金属学报, 2017, 53(7): 789-796
doi: 10.11900/0412.1961.2016.00538
钢中第二相粒子形貌预报理论和检测方法

Morphology Prediction Theory and Experimental Measurement for the Secondary Phase Particle in Steel
郭靖1,2, 郭汉杰1,2,, 方克明1, 段生朝1,2, 石骁1,2, 杨文晟1,2

摘要:

控制钢中第二相粒子(包括非金属夹杂物和碳氮化物)的形貌对降低非金属夹杂物的危害、提高钢材力学性能等具有重要作用。本工作通过引入Jackson α指数建立了钢中第二相粒子形貌的预测理论模型,指出钢中第二相粒子形貌由其熔化熵、生长方向和温度(过冷度)决定。通过非水溶液电解的方法和室温有机溶液包埋(RTO)技术,结合SEM分析了4个钢种各类夹杂物的三维形貌以及其内部特征,实测的第二相粒子形貌与理论预测一致。理论和实验观察结果均证明,当第二相粒子Jackson α指数大于3时,其形貌为小面状;Jackson α指数小于2时,呈非小面状。

关键词: 第二相粒子 ; 形貌 ; Jackson 指数 ; 熔化熵 ; 非水溶液电解 ; RTO技术

Abstract:

It is significant to reduce the negative effects of non-metallic inclusion on steel and to improve steel mechanical properties through controlling the morphology of the secondary phase particle including non-metallic inclusion, nitride and carbide. Compared with particles with irregular shape, globular second phase particle could reduce the stress concentration during rolling and heat treatment process obviously and lower its harmfulness to steel toughness. A theoretical model to predict the morphology of the secondary phase particle in steel has been established by introducing a dimensionless Jackson α factor, and the morphology of the secondary phase particle is determined by its dissolved entropy, growth direction and temperature or undercooling. Non-aqueous solution electrolysis extraction and room temperature organic (RTO) technique were applied to detect the 3D morphology of the secondary phase particle and its inner morphology combining with SEM. The morphologies of particles observed in four different types of steels are in good agreement with the theoretical predictions. Theoretical predictions and experimental observation were both confirmed that the secondary phase particle is faceted in morphology when its Jackson α factor is more than 3 and non-faceted when its Jackson α factor less than 2.

Key words: secondary phase particle ; morphology ; Jackson factor ; dissolved entropy ; non-aqueous solution electrolysis ; RTO technique

钢中非金属夹杂物和第二相粒子易引起钢基体性能的不连续,同时,由于其在轧制过程变形抗力与钢基体一般差别较大,在轧制过程中夹杂物周围容易产生应力集中,故易成为轧板内微裂纹的起点,微裂纹的扩展可能成为表面宏观裂纹等缺陷,影响钢的表面质量和力学性能。球形第二相粒子在轧制过程中的应力集中相对较轻,而多边形特别是有尖角的第二相粒子应力集中严重,容易成为微裂纹源[1,2]。此外,钢中第二相粒子的形貌对钢的切削性能等也有明显的影响[3,4]。Kim等[5]指出,控制Fe-Al金属间化合物粒子(B2)形貌(球形)以及弥散分布,不仅可以降低其对钢材韧性的不利影响,还可以作为有效的二次强化相,获得超高强度低密度Fe-Al-Ni合金。所以,控制钢中第二相粒子的形貌对降低夹杂物危害以及提高钢材的质量均有重要作用。但是,目前对第二相粒子形貌控制的研究还很不深入,主要有2个方面的难点:第一,尚未建立起第二相粒子形貌控制的理论,对于第二相粒子形貌的影响因素目前还未从理论上阐述清楚;第二,实验上缺乏有效分析手段,目前普遍使用的金相法只能观察第二相粒子一个截面,尚无法观察到非金属夹杂物等第二相粒子的整体形貌。

由于控制晶体形貌在材料、地质、珠宝等学科的重要意义,科研工作者对金属熔体[6~10]、无机非金属熔体[11~14]以及有机溶液[15,16]等晶体形貌控制的理论做了大量研究。液态第二相粒子属于玻璃质,由于表面张力的作用,一般呈球形。固态第二相粒子的形成是氧化物或碳氮化物晶体的析出长大过程,与其它类型晶体形核和长大过程相类似,所以文献中研究晶体形貌的方法和结果可以借鉴用来研究钢中第二相粒子形貌及其控制因素。对于钢中的第二相粒子形貌,亦有很多研究者[17,18]进行研究,但由于理论和实验手段的限制研究还很不充分。本文作者应用Jackson α指数建立了多元炉渣中晶体形貌的控制模型并将其应用于改善高Al先进高强钢保护渣润滑性能[19],但该理论在钢中第二相粒子的适用性尚需进一步验证。

针对金相方法的不足,人们开发使用电解或者酸浸的方法进行分析,但是这些方法使用酸液会溶解第二相粒子中的碱性成分,如钙铝酸盐和硫化物等,使第二相粒子的形貌失真,仅可用于分析少数与酸液较难反应的第二相粒子,如Al2O3等。方克明和王国承[20]开发出利用有机溶液进行电解的方法,避免了电解过程中对第二相粒子的损伤,为观察第二相粒子整体形貌提供了有力途径。

本工作通过引入Jackson α指数,建立预测钢中第二相粒子形貌的理论,应用非水溶解电解技术和室温有机溶液包埋(RTO)并切片技术,观察钢中第二相粒子三维形貌特征和第二相粒子内部形貌特征,并分析钢中第二相粒子形貌的影响因素。

1 钢中第二相粒子形貌预测理论

基于金属熔体中晶体/熔体界面自由能最小时最稳定的原理,Jackson[6,7]最先利用统计热力学原理建立预测合金熔体晶体/熔体界面形貌预测理论,并根据晶体/熔体界面形貌评判晶体的形貌。其理论认为:若晶体/熔体界面是粗糙的,则对应晶体是非面状的,若晶体/熔体界面是平的,则对应晶体是面状的,并提出一个无量纲的参数,即Jackson α指数,作为晶体形貌的判据,其理论已在金属熔体、有机溶液以及部分简单无机氧化物熔体中得到成功应用。钢中固态第二相粒子的形成符合Jackson假设体系的条件,可以应用并扩展该理论预报钢中第二相粒子形貌。Jackson[6,7]推导的固/液界面的相对自由能表达式为:

ΔF NkT = X ( 1 - X ) α + XlnX + ( 1 - X ) ln ( 1 - X ) (1)

式中, ΔF 为结晶过程晶体界面自由能, N 为晶体表面晶格数目, k 为Boltzman常数,T为热力学温度。以 X 为晶体/熔体界面晶体原子所占比例,α即为Jackson α指数,定义为[6]

α = ξ ( hkl ) Δ H m R T m = ξ ( hkl ) Δ S m R (2)

式中, ξ ( hkl ) 为晶体生长取向指数,为晶体/熔体界面晶胞原子数与配位数比值,由晶体的性质可知其为介于0.5~1.0的常数[21],且在不同的生长方向其值可能并不相同; Δ H m Δ S m 分别为晶体的熔解焓和熔解熵; T m 为熔点; R 为气体常数。

图1所示为由式(1)计算得到的界面相对自由能与界面晶体原子占比X的关系。由图可见,当α<2时,晶体/熔体界面的相对自由能在X=0.5的时候最小,此时晶体/熔体界面是最为“粗糙”的,根据Jackson的理论,此时对应的晶体是非面状的;同理,当α>3时,界面相对自由能在X=0或X=1时最小,此时界面最为“平坦”,则对应为面状晶体。因此,可以通过晶体的Jackson α指数的大小对晶体形貌进行评判。

图1 不同Jackson α指数时晶体/熔体界面相对自由能与界面晶体原子占比的关系

Fig.1 Relations between crystal/melt interface relative energy and fraction of crystal lattice atom (X) with different Jackson α factors (ΔF—crystal/melt interface free energy, N—the number of crystal lattice on the crystal/melt interface, k—Boltzman constant, T—temperature)

由式(2)可以得出,钢中第二相粒子的形貌由第二相的自身性质(熔化熵)、生长方向和温度(过冷度)所决定。Jackson α指数与晶体的熔解焓成正比,所以其物理意义即为通过评估晶体与对应熔体之间混乱度(熵)的差别来判断晶体特性强弱:α越大,表示生成的晶体与熔体的熵值差别越大,生成的晶体越有序,越表现为小面状形貌特征;反之则表现出非面状的形貌特征。由图1可知,面状晶体的临界α为3附近,而非面状晶体的临界α在2附近。对大量的金属晶体形貌的观察结果均已证实该判据的有效性[6,7]

需要指出的是,式(2)只有在平衡的条件下才成立,而在非平衡的条件下,如在过冷的熔体中,式(2)中的2个等式并不相等,因为在非平衡的条件下熔解Gibbs自由能 Δ G m 0 。对于过冷熔体,温度为T时晶体的熔解熵 Δ S m , T 表示为:

Δ S m , T = S m , T m f - T T m ( C l - C s ) T dT (3)

式中, C l C s 分别为液态和固态化合物的等容比热容, S m , T m f 为晶体熔点时熔化熵。显然,在 C l C s 差别不大或者过冷度较小时,温度T时熔解熵可以用熔点的熔化熵近似表示。

2 实验方法

图2为非水溶液电解第二相粒子的装置示意图。以试样作为阳极,不锈钢管作为阴极,一定配比的无水甲醇溶液作为电解液,使用直流电源提供电解电流,阳极发生的电解反应如式(4)所示,阴极发生的反应如式(5)所示。用非水溶液电解时,将试样切成直径8~12 mm、长80 mm左右的圆棒试样,电解温度控制为0~5 ℃,电解电流强度为30~60 mA/cm2。电解4 h后,停止通电,使用超声波清洗剩余试样,收集电解液,使用真空抽滤器抽滤以得到不同粒径尺寸范围颗粒的溶液,再使用淘洗的方法得到不同尺寸范围的第二相粒子。本工作对4个钢种进行了电解实验,各钢种成分如表1所示,其中包括铝镇静钢(A)、硅镇静钢(B),低碳钢(C)和高碳钢(D),钢AB主要的第二相粒子为非金属夹杂物,钢CD主要为碳氮化物。所有试样均在浇铸完铸坯中心处取得。为了观察第二相粒子内部的结构及形貌特点,使用RTO技术包覆第二相粒子后“切开”进行观察,其步骤简述如下:将电解后收集的第二相粒子均匀放置在Cu片上作为阴极,使用纯Cu片作为阳极,通过适当电流使阳极电解并让Cu2+在阴极上沉积,阳极和阴极的电化学反应分别如式(6)和(7)所示。在第二相粒子被Cu完全包覆后,再使用极细的砂纸将包覆的第二相粒子“切开”,以便后续使用EVO 18扫描电镜(SEM)、Supra 55场发射扫描电镜(FSEM)及X-Max Extreme能谱仪(EDS)进行观测分析,过程示意图如图3所示。

Fe = F e 2 + + 2 e - (4)

2 C H 3 OH + 2 e - = 2 C H 3 O - + H 2 ( g (5)

Cu = C u 2 + + 2 e - (6)

C u 2 + + 2 e - = Cu (7)

图2 非水溶液电解装置示意图.

Fig.2 Schematic of apparatus for non-aqueous solution electrolysis (1—specimen, 2—stainless steel sheet, 3—thermometer, 4—solution, 5—beaker, 6—holder, DC—direct current)

图3 RTO技术包埋和“切开”第二相粒子步骤示意图

Fig.3 Schematic of steps wrapping and cutting the extracted secondary phase particle by room temperature organic (RTO) technique

表1 实验所用钢种及成分
Table 1 Tested steel grades and compositions
Steel grade C Si Mn P S Als Ti Cr Ni Mo Co
A 0.04 0.02 0.15 0.01 0.005 0.04 0.06 - - - -
B 0.05 0.50 1.10 0.01 0.008 - - 18.22 8.10 - -
C 0.03 0.29 0.13 0.014 0.002 5.20 0.12 24.20 0.12 - -
D 1.14 0.50 0.60 0.03 0.007 - 0.0049 4.70 - 9.30 8.10

表1 实验所用钢种及成分

Table 1 Tested steel grades and compositions

3 结果与讨论
3.1 常见第二相粒子Jackson 指数

图4给出了B钢中使用非水溶液电解法收集的第二相粒子和使用RTO技术切开后的第二相粒子形貌,可见B钢中夹杂物粒子大多数为球形,切开后有些粒子内部可见有析出物。

图4 B钢中使用电解法收集的第二相粒子和RTO技术切开后的第二相粒子形貌

Fig.4 Morphologies of the secondary phase particles in steel B after extration by non-aqueous solution electrolysis (a) and after cutting by RTO technique (b)

表2列出了钢中常见第二相粒子的Jackson α指数,其中热力学参数摘自文献[22,23]。根据各类第二相粒子的α,可将其分为3类:第一类,α小于2,如SiO2、FeO和MnS等,推测这类第二相粒子形貌为表面光滑的球形或类球形等非多面体形状;第二类,第二相粒子由于生长方向不同,α有可能大于2,也有可能小于2,如CaF2、CaO、TiC和CaSiO3等,这类第二相粒子可能会呈小面状,也有可能呈非小面状;第三类,第二相粒子在各个方向生长其α均大于3,如Al2O3、TiN及各类钙铝酸盐等,这类第二相粒子一般呈多面体或不规则形状。

表2 钢中典型第二相粒子的Jackson α指数[22,23]
Table 2 Jackson α factor of some typical secondary phase particles in steel[22,23]
Particle type Crystalline structure ξ(hkl) Tm/ K ΔHm/ (kJmol-1) α
Al2O3 (corundum) hcp 0.5~1.0 2327 118.41 3.06~6.12
AlN (S-G)* hcp 0.5~1.0 4349 189.61 2.62~5.24
SiO2 (quartz) Tetragonal 0.5~1.0 1996 9.58 0.29~0.58
CaO (lime) fcc 0.5~1.0 2845 28.50 1.18~3.36
CaF2 cubic 0.5~1.0 1691 29.71 1.06~2.11
FeO fcc 0.5~1.0 1650 24.06 0.43~0.86
MgO fcc 0.5~1.0 3098 77.40 1.51~3.01
MnO fcc 0.5~1.0 2058 54.39 1.59~3.18
MnS fcc 0.5~1.0 1803 26.11 0.44~0.87
NbO fcc 0.5~1.0 2218 54.39 1.48~2.95
Nb2O3 0.5~1.0 1785 102.93 3.47~6.94
NiO fcc 0.5~1.0 2230 50.68 1.37~2.73
TiC fcc 0.5~1.0 3290 71.13 1.38~2.76
TiN fcc 0.5~1.0 2023 54.39 3.15~6.29
TiO 0.5~1.0 2112 110.46 4.06~8.11
Ti2O3 0.5~1.0 2047 138.07 1.88~3.76
Ti3O5 0.5~1.0 2143 66.94 4.17~8.33
TiO2 0.5~1.0 943 66.27 1.78~3.55
V2O5 0.5~1.0 2950 87.03 3.15~6.29
ZrO2 0.5~1.0 2023 54.39 4.06~8.11
MgAl2O4 - 0.5~1.0 2381 160.65 4.06~8.12
CaSiO3 - 0.5~1.0 1813 (1817) 57.00 (56.07) 1.85~3.70
CaAl4O7 - 0.5~1.0 2038 128.4 3.79~7.57
CaAl2O4 0.5~1.0 1877 55.0 1.76~3.51
Ca12Al14O33 0.5~1.0 1709 432.0 15.19~30.38
Ca3Al2O6 0.5~1.0 1814 72.0 5.59~11.18

Note: (S-G)*—from solid phase to gaseous phase, ξ(hkl)—a orientation factor, Tm—melting point, ΔHm—fusion enthalpy

表2 钢中典型第二相粒子的Jackson α指数[22,23]

Table 2 Jackson α factor of some typical secondary phase particles in steel[22,23]

3.2 典型第二相粒子形貌

图5为A钢中Al2O3、MgAl2O4和TiN 3类典型非金属夹杂物的形貌,图中夹杂物种类均由EDS确定。由图5a、c和e可以看出,这3类第二相粒子均为小面状。但由图5b和d可知,Al2O3与MgAl2O4似乎呈球形或类球形,而图5f所示的TiN粒子呈多角的齿轮状。由表2可知,这3类第二相粒子的α均大于3,其形貌应都是呈小面状的,造成这种偏差的原因即金相方法只能观察第二相粒子的一个平面,无法获得第二相粒子整体形貌。

图5 A钢中Al2O3、MgAl2O4和TiN典型形貌

Fig.5 Typical morphologies of Al2O3 with α=3.06~6.12 (a, b), MgAl2O4 with α=4.06~8.12 (c, d) and TiN with α=3.15~6.29 (e, f) inclusions in steel A(a) polyhedral (b) spheroidal (c) polyhedral (d) spheroidal (e) cubic (f) gear-like

图6a和b所示为A钢中使用非水溶液电解法收集的典型的Al2O3夹杂物的SEM像,图6c和d是B钢中典型夹杂物的SEM像。由图6a和b可见,Al2O3夹杂物呈小面状或不规则形貌,且夹杂物在不同方向生长,小面状形貌也并不相同。由表2可知,Al2O3夹杂物的α随生长方向不同,在3.06~6.12之间,均大于3,可知其形貌为小面状,理论预测与实测观察相符。图6c所示为球状的CaO-SiO2-MnO系夹杂物,在炼钢温度下其为液态,由于液面张力的作用,液态夹杂物为球形。根据α指数的定义,其并不能用来预测非晶体的形貌,但是由 Δ S m 的物理意义可知,生成液态夹杂物为完全无序结构, Δ S m 可认为近似为0,α指数最小,亦能解释为何其非晶体特征为最明显的球形形状。由图6d可见这类液态夹杂物表面析出大量的短棒状或颗粒状的白色MnS。

图7给出了用RTO技术包埋并“切开”后第二相粒子的内部形貌。如图7a和b所示,Al2O3夹杂物内部较为致密,没有观察到析出物,这也可以解释其坚硬难以变形的原因。如图7c和d所示,切开后球形CaO-SiO2-MnO系夹杂物内部析出了近似球形的富二氧化硅相,其成分主要为SiO2,在夹杂物边缘分布着椭球状或棒状的MnS (图7d)。文献[24,25]使用金相方法也得到与图7d相似的MnS粒子形貌,但是对比图6d所示的MnS三维形貌,可知二者相差非常大,仅凭二维形貌有时很难得到真实的形貌。如表2所示,SiO2和MnS的α分别在0.29~0.58和0.44~0.87,所以由理论预测其形貌应为非小面状的球形或椭球形,实际夹杂物形貌与理论预测结果相吻合。由图5~7可见,使用金相试样观察钢中第二相粒子形貌貌只能观察其中的一个平面,难以得到第二相粒子整体形貌信息,有时甚至容易产生误判;而应用非水溶液电解法以及RTO技术,可以清楚观察到夹杂物三维形貌以及内部结构,得到很多金相制样方法难以获得的有效信息。

图6 使用非水溶液电解后钢中非金属夹杂物的典型形貌

Fig.6 Morphologies of typical inclusion after non-aqueous solution electrolysis(a, b) faceted Al2O3 from steel A under different magnifications (c, d) spherical or spheroidal CaO-SiO2-MnO from steel B under different magnifications

图7 用RTO技术包埋并“切开”后第二相粒子的内部形貌

Fig.7 Inner morphologies of the secondary phase particle after being cut using RTO technique(a, b) polyhedral Al2O3 from steel A under different magnifications, no precipitates (c, d) spherical or spheroidal CaO-SiO2-MnO from steel B under different magnifications

由EDS分析C钢中的第二相粒子主要类型为氮化物,其典型形貌由图8a~c所示,其中图8a为TiN,图8b和c为AlN。TiN粒子为类似正六面体形貌,α为3.15~6.29,实验结果与理论预测结果吻合;对于AlN的形貌既观察到小面状(图8b),又观察到表面光滑的椭球状(图8c)。文献中尚鲜有AlN的熔点和潜热等数据,表2中列出了AlN的气化温度、气化焓及由气化焓估算的 α (2.62~5.24),其晶体结构与Al2O3相似,但α要明显小于Al2O3,可以推测AlN的α应该也属于前文所述的第二类情况。D钢中第二相粒子以各类碳化物为主,本文课题组[26]通过XRD确定D钢中主要的碳化物种类为MC、M2C、M6C和M7C3等。电解后典型的形貌如图8d~f所示,可见D钢中碳化物粒子形貌多样,既有小面状的(图8d),也有表面光滑的短棒状(图8e)和弯曲棒状的(图8f)。碳化物种类较多,熔点较高,熔化的热力学数据很少能够查到。表2中TiC (MC)的α为1.38~2.76,也属于第二种类型,与观察到的碳化物形貌相符。文献[27]报道了H13热作模具钢(中碳钢,C为0.40%左右)主要碳化物种类为MC、M8C7M23C6等,其形貌有方形(小面状),也有球形(非小面状),与本工作结果相一致,这也说明本模型具有较广的适用性。

图8 C钢中典型氮化物及D钢中典型碳化物的形貌

Fig.8 Morphologies of typical nitrides in steel C (a~c) and carbides in steel D (d~f)(a) TiN, cubic (b) AlN, polyhedral (c) AlN, spheroid (d) carbide, faceted (e) carbide, rod-like (f) carbide, needle-like

由Jackson α指数的定义(式(2))可以得出,钢中第二相粒子的形貌由第二相的自身性质(熔化熵)、生长方向和温度(过冷度)所决定,所以可以通过控制钢中第二相粒子的生长方向以及析出温度等对其形貌进行控制。当然,由于某些第二相粒子一般在固-液两相区以及固相线温度以下析出,钢液成分以及动力学条件对其形貌的影响可能也十分重要,对非平衡态过冷熔体中的第二相粒子的形貌需要更深入的研究。

4 结论

(1) 使用传统金相试样观察钢中第二相粒子形貌貌只能观察其中的一个平面,难以得到第二相粒子整体形貌信息,有时甚至容易产生误判;应用非水溶液电解法以及RTO技术,可以清楚观察到夹杂物的三维形貌以及内部结构,得到很多金相制样方法难以获得的有效信息。

(2) 钢中第二相粒子的形貌由其熔化熵、生长方向、温度(过冷度)决定。使用Jackson α指数可以有效评判钢中第二粒子的形貌特征,若其Jackson α指数大于3,则其形貌一般呈小面状;若Jackson α 指数小于2,则其形貌为非小面状的球形或类球形。Al2O3、MgAl2O4和TiN在不同方向生长形貌有所不同,但均为小面状;SiO2和MnS形貌为非小面状的;而AlN和碳化物粒子在不同的生长方向可能为小面状的,也有可能为非小面状的。

The authors have declared that no competing interests exist.

参考文献

[1] Záhumenský P, Merwin M.Evolution of artificial defects from slab to rolled products[J]. J. Mater. Process. Technol., 2008, 196: 266
In this study, an operational experiment was conducted where artificial defects were applied to a slab to observe the evolution of surface defects from slab to coated strip. The aim of this work is to find the effect of defect dimension (diameter, depth) and its filling (casting powder/open) on the defect shape and position in the strip after hot rolling, cold rolling, and tinning. Three identical sets of artificial defects were drilled in the trial slab made of tin-grade steel. The first set was sampled after hot rolling, the second set was sampled after cold rolling, and the third set was sampled after tinning. The defects were metallographically analyzed in cross-sections using light microscopy and scanning electron microscopy including energy-dispersive X-ray spectroscopy. Many of the induced defects were found to have healed during processing, and the appearance of a single defect was found vary substantially between positions.
DOI:10.1016/j.jmatprotec.2007.05.045      URL     [本文引用:1]
[2] Yu H L, Bi H Y, Liu X H, et al.Behavior of inclusions with weak adhesion to strip matrix during rolling using FEM[J]. J. Mater. Process. Technol., 2009, 209: 4274
Inclusions inevitably exist in steel strips, whose deformation behavior during rolling severely affects the quality of product. In this paper, the behavior of inclusions in stainless steel strip during cold rolling under various inclusion sizes and positions, and shapes (circle, square, and triangle) were simulated by the finite element method for both hard and soft inclusions when the inclusions were with weak adhesion to the strip matrix. The inclusion shape, the crack position, and size around inclusions after rolling were obtained. When the inclusions are hard, there are cracks around them after rolling. When the inclusions are soft, there are no cracks around them for the circle, square, and triangle inclusions. The calculated results of the relationship between the inclusions and the strip matrix after cold rolling are in good agreement with those of the experimental ones.
DOI:10.1016/j.jmatprotec.2008.11.004      URL     [本文引用:1]
[3] Jiang L Z, Cui K, Hänninen H.Effects of the composition, shape factor and area fraction of sulfide inclusions on the machinability of re-sulfurized free-machining steel[J]. J. Mater. Process. Technol., 1996, 58: 160
The effects of the composition, shape factor (length:width ratio) and area fraction of sulfide inclusions on the machinability of re-sulfurized free-cutting steels have been investigated in terms of cutting force, flank wear and surface roughness. The cutting force was reduced by sulfide inclusions in the following decreasing order: MnS, (Mn,Ca)S, MnS-RE 2 S 3 and (Mn,Ca)S-RE 2 S 3 . Flank wear of the cutting tools was also reduced by sulfide inclusions in the same increasing order as above. The elongated sulfide inclusions were more effective in reducing the cutting force than the globular sulfide inclusions, whilst the latter were more effective in reducing the flank wear of the tools. The increase of area fraction of sulfide inclusions resulted in reduction of both the cutting force and the flank wear of the tools. There were two conflicting factors concerning the effects of both the shape factor and area fraction of sulfide inclusions on the surface finish of the steel workpieces.
DOI:10.1016/0924-0136(95)02144-2      URL     [本文引用:1]
[4] Shao X J, Wang X H, Jiang M, et al.In situ observation of MnS inclusion behavior in resulfurized Free cutting steel during heating[J]. Acta Metall. Sin., 2011, 47: 1210
[本文引用:1]
(邵肖静, 王新华, 姜敏. 加热过程中硫系易切削钢中MnS夹杂物行为的动态原位观察. 金属学报,2011, 47: 1210)
URL    
[5] Kim S H, Kim H, Kim N J.Brittle intermetallic compound makes ultrastrong low-density steel with large ductility[J]. Nature, 2015, 518: 77
Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.
DOI:10.1038/nature14144      PMID:25652998      URL     [本文引用:1]
[6] Jackson K A.Growth and Perfection of Crystals[M]. New York: John Wiley and Sons Inc., 1958: 319
[本文引用:5]
[7] Jackson K A.Liquid Metals and Solidification[M]. Ohio, Metals Park: ASM, 1958: 174
[本文引用:3]
[8] Li D, Herlach D M.Direct measurements of free crystal growth in deeply undercooled melts of semiconducting materials[J]. Phys. Rev. Lett., 1996, 77: 1801
[本文引用:0]
[9] Lu Y P, Yang G C, Liu F, et al.The transition of alpha-Ni phase morphology in highly undercooled eutectic Ni78.6Si21.4 alloy[J]. Europhys. Lett., 2006, 74: 281
High undercooling up to 550 K (0.39 T) was achieved in eutectic NiSimelt using glass fluxing combined with the cyclic superheating. According to the microstructure evolution with the initial undercooling, surprisingly, a transition from non-faceted to faceted phase occurs for the as-solidified morphology of the alpha-Ni phase at the undercooling of 390 K. On the basis of the entropy of fusion criterion and the interface kinetics, this interesting morphology transition at high undercooling is analyzed.
DOI:10.1209/epl/i2005-10525-0      URL     [本文引用:0]
[10] Lipton J, Kurz W, Trivedi R.Rapid dendrite growth in undercooled alloys[J]. Acta Metall., 1987, 35: 957
The theory of dendritic growth into undercooled alloy melts is extended to the case of large undercoolings, i.e. to high growth rates. This is done by applying the results of the complete stability analysis of a plane interface to the tip of an Ivantsov dendrite. For small Péclet numbers this model corresponds to a model published previously. For large Péclet numbers i.e. large undercoolings, however, the stability parameters become functions of Péclet numbers and cause drastic changes in the growth behaviour of the dendrite. Furthermore the limit of absolute stability is predicted when the undercooling is equal to the sum of the thermal unit undercooling and the equilibrium freezing range of the alloy.
DOI:10.1016/0001-6160(87)90174-X      URL     [本文引用:1]
[11] Lofgren G.An experimental study of plagioclase crystal morphology; isothermal crystallization[J]. Am. J. Sci., 1974, 274: 243
ABSTRACT. Crystallization experiments on plagioclase gels using internally heated pressure vessels have shown that it is possible to grow plagioclase crystals sufficiently large to study mineral textures. By tirst melting the charge and then rapidly cooling to the
DOI:10.2475/ajs.274.3.243      URL     [本文引用:1]
[12] Kirkpatrick R J.Crystal growth from the melt: A review[J]. Am. Mineral., 1975, 60: 798
This paper reviews four aspects of crystal growth theory: the nature of the rate-controlling process, the mechanism controlling molecular attachment onto the growing crystal surface, the nature of the crystal-melt interface, and the stability of planar interfaces relative to cellular interfaces. The rate-controlling process may be diffusion in the melt, heat flow, or the reaction at the crystal-melt interface. Diffusion or heat-flow controlled growth generally leads to a cel- lular morphology. For most silicates, interface-controlled growth leads to a faceted morphology. If the rate-controlling process is the interface reaction, the mechanism at the in- terface may be either continuous, with molecular attachment occurring at all points on the crystal surface, or lateral, with attachment occurring only on steps of the surface. The mechanism actually occurring can be determined by the dependence upon undercooling of the growth rate corrected for the viscosity ofthe melt. The nature ofthe interface can be described in terms of the interface roughnegs, which may be considered to be the topographic relief on the surface. Materials with small latent heats of fusion, such as quartz, should have molecularly rough interfaces and grow with a nonfaceted morphology, while materials with large latent heats, such as most other silicates, should have smooth interfaces and grow with a faceted morphology. The stability of planar interfaces relative to cellular interfaces can be dis- cussed in terms of diffusional, heat-flow, surface-energy, and kinetic effects. For a freely grow- ing crystal, such as in a magma chamber, only the surface-energy and kinetic effects aid in stabilizing planar interfaces. An attempt has been made to illustrate each of the phenomena discussed with a silicate example, although in one case an organic example is necessary.
URL     [本文引用:0]
[13] Heulens J, Blanpain B, Moelans N.Analysis of the isothermal crystallization of CaSiO3 in a CaO-Al2O3-SiO2 melt through in situ observations[J]. J. Eur. Ceram. Soc., 2011, 31: 1873
Crystal growth of Wollastonite (CaO·SiO 2) in a 42CaO–10Al 2O 3–48SiO 2 melt is observed in situ at 1320 ° C and 1370 ° C using a high-temperature confocal scanning laser microscope (CSLM). The crystallization is initiated by seeding the melt with Wollastonite particles, which is the primary phase at these temperatures and composition. At 1370 °C, a faceted growth form is observed, while at 1320 °C, dendritic, non-faceted growth occurs. The dendrite tip velocity is measured and compared with Ivantsov’s theory. The presented experimental technique proofs to be successful for characterizing isothermal crystallization of minerals in silicate melts.
DOI:10.1016/j.jeurceramsoc.2011.03.038      URL     [本文引用:0]
[14] Li J L, Shu Q F, Chou K.Effect of agitation on crystallization behavior of CaO-Al2O3-SiO2-Na2O-CaF2 mold fluxes with varying basicity[J]. Metall. Mater. Trans., 2015, 46B: 1555
The effect of agitation on crystallization behaviors of CaO-Al 2 O 3 - SiO 2 -Na 2 O-CaF 2 mold fluxes with basicity of 1.1 and 1.2 was investigated. It was found that crystallization temperatures of agitated samples were higher than those of static samples. The morphology of cuspidine shifted from dendrites to facet crystals with the decrease of temperature. The agitation was conducive to the formation of small dendritic cuspidine and could lead to crystals with smaller size. Crystalline fraction could be significantly enhanced by agitation at the initial stage of crystallization.
DOI:10.1007/s11663-015-0357-3      URL     [本文引用:1]
[15] Hill A.Entropy production as the selection rule between different growth morphologies[J]. Nature, 1990, 348: 426
CRYSTALLIZATION of a solid phase from a melt or solution is a special case of pattern formation in which the dissipation of energy across the free energy gradient between the two phases can give rise to various growth morphologies in the steady state 1 . Experimental studies of crystallization from undercooled solutions 2 , electrolytic deposition 3,4 and the formation of fluid patterns in a Hele鈥揝haw cell 5 have revealed faceted, dendritic, 'dense-branching' and fractal morphologies 6 . For a system with fixed anisotropy and interfacial tension, changes in the driving force for the transition (such as the degree of undercooling) can cause changes in growth morphology which are usually accompanied by changes in growth rate. The selection rule that determines these morphologies remains unclear, although a recent suggestion 5,6 is that it is based on the growth velocity. Here I propose that selection is governed by the rate of entropy production per unit area of the different growth patterns. This principle allows accurate prediction of the morphology transition observed for the crystallization of NH 4 CI (ref. 2). I suggest that it may reflect a more general thermodynamic principle underlying a wide range of natural processes.
DOI:10.1038/348426a0      URL     [本文引用:1]
[16] Berge B, Faucheux L, Schwab K, et al.Faceted crystal growth in two dimensions[J]. Nature, 1991, 350: 322
CRYSTAL growth has attracted interest for centuries 1 . Three-dimensional crystals are usually faceted, but equilibrium thermodynamics prohibits faceting in two dimensions 2 : the one-dimensional perimeter of a two-dimensional crystal cannot exhibit long-range order at any non-zero temperature 3 . This need not, however, prevent facets from being stable dynamically during the growth process. Computer simulations have indeed produced nearly faceted two-dimensional crystals 4,5 . Here we describe the results of experiments on monolayers of a surfactant, sodium dodecyl sulphate (SDS), at the surface of an aqueous solution. Surface-tension measurements and fluorescence microscopy 6–8 reveal a solid–liquid transition in the surface monolayer at fixed SDS bulk concentration, as the temperature is decreased. At low SDS con-centration, faceted monolayer crystals appear, although increasing the concentration induces a change to smoother growth morpho-logies. The faceted crystals become unstable as growth proceeds, the corners emitting filaments of various shapes. Some of these growth processes seem not to have three-dimensional analogues.
DOI:10.1038/350322a0      URL     [本文引用:1]
[17] Van Ende M A, Guo M X, Proost J, et al. Formation and morphology of Al2O3 inclusions at the onset of liquid Fe deoxidation by Al addition[J]. ISIJ Int., 2011, 51: 27
The initial stage of deoxidation and the influence of the oxygen level on the inclusion features were examined. Liquid Fe with various dissolved oxygen content (O) was brought into contact with Al in a quartz tube for a short time, i.e. 1, 5, 30 and 60 s. Microscopic investigations of the quenched samples revealed the formation of Al2O3 inclusions in the Fe-Al reaction zone, resulting from the motion of the diffusion front with time. Specific attention is given to inclusion size, location and morphology as a function of interaction time and O content. The latter was found to influence the inclusion characteristics. The inclusion number increased drastically with O content, which is related to the degree of supersaturation of the melt, one of the most important factors influencing the formation of inclusions. The inclusion morphology evolved from angular to spherical with increasing O content.
DOI:10.2355/isijinternational.51.27      URL     [本文引用:1]
[18] Ye Z C, Wang S Y, Wang X C.Study of inclusions in IF steel[J]. Acta Metall. Sin., 1999, 35: 1057
[本文引用:1]
(叶仲超, 王石杨, 汪晓川. IF钢中的夹杂物[J]. 金属学报, 1999, 35: 1057)
[19] Guo J, Seo M D, Shi C B, et al.Control of crystal morphology for mold flux during high-aluminum AHSS continuous casting process[J]. Metall. Mater. Trans., 2016, 47B: 2211
In the present manuscript, the efforts to control the crystal morphology are carried out aiming at improving the lubrication of lime-alumina-based mold flux for casting advanced high-strength steel with high aluminum. Jackson α factors for crystals of melt crystallization in multi-component mold fluxes are established and reasonably evaluated by applying thermodynamic databases to understand the crystal morphology control both in lime-alumina-based and lime-silica-based mold fluxes. The results show that Jackson α factor and supercooling are the most critical factors to determine the crystal morphology in a mold flux. Crystals precipitating in mold fluxes appear with different morphologies due to their different Jackson α factors and are likely to be more faceted with higher Jackson α factor. In addition, there is a critical supercooling degree for crystal morphology dendritic transition. When the supercooling over the critical value, the crystals transform from faceted shape to dendritic ones in morphology as the kinetic roughening occurs. Typically, the critical supercooling degrees for cuspidine dendritic transition in the lime-silica-based mold fluxes are evaluated to be between 0.05 and 0.06. Finally, addition of a small amount of LiO in the mold flux can increase the Jackson α factor and decrease the supercooling for cuspidine precipitation; thus, it is favorable to enhance a faceted cuspidine crystal.
DOI:10.1007/s11663-016-0697-7      URL     [本文引用:1]
[20] Fang K M, Wang G C.Study on non-metallic inclusions in steel from characterization to denaturation[J]. J. Chin. Rare Earth Soc., 2006, 24(Spec. Issue): 439
[本文引用:1]
(方克明, 王国承. 钢中的夹杂物研究从表征到改性[J]. 中国稀土学报, 2006, 24(专辑): 439)
钢中的夹杂物对钢的性能有着重要的影响.以往的研究大多集中在对夹杂物形貌、尺寸和组成的表征上,表征方法不同准确性不一样.长期以来,冶金界比较注重夹 杂物的来源和去除,对夹杂物的改性研究较少.夹杂物的改性可能比去除夹杂物的成本更低,对钢性能的改善可能产生更重要的影响.
URL    
[21] Jackson K A, Uhlmann D R, Hunt J D.On the nature of crystal growth from the melt[J]. J. Cryst. Growth, 1967, 1: 1
The theory of interface motion as applied to crystal growth by Cahn and his coworkers is examined in detail. This theory, as derived, applied to systems which can have a second order phase transformation but not to liquid-solid or vapor-solid phase transformations which are first order. In this paper, the formalism of the theory is applied to these first order phase transformations. Reasonable agreement with experiment still cannot be obtained. This is because the molecular configuration of the interface is averaged out in the theory by considering a diffuse interface, rather than taking it into account properly in calculating the growth rate. Experimental data on crystal growth have been accumulated and analyzed. It is concluded from this analysis that the theory of Jackson on interface roughness qualitatively predicts crystal growth morphology. Most of the quantitative data on crystal growth are, however, of questionable reliability or are not sufficiently complete for detailed comparison with theory. None of the existent theories of crystal growth can account for these data.
DOI:10.1016/0022-0248(67)90003-6      URL     [本文引用:1]
[22] Barin I, Knacke O.Thermochemical Properties of Inorganic Substances[M]. Berlin Heidelberg: Springer-Verlag, 1973: 73
[本文引用:2]
[23] Barin I, Knacke O, Kubaschewski O.Thermochemical Properties of Inorganic Substances: Supplement[M]. Berlin Heidelberg: Springer-Verlag, 1977: 49
[本文引用:2]
[24] Kim H S, Lee H G, Oh K S.MnS precipitation in association with manganese silicate inclusions in Si/Mn deoxidized steel[J]. Metall. Mater. Trans., 2001, 32A: 1519
When manganese silicate inclusions were formed during cooling from 1600 C, manganese and sulfur contents in the manganese silicate inclusions were much lower than their equilibrium values within the steel matrix, i.e. , the steel matrix was supersaturated with Mn and S against the inclusions. The formation of a Mn-depleted zone around an inclusion and the precipitation of a MnS phase on the inclusion were greatly affected by the thermal history of the steel. Slow cooling helped the formation of both the Mn-depleted zone and the MnS phase on the inclusion, but fast cooling suppressed it. Subsequent isothermal holding at 1200 C diminished the existing Mn-depleted zone in slow-cooled steel, but created a Mn-depleted zone for fast-cooled steel. The mass transfer within an inclusion was sluggish, and the formation of a MnS phase is due to the local saturation of Mn and S at the outer part of an inclusion. It was suggested that the major factors affecting the formation of the Mn-depleted zone and the MnS phase are the cooling rate, isothermal holding, and the sulfide capacity of the inclusion.
DOI:10.1007/s11661-001-0239-y      URL     [本文引用:0]
[25] Wang K P, Jiang M, Wang X H, et al.Formation mechanism of SiO2-type inclusions in Si-Mn-killed steel wires containing limited aluminum content[J]. Metall. Mater. Trans., 2015, 46B: 2198
The origin, formation mechanism, and evolution of SiO-type inclusions in Si-Mn-killed steel wires were studied by pilot trials with systematical samplings at the refining ladle, casting tundish, as-cast bloom, reheated bloom, and hot-rolled rods. It was found that the inclusions in tundish were well controlled in the low melting point region. By contrast, MnO-SiO-AlOinclusions in the as-cast bloom were with compositions located in the primary region of SiO, and most CaO-SiO-AlO-MnO inclusions lied in primary phase region of anorthite. Therefore, precipitation of SiOparticles in MnO-SiO-AlOinclusions can be easier than in CaO-SiO-AlO-MnO inclusions to form dual-phase inclusions in the as-cast bloom. Thermodynamic calculation by the software FactSage 6.4 (CRCT-ThermFact Inc., Montr al, Canada) showed that mass transfer between liquid steel and inclusions resulted in the rise of SiOcontent in inclusions from tundish to as-cast bloom and accelerated the precipitation of pure SiOphase in the formed MnO-SiO-AlOinclusions. As a result, the inclusions characterized by dual-phase structure of pure SiOin MnO-SiO-AlOmatrix were observed in both as-cast and reheated blooms. Moreover, the ratio of such dual-phase SiO-type inclusions witnessed an obvious increase from 0 to 25.4 pct before and after casting, whereas it changed little during the reheating and rolling. Therefore, it can be reasonably concluded that they were mainly formed during casting. Comparing the evolution of the inclusions composition and morphology in as-cast bloom and rolled products, a formation mechanism of the SiO-type inclusions in wire rods was proposed, which included (1) precipitation of SiOin the formed MnO-SiO-AlOinclusion during casting and (2) solid-phase separation of the undeformed SiOprecipitation from its softer MnO-SiO-AlOmatrix during multipass rolling.
DOI:10.1007/s11663-015-0411-1      URL     [本文引用:0]
[26] Luo Y W, Guo H J, Chen X C.Effect of nitrogen on the microstructure of AISI M42 high-speed steel [A]. AISTech - Iron and Steel Technology Conference Proceedings[C]. Pittsburgh, USA: 2016: 1123
[本文引用:1]
[27] Ning A G, Guo H J, Chen X C, et al.Precipitation behaviors and strengthening of carbides in H13 steel during annealing[J]. Mater. Trans., 2015, 56: 581
Abstract Deploying optical microscopy, transmission electron microscopy, electron diffraction and energy dispersive spectrometer analysis. This article analyze the categories and shapes of carbides of three different positions in H13 ingot after annealing: upside, middle and bottom of ingot. It is found that the microstructure of H13 after annealing is composed of granular pearlite+ small amounts of ferrite and carbide phase. The categories of carbides mainly include M23C6 and MC, precipitation temperatures of which are figured out through thermodynamic calculation. Through the test of mechanical properties, it is found sample at the bottom has the optimal mechanical property. Through statistics of amounts and average sizes of precipitates and calculation of precipitation strengthening, it is found that, from upside to bottom of H13 after annealing, the size of precipitates decreases with increase of precipitation volume fraction, and contributions of precipitates to yield strength enhance gradually.
DOI:10.2320/matertrans.M2014452      URL     [本文引用:1]
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关键词(key words)
第二相粒子
形貌
Jackson 指数
熔化熵
非水溶液电解
RTO技术

secondary phase particle
morphology
Jackson factor
dissolved entropy
non-aqueous solution elec...
RTO technique

作者
郭靖
郭汉杰
方克明
段生朝
石骁
杨文晟

GUO Jing
GUO Hanjie
FANG Keming
DUAN Shengchao
SHI Xiao
YANG Wensheng