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1.
S. -H. Song A. -M. Guo D. -D. Shen Z. -X. Yuan J. Liu T. -D. Xu 《Materials Science and Engineering: A》2003,360(1-2):96-100
The effect of boron on the hot ductility of 2.25Cr1Mo steel is investigated by means of a Gleeble 2000 thermomechanical simulator. There is a trough in the hot ductility–temperature curve, which is located between 1000 and 700 °C. The ductility trough shifts to lower temperatures with increasing boron content and the hot brittle range becomes shallow and narrow. In general, boron may improve the steel hot ductility in that it may retard the formation of pro-eutectoid ferrite and increase grain boundary cohesion. These effects may be related to the segregation of boron to austenite grain boundaries. 相似文献
2.
《Materials Science & Technology》2013,29(7):818-826
AbstractThe automotive industry is under increasing pressure to: (1) reduce the weight of vehicles and (2) improve crash performance. ‘Hot stamped’ mild carbon–manganese–boron steel 22MnB5 has become common place in the body structure of the European vehicle over the past decade. The ultrahigh strength martensitic microstructure resulting from hot stamping (proof strength ~1200 MPa and ultimate tensile strength ~1500 MPa) enables down gauging while not compromising crash performance. However, with demands for yet higher strength in the final component so to enable further down gauging, novel grades must be developed. In this paper, development of the novel grade 38MnB5 was reported. Following hot stamping, 38MnB5 demonstrated proof strength in excess of 1400 MPa and ultimate tensile strength in excess of 2000 MPa. Owing to the immense strength, the novel grade 38MnB5 was considered to offer significant down gauging and weight reduction opportunities to the automotive industry. 相似文献
3.
《Materials Science & Technology》2013,29(2):537-545
AbstractThe influence of a low Ti addition (~0·01%) on the hot ductility of Nb containing HSLA steels has been examined. For conventional cooling conditions in which an average cooling rate from the melting point to the test temperature was used, the ductility decreased markedly with the addition of Ti. However, when cooling conditions after melting were more in accord with the thermal heat treatment undergone by the strand during continuous casting, i.e. cooling is fast to begin with, reaches a minimum and then reheats, after which the temperature falls more slowly to the test temperature, the Ti addition was found to be beneficial. 相似文献
4.
《Materials Science & Technology》2013,29(4):486-494
AbstractThe influence of B on the hot ductility of high Al, Ti containing twinning induced plasticity (TWIP) steels has been examined. It was established that provided the B was fully protected by adding sufficient Ti to combine with all the N, then B could segregate to the austenite grain boundaries and improve ductility. This improvement was particularly marked for the temperature range of 700–900°C, the range in which the straightening operation often takes place in continuous casting. Of most importance in the present work has been the detection of B at the boundaries using a secondary ion mass spectrometry technique. The cooling rate from the reheating temperature of 1250°C to the tensile testing temperature range of 700–1200°C was 60 K min?1, but it is likely that slower cooling rates ≤25 K min?1, more in keeping with the secondary cooling rate on continuous casting, will give even better ductility. Ti additions in themselves are beneficial to the hot ductility of these steels as precipitation of AlN at the austenite boundaries is avoided, but only if the cooling rate is sufficiently slow to allow the TiN particles to coarsen. However, to ensure freedom from cracking, an addition of B is also required. 相似文献
5.
《Materials Science & Technology》2013,29(11):1724-1731
AbstractIncreasing Al from 0·05 to 1% in Nb containing transformation induced plasticity steel resulted in deepening and considerable widening of the hot ductility trough. Further increase in the Al level to 1·5% produced a trough similar to the low Al steel but having better ductility in the temperature range of 650–800°C. This improved ductility could be ascribed to its finer austenite grain size. Nb(CN) was able to precipitate readily in these steels and was important in influencing the hot ductility of the 0·05 and 1·5%Al steel in the temperature range of 750–1000°C, with ductility improving as the particle size increased with test temperature. No AlN was found in 0·05%Al containing steel, and there was no significant dendritic precipitation of AlN in 1·5%Al containing steel, although precipitation of AlN in plate form was readily observed. In 1%Al steel, copious dendritic precipitation of AlN was present at the γ grain boundaries, leading to rock candy fracture. The poor ductility shown in 1%Al containing steel is due to a combination of this dendritic precipitation, which took place only in a steel of peritectic carbon composition, and its coarse grain size. Both low and 1·5%Al containing steels had compositions outside the peritectic range. It is strongly advised that for this type of steel, the composition should be designed to fall outside the peritectic carbon range. 相似文献
6.
《Materials Science & Technology》2013,29(10):1225-1232
AbstractThe addition of ~0·002%B and ~0·04%Ti as microalloying additions to improve the poor hot ductility and high risk of cracking on continuous casting of high Al containing twinning induced plasticity (TWIP) steels has been examined. Tensile specimens were either cast in situ or heated to 1250°C before cooling at 60 K min?1 to test temperatures in the range 700–1100°C and strained to failure at 3×10?3 s?1. For tensile specimens reheated to 1250°C, the presence of B with sufficient Ti to combine with all the N improved ductility over the temperature range of 700–950°C, the reduction in area (RA) values being >40%. For the higher strength more complex high Al, TWIP steels having Nb present, there was no improvement in ductility with a similar B and Ti addition, when the average cooling rate after melting to the test temperature was 60 K min?1. Reducing the cooling rate to 12 K min?1 resulted in the RA values being close to the minimum required to avoid transverse cracking throughout the temperature range 800–1000°C. Using these additions of B and Ti, transverse cracking was found not to be a problem when continuously casting these high Al containing TWIP steels. 相似文献
7.
Hot flow behavior of boron microalloyed steels 总被引:1,自引:0,他引:1
E. Lpez-Chipres I. Mejía C. Maldonado A. Bedolla-Jacuinde M. El-Wahabi J.M. Cabrera 《Materials Science and Engineering: A》2008,480(1-2):49-55
This research work studies the effect of boron contents on the hot flow behavior of boron microalloyed steels. For this purpose, uniaxial hot-compression tests were carried out in a low carbon steel microalloyed with four different amounts of boron over a wide range of temperatures (950, 1000, 1050 and 1100 °C) and constant true strain rates (10−3, 10−2 and 10−1 s−1). Experimental results revealed that both peak stress and peak strain tend to decrease as boron content increases, which indicates that boron additions have a solid solution softening effect. Likewise, the flow curves show a delaying effect on the kinetics of dynamic recrystallization (DRX) when increasing boron content. Deformed microstructures show a finer austenitic grain size in the steel with higher boron content (grain refinement effect). Results are discussed in terms of boron segregation towards austenitic grain boundaries during plastic deformation, which increases the movement of dislocations, enhances the grain boundary cohesion and modificates the grain boundary structure. 相似文献
8.
《Materials Science & Technology》2013,29(5):909-915
AbstractThe hot ductility of Nb/V containing high Al, twin induced plasticity (TWIP) steels has been examined over the temperature range 650–1150°C after melting and after ‘solution treatment’. Previous work had shown that the hot ductility is poor for the 1·5 mass-%Al, TWIP steel due to precipitation of AlN at the austenite grain boundaries, the depth of the trough being similar to that for an X65 grade pipeline steel but with the trough covering a much wider temperature range. Adding Nb and V made the ductility even worse due to the additional precipitation of NbCN and VN. Very low reduction of area values, 10–20% were obtained in the temperature range 700–900°C. Increasing the cooling rate to the test temperature resulted in even worse ductility. The ductility of these steels after ‘solution treatment’ is similar to that obtained after melting but when the cast was hot rolled followed by ‘solution treatment’ and cooling to the test temperature ductility improved due to grain refinement. 相似文献
9.
《Materials Science & Technology》2013,29(8):1309-1314
AbstractThe hot ductility of in situ melted tensile specimens of Ti–Nb containing steels having C contents in the peritectic C range 0·12–0·17% with and without V has been examined over the temperature range 700–1000°C. An improved testing regime for simulating the continuous casting process was used, which takes into account both primary and secondary cooling conditions. For the Nb containing steels, the ductility improved in the temperature range 750–850°C as the Ti/N ratio increased. However, ductility at 800°C was still below the 35–40% reduction in area values required to avoid transverse cracking. This was attributed to the copious precipitation of sub 40 nm NbTi(CN) precipitates along the grain boundaries and finer precipitates within the grains. Adding V to the Ti–Nb containing steels resulted in significantly improved ductility with reduction in area values at 800°C in excess of 45%. This improvement was due to a decrease in the fraction of fine particles, and in accord with this better ductility, transverse cracking of industrial slabs was avoided. 相似文献
10.
The beneficial effect of boron on mechanical properties of low carbon Al-killed steel has been reported in recent past. However, the effect of boron on strain hardening exponent (n) and ductility has not been fully understood. This aspect has been discussed in present work. The results of mill trials with reference to n and ductility with boron added steel are compared to those for commercial grade. The lowering of ‘n’ with increased total elongation in boron bearing steel has been related to the microstructural evolution as a result of boron addition. 相似文献
11.
The multiaxial creep ductility of austenitic stainless steels 总被引:1,自引:0,他引:1
M. W. SPINDLER 《Fatigue & Fracture of Engineering Materials & Structures》2004,27(4):273-281
Calculations of creep damage under conditions of strain control are often carried out using either a time fraction approach or a ductility exhaustion approach. In practice, calculations of creep damage are further complicated by the presence of multiaxial states of stress. In the case of the time fraction approach, there are a number of models that can be used to predict the effect of state of stress on creep rupture strength. In particular, Huddleston developed a model from data on stainless steels. The R5 procedure uses a ductility exhaustion approach to calculate creep damage and includes a model for use under triaxial states of stress. The aim of this paper is to describe the development of this model, which is based on considerations of cavity nucleation and growth and was developed from multiaxial creep data on Type 304 and 316 steels. 相似文献
12.
We report the synthesis of boron carbide powder via the reaction of hexagonal boron nitride with carbon black. The reaction between hexagonal boron nitride and carbon black completed at 1900 °C for 5 h in vacuum. The particle sizes of the synthesized boron carbide powder were about 100 nm from transmission electron microscopy. The possible reaction mechanism was that hexagonal boron nitride decomposed into elemental boron and nitrogen even when there was no carbon at a relatively low rate, and introduction of carbon into hexagonal boron nitride powder facilitated the decomposition process; the boron from the decomposition of boron nitride reacted with carbon to form boron carbide. 相似文献
13.
The authors examine the boric oxide—ammonia route with special stress on the yield and composition of the intermediate addition
compound (BN)
x
(B2O3)
y
(NH3)
z
. It has been concluded that B2O3 and NH3 present in the addition compound formed between 350°C and 900°C cannot be further reacted to convert the B2O3 into BN and the BN yield remains at around 66%. A formula (BN)12·7(B2O3)7·5NH3 has been suggested for the addition compound. 相似文献
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16.
The hot ductility of B-Ti-Nb-high Al (1.5%Al) containing TWIP steels having Ti/N ratios mainly in excess of 3.4/1 was obtained. After soaking at 1250°C, the tensile specimens were cooled at 12 or 60°C?min?1 to the test temperature and then strained to failure at 3?×?10?3?s?1. Ductility was always good (reduction of area >40%), independent of Ti/N ratio or cooling rate. The good ductility is due to B segregation strengthening the grain boundaries and the low S level (0.005%S) limiting the volume fraction of MnS inclusions and restricting AlN precipitation to the matrix. Increasing the cooling rate, higher N levels and Nb resulted in a small improvement in ductility. An addition of V to the Nb-containing steels caused a slight deterioration in the hot ductility. 相似文献
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18.
Boron nitride films on diamond buffer layers of varying grain size, surface roughness and crystallinity are deposited by the reaction of B2H6 and NH3 in a mixture of H2 and Ar via microwave plasma-assisted chemical vapor deposition. Various forms of boron nitride, including amorphous α-BN, hexagonal h-BN, turbostratic t-BN, rhombohedral r-BN, explosion E-BN, wurzitic w-BN and cubic c-BN, are detected in the BN films grown on different diamond buffer layers at varying distances from the interface of diamond and BN layers. The c-BN content in the BN films is inversely proportional to the surface roughness of the diamond buffer layers. Cubic boron nitride can directly grow on smooth nanocrystalline diamond films, while precursor layers consisting of various sp2-bonded BN phases are formed prior to the growth of c-BN film on rough microcrystalline diamond films. 相似文献
19.
T. K. Chaki 《Materials Science and Engineering: A》1995,190(1-2):109-116
A model is proposed to explain on a unified basis the role of boron in enhancing ductility and reducing environmental embrittlement in polycrystalline Ni3Al. The grain boundaries in strongly ordered Ni3Al have a porous structure with crack-like microcavities, which can open up under small stresses. Furthermore, atomic hydrogen, generated by the reaction of environmental moisture with Al, can diffuse to the tips of the microcavities under stress and can cause embrittlement. It is argued that strong bonding between interstitial B atoms and Ni atoms in B-doped Ni3Al reduces the strength of directional bonding between Ni and Al atoms in the interior of the grains. When two such grains with weakened Ni---Al bonding meet each other, the atoms near the grain boundary can relax easily and close up the microcavities. As a result, the ductility is enhanced in B-doped Ni3Al. The environmental embrittlement is also reduced, because a small amount of environmental hydrogen cannot nucleate microcracks. Numerous experimental observations have been explained with the proposed mechanism. 相似文献
20.
Using laser brazing process, we made the dissimilar joint of the boron nitride and tungsten carbide with an excellent functionality. In order to investigate the characteristic of joint, observation and structural analysis of its interface by the electron probe micro-analysis (EPMA) and the scanning acoustic microscopy were performed. The wetting property between h-BN and Ag–Cu–Ti braze was excellent, therefore no gaps were seen between them. Moreover, it was suggested that the Ti element, which is the active ingredient in Ag–Cu–Ti braze, reacted with N in h-BN to generate Ti–N composite phase as an interfacial precipitation and the generation of Ti–N composite phase was affected by the concentration of Ti in Ag–Cu–Ti braze. All fracture was formed in h-BN body near the interface and it seemed that the distribution of shear strength of 1.25%Ti to 1.68%Ti was within the margin of variation of bulk strength of h-BN. 相似文献