Cu/Sb/Sn/Mo/W对新国标09CrCuSb钢组织及力学性能的影响

采用金相显微镜、扫描电镜、电子探针、拉伸力学性能测试、夏比冲击测试,研究了新国标NB/T47019-2021的09CrCuSb钢合金元素Cu、Sb、Sn、Mo和W对其微观组织和力学性能的影响。研究表明,新标准中增加的合金元素将促进钢中δ-铁素体的析出,同时也会增加材料强度但会降低其塑性;δ-铁素体将显著降低材料冲击力学性能[其中,R_p0.2=365.64 MPa,夏比冲击功KV₂为243 J(室温)和192 J(-40℃)],使得冲击断口由塑性断口向脆性断口特征转变,特别是对-40℃的冲击功降低作用尤为显著。在新国标成分框架下,须通过合理的热加工工艺调整,降低钢中δ-铁素体的析出,从而提高材料力学性能。     

550 MPa级海洋工程用钢板低温韧性波动原因分析

 550 MPa级海洋工程用钢在低温冲击功波动较大。为了进一步探究产生低温韧性波动的原因,在不同温度(-100 ℃~室温)对试验钢进行冲击试验。结合光学显微镜、扫描电子显微镜、透射电镜等设备,分析冲击断口、显微组织、第二相、夹杂物。结合热力学计算等对低温韧性波动原因进行分析讨论。结果表明,试验钢强度满足等级要求,随着温度降低冲击吸收功不断降低,韧脆转变温度为-50 ℃左右。在-60 ℃下冲击功出现较大波动,出现了18 J的极低值,断口为准解理断裂,剪切断面率为8%,裂纹源处存在Ti,Nb(C,N)和MnS的复合夹杂。而在相同温度下冲击功为122 J的试验钢,剪切断面率为34%,断口发现有明显的韧窝。试验钢组织主要为回火贝氏体加极少量铁素体,贝氏体板条中存在高密度位错,晶界上有(Fe,Cr)₃C合金渗碳体与少量NbC和富Cu析出相。试验钢以小角度晶界为主,大角度晶界占比较低。基体中有少量(Ca,Al,Mg,Mn,S)等复合夹杂物,多呈近圆形和多边形,大小多为1~3 μm,占检测到的总数量的85.87%。占比例最高的是CaS-Oxide-MnS类夹杂,为31.2%。热力学计算结果表明试验钢凝固过程中TiN先于MnS析出。晶界与晶内粗大的析出相、夹杂物、较高比例的小角度晶界与塞积的不可动位错等多种因素对低温冲击韧性产生不利影响,存在大颗粒含钛析出相是造成冲击韧性波动大的关键原因。     

铈和磷对中碳锰钢低温回火脆性的影响

本文采用冲击试验和断口扫描电镜，俄歇谱分析等方法，研究了铈对不同磷含量的中碳锰钢低温回火脆性的影响。结果表明，磷在奥氏体晶界偏聚是导致含磷锰钢产生低温回火脆性的原因，而铈的加入，可减少磷的偏聚程度，增加回火马氏体的冲击值，从而降低中碳锰钢的回火脆性。     

厚规格船板钢拉伸断口分层的原因分析

针对莱钢厚规格船板钢DH36拉伸试样表面出现麻点、裂纹,拉伸断口分层,断后伸长率低的问题,利用低倍、金相及扫描电镜等分析手段,对问题试样的显微组织及断口情况进行分析。结果表明,钢板中心部位碳和合金元素偏析及夹杂物在晶界处析出导致的带状组织、魏氏组织及微裂纹是断口分层的主要原因。制定合适的加热温度,减小成分偏析,抑制心部魏氏组织,可减缓这种分层现象。     

Q345B钢冲击功不合原因分析

对Q345B钢在20℃下冲击功不合的钢带进行化学分析、力学性能、冲击功检验,以及对冲击样断口进行金相分析、扫描电镜分析,判断Q345B冲击不合的原因。结果表明,冲击样断口为解理断口,钢中非金属夹杂物Ti(C,N)破坏了基体的连续性,是钢带冲击不合的根本原因;而材料晶粒粗大,裂纹容易穿过晶界进行扩展是Q345B解理断裂的主要原因。     

TiN对高强度耐磨钢韧性的影响及其机制分析

采用 SEM、EDS、TEM等技术,结合热力学软件,研究Ti含量对低合金耐磨钢低温冲击韧性的影响、断口夹杂物尺寸和形态以及夹杂物形态与冲击韧性的关系。结果表明,Ti元素质量分数为0.03%的低合金耐磨钢的低温(-40 ℃)冲击性能最好,可达33.0 J;断口夹杂物TiN的形态呈现3种形貌,即出现细窄裂纹、出现孔洞以及直接被撕裂;随着Ti含量的增加,夹杂物形态由完整到破碎。分析TiN的破碎机制发现,TiN破碎由2种机制产生,即裂纹扩展形成孔洞导致破碎、主裂纹衍生出更多的次裂纹导致破碎。     

回火工艺对针状铁素体钢组织和性能的影响

对针状铁素体钢进行540～630℃回火后的组织、性能进行了研究.与轧态相比,630℃回火后钢的屈服强度提高75 MPa,伸长率的平均值降低1.9%,冲击功的平均值提高1.75 J.对回火前、后钢板的组织和析出物进行了对比分析,结果表明:回火后晶粒内部的位错密度减小,亚晶板条部分消失;回火后析出物粒子的平均尺寸减小;回火温度越高,析出物粒子的平均尺寸越大.630℃回火以后,在1～10 nm尺度范围内的粒子分布频度增加2～3倍,铌的析出量增加了166.9%,钒的析出量增加了584.6%.细小析出物的增加和亚晶板条的部分消失是强度提高、塑性改善的主要原因.     

电渣重熔对Ｆe—38Mn奥氏体合金低温沿晶脆性的抑制作用

研究了真空熔炼Ｆe-38Mn奥氏体合金电渣重熔纱列冲击试样的断口形貌以及杂质元素和锰在晶界及晶内的分布。结果表明：真空熔炼Ｆe-38Mn合金存在明显的韧脆转变现象,７７Ｋ冲击功仅为２５Ｊ,断口为沿晶断裂特征。经电渣重熔后,韧脆转变现象消失,７７Ｋ的冲击功高达３００Ｊ,断口以韧窝为主并有少量准解理小刻面。电渣重熔后硫的的偏聚明显降低。该合金低温沿晶断裂的产生与硫在晶界的偏聚有关。     

Fe-P-C-Cu-Mo系粉末合金的组织、性能及断口

研究了Fe-P-C-Cu-Mo系铁基粉末冶金材料中合金元素、烧结温度对合金组织及性能的影响,以及不同回火温度下磷的分布及其对合金断裂方式的影响。
通过研究得出:Fe-0.60%P-0-44%C-1.0%Cu-0.50%Mo合金在1160-1240℃烧结,保温1-2小时,可以获得较好的性能;若进一步经过850-900℃淬火,200℃或600℃回火,则合金的综合机械性能可以显著提高。通过试验发现:合金在200℃回火后,固溶在基体中的铝能抑制磷向晶界偏聚,使合垒断裂时呈现为穿晶断裂;400℃回火后,由于钼以碳化物形式析出,磷主要偏聚在晶界,造成合金沿晶断裂;600℃回火后,磷主要偏聚在孔隙表面,合金断口呈韧窝状。     

1Cr12Ni3Mo2VN（M152）耐热钢的脆化机制

12%Cr耐热钢的脆化一直是材料研究的热点问题,借助于力学性能测试、金相分析、断口扫描分析以及TEM微观结构分析,研究了1Cr12Ni3Mo2VN（M152）耐热钢在淬火、回火以及时效过程中产生的脆性,结果表明：淬火时的冷却速度对冲击韧性有显著的影响,冷却速度过慢将导致不可逆脆性,其脆化机制是由于缓冷时M23C6碳化物沿原奥氏体晶界连续析出,以及回火时残余奥氏体发生分解导致M2C碳化物沿奥氏体薄膜连续析出,杂质元素的原奥氏体晶界偏聚不是产生脆化的原因,导致不可逆脆化的淬火缓冷通过的温度区间为820℃～660℃;与回火温度有关的脆性有二类：450℃～500℃回火产生的（475脆性）,脆化严重,其脆化机制是杂质元素的原奥氏体晶界偏聚和脆性相的析出,去脆化处理可以恢复其韧性;另一类是在约625℃回火产生的,脆化程度较轻;高温回火后缓冷引起的脆化很复杂,杂质元素的晶界偏聚、粗碳化物的析出以及二次淬火均导致回火脆性,通过去脆化处理均可以恢复其韧性。杂质元素的晶界偏聚是脆化的主导机制,二次淬火引起的脆化受环境影响非常大,引起的脆化也非常严重,是产品质量不稳定的主要原因。595℃长期时效脆化主要是由碳化物的析出以及杂质元素的非平衡晶界偏聚引起的,临界时间约为100h,通过去脆化处理可以恢复其部分韧性。     

Precipitation of austenite particles at grain boundaries during aging of Fe-Mn-Ni steel

Precipitation of austenite particles at grain and lath boundaries after aging treatment of a Fe-8Mn-7Ni alloy was investigated by selected area electron diffraction (SAD), X-ray energy dispersive spectrometry (EDS) in a scanning transmission electron microscope (STEM), and high-resolution (HRTEM) analysis. High spatial-resolution (2 to 5 nm) EDS analysis revealed no significant segregation of alloying elements at grain boundaries but the precipitation of very fine particles of Mn- and Ni-rich phase. Detailed EDS, SAD, and HRTEM analyses all confirmed that these particles are austenite phase, which have a Kurdjumov-Sachs (K-S) orientation relationship with one of the adjacent grain. The concentration of Mn and Ni in austenite, measured by EDS, varied from ∼15 pct to a maximum of ∼30 pct. Low-voltage scanning electron microscopy (SEM) fractographs also revealed the presence of very fine, second-phase precipitates on the fracture surface of the embrittled alloys.     

On the scavenging effect of precipitated austenite in a low carbon Fe-5.5Ni alloy

The scavenging effect of precipitated austenite in a low carbon, commercial Fe-5.5Ni cryogenic alloy was investigated through observation of the dissolution of cementite precipitates during intercritical tempering and study of the associated change in Charpy impact toughness. Cementite precipitates initially located along prior austenite grain boundaries were gradually dissolved into reverted austenite as the intercritical tempering proceeded. The austenite tends to form at or around the carbide particles and may be catalyzed by their presence. The Charpy impact energy is changed through both a decrease in the ductile-brittle transition temperature and an increase in the upper shelf energy. The latter effect is specifically associated with the dissolution of the carbides which act as preferential void nucleation sites in the untempered alloy.     

Correlation of microstructure and tempered martensite embrittlement in two 4340 steels

This study is concerned with a correlation between the microstructure and fracture behavior of two AISI 4340 steels which were vacuum induction melted and then deoxidized with aluminum and titanium additions. This allowed a comparison between microstructures that underwent large increases in grain size and those that did not. When the steels were tempered at 350°C,K _Ic and Charpy impact energy plots showed troughs which indicated tempered martensite embrittlement (TME). The TME results of plane strain fracture toughness are interpreted using a simple ductile fracture initiation model based on large strain deformation fields ahead of cracks, suggesting thatK _Icscales roughly with the square root of the spacing of cementite particles precipitated during the tempering treatment. The trough in Charpy impact energy is found to coincide well with the amount of intergranular fracture and the effect of segregation of phosphorus on the austenite grain boundaries. In addition, cementite particles are of primary importance in initiating the intergranular cracks and, consequently, reducing the Charpy energy. These findings suggest that TME in the two 4340 steels studied can be explained quantitatively using different fracture models.     

Impact Toughness of an NM400 Wear-Resistant Steel

An NM400 wear-resistant steel was hot rolled and then the plates were heat-treated by direct quenching and tempering (DQT) and reheat quenching and tempering (RQT) techniques, respectively. The Charpy impact test was carried out with an instrumented Charpy impact tester. The microstructure and fracture surface were investigated by a combination of optical microscopy, transmission electron microscopy and scanning electron microscopy methods. It was found that the impact toughness of DQT specimen was much higher than that of RQT specimen. The microstructure of both DQT and RQT specimens was characterized by a mixture of tempered lath martensite and lower bainite. The lower bainite in DQT specimen extended into prior austenite grains and the content was higher than that in RQT specimen. The lower bainite in DQT specimen improved the impact toughness by increasing the proportion of large-angle boundaries and relieving the stress concentration at the crack tip. A number of fine and dispersed carbides in DQT specimen also contributed to the improvement of the impact toughness.     

微观组织对一种高强度船板用钢低温冲击韧性的影响

采用室温拉伸、示波冲击、光学和扫描电镜组织分析、EBSD及断口分析等方法,研究了微观组织对一种高强度船板用钢低温冲击韧性的影响。结果表明,在相同合金成分条件下,由于压下率和冷却速率的差别,板厚1/2和1/4处的有效晶粒尺寸、大角度晶界比例及M/A岛的形态分布不同。有效晶粒尺寸、大角度晶界比例及第二相M/A岛的形态是影响低温冲击韧性的主要因素,其对低温冲击的裂纹形成功影响并不明显,但较大的有效晶粒尺寸、较低的大角度晶界比例及呈方向性分布的M/A岛却显著降低了裂纹扩展功,导致板厚1/2处的低温冲击韧性低于板厚1/4处。     

HB450低合金超高强耐磨钢回火过程中的组织性能演变

  利用透射电镜（TEM）、扫描电镜（SEM）等试验方法,研究了新型低成本HB450低合金超高强耐磨钢在不同回火条件下组织和性能演变规律,并分析了其强韧变化机制。结果表明：回火对试验钢的硬度和强度均有较大影响。在200~250℃回火,试验钢表现出良好的强韧性配合,满足国标工程机械用高强度耐磨板GB/T24186—2009中NM450级别要求;在250℃回火时,试验钢出现硬化迹象。透射电镜分析表明,在该温度下回火,析出物中除了有大量弥散分布的ε 碳化物外,还出现了少量30~50nm的（Nb,Ti）（C,N）粒子,该2类粒子对试验钢的强化起着较大的作用。     

Effect of Carbon on Grain Boundary Segregation of Phosphorus and Phosphorus-Induced Intergranular Fracture in High Purity Iron with Phosphorus

Ａｓｗｅｌｌｋｎｏｗｎ ,ｔｈｅａｄｄｉｔｉｏｎｏｆｃａｒｂｏｎｃａｎｐｒｅ ｖｅｎｔｔｈｅｐｈｏｓｐｈｏｒｕｓ ｉｎｄｕｃｅｄｉｎｔｅｒｇｒａｎｕｌａｒｆａｉｌｕｒｅｉｎｉｒｏｎ .ＢｕｔｉｔｉｓｔｈｅｒｅｓｕｌｔｏｆｕｓｉｎｇＡＥＳ (Ａｕｇｅｒｅｌｅｃ ｔｒｏｎｓｐｅｃｔｒｏｓｃｏｐｙ)ａｎａｌｙｓｉｓｉｎｆｒａｃｔｕｒｅｄｓｕｒｆａｃｅａｎａｌ ｙｓｉｓ .ＥｒｈａｒｔＨｅｔａｌ[1] ,ｉｎｏｒｄｅｒｔｏｅｘｐｌａｉｎｔｈｅｍｅｃｈ ａｎｉｓｍｏｆｃａｒｂｏｎｓｕｐｐｒｅｓｓｉｎｇｔｈｅｉｎｔｅｒｇｒａ…     

The Evaluation of Tempered Martensite Embrittlement in 4130 Steel by Instrumented Charpy V-Notch Testing

Tempered martensite embrittlement (TME) was studied in vacuum-melted 4130 steel with either 0.002 or 0.02 wt pct P. TME was observed as a severe decrease in Charpy V-notch impact energy, from 46 ft-lb. at 200 °C to 35 ft-lb. at 300 °C in the low P alloy. The impact energy of the high P alloy was consistently lower than that of the low P alloy in all tempered conditions. Fracture was transgranular for all specimens; therefore, segregation of P to the prior austenitic grain boundaries was not a factor in the occurrence of TME. Analysis of load-time curves obtained by instrumented Charpy testing revealed that the embrittlement is associated with a drop in the pre-maximum-load and post-unstable-fracture energies. In specimens tempered at 400 °C the deleterious effect of phosphorus on impact energy became pronounced, a result more consistent with classical temper embrittlement rather than TME. A constant decrease in pre-maximum-load energy due to phosphorus content was observed. The pre-maximum-load energy decreases with increasing tempering temperature in the range of 200 °C to 400 °C, a result explained by the change in work hardening rate. Carbon extraction replicas of polished and etched as-quenched specimens revealed the presence of Fe₂MoC and/or Fe₃C carbides retained after austenitizing. Ductile crack extension close to the notch root was related to the formation of fine microvoids at the retained carbides.     

回火温度对中碳合金钢4Cr5MoSiV1Nb组织和性能的影响

 为了优化合金性能，研究了回火温度对中碳合金钢4Cr5MoSiV1Nb组织和性能的影响。试验结果表明，4Cr5MoSiV1Nb合金钢的二次硬化温度区间为300～550 ℃，峰值出现在550 ℃，此时硬度值为56.3HRC，同时伴有冲击韧性的显著降低，冲击韧性降低的原因是合金钢回火时含铬铬的细短棒状合金渗碳体在晶界析出，可以推测减少淬火合金钢中铬的偏析将会减少晶界析出，提高冲击韧性。微量铌的加入形成了（V，Nb）C强化相颗粒。合金在250～350 ℃回火综合性能最佳，可以达到冲击韧性15 J/cm2、硬度55HRC以上。