Ni-Cr-Mo-B低合金钢模拟焊接热影响区的组织和性能

用Gleeble-3800热模拟机对Ni-Cr-Mo-B低合金高强度钢进行不同焊接热输入条件的下热模拟试验,研究了模拟焊接热影响区的组织和性能,探讨了不同热输入条件(对应不同的t8/5)对钢中微观组织及形态的影响以及组织与低温韧性的关系。结果表明:随着热输入能量的增加,此类钢焊接热影响区的低温韧性呈现先增后降的规律。当以中等焊接热输入施焊,在热影响区形成贝氏体/马氏体复相组织,先形成的贝氏体对原始奥氏体晶粒的分割作用,使后生成的板条马氏体具有更细的板条束,从而获得最佳的低温韧性。而低热输入时形成全马氏体组织,高热输入时获得一定量的粒状贝氏体,两种组织的低温韧性均低于贝氏体/马氏体的复相组织。     

焊后热处理对ASTM 4130钢焊接热影响区组织与性能的影响

通过金相观察、硬度试验和扫描电镜分析,研究了不同焊后热处理保温时间对ASTM 4130钢焊接热影响区显微组织、硬度、低温冲击韧性和断口形貌的影响.结果表明,随焊后热处理保温时间的延长,热影响区硬度降低,粗晶区和细晶区韧性明显改善;经焊后热处理后,热影响区组织主要为回火马氏体、铁素体和贝氏体;造成粗晶区硬度较高、韧性较低的主要原因是该区出现了贝氏体和粗大的回火马氏体.     

Influences of post-weld heat treatment on fatigue crack growth behaviour of strength mismatched HSLA steel welds

Abstract

Welding of high strength low alloy steels (HSLA) involves usage of low, even and high strength filler materials (electrodes) compared with the parent material depending on the application of the welded structures and the availability of the filler material. In the present investigation, the influences of post-weld heat treatment (PWHT) on fatigue crack growth behaviour of under matched (UM), equal matched (EM) and over matched (OM) weld metals has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. The Shielded Metal Arc Welding (SMAW) process has been used to fabricate the single 'V' butt joints. Centre Cracked Tension (CCT) specimens have been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading (R = 0). From this investigation, it has been found that the fatigue performance of over matched joints is superior compared to under matched and equal matched joints. Moreover, PWHT reduced the magnitude of the tensile residual stress field in the weld region and subsequently enhanced the fatigue performance of the joints irrespective of weld metal strength mismatch.     

Effect of vibration on microstructures and mechanical properties of 304 stainless steel GTA welds

This study investigates the microstructures and mechanical properties of 304 stainless steel at various vibration frequencies during simultaneous vibration welding. The experimental results demonstrated that simultaneous vibration welding could accelerate the nucleation and grain refinement of the microstructures. The effect of the grain refinement was more evident at the resonant frequency (375 Hz) and a minimum content of residual δ-ferrite (4.0%). The γ phase grew in the preferential orientation of the (111) direction with and without vibration. The full width at half maximum of the diffraction peak widened after the vibration, which was attributed to the grain refinement. The residual stress could be efficiently removed through simultaneous vibration welding when the amplitude of the vibration was increased. Furthermore, the lowest residual stress (139 MPa) was found when the vibration frequency was 375 Hz. The hardness and Young’s modulus exhibited slight increases with low and medium frequencies. The hardness values were increased by 7.6% and Young’s modulus was increased by 15% when the vibration frequency was resonant (375 Hz).     

含Cu的HSLA钢中富Cu团簇的粗化行为及其对力学性能的影响

利用原子探针层析技术(APT)对含1.4 mass％ Cu的低合金高强度钢(High strength low alloy,HSLA)在450℃回火2～100 h后的富Cu团簇进行了表征,并对富Cu团簇的粗化行为及其强化行为进行了定量分析,通过拉伸实验测定了实验钢的力学性能.APT结果表明:随着回火时间的延长,富Cu团...     

In situ thermal studies and post-weld mechanical properties of friction stir welds in age hardenable aluminium alloys

Abstract

The 'quench sensitivity' of various friction stir welded (FSW) aluminium alloys were investigated. Cooling rates of FSW were altered by utilising various active (weld side) and passive (anvil side) cooling/heating conditions. Media used included a chilled water mist (active cooling) and hot air (active heating) immediately behind the tool, and water chilled (passive cooling) or heated (passive heating) anvil. Microhardness and transverse tensile properties were used to assess the natural aging response of friction stir welds (FSWs) in 2195-T8 and 7075-T7351 subject to these conditions. Test results indicated that the quench sensitive alloy 7075 exhibits a more rapid natural aging response and improved mechanical properties while the less quench sensitive 2195 exhibits little or no change in mechanical properties. In the present investigation FSWs in alloy 7075 under active and passive cooling conditions exhibited an increase of approximately 10% in tensile properties over conventional FSWs.     

400 MPa级超细晶粒钢板焊接热影响区的组织和力学性能

超细晶粒钢的强度和韧性比普通晶粒钢有大幅度的提高，其焊接性是该钢能否获得广泛应用的关键。通过采用实际焊接和焊接热模拟方法，研究了焊接热输入对超细晶粒钢组织和力学性能的影响。研究结果表明，超细晶粒钢的奥氏体晶粒长大倾向与普通晶粒钢相近，在热影响区和母材之间存在一再结晶软化区，板厚小于3mm时，粗晶热影响区的裂纹扩展吸收能大于母材，板厚大于5mm时，粗晶热影响区韧性比母材有较大幅度降低。对影响粗晶热影响区韧性的机理进行了探讨。     

回火时间对含铜HSLA钢板组织性能的影响

含铜HSLA钢板是高强度船舶用钢的理想材料,为确定其最佳热处理工艺,对不同回火时间下含铜HSLA钢板进行拉伸试验、冲击试验、测定宏观硬度,并借助OM、SEM等检测手段观察其金相组织.试验结果表明,随回火时间的延长,含铜HSLA钢板的基体组织中板条马氏体的板条结构逐渐消失,且钢板屈服强度、抗拉强度及硬度呈先升高后下降的趋...     

Effect of prior hot rolling on the microstructures and mechanical properties of duplex stainless steel containing tempered martensite and ferrite

A duplex structure of δ-ferrite and lath martensite with interlath retained austenite film is developed in this study by modifying the alloy addition. The presence of δ-ferrite can further strengthen the grain refinement of austenite during hot rolling. As a result, the amount of retained austenite is enhanced. Tempered martensite embrittlement occurs due to the decomposition of retained austenite, and grain refinement can in fact ameliorate the tempered martensite embrittlement by delaying the onset of the embrittlement to a higher temperature. The combined effect of uniform and small grains as well as a large amount of retained austenite provides a further increase in the mechanical properties. After identical tempering treatments, all mechanical properties measured in the as-rolled condition were found to be higher than those of direct quenching without rolling. After hot rolling, the increase in the hardness and tensile strength was not accompanied by a drop in the ductility and toughness.     

焊后处理对45钢基体模具堆焊层组织及力学性能的影响

在45钢基体上进行了堆焊试验,并将堆焊后的试样分别进行了直接空冷和焊后回火处理,研究了这两种焊层的显微组织、硬度以及耐磨性能.试验研究结果表明:堆焊后空冷试样的显微组织为粗大的板条状马氏体和大量残留奥氏体;堆焊后进行500～550℃回火处理,试样焊层的显微组织主要是细小托氏体和少量残留奥氏体.堆焊后回火处理试样的硬度比直接空冷试样的硬度低10％,邻近熔合区的基体硬度有所提高,熔合区硬度梯度减小,有利于改善堆焊层的韧性;焊后回火处理的试样的耐磨性比直接空冷试样的耐磨性提高35％.     

焊后热处理对P92钢焊接接头显微组织和力学性能的影响

采用光学金相显微镜和力学性能测试等方法,研究了电阻履带式和中频感应两种不同的焊后热处理方法对P92钢焊接接头显微组织和力学性能的影响。结果表明:中频感应处理下的焊缝组织较为细小,马氏体板条界面变得更加模糊;焊接接头各层母材、热影响区及焊缝硬度值分布均匀,内、中和外层的硬度差值较小;焊缝及热影响区冲击吸收能量沿壁厚方向分布较为均匀,且均高于P92母材标准要求值。因而,中频感应加热法不仅可以很好地改善焊缝组织,而且在壁厚方向上,可以使焊缝韧性等力学性能更加均匀。      

Welding behaviour,microstructure and mechanical properties of dissimilar resistance spot welds between galvannealed HSLA350 and DP600 steels

Abstract

Resistance spot welding experiments were conducted on dissimilar material combination of HSLA350/DP600 steels. The welds were characterised using optical and scanning electron microscopy. The fusion zone of the dissimilar material spot weld was predominantly martensitic with some bainite. Mechanical properties were also determined by tensile shear, cross tension and fatigue tests. The performance of dissimilar material spot weld was different from that of the similar ones in each of the HSLA350 and DP600 steels and exhibited different heat affected zone hardness. The DP600 weld properties played a dominating role in the microstructure and tensile properties of the dissimilar material spot welds. However, the fatigue performance of the dissimilar welds was similar to that of the HSLA350 welds. Fatigue tests on the dissimilar material spot welds showed that the 5·5 mm diameter nugget exhibited higher fatigue strength than the 7·5 mm diameter nugget.     

表面机械研磨处理对316L不锈钢组织和性能的影响

对2.8mm厚的316L不锈钢板的上下表层进行机械研磨处理(SMAT),对经过不同时间的SMAT后的样品的表层组织进行金相观察,并测量SMAT不同时间的样品的硬度、抗拉强度.结果表明,经过表面机械研磨处理不同时间后,在316L不锈钢板表层获得了不同厚度的表面强化层,强化层组织为沿厚度方向由纳米晶层向微米晶层过渡的梯度组织;随着SMAT时间的增加,总的强化层厚度增加;表面组织的变化导致了表面硬度明显增加,整体材料的屈服强度增加;表面机械研磨处理时间对性能的影响并非线性增加,表面硬度和整体材料的屈服强度在处理5min时增加显著,处理时间继续增加到15、30和60min,它们的增加速度很小.拉伸断口表面形貌的扫描电镜观察表明,经过5min处理后的样品,表层的剪切唇变形区域面积增加,断口微观特征为长条状的韧窝,但是随着处理时间的增加,剪切唇区的尺寸并没有继续增加,而是开始下降,表面硬化区域的增加造成了塑性变形能力的下降.     

焊后热处理对铝合金/镀锌钢接头组织与力学性能的影响

采用TIG熔-钎焊方法并添加AlSi_5焊丝,对1.5 mm厚的5A06铝合金和3 mm厚的镀锌Q235钢进行焊接。分析了焊后退火热处理对接头微观组织和力学性能的影响规律,热处理条件为280℃保温30 min。研究结果表明,采用TIG熔-钎焊的方法可以实现铝/钢异种金属的焊接,铝/钢界面处会产生金属间化合物层,焊态接头中金属间化合物层的厚度为4～5μm,化合物层主要由Al_8Fe_2Si相和少量的[Al,Fe,Si],Al13Fe4相组成,接头的抗拉强度值为163 MPa,断裂发生在焊缝处。对接头进行退火热处理后,接头中金属间化合物层的厚度增加到9～10μm,化合物层的组织无明显变化,主要由Al_8Fe_2Si相和少量的[Al,Fe,Si],Al₁₃Fe_4相组成,接头的抗拉强度值达到185 MPa,断裂发生在铝母材侧。     

焊后热处理对特厚板20MnNiMo焊接残余应力的影响

为了研究焊后热处理对8万吨模锻压机主缸材料20MnNiMo焊接接头残余应力的影响,制定了窄间隙焊接方案和15 h×(550±10)℃焊后热处理方案,并通过盲孔法对焊接接头表面残余应力进行了测定和记录。得到了15 h×(550±10)℃焊后热处理对20MnNiMo厚板焊接接头残余应力场分布的影响。结果表明:15 h×(550±10)℃去应力退火可以很好的减小20MnNiMo厚板焊接残余应力,去应力效果显著,可以很好地改善20MnNiMo焊接残余应力的分布,该热处理方案满足实际产品需要,可以用于实际焊接生产中。     

Microstructure and mechanical properties of friction welds between TiAl alloy and 40Cr steel rods

Direct friction welding of TiAl alloy to 40Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment (PWHT) states were investigated. The martensitic transformation occurred and brittle TiC phase formed near the interface due to C agglomeration, which degraded the joint strength and increased the microhardness at the interface in as-welded state. Feathery and Widmanstatten structure generated near the interface on TiAl alloy side. After PWHT at 580 °C and 630 °C for 2 h, the sorbite formed and C dispersed at the interface, leading to the increase of the joint strength from 86 MPa in as-welded state to 395 MPa and 330 MPa, respectively. The heat-treated specimen fractured with quasi-cleavage features through the zone 1 mm away from the interface on TiAl alloy side, but the as-welded specimen failed through the interface.     

Effect of different pre- and post-weld heat treatments on microstructures and mechanical properties of variable polarity TIG welded AA2219 joints

The microstructures and mechanical properties of 2219 aluminium alloy joints welded by variable polarity TIG welding in four kinds of different heat treatment conditions, namely, with/without pre-/post-weld heat treatment, were analysed and compared. The post-weld artificial aging treatment rendered fine dispersed precipitates (metastable θ′ phase) separate out of weld metal, which made the hardness of weld metal increase by ～20%. Meanwhile, the fracture location of joints during tensile test changed from weld zone to heat affected zone (HAZ). The pre-weld solution treatment reduced the overaging degree of HAZ and a large number of θ′ phase reprecipitated in HAZ after post-weld artificial aging treatment. Intermediate state welding, with pre-weld solution treatment and post-weld artificial aging treatment together, could increase 20% of the hardness of weld zone, increase 11.5% of the hardness of HAZ and increase 20.3% of the tensile strength of joint.     

脉冲MAG焊工艺方法对铁素体不锈钢热影响区组织性能的影响

由于铁素体不锈钢具有较好的经济性和良好的耐蚀性,其应用领域不断拓展.但铁素体不锈钢在高温加热过程中有晶粒急剧长大的特点,对焊接结构而言,经过焊接热循环的作用,铁素体不锈钢焊接热影响区的韧性将有较大幅度下降,因此必须采取措施加以控制.文中采用Cr12型铁素体不锈钢,研究了脉冲MAG焊与普通MAG焊工艺方法对其热影响区显微组织及力学性能的影响.研究结果表明,采用脉冲MAG焊工艺方法,可减弱焊接热输入对母材热影响区的作用,减小热影响区宽度,提高其低温冲击性能.     

ZG0Cr13Ni5Mo马氏体不锈钢模拟焊接HAZ组织与性能

建立ZGOCr13Ni5Mo马氏体不锈钢焊接热影响区(HAZ)CCT图，模拟不同焊接热循环条件下热影响区组织并对其硬度、冲击韧度及金相组织进行研究。结果表明，热影响区只发生A-M相变，相变开始点Ms基本不受冷却速度的影响；随冷却速度的降低，硬度略有下降。与母材相比，模拟热影响区的硬度有较大幅度提高，冲击韧度有较大幅度下降；冷却速度对硬度和冲击韧度影响不大。在模拟多层多道焊接热循环的条件下，层道间的热处理作用不明显，590℃焊后热处理是使热影响区冲击韧度得以恢复的必要途径。