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℃ 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 ℃. While when above 500 ℃, the hardness increases slightly as the tempering temperature increases and reaches a peak at 525 ℃ 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 ℃.

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.

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℃ to 400 ℃. The impact toughness is 4-11 J.cm^-2 at room temperature and the impact fracture fractogragh indicates that the fracture is caused by the brittle fracture of the borides.

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 ℃ 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℃. 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 （0.19wt.% C） to 302 （0.29wt.% C） and 312 HV （0.37wt.% C）; the tensile yield strength at 850 ℃ 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 ℃） indicate that the degree of thermal fatigue of the HBAS with 0.29wt.% C （rating of 2-3） is superior to those of the alloys with 0.19wt.% （rating of 4-5） and 0.37wt.% （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.

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.

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.

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 。

淬火温度对高硼高速钢显微组织的影响

在普通高速钢材料中,加入适量硼来取代普通高速钢中价格昂贵的合金元素,设计了一种新型的高硼高速钢材料。研究了淬火温度对0.4%～0.5%C和1.0%～1.5%B的高硼高速钢显微组织的影响。结果表明,高硼高速钢的铸态组织由铁素体、珠光体和少量马氏体以及硼碳化合物组成,硼碳化合物由M23(B,C)6、(W,Mo)2(B,C),M3(B1.5,C0.5)和M(B0.7,C0.3)组成,呈网状和鱼骨状沿晶界分布。淬火处理后,基体组织转变成板条马氏体,含有4%残留奥氏体,硼碳化合物的类型没有发生变化,但数量减少。在950～1100℃内淬火,硼碳化合物局部发生溶解,出现断网现象;随着淬火温度的升高,断网现象越来越明显,从而减轻了对基体的割裂作用。

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。

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。

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.

淬火温度对高硼铸钢显微组织和硬度的影响

研究淬火温度对含碳量小于0.4%和含硼量小于2.0%的高硼铸钢显微组织和硬度的影响。高硼铸钢铸态基体组织由珠光体和铁素体组成。淬火处理后,硼化物数量变化不明显,随着淬火温度升高,基体显微硬度和试样宏观硬度提高,淬火温度超过1000℃后,硬度略有降低。在900～1100℃内淬火,都可获得强韧性好的板条马氏体基体组织。高硼铸钢中的硼化物显微硬度超过1500HV,由Fe_2B和少量FeB组成。

高强钢B340LA与B1500HS钢激光拼焊板热冲压淬火性能

用质子光谱仪、光学显微镜、维氏硬度计等手段研究低合金高强钢B340LA与超高强硼钢B1500HS激光拼焊板焊接后的热冲压淬火特性。结果表明,拼焊板母材B340LA钢随着冷却速度的增加其相变点发生偏移,维氏硬度略有增加。拼焊板母材B1500HS钢随着冷速的增加硬度迅速提高。光学显微镜观察,当冷速超过30 K/s时母材B1500HS钢基本转化为马氏体组织。通过维氏硬度计测量,发现焊缝至母材过渡区硬度值平滑过渡,保证母材及焊缝力学性能良好的连续性。由于热冲压淬火后母材及焊缝区域显微硬度平滑过渡,应力应变分别更趋均匀,可显著提高低合金高强钢与超高强硼钢激光拼焊板拉深成形性。

变质高碳硼钢的冲击磨料磨损行为研究

对高碳硼钢进行稀土变质处理,在MLD-10动载磨料磨损试验机上研究了变质高碳硼钢的冲击磨料磨损性能,并与高铬铸铁(Cr26)进行了比较。结果表明,适量稀土元素的加入,能有效提高高碳硼钢的耐磨性和冲击韧度;冲击功为2.0J时,变质高碳硼钢的耐磨性不如高铬铸铁,冲击功为2.5J时,变质高碳硼钢的耐磨性相当于高铬铸铁(Cr26);在磨损过程中,高碳硼钢的冲击磨损机制主要是塑性变形及疲劳剥落,切削所占的比例较小。

超高强度硼钢板热弯曲数值模拟

为研究热自由弯曲和热接触弯曲方法的淬火效果和成形精度,应用ABAQUS软件,对超高强度硼钢板U形件的热弯曲过程进行了数值模拟研究.研究表明:热接触弯曲改善了热弯曲零件底部的淬火效果,且热接触弯曲可获得比热自由弯曲更好的成形精度;不同压边力下热接触弯曲回弹均随着压边力的增加而逐渐减小;数值模拟结果与实验结果吻合较好,验证了有限元模型的可靠性.

冷却速度对离心铸造高硼高速钢辊环组织的影响

采用空冷和水冷不同铸型方式,研究冷却速度对离心铸造高硼高速钢辊环组织的影响,制备出辊环。结果表明:铸态高硼高速钢辊环组织由树枝状基体和硼碳化物组成。快速冷却下,基体组织全部转化为马氏体;硼碳化物的类型没有发生变化,由M2(B,C)、M3(B,C)以及M23(B,C)6组成。随着冷却速率的增加,基体晶粒尺寸减小,硼碳化物数量减少,鱼骨状硼碳化物向筛网状转变,局部出现缩颈和孤立现象。冷却速度的增加影响了合金元素在基体和硬质相中的分布,硬质相的显微硬度不变,基体硬度略有增加。空冷砂型离心铸造时,随着距辊环外边缘距离的增加,出现菊花片状的包晶组织,并且数量也逐渐增加。