Development of Ti–V–Mo Complex Microalloyed Hot-Rolled 900-MPa-Grade High-Strength Steel

A new Ti–V–Mo complex microalloyed hot-rolled high-strength steel sheet was developed by controlling a thermo-mechanical controlled processing(TMCP) schedule, in particular with variants in coiling temperature. The effects of coiling temperature(CT) on various hardening mechanisms and mechanical properties of Ti–V–Mo complex microalloyed high-strength low-alloy steels were investigated. The results revealed that the steels are mainly strengthened by a combined effect of ferrite grain refinement hardening and precipitation hardening. The variation in simulated coiling temperature causes a significant difference in strength, which is mainly attributed to different precipitation hardening increment contributions. When the CT is 600 C, the experimental steel has the best mechanical properties: ultimate tensile strength(UTS) 1000 MPa, yield strength(YS) 955 MPa and elongation(EL) 17%. Moreover, about 82 wt% of the total precipitates are nano-sized carbide particles with diameter of 1–10 nm, which is randomly dispersed in the ferrite matrix.The nano-sized carbide particles led to a strong precipitation hardening increment up to 310 MPa.     

Enhanced mechanical properties of Mg-Gd-Y-Zr casting via friction stir processing

Mg-10Gd-3Y-0.5Zr casting was subjected to friction stir processing (FSP) at a tool rotation rate of 800 rpm and a traverse speed of 50 mm/min. FSP resulted in the fundamental dissolution of the coarse network-like β-Mg₅(Gd,Y) phase and remarkable grain refinement (∼6.1 μm), thereby significantly improving the strength and ductility of the casting. Post-FSP aging resulted in the precipitation of fine β′′ and β′ particles in a fine-grained magnesium matrix, producing an ultimate tensile strength of 439 MPa and a yield strength of 330 MPa. FSP combined with aging is a simple and effective approach to enhancing the mechanical properties of Mg-Gd-Y-Zr casting.     

汽车用800 MPa级冷轧低合金高强钢的研制

采用C-Si-Mn-Nb-Ti-Cr-Mo合金成分体系,全流程控制关键生产工艺参数,研发出具有良好塑性和成形性的800 MPa级冷轧低合金高强钢。结果表明,试验钢的显微组织由铁素体、马氏体和少量贝氏体组成,铁素体基体中有弥散分布的第二相粒子和碳化物沉淀相。试验钢的屈服强度在800 MPa以上,断后伸长率大于10.5%,抗拉强度和屈服强度相差小于35 MPa,扩孔率在56.5%以上,180°冷弯角度下弯曲无可见裂纹,表现出良好的成形性能。     

Transformation hardening of steel sheet for automotive applications

Among high-strength steels, transformation hardening steels such as dual-phase (DP) steel and transformation-induced plasticity (TRIP) steel offer a superior relationship between tensile strength (TS) and elongation (El) on a commercial scale. As demand has grown for lighter-weight automobiles, so also has the demand for higher TS, lower yield ratio, and higher hole expansion ratio grown. Recently DP steel has been developed with precipitation hardening and grain refining by TiC. A new TRIP steel composed of 5Mn-2Si and control-rolled with niobium addition suggests the formation of retained austenite (γ _R ) as much as 30% and TS × El = 3,000 kgf/mm²·%.     

Effect of joining temperature on the microstructure and strength of tungsten/ferritic steel joints diffusion bonded with a nickel interlayer

A diffusion bonding process, for joining of tungsten to ferritic steel using nickel as an interlayer, was developed for nuclear component application. The effect of joining temperature on the microstructure and tensile strength of the joint was investigated in this work. Metallographic analysis revealed that a good bonding was obtained at both the tungsten/nickel and nickel/steel interfaces, and the diffusion products were identified in the diffusion zone. Nano-indentation test across the joining interfaces demonstrated the effect of solid solution hardening in the diffusion zone. Tensile test showed that the maximum average tensile strength of ∼200 MPa was obtained for the joint diffusion bonded at 900 °C. The results were discussed in terms of the joining temperature and of the residual stress generated during joining process.     

Effect of prior heat treatment on microstructure and mechanical properties of 0·23% carbon dual phase steel

Abstract

The present study is aimed at understanding the effect of prior heat treatment on the microstructure and mechanical properties of 0·23% carbon dual phase steel. The as received steel was subjected to annealing, normalising and hardening treatment before actual dual phase heat treatment. These steels along with the as received steel were intercritically annealed at 745°C followed by water quenching in order to produce a dual phase microstructure consisting of varying quantities and morphologies of ferrite and martensite. Mechanical properties were evaluated by tensile testing and hardness measurement. It was found that prior heat treatment affects the final dual phase microstructure in terms of size and relative amount of ferrite and martensite. It was also found that dual phase treatment resulted in improved mechanical property. Optimum combination of strength and ductility was obtained with the steel subjected to prior hardening (DPLA-3) treatment. The maximum in ultimate tensile strength (762 MPa) was obtained with the steel subjected to prior annealing treatment (DPLA-1). The X-ray diffraction study confirmed the presence of carbides in DPLA-1 steel, which contribute to the increased strength by precipitation hardening.     

Microstructure and mechanical properties of 7A09 aluminium alloy after isothermal compression and solution treatment

In this paper, the effect of processing parameters on the microstructure was investigated during the isothermal compression of 7A09 aluminium alloy. The optimal deformation parameters for the hot compression of 7A09 aluminium alloy were determined to be 733 K and a strain rate of 0.01 s⁻¹. The effect of solution temperature and solution time on the microstructure and mechanical properties of 7A09 aluminium alloy after isothermal compression was also investigated. A low deformation temperature was beneficial for preventing the grain coarsening, while a high deformation temperature contributed to the dissolution of the second phase particles and the occurrence of static recrystallisation during the solution treatment process. The second phase particles were more dissolved in the Al matrix as the solution time increased. The optimal solution treatment of 7A09 aluminium alloy was 723 K for 55 min, followed by rapid quenching in water and an ageing treatment at 413 K for 16 h. The tensile yield strength, ultimate strength, and elongation of 7A09 aluminium alloy after the optimal solution treatment were 580 MPa, 630 MPa, and 11.5%, respectively.     

不同镍含量奥氏体基低密度热轧钢的组织与力学性能

研究了3种Fe-18Mn-10Al-1C-(0, 3, 5)Ni-0.08V-0.03Nb(wt%)奥氏体基低密度双相钢在热轧后的组织和力学性能。结果表明,热轧后,试验钢的组织由拉长的奥氏体、条带状B2相及沿再结晶奥氏体晶粒晶界处的块状B2颗粒组成。此外,在奥氏体晶粒和B2颗粒中分别形成了纳米级κ-碳化物和DO₃相。5Ni钢屈服强度高达1352 MPa,这主要是由于奥氏体晶界存在大量纳米级别的B2颗粒以及VC相产生析出强化效果。随着Ni含量的增加,钢的强度与硬度均增加,5Ni钢屈服强度比0Ni钢高116 MPa,归因于5Ni钢中更多的B2相含量(16.9%)。但含Ni钢在强度增加的同时,极大损失了塑性,导致钢的伸长率极低,分析其原因为条带状B2相主要分布在奥氏体晶界处,试样在变形过程中裂纹更易沿晶界断裂,断口有分层现象。     

The microstructure and properties of 17-4PH martensitic precipitation hardening stainless steel modified by plasma nitrocarburizing

17-4PH martensitic precipitation hardening stainless steel was plasma nitrocarburized at 430 °C and 460 °C for 8 h. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, microhardness tests, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The results show that the microstructure of plasma nitrocarburized layer is characterized by a compound layer with no evident diffusion zone. The phases in the 430 °C treated layer are mainly of γ′-Fe₄N, nitrogen and carbon expanded martensite (α′_N), and some incipient CrN phases. When the temperature increases up to 460 °C, there is no evidence of α′_N phase. The processes of bulk precipitation hardening and surface treatment by plasma nitrocarburizing can be successfully combined in a single-step process on this steel. The hardness of modified layer can reach up to 1186HV, which is 3 times higher than that of untreated steel. The wear and corrosion resistance of the specimens can be apparently improved by plasma nitrocarburizing. The 460 °C/8 h treated specimen has the best wear and corrosion resistance in the present test conditions.     

冷却方式对Nb-Ti微合金钢组织和性能及沉淀行为的影响

两阶段控制轧制后,采用不同的冷却路径进行冷却,研究冷却路径对Nb-Ti微合金钢组织和性能及沉淀行为的影响.结果表明,超快冷+空冷冷却路径可获得细晶组织,晶粒平均尺寸约为7.76μm,屈服强度高达425 MPa,抗拉强度高达500 MPa.超快冷+炉冷试样中存在细小的沉淀粒子,沉淀粒子尺寸主要集中在2—7 nm,而超快冷+空冷试样中只存在少量球形沉淀粒子,轧后直接空冷可获得相间沉淀粒子.不同冷却路径获得的热轧板在700℃下退火300 s后,沉淀粒子发生明显的粗化;退火处理后,超快冷+炉冷试样的晶粒平均尺寸减小为6.47μm,相对于退火前,其屈服强度和抗拉强度分别增加50和30 MPa、强度的增加主要源于细晶强化.对于含0.03%Nb(质量分数)的Nb-Ti微合金钢,由于沉淀粒子的体积分数有限,因此细晶强化效果远高于沉淀强化效果,强度的变化与晶粒尺寸的变化具有很好的对应性.另外,加工硬化指数与晶粒尺寸密切相关.随着晶粒平均尺寸的增加使加工硬化指数增加.     

冷却方式对Nb-Ti微合金钢组织和性能及沉淀行为的影响

两阶段控制轧制后,采用不同的冷却路径进行冷却,研究冷却路径对Nb-Ti微合金钢组织和性能及沉淀行为的影响.结果表明,超快冷+空冷冷却路径可获得细晶组织,晶粒平均尺寸约为7.76μm,屈服强度高达425 MPa,抗拉强度高达500 MPa.超快冷+炉冷试样中存在细小的沉淀粒子,沉淀粒子尺寸主要集中在2-7 nm,而超快冷+空冷试样中只存在少量球形沉淀粒子,轧后直接空冷可获得相间沉淀粒子.不同冷却路径获得的热轧板在700℃下退火300 s后,沉淀粒子发生明显的粗化;退火处理后,超快冷+炉冷试样的晶粒平均尺寸减小为6.47μm,相对于退火前,其屈服强度和抗拉强度分别增加50和30 MPa,强度的增加主要源于细晶强化.对于含0.03%Nb(质量分数)的Nb-Ti微合金钢,由于沉淀粒子的体积分数有限,因此细晶强化效果远高于沉淀强化效果,强度的变化与晶粒尺寸的变化具有很好的对应性.另外,加工硬化指数与晶粒尺寸密切相关,随着晶粒平均尺寸的增加使加工硬化指数增加.     

回火温度对Ti-V-Mo微合金化马氏体钢析出相和力学性能的影响

利用微观分析和物理化学相分析法,对不同回火温度(550,600,650 ℃)保温1 h后的Ti-V-Mo微合金化马氏体钢的组织和析出相表征,并进行了强化分量的计算。结果表明,在600 ℃回火时具有最佳的综合力学性能:抗拉强度为1298 MPa,屈服强度为1286 MPa,伸长率为14%。强化分量计算结果表明:析出强化和细晶强化是主要的强化方式,约占总强度的40%和30%,其中析出强化分量σ_p为517 MPa,由5 nm以下的(Ti,V,Mo)C粒子(质量分数22%)提供。回火温度由550 ℃升高到600 ℃,抗拉强度和屈服强度均有增加,同时伸长率变化不大,其主要原因是σ_p对屈服强度的贡献量提高,在提高强度的同时改善了塑性。     

Si对高强热轧双相钢组织性能的影响

实验试制了590MPa级C Si Mn Cr系高强热轧双相钢,同时分析了合金元素Si对双相钢微观组织和力学性能的影响。结果表明,Si含量增加05%后,组织中铁素体含量增加了3%,硬度提高了HV20;双相钢抗拉强度提高了41MPa,屈服强度提高了8MPa,降低了屈强比,伸长率提高了8%,塑性得到显著改善。     

抗震用160MPa级低屈服点钢制备工艺研究

通过合理成分设计和采用高温终轧及空冷的生产工艺,在实验室制备出厚度分别为12mm和16mm的160MPa级抗震用低屈服点钢板。钢板组织均为单一的多边形铁素体,晶粒平均直径分别为4418μm和4717μm,屈服强度分别为177MPa和172MPa,具有良好的高应变低周疲劳性能,满足160MPa级建筑抗震用钢的性能要求,为160MPa级低屈服点钢的工业试制提供了依据。     

Development of high Mn-N duplex stainless steel for automobile structural components

A new high Mn-Ni free (duplex stainless steel) DSS containing 18Cr-6Mn-1Mo-0.2N has been developed by examining the effects of manganese on the corrosion and mechanical properties of high Mn SSs containing 18Cr-4 ∼ 11Mn-0 ∼ 2Ni-0 ∼ 1Mo-0.2N. The alloy with 45% ferrite is found to be an optimum alloy with much higher mechanical strength and similar corrosion resistance compared with those of standard SS304. In addition, the alloy was free of precipitation of sigma phase and Cr-nitride when exposed to high temperatures due primarily to relatively low contents of Cr, N and Mo. With an increase in Mn content, the resistance to pitting and metastable pitting corrosion of high Mn DSS decreased since the number of (Mn, Cr) oxides, acting as preferential sites of pitting, increased with the Mn content.     

Kinetics of nanoscale precipitation in Ni-Fe-Al alloys: A magnetic monitoring approach

In this study, time-temperature dependence and kinetic aspects of nanoscale precipitation responsible for strengthening of Ni₅₀Fe_xAl_50−x alloys with x = 20, 25 and 30 were investigated by temperature-scan and isothermal magnetic measurements in a vibrating sample magnetometer. Temperature-scan magnetization curves contained a magnetization rise for all studied alloys at temperatures above the Curie transition of the primary phase. These transient rises at relatively higher temperatures were associated with the formation of secondary ferromagnetic precipitates, identified as nano-sized body centered cubic α crystallites by microstructural observations under the transmission electron microscope. The isothermal kinetics of ferromagnetic α-phase precipitation was analyzed with the Johnson-Mehl-Avrami model. The Avrami exponent was determined to be close to unity and independent of the extent of precipitation, annealing temperature and alloy composition. It was concluded that α-phase precipitation was governed by a diffusion controlled growth process with decreasing growth rate, which closely resembles continuous precipitation kinetics. The activation energies, ranging between 75 and 83 kJ/mol, were utilized to construct magnetically assessed isothermal transformation diagrams of precipitation. Conforming to the kinetic analysis, annealing at an intermediate temperature ensures precipitation of fine second phase particles and brings about a significant hardening effect, whereas a higher annealing temperature yields coarser precipitates and a smaller extent of precipitation hardening.     

2000 MPa级低成本复合强化超高强度钢的二次硬化行为

采用SEM、HRTEM等试验方法,对2000 MPa级低成本复合强化超高强度AIR0509钢的二次硬化行为进行了研究,并与目前广泛应用于航空领域的AerMet100钢进行了对比。试验结果表明:试验钢具有明显的二次硬化现象,在535 ℃回火4 h时达到最佳强韧性配合,室温抗拉强度、屈服强度以及U型缺口冲击吸收能量分别为2020 MPa、1780 MPa和68 J,同淬火态相比屈服强度提高了480 MPa,这是由析出的复合强化相碳化物M₂C与金属间化合物β-NiAl共同作用的结果;此外,同AerMet100钢相比,AIR0509钢抗过时效的能力更强。     

双相钢板应变强化和烘烤硬化特性试验研究

近年,国内高强度钢板品种开发取得了快速的进步,双相钢等先进高强度钢板日趋系列化,同时强度等级也有了大幅度的提高。但是与国外先进钢厂相比,国内先进高强度钢板的推广应用步伐相对缓慢。该文针对C-Mn钢、高强度低合金钢、590MPa双相钢和780MPa双相钢的应变强化特性和烘烤硬化特性开展了深入的试验研究。研究结果表明,与C-Mn钢和HSLA钢相比,双相钢应变强化和烘烤硬化效应十分显著,有利于提高零件的使用强度。     

Microstructure and room temperature properties of a high-entropy TaNbHfZrTi alloy

A new refractory alloy, Ta₂₀Nb₂₀Hf₂₀Zr₂₀Ti₂₀, produced by vacuum arc-melting followed by hot isostatic pressing (HIPing) at T = 1473 K and P = 207 MPa for 3 h has predominantly a single-phase body-centered cubic (BCC) structure with the lattice parameter a = 340.4 pm. The alloy density and Vickers microhardness are ρ = 9.94 g/cm³ and H_v = 3826 MPa. The alloy has high compression yield strength (σ_0.2 = 929 MPa) and ductility (? > 50%). The alloy shows considerable strain hardening and homogeneous deformation. A simple model of solid-solution strengthening is proposed to explain the behavior.     

Interactions between deformation-induced defects and carbides in a vanadium-containing TWIP steel

Interactions of deformation-induced defects with nanometer-sized vanadium carbides in a Fe–21.6Mn–0.63C–0.87V (wt.%) TWIP steel have been studied by transmission electron microscopy. The increased yield strength due to precipitation hardening has been estimated to be about 200 MPa, according to the bypass mechanism. Mechanical twins were also observed to bypass carbides, but the carbides were not sheared or rotated. Moreover, the nature of stacking fault can also be changed due to the precipitation of V₄C₃ carbides.