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1.
Seokmin Hong Jaemin Song Min-Chul Kim Kwon-Jae Choi Bong-Sang Lee 《Metals and Materials International》2016,22(2):196-203
The effects of microstructural changes in heavy-section Mn-Mo-Ni low alloy steel on Charpy impact properties were investigated using a 210 mm thick reactor pressure vessel. Specimens were sampled from 5 different positions at intervals of 1/4 thickness from the inner surface to the outer surface. A detailed microstructural analysis of impact-fractured specimens showed that coarse carbides along the lath boundaries acted as fracture initiation sites, and cleavage cracks deviated at prior-austenite grain boundaries and bainite lath boundaries. Upper shelf energy was higher and energy transition temperature was lower at the surface positon, where fine bainitic microstructure with homogeneously distributed fine carbides were present. Toward the center, coarse upper bainite and precipitation of coarse inter-lath carbides were observed, which deteriorated impact properties. At the 1/4T position, the Charpy impact properties were worse than those at other positions owing to the combination of elongated-coarse inter-lath carbides and large effective grain size. 相似文献
2.
A. Saxena S. K. Chaudhuri Ram Avtar S. N. Sinha 《Journal of Materials Engineering and Performance》2003,12(4):445-451
In the current study, granular bainite was found to be the major component in the microstructure of air cooled 80 mm thick
plates of medium carbon microalloyed steel. The second constituent in this granular bainite was identified as cementite. It
was further observed that (1) ferrite lath size and (2) amount of cementite in granular bainite varied with slab reheating
time before plate rolling. Smaller ferrite laths and a lesser amount of cementite were found in the plate processed with the
longer slab reheating time of 26 h. Contrary to this, very large sized ferrite laths and a larger population of cementite
were formed in the plate processed with the shorter slab reheating time of 4 h. Subsequent quenching and tempering of these
plates favored the formation of lower bainite and tempered martensite in the plate with 26 h slab reheating time. On the other
hand, upper bainite and coarser cementite were formed after the quenching and tempering of the plate with 4 h of slab reheating
time. The influence of different microstructures, formed due to varied slab reheating time, on the toughness property of tempered
plates was evaluated under different test conditions. In tensile test and fracture toughness testing of thinner specimens,
a ductile mode of fracture was observed, irrespective of varied microstructures in the tempered plates. However, in the three-point
bend test of full thickness specimens, the mode of fracture was ductile in the tempered plate with 26 h slab reheating time,
while the tempered plate from the slab with 4 h reheating time gave rise to a predominantly brittle mode of fracture. These
observations showed that the toughness property of these tempered plates was sensitive to the microstructure only under the
specific condition, which prevailed during the three-point bend test of full thickness specimens. Under this condition, coarse
cementite and upper bainite became prone to cracking resulting in a lower toughness of the tempered plate associated with
lower slab reheating time. 相似文献
3.
4.
Effect of austempering time on mechanical properties of a low manganese austempered ductile iron 总被引:1,自引:0,他引:1
Susil K. Putatunda Pavan K. Gadicherla 《Journal of Materials Engineering and Performance》2000,9(2):193-203
An investigation was carried out to examine the influence of austempering time on the resultant microstructure and the room-temperature
mechanical properties of an unalloyed and low manganese ductile cast iron with initially ferritic as-cast structure. The effect
of austempering time on the plane strain fracture toughness of this material was also studied. Compact tension and round cylindrical
tensile specimens were prepared from unalloyed ductile cast iron with low manganese content and with a ferritic as-cast (solidified)
structure. These specimens were then austempered in the upper (371 °C) and lower (260 °C) bainitic temperature ranges for
different time periods, ranging from 30 min. to 4 h. Microstructural features such as type of bainite and the volume fraction
of ferrite and austenite and its carbon content were evaluated by X-ray diffraction to examine the influence of microstructure
on the mechanical properties and fracture toughness of this material.
The results of the present investigation indicate that for this low manganese austempered ductile iron (ADI), upper ausferritic
microstructures exhibit higher fracture toughness than lower ausferritic microstructures. Yield and tensile strength of the
material was found to increase with an increase in austempering time in a lower bainitic temperature range, whereas in the
upper bainitic temperature range, time has no significant effect on the mechanical properties. A retained austenite content
between 30 to 35% was found to provide optimum fracture toughness. Fracture toughness was found to increase with the parameter
(XγCγ/d)1/2, where Xγ is the volume fraction of austenite, Cγ is the carbon content of the austenite, and d is the mean free path of dislocation motion in ferrite. 相似文献
5.
The dynamic fracture toughness of TA15ELI alloy with two types of microstructures was studied by instrumented impact test.Charpy specimens with both the 0.2 mm U-notch and the a/W = 0.2 pre-crack were adopted to compare notch sensitivity in the two microstructures.The result shows that the specimen with Widmanst?tten microstructure exhibits a better dynamic fracture toughness and lower notch sensitivity than that with lath-like microstructure.Fracture surfaces in the case of the two microstructures are analyzed to have a ductile and brittle mixed feature under dynamic loading.The fracture surface of lath-like microstructure is composed of dimples and tear ridges,while that of Widmanst?tten microstructure is covered with rough block-like facets and dimples and tear ridges.The α phase boundaries and α/β interfaces act as locations for void nucleation and crack arrest and deviation.The decrease in width of α phase lamellae leads to the increase in the amount of boundaries and interfaces,which causes the increase in the consumption of impact energy and results in the improvement in dynamic fracture toughness. 相似文献
6.
The use of an atomizer for accelerated cooling is discussed. An atomizer is an effective tool for controlling the microstructure
and properties of a microalloyed steel because of its flexibility of operation and control of cooling rate over a broad range
of temperatures. Some basic issues regarding heat transfer in pool boiling and in spray cooling also are presented. Reheating
response studies were conducted in addition to studies of the effect of accelerated cooling on the microstructure and properties
of a low- carbon steel microalloyed with niobium and vanadium. This steel produces a tempered martensitic microstructure on
quenching and a predominantly bainitic microstructure at slower cooling rates. The yield, tensile, and fracture strengths
can be tailored by controlling the cooling rate, which in turn can be controlled by the air/water ratio and flow rates in
the atomizer. Impact toughness is a function of cooling rate and reaches a maximum followed by a decrease,probably due to the formation of upper bainite at lower cooling rates. Fractographic studies indicated that tensile fracture
occurred by microvoid coalescence, with the dimple size decreasing as the cooling rate decreased. Charpy impact fracture studies
indicated that the primary mode of failure was by quasi- cleavage, with the number of secondary cracks also decreasing as
the cooling rate decreased. 相似文献
7.
低温回火态新型贝氏体钢的组织性能 总被引:2,自引:0,他引:2
研究了回火工艺对新型低合金贝氏体钢组织和性能的影响,了解了该材料的回火特性.结果表明:正火和低于400℃回火后的组织由贝氏体、铁素体和残余奥氏体组成,具有较好的力学性能、回火抗性、良好的焊接性和机械加工性;在高于500℃回火后出现回火脆性,由新型贝氏体组织转变为典型贝氏体组织,其原因与回火过程中残余奥氏体和贝氏体铁素体的分解、碳化物析出有关.通过研究回火后的组织转变、残余奥氏体热稳定性、机械稳定性的变化,探讨了无碳贝氏体韧化及脆化机理,提出了适于该钢的最佳回火工艺. 相似文献
8.
研究了不同热处理工艺下无碳化物贝氏体无缝钢管的显微组织和力学性能。结果表明,热轧态无碳化物贝氏体无缝钢管的组织粗大,强度较高,韧性很低。热轧+低温回火后韧性的提高幅度不大,仍然较低。热轧+正火+低温回火可以改善无碳化物贝氏体无缝钢管的韧性,但仍存在部分粗大的组织。热轧后先长时间高温回火(690 ℃×300 min),再正火和低温回火可以细化无碳化物贝氏体无缝钢管的组织,消除组织遗传性,大幅度提高韧性,冲击断裂特征由脆性断裂转变为韧性断裂。 相似文献
9.
A modified tempering treatment has been designed in order to avoid the direct transformation of retained austenite (Ar) during tempering of a low-alloy Cr-Mo-V steel. Instead of the direct transformation of Ar into ferrite and M23C6 carbides during conventional tempering at 700 °C, transformation into aggregate of ferrite and cementite has been forced by a pre-tempering at 455 °C before conventional tempering. Experiments have been performed on specimens quenched with cooling rates 1.5, 3 and 12 °C/s, providing different types of Ar within the as-quenched microstructures. The results show that the tempering modification does not improve the Charpy impact toughness at the highest quenching rate of 12 °C/s, where the specimens cannot incur cleavage cracking induced from fine and discontinuous M23C6 carbides along lath interfaces. For the lowest quenching rate 1.5 °C/s, the Charpy impact toughness can be improved, and the failure is dominated by carbide aggregates, which originate from the decomposed products of blocky Ar. This is because the tempering modification effectively suppresses the formation of coarse M23C6 carbides at interfaces between the carbide aggregate and bainitic matrix, thereby resulting in a relatively homogeneous distribution of M23C6 carbides inside carbide aggregates. Therefore, the tempering modification is recommended for large-scale forgings, in which relatively high quenching rates are difficult to achieve. 相似文献
10.
11.
A. M. Nasreldin M. M. Ghoneim F. H. Hammad R. L. Klueh R. K. Nanstad 《Journal of Materials Engineering and Performance》1993,2(3):413-419
The effect of tempering on impact and fracture toughness properties of a Cr-Mo bainitic steel was studied in the quenched
and stress relieved (Q & SR) condition. The lowest tempering parameter used resulted in considerable improvement in impact
properties. Further tempering increased the upper shelf energy, had a minor effect on the transition temperature, and increased
both the initiation fracture toughness (JIC) and the tearing modulus(T). However, the effect on JIC andT was much greater than the effect on the impact upper shelf energy. The results were discussed in light of the changes in
microstructure and flow properties due to tempering. 相似文献
12.
对高强度船体结构钢DH36钢板进行了摩擦柱塞焊工艺试验研究,对焊接接头微观组织、显微硬度、抗拉强度及连接界面处冲击吸收功进行了观察与测试,对连接界面处拉伸断口进行了扫描电镜观察.结果表明,采用优化摩擦柱塞焊工艺可成功实现DH36高强度钢和柱塞的冶金连接,焊缝区出现明显的硬化倾向,其显微硬度最高可达333 MPa;焊接接头抗拉强度高于母材,连接界面处拉伸断口具有微小等轴韧窝和解理断裂的混合特征,但接头连接界面处冲击吸收功为37 J±5 J,明显低于母材205 J.这是由于焊接热循环过程中在母材与柱塞连接界面附近产生了大量贝氏体及魏氏体铁素体组织导致的韧性降低造成的. 相似文献
13.
0 IntroductionWiththedevelopingofpetroleumandnaturalgasindustry,thenewoilfieldsandnaturalgasfieldswerecontinuouslyfoundandopenedup.Oilandanturalgasweretransportedtoaharbor,largechemicalplants,orthecitybylongpetroleumpipelines.Thediameteroftheoilpipesbec… 相似文献
14.
为了研究大厚度高强海工用钢板S355G10+N焊接接头的韧性和微观性能,按照BS7448和EN 10225的要求进行了CTOD试验和夏比冲击试验并在扫描电镜(SEM)下进行了微观性能分析.结果表明:(1)所有试样试验结果均符合规范要求;(2)夏比冲击能在焊缝位置(WP)和熔合线位置(FL)的分布规律与CTOD值相同,即正相关;在熔合线向母材+2mm (FL+2)位置二者则有相反的分布,这与已有的研究不同;(3)试样S3554焊缝中出现的珠光体和上贝氏体可能是韧性相对较低的原因;(4)对比S35510微观断口中出现的空洞和准解理,可以推断S3552中出现的韧窝和表现为滑移分离的涟波形貌具有更好的韧性表现;这与试验中CTOD值的分布规律相吻合. 相似文献
15.
Tsunehisa Handa Koutarou Inose Susumu Tskamoto Fumiyoshi Minami Mitsuru Ohata Yukito Hagihara 《Welding International》2013,27(8):565-571
Fracture toughness and microstructure of laser weld metal of 780 MPa class steels are investigated and compared with those of SM490A and SM570Q. In SM490A and SM570Q, Charpy energy transition temperature of laser weld metals is 60–90°C higher than that of base metal, and upper bainite microstructures are observed in the laser weld metals. In 780 MPa class steels, difference of Charpy energy transition temperatures between laser weld metal and base metal are only 10–30°C, and no upper bainite microstructures are observed in the laser weld metals. Hardness of the laser weld metals of 780 MPa class steels is identical to that of martensite microstructure. A superior toughness of the laser weld metal of 780 MPa class steels would be owing to the martensite microstructure resulted from a high carbon equivalent. 相似文献
17.
采用Gleeble1500热模拟试验机,研究不同热输入对Q890高强钢焊接热影响区粗晶区的微观组织和韧性影响规律. 结果表明,随着热输入的增加,粗晶区的微观组织表现出从马氏体组织向马氏体、贝氏体的混合组织,再向贝氏体、粒状贝氏体的混合组织的转变. 当热输入为19.7 kJ/cm时,冲击吸收功最高为83 J,主要原因是由于先相贝氏体分割后相马氏体,大角度晶界密度最大,改善了冲击韧性. 当热输入较高时,粗晶区脆化的原因是由于M-A组元呈链状分布,造成局部应力集中,成为裂纹起裂和扩展的主要通道. 相似文献
18.
研究了17Cr2Ni2Mo钢粒状组织和粒状贝氏体经低温和高温回火后的断裂特性。结果表明;粒状组织和粒状贝氏体经低温回火后,由于M-A岛的分布,尺寸及应变诱发相变的影响而具有良好的强韧性,特别是其断裂韧性J1c值较板条马氏体几乎高了一倍;而经高温回火后,由于M-A岛分解出来的碳化物的偏聚,呈现出准解理特征,其断裂韧性远低于回火索氏体。 相似文献
19.
以大口径(OD1422 mm)、大壁厚(38.5 mm)X80级管线钢热轧板为研究对象,采用光学显微镜和扫描电镜对其显微组织和-20 ℃低温落锤撕裂试验断口形貌进行分析,研究了断裂与组织之间的关系。结果表明,带状组织和不同厚度位置晶粒度大小不均,粒状贝氏体、退化珠光体、准多边形铁素体和马奥岛等混合组织会导致裂纹的萌生和扩展,出现解理断裂,对低温韧性不利,而尺寸为3 μm以下的马奥组织和均匀分布的贝氏体铁素体对裂纹扩展起阻碍作用,说明细小的马奥组织和贝氏体铁素体能够提高钢板的断裂韧性,对低温断裂控制十分有利。 相似文献