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Toshihiko KOSEKI 《Baosteel Technical Research》2010,(Z1):19
The reliability of steel welds becomes more critical issue with increasing steel strength,because brittle phases are more likely to form in the weld metals and heat-affected zone(HAZ) and thereby the toughness and ductility of the welds are degraded.Therefore,refinement of microstructure and minimization of the brittle phases are necessary to improve the reliability of the high-strength steel welds.In this presentation,microstructure formation that controls the toughness of weld metals and HAZ in high-strength low-alloy(HSLA) steel welds is reviewed and possible routes to the improvement of the weld microstructure and weld toughness are discussed. 相似文献
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对钢结构而言,诸如海洋平台、船舶、桥梁、建筑和油气管线等,焊接后的性能直接决定了其服役寿命和安全性,重要性不言而喻.在针对焊接相关问题的研究中,焊接热影响区的韧性提升一直是重点和难点.焊接热影响区会经历高达1400℃的高温,从而形成粗大的奥氏体晶粒,如果焊接参数控制不当,不能通过后续冷却过程中的相变细化组织,就会造成韧性的降低.而多道次焊接的情况更为复杂,前一道次形成的粗晶区还会在后续焊接过程中经历二次热循环,从而形成链状M-A,造成韧性的急剧下降.本文旨在对一些现有焊接热影响区的相关研究结果进行总结,探讨母材的成分、第二相及焊接工艺等因素对热影响区微观组织和性能的影响,为低温环境服役的大型钢结构的焊接性能改善提供一些设计思路. 相似文献
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M. T. Miglin J. P. Hirth A. R. Rosenfield 《Metallurgical and Materials Transactions A》1983,14(10):2055-2061
Fracture toughness and ductile-brittle transition behavior were measured for a copper-bearing HSLA steel. The value ofK
lc for cleavage failure was independent of heat treatment, whileJ
lc for ductile failure decreased monotonically with increasing strength level. With both failure modes, fracture appears to
be controlled by cracking of sulfide inclusions. The decrease in ductile-failureJ
lc is caused by decreased work-hardening rates that suppress cleavage and facilitate void coalescence. Both higher austenitizing
temperature and quenching rate after austenitization influence the ductile/brittle transition temperature, either through
grain-size and precipitate refinement or through an increase in the resistance of the steel to shear failure.
Formerly Graduate Student, The Ohio State University 相似文献
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B. C. Meyer G. Tempus H. Doyen D. Emanowski T. Hirsch P. Mayr 《Metallurgical and Materials Transactions A》2000,31(5):1453-1459
The local microstructure in the heat-affected zone 1 (HAZ1) of a laser beam-welded Al-Mg-Si-Cu aluminum alloy is investigated
closely. Dispersoid-free zones (DFZs), where the dispersoids of the base material (BM) are dissolved, are found in the vicinity
of the fusion line (FL). They are not uniformly surrounding a grain, but oriented toward the FL. Their width can be as large
as 10 μm. Detailed analysis has revealed a decreased silicon concentration as well as a decreased hardness of the oriented dispersoid-free
zones (ODFZs). Two mechanisms for the formation of this welding metallurgical feature are discussed. 相似文献
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Jae-Il Jang Baik-Woo Lee Jang-Bog Ju Dongil Kwon Woo-Sik Kim 《Metallurgical and Materials Transactions A》2002,33(8):2615-2622
The present study investigates the influence of local brittle zones (LBZs) on the fracture resistance of the heat-affected
zones (HAZs) in quenched, lamellarized, and tempered (QLT) 9 pct Ni steel weld joints. The results of Charpy impact tests
using simulated coarse-grained, heat-affected zone (CGHAZ) specimens show that the intercritically reheated (IC) CGHAZ and
unaltered (UA) CGHAZ are the primary and secondary LBZs, respectively, of the steel at cryogenic temperature. Compact crack
arrest (CCA) tests and crack-tip opening displacement (CTOD) tests were conducted at a liquefied natural gas (LNG) temperature
to measure the variations in crack-arrest toughness and crack-initiation toughness along the distance from the fusion line
(FL) within the actual HAZ. While CTOD tests show a decrease in toughness when approaching the FL, i.e., the regions containing LBZs, the crack-arrest-toughness values are found to be higher than those in the regions near the
base materials. This is due to the fact that the crack-arrest toughness is governed by the fraction of microstructures surrounding
LBZs instead of the LBZs themselves. By direct comparison of the brittle-crack-arrest toughness (K
a
) with the brittle-crack-initiation toughness (K
c
), this investigation has determined that, with regard to crack-arrest behavior, the LBZs of QLT-9 pct Ni steel do not limit
the practical safety performance of the weld joints in LNG storage tanks. 相似文献
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M. Yu. Matrosov I. V. Lyasotskii A. A. Kichkina D. L. D’yakonov A. A. Efimov 《Steel in Translation》2012,42(1):84-93
The microstructure of a broad range of low-carbon low-alloy high-strength pipe steels produced by thermomechanical treatment
is studied by transmission electron microscopy. Such steels consist of a mixture of various types of ferrite matrix with high-carbon
phases and structural components. The classification of the structures is refined, with separate consideration of the components
forming the low-carbon ferrite matrix and the high-carbon components that appear as isolated regions and also as layers and
inclusions in bainitic ferrite. A deformational dilatometer is used to determine the temperatures ranges in which the various
phases and structural components are formed. 相似文献
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借助热力学软件Thermo-Calc和ASPEX自动扫描电镜等分析手段,研究了低合金高强钢精炼过程渣-钢反应和钙处理对夹杂物改性行为的影响.通过提高炉渣碱度和w(CaO)/w(Al2O3)值以及降低炉渣氧化性等措施,钙处理前钢中Al2O3夹杂物转变为靠近1600℃液相区的CaO-MgO-Al2O3复合夹杂物和少量的MgO·Al2O3尖晶石.在渣-钢反应对Al2O3部分变性的基础上,钙线喂入量每炉由优化前的800 m减少到300 m仍能达到夹杂物改性的目的. 相似文献
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Correlation of the microstructure and fracture toughness of the heat-affected zones of an SA 508 steel 总被引:1,自引:0,他引:1
Sangho Kim Suk Young Kang Sunghak Lee Sei J. Oh Soon-Ju Kwon Oo Hag Kim Jun Hwa Hong 《Metallurgical and Materials Transactions A》2000,31(4):1107-1119
In this study, microstructures of a heat-affected zone (HAZ) of an SA 508 steel were identified by Mossbauer spectroscopy
in conjunction with microscopic observations, and were correlated with fracture toughness. Specimens with the peak temperature
raised to 1350 °C showed mostly martensite. With the peak temperature raised to 900 °C, the martensite fraction was reduced,
while bainite or martensite islands were formed because of the slow cooling from the lower austenite region and the increase
in the prior austenite grain size. As the martensite fraction present inside the HAZ increased, hardness and strength tended
to increase, whereas fracture toughness decreased. The microstructures were not changed much from the base metal because of
the minor tempering effect when it was raised to 650 °C or 700 °C. However, fracture toughness of the subcritical HAZ with
the peak temperature raised to 650 °C to 700 °C was seriously reduced after postweld heat treatment (PWHT) because carbide
particles were of primary importance in initiating voids. Thus, the most important microstructural factors affecting fracture
toughness were the martensite fraction before PWHT and the carbide fraction after PWHT. 相似文献
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L. P. Zhang C. L. Davis M. Strangwood 《Metallurgical and Materials Transactions A》1999,30(8):2089-2096
Thermally stable TiN particles can effectively pin austenite grain boundaries in weld heat-affected zones (HAZs), thereby
improving toughness, but can also act as cleavage initiators. The HAZs simulated in a GLEEBLE 1500 TCS using two peak temperatures
(T
p
) and three cooling times (Δ∼
8/5) have determined the effects of matrix microstructure and TiN particle distribution on the fracture toughness (crack tip
opening displacement (CTOD)) of three steels microalloyed with 0.006, 0.045, and 0.1 wt pct Ti. Coarse TiN (0.5 to 6 μm) particles are identified in steels with the two higher levels of Ti, and fine Ti(C, N) (35 to 500 nm) particles were present
in all three steels. Large prior austenite grain size caused by higher T
p
decreased fracture toughness considerably in steels containing coarse TiN particles but had little effect in their absence.
Fracture toughness was largely independent of matrix microstructure in the presence of coarse particles. Cleavage fracture
initiation was observed to occur at coarse TiN particles in the samples with a large prior austenite grain size. Alloy thermodynamics
have been used to rationalize the influence of Ti content on TiN formation and its size. 相似文献
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The effect of Zr addition on the microstructure and impact toughness in the coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels subjected to 100?kJ?cm-1 heat input was investigated. The second- phase particles were mainly Al–Ti complex oxides and (Ti,Nb)N precipitates in Zr-free steel, whereas lots of finer Zr–Al–Ti complex oxides and (Al,Ti,Nb)N precipitates were formed in Zr-bearing steel because of Zr addition. These finer oxides and precipitates effectively restricted the austenite grain growth by pinning effect during welding thermal cycle, and smaller and more uniform prior austenite grains were obtained in CGHAZ of Zr-bearing steel. Furthermore, more acicular ferrite grains nucleated on Zr–Al–Ti complex oxides, inducing formation of fine-grained microstructure in CGHAZ of Zr-bearing steel. The toughness improvement in CGHAZ of Zr-bearing steel with dimple fracture surface was attributed to the grain refinement by pinning effect and acicular ferrite formation. 相似文献
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Sangho Kim Young-Roc Im Sunghak Lee Hu-Chul Lee Sung-Joon Kim Jun Hwa Hong 《Metallurgical and Materials Transactions A》2004,35(7):2027-2037
This study is concerned with the effects of alloying elements on fracture toughness in the transition temperature region of
base metals and heat-affected zones (HAZs) of Mn-Mo-Ni low-alloy steels. Three kinds of steels whose compositions were varied
from the composition specification of SA 508 steel (grade 3) were fabricated by vacuum-induction melting and heat treatment,
and their fracture toughness was examined using an ASTM E1921 standard test method. In the steels that have decreased C and
increased Mo and Ni content, the number of fine M2C carbides was greatly increased and the number of coarse M3C carbides was decreased, thereby leading to the simultaneous improvement of tensile properties and fracture toughness. Brittle
martensite-austenite (M-A) constituents were also formed in these steels during cooling, but did not deteriorate fracture
toughness because they were decomposed to ferrite and fine carbides after tempering. Their simulated HAZs also had sufficient
impact toughness after postweld heat treatment. These findings indicated that the reduction in C content to inhibit the formation
of coarse cementite and to improve toughness and the increase in Mo and Ni to prevent the reduction in hardenability and to
precipitate fine M2C carbides were useful ways to improve simultaneously the tensile and fracture properties of the HAZs as well as the base
metals. 相似文献
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Fracture mechanism and toughness of the welding heat-affected zone in structural steel under static and dynamic loading 总被引:2,自引:0,他引:2
Due to the influence of the welding thermal cycle, the toughness of structural steel generally degenerates. Recently, the
intercritically reheated coarse-grained heat-affected zone (IC CG HAZ) was found to demonstrate the worst toughness in welded
joint, which was associated with its fracture mechanism. In this article, two IC CG HAZs of a structural steel were prepared
by welding thermal-cycle simulation techniques. For the two IC CG HAZs, the static and dynamic fracture toughness were evaluated;
the fracture mechanism was also studied. Under both static and dynamic loading, cracks in the IC CG HAZ were found to initiate
at the intersection of bainitic ferrite α
B
/0
packets with different orientations, followed by propagation in cleavage. In some crack propagation regions, adjacent cleavage
facets are connected by shear, thus producing dimple zones. Though the brittle fracture initiation mechanism remains unchanged,
the cleavage facet size, the proportion of the dimple zones between facets, and the distance from the cracking initiation
site to the crack tip vary with loading speed and welding conditions. These changes were found to be related to the variations
caused by strain rate and welding conditions in fracture toughness for the IC CG HAZs. 相似文献
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