Effects of overaging temperature on the microstructure and properties of 600 MPa cold-rolled dual-phase steel

C–Mn steels prepared by annealing at 800°C for 120 s and overaging at 250–400°C were subjected to pre-straining (2%) and baking treatments (170°C for 20 min) to measure their bake-hardening (BH2) values. The effects of overaging temperature on the microstructure, mechanical properties, and BH2 behavior of 600 MPa cold-rolled dual-phase (DP) steel were investigated by optical microscopy, scanning electron microscopy, and tensile tests. The results indicated that the martensite morphology exhibited less variation when the DP steel was overaged at 250–350°C. However, when the DP steel was overaged at 400°C, numerous non-martensite and carbide particles formed and yield-point elongation was observed in the tensile curve. When the overaging temperature was increased from 250 to 400°C, the yield strength increased from 272 to 317 MPa, the tensile strength decreased from 643 to 574 MPa, and the elongation increased from 27.8% to 30.6%. Furthermore, with an increase in overaging temperature from 250 to 400°C, the BH2 value initially increases and then decreases. The maximum BH2 value of 83 MPa was observed for the specimen overaged at 350°C.     

Effects of pre-strain and baking parameters on the microstructure and bake-hardening behavior of dual-phase steel

In a typical process, C-Mn steel was annealed at 800°C for 180 s, and then cooled rapidly to obtain the ferrite-martensite microstructure. After pre-straining, the specimens were baked and the corresponding bake-hardening (BH) values were determined as a function of pre-strain, baking temperature, and baking time. The influences of pre-strain, baking temperature and baking time on the microstructure evolution and bake-hardening behavior of the dual-phase steel were investigated systematically. It was found that the BH value apparently increased with an increase in pre-strain in the range from 0 to 1%; however, increasing pre-strain from 1% to 8% led to a decrease in the BH value. Furthermore, an increase in baking temperature favored a gradual improvement in the BH value because of the formation of Cottrell atmosphere and the precipitation of carbides in both the ferrite and martensite phases. The BH value reached a maximum of 110 MPa at a baking temperature of 300°C. Moreover, the BH value enhanced significantly with increasing baking time from 10 to 100 min.     

Effect of continuous annealing temperature on microstructure and properties of ferritic rolled interstitial-free steel

In this report, the microstructure, mechanical properties, and textures of warm rolled interstitial-free steel annealed at four different temperatures (730, 760, 790, and 820℃) were studied. The overall structural features of specimens were investigated by optical microscopy, and the textures were measured by X-ray diffraction (XRD). Nano-sized precipitates were then observed by a transmission electron microscope (TEM) on carbon extraction replicas. According to the results, with increased annealing temperatures, the ferrite grains grew; in addition, the sizes of Ti₄C₂S₂ and TiC precipitates also increased. Additionally, the sizes of TiN and TiS precipitates slightly changed. When the annealing temperature increased from 730 to 820℃, the yield strength (YS) and the ultimate tensile strength (UTS) showed a decreasing trend. Meanwhile, elongation and the strain harden exponent (n value) increased to 49.6% and 0.34, respectively. By comparing textures annealed at different temperatures, the intensity of {111} texture annealed at 820℃ was the largest, while the difference between the intensity of {111}<110> and {111}<112> was the smallest when the annealing temperature was 820℃. Therefore, the plastic strain ratio (r value) annealed at 820℃ was the highest.     

大变形轧制超细晶TWIP钢的组织及性能研究

通过大变形异步-同步轧制及随后600 ℃和700 ℃退火处理,成功制备了超细晶高锰TWIP钢,并研究了退火处理对大变形TWIP钢的组织和性能的影响.研究结果表明:经96%异步-同步大变形轧制后,材料组织显著细化,抗拉强度从621 MPa大幅提升至2 050 MPa; 经过600 ℃退火后,大变形轧制TWIP钢的组织基本完成了再结晶,材料的平均晶粒尺寸约为500 nm,抗拉强度1 079 MPa,延伸率达到了29%; 而经过700 ℃退火后,大变形TWIP钢的组织发生了完全再结晶,平均晶粒尺寸约为600 nm,抗拉强度达到了1 101 MPa,延伸率达到了54%.退火后的组织中存在大量的层错、位错胞等亚结构.相对于大变形轧制态和600 ℃退火态,700 ℃退火态的超细晶TWIP钢的优异的综合力学性能,主要源于孪晶诱发塑性变形机制及合金较低的层错能.     

Effect of continuous induction annealing on the microstructure and mechanical properties of copper-clad aluminum flat bars

Copper-clad aluminum (CCA) flat bars produced by the continuous casting–rolling process were subjected to continuous induction heating annealing (CIHA), and the effects of induction heating temperature and holding time on the microstructure, interface, and mechanical properties of the flat bars were investigated. The results showed that complete recrystallization of the copper sheath occurred under CIHA at 460°C for 5 s, 480°C for 3 s, or 500°C for 1 s and that the average grain size in the copper sheath was approximately 10.0 μm. In the case of specimens subjected to CIHA at 460–500°C for longer than 1 s, complete recrystallization occurred in the aluminum core. In the case of CIHA at 460–500°C for 1–5 s, a continuous interfacial layer with a thickness of 2.5–5.5 μm formed and the thickness mainly increased with increasing annealing temperature. After CIHA, the interfacial layer consisted primarily of a Cu₉Al₄ layer and a CuAl₂ layer; the average interface shear strength of the CCA flat bars treated by CIHA at 460–500°C for 1–5 s was 45–52 MPa. After full softening annealing, the hardness values of the copper sheath and the aluminum core were HV 65 and HV 24, respectively, and the hardness along the cross section of the CCA flat bar was uniform.     

热轧工艺对409L铁素体不锈钢深冲性的影响

对含有单一柱状晶的409L铁素体不锈钢连铸坯,采用不同终轧温度的热轧工艺,由常规热轧转变为温轧,再经过相同后续工艺;较低终轧温度的成品获得了较高rm值和较低△r值.终轧温度的降低使组织演变发生变化:热轧和冷轧组织中晶界和晶内剪切带增多,变形组织被细化、硬化,尤其是中心层附近的粗大带状晶粒;两者的增多又增加了退火过程中的...     

超纯铁素体不锈钢的组织、织构及深拉伸性能

重点研究了冷轧压下率对冷轧、再结晶织构的影响.结果表明:当终轧温度为750℃时,热轧带退火后以{111}再结晶织构为主.随着冷轧压下量的增加,γ织构减弱,α织构增强,{111}再结晶织构明显增强.当冷轧压下率为84%时,{111}再结晶组分的体积分数达到64.5%,退火板的平均塑性应变比(-R)高达1.69,平面各向异性(ΔR)仅为-0.17,深拉伸性能优良.     

Experimental study on Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the ferrite region

A Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied. Subsequent cold rolling and continuous annealing processes were also conducted. The results show that microstructures of ultra-low carbon bake hardening hot strips at room temperature are basically irregular polygonal ferrites. The yield strength, ultimate tensile strength, n value, and r value of the No.2 specimen hot-rolled in the ferrite region with lubrication are 243 MPa, 364 MPa, 0.29, and 1.74, respectively, which are similar to those of the No.1 specimen hot-roiled in the conventional austenite region. The elongation rate and bake hardening value of No.2 specimen are 51% and 49.4 MPa, respectively, which are greater than those of No. 1 specimen. The No.2 specimen hot-rolled in the ferrite region with lubrication exhibits good mechanical properties and relatively excellent baking hardening performance. Therefore, the hot rolling experiment of Ti+Nb bearing ultra-low carbon bake hardening steel in the ferrite region with lubrication is feasible and can be considered in the future industrial trial production.     

两相区退火温度对高铝低硅TRIP 钢组织性能的影响

对高铝低硅TRIP钢进行两相区退火,通过分析退火后实验钢的微观结构和力学性能,建立了加工硬化指数与相组成的关系,探讨了残余奥氏体稳定性对力学性能的影响.结果表明,随着两相区退火温度的升高,实验钢中贝氏体含量逐渐降低,残余奥氏体含量先增大后降低,并在930℃退火时达到最大.随着两相区退火温度的升高,实验钢的抗拉强度逐渐降低,延伸率先增大后降低,930℃退火时抗拉强度为665MPa,延伸率达到最大,为30%,强塑积约为20GPa·%.EBSD统计和拉伸试验的结果表明,两相区退火温度为930℃时,残余奥氏体稳定性适中,从而在拉伸过程中不断地提供加工硬化,推迟颈缩的发生,大幅度提高塑性.     

热轧工艺中加热温度对IF钢组织性能的影响

选取Ti-Nb-IF钢热轧工艺中的加热温度为影响因素,采用显微观察、TEM二相粒子分析、织构分析等实验分析手段,研究了1 140℃和1 214℃两种热轧加热温度制备的Ti-Nb-IF钢样品在随后的冷轧、退火和平整过程中显微组织演变和织构演变特征的影响及最终产品的力学性能.结果表明,低温加热有利于IF钢屈强比的降低及深冲性能的提高,加热温度为1 140℃比1 214℃,其屈服强度可降低30 MPa,塑性应变比可提高0.16.其主要原因为低温加热工艺保障IF钢热轧后产生粗大的二相粒子和细小铁素体晶粒,在随后的冷轧和退火处理过程中产生分布均匀和强的γ再结晶织构.     

应用铁素体区热轧工艺开发超低碳热轧深冲板

研究了铁素体轧制工艺条件对一种Ti-IF钢的性能,特别是深冲性能的影响.采用铁素体区润滑轧制和高温卷取,r值最高为1.38,延伸率达到50%以上.而奥氏体轧制条件下r值低于1.0.织构分析证实在润滑轧制条件下,强的{111}再结晶织构沿厚度方向较均匀分布,剪切织构较弱,而在无润滑轧制条件下,{111}再结晶织构很弱,并且形成了较强的{110}剪切织构.为获得具有良好深冲性能的热轧板,要求加热温度在1 100-1 150℃之间,终轧温度在750-800℃之间, 卷取温度大于650℃.     

对86CrMoV7大型冷轧辊预备热处理工艺的研究

对86CrMoV7冷轧辊用钢进行了锻后正火、等温球化退火、去H退火的试验研究，研究了轧辊的预备热 处理工艺对冷轧工作辊组织的影响，加热温度和时间对组织的影响。结果表明，适宜的预备热处理工艺为：950 ± 10℃正火，等温球化退火温度790±10℃，去氢退火温度660～690℃。     

铁素体区轧制工艺对IF钢织构及深冲性能的影响

研究了不同铁素体区热轧压下量和终轧温度下一种Ti-IF钢的冷轧和退火后性能和织构的特点.结果表明,较低的铁素体轧制温度和较高的铁素体区压下量时,IF钢具有更高的深冲性能、相对较高的强度、延伸率以及织构强度.IF钢的冷轧织构类型为典型的部分〈110〉∥RD纤维和〈111〉∥ND纤维;再结晶退火后,〈110〉∥RD纤维织构强度明显降低,转变为〈111〉∥ND再结晶纤维织构,因此〈111〉∥ND织构强度大幅度增加.其中终轧温度为750℃,热轧压下率为80%的试样的〈111〉∥ND再结晶纤维织构的强度最高.     

初始组织对钒微合金化TRIP钢组织性能的影响

对一种低硅含磷和钒的TRIP钢进行热轧、冷轧及连续退火,研究不同热轧初始组织对组织特征与力学性能的影响.通过不同工艺得到两种不同的热轧初始组织:F+P钢;F+B钢.在相同的冷轧连续退火工艺条件下,初始组织为F+B钢相比较F+P钢,组织中含有较多体积分数的贝氏体和残余奥氏体组织,而且残余奥氏体尺寸更为细小,分布更为弥散,屈服强度和抗拉强度较高,但延伸率、n值和r值略低.初始组织为F+B钢的抗拉强度可达980MPa,强塑积为21 952MPa.%.     

退火时间对IF深冲钢板再结晶织构的影响

借助于三维取向分布函数(ODF)分析,研究了IF深冲钢板在750℃和800℃退火时不同保温时间对其再结晶织构的影响.实验结果表明,750℃和800℃退火试样的再结晶γ纤维织构({111}〈uvw〉)的强度随退火时间的延长而逐渐增强,再结晶α纤维织构中从{001}〈110〉至{112}〈110〉的强度随着退火保温时间的延长而下降然后再回升.同时800℃退火试样的γ纤维织构的强度明显高于750℃退火试样的γ纤维织构的强度,与之对应800℃退火试样的α纤维织构的强度显著低于750℃退火试样的α纤维织构的强度.     

Grain boundary segregation of minor arsenic and nitrogen at elevated temperatures in a microalloyed steel

Auger electron spectroscopy (AES) was used to investigate the grain boundary segregation of arsenic and nitrogen in a kind of microalloyed steel produced by a compact strip production (CSP) technology at 950 to 1100℃, which are similar to the hot working temperature of the steel on a CSP production line. It was discovered that arsenic segregated on grain boundaries when the steel was annealed at 950℃ for 2 h. When the annealing temperature increased to 1100℃, arsenic was also found to have segregated on grain boundaries in the early annealing stage, for instance, within the first 5 min annealing time. However, if the holding time of the steel at this temperature increased to 2 h, arsenic diffused away from grain boundaries into the matrix again. Nitrogen was not found to have segregated on grain boundaries when the steel was annealed at a relatively low temperature, such as 950℃. But when the annealing temperature increased to 1100℃, nitrogen was detected to have segregated at grain boundaries in the steel.     

磁场作用下取向硅钢薄带的再结晶织构

对由成品取向硅钢片经对称和非对称轧制获得的薄带进行普通与磁场退火,考察了磁场及非对称轧制对取向硅钢薄带初次再结晶织构的影响·发现磁场退火显著增加对称轧制薄带的再结晶Goss织构组分,减少非对称轧制薄带的Goss织构组分;非对称轧制在普通退火时增加Goss织构组分,而在磁场退火时使之明显减少·磁场的作用可以通过磁晶各向异性能和磁有序对晶界迁移的影响来解释·     

SAF 2205双相不锈钢织构与冲压特性

研究SAF 2205双相不锈钢冷轧退火板的冲压特性以及冷轧和退火织构对其冲压性能的影响.实验钢冷轧退火板表现出较差的深冲性能和明显的45°制耳,其r平均值和Δr值分别为0.7和-0.27,这主要与其在冷轧及退火后形成的织构有关. ODF图显示,退火后SAF 2205双相不锈钢中铁素体相未形成γ纤维再结晶织构,仍然为分散的α纤维织构.实验钢中铁素体相的织构强度明显高于奥氏体相,其对钢板成形性的影响更显著,即其各种〈110〉退火织构组分均不利于实验钢r平均值的提高,并且使得Δr<0.此外,奥氏体相的{110}〈001〉织构也对钢板成形性能产生一定程度的影响.     

超快冷工艺下780MPa级工程机械用钢的组织与性能

对780MPa级工程机械用钢进行了现场批量生产试制,对其组织与性能进行了研究.通过合理的成分设计,采用控制轧制和超快冷+层流冷却的两阶段冷却路径控制,获得了良好的组织与性能.结果表明:终轧后采用超快冷+层流冷却工艺,超快冷的出口温度在650℃,卷取温度在570℃,试验钢的屈服强度大于685 MPa,抗拉强度大于785 MPa,并具有良好的冲击性能、成形性能及焊接性能.试验钢的组织为铁素体+少量珠光体,同时,在铁素体的基体上,存在大量10nm左右的弥散析出或相间析出(Nb,Ti)(C,N),有效提高了试验钢的强度.     

Influence of sintering temperature on the thermoelectric properties of Ba8Ga16Si30 clathrate treated by spark plasma sintering

A series of Ba8Ga16Si30 clathrate samples were prepared by arc melting, ball milling, acid washing, and spark plasma sintering (SPS). X-ray diffraction analysis revealed that the lattice of the Ba8Ga16Si30 samples expanded as the SPS temperature was increased from 400 to 750°C. Lattice contraction recurred when the SPS temperature was further increased in the range of 750–1000°C. This phenomenon can be explained by the variation of Ga content in the lattice. The thermoelectric figure of the merit ZT value of clathrates increased with the increase in SPS temperature and reached a maximum when the sample was subjected to SPS at 800°C. A further increase in SPS temperature did not contribute to the improvement of ZT. The variation of the lattice parameter a vs. SPS temperature T was similar to the variation ob-served in the ZT–T curve.