纳米贝氏体钢再纳米化焊接接头组织和性能

采用TIG焊方法对纳米贝氏体钢板进行表面堆焊并快速进行再纳米化处理,通过SEM和TEM观察了焊接接头不同区域的组织特征和形态,使用XRD和TEM电子衍射花样对各种相进行鉴定,并获得相应相的含量,采用拉伸试验和硬度测试获得了再纳米化焊接接头的力学性能.结果表明,经过再纳米化处理,纳米贝氏体钢焊缝区和淬火区组织转变为纳米级片层状的贝氏体和奥氏体,其中焊缝奥氏体含量为13%,而且淬火区片层厚度与母材相当约为70 nm,焊缝区片层厚度大于母材约为300 nm.力学性能测试结果表明,再纳米化焊接接头抗拉强度为1500 MPa,硬度为7000 MPa,与母材相差无几,其中接头断裂位置为回火区,是由于回火区析出大量碳化物导致的.     

纳米贝氏体钢再纳米化焊接接头组织和性能

采用TIG焊方法对纳米贝氏体钢板进行表面堆焊并快速进行再纳米化处理,通过SEM和TEM观察了焊接接头不同区域的组织特征和形态,使用XRD和TEM电子衍射花样对各种相进行鉴定,并获得相应相的含量,采用拉伸试验和硬度测试获得了再纳米化焊接接头的力学性能.结果表明,经过再纳米化处理,纳米贝氏体钢焊缝区和淬火区组织转变为纳米级片层状的贝氏体和奥氏体,其中焊缝奥氏体含量为13%,而且淬火区片层厚度与母材相当约为70 nm,焊缝区片层厚度大于母材约为300 nm.力学性能测试结果表明,再纳米化焊接接头抗拉强度为1 500 MPa,硬度为7 000 MPa,与母材相差无几,其中接头断裂位置为回火区,是由于回火区析出大量碳化物导致的.     

国产06Ni9DR 钢焊接热影响区组织和低温韧性

采用扫描电镜(SEM)、背散射电子衍射(EBSD)和焊接热模拟技术,研究了单次热循环不同峰值温度对国产06Ni9DR 钢焊接热影响区(HAZ)显微组织和低温冲击韧性的影响. 结果表明,06Ni9DR 钢HAZ的-196 ℃冲击吸收能量均低于母材,HAZ整体发生了脆化. 粗晶区脆化最为严重,原因是原始奥氏体晶粒粗大及其导致的有效大角度晶界较少,残余奥氏体量少且不稳定,以及较大的位错密度和粗大马氏体的存在. 晶界呈链状分布的大块逆转奥氏体和M-A组元的存在导致回火区脆化程度仅次于粗晶区. 细晶区和不完全脆化区的韧性低于母材,主要是因为淬火马氏体的存在和残余奥氏体的低温稳定性差.     

06Cr18Ni12Mo2Cu2奥氏体不锈钢焊接接头组织与力学性能

通过拉伸、弯曲、维氏硬度等试验以及金相分析,对06Cr18Ni12Mo2Cu2奥氏体不锈钢焊接接头的显微组织和力学性能进行了研究。结果表明:焊条电弧焊焊接接头有良好的抗拉性能和弯曲性能,焊缝区硬度略高于母材,而热影响区硬度略低于母材。焊缝组织为奥氏体+5%铁素体组织。焊接热影响区过热区奥氏体晶粒粗大,导致材料强度和硬度下降。     

316L不锈钢焊接接头耐晶间腐蚀试验

根据316L不锈钢的焊接特点,开发了一种钨极氩弧焊背部免充气保护焊接工艺。对焊接接头进行了金相组织、草酸刻蚀试验和晶间腐蚀试验。试验结果表明:316L母材显微组织为纯奥氏体;316L热影响区靠母材一侧的显微组织为粗大的奥氏体晶粒,靠焊缝一侧为奥氏体基体上分布着铁素体;316L根部焊缝的显微组织为奥氏体基体上分布着铁素体。刻蚀试验结果表明:焊缝和热影响区处的刻蚀形貌均是沟槽连成一片。虽然没有通过草酸刻蚀试验,但是所有试样均通过了Cu-CuSO4-硫酸晶间腐蚀试验。因此,钨极氩弧焊背部免充气保护焊接工艺是成功的。     

00Cr13Ni5Mo焊丝焊接1Cr13马氏体不锈钢的组织与性能

应用不锈钢焊丝00Cr13Ni5Mo对1Cr13马氏体不锈钢进行焊接实验,并对其焊缝及热影响区的金相组织进行了观察分析,对焊接试样的维氏硬度、抗拉强度进行了测量.结果表明,焊缝处为整齐排列的细柱状晶组织,晶间残余奥氏体均匀交替分布,同时基体上弥散分布着碳化物和粗大的合金化合物质点,晶粒度6级;焊缝组织均匀,强度高,焊接性能好.     

激光焊接热轧态1000MPa级高强钢焊接接头组织及性能

采用CO2激光焊接抗拉强度为1 000 MPa,厚度6 mm的热轧高强钢板,对焊接接头的显微组织、硬度、抗拉强度、抗冲击性能及断口形貌进行了研究。结果表明,焊缝组织以粗大的板条马氏体为主,有少量的下贝氏体组织;热影响区组织以细小的板条马氏体、粒状贝氏体及少量的残余奥氏体为主,其中回火区和不完全正火区,组织分布极不均匀,呈与母材相一致的细长带状分布,晶界处以细小的马氏体和贝氏体为主,割裂了组织的连续性;焊接接头的显微硬度值为母材焊缝热影响区,异于一般钢材的焊接,这与母材热轧态的组织特征密切相关,其中回火区和不完全正火区是焊接接头的软化区,由于组织粗大且生成了大量贝氏体的缘故;接头的拉伸和冲击性能与显微硬度的分布吻合较好,接头强度虽与母材等强,而塑性只有母材的一半,断裂部位位于热影响区回火区和不完全正火区,需通过改变焊接工艺或焊后回火处理来改善焊接接头的力学性能。     

纳米贝氏体钢TIG焊接头组织和性能

采用TIG焊接方法对1500 MPa级纳米贝氏体钢进行焊接.利用光学显微镜(OM),扫描电镜(SEM),X射线衍射(XRD)和透射电镜(TEM)对焊接接头的微观组织和断口形貌进行了观察与分析,通过硬度测试与拉伸试验考察了接头的力学性能.结果表明,纳米贝氏体钢的焊接性较差,TIG焊焊缝和淬火区组织为淬硬的马氏体,硬度高达1000 HV;焊缝偏析严重,在枝晶间出现残余奥氏体;焊接接头出现冷裂纹,且为沿晶脆性断裂;回火区析出大量碳化物,主要为M₇C₃(M表示Fe,Cr,Mn)和渗碳体Fe₃C,并随着回火温度的升高,碳化物析出量增大,成为焊接接头的又一薄弱环节.     

30CrMnSiNi2A钢焊接接头热处理后的组织与性能

研究了30CrMnSiNi2A钢电子束焊接接头热处理后的组织和性能。试验结果表明，该钢电子束焊接接头焊缝为典型的粗大针状马氏体加残余奥氏体组织，HAZ（热影响区）为中温组织，经过900℃油淬加低温回火处理后，焊缝和热影响区组织转变为回火马氏体和残余奥氏体。焊态下，由于母材的强度较低，此种电子束焊接接头的拉伸试验断裂部位均在母材；经过上述热处理，母材的强度有了大幅度的提高，焊缝的强度虽然稍有降低，但伸长率提高了将近1倍，获得了良好的综合力学性能。但上述热处理后，焊缝和热影响区的冲击韧度和断裂韧度值较低，这主要是因为中碳马氏体中含碳量略高造成的。焊缝由于组织细小且均匀，与热影响区相比，具有相对较高的断裂韧度。     

304/Q345R复合板焊接接头微观组织及残余应力

为研究复合板在焊接过程中复杂的热力学行为,利用ABAQUS有限元软件对304/Q345R复合板的焊接过程进行了数值模拟,通过热电偶和盲孔法获得了焊接接头的热循环曲线和残余应力分布规律,验证了有限元模型的正确性. 同时采用光学显微镜和扫描电镜对焊接接头的微观组织、晶粒形貌和元素分布进行了分析,研究焊接接头部位的微观组织演化规律. 结果表明,焊接残余应力最大值为312 MPa,位于焊趾附近,残余应力沿焊缝至母材方向逐渐降低并趋于稳定. 在两种材料的交界面处发现残余应力不连续现象. 焊接接头微观组织主要由奥氏体和铁素体组成,复层熔合线附近的铁素体以板条状和针状形成带状过渡区,而熔合线附近的奥氏体晶粒成柱状形貌且尺寸更为微小.     

800MPa级高强钢焊缝金属热处理组织与性能

在10Ni5CrMoV高强结构钢焊接中,为了获得良好的强韧性匹配,焊后需要进行热处理来改善焊缝金属的组织和性能.试验采用富氩气体保护焊焊接10Ni5CrMoV钢,分析了不同调质热处理工艺下焊缝组织、性能的变化规律.结果表明,焊缝金属焊态的组织主要是贝氏体、少量马氏体和残余奥氏体组织,调质热处理后焊缝组织主要为回火马氏体,随着回火温度的升高,焊缝中残余奥氏体减少,马氏体中碳化物析出长大并有球化趋势.调质态焊缝金属的强度随着回火温度的升高而逐渐降低,而韧性随着回火温度的升高而显著提高.     

焊接方法对1000MPa级熔敷金属组织及力学性能的影响

在相同热输入下分别采用熔化极活性气体保护焊(MAG)和钨极氩弧焊(TIG)进行1 000 MPa级熔敷金属试验,通过光学显微镜、透射电镜及断口分析等手段研究焊接方法对其组织和性能的影响. 结果表明,MAG焊熔敷效率明显高于TIG焊,MAG焊中出现了明显的"指状熔深". MAG焊熔敷金属及道间热影响区组织明显较TIG焊粗化. TIG焊熔敷金属组织细化、分布取向多样化且均匀分布的较多残余奥氏体是TIG焊低温冲击韧性优异的原因之一;MAG焊中生成大量非金属夹杂物易成为解理断裂起裂源,是导致熔敷金属冲击韧性恶化的因素之一. TIG焊力学性能明显优于MAG焊,这与焊接方法所导致的组织构成及夹杂物有直接关系.     

MODELING OF AUSTENITE GRAIN SIZE IN LOW-ALLOY STEEL WELD METAL

The size of austenite grain has significant effects on components and proportions of various ferrites in low-alloy steel weld metal.Therefore, it is important to determine the size of austenite grain in the weld metal. In this paper, a model based upon the carbon diffusion rate is developed for computing austenite grain size in low-alloy steel weld metal during continuous cooling. The model takes into account the effects of the weld thermal cycles,inclusion particles and various alloy elements on the austenite grain growth.The calculating results agree reasonably with those reported experimental observations.The model demonstrates a significant promise to understand the weld microstructure and properties based on the welding science.     

控锻控冷工艺对GCr15轴承钢组织演变规律的影响

采用微观组织表征的方法对比研究了GCr15轴承钢在传统工艺和控锻控冷工艺下的组织和网状碳化物分布的演变规律,并统计和分析了不同工艺下的晶粒度和残留奥氏体含量的变化规律。结果表明,GCr15轴承钢经控锻控冷工艺处理后,GCr15钢中粒状珠光体组织相对更细小,淬回火组织基体中的C元素分布更为均匀,同时洛氏硬度提高0.7 HRC;残留奥氏体含量降低;碳化物颗粒尺寸细化,平均颗粒尺寸减小40%以上,同时抑制粗大碳化物网状的形成;可使奥氏体晶粒度细化2级以上。     

Tensile behavior of TRIP-aided multi-phase steels studied by in situ neutron diffraction

TRIP-aided multi-phase steels were made by thermo-mechanically controlled process, where the ferrite grain size and the amount of the retained austenite were changed by controlling process conditions. The tensile behavior of four steels was studied by in situ neutron diffraction. It is found that the retained austenite bearing about 1.0 wt% C is plastically harder than the ferrite matrix. The steel with a ferrite grain size of ≈2.0 μm showed tensile strength of 1.1 GPa and a uniform elongation of 18.4%, in which stress-induced martensitic transformation occurs during plastic deformation but a considerable amount of austenite remains even after the onset of necking. It is concluded that the enhancement of uniform elongation is caused mainly by the work-hardening due to the hard austenite and martensite, where the contribution of the transformation strain is negligible.     

焊前热处理对440C不锈钢电子束焊接接头组织与性能的影响

研究了焊前退火和调质2种热处理工艺对440C不锈钢电子束焊接接头的组织和力学性能的影响,分析了2种状态下的组织演变规律、接头拉伸力学性能和硬度分布特点. 结果表明:2种热处理状态的板材经过电子束焊接后,焊缝成形良好,焊缝区域均为马氏体和残留奥氏体组织,呈现出非平衡凝固组织,碳及合金元素以固溶形式存在于马氏体及残余奥氏体中,焊缝区域硬度达到398 HV. 焊前经调质热处理后,母材基体由铁素体转变成回火马氏体和残余奥氏体混合组织,同时部分碳化物固溶在基体组织中,使基体组织硬度提高了60％. 与焊前退火态相比,焊前调质热处理板材经电子束焊接后,可使焊接接头抗拉强度提高20％,焊接热影响区硬度提高35％,但接头的塑性变形能力有所下降,断裂均发生在热影响区.     

双相钢中残余奥氏体对性能的影响及其热稳定化

用声发射法研究了一种低合金钢于双相区热处理所得残余奥氏体的马氏体相变。发现残余奥氏体的热稳定化程度和稳定性均与奥氏体的颗粒尺寸有关。颗粒愈小，热稳定化程度愈高，且愈稳定。不存在马氏体核胚的极小奥氏体颗粒不能仅靠过冷来使其转变。形变能诱发试验钢中残余奥氏体转变，且增加钢的塑性。但只有奥氏体颗粒尺寸有合适的分布，其中小部分稳定性很高，才能使马氏体相变随应变增加而逐渐发生并延伸到大的应变，使延伸率明显增加。     

Comparison of two types of low-transformation-temperature weld metals based on solidification mode

Two types of low-transformation-temperature weld metals were devised, one associated with primary austenite solidification, the other primary ferrite solidification. The martensite start temperature of both low-transformation-temperature weld metals was about 125°C. Experimental results showed that low-transformation-temperature weld microstructure associated with primary austenite solidification was martensite with 8.0% retained austenite, whereas that one related to primary ferrite solidification primarily consisted of martensite and δ-ferrite. Accordingly, both welded joints had little distinction between distortion and residual stress, indicating that weld metal associated with primary ferrite solidification played the same function as primary austenite solidification on residual stress reduction. Moreover, the low-transformation-temperature weld metal associated with primary ferrite solidification had higher tensile strength and hardness than that based on primary austenite solidification.     

Roles of bulk carbon content on grain size,carbide reactions and intergranular rupture life in 2.25cr martensitic heat resistant steels

The steel of a higher bulk carbon content shows the denser precipitation distribution of carbides after the solution treatment followed by tempering. Such a carbide distribution produces the smaller prior austenite grain size after the welding simulation at a high temperature. Because the equilibrium segregation concentration of phosphorus decreases with decreasing prior austenite grain size, the specimen of the higher bulk carbon content shows therefore the longer intergranular rupture life. The rupture life is also increased by the partitioning of phosphorus pre-segregated at prior austenite grain boundary/carbide interfaces onto the fresh surface of precipitates formed on the surface of pre-formed carbides. The intergranular rupture life is additionally increased by the repulsive segregation between carbon and phosphorus which decreases the overall phosphorus segregation concentration at the prior austenite grain boundaries.     

Microstructure and mechanical properties of nanostructured bainite weld with regeneration

Because of the brittle martensite crystalline structure, nanostructured bainitic steel is very difficult to be welded and easily form cracks in the welded joint, which limits the scope of their application. Regeneration treatment can lead to nanostructured bainite formation in the welded joints, preventing further degradation of the welded joint. Detailed changes of microstructures and mechanical properties of the weld are characterized here. Coarse inter-dendrite structures appear in the weld due to welding segregation, and are confirmed to be retained austenite by TEM. Moreover, an extraordinary combination of strength and ductility of the weld is achieved. The ultimate tensile strengths are 1913MPa and 2115MPa when regeneration temperatures are 250 °C and 230 °C. The corresponding elongations are 5.14% and 2.3%. In addition, the tension fracture behaviour and crack propagation mode of the weld are investigated.