High Cr Stainless Steels Research Articles

Influence of metallic matrix on erosion-corrosion behaviour of high chromium cast irons under slurry impingement conditions

Chromium cast irons (CCI) comprise versatile materials that encompass a range of compositions and microstructures often chosen to promote good wear resistance. There are, however, issues that arise when the cast iron is required to operate in conditions where corrosion, as well as, wear is a factor. This scenario usually results in adapting the composition of the CCI in order to achieve higher chromium content in the metallic matrix and, thereby, to attain the corrosion resistance exhibited by high-Cr stainless steels. This paper comprises a comparison of the corrosive wear behaviour of an austenitic-based hypoeutectic cast iron and a martensitic-based, near-eutectic cast iron with the associated stainless steels, in a saline water under solid-liquid submerged jet conditions. A comprehensive experimental methodology has been adopted including evaluation of the behaviour of the materials in free erosion-corrosion conditions and with the application of cathodic protection. This approach has extended the understanding of the fundamental deterioration mechanisms in different hydrodynamic conditions and has highlighted the complexities of the mechanical/electrochemical interactions occurring during erosion-corrosion. An important feature is the influence of micro-galvanic interactions at phase boundaries. The impact of the findings has been discussed in terms of CCI alloy selection and corrosion control strategies.

Aluminum-Titanium Complex Deoxidation Equilibria in Fe-Cr-Al-Ti-O Melts

Al-Ti complex deoxidation equilibria in high Cr stainless steels were studied by measuring the thermodynamic behavior of O in the Fe-Cr-Al-O, Fe-Cr-Ti-O, and Fe-Cr-Al-Ti-O melts. The present deoxidation experiments were thermodynamically analyzed along with available data in the literature using Wagner’s formalism. The compatible set of parameters for the multicomponent Fe-Cr-Al-Ti-O system was selected, and its applicable concentration and temperature limits were discussed. The parameter set successfully reproduced the present experimental results and literature data of deoxidation equilibria in the Fe-Cr-Al-O and Fe-Cr-Ti-O alloy melts over the wide Cr concentration up to 40 mass pct at 1823 K to 1996 K (1550 °C to 1723 °C). The validity of the parameters was also checked by carrying out the Al-Ti complex deoxidation experiments with the construction of the predominance diagram for inclusions in the Fe-Cr-Al-Ti-O melts at 1873 K (1600 °C).

Oxide scale on stainless steels and its effect on sticking during hot-rolling

The failure of oxide scales on ferritic stainless steels (STSs) has been known to cause an unexpected and severe sticking problem during the hot-rolling process. The oxide scale fragments formed during hot-rolling are stuck on the surfaces of the working roll, deteriorating the surfaces of both the roller and the rolled materials. In this study, we investigate the effects of the compositions and microstructures of thermally grown oxide scales on the degree of sticking during hot-rolling in three different kinds of commercial ferritic STSs and one austenitic STS. The STS samples are oxidized at around 1280 °C for 2 h, and the oxide scales formed on the STSs are identified by X-ray diffraction (XRD). Additionally, the cross-sectional microstructure and chemical compositions of the oxide scales on the STSs are examined by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM), respectively. The oxide scales adjacent to the interfaces with the bulk STS are analyzed by high-resolution transmission electron microscopy (HR-TEM). The Gleeble test, which is a high-temperature (1250 °C) tensile test, is conducted to analyze the effects of the stress induced in the oxide scales during hot-rolling on the fracture of the scales. According to the microstructural analysis and mechanical test results, a brittle Cr2O3 layer, where cracks are easily formed and propagate through the scale thickness under the stress induced by hot-rolling, is formed along the interfaces of STSs with high Cr contents. This effect increases the probability of sticking failure in high-Cr STSs. In contrast, scales with a composite-like structure of Fe- and Cr-oxides are formed on the surface of STSs containing low and medium levels of Cr. According to the Gleeble test results, the composite-like oxide scales show higher mechanical resistance to tensile stress than the Cr2O3 layers in the high-Cr STSs. In addition, our microstructural analysis results reveal that FexNiy intermetallic compounds are observed as a form of a composite-like structure inside the oxide scales in the austenitic STS and that this structure also delays crack propagation through the oxide scales and reduces the degree of sticking.

Corrosion Behavior of a New Developed Ferritic Stainless Steels Used in Automobile Exhaust System

The inside corrosion of failed automotive mufflers collected in China was investigated and the composition of the automotive exhaust gas condensate collected from HONGQI automobile was analyzed. According to the analyzed result of collected condensate’s composition, the corrosion resistance of a new designed high Cr stainless steel (B439M) bearing Nb and Ti and a low Cr T409L stainless steel were studied with a condensate corrosion test method which simulates the inside corrosion of automotive mufflers. The life of the two materials was estimated by extreme value analysis of the maximum corrosion depth obtained by the dip dry test (DDT). The life of type B439M steel was 1.6 times as long as that of type T409L steel. To clarify the corrosive process of the simulated condensate test, the electron work function (EWF) on the two stainless steels’ surface was evaluated. It was demonstrated that the surface of new designed stainless steel exhibited markedly improved resistances to corrosion during a simulated condensate test cycle and the corrosive process of simulated condensate test was evaluated and discussed.

Accelerated corrosion of five commercial steels under a ZnCl 2–KCl deposit in a reducing environment typical of waste gasification at 673–773 K

The corrosion of five Fe–Cr commercial steels containing 0–18 wt.% Cr at 673–773 K has been studied in a reducing H 2–HCl–CO 2 atmosphere under a ZnCl 2–KCl deposit typical of waste gasification environments. In comparison with the behavior of the same steels in a similar gas mixture without salt deposit, all steels suffered from accelerated corrosion induced by the salt and formed porous scales with poor adherence to the underlying steels. Some Cl was detected close to the steels/scale interface, indicating that Cl-containing species were able to go through the scale down to the metal matrix. Even though the corrosion rates generally decreased with increasing Cr content, the high-Cr stainless steel SS304 was still unable to provide a good corrosion resistance against the ZnCl 2–KCl deposit. The reaction mechanisms are discussed on the basis of thermodynamic considerations and of the “active oxidation” model.

Corrosion Behavior of Ceramic Dispersion Strengthened High-Cr Stainless Steel

In the present work, corrosion characteristics of ceramic dispersion strengthened (CDS) high-Cr stainless steel (SS) has been investigated. For the preparation of CDS SS with uniformly distributed reinforcements, TiC particles were mechanically activated with Cu powder by using high-energy ball mill machine, and then Cu-coated TiC particles were mixed with molten SS. Potentiodynamic polarization curves were experimentally measured on unmodified SS and CDS SS in 0.05 M NaCl solution. The values of corrosion potential Ecorr, corrosion current io, pitting potential Epit and polarization resistance Rp were quantitatively determined from the measured potentiodynamic polarization curves. From the result, it is concluded that CDS SS exhibits higher corrosion resistivity than unmodified SS.

Corrosion of Three Commercial Steels Under ZnCl2 –KCl Deposits in a Reducing Atmosphere Containing HCl and H2S at 400–500°C

The corrosion of three commercial steels in a reducing atmosphere containing HCl plus H2S in the presence of ZnCl2-KCl deposits has been investigated at 400-500 degrees C and compared with the corrosion of the same materials in a similar gas mixture free from H2S. The presence of H2S in the gas accelerated the corrosion of the three commercial steels beneath ZnCl2-KCl deposits. All materials suffered from severe corrosion with partial detachment and spalling of the external scales. Degradation of the steels resulted from the penetration of chlorine-containing species through the scale formed initially down to the metal matrix, because chorine-rich species were detected close to the alloy/scale interface. Although the corrosion resistance generally increased with increasing Cr content, even the high-Cr stainless steel SS304 is still unable to provide good corrosion resistance against the ZnCl2-KCl deposits in the presence of H2S due to the bad adherence of the scales to the alloy. The mechanisms of attack are discussed on the basis of thermodynamic considerations and of the active-oxidation model.

腐食防食 自動車排気ガス凝縮水環境におけるマフラー用材料の耐食性評価

The inside corrosion of automotive mufflers collected in North America way investigated. Aluminized steel corroded severely by automotive exhaust gas condensates. The morphology of the corrosion of aluminized steel was a pit with a diameter of a couple of millimeters and Al coating remained around the pit. This pit-shaped corrosion is characteristic of the inside corrosion of aluminized steel and causes large corrosion depth. Low-Cr steels (type 409: 11%Cr-0.2%Ti, type 410L: 13%Cr-0.01%C) sustained a large number of pits, while high-Cr stainless steel (type 430J1L: 19%Cr-0.5%Cu-0.5%Nb) corroded slightly. The corrosion resistance of these materials was studied with a newly developed condensate corrosion test method which simulates the inside corrosion of automotive mufflers, especially the pit-shaped corrosion of aluminized steel. The life of the materials was estimated by extreme value analysis of the maximum corrosion depth obtained by the new test. The life of type 409 steel was 3.3 times as long as that of aluminized steel and the life of type 436 stainless steel (18%Cr-1%Mo-0.3%Ti) was 1.7 times as long as that of type 409 steel.

高Crステンレス急冷薄帯の微細組織に及ぼす二次冷却の効果

高Crステンレス急冷薄帯の微細組織に及ぼす二次冷却の効果

建材用高Crステンレス鋼の耐候性と素材の選定法

建材用高Crステンレス鋼の耐候性と素材の選定法

The influence of Pd on the surface segregation of Cr and impurities in high chromium stainless steel

The surface segregation of the components in an Fe-40Cr-3Pd alloy as well as an Fe-40Cr alloy covered with a thin surface layer of Pd was studied using AES and ESCA as surface probes. Evidence of an attractive interaction between Fe and Pd was found and it was shown that the Pd layer does provide easy diffusion paths to Cr in contrast to Fe and that impurities such as S and C probably enhance the segregation of Cr in these high Cr stainless steel alloys.

Frictional and structural characterization of ion-nitrided low and high chromium steels

Low Cr steels AISI 4140, AISI 4340, and high Cr austenitic stainless steels AISI 304. AISI 316 were ion nitrided in a dc glow discharge plasma consisting of a 75% H2–25% N2 mixture. Surface compound layer phases were identified, and compound layer microhardness and diffusion zone microhardness profiles were established. Distinct differences in surface compound layer hardness and diffusion zone profiles were determined between the low and high Cr alloy steels. The high Cr stainless steels after ion nitriding displayed a hard compound layer and an abrupt diffusion zone. The compound layers of the high Cr stainless steels had a columnar structure which accounts for brittleness when layers are exposed to contact stresses. The ion nitrided surfaces of high and low Cr steels displayed a low coefficient of friction with respect to the untreated surfaces when examined in a pin and disk tribotester.

高Cr不銹鋼の熔接について(第1報)

It must be recommended in our country where nickel is now in short supply, to use high chromium stainlees steel as a substitute of chromium-nickel stainless steel. High Cr stainless steels studied here contains 20-24 pet Cr, 2-3 pet Ni, 0.08 pet C and are so called ferritic stainless steels and not hardened significantly by heat treatmet. However, because these steels are susceptible to several types of embrittlement, their welding characteristics should be understood.The oxyacetylene welding process is not recommended for joining these stainless steels, because of considerable grain growth and carbon pick up.Metal arc welding is the process most wideey used, and the amount of heating at the joint is usually substantially less than with the oxyacetylene process.Argon-shielded tungsten-arc welding is, well suited for these steels.Satisfactory results are obtained by welding the ferritic stainless steels with electrodes having composition identical to those of the parent metals, but post annealing treatments are essential.Austenitie chromium-nickel electrodes can be used satisfactorily because the austenitic weld metal is not susceptible to the high-temperature embritteement.On the other hand, ferrite grain size increases when heated above approximately 1050°C. This feature is the factor which exerts the greatest influence on the properties of a weld joint.Such commercial alloys as these can contain austenite at high temperature. A mixed structure of ferrite and austenite at high temperature can be retained, if cooled fairly rapidly.This austenite may transform into martensite. This will make the heat-affected zone relatively brittle.Sigma-phase precipitation was not found in welded joint. 475°C brittleness can occur in the welded joint, so it must be avoided to cool slowly through this temperature.Lack of ductility in the as welded condition may be due to phenomena associated with the solution of carbides at temperature above 1, 200°C.