Interfacial structure and mechanical properties of hot-roll bonded joints between titanium alloy and stainless steel using niobium interlayer

The hot-roll bonding was carried out in vacuum between titanium alloy and stainless steel using niobium interlayer. The interfacial structure and mechanical properties were analyzed. The results show that the plasticity of bonded joint is improved significantly. When the bonding temperature is 800 °C or 900 °C, there is not intermetallic layer at the interface between stainless steel and niobium. When the bonding temperature is 1000 °C or 1050 °C, Fe-Nb intermetallic layer forms at the interface. When the bonding temperature is 1050 °C, cracking occurs between stainless steel and intermetallic layer. The maximum strength of -417.5 MPa is obtained at the bonding temperature of 900 °C, the reduction of 25% and the rolling speed of 38 mm/s, and the tensile specimen fractures in the niobium interlayer with plastic fracture characteristics. When the hot-roll bonded transition joints were TIG welded with titanium alloy and stainless steel respectively, the tensile strength of the transition joints after TIG welding is -410.3 MPa, and the specimen fractures in the niobium interlayer.

Effect of intermetallic compounds on heat resistance of hot roll bonded titanium alloy-stainless steel transition joint

The effect of intermetallic compounds on the heat resistance of transition joint was investigated. The experiment of post-weld heat treatment for the hot roll bonded titanium alloy-stainless steel joint using nickels interlayer was carried out, and the interface microstructure evolution due to heat treatment was presented. There was not found significant interdiffusion at stainless steel/nickel interface, when the specimens were heat treated in the temperature range of 600-800 °C for 10 and 30 min, while micro-cracks occurred at the stainless steel/nickel interface heat treated at 700 °C for 30 min. The thickness of intermetallic layers at nickel/titanium alloy interface increased at 600 °C, and micro-cracks occurred at 700 and 800 °C. The micro-cracks occurred between intermetallic layers or between intermetallic layer and nickel interlayer as well. The tensile strength of the transition joint decreased with the increase of heat treatment temperature or holding time.

Development of Tailored Structure and Tensile Properties of Thermomechanical Treated Micro Alloyed Low Carbon Dual Phase Steel

Direct hot rolled dual phase steel production represents a challenging route, compared with cold rolled and intercritical annealing process, due to complex and sophisticated control of the hot strip mill processing parameters. Instead, high technology compact slab production plant offers economic advantages, adequate control and prompt use of the advanced thermomechanical controlled rolling. The current work aims to obtain different structures and tensile properties by physical simulation of direct hot rolled niobium micro alloyed dual phase low carbon steel by varying the metallurgical temperatures of hot strip mill plant. This starts with adaptation of the chemical analysis of a low carbon content to fall far from the undesired peritectic region to avoid slab cracking during casting. Thermodynamic and kinetics calculations by Thermo-Calc 2020 and JMat pro software are used to define the transformation’s temperatures Ae1 and Ae3 as well as processing temperatures;namely of reheating, finishing rolling, step cooling and coiling temperatures. The results show that the increase of finishing rolling temperature from 780°C to 840°C or decreasing either of step cooling duration at ferrite bay from 7 to 4 seconds, enhances yield and tensile strengths, all due to more martensite volume fraction formation. The yield and tensile strengths also increase with decreasing coiling temperature from 330°C to 180°C, which is explained due to the increase of dislocation densities resulted from the sudden shape change during martensite formation at the lower coiling temperature in additional to the self-tempering of martensite formed at higher coiling temperatures which soften the dual phase steel.

Effect of Nb content on strength of Nb micro-alloyed steels

Microstructures and properties of three Nb micro-alloyed steels were studied through hot rolling experiment. The result indicates that the ferrite grain size （dF ） decreases with increasing Nb content （Nb）, and the bainite fraction （fB） increases with increasing Nb content （Nb）. The effect of ferrite grain size （dF） on yield strength （δy） is related to Nb content （Nb）, and the effect of bainite fraction （fB） on yield strength （δy） is unrelated to Nb content （Nb）. Modelling of yield strength （δy） for Nb micro-alloyed steels with high accuracy has been built up with Nb content （Nb） and bainite fraction （fB） taken into account as new parameters, and formulas for ferrite grain size （dF ） and bainite fraction （fB） vs Nb content （Nb） have also been established under the experiment conditions. The research results could provide instructions for industrial productions.

热处理温度对0Cr21Al6热轧板材组织结构及性能的影响

为提高热轧态0Cr21A16合金板材的组织均匀性和塑性,以改善其高温性能及冷加工特性,分析研究了不同温度的热处理试验及组织性能。采用光学显微镜、X射线衍射仪、Gleeble高温热拉伸实验、扫描电镜和纳米压痕仪等研究了热处理前后0Cr21Al6合金板材的显微组织和力学性能。结果表明,通过热处理的方式改善0Cr21Al6合金板材的组织均匀性,在960℃保温6 min 40 s后快速冷却,晶粒平均尺寸为42μm,整体的晶粒尺寸相对于940、980、1000、1020℃热处理后较为均匀、细小,硬度和塑性达到最佳匹配,断裂韧度KIC在960℃处理下达到最佳,拥有最佳的综合性能,可有效避免生产过程中材料的脆性断裂问题。另外Gleeble实验显示1000℃以上的热处理温度不再适合于热加工。

Role of Microstructural Constituents on Surface Crack Formation During Hot Rolling of Standard and Low Nickel Austenitic Stainless Steels

The effect of alloy segregation and delta （δ） ferrite contents on surface cracking of three standard （i.e. AISI 304L, AISI 310S and AISI 321） and two low nickel （i.e. LNi-1 and LNi-0.3） austenitic stainless steels （ASS） during hot roiling was investigated using optical microscopy （OM）, automatic image analyzer, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDX） and electron probe micro analyzer （EPMA）. It was observed that the amount of 6-ferrite varied among different grades and also distributed heterogeneously across the width of the steel plates. In general, low nickel ASS showed higher amount of 6-ferrite compared to the standard ASS grades. The tendency to surface cracking during hot rolling gradually increased with increasing 6-ferrite content. Interestingly, carbon and nitrogen exerted maximum effect on 6-ferrite formation. The higher carbon and nitrogen content in the steel decreased 6-ferMte content. In addition, the segregation of Cu and Mn plays significant role in low nickel ASS and Ni-Cr in case of standard ASS has profound effect on surface cracking of the steel plates. A possible cause of surface crack formation/origination in steel plates during hot rolling was discussed.

Effects of Al contents on microstructure and properties of hot-dip Zn-Al alloy coatings on hydrogen reduced hot-rolled steel without acid pickling

A new hot-dip galvanizing method was employed on hot-rolled low carbon steel.The effects of Al contents on microstructure,micro-hardness and corrosion resistance of Zn-Al alloy coatings were systematically investigated.Phase composition,microstructure and element distribution in Zn-Al alloy coatings were analyzed using X-ray diffraction（XRD）and electron probe micro analysis（EPMA）,respectively.It is found that Al content（0.6-6.0 wt.%）in galvanizing zinc affects surface quality and adhesion between coatings and matrix in the newly developed method.In addition,with increasing Al content,micro-hardness significantly increased due to the increase in Zn-Al eutectoid phases.Potentiodynamic polarization and electrochemical impedance spectroscopy（EIS）also revealed that increase in Al plays a noticeable role in improving the corrosion resistance of Zn-Al alloy coatings.

SUS441不锈钢/Al金属间化合物微叠层复合板的界面结构与力学性能

采用“表面预处理—交替层叠—热轧复合—热处理”的工艺流程制备了SUS441不锈钢/Al金属间化合物微叠层复合板。利用光学显微镜、X射线衍射仪、扫描电子显微镜等检测与表征方法研究了热处理温度对复合板界面形貌、微观组织、物相组成、维氏硬度、拉伸性能的影响。结果表明:复合板界面结合良好;热处理后,固–液反应界面氧化严重,易导致界面分层而开裂;固–固、固–半固、固–液热处理后,金属间化合物层由均匀层和两相层组成,均匀层的物相组成为Fe_(2)A_(15),两相层的物相组成为Fe_(4)Al_(13)和Al_(13)Cr_(2),且两相层具有韧性特征,固–半固反应所得到的复合板的综合力学性能最佳。

安钢低合金高强钢CR340LA的生产实践

为了使低合金高强钢在强度、韧性、深冲性能和焊接性能等方面满足客户要求,需采用热轧方式对其进行处理。经过不断地探索和实践,对冷轧高强钢CR340LA热轧生产技术条件进行了改进,克服了生产技术上的难点,轧制出了性能指标符合要求的低合金高强钢CR340LA。

结构用铌钒低合金高强度热轧型钢标准浅析

本文针对结构用铌钒低合金高强度热轧型钢的技术条件和尺寸标准进行了全面解析。文章首先介绍了钢结构建筑在国内的发展现状以及面临的挑战,进而阐述了《结构用铌钒低合金高强度热轧型钢》标准的制定背景和重要性。在技术条件解析部分,本文详细分析了该型钢的化学成分、力学性能指标、尺寸规格及其允许偏差,并对不同钢级和质量等级的要求进行了明确。此外,本文还重点探讨了铌、钒、钛等微合金化元素在提高型钢性能方面的作用,以及这些元素在焊接热影响区性能提升中的重要性。

连轧大规格合金芯棒钢三维热力耦合模拟仿真

采用 MSC.Marc/ Autoforge3.1sp1三维大变形热力耦合弹塑性有限元软件及其接触分析技术 ,在分析现场工艺设备条件给出准确边界条件的基础上 ,对2 0 0 m m大规格合金圆钢在 6 VH钢坯连轧机组上两道次热连轧过程进行了三维模拟仿真 ,准确地计算、分析、校核了轧件的应力场、温度场和轧制力、轧制力矩等重要参数的分布值 ,以此对轧辊强度、孔型尺寸及相关的轧制工艺参数进行分析、校核、修正和改进 。

热轧Nb-Ti钢静态再结晶组织演变及模型研究

在热模拟实验的基础上,对Nb-Ti微合金钢热轧中微观组织的变化进行了分析,介绍了影响组织演变的主要因素及模拟实验方法,对静态再结晶行为和组织演变过程的数学模型进行了研究。研究表明,预报结果与实验结果吻合较好,这种理论处理方法可用来模拟静态再结晶行为。

700MPa级超高强度汽车大梁用钢研究与开发

根据超高强度汽车大梁钢的特点和要求,介绍了莱钢开发700MPa级大梁钢的Nb-Ti微合金化成分设计及控轧控冷技术,以及该钢的组织形态和析出相分布与形貌。经检测,产品的力学性能和成型性能良好,均满足制造汽车大梁的要求。

Ti微合金化700MPa级汽车大梁钢的研究

通过实验，采用低成本Ti微合金元素进行强化，获得了抗拉强度745～760MPa，下屈服强度640～655MPa，伸长率为23．0％～23．5％的热轧钢板。同时，通过调整热轧工艺，获得了终冷温度与热轧板强度的关系。此外，研究了轧制过程不同阶段析出相的种类、分布以及析出量的变化情况。结果表明，钢板屈服强度、抗拉强度与其终冷温度基本呈线性关系，随终冷温度的降低，屈服强度和抗拉强度均明显提高。析出相的定量分析结果表明，在粗轧结束时，Ti的析出率接近50％，在精轧结束时，Ti的析出率接近60％。在700℃等温卷取后，Ti的析出率超过95％。降低卷取温度到650、600℃时，Ti的析出率分别降低到87．5％、75．2％。如果700℃终冷后采用空冷方式冷却，Ti的析出率最低，降低到只有63．3％，与精轧结束时析出量相近。

采用铜和铌复合中间层的钛合金与不锈钢的真空热轧焊接

采用铜(纯铜及含稀土元素钇的铜)+铌的复合中间层进行了钛合金与不锈钢板的真空热轧焊接试验,测试了接头拉伸强度,并利用金相显微镜、扫描电镜、XRD、能谱对连接界面的微观结构、断口形貌及中间层材料铜的组织进行了分析,结果表明,连接界面结合良好,无未焊合或开裂处;焊后未生成金属间化合物,在铌-钛合金界面处存在一厚度约为2.5μm的过渡层,而铜-不锈钢、铌-铜界面的过渡层厚度约为1.9μm;焊后铜晶界处产生了空洞,断口形貌显示出现了沿晶开裂的现象;稀土元素r的加入可以细化铜的晶粒,在相同的焊接工艺参数时含有稀土元素Y的铜层中未形成空洞,随着钇在铜中的质量百分含量由0.01%增加到0.02%,细化晶粒的效果更加显著,与采用纯铜作为中间层材料时的抗拉强度(326.9 MPa)相比分别提高了51.3MPa(铜中含钇0.01%,质量分数)和61.7 MPa(铜中含钇0.02%质量分数)。

两相区热轧对低碳合金钢板组织性能的影响

为了提高低碳合金钢板的强度,进行了终轧温度为710℃的(α+γ)两相区和γ单相区的热轧对比试验。结果表明:与终轧温度为800℃奥氏体单相区轧制的钢板相比,采用终轧温度为710℃的两相区热轧工艺所得到的钢板强度并没有增加;而且,(α+γ)两相区轧制条件下所得到的多边形铁素体组织具有二个特征,一是呈现仿晶界型铁素体形貌,二是部分铁素体晶粒沿轧制方向被拉长,一定程度上出现织构现象,但不十分明显。

微合金钢碳氮化物析出的热力学仿真

建立热连轧过程中复合微合金钢碳氮化物析出的热力学模型,考虑碳氮化物和AlN的相互作用。针对该模型求解变量多、方程非线性、初始条件难确定等问题,采用耦合问题特征的牛顿拉夫森数值求解算法,确定不同成分下的碳氮化物和AlN的析出开始温度与析出顺序,获得奥氏体相中各元素平衡成分、碳氮化物析出成分及质量分数等随轧制温度的变化规律。对某轧钢厂生产的微合金钢进行仿真分析,模型计算结果符合冶金机理,对钢材组织性能进行有效的控制具有重要的指导意义。

TC4钛合金与0Cr18Ni10Ti不锈钢真空热轧连接

利用真空热轧焊接的方法实现了镍作中间层材料的TC4钛合金与0Cr18Ni10Ti不锈钢板的连接。通过扫描电镜、能谱、X射线衍射等方法对连接界面的微观结构进行了描述,测试了Ni-TC4连接界面的金属间化合物层的成分,研究了焊接温度对焊接接头连接强度的影响规律。结果表明,金属间化合物层的厚度随着焊接温度的升高而增大,接头连接强度随之降低,当焊接温度为760℃、压缩率为20%、轧制速度为38mm/s时焊接接头的抗拉强度达到最高值452.1MPa。拉伸试样断口均呈脆性断裂特征,XRD分析表明,在拉伸试样断口处存在多种Ni-Ti的金属间化合物。

HSLA钢热轧板带组织性能预测数学模型及软件开发

以物理冶金学原理为理论基础,研究了HSLA钢热轧板带生产过程中发生的再结晶、析出、相变等各种冶金学现象的数学模型·对影响板带组织性能的参数进行定量计算,开发出符合实际生产工艺要求的组织性能预测软件,对轧后板带性能进行预测·计算结果与实际测量结果比较,吻合较好·使用该软件对轧后产品的组织性能进行预测,可以节省大量的人力物力,此外该软件操作方便,界面友好,易于维护,因此有广阔的应用前景·

钛合金与不锈钢真空热轧连接界面微观结构及性能

完成了TC4钛合金与304不锈钢的直接真空热轧连接,连接界面微观结构的研究结果表明,当压缩率20%,轧制速度0.038 m/s时,轧制温度800℃时连接界面存在未连接的孔洞,轧制温度850℃时连接界面形成了三层金属间化合物层,其中富铬层硬度约为母材钛合金硬度的2倍,轧制温度900℃时连接界面产生了金属间化合物层之间或金属间化合物层与母材之间的开裂现象.轧制温度850℃时接头抗拉强度最高,可达77.33 MPa.拉伸试样均为脆性断裂,不锈钢一侧的断口存在γFe,Cr,Fe_2Ti,σ和Cr_2Ti.