Research on microstructure and properties of boron/Q235 steel laser welded dissimilar joints under synchronous thermal field

The mechanical mismatch effect frequently occurs in the dissimilar materials welded joints, thus leading to plastic gradient at the interface between the weld and heat-affected zone(HAZ). In this work, the boron steel and Q235 steel were selected for laser tailor welding,which obtained boron/Q235 steel tailor-welded blanks(TWBs). The method of welding with synchronous thermal field(WSTF) was utilized to eliminate the mismatch effects in TWBs. The WSTF was employed to adjust cooling rates of welded joints, thereby intervening in the solidification behaviors and phase transition of the molten pool. Boron/Q235 steel was welded by laser under conventional and WSTF(300-600 ℃) conditions, respectively. The results show that the microstructure of weld and HAZ(boron) was adequately transitioned to ferrites and pearlites instead of abundant martensite by WSTF. Meanwhile, the discrepancy of microhardness and yield strength between various regions of welded joints was greatly reduced, and the overall plasticity of welded joints was enhanced by WSTF. It is indicated that WSTF can effectively contribute to reducing plastic gradient and achieving mechanical congruity in welded joints by restraining the generation of hardbrittle phase, which could significantly improve the formability of TWBs in subsequent hot stamping.

Microstructure evolution and mechanical properties of high-boron steel with different ratios of boron and carbon

Boron and carbon contents are the main factors influencing the properties of high-boron steel.In this study,experimental samples with different boron-to-carbon ratios(%B/%C)were prepared.The microstructures of the different samples were observed,and their hardness,bending strength,and impact toughness were investigated.Results show that the main microstructures in the investigated high-boron steel samples are the eutectic Fe_(2)B structure with a fishbone shape and the ternary peritectic Fe_(3)(C,B)structure with a chrysanthemum shape.When the boron content is 2.5wt.%and the carbon content is 0.43wt.%(i.e.,%B/%C=5.82),the overall mechanical properties of the alloy are the best.The alloy's hardness,bending strength and impact toughness reach their maximums,which are 67.3 HRC,1,267.36 MPa and 6.19 J·cm^(-2),respectively.The optimized alloy is compared with conventional materials exhibiting excellent wear resistance(namely,high-manganese steel and high-chromium cast iron)through two-body and three-body abrasion tests.The wear resistance of this high-boron steelinvestigated in this work is found to be superior to those of the more common materials.

Heterogeneous structure-induced strength and ductility synergy of α-brass subjected to rapid cooling friction stir welding

The 2 mm-thickα-brass plates were successfully joined using conventional friction stir welding(CFSW)with air cooling and rapid cooling friction stir welding(RCFSW)with liquid CO2 cooling.The microstructure and mechanical properties of the two welds were carefully investigated by electron back-scattered diffraction and transmission electron microscopy.The stir zone of CFSW exhibited homogeneous equiaxed grains,while the stir zone of RCFSW showed a heterogeneous grain structure,i.e.ultrafine grains containing massive dislocations and nano twins.Compared with the CFSW,yield strength and ultimate tensile strength of RCFSW were increased by 31%and 24%,respectively.The enhanced yield strength and improved strain hardening capacity were attributed to grain boundary strengthening and dislocation strengthening.Furthermore,good ductility was achieved due to the released stress concentration of the nano twins caused by the plastic deformation.

Microstructure and mechanical properties evolution of 65Cu-35Zn brass tube during cyclic rotating−bending process

The cyclic rotating−bending(CRB)processes under different deformation conditions were carried out to refine the microstructure and improve the mechanical properties of the 65Cu−35Zn brass tubes.The microstructure and the mechanical properties in the axial direction of the tubes after the CRB process were studied with the OM,EBSD and conventional tensile test.To obtain the accumulated effective plastic strain of the tube during the CRB process,the FEM simulation was also executed.The results show that the average grain size decreases with the increase of rotation time at RT,and with the decrease of bending angle at 200℃.With the increase of accumulated effective plastic strain during the CRB process,the reduction rate of average grain size of the brass tube increases,the tensile strength of the brass tube increases in wave shape and the elongation increases first and then sharply decreases.

Friction and wear properties of PM cam materials with different boron contents

In this study,effects of B addition on the sintering densification,microstructure,hardness,friction and wear properties of sintered Fe-2.4C-4Cr-1Mo-0.5P-0.7Si-2.5Cu(in wt%)were investigated.In spite of the decreased sintered density,the addition of B changes the phase composition of the materials and their ratio.Moreover,hardness of either the matrix or the liquid solidification structure dramatically increases.These changes in micro structure result in higher friction coefficient and lower wear loss.It is observed that the addition of0.1 wt%B offers the optimum friction and wear properties with a running-in period of only 30 s and wear volume loss of 0.006 mm^(3) under the testing conditions.Such friction and wear properties are superior to those of the other two widely used cam materials,cast iron and 45 steel.

薄壁H65黄铜管高频感应焊接接头组织和力学性能

对薄壁H65黄铜高频感应焊接后的焊接接头微观组织和力学性能进行了研究。结果表明,利用高频感应焊接技术焊接H65黄铜管,获得了表面成型良好的焊接接头,实现了高质量焊接。焊接接头熔合区和热影响区均呈上下宽,中间窄的腰鼓状,焊接接头宽度约为173μm,其中熔合区宽约15μm,由大量细小的等轴状晶粒和少量条状晶粒组成,熔合区和热影响区的晶粒较母材得到细化。焊接接头抗拉强度为400 MPa,达到母材抗拉强度的97.6%,这是由于在拉伸变形过程中,晶粒的细化阻碍位错变形,且各晶粒间的位向差使位错相互交割,提高了焊接接头的强度,焊接接头断裂发生在热影响区,为韧性断裂,这是焊接过程中挤压辊的加工硬化与焊后退火软化共同作用影响热影响区力学性能所致。焊接接头显微硬度呈现“ʌ”形分布,熔合区平均硬度值为145HV,热影响区137HV,母材129HV,熔合区硬度较母材提高了16%,焊接时产生的加工硬化使熔合区强度得到提升。

超薄壁黄铜散热器扁管高频感应焊接接头的组织和性能

采用高频感应焊接技术对0.13 mm壁厚的H65黄铜扁管进行焊接,利用光学显微镜、扫描电镜、电子探针、电子背散射衍射、显微硬度仪以及拉伸实验对焊接接头的微观组织和力学性能进行了研究。结果表明:高频感应焊接H65黄铜扁管的焊接接头无裂纹、气孔等缺陷,焊缝区没有出现Zn的大量蒸发。焊接接头的抗拉强度达到400 MPa,达到母材的94%,伸长率为33.89%,与母材接近;焊接接头的显微硬度呈W型分布,熔合区最高,母材区次之,热影响区最小。焊接过程的挤压作用导致焊缝位错密度增加,产生加工硬化,是影响焊接接头硬度分布的主要原因;与母材相比,焊接接头的显微组织得到明显的细化,平均晶粒尺寸为1μm,是母材的50%,小角度晶界增加到了72%,大角度晶界下降到了28%,其中孪晶界下降到2%,进一步提高了焊接接头的力学性能。

Effect of Heat Treatment on Structure and Wear Resistance of High Chromium Cast Steel Containing Boron

The microstructure, mechanical properties and wear resistance of high chromium cast steel containing boron after different heat treatments were studied by means of the optical microscopy （OM）, the scanning electron microscopy （SEM）, X-ray diffraction （XRD）, hardness, impact toughness, tensile and pin-on-disc abrasion tests. The results show that as cast microstructures of boron-free high chromium steel consist of martensite and a few （Cr, Fe）_7C_3 carbide, and the macro-hardness of boron-free high chromium steel is 55-57 HRC. After 0.5 mass% B was added into high chromium cast steel, as-cast structure transforms into eutectic （Fe, Cr）2B, （Cr, Fe）7 （C, B）a and martensite, and the macro-hardness reaches 58-60 HRC. High temperature quenching leads to the disconnection and isolated distribution of boride, and there are many （Cr,Fe）_23 （C,B）_6 precipitated phases in the quenching structure. Quenching from 1050 ℃, high chromium steel obtained the highest hardness, and the hardness of high chromium cast steel containing boron is higher than that of boron-free high chromium steel. The change of quenching temperature has no obvious effect on impact toughness of high chromium steel, and the increase of quenching temperature leads to tensile strength having an increasing tendency. At the same quenching temperature, the wear resistance of high chromium cast steel containing boron is more excellent than that of boron-free high chromium steel. High chromium cast steel guide containing boron has good performance while using in steel bar mill.

Study on microstructure and properties of brass containing Sb and Mg

A novel free-cutting unleaded brass containing antimony and magnesium was prepared by gravity casting and hot extrusion. Microstructure of the hot extruded Sb-Mg brass was studied with scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS). Its mechanical properties were measured by tensile test, and cutting performance was investigated by lathe turning experiment. Results showed that microstructure of the hot extruded Sb-Mg brass was composed of α, β phases and Sb-Mg containing intermetallic compounds. The newly developed brass was compared with the HPb59-1 brass for its mechanical property. Its cutting performance was close to that of a German free-cutting unleaded brass. Sb-Mg brass has potential to replace HPb59-1 brass so as to reduce cost and protect environment.

Microstructure,Phase Transformation,Precipitation Behavior and Mechanical Properties of P/M Cu40Zn-1.0 wt%Ti Brass Alloy via Spark Plasma Sintering and Hot Extrusion

The effect of titanium addition on the microstructure and mechanical properties of brass Cu4OZn has been studied via the powder metallurgy （P/M） route. The water-atomized Cu4OZn-1.0 wt% Ti alloy powder was consolidated at different temperatures in the range of 400-600℃ using spark plasma sintering （SPS） and hot extrusion subsequently. Results show that the super-saturated solid solution titanium element in rapidly cooled brass Cu4OZn powder created high chemical potential for a precipitate reaction, showing significant grain refinement effects on the consolidated Cu4OZn matrix. Consequently, excellent mechanical properties were obtained by precipitation hardening and work hardening after sintering and extrusion, with yield strength of 390 MPa, ultimate tensile strength of 617 MPa, and Vickers micro-hardness of 192 HV, which are 28.7%, 23.4%, and 23.9% higher values than those of extruded Cu4OZn brass, respectively.

Reactive sintering of B4C-TaB2 ceramics via carbide boronizing:Reaction process, microstructure and mechanical properties

Carbide boronizing is a promising approach to obtain fine grained boron carbide based ceramics with improved mechanical properties. In this work, reaction process, microstructural characteristics and mechanical properties of BxC-TaB2(x = 3.7, 4.9, 7.1) ceramics were comprehensively investigated via this method. Dense BxC-TaB2 ceramics with refined microstructure were obtained from submicro tantalum carbide and boron powder mixtures at 1800℃/50 MPa/5 min by spark plasma sintering. The stoichiometry of boron carbide was determined from lattice parameters and Raman shift. It was found that uniformly distributed TaB2 grains in the BxC matrix is favor of the densification process and restricting grain growth.Besides, planar defects with high density were observed from the as-formed B7.1 C grains and transient stress was considered to contribute to the densification involved with plastic deformation. Microstructural observations indicate the dissolution of oxygen in the TaB2 lattice and most of the B7.1 C/TaB2 phase boundaries were clean. Owing to the highly faulted structure and finer grain size, as-obtained BxC-TaB2 ceramics exhibit high Vickers hardness(33.3–34.4 GPa at 9.8 N) and relatively high flexural strength ranging from 440 to 502 MPa.

Influences of boron contents on microstructures and mechanical properties of as-casted nearαtitanium alloy

Ti-6.5 Al-2.5 Sn-9 Zr-0.5 Mo-0.25 Si-1 Nb-1 W-0.1 Er-x B(x=0,0.1,0.2,0.4,0.6 and 0.8 wt%)with different boron contents are fabricated for investigation.Influences of boron element and its amounts on phase constitutions,microstructures,textures and compression mechanical properties are carefully studied.With the increasing boron additions,contents of TiB phase increase,and the maximum intensities of textures decrease.Microstructures are significantly and continuously refined after adding boron element and with the increasing boron additions,and turning point of refinement rates for different microstructural parameters is found at 0.2 wt%boron content.Strengths increase monotonously,while elongations increase firstly and decrease afterwards.The maximum value of elongation is acquired at boron content of 0.2 wt%.On the premise of ensuring plasticity,0.2 wt%boron content is the most appropriate amount for microstructural refinement and mechanical properties enhancement for current nearαtitanium alloys.Meanwhile,aspect ratios of TiB whiskers increase with the increasing boron contents.Lots of near equiaxedαgrains orαgrains with irregular morphologies are discovered around TiB phase.Distorted and twistedαgrain boundaries are also obviously detected in boron containing alloys.Moreover,premature fracture of alloys containing TiB whiskers is largely influenced by the fracture of these brittle reinforcements.

H65黄铜厚板旋转压力焊焊接接头的组织和性能分析

对H65黄铜厚板材旋转压力焊过程中搅拌头旋转速度对焊接质量的影响进行了研究与分析,所选用的旋转速度分别为600,800,1000r/min。研究过程中通过光学显微镜(OM)、扫描电镜(SEM)对H65黄铜合金旋转压力接头区域的微观组织进行观察,并检测接头区域的力学性能。结果表明:旋转压力焊工艺能够有效连接H65黄铜大尺寸厚板材,接头区无明显裂纹,但其微观组织中存在少量气孔,且随旋转速度的增加逐渐减少;接头区域的H65黄铜晶粒明显细化,随旋转速度的增加β相占比减少,有效提升了接头区域的塑性;当搅拌头旋转速度为1000r/min时,H65黄铜连接效果最好,接头的拉伸强度为348MPa,延伸率为48.4%,断口呈韧性断裂。

铌对低铬低碳含硼铸铁的组织和性能的影响

采用感应熔炼法制备了不同Nb含量的Fe-4Cr-2B-0.5C-(0.1~3)Nb合金。运用金相显微镜、扫描电镜、X射线衍射仪、万能实验机、洛氏硬度计和显微维氏硬度计等设备,研究了不同Nb含量的Fe-Cr-B-C合金的物相、微观组织和力学性能的变化规律。通过Origin函数模拟、EXPGUI结构精修、Image-ProPlus图像分析和Image J二值化阈值处理等软件获得一些研究结果。结果表明,含铌高硼铸铁初晶基体相主要是马氏体组织,硼碳化物形成网状共晶组织。合金由α-Fe、Fe_(2)B、NbC等物相组成。随着Nb含量增加,硬度由65.8 HRC下降到52.2 HRC,弯曲强度由1304.97 MPa提高到1731.45 MPa,断裂韧性由29.76 MPa·m1/2提高到32.89 MPa·m1/2。NbC型硼碳化合物分布在共晶组织中,造成网状共晶出现断网现象,且降低了基体碳含量。故宏观硬度、强度和韧性的变化与Nb元素含量存在一定的关系。

β相控制法改进黄铜合金的热加工性能

通过立式半连铸方法制备了Cu-40Zn-1Pb-0.15Fe-0.03Ni双相黄铜合金,针对热轧开裂问题,采用Gleeble-3500热模拟机对合金进行圆柱体压缩试验和扁平压缩试验,研究了双相黄铜合金在变形温度为600~780℃及应变速率为0.01~10 s^(-1)的条件下的热变形行为和热轧工艺性能。通过应力-应变曲线分析得到了合金的本构方程,计算绘制了热加工图,分析了热机械加工(TMP)诱导的α-β相变对α和β相的形成和铅颗粒分布的影响,利用热加工图结合显微组织确定了合金的热变形的流变失稳区和最佳变形参数。结果表明:双相黄铜合金加工过程主要存在两个失稳区:1)变形温度为670~710℃,应变速率为2.5~10 s^(-1)的区域;2)变形温度为750~780℃,应变速率为5~10 s^(-1)的区域。在较低温区(690℃以下),合金为α+β双相组织,且随着温度升高合金中β相占比逐渐增大、α相逐渐球化;在中温区(700~750℃),合金基本为β单相组织,利于热轧加工;在高温区(750℃以上),从β相组织的晶界处生长出针状α相,容易造成合金热轧开裂。

Effect of B_2O_3 on microstructures and mechanical properties of cast Mg-Al-Ti-B alloys

The Mg-Al-Ti-B alloy prepared by mechanical alloying is poor in microstructural uniformity and compactness. In order to improve the microstructural uniformity and compactness of Mg-Al-Ti-B alloy and thus to improve the mechanical properties, effect of B2O3 on microstructure and mechanical properties of cast Mg-9Al-6Ti alloy was studied by optical microscopy, scanning electron microscopy, X-ray diffraction and mechanical property testing. The results show that due to the addition of B2O3, the average grain size of Mg-Al-Ti-B alloys is refined to 12μm, dispersed Ti phases completely disappear, the amount of precipitation phase Mgl7All2 is reduced and TiA13 is increased, and new phases MgB6 and TiaB4 are precipitated. The average hardness, average tensile strength, yield strength and elongation of the alloy are HV 77.1, 171.2 MPa, 113.5 MPa and 5.2%, respectively.

锑黄铜组织与性能的研究

采用熔铸、轧制的方法生产出了以锑代铅的环保型无铅易切削黄铜板材。通过SEM、OM对锑黄铜的微观组织进行了分析,并对其力学性能进行了研究。结果表明,锑主要以金属间化合物存在于β相以及α和β相的相界处;主要力学性能与HPb59-1铅黄铜相当,锑黄铜的抗拉强度为461.72MPa,屈服强度为213.3MPa,伸长率为15.67%。研制的锑黄铜替代铅黄铜,具有可行性。

含Bi易切削黄铜的研究

无铅黄铜是以Bi来代替Pb,同时加入一定量的Mn元素来提高其性能。通过X衍射和扫描电镜分析发现,Bi呈薄膜和颗粒状存在于α相的晶界以及α和β的相界上;Mn部分固溶到基体中,起到固溶强化的作用。无论从力学性能上,还是从环保的角度,含Bi易切削黄铜完全可以取代HPb59-1。

添加硼对铸造Ti-46．5Al-8Nb合金组织和性能的影响

全片层Ti-46．5Al-8Nb合金中添加硼(≤0．7％,原子分数)的显微组织观察表明,细化组织的临界硼含量约为0．5％(原子分数)．细化机制与凝固前沿硼产生了附加的成分过冷和硼化物钉扎晶界双重机制有关．由于硼减小了片层形成所需要的过冷度,片层间距随硼含量的增加而增加,片层间距λ与晶粒尺寸d-1／2符合线性关系．添加硼的Ti-46．5Al-8Nb合金的α2相体积分数越高,硬度也越高．合金的断裂强度和延伸率随硼含量增加而增加．室温断裂强度与晶粒尺寸符合Hall-Petch关系．

微量元素硼对碳钢、不锈钢组织与性能的影响

综述了近年来国内外有关硼在钢中作用的研究进展,重点总结了微量硼在钢中的存在形式,硼在碳钢和不锈钢中的作用机理以及对其组织和性能的影响,以期对硼合金化钢的研究、生产和应用提供帮助。