摘要:

AbstractThe effect of a 0·05 wt-%Nb addition on the austenite decomposition in a Fe–0·2C–10Cr (wt-%) steel has been studied. Addition of Nb substantially retards the transformation kinetics and also changes the resulting microstructure. In the Nb free steel the transformed microstructure consisted of a ferrite–(Cr,Fe)23C6aggregate over the whole temperature range studied. In the Nb steel this aggregate also formed initially, but carbide free ferrite eventually grew in the later stages of the reaction. These microstructural differences are consistent with the significantly different Avrami plots obtained for each steel.MST/1640

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1057

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe microstructural evolution and creep behaviour of Cr–2W–0·lC (wt-%) steels containing from 2 to 15%Cr have been investigated after creep rupture testing at 873 K for up to about 72×106s (20 000 h). The creep curves consisted mainly of a transition creep region, where creep rate decreased with time, and an accelerated creep region, where creep rate increased with time. For the bainitic or martensitic steels, which contain from 2 to 9%Cr, the minimum creep rate decreased and the time to rupture increased with increasing Cr concentration. However, for the dual phase martensite andδferrite steels (12–15%Cr), the minimum creep rate increased and the time to rupture decreased with increasing Cr concentration, i.e. with increasingδferrite volume fraction. The microstructural evolution during creep was greater in the bainitic than in the martensitic steels. Evolution was not observed in theδferrite. The resistance to creep deformation is considered to depend on pinning by carbides preferentially arranged along the lath subgrain boundaries in the bainite and martensite. The effect of microstructural evolution during creep on the creep rate and time to rupture of the steels is comprehensively discussed.MST/1617

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1063

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe pitting corrosion resistance of AISI 304 stainless steel (SS), which was laser melted in both nitrogen and argon atmosphere, was studied using the potentiodynamic anodic polarisation method. An attempt was made to introduce nitrogen onto the surface layers by melting in nitrogen atmosphere and argon atmosphere using a continuous wave CO2laser as the heat source at a power output of 3·06 kW at the laser head. The pitting corrosion resistance was determined by measuring the critical pitting potential during anodic polarisation. Secondary ion mass spectrometry (SIMS) was carried out on the laser melted surface to characterise the chemical composition. It was found that the pitting corrosion resistance of 304 SS was improved when laser surface melting was carried out in argon and was improved further when melting was carried out in nitrogen atmosphere. However, the improvement in pitting corrosion resistance in laser melted material was observed only in the reabraded condition and the pitting corrosion resistance in the as melted condition was lower than for the unmelted 304 SS. The improvement in localised corrosion behaviour was attributed to the increase of nitrogen content which was incorporated onto the surface layer during laser surface melting and this was confirmed using SIMS.MST/1530

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1070

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractUsing the modified Crussard–Jaoul analysis, the strain hardening behaviour of a predeformed 1020 dual phase steel with quenching and quenching plus tempering treatments was examined, showing that this dual phase steel deforms in two stages. The relationships between the maximum uniform strainεu, the stress ratio (true initial stressσ0true maximum stressσu) and the strain hardening exponents in the first stage and the second stage (m1and m2) were derived based on the Swift equation and the Considere instability criterion, which showed good agreement with the experimental results for the present 1020 dual phase steel. The dependence of strengthσuand ductilityɛuof dual phase steel on the exponents m1and m2was discussed using the two derived relationships.MST/1631

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1075

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractComplex copper bearing sulphide phases have been observed for the first time in controlled rolled niobium bearing high strength low alloy steels. Analytical electron microscopy studies were carried out on these copper bearing sulphides. The observations show that, in many cases, these particles have duplex sizes and are multiphase. The smaller particles have diameters from 0·2 to 0·7μm with round or ellipsoidal disclike morphology, mainly present close to and/or within the pearlite banding where the segregation of the alloying elements is severe; they tend to be associated with other precipitates such as manganese sulphide, and titanium carbonitrides in the steels having titanium additions. The larger particles (>1μm) occur occasionally, and are often associated with spinel MgO.Al2O3and/or A12O3, Ti(C,N), MnS, and silica. These particles have complex chemical compositions with a ratio of (Cu + Mn)/S ranging from 0·77 to 1·42; their electron diffraction patterns lead to lattice parameters which are very close to either that of covellite (CuS) or digenite (Cu1·765S to Cu1·79S), The particles are probably the complexes of different phases, such as covellite phases and manganese sulphide, or digenite, covellite phases, and manganese sulphide. Some of the observed manganese sulphide particles also contain a small percentage of copper. With segregation of copper and sulphur in the as cast state, and in the presence of more strongly sulphide forming elements, such as manganese, the formation of copper bearing sulphide complexes can occur as the temperature decreases.MST/1603

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1082

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractTwo models have been combined to calculate the mechanics and metallurgy of hot rolling processes. An Eulerian finite element model is used to predict the temperature, strain rate, and strain distribution within the roll bite during steady state hot flat rolling. A finite difference model is used to calculate the temperature distribution, and the evolution of microstructure between passes resulting from recrystallisation. This combined model predicts that the kinetics of static recrystallisation varies systematically through the thickness of the stock. Experimental rolling trials on type 316L stainless steel have been followed by annealing treatments and metallographic studies to establish the form and extent of the through thickness microstructural gradients that develop in rolled slabs. The results of these trials reveal that the gradients exist in the general form predicted by the model, but are much smaller. The discrepancy appears to result from the use of equivalent strains to describe recrystallisation kinetics, when the sign of redundant shears changes during a rolling pass.MST/1575

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1090

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAn unalloyed nodular cast iron has been used to investigate the development of microstructure on heat treating in the bainite temperature region. Specimens were austenitised at 900°C for 1·5 h, then austempered for 1, 2, or 3 h at 250,300, and 350°C, respectively, and examined by light, transmission electron, and scanning electron microscopy. Experimental results indicate a microstructure consisting of a stable, highly enriched, retained austenite with one of two lower bainitic ferrite morphologies. One of these morphologies is carbide free acicular ferrite for specimens austempered at 350°C for 1 h and the other is bainitic ferrite in which carbide is distributed within the ferrite produced by different heat treatment conditions. Austempering at 350°C for 2 h and at 300°C for 1 and 2 h resulted in the formation of transition carbides in bainitic ferrite platelets. Theηcarbide was formed at 350°C for 2 h by precipitation from a bainitic ferrite supersaturated with carbon. By contrast,ɛcarbide was associated with austempering at 300°C for 1 and 2 h and precipitates either on the austenite twin/bainitic ferrite boundaries or within the bainitic ferrite. The fracture mode of tensile and impact specimens in the austempered condition was fully ductile compared with as cast specimens, which had mixed fracture characteristics.MST/1646

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1095

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractSintered compacts of copper and a 50Cu–50Fe mixture have been plastically deformed to large strains (total strainɛt=13·8) by cyclic extrusion and compression. The hardness changes after deformation indicate that no further work hardening occurs with either material whenɛt>4·6. With copper, strain accommodation at large strains would appear to occur solely by dynamic recovery and recrystallisation. With the Cu–Fe mixture, shear banding is still found at the highest strains used.MST/1609

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1104

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractVarious Cu–Ti–B alloys were produced via argon atomisation at 1400°C. Rapidly solidified powders, containing dispersed TiB2particles, were subsequently subjected to thermal treatment in hydrogen at temperatures between 300 and 600°C. This process resulted in the formation of fine, metastable Cu4Ti precipitates from the supersaturated solid solutions, which appreciably strengthened the copper matrix. Compared with the Cu–Ti powder particles obtained using the same procedure, the strengthening effect in Cu–Ti–B powder particles is much greater. The binary and ternary powders both reveal properties superior to those of Cu–Ti alloys produced via ingot metallurgy. This property is of interest for high conductivity electroengineering applications, since Cu–Ti–B alloys would provide a superior combination of strength and conductivity.MST/1549

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1108

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe deformation behaviour of a series of alloys containing from 32 to 52 at.-%Al and containing various proportions ofα2andγhas been studied through compression tests at room temperature. The results showed that strain hardening tendency increases with increasing amount of lamellar constituent in the two phase alloys, which could be attributed to increased slip activity in these alloys as compared with single phaseα2orγalloys. It is found that, in the two phase alloys, microcrack formation occurs by the mechanism of microvoid formation due to decohesion of theα2/γinterface and the coalescence of these microvoids.MST/1612

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.12.1117

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor