新型奥氏体—贝氏体双相钢滑动磨损特性的研究

本研究了在边界润滑、滑动磨损条件下，新型奥氏体－贝氏体双相钢的磨损规律，磨面及磨屑形貌，磨损表层微观组织及硬度变化，动态摩擦系数及表面氧化膜与微观磨损机制的关系，并首次建立了“载荷－滑动速度－滑动时间”三维磨损机制图。     

辙叉贝氏体焊条连接修复组织性能研究

针对现场焊补及修复不便问题,本文提供了一种铁路钢轨及组合辙叉专用贝氏体焊条,该堆焊焊条焊前不用预热,焊后不用热处理。通过对该焊条连接及修复的组织性能特征分析,结果表明,无论是堆焊修复还是连接其焊缝组织都是粒状贝氏体,堆焊层显微硬度与基体基本一致,连接焊缝的冲击强度达到70J/cm2,焊条的组织性能满足贝氏体辙叉钢修复要求。     

新型奥氏体─贝氏体双相钢滑动磨损特性的研究

本文研究了在边界润滑、滑动磨损条件下，新型奥氏体─贝氏体双相钢的磨损规律，磨面及磨屑形貌，磨损表层微观组织及硬度变化，动态摩擦系数及表面氧化膜与微观磨损机制的关系，并首次建立了“载荷─滑动速度─滑动时间”三维磨损机制图。     

双相20Cr钢冲击载荷应变速率敏感性研究

利用分离式霍普金斯杆技术，在旋转盘击拉伸试验机上测试了双相２０Ｃｒ钢冲击拉伸应力一应变曲线，研究了应变速率及组织对动态力学性能的影响。结果表明，双相２０Ｃｒ钢是一种应变速率敏感材料，在相当高应变速率下仍可保持高的初始加工硬化并具有较大应变速率敏感系数，正是这种特性维持了双相２０Ｃｒ钢在冲击戴荷作用下的高强度，塑性水平。马氏体相的加入使体铁素体晶粒明显细化，马氏体对强度的贡献主要通过增加强化相比例和     

合金元素Mo对冷轧双相钢组织的影响

分析Mo微合金冷轧双相钢和普通C-Mn冷轧双相钢在不同双相热处理工艺下微观结构,讨论Mo对冷轧双相钢组织变化规律的影响。实验结果表明：当两种双相钢以1700℃／s冷却时,均获得了铁素体、马氏体双相组织,马氏体均匀分布在铁素体基体上,随着加热温度的升高,普通C-Mn双相钢得到的马氏体体积分数多。当以5．4℃／s冷却时,Mo微合金双相钢得到的马氏体体积分数多;当加热到820℃保温结束后以5．4℃／s的速率冷却时,普通C-Mn钢的组织组成相为铁素体、珠光体、马氏体;Mo微合金钢的组织组成相为铁素体、贝氏体、马氏体;Mo对铁素体晶粒的细化作用不明显。     

无钼热轧双相钢相变和组织的研究

研究了Ｓｉ－Ｍｎ－Ｃｒ型热轧双相钢的相变动力学，发现在ＣＣＴ曲线上存在温度间隔约１００℃的奥氏体亚稳区。随着冷却速率的降低，连续冷却转变后的组织中多边表铁素体量增多，贝氏体量减少，当冷却速度减小到一定程度时组织中出现针状马氏体。     

高强度冷轧双相钢应变硬化行为

为了研究双相钢在变形过程中的应变硬化特性,采用Hollomon法与修正的Crussard Jaoul法分析了试验钢的应变硬化曲线,并利用力学测试与显微组织观察等手段研究了组织结构对应变硬化行为的影响机制.结果表明：三种试验钢,均表现出较高的初始加工硬化能力.具有岛状马氏体与类针状马氏体的双相钢表现出两个阶段的应变硬化特征,具有粗大块状马氏体的双相钢则表现出三个阶段的硬化特征.与类针状和粗大块状马氏体相比,含有岛状马氏体的双相钢表现出较强的加工硬化能力和强度与塑性的良好配合.块状马氏体较早的进入塑性变形,导致双相钢变形协调难度加大并在晶界周围产生孔洞而使塑性恶化.     

Development of grain boundary allotriomorphic ferrite/granular bainite duplex steel

A new hot-rolled low alloy high strength steel with grain boundary allotriomorphic ferrite/granular bainite duplex micro-structure has been developed through novel microstructure and alloying designs without any noble metal elements such as nickel and molybdenum. Its as-rolled microstructure and mechanical properties, fatigue crack propagation behavior compared with single granular bainitic steel as well as continuous cooling transformation, were investigated in detail. The measured result of CCT (continuous cooling transformation) curve shows that such duplex microstructure can be easily obtained within a wide air-cooling rate range. More importantly, this duplex microstructure has much better combination of toughness and strength than the single granular bainite microstructure. It is found that the grain boundary allotriomorphic ferrite in this duplex microstructure can blunt the rni-crocrack tip, cause fatigue crack propagation route branching and curving, and thus it increases the resistance to fati     

700MPa级超低碳高强度贝氏体厚钢板的晶粒细化机制研究

根据超低碳微合金化的成分设计意图,采用控制轧制和控制冷却工艺得到细化的贝氏体组织,利用光学显微镜、FE-SEM和TEM对各类微观组织和析出物进行了研究和分析。结果表明,700MPa级超低碳贝氏体厚钢板为细小均匀的粒状贝氏体和少量针状铁素体与多边形铁素体的复合组织,其屈服强度不小于580MPa,抗拉强度不小于700MPa,低温冲击韧性为-20℃,Akv不小于150J。钢板具有强度高、韧性好和焊接性能良好的特点,其强度和韧性的良好匹配主要是由于在粒状贝氏体相变前形成了少量的针状铁素体分割奥氏体晶粒,从而细化了最终的复合组织。     

C—Si—Mn系热轧双相钢显微组织与力学性能之间的关系

通过对热轧试样的组织性能测试,研究了热轧双相钢显微组织与力学性能之间的关系。研究发现,铁素体和马氏体强度是影响力学性能的主要因素。建立了C-Si—Mn系热轧双相钢力学性能的数学模型,可以作为热轧双相钢基本力学性能参数预测的理论依据。     

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℃ 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 ofpre-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℃. Moreover, the BH value enhanced significantly with increasing baking time from 10 to 100 min.     

Ultra-high cycle fatigue behavior of high strength steel with carbide-free bainite/martensite complex microstructure

The ultra-high cycle fatigue behavior of a novel high strength steel with carbide-free bainite/martensite (CFB/M) complex microstructure was studied. The ultra-high cycle fatigue properties were measured by ultrasonic fatigue testing equipment at a fre-quency of 20 kHz. It is found that there is no horizontal part in the S-N curve and fatigue fracture occurs when the life of specimens exceeds 107 cycles. In addition, the origination of fatigue cracks tends to transfer from the surface to interior of specimens as the fa-tigue cycle exceeds 107 , and the fatigue crack originations of many specimens are not induced by inclusions, but by some kind of soft structure. It is shown that the studied high strength steel performs good ultra-high cycle fatigue properties. The ultra-high fa-tigue mechanism was discussed and it is suggested that specific CFB/M complex microstrueture of the studied steel contributes to itssuperior properties.     

超高强度钢与微合金钢点焊接头的组织与性能

以超高强度钢EN 10 292 TL4225和微合金钢H340 LAD为研究对象,采用先进的中频点焊连接技术,利用合适的焊接参数实现了超高强度钢与微合金钢的优质连接。对中频点焊接头横截面进行微观组织分析和硬度分布实验,并对中频点焊接头进行拉伸实验,采用扫描电镜对拉伸断口进行研究和分析。结果表明,中频点焊接头熔合良好、组织均匀,没有发现气孔、裂纹等缺陷,具有良好的中频点焊性能,能够满足实际生产需求。     

无碳化物贝氏体在曲轴上的应用与展望

介绍了无碳化物贝氏体钢的特点、合金化原理、获得方法和在曲轴上的应用前景。     

Microstructure and mechanical properties of railway wheels manufactured with low-medium carbon Si-Mn-Mo-V steel

The suitability of carbide-free bainite steel as railway wheel materials was investigated. The low-medium carbon Si-Mn-Mo-V steel was designed to make railway wheels by forging and rolling. The slack quenching with water was conducted on the tread of rim section by programmed control to simulate isothermal heat treatment after being austenitized. Microstructures and mechanical properties have been studied. The results indicate that the microstructure of the rim is mainly carbide-free bainite, and the mixed microstructure of bainitic ferrite and granular bainite is observed in web and hub. The mechanical properties are superior to both the standard requirements and the commercial production, such as CL60 plain carbon. The Charpy impact energy is relatively high at room and/or subzero temperatures. The force-displacement curves and fractographies reveal the excellent ability of resistance to crack initiation and propagation.     

Toughening mechanisms of a high-strength acicular ferrite steel heavy plate

An ultra-low carbon acicular ferrite steel heavy plate was obtained with an advanced thermo-mechanical control process-relaxed precipitation controlled transformation (TMCP-RPC) at Xiangtan Steel, Valin Group. The heavy plate has a tensile strength of approximately 600 MPa with a lower yield ratio. The impact toughness of the heavy plate achieves 280 J at ?40°C. The fine-grained mixed microstructures of the heavy plate mainly consist of acicular ferrite, granular bainite, and polygonal ferrite. The high str...     

Effect of acicular ferrite on banded structures in low-carbon microalloyed steel

The effect of acicular ferrite （AF） on banded structures in low-carbon microalloyed steel with Mn segregation during both iso- thermal transformation and continuous cooling processes was studied by dilatometry and microscopic observation. With respect to the iso- thermal transformation process, the specimen isothermed at 550℃ consisted of AF in Mn-poor bands and martensite in Mn-rich bands, whereas the specimen isothermed at 450℃ exhibited two different morphologies of AF that appeared as bands. At a continuous cooling rate in the range of 4 to 50℃/s, a mixture of AF and martensite formed in both segregated bands, and the volume fraction of martensite in Mn-rich bands was always higher than that in Mn-poor bands. An increased cooling rate resulted in a decrease in the difference of martensite volume fraction between Mn-rich and Mn-poor bands and thereby leaded to less distinct microstrucmral banding. The results show that Mn segregation and cooling rate strongly affect the formation of AF-containing banded structures. The formation mechanism of microstructural banding was also discussed.