热处理工艺对中碳钢丝显微组织及其拉拔性能的影响

系统分析了热处理工艺对中碳钢丝显微组织及其拉拔性能的影响，结果表明，铅浴等温淬火处理组织中虽然还存在少量先共析铁素体，但其所占比例明显低于正火处理组织。经大压缩率变形后，铅浴等温淬火处理后大变形组织中微空洞的数量远少于正火组织，不论是钢丝强度，还是钢丝扭转性能，铅浴等温淬火处理钢丝都优于正火处理钢丝。采用中碳钢正火工艺...     

热处理工艺对中碳钢丝显微组织及其拉拔性能的影响

系统分析了热处理工艺对中碳钢丝显微组织及其拉拔性能的影响,结果表明,铅浴等温淬火处理组织中虽然还存在少量先共析铁素体,但其所占比例明显低于正火处理组织。经大压缩率变形后,铅浴等温淬火处理后大变形组织中微空洞的数量远少于正火组织,不论是钢丝强度,还是钢丝扭转性能,铅浴等温淬火处理钢丝都优于正火处理钢丝。采用中碳钢正火工艺生产其断丝率略高于以高碳钢为原料的生产工艺,而引入铅浴等温处理后大大降低了高强度中碳钢丝绳的断丝率,提高了生产效率。     

先共析铁素体与热处理工艺的关系

通过热处理试验、显微组织鉴别、截点法等手段,重点探讨并详细总结了热处理工艺对亚共析钢先共析铁素体组织的影响规律。结果表明:随着碳含量的增加,先共析铁素体由块状变成网状,数量不断减少;冷却速度加快,先共析铁素体一般呈网状析出;淬火时,随着预冷时间的增长,先共析铁素体由断续网状向块网状以及块状过渡;中碳钢正火时,随着加热温度的升高,奥氏体晶粒粗化,先共析铁素体呈针状析出的趋势增大。     

正火温度对建筑耐火钢的组织与性能的影响

研究了正火温度对耐火钢组织与力学性能的影响。结果表明,当正火温度为700℃和750℃时,组织由针状或者条状铁素体和少量马氏体组成;升高正火温度至800℃,耐火钢基体组织中条状铁素体含量有所减少,而块状铁素体含量有所增多;继续升高正火温度至850℃,基体组织中主要为块状铁素体;当正火温度为700℃和750℃时,虽然耐火钢的强度较高,但是塑性较差,且屈强比高于0.8,无法满足耐火钢的使用要求;正火温度为800℃时,耐火钢的抗拉强度、屈服强度和断后伸长率分别为595 MPa、465 MPa和22%。     

组织对冷轧双相钢性能的影响

采用金相显微镜和透射电镜对两卷冷轧双相钢（7#和16#）的微观组织进行了观察并分析了其组织与性能的关系。结果表明,7#试样组织为多变形铁素体＋岛状马氏体;16#试样组织为饼形铁素体＋岛状马氏体＋大量游离渗碳体,铁素体的尺寸较大,数量较多,马氏体岛的数量较少,尺寸偏大,发生分解的马氏体岛数量较多。16#试样组织未完全再结晶导致组织粗大、细晶强化贡献弱是其屈服强度较低的主要原因;大量未奥氏体的渗碳体导致马氏体岛数量少及发生碳化物分解的马氏体量多是其抗拉强度低的主要原因。     

珠光体钢(α+θ)微复相组织的形成与力学性能

系统研究了珠光体钢在冷轧与随后退火及温变形(温楔横轧)过程中的组织演变规律、力学性能变化、合金元素添加的影响等,发现共析珠光体钢经大冷变形及随后适当温度退火可以形成铁素体晶粒与渗碳体颗粒尺寸均在亚微米量级的(α+θ)微复相组织.冷轧变形后的珠光体组织非常不均匀,主要由不规则弯曲片层、带有剪切带的粗大片层以及精细片层组成.大冷变形能明显提高共析珠光体钢的屈强比和加工硬化指数,随轧制压下率的增大,共析珠光体钢冷轧态试样的强度提高,延性在冷轧压下率小于60%时出现急剧下降后又几乎保持不变.合金元素的添加使冷轧态试样的强度提高,但对延性的影响几乎可以忽略.实际温楔横轧后高碳钢棒件表层也具有超微细(α+θ)复相组织,温楔横轧过程中靠近表层的铁素体基体发生了动态连续再结晶,铁素体晶粒及渗碳体颗粒尺寸分别在0.4μm和0.2μm左右.温楔横轧后硬度与抗拉强度沿高碳钢棒件截面分布不均匀,心部略高于表层,但是在屈服强度方面.表层最高(约600MPa),心部次之(580MPa),其余部位介于二者之间.     

V、N含量和热处理对抗腐蚀油套管组织和性能的影响

研究了不同正火温度和不同V、N含量对1%Cr中碳钢的组织和力学性能的影响,结果表明,V、N含量提高,虽然增加了析出强化作用,但材料强度却随之降低,韧性大幅度提高。在950℃正火温度下较高V、N含量V3钢中的铁素体含量是较低V、N含量的V1钢中铁素体的6倍,而在850℃正火温度下V1钢中的珠光体晶粒尺寸是V3钢的3倍。随着正火温度提高,铁素体和珠光体含量均降低,贝氏体含量增加。因此可以看出增加V、N含量以及降低正火温度都有利于铁素体和珠光体组织转变。通过分析可知,未溶解的V(C,N)会阻碍奥氏体晶粒的粗化,并作为先共析铁素体的形核质点促进了铁素体转变,阻碍了贝氏体的形成,从而获得了具有良好抗腐蚀性能的铁素体+珠光体组织结构,并且使材料强度达到80ksi(552 MPa)。     

V-Ti钢热变形奥氏体的连续冷却转变行为

为研究V—Ti微合金钢热变形奥氏体的连续冷却转变行为,在对V—Ti徽合金钷进行Gleeble3800热模拟后,建立了连续冷却转变曲线（CCT图）,探讨了变形量和高温停留对CCT曲线和相变组织的影响．研究表明：变形量的增大,促进了先共析铁素体和珠光体转变,使其孕育期缩短,一定程度上也促进了高冷速下的贝氏体转变,但使低冷速下的贝氏体转变受阻;马氏体转变温度的降低说明变形量的增大在一定程度上使马氏体相变受阻;变形后若高温停留,组织发生静态回复,对扩散型相变的先共析铁素体和珠光体转变以及半扩散型相变的贝氏体转变均不利,使先共析铁素体转变量和珠光体转变量都有相对减少,而对马氏体转变影响不大．     

再热蒸汽热段管道弯头软化原因分析

某电厂再热蒸汽热段管道弯头在热推制后出现硬度偏低、组织异常的现象,为了分析该弯头组织性能劣化的原因,进行了模拟折弯试验及弯后热处理试验。结果表明:在热变形过程中弯头组织发生动态再结晶,马氏体向铁素体+碳化物转变,导致硬度下降,再结晶后继续变形使铁素体沿变形方向被拉长;在成型结束后没有通过正火+高温回火处理来消除这种不正常的形变组织,是该弯头软化的主要原因。     

新型贝氏体钢的组织和冲击疲劳性能研究

通过显微组织观察和冲击疲劳实验,研究了不同热处理新型贝氏体钢的组织和冲击疲劳性能.结果表明:新型贝氏体钢正火低温回火的组织由贝氏体铁素体和奥氏体组成,淬火低温回火组织为回火马氏体和残余奥氏体,正火低温回火热处理的冲击疲劳寿命高于淬火低温回火热处理的冲击疲劳寿命.分析了多冲疲劳裂纹扩展的行为,讨论了正火低温回火提高冲击疲劳的原因.     

Microstructure and mechanical properties of V–Ti–N microalloyed steel used for fracture splitting connecting rod

A new kind of V–Ti–N high strength microalloyed medium carbon steel has been developed, which is used for fracture splitting connecting rod. In this article, the characteristics of this carbon steel and its production process were studied. The microstructure, precipitated phases and their effects on mechanical properties were investigated by optical microscope, SEM, and TEM. The results showed that the steel was constituted of ferrite and pearlite. By reducing the finish rolling temperature and accelerating the cooling rate after rolling, microstructure with fine grain ferrite and narrow lamellar space pearlite could be obtained in V–Ti–N microalloyed medium carbon, and a large number of precipitated phases distributed over ferrite. These led the tensile strength to be more than 1000 MPa, yield strength (YS) more than 750 MPa. The impact fractograph showed typically brittle fracture characteristic.     

Experimental study of the distribution of alloying elements after the formation of epitaxial ferrite upon cooling in a low-carbon steel

The distributions of carbon and substitutional elements in a low-carbon steel during the formation of epitaxial ferrite on cooling after intercritical annealing have been studied by electron probe microanalysis (EPMA). The analysis has shown that the formation of epitaxial ferrite takes place with a partial redistribution of alloying elements between the epitaxial ferrite and the austenite. This redistribution of alloying elements causes compositional gradients in the epitaxial ferrite that lead to a different etching behaviour with respect to the intercritical ferrite. Contrary to Thermo-Calc predictions, a distinct partitioning behaviour of silicon has been observed.     

Evolution of bainitic microstructure in vanadium-bearing microalloyed steel with two-step cooling

In the present work, a medium carbon vanadium-bearing microalloyed steel with low-alloy contents was subjected to air cooling followed by quenching (two-step cooling) which resulted in multiphase structures that consist of ferrite, bainite, martensite and austenite. The characterisation of the samples obtained by various two-step cooling methods was done using a SEM, a X-ray diffractometer and a magnetometer. Volume fractions of retained austenite (RA) and its carbon contents were determined and tensile properties were also evaluated. The RA content along with its carbon content has been found to increase to a maximum value and quenching at that point improves the ductility. Also, the lower transformation temperature of bainite enhances the toughness.     

Effect of welding heat input on microstructure and mechanical properties of simulated HAZ in Cu containing microalloyed steel

The influence of weld thermal simulation on ICGC HAZ microstructure and mechanical properties of Cu containing Nb-Ti-microalloyed steel has been investigated. Low heat input of 0.7 kJ/mm (simulated fast cooling of Δt _8/5 = 5 s) and high heat input of 4.5 kJ/mm (simulated slow cooling of Δt _8/5 = 61 s) were used to generate double-pass thermal cycles with peak temperatures of 1350 and 800 °C, respectively. The microstructure after high heat input mainly consisted of polygonal and quasi-polygonal ferrite (QF) grains with certain amount of acicular ferrite, whereas, after the low heat input, microstructure mainly consisted of lath or elongated bainite–ferrite, QF and M–A constituents. The size of ferrite grains decreased and volume of M/A constituents increased with fast cooling rate. The precipitation characteristics were found to be similar in both cooling rates. However, the precipitation of Cu-related phases was promoted by slow cooling rate. By fast cooling rate, the investigated steel exhibited an increase in hardness from 187_HV to 197_HV. Consequently higher yield strength with considerable loss in the (−10 °C) CTOD fracture toughness (δ_{fast cooling} = 0.86 mm and δ_{slow cooling} = 1.12 mm) were demonstrated.     

Recrystallisation and dilatometric behaviour of low carbon and ultralow carbon steels

Abstract

During continuous heating of a cold rolled low carbon steel, a dilatometric anomaly has been detected before the well known ferrite to austenite transformation. The detailed study of the processes occurring during the heating and comparison with the case of an ultralow carbon steel showed that this anomaly is related to the change in dislocation density during recrystallisation.     

Effect of controlled rolling/controlled cooling parameters on microstructure and mechanical properties of the novel pipeline steel

The study of controlled rolling/controlled cooling process parameters which affect the microstructure and mechanical properties of a novel pipeline steel has been optimized by the orthogonal experiment with four factors and three levels in this paper.However,the parameters of thermo-mechanical control process(TMCP)optimized by the Gleeble-3500 hot simulator could not satisfy performance requirements of the X100 pipeline steel.In order to improve the performance of this steel,the influence of finish cooling temperature(FCT) on the microstructure and property is studied in detail.It is found that,as this steel is thermo-mechanically treated by this set of parameters(the start heating temperature,finish rolling temperature(FRT),FCT and cooling rate of 1,180℃,810℃,350℃ and 35℃/s,respectively),the microstructures are mainly composed of granular bainite(GB)and acicular ferrite(AF).The effective grain sizes are below 20μm;the steel reaches the optimal balance between the strength and the toughness;the yield strength is 695 MPa;the tensile strength is 768 MPa;the elongation is 16.6%;the impact energy is 262 J at room temperature.All indexes could meet the requirements of X100 pipeline steel.     

Using direct hot-rolling approach to obtain dual-phase weathering steel Cu–P–Cr–Ni–Mo

A weathering steel Cu–P–Cr–Ni–Mo has been developed which exhibits special continuous cooling transformation characteristics which permit the desired dual-phase (DP) microstructure to be obtained by direct hot-rolling. Hot-rolling procedures to obtain DP microstructures have been designed based on the continuous cooling transformation diagram of weathering steel Cu–P–Cr–Ni–Mo. The results show that the microstructures of DP weathering steels Cu–P–Cr–Ni–Mo are characterized by an irregular distribution of island-shaped martensite–austenite in the matrix of polygonal ferrite grains. DP weathering steel Cu–P–Cr–Ni–Mo with favorable corrosion resistant property, weldability and mechanical properties, such as, high strain hardening exponent values, a lower ratio of yield to tensile strength, and higher strengths; and is obtained successfully by direct hot-rolling.     

Combined effects of high-temperature rolling and ultrafast cooling on the mechanical properties of low-carbon steel

The role of ultrafast cooling (UFC) on the grain refinement of ferrite, the precipitation behavior of cementite particles and the mechanical properties of a mild steel (Q235 grade) was evaluated by applying laminar cooling and UFC and varying the finish cooling temperature ranges during UFC after hot rolling. While UFC refined the ferrite grains, it accumulated the degeneration of pearlite, resulting in complete disappearance of the laminar pearlite at relatively low finish cooling temperatures. The minimum mean size of spheroidized cementite particles reached ~110?nm. Meanwhile, the enhancement of UFC on tensile strengths of mild steels mainly resulted from the grain refinement of ferrite and the precipitation strengthening of cementite particles; however, the contribution varied with the finish cooling temperature of UFC. A modified Ashby–Orowan model was also used for evaluating the yield strength increment of medium plates. This work will provide a theoretical basis for the diversity control of microstructure and for developing stronger and tougher mild steels by introducing UFC technology after high-temperature rolling.     

Strength,microstructure and chemistry of ingot mould grey iron after different cycles of low frequency high temperature loads

A kind of grey iron for producing large steel ingot moulds has been analyzed by thermal simulation experiment, and its tensile strength, matrix microstructure, fracture morphology and chemistry after different cycles of low frequency high temperature loads with oxidizing atmosphere have been studied. The micro and macro-mechanisms of large mould fatigue cracking have been discussed. As the period of low frequency high temperature pretreatments increases, the carbon content in grey iron decreases, resulting in the decrease of pearlite fraction and also the tensile strength. A new kind of graphite flake in short and small size appears in the matrix after heating and cooling treatments, leading to the rise of graphite exposure rate in the fracture under low frequency high temperature periodic loads. Although the decarburization rate in the specimens with ferrite matrix is much lower than that with pearlite matrix, the carbon content has more influence on tensile strength, induced by the following grains coarsening and grain boundary weakening. Accordingly, some feasible measures for extending mould service life have been proposed.     

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。