45钢吊环断裂失效分析

采用火花直读光谱仪、布氏硬度计、扫描电镜和光学显微镜等对断裂45钢垃圾箱吊环的化学成分、硬度、断口形貌和显微组织进行了分析。结果表明:吊环断裂为脆性断裂;吊环的显微组织显示材料呈过热状态,析出片状铁素体和粗大晶粒,导致材料的冲击韧度下降,是吊环脆性断裂失效的主要原因。     

Ni合金化球墨铸铁组织和性能研究

为获得兼具较高强度和良好低温冲击韧性的球墨铸铁铸件,向球墨铸铁中加入质量分数约0.5%的Ni进行合金化,并对其进行中温奥氏体化(880℃+3 h)和低温退火(720℃+4 h)处理.采用光学显微镜(OM)、扫描电子显微镜(SEM)对铸态和热处理态试样的显微组织和冲击断口形貌进行分析;利用万能试验机、布氏硬度计和摆锤式冲击试验机等对铸态和热处理态试样进行了室温拉伸、硬度检测、低温冲击等力学性能测试.结果表明:铸态球墨铸铁的微观组织由珠光体、铁素体和球状石墨及少量的渗碳体组成,其强度、硬度偏高,塑性、韧性较差;热处理态试样中的珠光体向铁素体转变后为铁素体和球状石墨,试样强度、硬度有所降低,塑性、韧性得到明显的改善;铸态试样呈现典型的脆性断裂特征,热处理态试样冲击断口处存在少量韧窝,断裂模式以解理断裂为主,伴有少量塑性变形的韧脆混合断裂,且在-40℃冲击功达到12.4 J;比较铸态与热处理态的冲击断口形貌可知,试样断裂方式由脆性断裂转变为韧脆混合断裂.     

示波冲击试验评价正火12Cr1MoV钢回火脆化敏感性

采用示波冲击试验及断口形貌分析技术，研究了正火１２Ｃｒ１ＭｏＶ钢回火试样的夏比冲击断裂过程及能量消耗，提出了采用裂纹扩展功与萌生功之比做为衡量回火脆化敏感性及一般材料韧脆断裂状态的性能指标，该指标与冲击断口形貌特征有较好的对应关系。文中还对正火１２Ｃｒ１ＭｏＶ钢的回火脆化敏感性进行了评价。     

HFW钢管焊缝韧性失效分析

对钢级为X52的HFW焊管的焊缝进行连续的0℃夏比冲击试验，其中个别的冲击试样冲击功明显低于正常试样的平均值。对冲击功异常的冲击试样断口借助扫描电镜和能谱仪等设备进行观察分析。发现冲击功异常的冲击断口为解理断裂形貌，解理面成明显的带状特征，而且解理面存在突起物。汇总为钢级为x52的HFW烨管的夏比冲击功异常主要与原材料的组织形貌和焊接工艺有关。     

显微组织对X80钢氢致裂纹敏感性和氢捕获效率的影响

对以针状铁素体为主的X80管线钢进行不同工艺的热处理,分别得到具有多边形铁素体组织或板条马氏体组织的试样。研究了显微组织对不同试样在饱和H_2S环境中的氢致裂纹(HIC)敏感性和氢渗透行为的影响。结果表明:具有不同显微组织的X80钢其HIC敏感性从大到小的排序为:1水淬处理的板条马氏体组织试样,2空冷处理的多边形铁素体组织试样,3原始针状铁素体组织试样;氢在材料中的捕获效率是影响材料HIC敏感性的主要因素之一,渗氢通量J_∞、氢扩散系数D_(eff)越低,氢捕获效率越高,管线钢的氢致裂纹敏感性越高。     

表面渗锌双头螺栓断裂原因分析

部分表面渗锌双头螺栓在安装过程中断裂。通过对断裂螺栓、同批螺栓及调质处理后待加工的同批棒料进行理化检验，发现断裂螺栓所用材料为45Cr钢，而非规定的40Cr钢；材料中硅酸盐夹杂多且呈块状集中分布；在螺栓纵、横面有多处显微缩孔，显微组织出现半网状铁素体和针状铁素体，同时材料强度和硬度值偏高，而塑性和韧性值偏低；断裂螺栓断口及高倍金相检查均发现有明显腐蚀产物及腐蚀特征。分析认为，腐蚀造成组织问结合力降低是螺栓断裂的主要原因，调质处理工艺不当，材料冶金缺陷是造成螺栓断裂的次要原因。提出了相应的改进及预防建议。     

25Mn钢冲击性能的研究

为研究25Mn钢不同状态的冲击性能的差异,采用示波冲击试验、硬度测定、显微组织观察和冲击断口的SEM形貌分析等方法,分别对轧制态、正火和淬火＋回火的试样进行了测定。结果表明,用示波冲击试验能得到不同变形和断裂阶段载荷、变形及能量消耗的变化。如淬火＋回火态的变形抗力和变形能力都较高,但其总冲击功仅比正火态平均高6J,可却使其材料的裂纹扩展功平均提高16．78J。分析冲击试样的裂纹形成功和裂纹扩展功,以及断口形貌可以判断材料的韧脆性。     

针状铁素体钢的组织类型及对性能的影响

透射电镜下针状铁素体组织典型形貌为非常细微的亚结构、高密度的位错,应用透射电镜(TEM)原位拉伸、扫描电镜(SEM)原位拉伸,对F40船体结构钢的塑性变形与裂纹扩展的动态过程进行了动态观察,同时对F40钢低温下冲击断口形貌进行了详细的研究,结果表明,针状铁素体组织具有良好的抗塑性变形及阻止裂纹扩展的性能。     

夹杂物和晶粒尺寸对洁净车轮钢室温冲击韧度的影响

对洁净车轮钢在不同温度下进行正火处理,得到不同晶粒尺寸的显微组织,然后对车轮钢进行室温冲击试验,利用扫描电镜对冲击试样断口形貌进行观察,研究了夹杂物和晶粒尺寸对洁净车轮钢室温冲击韧度的影响。结果表明：部分车轮钢冲击试样以夹杂物起裂,夹杂物类型为Ti（C,N）,另一部分冲击试样断口起裂源处则未发现有夹杂物,但尺寸在10μm以下的Ti（C,N）夹杂物对车轮钢的冲击韧度没有明显的影响,而晶粒尺寸对车轮钢的冲击韧度有明显影响;其主要原因是室温下车轮钢冲击断裂的临界事件是微裂纹穿过晶界扩展引发解理断裂,因此晶粒尺寸是决定洁净车轮钢冲击韧度的主要因素。     

压力对挤压铸造E级钢低温冲击韧性的影响

本工作采用挤压铸造工艺制备了不同压力下的E级钢调质态试样,并进行了低温夏比冲击试验和布氏硬度检测,研究了挤压压力对E级钢低温冲击韧性的影响规律,并用光学显微镜(OM)和扫描电镜(SEM)对显微组织和冲击断口进行了观察。研究结果表明,当挤压压力在0～150 MPa范围内,E级钢的40℃低温冲击韧性先增大后减小。在挤压压力为38 MPa时,E级钢低温冲击韧性最佳,比金属型重力铸造E级钢提高65. 4%,硬度仅降低了6. 17%。进一步提高压力,冲击吸收功呈线性下降,硬度小幅上升。显微组织分析表明,随着挤压压力的提高,E级钢晶粒明显细化,铁素体含量增多,有利于E级钢冲击韧性的提高。另一方面,由于过冷度的提高,E级钢在压力为60 MPa时析出了魏氏组织,导致低温冲击韧性显著下降。断口分析表明,金属型重力铸造E级钢低温冲击断口为准解理形貌,而采用38 MPa挤压铸造的E级钢即使在40℃低温下,断口仍存在大量细密的韧窝,属于韧性断裂。     

The role of Cu and Al addition on the microstructure and fracture characteristics in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels with superior toughness

The effects of Cu and Al addition on the microstructure and fracture in the coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels with superior toughness were studied and compared with the X70 pipeline base steel counterpart. The microstructure in base steel was dominated by a small fraction of acicular ferrite and predominantly bainite. However, acicular ferrite microstructure was obtained in Cu-bearing steel, which nucleated on complex oxide with outer layer of MnS and CuS because of Cu addition. The microstructure in Al-bearing steel consisted of bainite with ultrafine martensite–austenite constituent, which was refined by Al addition. CGHAZ in Cu-bearing and Al-bearing steels had superior impact toughness and ductile fracture, which were attributed to acicular ferrite and ultrafine martensite–austenite constituent, respectively.     

Characterization on strength and toughness of welded joint for Q550 steel

Q550 high strength steel was welded using gas shielded arc welding and three different welding wires without pre- or post-heat treatments. The paper investigates the influence of welding wire on the microstructure, tensile strength and impact toughness of Q550 steel weld joints. Results showed that the microstructure of the weld metal of joints produced using ER50-6 wire was a mixture of acicular ferrite and grain boundary ferrite including pro-eutectoid ferrite and ferrite side plate. Acicular ferrite was mainly obtained in the weld metal of the joints produced using MK·G60-1 wire. Pro-eutectoid ferrite was present along the boundary of prior austenite. Crack initiation occurred easily at pro-eutectoid ferrite when the joint was subjected to tensile. Tensile strength and impact toughness were promoted with increasing acicular ferrite. Tensile strength of the joint fabricated using MK·G60-1 wire was close to that of base metal. And tensile samples fractured at location of the fusion zone, which had lower toughness and thus became the weak region in the joint. Impact absorbing energy was the highest in the heat affected zone. Fibrous region in fracture surfaces of impact specimens was characterized as transgranular fracture with the mechanism of micro-void coalescence. Acicular ferrite microstructure region corresponded to relatively large dimples while boundary ferrite microstructure corresponded to small dimples.     

热输入对10CrNi3MoV钢MAG焊接头组织和性能的影响

为制定合理的焊接工艺,保证焊接质量,设置不同焊接热输入进行了10CrNi3MoV钢MAG焊接。采用微观组织分析、断口观察、力学测试等手段研究了焊接热输入对接头组织及性能的影响。结果表明,热输入较小时（E=11.0 kJ·cm^-1、E=14.4 kJ·cm^-1）,焊缝组织以针状铁素体为主,并含有部分粒状贝氏体、先共析铁素体等;热输入较大时（E=18.1 kJ·cm^-1）,针状铁素体占比降低,粒状贝氏体、先共析铁素体等增多,组织粗化。随热输入的增大,粗晶区晶粒粗化,组织由板条马氏体逐步转变为板条贝氏体,板条界限模糊,并有粒状贝氏体出现;焊缝金属强度降低,冲击韧性先略有升高后显著降低,断裂形式由微孔聚缩型韧断变为准解理/韧性混合断裂。热输入E=14.4 kJ·cm^-1时,焊缝组织以细密的针状铁素体为主,具有最佳强韧性匹配。     

Effects of Mn and Ti on microstructure and inclusions in weld metal of high strength low alloy steel

Abstract

The influences of alloying elements on chemical composition of non-metallic inclusions, impact toughness and microstructure in weld metals of high strength low alloy steels have been studied. Results indicated that microstructure had changed from a mixture of acicular ferrite, proeutectoid ferrite, ferrite side plates and microphases to a mixture of acicular ferrite, bainite and microphases due to the addition of Mn and Ti. The impact toughness of weld metal was improved correspondingly. The volume fraction and composition of inclusions both influenced the proportion of acicular ferrite. Mn and Si based oxide globular inclusions located at the boundary of acicular ferrite plates in the weld metal produced using C–Mn–Si–Cu wire. When Mn and Ti were added to welding wires, the inclusions within acicular ferrite plates permitted fewer primary acicular ferrite plates to grow into relatively larger dimensions. Secondary acicular ferrites nucleating on pre-existing ferrite plates refined microstructure effectively.     

Effect of Cu addition on microstructure and impact toughness in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels

The effects of Cu content on microstructure and impact toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels were investigated. It has been observed that the microstructure in the simulated CGHAZ of Cu-free steel is dominated by a small proportion of acicular ferrite and predominantly bainite with martensite–austenite constituent. Whereas, in the 0.45 and 1.01% Cu-containing steels, the acicular ferrite increased significantly due to the effective nucleation on intragranular inclusions with outer layer of MnS and CuS. The formation of acicular ferrite is attributed to superior high heat-affected zone impact toughness in the 0.45% Cu-containing steel. Furthermore, the increasing martensite–austenite constituent and ε-Cu precipitates in the simulated CGHAZ of 1.01% Cu-containing steel caused degradation in impact toughness.     

氮对钒微合金钢粗晶热影响区(CGHAZ)的组织和性能的影响

用热模拟方法研究了氮含量对钒微合金钢粗晶热影响区(CGHAZ)的组织和性能的影响。结果表明,氮含量为0.0031%或0.021%时,CGHAZ的韧性较差。氮含量0.0031%时CGHAZ中有少量的Ti(C,N),晶界铁素体(GBF)较少,晶内有大量尺寸较大的侧板条铁素体(FSP),解理裂纹沿FSP的直线扩展使其韧性较差。氮含量0.021%时在CGHAZ中生成了较为粗大的(Ti, V)(C, N)和GBF,解理裂纹沿GBF扩展使其韧性较差。氮含量为0.012%时低温韧性较好,在CGHAZ中生成了大量细小的(Ti, V)(C, N)粒子,且GBF尺寸相对较小,晶内有大量的针状铁素体(AF)。这些因素都有利于阻止裂纹扩展,使其低温韧性显著提高。     

Improvement of impact toughness of AWS E6010 weld metal by adding TiO2 nanoparticles to the electrode coating

The effect of TiO₂ nanoparticles in the electrode coating on the impact toughness of three weld metals prepared by the shielded metal arc welding process was investigated and the main factors affecting the impact toughness were discussed. The microstructure, mechanical properties and fracture surface morphology of the weld metals have been evaluated and the results are compared. When the content of TiO₂ nanoparticles in the composition of electrode coating is increased, the morphology of ferrite in the microstructure of columnar zone will change from Widmanstätten ferrite to acicular ferrite. This finally changes to allotriomorphic ferrite when the amount of TiO₂ nanoparticles in the electrode coating goes relatively high. Furthermore, the addition of TiO₂ nanoparticles is effective in refining the ferrite grain size of the reheated microstructures of weld metals. This effect is attributed to the increased number of nucleation sites on the oxide nanoparticles. The impact toughness of the weld metal was improved by adding TiO₂ nanoparticles, especially when a medium TiO₂ nanoparticle content was used in the electrode coating. A significant increase in the impact toughness of weld metal was shown to be due to the increased percentage of acicular ferrite and refinement of microstructure.     

Acicular ferrite microstructure in titanium bearing low carbon steels

Abstract

Different microstructures having acicular ferrite as the major phase but with various types and amounts of microphases were obtained by applying different cooling processes to C–Mn steels containing fine non-metallic inclusions. Optical and electron microscopy were carried out to identify the various microphases in the acicular ferrite microstructure, and their mechanical properties were measured and compared to study the effect of the microphases on the microstructure–properties relationship in C–Mn wrought steels. The existence and increase of the fraction of small isolated martensite between the acicular ferrite laths were found to play an important role in determining the tensile strength and low temperature impact toughness of the steels. However, the elongation and room temperature impact toughness were rather insensitive to the microphases. This may be attributed to the uniform distribution and isolation of relatively small martensite due to the fine interlocking character of the acicular ferrite microstructure.     

超细晶Q460高强钢焊接接头组织与韧性研究

采用手工焊条电弧焊和熔化极活性气体保护焊对超细晶Q460钢进行了焊接,分析表征了焊接接头的组织结构、显微硬度和冲击韧性的变化规律。研究结果表明,采用E5515焊条焊接,焊缝金属主要为先共析铁素体、多边形铁素体与少量珠光体。采用ER55-G焊丝,熔化极活性气体保护焊,焊缝金属主要由针状铁素体和少量多边形铁素体组成,焊丝中Ti元素的添加有利于获得针状铁素体组织。采用较小的焊接线能量,超细晶Q460钢热影响区粗晶区组织为粒状贝氏体组织。焊缝金属的显微硬度高于热影响区和母材的显微硬度,热影响区未出现软化现象。冲击试验表明,焊缝金属和热影响区均具有较高的冲击韧性,而且热影响区的韧性高于焊缝金属的韧性。     

Effect of cooling rate on microstructure,inclusions and mechanical properties of weld metal in simulated local dry underwater welding

Quenched and tempered E550 steel was joined using flux-cored arc welding. The effect of cooling rate on microstructure, inclusions and mechanical properties of the weld metal was investigated by optical microscope, scanning electron microscope, transmission electron microscope and mechanical testing. Results show that weld metal microstructures consist of proeutectoid ferrite, ferrite side plate and acicular ferrite. As the cooling rate increased, the volume fraction of proeutectoid ferrite and ferrite side plate decreased, acicular ferrite increased accompanied with refined grain. Furthermore, inclusions of Ti, Mn oxide with diameter below 2.0 μm were found in the weld metal and rapid cooling rate causes distinct Mn-depleted zone between inclusions and matrix. Excellent balance of high strength and toughness is obtained as more acicular ferrite in weld metal with rapid cooling rate. This can attribute to the increased of acicular ferrite with its refined grain and high density dislocation. These findings suggest that the rapid cooling rate can improve the impact toughness and tensile strength of weld metal in local dry underwater welding.