MICROSTRUCTURE AND PROPERTIES OF HIGH BORON BEARING STEEL

High boron bearing steel, in which boron homogeneously distributed, wassuccessfully produced in the vacuum induction furnace. The microstructural observations of cast andhot rolled steels showed that the addition of titanium can eliminate the quantity of ferrous boridesprecipitated at the grain boundaries and break the net microstructure, as a result, its hotworkability is improved. The titanium boride TiB_2 homogeneously distributes in the matrix ofalpha-Fe. The parameters of hot rolling process, including preheated temperature, initial rollingtemperature, finished rolling temperature and the total deformation, have been optimized.

Effect of Boron on Delayed Fracture Resistance of Medium-Carbon High Strength Spring Steel

The delayed fracture behavior of medium carbon high strength spring steel containing different amounts of boron （0. 000 5%, 0. 001 6 %） was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron eontent from 0. 000 5% to 0. 001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initia tion area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3 （C, B） phase.

Effects of carbon content on high-temperature mechanical and thermal fatigue properties of high-boron austenitic steels

High-temperature mechanical properties of high-boron austenitic steels(HBASs) were studied at 850 °C using a dynamic thermal-mechanical simulation testing machine. In addition, the thermal fatigue properties of the alloys were investigated using the self-restraint Uddeholm thermal fatigue test, during which the alloy specimens were cycled between room temperature and 800°C. Stereomicroscopy and scanning electron microscopy were used to study the surface cracks and cross-sectional microstructure of the alloy specimens after the thermal fatigue tests. The effects of carbon content on the mechanical properties at room temperature and high-temperature as well as thermal fatigue properties of the HBASs were also studied. The experimental results show that increasing carbon content induces changes in the microstructure and mechanical properties of the HBASs. The boride phase within the HBAS matrix exhibits a round and smooth morphology, and they are distributed in a discrete manner. The hardness of the alloys increases from 239(0.19 wt.% C) to 302(0.29 wt.% C) and 312 HV(0.37 wt.% C); the tensile yield strength at 850 °C increases from 165.1 to 190.3 and 197.1 MPa; and the compressive yield strength increases from 166.1 to 167.9 and 184.4 MPa. The results of the thermal fatigue tests(performed for 300 cycles from room temperature to 800 °C) indicate that the degree of thermal fatigue of the HBAS with 0.29 wt.% C(rating of 2–3) is superior to those of the alloys with 0.19 wt.%(rating of 4–5) and 0.37 wt.%(rating of 3–4) carbon. The main cause of this difference is the ready precipitation of M23(C,B)6-type borocarbides in the alloys with high carbon content during thermal fatigue testing. The precipitation and aggregation of borocarbide particles at the grain boundaries result in the deterioration of the thermal fatigue properties of the alloys.

Microstructure and mechanical properties of a new type of austempered boron alloyed high silicon cast steel

In the present paper, a new type of austempered boron alloyed high silicon cast steel has been developed, and its microstructures and mechanical properties at different temperatures were investigated. The experimental results indicate that the boron alloyed high silicon cast steel comprises a dendritic matrix and interdendritic eutectic borides in as-cast condition. The dendritic matrix is made up of pearlite, ferrite, and the interdendritic eutectic boride is with a chemical formula of M2B (M represents Fe, Cr, Mn or Mo) which is much like that of carbide in high chromium white cast iron. Pure ausferrite structure that consists of bainitic ferrite and retained austenite can be obtained in the matrix by austempering treatment to the cast steel. No carbides precipitate in the ausferrite structure and the morphology of borides remains almost unchanged after austempering treatments. Secondary boride particles precipitate during the course of austenitizing. The hardness and tensile strength of the austempered cast steel decrease with the increase of the austempering temperature, from 250 oC to 400 oC. The impact toughness is 4-11 J?cm-2 at room temperature and the impact

Effect laws and mechanisms of different temperatures on isothermal tensile fracture morphologies of high-strength boron steel

The fracture behaviour and morphologies of high-strength boron steel were investigated at different temperatures at a constant strain rate of 0.1 s-1 based on isothermal tensile tests. Fracture mechanisms were also analyzed based on the relationship between microstructure transformation and continuous cooling transformation(CCT) curves. It is found that 1) fractures of the investigated steel at high temperatures are dimple fractures; 2) the deformation of high-strength boron steel at high temperatures accelerates diffusion transformations; thus, to obtain full martensite, a higher cooling rate is needed; and 3) the investigated steel has the best plasticity when the deformation temperature is 750 °C.

On microstructure and performance of tempered high-boron high-speed steel roll

Influences of the tempering temperature on the microstructure, mechanical property and wear resistance of High-Boron High Speed Steel (HBHSS) roll materials were investigated by means of optical microscopy, scanning electron microscopy (SEM), X-ray diffraction, hardness measurement, impact tester, tensile tester and pin abrasion tester. The results show that the as-cast structure of HBHSS consists of a great amount of martensite and M2(B,C) and a few retained austenites and M23(B,C)6. After solution treated at 1,050 °C and followed by oil cooling, the amount of M23(B,C)6 carbo-borides in quenched HBHSS increases obviously and the macrohardness of the quenched HBHSS is 66 HRC, which is very close to the 65.8 HRC of as-cast HBHSS. On the whole, the hardness of HBHSS alloy shows a trend of slight decrease with increasing tempering temperature when tempered below 500 °C. While when above 500 °C, the hardness increases slightly as the tempering temperature increases and reaches a peak at 525 °C and then decreases obviously. The impact toughness of HBHSS has a tendency to increase as the tempering temperature increases. Tempering can improve the tensile strength and elongation of HBHSS, but a higher tempering temperature causes a slight decrease in both tensile strength and elongation. Excellent wear resistance can be obtained by tempering at 500 to 550 °C.

The Adhesion Improvement of Cubic Boron Nitride Film on High Speed Steel Substrate Implanted by Boron Element

Cubic boron nitride(c-BN) films were deposited on W6Mo5Cr4V2 high speed steel(HSS) substrate implanted with boron ion by RF-magnetron sputtering. The films were analyzed by the bending beam method, scratch test, XPS and AFM. The experimental results show that the implantation of boron atom can reduce the internal stress and improve the adhesion strength of the films. The critical load of scratch test rises to 27.45 N, compared to 1.75 N of c-BN film on the unimplanted HSS. The AFM shows that the surface of the c-BN film on the implanted HSS is low in roughness and small in grain size. Then the composition of the boron implanted layer was analyzed by the XPS. And the influence of the boron implanted layer on the internal stress and adhesion strength of c-BN films were investigated.

IMPROVEMENT OF TYPE IV CRACKING RESISTANCE OF 9Cr HEAT RESISTING STEEL WELDMENT BY BORON ADDITION

Creep lives of high Cr ferritic heat resisting steel weldments decrease due to Type Ⅳ fracture, which occurs as a result of formation and growth of creep voids and cracks on grain boundaries in fine-grained heat affected zone (HAZ). Because boron is considered to suppress the coarsening of grain boundary precipitates and growth of creep voids, we have investigated the effect of boron addition on the creep properties of 9Cr steel weldments. Four kinds of 9Cr3WSCoVNb steels with boron content varying from 4.7×10-5 to 1.8×10-4 and with nitrogen as low as 2.0×10-5 were prepared. The steel plates were welded by gas tungsten arc welding and crept at 923K. It was found that the microstructures of HAZ were quite different from those of conventional high Cr steels such as P91 and P92, namely the fine-grained HAZ did not exist in the present steel weldments. Boron addition also has the effect to suppress coarsening of grain boundary carbides in HAZ during creep. As a result of these phenomena, the welded joints of present steels showed no Type Ⅳ fractures and much better creep lives than those of conventional steels.

高硼奥氏体钢硼化物形态及分布优化

传统高硼铁基合金中硼化物一般位于晶界位置,沿晶界呈网状或鱼骨状分布,具有尖锐边角,破坏了基体连续性,大大降低材料的力学性能。本文采用光学金相显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、飞行时间二次离子质谱仪(TOF-SIMS)和X射线衍射(XRD)研究了碳含量对高硼奥氏体钢组织的影响。采用热力学模拟试验机分析了碳含量对实验钢850℃高温力学性能的影响。结果表明,高硼奥氏体钢的碳含量较高(0.37%~0.42%,质量分数)时,可稳定得到形态圆整的硼化物,且硼化物在基体内呈粒状离散化均匀分布,无网状、鱼骨状沿晶界连结贯通的分布状态。粒状离散化硼化物为Fe_(1.1)Cr_(0.9)B_(0.9)、Mn_(2)B_(0.98)、Cr_(2)B的络合产物,硼化物中Cr、Mn的加入,以及基体C含量的提高,促进了硼化物形态圆整、分布粒状离散化。锻造工艺同样对硼化物的粒状离散分布起到直接促进作用。锻造的始锻温度达到1 150℃是硼化物实现粒状离散分布的基本条件。

硼对奥氏体不锈钢高温氧化性能的作用机理

采用氧化增重法研究了B对0Cr25Ni20B钢的高温抗氧化性能的影响,通过透射电子显微镜、扫描电子显微镜、能谱分析和X射线衍射等方法分析了0Cr25Ni20B钢高温氧化膜的形貌、组成结构及元素分布等,揭示了B对其高温氧化性能的作用机理。结果表明,在高温氧化过程中,加入0.4%的B可以促使耐热钢板材表面形成致密的氧化物薄膜,形成的硼酸盐(Fe_(3)BO_(6))能够抑制氧化行为的深入发展,对材料的抗高温氧化性能有增益作用。

Q&P工艺对Fe-0.45C-1.6B高硼耐磨钢组织和性能的影响

利用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)、洛氏硬度计和冲击磨损试验机,研究了铸态和经Q&P工艺处理后的Fe-0.45C-1.6B高硼耐磨钢的组织和性能。结果表明,高硼耐磨钢的显微组织由金属基体和共晶硼化物组成。基体组织主要为马氏体,铁素体和少量残余奥氏体。硼化物主要为Fe_(2)B和Fe_(23)(B,C)_(6)。Q&P工艺后,铁素体被消除,合金元素分布均匀,硼化物的形态和分布随之发生变化。经Q&P工艺后,高硼耐磨钢的综合力学性能和耐磨性都得到改善。与铸态相比,Q&P工艺后高硼耐磨钢中残余奥氏体的体积分数由9.8%上升到17.6%,冲击吸收功由3.76 J上升至7.50 J,耐磨性为铸态时的1.64倍。

钒对高硼高速钢组织及回火析出的影响

通过钒合金化制备了不同钒含量的高硼高速钢,采用光学显微镜、扫描电镜、能谱等手段,研究了钒含量对高硼高速钢组织和宏观硬度的影响,并探究了热处理后含钒高硼高速钢的析出相形貌及结构。结果表明,高硼高速钢铸态组织主要由枝晶马氏体和M_2B硼化物组成,随着钒含量增加,基体中马氏体数量减少,铁素体数量增加,同时硼化物逐渐细化,合金的宏观硬度随钒含量增加而逐渐降低。微观分析表明,随V含量的增加,M_2B硼化物中V元素的固溶含量均增加。同时,V在硼化物中的固溶不改变富Fe硼化物中Cr的含量,但富Mo硼化物中Mo、W元素含量随合金中V含量的增加而逐渐降低。淬火加回火处理后,基体中出现了富Mo、W、V元素的二次析出相,且随着合金中V含量的提高,二次析出相的数量不断增加,其尺寸反而减小。同时,基体为细小的板条马氏体,二次析出颗粒形态为球状及短杆状,钒的加入促进了二次硼碳化物M_(23)(B,C)_6、M(B,C)、M_6(B,C)的析出。

Effect of Heat Treatment on Structure and Wear Resistance of High Chromium Cast Steel Containing Boron

The microstructure, mechanical properties and wear resistance of high chromium cast steel containing boron after different heat treatments were studied by means of the optical microscopy （OM）, the scanning electron microscopy （SEM）, X-ray diffraction （XRD）, hardness, impact toughness, tensile and pin-on-disc abrasion tests. The results show that as cast microstructures of boron-free high chromium steel consist of martensite and a few （Cr, Fe）_7C_3 carbide, and the macro-hardness of boron-free high chromium steel is 55-57 HRC. After 0.5 mass% B was added into high chromium cast steel, as-cast structure transforms into eutectic （Fe, Cr）2B, （Cr, Fe）7 （C, B）a and martensite, and the macro-hardness reaches 58-60 HRC. High temperature quenching leads to the disconnection and isolated distribution of boride, and there are many （Cr,Fe）_23 （C,B）_6 precipitated phases in the quenching structure. Quenching from 1050 ℃, high chromium steel obtained the highest hardness, and the hardness of high chromium cast steel containing boron is higher than that of boron-free high chromium steel. The change of quenching temperature has no obvious effect on impact toughness of high chromium steel, and the increase of quenching temperature leads to tensile strength having an increasing tendency. At the same quenching temperature, the wear resistance of high chromium cast steel containing boron is more excellent than that of boron-free high chromium steel. High chromium cast steel guide containing boron has good performance while using in steel bar mill.

Effect of Boron on CGHAZ Microstructure and Toughness of High Strength Low Alloy Steels

Effect of boron on the microstructure and impact toughness in the coarse-grained heat-affected zone（CGHAZ）of two high strength low alloy steels,boron-free and boron-containing,was investigated by means of weld thermal simulation test.The result shows that,for the boron-free steel,a microstructure consisting of grain boundary ferrite degenerates pearlite and granular bainite for longer t8/5（the cooling time from 800 to 500 ℃）,while lath bainite for shorter t8/5.For the boron-containing steel,granular bainite is dominant for a wide range of t8/5.Continuous cooling transformation（CCT）study on the CGHAZ indicates that the transformation start temperature decreases by about 50-100℃under different t8/5,for the boron-containing steel compared with the boron-free steel.The presence of boron suppresses the nucleation of ferrite at prior austenite grain boundaries and hence enlarges the range of t8/5for granular bainite transformation.However,the addition of boron deteriorates the impact toughness of CGHAZ,which may be due to a markedly increased fraction of martensite-austenite（M-A）constituents and decreased fraction of high angle grain boundaries.

高硼高速钢研究进展

高速钢是一种具有高硬度、高耐磨性、高耐热性和优良红硬性的工具钢,然而由于合金元素价格高,其使用范围受到很大限制。在高速钢生产中以廉价的硼替代钨、钼、钒、铌等贵重金属制得的高硼高速钢既降低了成本,又能保证优异的硬度、耐磨性、强韧性、抗高温氧化性。本文综述了合金化、变质处理和热处理对高硼高速钢组织和性能影响,最后对高硼高速钢未来的发展进行了展望。

硼对高强度弹簧钢力学性能的影响

研究了不同含量硼元素 ( 0 .0 0 0 6 %～ 0 .0 0 2 7% )对中碳高强度弹簧钢力学性能的影响。研究结果表明 ,添加微量硼能够显著提高钢的淬透性 ,且不同硼含量试验钢的淬透性无明显差别。适当提高钢中的硼含量 ,试验钢的强度虽有所降低 ,然而其冲击韧性却得到明显提高。在相同的硬度水平下 ,随着钢中硼含量的增加 。

汽车用高强度钢热成型技术

高强度钢的热成型技术可解决传统成型高强度钢板在汽车车身制造中遇到的各种问题。介绍了汽车用高强度钢热成型的加工工艺、加工关键技术、热成型零件的检测方法以及国内外的研究现状。以用于热冲压成型的高强度钢——硼钢为例,对我国热成型技术的应用情况及未来热成型技术需要解决的问题进行了阐述。

热处理对高硼铸钢耐磨性的影响研究

为了研究高硼铸钢的耐磨性,借助光学显微镜、X衍射分析仪(XRD)等手段研究了热处理工艺对高硼铸钢耐磨性的影响。实验选用ML-10型销盘磨损试验机,将热处理后的高硼铸钢、高锰钢进行耐磨性对比,研究发现高硼铸钢的耐磨性与高韧性低碳马氏体及高硬度相-硼化物Fe2B密切相关,热处理能显著改善高硼铸钢的强度、硬度。研究结果表明:在冲击磨损条件下高硼钢比高锰钢有较好耐磨性。

硼对高强度弹簧钢脱碳敏感性的影响

弹簧表面形成脱碳层将恶化其疲劳性能,因此要求弹簧钢具有低的脱碳敏感性.研究了不同硼含量(0.000 6%～0.002 7%)对中碳高强度弹簧钢脱碳敏感性的影响.采用等温处理和等时处理研究了含硼中碳弹簧钢和作为对比的60Si2Mn钢的脱碳层深度和氧化失重量的变化情况.结果表明:实验钢的脱碳层深度和氧化失重量均随硼含量的增加而减少.这表明,钢中添加微量硼能够抑制弹簧钢的氧化和脱碳.硼的这种良好作用主要与其在原奥氏体晶界的偏聚有关.含硼中碳弹簧钢的氧化和脱碳敏感性明显低于所对比的60Si2Mn钢,这除了与硼抑制钢的氧化和脱碳的作用有关外,前者较低的碳含量也是一个主要原因.

新型高硼合金钢的研究

研究了稀土-钛-氮复合变质处理对高硼合金钢组织和性能的影响。结果表明含稀土-钛-氮的高硼合金钢的凝固组织明显细化,且组织分布均匀。经高温热处理后,硼化物变成了球状和棒状,高硼合金钢强度得到改善,韧性明显提高,由12-15J／cm2提高至28-32J／cm2,分析了高硼合金钢强度和韧性提高的原因。含稀土 -钛-氮的高硼合金钢用于制造破碎机锤头,使用安全可靠,耐磨性比高锰钢提高220％-250％,且生产成本相当。