低碳钢形变强化相变时铁素体织构类型的分析

利用背散射电子衍射取向成像技术分析了在热模拟单向压缩条件下Q235碳素钢形变强化相变时铁素体织构的类型。结果表明,在利用形变强化相变实现铁素体的超细化过程中会出现铁素体的相交织构和形变织构,在大应变条件下还会出现动态再结晶织构。在形变强化相变后细晶铁素体在整体上表现为以〈111〉方向为主的线织构。主要的相交织构在粗晶奥氏体内部形变带形核时产生并与〈111〉织构对应。形变织构是在形变时形成的铁素体受到继续变形所致,在形变强化相变过程中及完成后都会产生,对应〈111〉及〈100〉方向的线织构,随着形变的加大,〈100〉方向的织构增加得更快,形变温度的降低有利于形变织构的加强。在形变量很大且形变温度比较合适时(但不能过低)会发生铁素体的动态再结晶,它以连续的方式进行,导致形变织构的进一步加强,并使晶粒均匀细化。     

低碳钢热变形过程中铁素体的织构形成规律

利用背散射电子衍射取向成像技术定量分析了热模拟单向压缩条件下Q235碳素钢热变形时铁素体的织构形成规律。结果表明,在710℃纯铁素体热压缩过程中,形成〈100〉和〈111〉方向的线织构。〈111〉方向织构增强的速度较快,到应变为1.0时达最大值,然后随应变的加大而减弱;〈100〉方向织构在形变量较小时增强的速度较慢,在大应变时增强的速度很快。大应变时虽导致一定程度的动态再结晶,使铁素体晶粒细化,但组织不均匀,织构过强,造成强烈的各向异性。在奥氏体与铁素体两相区变形时,先共析铁素体因形变同样产生强烈的织构。随着形变温度的提高和先共析铁素体的减少,织构减弱。     

低碳钢形变强化相变的组织细化

利用热模拟压缩变形试验研究了应变速率,形变温度和应变量对Q235级别低碳20钢过冷奥氏体形谱强化相谱的组织演变规律,探讨了了奥氏体昌粒控制对形变强化相变的影响,分析了组织细化的原因,结果表明,形变强烈促进过冷奥氏体相变,过冷奥氏体在800－740℃温度范围名义变形量为70％,应变速率为Is^-1,可获得了平均截径为2－3um及小于2um的铁索体细晶与珠光体混合组织,还观察到在局部细小铁素体晶粒的晶界上渗碳体以离异珠光体形式析出的现象,适当控制奥氏体晶粒尺寸有利于形变强化强晶组织的获得。     

低碳钢形变诱导相变组织在保温中的变化

通过热模拟实验，考察了在不同变形温度和不同奥氏体晶粒尺寸等条件下保温对低碳钢形变后组织演变的影响。结果表明，在较低温度下变形得到的铁素体在保温时更稳定，随温度升高，易发生铁素体向奥氏体的逆相变。细晶奥氏体转变后的铁素体在保温时长大缓慢，所得组织稳定，并且保温后的组织也更为均匀。     

Al—Li合金形变热处理的织构组织研究

用取向分布函数和金相技术研究了Al-Li合金不同热处理工艺与织构组织的关系。结果表明,采用冷轧→再结晶→粹火→时效处理工艺,得到的显微组织充分细化,第二相粒子分布更均匀,并首次获得{111}//ND为主的纤维织构。对其相关机制进行了分析讨论。     

无取向硅钢形变储能取向依赖性及其对再结晶织构的影响

采用晶体塑性有限元模拟与实验相结合的方式,研究无取向硅钢冷轧过程中不同初始织构组分的取向流动与形变储能累积。结果表明:冷轧后形成了较强的α,γ形变织构和较弱的λ形变织构。再结晶织构由γ,α,η和λ织构组成,其取向密度依赖于冷轧压下率。随冷轧压下率增大,λ再结晶织构逐渐增强,η织构先增强后减弱,γ织构先减弱后增强,α织构稍有弱化。冷轧过程中形变储能累积具有明显的初始取向依赖性,初始γ取向储能累积速率在低于50%压下率时与初始α取向接近,高于50%压下率时则明显大于后者,初始λ取向储能累积速率始终显著低于γ和α取向,转至同一形变取向的不同初始取向间的储能累积也会产生差异。冷轧过程中不同初始织构组分的取向流动与形变储能累积规律,决定了无取向硅钢再结晶织构组分的发展。     

低碳钢在Ae3以上形变诱导铁素体的形成和性能

对低碳钢在Ae_3以上进行了单道次快速大形变量变形,测定了材料在高温变形前后的室温拉伸曲线并观察其断口形貌。对结果的分析表明,低碳钢在Ae_3以上的温度发生形变诱导铁素体相变,是形成超细晶粒(3μm左右)的主要原因。应变速率大于0.1 s~(-1)时,可诱导形成铁素体晶粒,且随着应变速率的提高铁素体分数增加而晶粒尺寸减小;当应变速率大于10 s~(-1)时铁素体分数达到饱和,晶粒尺寸的变化不大。与先共析铁素体相比,形变诱导铁素体的强度和硬度大大提高,低碳钢Q235的屈服强度由250 MPa左右提高到510 MPa,抗拉强度则达到615 MPa,而形变诱导铁素体的塑性有所降低,但仍保持较高的水平。     

两相区形变对含铜低碳钢合金元素配分的影响

采用DIQ(两相区形变-保温-淬火)热处理工艺,借助扫描电镜(SEM)及透射电镜(TEM)等测试手段研究了两相区不同变形量对一种含Cu低碳钢组织演变、位错密度和Mn、Cu合金元素配分行为与分布的影响规律。结果表明,对于经历了两相区热模拟压缩变形处理的含Cu低碳钢,随变形量的增加,铁素体和马氏体组织均趋于细化,位错密度逐渐增加,合金元素配分行为先增强后减弱。两相区变形处理的变形量为10%时,Mn、Cu原子的配分效果最好,二者在马氏体中的平均含量较原实验钢分别提高了62.82%和20.73%。     

镁合金AZ31高温形变机制的织构分析

利用X射线衍射和背散射电子衍射方法测定了镁合金AZ3l高温动态再结晶和超塑形变时的宏观和微观织构,分析了晶粒内部的形变机制.结果表明,在动态再结晶和超塑形变过程中,晶粒内部的滑移机制仍起重要作用,表现为再结晶晶粒出现择优取向以及一些晶粒可充分均匀形变成长条状.宏观织构的测定表明,具有不同初始织构的两类样品高温动态再结晶时,新晶粒有不同的取向择优过程,形成相似的织构;长条形变晶粒内部开动的滑移系也有一定的差异.分析了不同温度下相同的织构对应的不同塑变机理取向成像分析表明,基面织构取向的晶粒间总伴随着较高比例的小角晶界和30°(0001)的取向关系,这是六方结构的六次对称性限制了动态再结晶时(亚)晶粒间取向差的有效增大的缘故.     

温轧温度对Cr-Ti-B系低碳钢组织与织构的影响

使用扫描电镜、电子背散射衍射、透射电子显微镜和固体内耗仪研究了温轧温度对Cr-Ti-B系低碳钢组织和织构的影响.结果 表明,温轧后钢的组织由变形铁素体和少量珠光体所组成,随着温轧温度的提高铁素体晶内剪切带的含量呈现先提高后降低的趋势,在450℃温轧剪切带的含量最高.剪切带的形成,与Ti和B元素的偏聚密切相关.在350℃...     

变形制度对低碳锰钢组织性能的影响

为了获得细晶铁素体/贝氏体的复相组织,通过控轧控冷工艺研究了低碳锰钢在奥氏体区变形时变形量、终轧温度和卷取温度对组织演变和力学性能的影响规律.研究表明,增加变形量(对应道次间隔时间缩短)可以细化铁素体晶粒,但当终轧温度降低到800℃时,变形量的增加以及开冷温度的降低不利于贝氏体组织的获得.通过调整变形量、终轧温度、可开冷温度并适当降低卷取温度,可使实验钢获得晶粒尺寸约为5μm的铁素体和10%~20%的贝氏体组织,低碳锰钢强塑性能良好.     

Deformation behaviour of a low carbon high Mn TWIP/TRIP steel

TWIP and TRIP phenomena have been observed in Fe–20Mn–2.5Si–0.3Al–0.06C (wt-%) steel during cold deformation (CD). Mostly austenite, annealing twins and stacking faults are observed in hot rolled solution treated (HRACST) samples. Cold deformation results in γ→?→α′ transformation due to its low stacking fault energy (18?mJ?m^?2). 50CD (50% CD) sample reveals strong Goss, Brass and weak Copper Twin texture components due to slipping and micro-twinning. Maximum ductility of 62% with lower tensile strength is perceived in HRACST sample, whereas, 30CD sample shows excellent tensile strength (1039?MPa) with a lower ductility (23%). Premature failure in 50CD samples is related to the formation of α′-martensite (≈35%) and deformation twins along with a higher strain hardening due to low Al content.     

Fatigue life studies in carbon dual-phase steels

An investigation has been conducted to examine the morphological influence on fatigue life of low carbon steel with dual phase microstructure. The results showed that dual-phase microstructure, composed by ferrite and martensite had superior symmetrical bending fatigue strength when compared with ferrite-pearlite steel. Through those tests, evidences of different mechanisms were verified (such as ferrite cyclic hardening, slip band formation and beginning of crack nucleation and propagation). Based on the fatigue tests results, various mechanisms stages were discussed associated with different microstructure morphology.     

The effect of microstructure on the mechanical behaviour of a low carbon, low alloy steel

The effect of microstructure on the mechanical behaviour of a low carbon, low alloy steel was studied. The hot-rolled ferrite-pearlite showed low monotonic and cyclic strengths with high ductility in terms of true fracture strain and a high shreshold stress intensity. The quenched and tempered low carbon martensite showed high monotonic and cyclic strengths and high ductility. However, the threshold stress intensity was significantly lower than that of the ferrite-pearlite. Both the strength and threshold stress intensity of an austempered bainite and a duplex ferrite-martensite are greater than those of the hot-rolled ferrite-pearlite. At a same strength level, the ductility and the threshold stress intensity of the low carbon martensite are higher than those of a medium carbon martensite.     

Formability of friction stir processed low carbon steels used in shipbuilding

The stretch formability of a low carbon steel processed by friction stir processing (FSP) was studied under biaxial loading condition applied by a miniaturized Erichsen test. One-pass FSP decreased the ferritic grain size in the processed zone from 25 μm to about 3 μm, which also caused a remarkable increase in strength values without considerable decrease in formability under uniaxial loading. A coarse-grained (CG) sample before FSP reflected a moderate formability with an Erichsen index (EI) of 2.73 mm. FSP slightly decreased the stretch formability of the sample to 2.66 mm. However, FSP increased the required punch load (F_EI) due to the increased strength by grain refinement. FSP reduced considerably the roughness of the free surface of the biaxial stretched samples with reduced orange peel effect. The average roughness value (Ra) decreased from 2.90 in the CG sample down to about 0.65 μm in fine-grained (FG) sample after FSP. It can be concluded that the FG microstructure in low carbon steels sheets or plates used generally in shipbuilding provides a good balance between strength and formability.     

Nb-V-Ti低碳微合金钢的热变形加工图及其应用

为了优化Nb-V-Ti低碳微合金钢的变形工艺参数,利用Gleeble-1500热/力模拟实验机对其进行了热压缩实验,得到热加工图用于研究热变形行为.研究发现,加工图中存在两个动态再结晶蜂区及失稳区:峰区Ⅰ:峰值对应的变形温度和变形速率分别为1000℃,2 s-1,峰值效率21%;峰区Ⅱ:变形温度1050℃,变形速率0....     

Ferrite recrystallisation and characteristics of non-recrystallised ferrite grains in Ti added low carbon steels

The progress of ferrite recrystallisation in low carbon steel was slower than in ultralow carbon steel. The hardness of the non-recrystallised ferrite grains gradually decreased with increasing annealing time in ultralow carbon steel, but gradually increased with increasing annealing time in low carbon steel. The amount of Ti containing precipitates increased slightly during annealing in ultralow carbon steel, but increased remarkably with increasing annealing time in low carbon steel. These results suggest that the softening of non-recrystallised ferrite grains during annealing in ultralow carbon steel may reflect the progress of recovery and the Ostwald ripening of Ti containing precipitates formed during annealing. In contrast, the hardening of non-recrystallised ferrite grains in low carbon steel may be due to the precipitation hardening of TiC formed during annealing.     

低温变形Nb微合金钢铁素体相变的数学模型

以热力学和动力学理论为基础，研究了Nb微合金钢热变形过程中铁素体相的形核及长大过程，在形核速率计算中引入变形储能、晶界凸阶及微合金元素的作用，建立了低温变形诱导铁素体相变的动力学模型，分析了热变形参数和化学成分对相变分数和晶粒尺寸的影响．变形温度的降低和变形程度的增加，促进了α相变过程，相变体积分数增加，晶粒得到细化．C与Mn含量增加的效果则相反．模型应用于热轧带钢生产过程的模拟，计算结果和实测结果吻合良好．