OOH into α-Fe OOH. Moreover, V and Cr exhibited obvious synergy and were enriched in the inner layer of the corrosion products.

Manifestations in Corrosion Prophase of Ultra-high Strength Steel 30CrMnSiNi2 A in Sodium Chloride Solutions

The corrosion behaviors of ultra-high strength steel 30CrMnSiNi2A in sodium chloride solution were studied by weight loss and electrochemical methods. The morphology of corrosion products was observed using scanning electron microscopy（SEM） and the composition was analyzed using an energy dispersive spectroscopy（EDS） and X-Ray diffraction （XRD）. The experimental results showed that the corrosion came from pitting corrosion and the rust layer was composed of outer rust layer γ-FeOOH and inner rust layer Fe_2O_3 with a little β-FeOOH. The correlation between corrosion rate and test time accorded with exponential rule. The corrosion current measured by polarization methods was higher than that calculated by weight loss method after a long-time immersion, the main reason was that,β-FeOOH and γ-Fe_2O_3 transformed by γ-FeOOH led to overestimating corrosion rate. The processes of corrosion prophase were obtained from XRD and EIS results. The corrosion product, Fe（OH）_2 formed at the initial stage stayed at a non-steady state and then consequently transferred to γ-FeOOH, γ-Fe_2O_3 or β-FeOOH.

Effect of anions on stress corrosion cracking behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo

The effects of chloride,sulfate and carbonate anions on stress corrosion behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo were studied by stress corrosion cracking(SCC)test method using double cantilever beam(DCB)specimens.The SCC morphology was observed by using scanning electron microscopy(SEM)and the composition of corrosion products was analyzed by using energy dispersive spectrometer(EDS).The results show that the crack propagates to bifurcation in NaCl and Na2SO4 solution,while the crack in Na2CO3 solution propagates along the load direction.The SCC rate in NaCl solution is the highest,while lower in Na2SO4 solution and little in Na2CO3 solution.From the SEM morphologies,quasi-cleavage fracture was observed in NaCl and Na2SO4 solutions,but intergranular features in Na2CO3 solution.The mechanism of anion effect on SCC of steel 23Co14Ni12Cr3Mo was studied by using full immersion test and electrochemical measurements.

Effect of microstructure variation on the corrosion behavior of high-strength low-alloy steel in 3.5wt% NaCl solution

The effect of microstructure variation on the corrosion behavior of high-strength low-alloy（HSLA） steel was investigated. The protective property of the corrosion product layer was also explored. Experimental results reveal that the type of microstructure has significant effect on the corrosion resistance of HSLA steel. The measurement results of weight loss, potentiodynamic polarization curves, and electrochemical impedance spectroscopy indicate that the steel with acicular ferrite microstructure exhibits the lowest corrosion rate. Martensite exhibits a reduced corrosion resistance compared with polygonal ferrite. It is found that the surface of the acicular ferrite specimen uniformly covered by corrosion products is seemingly denser and more compact than those of the other two microstructures, and can provide some amount of protection to the steel; thus, the charge transfer resistance and modulus values of the acicular ferrite specimen are the largest. However, corrosion products on martensite and polygonal ferrite are generally loose, porous, and defective, and can provide minor protectiveness; thus, the charge transfer resistance values for polygonal ferrite and martensite are lower.

Corrosion Behavior of Ultra-high Strength Steel 300M in Different Simulated Marine Environments

Corrosion behavior of 300M in neutralcorrosion environments containing Na Clsimulated by totalimmersion（TI）,salt spraying（SS）and periodic immersion（PI）,was investigated by surface analysis techniques,corrosion weight-loss method,and electrochemicalmeasurements.In totalimmersion environment,rust on the steelconsisted of a porous outer rust layer with main constituent of γ-Fe OOH,and an inner rust layer of dense Fe_3O_4 film with network broad cracks.In salt spraying environment,outer rust with main composition of γ-Fe OOH/α-Fe OOH/Fe_3O_4 was compact,and inner rust showed dense Fe_3O_4 film.Rust formed by periodic immersion exhibited a compact outer rust layer with constituent of α-Fe OOH/γ-Fe OOH/Fe_3O_4 and an inner rust layer with composition of α-Fe OOH/α-Fe_2O_3;inner rust showed a ultra-dense film adherent to the steel.The corrosion rate showed a rule of vss（salt spraying）〉vti（totalimmersion）〉〉vpi（periodic immersion）in 0-240 h,and vss≈vti？vpiin 240-720 h.The rust formed by periodic immersion was dense and compact,with stable electrochemicalproperties,and had excellent protection on the steel.Humidity and oxygen concentration in allthe environments played major roles in rust formation.

Threshold Stress Intensity of Hydrogen-Induced Cracking and Stress Corrosion Cracking of High Strength Steel

The threshold stress intensity of stress corrosion cracking(SCC) for 40 CrMo steel in 3.5%NaCl solution decreased exponentially with the increase of yield strength.The threshold stress intensity of hydrogen-induced cracking during dynamical charging for 40 CrMo steel decreased linearly with the logarithm of the concentration of diffusible hydrogen.This equation was also applicable to SCC of high strength steel in aqueous solution.The critical hydrogen enrichment concentration necessary for SCC of high strength steel in water decreased exponentially with the increase of yield strength.Based on the results,the relationship between K_(ISCC) and σ_(ys) could be deduced.

IMPROVEMENT ON SUSCEPTIBILITY OF ULTAR-HIGH STRENGTH STEEL TO STRESS CORROSION CRACKING BY HIGH TEMPERATURE QUENCHING

The effect of quenching temperature on the stress corrosion cracking of 30Cr3SiNiMoV ultra-high strength steel in 3.5% NaCl aqueous solution has been studied.The threshold K_(ISCC) may continuously increase with the quenching temperature raised from 870 to 1200℃ . All of the fractures are intergranular.The analyses of the segregation along prior austenitic grain boundaries,grain size and other microstructural factors reveal that the inerease of K_(ISCC) is mainly due to the coarsening of prior austenitic grains.

Effect of Ni on the corrosion resistance of bridge steel in a simulated hot and humid coastal-industrial atmosphere

The corrosion resistance of weathering bridge steels containing conventional contents of Ni(0.20 wt%, 0.42 wt%, 1.50 wt%) and a higher content of Ni(3.55 wt%) in a simulated hot and humid coastal-industrial atmosphere was investigated by corrosion depth loss, scanning electron microscopy–energy-dispersive X-ray spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical methods. The results showed that, with increasing Ni content, the mechanical properties of the bridge steel were markedly improved, the welding parameters were satisfactory at room temperature, and the corrosion resistance was enhanced. When the Ni content was low(≤0.42 wt%), the crystallization process of the corrosion products was substantially promoted, enhancing the stability of the rust layer. When the Ni content was higher(~3.55 wt%), the corrosion reaction of the steel quickly reached a balance, because the initial rapid corrosion induced the formation of a protective rust layer in the early stage. Simultaneously, NiO and NiFe_2O_4 were generated in large quantities; they not only formed a stable, compact, and continuous oxide protective layer, but also strongly inhibited the transformation process of the corrosion products. This inhibition reduced the structural changes in the rust layer, thereby enhancing the protection. However, when the Ni content ranged from 0.42 wt% to 1.50 wt%, the corrosion resistance of the bridge steel increased only slightly.

1300 MPa High Strength Steel for Bolt with Superior Delayed Fracture Resistance

By the increase in Mo content,the addition of microalloying elements V and Nb and by reducing the contents of Mn,P and S based on the composition of steel 42 CrMo,we have developed a 1 300 MPa-grade high strength steel(ADF1)for bolts.The sustained load bending test,sustained load tensile test and stress corrosion cracking test have been carried out to evaluate the delayed fracture resistance of steel ADFl and commercial steel 42 CrMo.The results showed that steel ADF1 has superior delayed fracture resistance to that of 42 CrMo steel.It's concluded that the superior delayed fracture resistance of ADF1 is mainly due to the increase of tempering temperature,fine homogeneously distributed MC carbide and fine prior austenite grain size.

Effect of Boron on Delayed Fracture Resistance of Medium-Carbon High Strength Spring Steel

The delayed fracture behavior of medium carbon high strength spring steel containing different amounts of boron （0. 000 5%, 0. 001 6 %） was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron eontent from 0. 000 5% to 0. 001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initia tion area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3 （C, B） phase.

Microstructure and mechanical property of resistance spot welded joint of aluminum alloy to high strength steel with especial electrodes

Dissimilar material joining of 6008 aluminum alloy to H220 YD galvanized high strength steel was performed by resistance spot welding with especial electrodes that were a flat tip electrode against the steel surface and a domed tip electrode upon the aluminum alloy surface. An intermetallic compound layer composed of Fe2Al5 and FeAl3 was formed at the steel/ aluminum interface in the welded joint. The thickness of the intermetallic compound layer increased with increasing welding current and welding time, and the maximum thickness being 7. 0 μm was obtained at 25 kA and 300 ms. The weld nugget diameter and tensile shear load of the welded joint had increased tendencies first with increasing welding current （ 18 -22 kA） and welding time （ 50 - 300 ms）, then changed little with further increasing welding current （ 22 - 25 kA） and welding time （300 -400 ms）. The maximum tensile shear load reached 5.4 kN at 22 kA and 300 ms. The welded joint fractured through brittle intermetallic compound layer and aluminum alloy nugget.

Effect of cold working and sandblasting on the microhardness, tensile strength and corrosion resistance of AISI 316L stainless steel

The aim of this work is to investigate the effect of cold working and sandblasting on the microhardness, tensile strength and corro-sion rate of AISI 316L stainless steel. The specimens were deformed from 17% to 47% and sandblasted for 20 min using SiC particles with a diameter of 500-700 μm and an air flow with 0.6-0.7 MPa pressure. The microhardness distribution and tensile test were conducted and a measurement on the corrosion current density was done to determine the corrosion rate of the specimens. The result shows that the cold working enhances the bulk microhardness, tensile and yield strength of the specimen by the degree of deformation applied in the treatment. The sandblasting treatment increases the microhardness only at the surface of the specimen without or with a low degree of deformation. In addition, the sandblasting enhances the surface roughness. The corrosion resistance is improved by cold working, especially for the highly deformed specimen. However the follow-up sandblasting treatment reduces the corrosion resistance. In conclusion, the cold working is prominent to be used for improving the mechanical properties and corrosion resistance of AISI 316L stainless steel. Meanwhile, the sandblasting subjected to the cold worked steel is only useful for surface texturing instead of improving the mechanical properties and corrosion resistance.

Prediction and Verification of Resistance Spot Welding Results of Ultra-High Strength Steels through FE Simulations

Resistance spot welding (RSW) is the most common welding method in automotive engineering due to its low cost and high ability of automation. However, physical weldability testing is costly, time consuming and dependent of supplies of material and equipment. Finite Element (FE) simulations have been utilized to understand, verify and optimize manufacturing processes more efficiently. The present work aims to verify the capability of FE models for the RSW process by comparing simulation results to physical experiments for materials used in automotive production, with yield strengths from approximately 280 MPa to more than 1500 MPa. Previous research has mainly focused on lower strength materials. The physical weld results were assessed using destructive testing and an analysis of expulsion limits was also carried out. Extensive new determination of material data was carried out. The material data analysis was based on physical testing of material specimens, material simulation and comparison to data from literature. The study showed good agreement between simulations and physical testing. The mean absolute error of weld nugget size was 0.68 mm and the mean absolute error of expulsion limit was 1.10 kA.

SCC evaluation of ultra-high strength steel in acidic chloride solution

The stress corrosion crack(SCC) susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique(SSRT),tensile with polarization and surface analysis technique.The curves of t fC l/tfW-strain rate are divided into three regions:stress-dominated region,SCC-dominated region,and corrosion-dominated region,so as the curves of tfCl/tfW-strain rate and tm/tf-strain rate.The results of tensile tests with polarization show that the main SCC mechanism of AerMet 100 is anodic dissolution,which controls the corrosion process.The three regions have been discussed according to the relationship between the rate of slip-step formation and the rate of dissolution.Fracture appearances in different environments were analyzed by scanning electron microscopy(SEM).SCC fracture appears as a mixture of intergranular and dimples,while it is totally dimples in the inert environment.The εf becomes the parameter to predict tf because the relationship between tfCl/tfW and tfC l/tfW is a straight line for AerMet 100.

Cause analysis of and solution to furnace roller pick-up in the high strength automotive steel sheet processing line

Cold-rolled high strength steel sheets for automobiles contain more Mn and Si based alloy elements, which, under the reducing atmosphere in the annealing furnace, will get enriched on the strip surface. Since the furnace rollers and the strips contact frequently, alloy elements on the roller surface will form hard protuberance. We call this protuberance ＂pick-up＂. In addition, with the increase of the amount of dust in the furnace atmosphere, the occurrence of furnace roller pick-up will also increase. Through chemical reaction and physical accumulation analysis combined with practical experience, the causes of pick-up in different furnace sections were analyzed. Methods of preventing furnace roller pick-up in the high strength steel sheet processing line were discussed and solutions to improving the strip surface quality in the continous annealing furnace were provided.