Sintered 434L ferritic stainless steel-Al2O3 particulate composites containing phosphorus

Sintering of 434£ ferritic stainless steel powder compacts containing 0-8 volume %

cx-AI20 a (1 J.1m size) and 0-4 weight % phosphorus in the form of either FesP or Fe2P was carried out in the temperature range 1150°C-1300°C, and the resultant densification parameters, ultimate compressive strengths and hardnesses were measured. The results reveal that temperatures of 1150°C and 1200°C produced liquid-phase sintering when phosphorus was added in the form of FeaP. With Fe2P additions, a higher sintering temperature of 1300°C densified the composites, and an increase in the phosphorus content to 3% uniformly enhanced the sintered properties: The presence of Al20 a particles at an optimum level only improved the properties of the liquid-phase sintered composites.     

Sintered duplex stainless steels from premixes of 316L and 434L powders

Duplex austenite–ferrite stainless steels were prepared from the premixes of 316L and 434L stainless steel atomized powders. Pronounced densification was observed after 1350°C sintering in hydrogen. 316L-60w/o 434L steel composition exhibited maximum transverse rupture strength, while 40 and 60w/o 434L containing compositions showed total immunity in 1N H₂SO₄ even after a exposure time of 360 h. Anodic polarization curves also suggest high-corrosion resistance of those two compositions. Magnetic coercivity decreased with increase in sintering temperature while magnetic saturation follows the reverse trend. Wear resistance of the duplex stainless steels under sliding condition was in between the straight steels.     

Textures of ferritic stainless steels

Abstract

Whereas much research has been carried out on the texture development of Fe–Si steels or low carbon steels, very little attention has been given to the texture formation and investigation of the underlying mechanisms in Fe–Cr steels. Ferritic stainless steels containing between 11 and 17%Cr establish an important group of alloys owing to their good mechanical behaviour and corrosion resistance. Various industrial problems, such as roping or optimisation of deep drawability, can be tackled by means of quantitative texture analysis. Therefore, fundamental aspects concerning the inhomogeneity of the hot and cold rolled band, the origin of Goss texture after annealing, and selective particle drag during recrystallisation of alloys with finely dispersed Nb and Ti carbonitrides have been discussed.

MST/1678     

Roping phenomena in ferritic stainless steels

Abstract

The mechanism of roping in two ferritic stainless steels (type 18·2 and type 430) has been studied. The effects of structure, substructure, and texture are considered in relation to hot and cold process parameters and results obtained from deep drawn cups and tensile specimens. The mechanism of roping is shown to result from differential yielding under tension, caused by heterogeneous bands of material which are developed during the hot rolling schedule. It is shown that small dispersions of austenite can prevent this banding effect.

MST/335     

Hydrogen-induced microtwinning in ferritic stainless steels

Electrochemical hydrogen charging of thin foil specimens of ferritic stainless steels resulted in extensive microtwinning. Microtwins were plate- or needle-like on {110}-planes with a common 〈111〉 growth direction. Hydrogen-induced microtwinning was similar in both steels. Hydrogen embrittlement is expected to be related to hydrogen-induced microtwinning of the ferritic stainless steels.     

Effect of heating mode and temperature on sintering of YAG dispersed 434L ferritic stainless steel

This study examines the effect of heating mode, sintering temperature, and varying yttria alumina garnet (YAG) addition (5 and 10 wt%) on the densification and properties of ferritic (434L) stainless steel. The straight 434L stainless steel and 434L–YAG composites were sintered in a conventional and a 2.45 GHz microwave furnace. The composites were sintered to solid-state as well as supersolidus sintering temperature at 1200 and 1400 °C, respectively. Both 434L and 434L–YAG compacts coupled with microwaves and underwent rapid heating (∼45 °C/min). This resulted in about 85% reduction in the processing time. For all compositions microwave sintering results in greater densification. As compared to conventional sintering, microwave sintered compacts exhibit a more refined microstructure, thereby, resulting in higher bulk hardness. The mechanical properties and sliding wear resistance of 434L stainless steel is shown to be sensitive both to the sintering condition as well as YAG addition and has been correlated to the effect of heating mode on the pore morphology.     

Sintering and characterization of YAG dispersed ferritic stainless steels

The present study investigates the effect of yttrium aluminium garnet (YAG) addition on the densification, mechanical, tribological and corrosion behaviour of ferritic (434L) stainless steels. The composites were sintered at both solid-state (1200 °C) and supersolidus (1400 °C) sintering conditions. Supersolidus sintering results in superior densification, hardness and corrosion resistance of both straight 434L stainless steel as well as YAG reinforced 434L stainless steels. The addition of YAG to 434L stainless steels at supersolidus sintered conditions improves the strength and wear resistance of 434L stainless steels without significantly degrading the corrosion performance.     

Stabilisation of ferritic stainless steels with Zr and Ti additions

Abstract

Traditional 11·5 wt-%Cr ferritic stainless steels are single stabilised with Ti or dual stabilised with Ti–Nb additions. A dual-stabilised ferritic stainless steel 409 with Zr–Ti additions was studied, which was selected through thermodynamic and kinetics analysis. The alloy was subjected to thermomechanical processing using both hot and cold rolling and annealing. The intergranular corrosion resistance and microstructure of this alloy was evaluated. Of particular interest was to study the stabilisation behaviour of this alloy under all processing conditions. The results showed that the precipitation of Cr_xC_y was effectively prevented; hence, the alloy used in this investigation had an excellent resistance to intergranular corrosion.     

Thermomechanical fatigue behavior and lifetime prediction of niobium-bearing ferritic stainless steels

In this study, the thermomechanical fatigue (TMF) and isothermal low-cycle-fatigue (LCF) behaviors of niobium-containing ferritic stainless steels are presented for the temperature range from 100 °C to the maximum temperatures between 500 and 800 °C; furthermore, we propose a new fatigue failure criterion to predict the fatigue lives of the components for different thermal cycle ranges using the TMF condition. Higher maximum temperatures during TMF cycle resulted in shorter TMF life. By modifying the Coffin–Manson equation using the temperature factor, we obtained a new parameter that was successfully correlated with the life under different maximum temperatures. The deformation responses during fatigue cycling and the fatigue microstructure were compared to elucidate the different fatigue behaviors under the TMF and LCF conditions.     

Cyclic oxidation resistance of ferritic stainless steels used in mufflers of automobiles

This work investigates the cyclic oxidation resistance of AISI 439 and AISI 441 ferritic stainless steels (FSS) at a typical temperature of muffler (300 °C). This temperature is characteristic of the cold exhaust of an automobile. The oxidation testing of steels was performed in synthetic air in a tube furnace under two different conditions: after immersing in the synthetic condensed (TOC) for 10 h and without immersion in the synthetic condensed (TOP). The mass gain of AISI 439 steel without previous immersion in condensate was the half of the mass gain of AISI 439 steel oxidized after immersion in condensate. In all samples, the Fe₂O₃ was only identified in the oxide layer on samples that oxidized after immersion in a condensate solution. The corrosion perforation of mufflers is mostly attributed to the cyclic and synergetic effect of oxidation and condensation processes of hot moisture-bearing exhaust gas.     

Effect of nitrogen contamination on intergranular corrosion of stabilized ferritic stainless steels

Abstract

Three different alloys of AISI Type 444 (18Cr–2Mo) ferritic stainless steel, stabilized to different levels with titanium and/or niobium, were melted as welds or weld simulations with deliberate additions of nitrogen to the argon shielding gas in order to simulate the effects of accidental contamination by nitrogen during production welding. The oxalic acid etch test (ASTM A262–A) was used to assess the susceptibility of the melts prepared in this way to intergranular attack, and the extent of attack was quantified. It is shown that a clear correlation exists between the extent of intergranular corrosion and the amount of nitrogen taken up by the steel on melting. The implications of sensitization by nitrogen contamination both for steel design and integrity of production welds are discussed.

MST/415     

Structural and substructural observations during thermomechanical processing of two ferritic stainless steels

The substructural and structural features of two ferritic stainless steels were investigated and their variation with process variables noted. The influence of certain structural features on recrystallization and grain growth are discussed.     

Absorption of gaseous contaminants by welds and weld simulations in ferritic stainless steels

Abstract

The factors influencing absorption by Type 444 ferritic stainless steel of interstitial elements from gaseous environments deliberately contaminated with nitrogen and oxygen have been studied for induction melted weld simulations and actual tungsten inert gas welds. For weld simulations, nitrogen pick-up is limited by factors such as the formation of stable TiN surface films; induction melting is therefore considered unsatisfactory as a weld simulation for the purpose of studying gas absorption. It is found that titanium is consumed by both gaseous species, whereas niobium is not; dual stabilization is therefore recommended. Welds show greater nitrogen pick-up than simulations, the effect increasing with increasing heat input, while at the highest heat inputs the quantity absorbed exceeds predictions based on solubility equilibria. These effects are explained in terms of the enhanced gas transfer conditions that obtain and the dissociation of the gas that occurs in the welding arc.

MST/416     

A new high temperature life correlation model for austenitic and ferritic stainless steels

Low-cycle fatigue tests on 429EM ferritic stainless steel and 316L austenitic stainless steel were carried out in a wide range of temperatures from room temperature to 750 °C. The Tomkins fatigue life model was applied to correlate the fatigue life with crack propagation rate and this model matched well with the fatigue life of 429EM stainless steel but not for the 316L stainless steel. A new life prediction model was developed to consider the temperature effect on fatigue life. The predictions show good agreement with experimental results for both materials. The predicted lives were within a±2X scatter band at all test temperatures.     

Corrosion behaviour of sintered 434L ferritic stainless steel-A12O3 composites containing early transition metals

In the present investigation, the effect of the addition of 0.5 wt % of transition metals such as titanium or niobium on the corrosion behaviour of sintered ferritic stainless steel-Al₂O₃ particulate composites in IN H₂SO₄ solution at room temperature has been studied. It is found that the weight loss of the compacts containing such an addition reduces to great extent, when studied in IN H₂SO₄ environment. However, the passivation properties observed in a potentiodynamic study are lowered in the presence of titanium or niobium.     

初始凝固组织对Cr17表面皱折的影响机制

研究了Cr17铁素体不锈钢的初始凝同组织对与皱折特性相关的晶粒簇演变的影响和对冷轧退火板铍折的影响机制.结果表明:1.柱状晶和等轴晶铸坯在轧制和退火过程中其晶粒簇演变是不同的;2.等轴晶铸坯的冷轧退火试样比柱状晶铸坯的冷轧退火试样具有更少的{001}<110>晶粒簇和更多的{111}<112>晶粒簇;3.两种铸坯冷轧退火试佯皱折特性的差异归因于两者的{001}<110>、{111}<112>晶粒簇数量和分布的不同,而与{001}<010>、{111}<110>、{112}<110>晶粒簇无关.     

Compatibility of ferritic and duplex stainless steels as implant materials: in vitro corrosion performance

The pitting corrosion, crevice corrosion and accelerated leaching of iron, chromium and nickel of super-ferritic and duplex stainless steels, and for effective comparison the presently used 316L stainless steel, have been studied in an artificial physiological solution (Hank's solution) by the potentiodynamic anodic polarization method. The results of the above studies have shown the new super-ferritic stainless steel to be immune to pitting and crevice corrosion attack. The pitting and crevice corrosion resistances of duplex stainless steel were found to be superior to those of the commonly used type 316L stainless steel implant materials. The accelerated leaching study conducted for the above alloys showed very little tendency for the leaching of metal ions when compared with 316L stainless steel. Thus the present study indicated that super-ferritic and duplex stainless steels can be adopted as implant materials due to their higher pitting and crevice corrosion resistance.     

Electrochemical corrosion behavior of novel Cu-containing antimicrobial austenitic and ferritic stainless steels in chloride media

The electrochemical corrosion behavior of novel Cu-containing antibacterial austenitic and ferritic stainless steels in 0.05 mol/L NaCl solution has been investigated by dc polarization and ac impedance measurements and compared with that of the conventional stainless steels. Cu was found to particularly affect the kinetics of the anodic reaction. The corrosion performance of the austenite was greatly improved by Cu addition in the studied anodic potential range, whereas Cu effects on the ferrite showed remarkable sensitivity to the applied potential and improved corrosion resistance only in the low anodic potential range. Three-dimensional presentation of the variable-potential impedance data was employed in analyzing the electrochemical corrosion processes and revealed a close relationship between the impedance parameters and the applied potential. The trends of impedance results agree well with those obtained from potentiodynamic polarization measurements.     

Effects of high-temperature hardness and oxidation on sticking phenomena occurring during hot rolling of two 430J1L ferritic stainless steels

Effects of high-temperature hardness and oxidation on sticking phenomena occurring during hot rolling of two STS 430J1L ferritic stainless steels were investigated in this study. Hot-rolling simulation test was conducted using a high-temperature wear tester. The sticking started from the initial nucleation stage in which the rolled materials were stuck onto the roll specimen surface, proceeded to the growth stage in which stuck fragments grew further, and reached the saturation stage. The modified 430J1L steel had a smaller number of sticking nucleation sites and slower growth rate than the conventional 430J1L steel because of higher high-temperature hardness, thereby leading to less serious sticking. When the simulation test was conducted at 1070 °C, Cr oxides were formed on the surface of the rolled materials, and thus the sticking was drastically reduced because of the increased surface hardness of the rolled materials. In order to prevent or minimize the sticking, thus, it was suggested to improve high-temperature properties of stainless steels in the case of hot rolling at 900–1000 °C, and to promote the formation of oxides in the case of hot rolling at temperatures higher than 1000 °C.