MICROSTRUCTURE OF LASER MELTED-RESOLIDIFIED LAYER ON HIGH SPEED TOOL STEEL

The laser melted-resolidified processing on W18Cr4V high speed tool steel has been made us-ing a 1 kW CO_2 continuous wave laser device.The microstructure of the laser melted-resolidified layer has been examined by optical microscopy and transmission electronmicroscopy(TEM).It was characteristic of extremely fine dendrite in the laser melted-resolidified layer and δ-ferrite in bulk form in the center of dendrite.The predominant twinmartensite and a little dislocation martensite existed in the dendrite.The thin plate-likeM_(213)C_6 carbide precipitated coherently on the twin martensites along their twin plane.Therewere both austenite rich in W,V and Cr and M_6C carbide in the interdendritic regions.     

高碳马氏体片中脊的研究

研究马氏体中脊形貌和形成机制具有理论意义.采用Fe-C合金、CrWMn、W6Mo5Cr4V2等材料,淬火得马氏体组织,应用QUENTA-400型扫描电镜和JEM-2100高分辩电镜观察马氏体中脊.发现在高碳孪晶型马氏体片中存在中脊,中脊宽窄不等,中脊周围可为孪晶,也可为高密度位错.中脊由精细孪晶片构成,李晶片与中脊线呈夹角分布.中脊的形成与应变能有关,温度越低,弹性模量越高,为调节应变能而形成了中脊.     

Dry friction and wear characteristics of MoSi2 against ahoy steels

The dry friction and wear characteristics of three kinds of friction couples under different loads, MoSi2/45 tempered steel, MoSi2/45 quenched steel, and MoSi2/CrWMn steel, were investigated by using a friction and wear tester. SEM and X-ray diffraction were employed to analyze the microphotograph of the worn surface and the phase of worn pieces in order to reveal the wear mechanisms of MoSi2 material. The results show that MoSi2/CrWMn steel friction pair has good dry friction and wear properties under the load of 80 N, where the friction coefficient is 0.255 and the wear rate of MoSi2 is only 14.72 mg.km-1. But under the load of 150 N, it is MoSi2/45 tempered steel friction pair that has good tribological properties,MoSi2 under low loads is brittle fracture. With the increase of load, the main wear mechanism of MoSi2 against 45 quenched steel or CrWMn steel is adhesive wear. However, the wear mechanism of MoSi2 against 45 tempered steel is changed from oxidation-fatigue wear to adhesive wear.     

几种工业用钢的马氏体相变及组织

研究了工业用钢65Mn、60Si2Mn、9CrSi、CrWMn、5CrMnMo、42CrMo淬火马氏体的形成过程。结果表明，上述钢种马氏体均优先在晶界形成且为片状。Mo钢中晶界马氏体少，且马氏体片很小，而Cr、Mn钢中晶界马氏体较多且为大的片状。对晶界处优先形成片状马氏体的原因进行了初步的讨论分析。     

钢中fcc/bcc(bct)马氏体形核与长大的一种晶体学模型

将不变线理论和O点阵理论应用于fcc／bcc(bct)马氏体相变的可滑移生长界面的设计,建立了马氏体形核与长大的晶体学模型．通过模型分析表明:fcc／bcc(bct)马氏体形核与长大过程是通过(121)fcc型择优界面推移进行的,界面上的错配位错可以完成马氏体晶体学唯象理论(PTMC)要求的点阵不变变形(LID),但LID要稍滞后于界面迁移,即在马氏体形核与长大过程中推移界面新相一侧存在一未发生LID的新相薄区;当相变温度达到马氏体相变点Ms时,母相奥氏体与这一薄区的晶格常数比为、√3/2,这一几何条件和Olson-Cohen形核模型中要求扩展位错层错区界面能γ≤0是等价的．     

Microstructure of martensite in chromium-nickel steel

Conclusions The structure of the martensite in steel of the transition type depends on the conditions under which it was produced: when martensite results from treatment at –70°C there is a predominance of plate-like crystals containing twins. Cooling from high temperature tempering, leads to the formation of needle-like crystals alone without any sign of internal twinning.The ultimate strength and the yield strength of martensite formed as the result of treatment at –70° are higher.Stacking defects may be areas of preferential nucleation of martensite crystals and at the same time limit the growth of martensite crystals.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 49–51, October, 1964     

CrWMn导轨板裂纹分析

本文分析了CrWMn导轨板裂纹,分别检验并分析了碳化物形态、锻造后的晶粒度、马氏体形态,确定开裂的原因为碳化物偏析、晶粒度超标、淬火温度偏高,最后提出了改进措施.     

On the Ti2Ni precipitates and Guinier–Preston zones in Ti-rich Ti–Ni thin films

After heat treatment, there may exist different types of precipitates in Ti-rich thin films, i.e. spherical Ti₂Ni precipitates and plate-like Guinier–Preston (GP) zones. While the Ti₂Ni precipitates impede the shear deformation of martensitic transformation, the GP zones do not stop both the shear deformation of martensitic transformation and the twinning shear of (001) deformation twin in the martensite phase. An elastic deformation model of the GP zone during martensitic transformation and subsequent deformation in the martensite was built up. The model can explain the GP zones-related shape memory properties self-consistently. These results supply microstructural explanation for the previous results that Ti-rich Ti–Ni thin films with GP zones show a large transformation strain despite the presence of the GP zones, while thin films with Ti₂Ni precipitates show a relatively small transformation strain.     

微合金高强钢焊接热影响区中粒状贝氏体微观结构的实验研究

运用电子显微技术研究了ＱＴ型微合金钢模拟焊接热影响区粒状贝氏体的微观结构。结果显示,在金相截面上呈长条形的Ｍ－Ａ组元的空间形态为薄板状;而在金相截面上呈不规则多边形的Ｍ－Ａ组元的空间形态为近似于等轴的块状。Ｍ－Ａ组元与铁素体之间的界面可进一步划分为马氏体／铁素体界和残余奥氏体／铁素体界。在具有块状Ｍ－Ａ组元的粒状贝氏体团中,贝氏体与铁素体之间有高角晶界相隔,并分析和讨论了这些现象与理解断裂和韧性的     

Key role of transformation twins in comparison of results of crystal geometric and dynamic analysis for thin-plate martensite

The experimental data on the ratio of transformation twins fractions for crystals of thin-plate α-martensite (with the habit planes of the {2 5 9}_γ?{3 10 15}_γ type) are considered. It is shown that the dynamic theory of the martensite crystals formation is free from the difficulties encountered in the formal crystal geometric approach. The intervals of parameter values that correspond to the observed fractions of the twin component, δ_tw, within the same crystal are given. The absence of twinning in thin plate-like crystals, which sometimes are observed in experiments on the γ-α martensite transformation induced by strong magnetic field is discussed.