镀锌螺栓的断裂分析

镀锌螺栓在组装后放置1～2d于根部或头部发生大量断裂,采用化学成分分析、金相检验、硬度检测及断口分析等方法对螺栓的断裂性质及断裂原因进行了分析。结果表明：螺栓断裂为典型的氢脆断裂;主要原因是螺栓在后期酸洗和电镀过程中除氢不彻底,吸入了大量的氢;次要原因是热处理工艺控制不当,使螺栓心度硬度偏高,增加了其对氢脆的敏感性;两者共同作用最终导致螺栓发生氢脆断裂。     

Intergranular brittle cracking of truck diesel fuel filter-cases

Several truck diesel fuel filter-cases split successively only after 500 km–1300 km of running mileage on highway. All the cracked filter-cases are made from the hot-dip galvanized cold-working extra low carbon steel plate using deep-drawing shaping process. Visual inspection indicates that longitudinal cracking occurred on the filter-cases and crack initial locations are all situated at the contact points of inner surface of the filter-case with the three convexes of the cover on the filter-core. Fractographic analysis indicates that intergranular fracture is much more dominant. The fracture surfaces of the tensile specimens taken from the steel plate of the cracked filter-cases reveal ductile fracture with dimples formation. Fracture mechanism considerable difference between the tensile specimens and the failed filter-cases suggests that intergranular brittle cracking of the filter-cases depends heavily on the state of applied stress. Occurrence of the great contact compressive load between the inner surface of the filter-case and the convexes of the cover on the filter-core makes the circumferential tensile stress on the outer surface of filter-case at the contact locations increase intensely, which lower the threshold value of hydrogen embrittlement (HE). Hydrogen atoms were introduced into the steel plate mostly probably during acid pickling operating before hot-dip galvanizing or fluxing operating in hot-dip galvanizing. The cold working microstructure greatly enhances the hydrogen diffusion capacity and a large number of defects produced in cold-worked steel may increase the density of hydrogen traps.     

Hydrogen and temper embrittlement interactions in fatigue of 2·25Cr–1Mo steel

Abstract

The influence of strength, precipitate microstructure, temper embrittlement, and environment on fatigue crack growth in 2·25Cr–1 Mo steel has been investigated. Particular attention was paid to the interaction between hydrogen embrittlement and temper embrittlement in fatigue. A range of tempered and aged conditions was examined in air, vacuum, and gaseous hydrogen environments at growth rates between 10^?10 and 10^?5 m/cycle. In this paper, discussion focuses on effects observed in hydrogen. Gaseous hydrogen was found to encourage crack growth by promoting intergranular fracture, which peaked at intermediate growth rates, and by reducing the general plasticity associated with transgranular fracture at high growth rates. Mechanisms underlying these effects, which involve stress-driven hydrogen segregation and the facilitation of crack-tip dislocation emission, are considered in detail. Reversible temper embrittlement encouraged crack growth at near-threshold and intermediate rates in hydrogen by increasing susceptibility to intergranular fracture. The magnitude of this effect was directly related to the degree of intergranular phosphorus enrichment, thus clearly demonstrating synergy between hydrogen embrittlement and temper embrittlement in fatigue. In contrast, one-step temper embrittlement encouraged transgranular crack growth in hydrogen only at high growth rates. This is considered to result from a concentration of slip on glide planes intersecting the crack tip under the combined influences of hydrogen and an increasingly dense precipitate microstructure.

MST/583     

杂质元素磷对中碳硅—锰钢回火马氏体脆性的影响

本文就杂质元素磷对中碳硅—锰钢回火马氏体脆性(TME)的影响作了研究,试验结果表明:钢中TME的存在并不决定于磷含量的多少,因为低磷钢或高磷钢中均可观察到TME现象。磷对TME的影响主要体现在两个方面:一是提高钢中TME显现的冲击试验温度;二是使TME表现的断裂方式由穿晶脆断向沿晶脆断转化。     

Hydrogen effects in a dual-phase microalloy steel

A dual-phase steel containing niobium, vanadium and titanium as microalloying elements was tested for hydrogen embrittlement (HE). The susceptibility to HE was observed to be closely related to the microstructural state. Hydrogenated specimens intercritically annealed at relatively low temperatures to develop martensite islands in a ferrite matrix basically exhibited quasi-cleavage fracture with some ductile dimpling. The mode of fracture in charged specimens quenched from higher intercritical annealing temperatures was predominantly intergranular fracture along prior austenite grain boundaries and cracking of martensite laths. The detrimental role of residual stresses, retained austenite and microalloying carbides in the process of HE is discussed.     

Hydrogen embrittlement susceptibility of microstructures formed in multipass weld metal for HT780 class steel

The effect of reheating by following passes on the hydrogen embrittlement of MAG weld metal for HT780 class steels has been investigated by using specimens subjected to simulated thermal cycles. The hydrogen-charged specimens exhibited transgranular quasi-cleavage fracture and intergranular fracture along prior austenite grain boundaries on slow strain rate tensile (SSRT) tests, depending on the reheated temperature and charged hydrogen content. The reduction in elongation of hydrogen-charged specimens became more significant when intergranular fracture occurred. When specimens in as-welded state and precedently reheated at coarse grained HAZ temperature of 1,623 K were reheated at a tempering temperature of 873 K, significant amount of intergranular fracture occurred at charged hydrogen contents above 3 ppm in spite of the decrease in hardness. The specimen reheated at 1,173 K showed no intergranular fracture even after receiving the reheating at 873 K at a hydrogen content of 6 ppm, suggesting the strong influence of the prior austenite grain size on the hydrogen-induced intergranular embrittlement. The measurement of hydrogen content desorbed from the hydrogen-charged specimen at room temperature suggested that the intergranular fracture caused by the reheating at 873 K was associated with an increase in susceptibility to hydrogen embrittlement of the prior austenite grain boundary itself rather than a decrease in the amounts of trapping sites such as dislocation and retained austenite.     

Q&P980镀锌高强钢电阻点焊工艺及液态金属脆化裂纹分布EI北大核心

通过设计电阻点焊工艺的正交实验,确定了Q&P980镀锌高强钢的点焊工艺参数范围,并对其焊接接头进行显微组织表征和力学性能分析。结果表明:熔核区组织以交错分布的板条马氏体为主;热影响区组织由板条马氏体、残余奥氏体和铁素体组成,马氏体板条平均宽度在不完全淬火区最大为4.86μm。显微硬度测试发现,焊接接头硬度值呈“W”形对称分布,硬度峰值出现在细晶区,达到559HV,硬度最低值出现在不完全淬火区,为338HV,呈现明显的软化现象。对焊接接头进行室温拉伸,最大拉剪载荷的峰值为27.92 kN,其断口形貌呈现典型的韧窝状,属于韧性断裂。由于Zn的熔点较钢基体低,镀锌高强钢点焊时易发生Zn层优先熔化并沿晶界向基体渗透,在焊接接头处可观察到明显的液态金属脆化裂纹。     

热处理对特种设备用高强钢激光–电弧复合焊接头氢脆断裂行为的影响研究

目的 提高800 MPa级特种设备用低碳贝氏体高强钢激光–电弧复合焊接头的抗氢脆性能。方法 采用预充氢后慢应变速率拉伸试样的方法,定量评估焊态、焊后直接高温回火和焊后调质3种状态下800MPa级低碳贝氏体高强钢激光–电弧复合焊接头的氢脆敏感性,结合扫描电镜下的初始微观组织和断裂特征,讨论抗氢脆性能的改善机理。结果 焊后调质处理有效消除了焊接热循环形成的马氏体组织,使接头各区域的微观组织趋于一致,接头的抗氢脆性能较焊态和直接焊后高温回火态的显著提高,断裂特征也从沿晶和穿晶的混合断裂转变为穿晶解理断裂。结论 焊后调质处理可以有效提高800MPa级低碳贝氏体高强钢激光–电弧复合焊接头的抗氢脆性能。     

Hydrogen embrittlement of maraging steel

Specimens of 18 Ni 1800 MPa (M250) grade maraging steel were charged with different quantities of hydrogen by an electrochemical method. The tensile properties and fracture characteristics have been correlated with the quantity of hydrogen picked up by the material. A drastic decrease in ultimate tensile strength from 1768 M Pa to 750 M Pa, elongation from 6% to less than 2%, and reduction in area from 55% to less than 5%, were observed as the hydrogen content of the steel increased from less than 2 p.p.m. to 7 p.p.m. However, hydrogen does not affect the hardness of the steel. The effect of baking at different temperatures on hydrogen embrittlement was also studied. A change in fractographic features from ductile dimples to mixed mode, intergranular separation and transgranular cleavage was observed as the amount of absorbed hydrogen increased.     

Brittle intergranular fracture of a thread: The role of a carburizing treatment

Carburised mechanical components that have to sustain contact compressive loads or fatigue loads with limited tensile stresses, usually do not display brittle fracture in service. However, when high tensile stresses combined with high stress concentrations and a martensitic microstructure is present, such a damage mechanism may play an important role. In these cases, a careful control and optimization of the production processes is required. In the present investigation, the role of a carburizing treatment on the intergranular fracture behaviour of a pinion thread has been investigated. A simplified evaluation of the maximum tensile stress at the thread root after tightening is presented, and specific three-point bending and instrumented impact tests on Charpy-U carburised specimens were carried out, in order to highlight the role of hydrogen embrittlement and to provide guidelines for the optimization of the production process.     

Effect of Hydrogen Charging on the Tensile and Constant Load Properties of an Austenitic Stainless Steel Weldment

The effect of cathodic hydrogen charging on the tensile and constant load properties was determined for an austenitic stainless steel weldment comprising a 304L steel in the solution treated condition as a base metal and a 308L filler steel as a weld metal. Part of the 304L solution treatedsteel was separately given additional sensitization treatment to simulate the microstructure that would develop in the heat affected zone. Tests were performed at room temperature on notched round bar specimens. Hydrogen charging resulted in a pronounced embrittlement of the tested     

Hydrogen and temper embrittlement in 9Cr–1Mo steel

Abstract

The synergism between hydrogen embrittlement and temper embrittlement has been investigated in a 9Cr–1Mo martensitic steel. Measurements of tensile ductility were used to monitor the development of embrittlement with increasing hydrogen content in material as tempered and aged for up to 5000 h at 500 or 550°C. A detailed examination was made of associated changes in fracture mechanism, precipitate microstructure, and interfacial and precipitate chemistry. A strong interaction between hydrogen and temper embrittlement was observed. Both types of embrittlement in isolation reduced tensile ductility by promoting a ductile interlath fracture mechanism: ‘chisel fracture’. Hydrogen and temper embrittlement acted synergistically to reduce ductility further by the promotion of brittle intergranular fracture and transgranular cleavage. The dominant factor controlling the interaction was the precipitation of a brittle intermetallic Laves phase containing phosphorus in solution. Phosphorus segregated to interfaces was considered to make an important, but secondary, contribution to the embrittlement observed.

MST/791     

Q960E超高强钢焊接接头组织和性能研究

目的 对Q960E超高强钢的焊接工艺进行研究以获得高强高韧的焊接接头。方法 选择超高强钢Q960E作为母材、FK1000ER120S–G焊丝作为填充材料进行MAG焊,采用改变焊接电流的方式来研究焊接热输入对焊接接头组织和性能的影响。结果 当焊接电流为155～230 A时,均获得了全焊透无明显缺陷的焊缝。随着焊接热输入的增大,焊接接头中各亚区宽度增大,其中焊缝区变化最为显著,在最小热输入条件下焊缝宽度为3.98 mm,在最大热输入条件下焊缝宽度增至5.53 mm。对焊接接头进行组织分析发现,焊缝组织主要为针状铁素体和板条马氏体;完全相变区组织主要为板条马氏体;未完全相变区组织主要为回火马氏体和部分重结晶形成的马氏体。硬度测试表明,在热影响区的回火区发生了软化现象,最低硬度仅为290HV;在完全相变区发生了硬化现象,硬度最大值可达500HV。在不同热输入条件下,焊接接头各亚区硬度变化趋势一致,焊接接头抗拉强度为995～1 076 MPa,拉伸试验均断裂在热影响区,断后伸长率为9.33%～10.21%,断裂时存在颈缩现象,为韧性断裂。随着热输入的增加,粗晶区马氏体板条束宽度增大,未完全相变区...     

Atom probe tomographic observation of hydrogen trapping at carbides/ferrite interfaces for a high strength steel

A three-dimensional atom probe (3DAP) technique has been used to characterize the hydrogen distribution on carbides for a high strength AISI 4140 steel. Direct evidence of H atoms trapped at the carbide/ferrite interfaces has been revealed by 3DAP mapping. Hydrogen is mainly trapped on carbide/ferrite interfaces along the grain boundaries. Slow strain rate tensile (SSRT) testing shows that the AISI 4140 steel is highly sensitive to hydrogen embrittlement. The corresponding fractographic morphologies of hydrogen charged specimen exhibit brittle fracture feature. Combined with these results, it is proposed that the hydrogen trapping sites present in the grain boundaries are responsible for the hydrogen-induced intergranular fracture of AISI 4140. The direct observation of hydrogen distribution contributes to a better understanding of the mechanism of hydrogen embrittlement.     

有序度对Ni3Fe合金环境氢脆的影响

研究了室温下不同有序度的Ni3Fe在真空和氢气气氛中的力学性能及断口形貌特征．结果表明：具有不同有序度的Ni3Fe在真空中拉伸时，均不发生环境氢脆；但在氢气中氢对其有强烈的脆化作用，且其敏感性随着有序度的增加而加剧．扫描电镜观察表明：在真空中或H2中拉伸时，无序Ni3Fe的断口都为韧性穿晶断口，而在氢气中拉伸时，1000h有序化Ni3Fe为100％沿晶脆性断口，但是有序化60h和200h的Ni3Fe的断口为穿晶和沿晶混合断口．     

Failure analysis of induction hardened injector body

The failure analysis of induction hardened injector body was carried out to identify surface defects. Producer revealed the defects using nondestructive testing method and requested a detailed analysis to determine the cause of their origin. Metallographic and fracture analysis were performed to study the material microstructure and fracture surface. Metallographic analysis proved the existence of a crack, initiated from the front face of component. Microstructure of the crack vicinity as well as hardness was significantly different with increasing distance from the face of component. Microstructure near the front face consisted of coarse martensite, while finer martensitic structure was observed with increasing distance from the front face. Hardness showed decreasing tendency with increasing distance from the front face. Fractographic analysis revealed the intergranular cleavage fracture near the front face of component. With increasing distance from the front face, quasicleavage fracture was observed with increasing areal fraction characterized by ductile fracture. Due to significant difference in microstructure and corresponding difference in hardness within a small area of component can be assumed, that the crack initiation occurred due to internal stress of the material caused by heat treatment. It is necessary to optimize the parameters of induction hardening process with respect to the different thicknesses of the product.     

爆轰处理对20CrMo 钢氢脆敏感性的影响

本文研究了爆轰处理对不同组织和强度水平的20CrMo 钢氢脆敏感性的影响。结果发现爆轰处理加高温时效可显著降低钢的氢脆敏感性。对屈服强度分别为830MPa 和620MPa 的均相珠光体组织、爆轰处理对其氢脆敏感性没有或略有影响。爆轰处理显著增加了屈服强度为680MPa,组织为铁素体加珠光体材料的氢脆敏感性系数,同时显著降低它对不可逆氢脆的敏感性系数。     

Influence of precipitation and segregation on hydrogen embrittlement in aged 9Cr–1Mo steel

Abstract

A study is reported of temper embrittlement and hydrogen embrittlement in a series of model 9Cr–1Mo steel alloys in which the levels of silicon and phosphorus have been varied to separate the formation of the brittle intermetallic (Laves) phase from the segregation of phosphorus during aging. Phosphorus segregation was mildly detrimental to ductility properties, Laves phase formation was more detrimental, and their effects combined produced the most severe loss in ductility. Hydrogen effects were additive to those of aging. In unaged material without silicon enrichment, only M₂₃C₆ precipitates were detected, with little phosphorus segregation. With silicon enrichment, phosphorus segregation to lath and grain boundaries was enhanced. This enhancement increased the susceptibility of the materials to hydrogen embrittlement, promoting transgranular cleavage and chisel fracture. In aged material, the high phosphorus alloys showed some grain boundary segregation, but only limited interaction with hydrogen. In the high silicon alloys, the formation of Laves phase was most evident. This enhanced hydrogen embrittlement resulted in extensive chisel, transgranular cleavage, and some intergranular fracture. In the high silicon high phosphorus alloy, both Laves phase formation and phosphorus segregation were evident. This resulted in enhanced susceptibility to hydrogen embrittlement, producing intergranular fracture. Thus, silicon controls the susceptibility to hydrogen embrittlement in unaged alloy by promoting phosphorus segregation and in aged alloy by promoting Laves phase formation. In the aged alloy, segregation of phosphorus can enhance the effect of silicon.

MST/1785     

Caustic stress corrosion cracking of a spheroidal graphite cast iron: characterisation of ex-service component

Abstract

This paper discusses observations of features suggesting grain boundary embrittlement ahead of stress corrosion crack tips in ex-service cast iron components exposed to strong caustic environments during Bayers process for alumina processing. The cracks and the neighbouring areas in the ex-service specimens were examined using conventional metallography, SEM, the extraction replica technique in the TEM and Auger electron spectroscopy. In all cases, the cracking was initiated at the surface of the steel exposed to the corrosive environment and it appeared that crack nucleation may have been aided by local stress concentrations and/or zones of local residual stress concentration. The fracture mode was almost exclusively intergranular and the crack path followed ferrite grain boundaries. There was clear evidence of a local zone of grain boundary embrittlement extending ahead of the tip of the major cracks examined. The phenomenon was established by investigating the fresh fracture surfaces produced by extending pre-existing cracks under impact loading at liquid nitrogen temperature. Auger electron spectroscopy of the fresh intergranular fracture surface failed to reveal any evidence of local elemental grain boundary segregation that might account for the observed embrittlement. In the absence of evidence of any other embrittling species on the exposed intergranular facets, there arises the possibility of hydrogen being involved in the embrittlement. The paper discusses hydrogen assisted intergranular cracking, as observed in the case of similar materials, to be the possible mechanism.     

65Mn钢弹簧垫圈开裂原因分析

通过宏观检验、化学成分分析、硬度测试、金相检验和断口分析等方法对65Mn钢弹簧垫圈的开裂原因进行了分析。结果表明:该垫圈氢含量较高,服役时大部分区域处于悬空状态,造成垫圈变形不均匀,形成应力集中。另外,垫圈凸面的防滑压花以及压花边缘的轮廓线处也存在应力集中,氢原子容易在此聚集,最终导致垫圈发生了氢致延迟脆性开裂。