Ultra-Pure Ferritic Stainless Steels-Grade,Refining Operation,and Application

The grades of ultra-pure ferritic stainless steels, especially the grades used in automobile exhaust system, were reviewed. The dependence of properties on alloying elements, the refining facilities, and the mechanism of the reactions in steel melts were described in detail. Vacuum, strong stirring, and powder injection proved to be effective technologies in the melting of ultra-pure ferritic stainless steels. The application of the ferritic grades was also briefly introduced.

Effects of TiC on the microstructure and formation of acicular ferrite in ferritic stainless steel

The formation mechanism of acicular ferrite and its microstructural characteristics in 430 ferrite stainless steel with TiC additions were studied by theory and experiment.Using an"edge?to?edge matching"model,a 5.25 mismatch between TiC(FCC structure)and ferritic stainless steel(BCC structure)was identified,which met the mismatch requirement for the heterogeneous nucleation of 430 ferritic stainless steel.TiC was found to be an effective nucleation site for the formation of acicular ferrite in a smelting experiment,as analyzed by metallographic examination,Image-Pro Plus 6.0 analysis software,and SEM–EDS.Furthermore,small inclusions in the size of 2–4?m increased the probability of acicular ferrite nucleation,and the secondary acicular ferrite would grow sympathetically from the initial acicular ferrite to produce multi-dimensional acicular ferrites.Moreover,the addition of Ti C can increase the average microstrain and dislocation density of 430 ferrite stainless steel,as calculated by Williamson-Hall(WH)method,which could play some role in strengthening the dislocation.

Effect of welding parameters on the heat-affected zone of AISI409 ferritic stainless steel

One of the main problems during the welding of ferritic stainless steels is severe grain growth within the heat-affected zone （HAZ） In the present study, the microstmctural characteristics of tungsten inert gas （TIG） welded AISI409 ferritic stainless steel were investigated by electron backscattered diffraction （EBSD）, and the effects of welding parameters on the grain size, local misorientation, and low-angle grain boundaries were studied. A 3-D finite element model （FEM） was developed to predict the effects of welding parameters on the holding time of the HAZ above the critical temperature of grain growth. It is found that the base metal is not fully recrystallized. During the welding, complete recrystallization is followed by severe grain growth. A decrease in the number of low-angle grain boundaries is observed within the HAZ. FEM results show that the final state of residual sWains is caused by competition between welding plastic strains and their release by recrystallization. Still, the decisive factor for grain growth is heat input.

Effect of tin addition on the microstructure and properties of ferritic stainless steel

This article reports the effects of Sn on the inclusions as well as the mechanical properties and hot workability of ferritic stainless steel. Precipitation phases and inclusions in Sn-bearing ferritic stainless steel were observed, and the relationship between the workability and the microstructure of the steel was established. Energy-dispersive X-ray spectroscopic analysis of the steel reveals that an almost pure Sn phase forms and MnS-Sn compound inclusions appear in the steel with a higher Sn content. Little Sn segregation was observed in grain boundaries and in the areas around sulfide inclusions;however, the presence of Sn does not adversely affect the workability of the steel con-taining 0.4wt%Sn. When the Sn content is 0.1wt%-0.4wt%, Sn improves the tensile strength and the plastic strain ratio and also improves the plasticity with increasing temperature. A mechanism of improving the workability of ferritic stainless steel induced by Sn addition was discussed：the presence of Sn lowers the defect concentration in the ultra-pure ferritic lattice and the good distribution of tin in the lattice overcomes the problem of hot brittleness that occurs in low-carbon steel as a result of Sn segregation.

Interfacial Microstructure of Diffusion Bonded Inconel 738 and Ferritic Stainless Steel Couple

In this study, Inconel 738 alloy was diffusion bonded to a ferritic stainless steel. The effect of bonding temperature on the microstructural development across the joint region was investigated. Following the diffusion bonding, conventional characterization techniques such as scanning electron microscopy （SEM）, energy dispersive X-ray （EDX） and microhardness were used to examine the interracial microstructure. It was seen that bonding temperature was effective on the diffusion of Ni from Inconel 738 to ferritic stainless steel that affected the microstructure of the interface. Austenite phase was formed at the interface as a result of Ni diffusion from the Inconel 738 to the interface.

Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints

The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.

Corrosion behavior of ferritic stainless steel with 15wt% chromium for the automobile exhaust system

The effect of chloride ion concentration, pH value, and grain size on the pitting corrosion resistance of a new ferritic stainless steel with 15wt% Cr was investigated using the anodic polarization method. The semiconducting properties of passive films with different chloride ion concentrations were performed using capacitance measurement and Mott-Schottky analysis methods. The aging precipitation and intergranular corrosion behavior were evaluated at 400- 900℃. It is found that the pitting potential decreases when the grain size increases. With the increase in chloride ion concentration, the doping density and the flat-bland potential increase but the thickness of the space charge layer decreases. The pitting corrosion resistance increases rapidly with the decrease in pH value. Precipitants is identified as Nb（C,N） and NbC, rather than Cr-carbide. The intergranular corrosion is attributed to the synergistic effects of Nb（C,N） and NbC precipitates and Cr segregation adjacent to the precipitates.

Activating Flux Design for Laser Weldingof Ferritic Stainless Steel

The behaviors of YAG laser welding process of ferritic stainless steel with activating fluxes were investigatedin this study. Some conventional oxides, halides and carbonates were applied in laser welding. The resultsshowed that the effect of oxides on the penetration depth was more remarkable. Most activating fluxes improved thepenetration more effectively at low power than that at high power. The uniform design was adopted to arrange theformula of multicomponent activating fluxes, showing that the optimal formula can make the penetration depth up to2.23 times as large as that without flux, including 50% ZrO2, 12.09% CaCO3, 10.43% CaO and 27.48% MgO. Throughthe high-speed photographs of welding process, CaF2 can minimize the plasma volume but slightly improve the penetrationcapability.

Effect of Cr, Mo, and Nb additions on intergranular cohesion of ferritic stainless steel: First-principles determination

Effects of Cr, Mo, and Nb on the ferritic stainless steel ]2（210） grain boundary and intragranularity are investigated using the first-principles principle. Different positions of solute atoms are considered. Structural stability is lowered by Cr doping and enhanced by Mo and Nb doping. A ranking on the effect of solute atoms enhancing the cohesive strength of the grain boundary, from the strongest to the weakest is Cr, Mo, and Nb. Cr clearly prefers to locate in the intragranular region of Fe rather than in the grain boundary, while Mo and Nb tend to segregate to the grain boundary. Solute Mo and Nb atoms possess a strong driving force for segregation to the grain boundary from the intragranular region, which increases the grain boundary embrittlement. For Mo- and Nb-doped systems, a remarkable quantity of electrons accumulate in the region close to Mo （Nb）. Therefore, the bond strength may increase. With Cr, Mo, and Nb additions, an anti-parallel island is formed around the center of the grain boundary.

Test research on sticking mechanism during hot rolling of SUS 430 ferritic stainless steel

The sticking phenomenon during hot rolling of SUS 430 ferritic stainless steel was investigated by means of a two-disc type high-temperature wear tester. The test results indicate that sticking particles on the surfaces of high chromium steel （HiCr） and high-speed steel （HSS） rolls undergo nucleation, growth, and saturation stages. Grooves on the roll surface generated by grinding provide nucleation sites for sticking particles. The number of sticking particles on the HiCr roll surface is greater than that on the HSS roll surface. The average surface roughnesses （Ra） of HiCr and HSS rolls change from 0.502 and 0.493 μm at the initial stage to 0.837 and 0.530 μm at the saturation stage, respectively. The test further proves that the sticking behavior is strongly dependent on roll materials, and the HSS roll is more benefi- cial to prevent particles sticking compared with the HiCr roll under the same hot-rolling conditions.

Application and failure evaluation of ferritic stainless steels for automotive exhaust systems

In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferritic stainless steels （FSS） used to make automobile parts have been improved. This paper introduces the construction of automotive exhaust systems and describes their main failure behaviors and corrosion evaluation procedures.

Effect of micro-alloying Nb and Ti on solidification structure in 430 ferritic stainless steel

With the increase in the content of carbon, nitrogen and titanium in 430 ferritic stainless steel, the refinement of the solidification structure is obvious and the proportion of equiaxed grain increases remarkably as well. This is attributed to the increasing role of the inhomogeneous nucleation by TiN particles during solidification. In addition, more fine precipitations of （Ti ,Nb）N are found in steel with increased carbon and nitrogen content.

Surface segregation of copper in antibacterial ferritic stainless steel

By using auger electron spectroscopy （AES） and diffusion theory to analyze the surface segregation of copper in antibacterial ferritic stainless steel, establishing a diffusion model, and calculating the activation energy of diffusion of the copper in ferrite, the affect of surface segregation on the antibacterial capabilities were researched. The results show that the concentration of the copper surface at 973 K and 1 073 K could be expressed asln X^sCu/X^bCu = k0 √Dt/d（-△Hv^Cu＋△Hf^tron＋ △Hs^Cu）/3RT , with the parameters relating to the concentration of the diffusion layer, the coefficient of diffusion, the length of diffusion, the latent heat of evaporation and the latent heat of fusion. The activation energy of diffusion of copper in ferrite is approximately 221. 688 kJ/mol. The antibacterial property of the steel is improved as the surface segregation of the copper is increased. At 1 073 K for 60 min, the concentration of the surface copper is over three times higher than the basic concentration. The antibacterial property of the stainless steel can reach approximately 99.9%.

Effect of stabilizing elements Nb and Ti on the microstructure and properties of low carbon ferritic stainless steel

The effect of stabilizing elements, such as Nb and Ti, on the microstructure and properties of low carbon ferritic stainless steel （FSS） has been investigated. The results of the Thermo-calc simulation have shown that the interstitial elements, such as C and N, may be completely stabilized by the addition of Nb and Ti. With the increase of Nb and Ti contents ,the α ＋ γ two phases gradually transfer to a single α-phase under a high temperature condition ,and the content of the carbide M23 C6 gradually decreases. The microstructure has indicated that the combined addition of Nb and Ti can promote the recrystallization of the band structure and form more uniform equiaxed grains. Also, with the increase of Nb and Ti contents,the elongation, the r-value and the corrosion resistance of cold-rolled and annealed sheets are improved prominently. In comparison with the effect of Ti ,the addition of Nb is more beneficial to the increase of r-value and the corrosion resistance.

Study on the corrosion properties of 0Cr11 ferritic stainless steel for automotive exhaust systems

This study investigates the corrosion properties of 0Cr11Ti and 0Cr11NbTi ferritic stainless steels （FSS） for automotive exhaust systems. The results indicate that the base metal and weld seam of 0Cr11NbTi steel exhibit better intergranular and condensate corrosion resistant properties because carbon and nitrogen are stabilized by Nb and Ti, and the precipitation of Cr carbide is retarded in grain boundaries.

Mechanism of Brittle Cracking for High-Purity Cr18Mo2 Ferritic Stainless Steel

A study has been carried out on the effect of continuous cooling with different rate from 1 200 ℃ on the brittleness of vacuum melted,extra-low interstitial Cr18Mo2 ferritic stainless steels.The ductile-brittle transition temperature was found to be the lowest after water cooling and the highest after furnace cooling.The increase of brittleness with cooling rate decrease is attributed to the formation of more nitrides.With the increase of titanium content the ductile- brittle transition temperature increases significantly.A low transition temperature occurred in steel containing0.18%Nb,and further increase of niobium brought about an increase of transition temperature.The transition temperature of ferritic stainless steel was raised severely by the precipitation of nitrides(Cr2N,Cr2Nb2N2and TiN)and oxides(Al2O3)promoting brittle crack initiation.

Development of ferritic stainless steel B445R with superior corrosion resistance for architectural applications

The dull-finish ferritic stainless steel （FSS） sheet B445R for architectural roofing has been developed by Baosteel. This steel product exhibits excellent corrosion resistance superior to that of SUS 316L with a lower cost. It can be easily formed into roofing panels by ordinary processes. Moreover,the thermal strain of it is less than SUS 316L because of its lower thermal expansion coefficient, and its reflectivity is lower due to the dull-finish treatment. All of these features make it capable of being used as architectural roofing materials in coastal regions.

Effects of asymmetric rolling process on ridging resistance of ultra-purified 17%Cr ferritic stainless steel

In ferritic stainless steels, a significant non-uniform recrystallization orientation and a substantial texture gradient usually occur, which can degrade the ridging resistance of the final sheets. To improve the homogeneity of the recrystallization orientation and reduce the texture gradient in ultra-purified 17%Cr ferritic stainless steel, in this work, we performed conventional and asymmetric rolling processes and conducted macro and micro-texture analyses to investigate texture evolution under different cold-rolling conditions. In the conventional rolling specimens, we observed that the deformation was not uniform in the thickness direction, whereas there was homogeneous shear deformation in the asymmetric rolling specimens as well as the formation of uniform recrystallized grains and random orientation grains in the final annealing sheets. As such, the ridging resistance of the final sheets was significantly improved by employing the asymmetric rolling process. This result indicates with certainty that the texture gradient and orientation inhomogeneity can be attributed to non-uniform deformation, whereas the uniform orientation gradient in the thickness direction is explained by the increased number of shear bands obtained in the asymmetric rolling process.

Effect of Pulse Frequency on Microstructure of 21% Cr Ferritic Stainless Steel in Pulsed Gas Tungsten Arc Welding

Thin plates of 21% Cr ferritic stainless steel welded by pulsed gas tungsten arc welding at different pulse frequencies were investigated for the microstructure characteristics and hardness behavior.The welds contained columnar grains in the outer part and fine equiaxed grains in the central region due to the pulsed process.

Electrodeposition of Fe-Ni alloy coating on ferritic stainless steel

Fe-Ni alloy coatings were electrodeposited on ferritic stainless steel(FSS)in solutions containing FeSO4 and NiSO4.The effects of pH,[Fe2 +]/[Ni 2+](molar ratio)of electroplating solutions and cathode current density on deposition rate and surface appearances of the coatings were investigated.The results indicated that the deposition rate of the coating in solution with [Fe 2+ ]/[Ni 2+ ]of 0.4 slightly increased with increasing pH from 2.5 to 3.5 under the current density of 5.5 mA/cm 2 ,and then the deposition rate of the coating in solution with pH 4.0 began to decrease.The deposition rate also slightly increased with pH up to 3.5 under higher cathode current densities of 13.5 and 27 mA/cm2.Under 13.5 mA/cm 2,however,the coating deposited in solution with pH 4 was prone to crack or flake.The deposition rate increased and the surface of coatings became less smooth with increasing cathode current density.The effect of the ratio of[Fe2 +]to[Ni 2+]on deposition rate was not obvious.With increasing the ratio of [Fe2 +]to[Ni 2+]in plating solution,the content of Fe in the coatings increased;while the Ni content in the coatings decreased with the increase in the ratio of[Fe 2+ ]to[Ni 2+ ].The deposited coating consisted of Fe-Ni alloy phase.