冷成型制管对钢材力学性能的影响

对冷成型直缝焊接圆钢管弯制前的原料板材和弯制后的管材的力学性能变化进行了试验对比研究。结果表明：管材的屈强比不小于原料板材的屈强比,且屈服强度和抗拉强度都有所增长;管材塑性降幅较大;管材纵向冲击功变化不明显,横向冲击功有显著降低;因此钢管的力学性能不能以原料板材的力学性能代替。     

终冷温度对高强度抗震钢筋组织和性能的影响

用Gleeble-3800热模拟机进行高强度抗震钢筋的热模拟实验,使用金相显微镜(OM)、场发射扫描电子显微镜(SEM)、高分辨透射电子显微镜(TEM)和万能拉伸试验机等手段表征其微观结构、第二相、力学性能和断口形貌,研究了终冷温度对高强度抗震钢筋的组织和性能的影响并揭示微合金元素细化晶粒的机理。结果表明：实验钢的显微组织主要为铁素体和珠光体,随着终冷温度的降低铁素体晶粒细化。终冷温度为650℃时实验钢中分布在铁素体基体上的主要析出相 (Nb, Ti, V)C和(V, Nb, Ti)C的平均粒径约为2 nm和5 nm。随着终冷温度的降低实验钢的抗拉强度和屈服强度都增加,终冷温度为650℃时其抗拉强度和屈服强度分别为638.75 MPa和467 MPa,强屈比为1.37。在不同终冷温度实验钢的拉伸断口主要为等轴韧窝,其尺寸和深度不同。     

Modelling of Microstructural Evolution and Prediction of Mechanical Properties of Plain Carbon Strip Steel in Hot Rolling Process

Based on hot rolling production line of strip steel, the off-line in-house software, termed as ROLLAN (Rolling Analysis), is developed. The code is mainly used to predict the evolution of temperature, rolling force, fraction and grain size of recrystallization, fraction and grain size of phase transformation and final mechanical properties. Almost all the processing parameters affecting microstructure and mechanical properties in the schedule from reheating to the coiling process are considered in detail. Self-learning coefficient is adopted to adjust the deviation between predicted and measured temperatures, such as roughing exit temperature (RT2), finishing exit temperature (FT7) and coiling temperature (CT). Due to the application of low-speed-threading, increasing-speed-rolling and decreasing-speed-delivery process during finishing rolling and different cooling condition, after coiling the thermal-mechanical history of different position, along strip longitudinal direction is different resulting in     

Effects of carbon and niobium on microstructure and properties for Ti bearing steels

The objective of the study described here is to elucidate the effect of carbon and niobium on the microstructure, precipitation behaviour, and mechanical properties of 0·09C–0·11Ti (%) steel and 0·05C–0·025Nb–0·11Ti (%) steel under ultra fast cooling condition. The strengthening mechanisms are also discussed. The ferrite grains size and the size of precipitates in Ti and Nb–Ti steels were measured respectively. The mechanical properties obtained in Ti steel were similar to Nb–Ti steel with yield stress >700 MPa, elongation >20%, and good low temperature impact toughness. The study underscores that addition of higher carbon content by 0·04% under controlled rolling and ultra fast cooling conditions, we can achieve similar strength in the absence of micro-alloying element, niobium.     

热轧C-Si-Mn系TRIP钢的组织与力学性能

为了探讨热轧TRIP钢的制备工艺与其组织及力学性能的关系,采用热轧控冷工艺在实验室制备了C-Si-Mn系TRIP钢,利用光学显微镜、扫描电镜及透射电镜对试验钢的组织进行了观察,利用能谱仪对试验钢中的夹杂进行了观察.研究得到试验钢的力学性能为:σb=605 Pa,σs=440 Pa,δ=28.4%,σs/σb=0.73.定量金相检测结果表明,试验钢中三相含量分别为:残余奥氏体5.6%,铁素体67.6%,贝氏体26.8%.     

Nitrocarburizing of low-carbon unalloyed steel

Low-carbon unalloyed steel has been investigated after nitriding accomplished by either the salt-bath method (Tenifer) or the gas method (Nitroc). The resulting changes in the mechanical properties are reported in this paper, while changes in positron annihilation parameters are reported in Part 2. The mechanical properties show that the increase in both the lower yield stress and the ultimate stress is influenced greatly by the cooling rate after nitriding. A rapid cooling rate resulted in an increase of ～200 MPa while an increase of only 55 Mpa was observed for a slow cooling rate. These increases proved independent of prior straining in the range 0 to 20%, showing that the nitrogen uptake is not significantly influenced by internal defects. Annealing of rapidly cooled nitrided specimens resulted in a maximum of both the lower yield stress and the ultimate yield stress around 100° C. A transition from brittle to ductile fracture around this temperature was also observed. A large recovery of elongation to fracture was obtained after annealing at 140° C, which was not accompanied by any significant decrease in the lower yield stress. Dilatometer measurements indicated two precipitation stages, one around room temperature and another around 100° C.     

正火控冷12MnCrNiMoV钢板性能和微观组织研究

研究了正火控冷 +高温回火热处理工艺对 12MnCrNiMoV钢板力学性能、冲击韧性的影响 ,用透射电镜分析了 12MnCrNiMoV钢的微观组织。结果表明 ,与正火钢板相比 ,正火控冷的钢板具有较好的强韧性 ,Akv ,-4 0℃ 提高约 45 % ,特征转变温度TFAT50 降低了 2 0℃。组织观察表明 ,正火控冷的 12MnCrNiMoV钢板组织中的粒状贝氏体中的M A岛主要以板条马氏体为主。高温回火后 ,正火控冷工艺的微观组织为板条铁素体 ,碳化物呈弥散均匀分布     

Modeling of Microstructure Evolution and Mechanical Properties of Steel Plates Produced by Thermo-Mechanical Control Process and Its On-line Application

An integrated metallurgical model was developed to predict microstructure evolution and mechanical properties of low-carbon steel plates produced by TMCP. The metallurgical phenomena occurring during TMCP and mechanical properties were predicted for different process parameters. In the later passes full recrystallization becomes difficult to occur and higher residual strain remains in austenite after rolling. For the reasonable temperature and cooling schedule, yield strength of 30 mm plain carbon steel plate can reach 310 MPa. The first on-line application of prediction and control of microstructure and properties (PCMP) in the medium plate production was achieved. The predictions of the system are in good agreement with measurements.     

高强度耐火钢高温冷却后力学性能试验研究EI北大核心CSCD

该文对国产Q460FR、Q420FR、Q345FR等高强度耐火钢进行了200℃~800℃高温过火、自然冷却后的拉伸试验,在获得高强度耐火钢高温冷却后的应力-应变关系曲线和力学性能参数,并与普通结构钢的高温冷却后力学参数进行对比后,给出了屈服强度和抗拉强度变化系数拟合公式。研究表明:国产高强度耐火钢在高温冷却后的屈服强度和抗拉强度均得到提高,弹性模量基本稳定。该文研究的结果可以用来评估耐火钢结构火灾后的承载性能。     

单向预应变对X70大变形管线钢拉伸性能的影响

对X70大变形管线钢进行应变量小于2.5％的单向预拉伸和预压缩应变处理,而后卸载,再次拉伸至断裂,研究单向预应变对管线钢拉伸性能的影响.结果表明:同种单向预应变时,不同预应变量下管线钢的弹性变形、屈服变形和形变强化特征基本相同,弹性应变总体上随预应变量的增大而增大;预拉伸后再次拉伸时,管线钢在应变ε小于0.5％即发生屈...     

Low carbon high manganese bainitic steel

Abstract

The present study concerns the mechanical properties of low carbon (0·05 wt-%) high Mn bainitic steel. The continuous cooling transformation diagram exhibited bainitic transformation without any prior diffusive transformation of austenite even for a cooling rate as low as 0·5°C/s. The bainitic steels have shown continuous elongation behaviour with attractive combination of strength (>1200 MPa) and elongation (>14%). The bainitic microstructure obtained after annealing treatment has yielded excellent combination of strength, uniform elongation, yield ratio and static toughness value.     

高温后高强Q690钢材循环加载试验及本构模型研究

钢材经历火灾高温和冷却后其材料力学性能会发生不同程度退化,已有研究主要关注过火后钢材的残余静力性能。为研究经历火灾高温且不同方式冷却后高强钢的残余静力和滞回性能,对于历经500 ℃~1000 ℃高温后高强Q690在自然冷却和浸水冷却后的钢材进行了单调拉伸试验以及4种不同加载制度下的循环加载试验。结果表明,当过火极限温度不高于600 ℃时,在自然冷却和浸水冷却模式下,高温后Q690钢材单调拉伸和循环荷载下强度发展基本与常温未处理钢材类似。未过火高强Q690钢在循环荷载下表现出应变强化和循环软化效应。过火温度高于600 ℃且自然冷却下,过火后Q690钢随过火温度提高,其初始屈服强度下降。在浸水冷却下,过火冷却后高强钢初始屈服强度提升。且在循环荷载作用下,高温过火后Q690钢均表现出更为显著的应变强化效应,以及在等应变幅循环下均由未过火状态时的循环软化逐步转化为高温过火后的循环硬化效应。根据试验结果拟合了过火后Q690钢的Chaboche循环本构模型参数,可用于火灾后Q690钢结构的残余抗震性能评估。     

低硅TRIP钢的力学性能及残余奥氏体稳定性研究

通过常温拉伸实验研究低SiTRIP钢的力学性能及其加工硬化特点,利用扫描电镜(SEM)、X射线衍射(XRD)、电子背散射衍射(EBSD)、透射电镜(TEM)等手段研究低SiTRIP钢在拉伸变形前后组织变化特别是残余奥氏体特性的变化。结果表明:低SiTRIP钢表现出良好的力学特性,没有屈服平台,低的屈强比,同时又拥有比双相钢更好的延伸率和均匀应变。TRIP钢的残余奥氏体的分布也影响着其稳定性,分布在铁素体晶内的残余奥氏体在拉伸变形后仍然存在。     

4．5Ni钢淬透性试验研究

通过４．５Ｎｉ钢淬透性曲线、等温转变曲线及常规力学性能试验，研究了４．５Ｎｉ钢的淬透性；同时分析了合金元素对淬透性的影响；并用临界冷却速度预测了厚板能否淬透。研究结果表明，由于合金元素的交互作用，４．５Ｎｉ钢的淬透性优良，不但８０ｍｍ厚板可以淬透，而且只要严格控制化学成分，同时提高淬火剂的冷却强度，厚度不大于１００ｍｍ的板材也能淬透。     

Effect of increasing cooling rate from normalising temperature on structure and properties of a Mn–Cr–Mo–V steel

Abstract

The work was undertaken to study the effect of increasing the cooling rate from the normalising temperature on the microstructure and mechanical properties of a Mn–Cr–Mo–V steel. The steel was to a chemical composition suitable for grade 271 in BS 1501 Part 2 and as such would be used in the normalised and tempered condition. Three linear rates of cooling (12, 36, and 120 K min ^?1) from the normalising temperature were used. With the tenfold increase in cooling rate, yield strength increases of about 20% and tensile strength increases of about 15% were obtained in the final tempered steel. Although these strength increases resulted in a loss in ductility and toughness, the values of these properties were still relatively high. The improvements in strength with increases in cooling rate have been related to an increase in the proportion of bainite and a decrease in the amount of ferrite in the resulting microstructure.

MST/683     

Thermal and mechanical properties of high-strength structural steel HSA800 at elevated temperatures

The temperature dependent material properties of structural steel are important for fire resistant (FR) design and fire simulation of steel structures. In this study, the material tests were conducted for a high-strength steel developed in Korea, namely HSA800, to determine thermal and mechanical properties at elevated temperatures up to 1000 °C. Then test results were compared with current design models – ASCE, Eurocode 3 and AISC to verify which design models are fit well to the HSA800 at the elevated temperature. The thermal properties test results show that the specific heat and thermal strain at elevated temperatures agreed well with those predicted by current design models but thermal conductivity was slightly less than the design models. In the mechanical properties test results, the ASCE model was adequate for predicting yield strength of HSA800. Eurocode 3 and AISC models were unconservative for predicting yield strength but conservative for elastic moduli. The stress–strain relationships of HSA800 at elevated temperatures were developed using Ramberg–Osgood model and they agreed well with the test results up to 2% strain.     

Cooling process and mechanical properties design of hot-rolled low carbon high strength microalloyed steel for automotive wheel usage

For the purpose of developing Nb–V–Ti microalloyed, hot rolled, high strength automotive steel for usage in heavy-duty truck wheel-discs and wheel-rims, appropriate cooling processes were designed, and microstructures and comprehensive mechanical properties (tension, bending, hole-expansion, and Charpy impact) of the tested steels at two cooling schedules were studied. The results indicate that the steel consists of 90% 5 μm polygonal ferrite and 10% pearlite when subjected to a cooling rate of 13 °C/s and a coiling temperature of 650 °C. The yield strength, tensile strength, and hole-expansion ratio are 570 MPa, 615 MPa, and 95%, respectively, which meet the requirements of the wheel-disc application. The steel consists of 20% 3 μm polygonal ferrite and 80% bainite (granular bainite and a small amount of acicular ferrite) when subjected to a cooling rate of 30 °C/s and a coiling temperature of 430 °C. The yield strength, tensile strength, and hole-expansion ratio are 600 MPa, 655 MPa, and 66%, respectively, which meet the requirements of the wheel-rim application. Both the ferrite–pearlite steel and ferrite–bainite steel possess excellent bendability and Charpy impact property. The precipitation behavior and dislocation pattern are characterized and discussed.     

轧后冷却速率对14CrMoR钢板热处理后显微组织和力学性能的影响

首先对14CrMoR钢进行了轧制后不同冷却速率的冷却,然后进行了相同工艺的正火+回火热处理,研究了轧后冷却速率对14CrMoR钢板热处理后显微组织和力学性能的影响。结果表明:轧后冷却速率越小,钢板热处理后的各类显微组织越细小,珠光体和回火贝氏体组织的分布越均匀,综合力学性能也越好。     

高强度低屈强比铆螺钢轧制工艺的研究

为消除螺栓在热处理中产生的各种缺陷,缩短生产周期,使铆螺钢免热处理.采用热模拟试验机、实验室轧机和多工位冷镦机对铆螺钢轧制实验,铆螺钢原料和成品分别在拉力试验机和万能试验机上进行拉力试验,并对其组织进行了分析.结果表明,铆螺钢经过控轧控冷,获得具有多边形铁素体、细片状珠光体、粒状贝氏体、残余奥氏体和少量MA岛的多相组织.由于控轧控冷后的多相组织及TRIP效应,改善了螺栓的强韧性.铆螺钢因低的屈强比可以直接由热轧棒材冷镦成螺栓,螺栓无需最终热处理,产品的力学性能满足8.8级螺栓国家标准的相应要求.     

Microstructure and Mechanical Properties of a Duplex Martensite Austenitic Steel Precipitation-hardened by VC Carbide

This paper presents an investigation on the primary microstructure and mechanical properties of a martensite-austenitic duplex steel precipitation-hardened by VC carbide. The results show that the mechanical properties at room temperature are strongly dependent upon the volume fraction of austenite fA. When fA < 32 % both ultimate strength and Vield strength are decreased with increasing fA. however. whenfA>32%, with increasing the.fA. ultimate strength rises and yield strength drops down. Experimental results at elevated temperatures. show that when test temperature ≤500℃. the yield strength to modulus ratio remains unchanged, however. as the temperature rises a substantial fall in the ratio occurs. The strength values at 600 and 700℃ are increased with increasing strain rate measured by cross-head speed of testing rnachine, The law of mixtures and the contribution of strain-induced transformation from unstable austen ite to martensite to the mechanical properties are discussed.