外文翻译---根据高速钢不同的加工条件T42冶金粉末烧结机制和微观结构的发展

1、sintering behaviour and microstructure development of t42 powder metallurgy high speed steel under different processing conditions high speed steel powders (t42 grade) have been uniaxially cold-pressed and subsequently densified through different sintering routes including: supersolidus liquid phase

2、 sintering (slps) under vacuum and different nitrogen pressures (0.2, 0.9, and 8bar) and through solid state sintering (sss) by hot isostatic pressing (hip). hip temperatures as low as 850c led to near full densification of the material (98% theoretical density) with average size of m6c and mc carbi

3、des lower than 1m and grain size 3m. pressureless sintering under different nitrogen pressures (up to 0.39wt.%n absorption) led to a significant reduction of the optimum sintering temperature (ost) and a pronounced increase in the sintering window (sw) as compared to vacuum sintering. pressureless s

4、intering under 8bar n2 led to a further reduction in ost together with the precipitation of massive eutectic structures. therefore, the sw was judged to be negligible. the response of the as-sintered materials to the heat treatment is basically determined by the amount of c available in the matrix p

5、rior to quenching and the grain size. the highest hardness achievable for the sintering conditions evaluated ranges 7001100 hv2 after austenitizing at 1100c, oil quenching and multitempering at 500550c. tool steels serve a large range of applications including hot and cold working of metals and inje

6、ction moulding of plastics or light alloys. high speed steels (hss) are more specifically used as cutting tools and wear parts. more recently, these materials have also been used for structural applications. the high performance exhaust valve seat inserts for passenger vehicles constitute the most n

7、otable example 1. in general terms, for these structural applications, a combination of high strength, wear resistance and hardness together with an appreciable toughness (compared with other materials used as tools) and fatigue resistance is required. from a microstructural point of view, hss can b

8、e described as metallic matrix composites formed by a ferrous matrix with a dispersion of hard, wear resistant carbides. the type, size, morphology, distribution and volume fraction of carbides as well as the characteristics of the ferrous matrix depend on both the composition of the material and th

9、e manufacturing process 2 and 3. the basic alloying elements of high speed steels are approximately 1530wt.% of carbide formers (cr, mo, w, v), sometimes co and sufficient carbon to promote the formation of carbides. tungsten and molybdenum mainly contribute to the formation of the primary m6c and m

10、2c carbides and vanadium is the main constituent of the mc type. conventional manufacturing processes for the production of components with these materials include wrought metallurgy and powder metallurgy (direct sintering and hot isostatic pressing; hip). the main manufacturing steps for wrought pr

11、ocessing are melting, casting, hot working, machining and heat treating. normally, extensive hot working (area reductions 90%) is necessary to disperse the carbide networks formed during the solidification of the as-cast ingots. this hot working process leads to the alignment of carbide in strings,

12、which is responsible for anisotropic properties 2. powder metallurgy (pm) techniques were initially developed to overcome these problems. the starting raw materials are pre-alloyed gas or water atomised powders. gas atomised powders are cleaner than water atomised powders and both of them are free o

13、f segregations due to the high cooling rates involved. gas atomised powders are used for hip 4 and powder injection moulding (pim) 5. hip is devoted for a prime quality product due to the cleanness of the raw material and to the fact that densification takes place by a solid state sintering (sss) pr

14、ocess. consequently, a fine and homogeneous distribution of carbides embedded in a pore-free ferrous matrix is obtained leading to exceptional properties. pim is best suited for small components with complex geometries and densification takes place by direct sintering (i.e., pressureless sintering)

15、through a supersolidus liquid phase sintering (slps) mechanism 5 and 6. water atomised powders are normally processed by the direct sintering route. partial densification is achieved by cold-pressing the powders with a suitable compaction lubricant. subsequently, sintering to full density takes plac

16、e by a slps mechanism. the direct sintering route has inherent advantages in terms of achievable properties versus processing costs and environmental considerations related to the highly efficient material use. during the last 20 years, a high research effort has been mainly addressed at the underst

17、anding of the physical and chemical mechanisms involved in the densification via slps 7 and sss 4. additionally, research has also been focused on the microstructural changes occurring during heat treatments leading to the desired mechanical properties (i.e., strength, toughness, wear, fatigue) depe

18、ndent on the service applications 8. previous studies 9, 10, 11 and 12 have been focused on the optimisation of the direct sintering route of high vanadium hss grades (mainly m35mhv) by understanding the effect of the sintering atmosphere. this approach has led to a significant decrease of the sinte

19、ring temperatures needed for full densification in nitrogen rich atmospheres compared to vacuum sintering. the optimum sintering temperature (ost) for m35mhv decreased from 1220c for vacuum sintering to 1140c when sintered under nitrogen-rich atmosphere 3 and 10. the effect of both the sintering atm

20、osphere and alloy modifications (i.e., carbon additions) has been understood by the use of computational thermodynamics (calculation of multicomponent phase diagrams) 10 and 11. moreover, the correspondence between computational thermodynamics and experimental data constituted a preliminary step for

21、 alloy design of new hss compositions 12 and 13. the present study is aimed at the description of the sintering behaviour of the pm t42 grade under different nitrogen pressures. this material has been chosen for the investigation since it is a commercial grade containing an adequate amount of v for

22、microstructural design through the addition of n. additionally, the excellent hot hardness of t42 due to the 10.58wt.%co, makes this material very interesting for both structural and tribological applications. the satisfactory results of earlier investigations on the sintering behaviour of t42 in n-

23、rich atmospheres 9 invited for a more detailed investigation striving for a commercial impact of the research. the main objective was the microstructural design of pm hss through the densification route and the heat treatment sequence selected. a wide set of different microstructures has been obtain

24、ed by using the different sintering conditions. the effect of the as-sintered microstructure (mainly absorbed n content and grain size) on the heat treatment (austenitizing+quenching+multitempering) is also discussed. references1 h. kawata, k. hayashi, k. ishii, k. maki, a. ehira and m. toriumi, sae

25、 trans. 107 (5) (1998), pp. 194200. 2 g. hoyle, high speed steels, butterworths, borough green, sevenoaks kent (1988). 3 s. gimenez and i. iturriza, j. mater. process. technol. 143/144 (2003), pp. 555560. 4 e. arzt, m.f. ashby and k.e. easterling, metall. trans. a 14a (1983), pp. 2112215 z.y. liu, n

26、.h. loh, k.a. khor and s.b. tor, mater. lett. 45 (2000), pp. 3238. 6 b. levenfeld, a. varez and j.m. torralba, metall. mater. trans. a 33 (6) (2002), pp. 18431851. 7 r.m. german, int. j. powder metall. 26 (1) (1990), pp. 2334. 8 g. krauss, heat treatment and processing principles (6th ed.), asm inte

27、rnational (2000). 9 r.h. palma, v. martinez and j.j. urcola, powder metall. 32 (4) (1989), pp. 291299. 10 i. aguirre, s. gimenez, t. gomez-acebo, s. talacchia and i. iturriza, powder metall. 44 (3) (2001), pp. 211220. 11 i. aguirre, s. gimenez, t. gomez-acebo, s. talacchia and i. iturriza, powder me

28、tall. 42 (4) (1999), pp. 353357. 12 s. gimenez and i. iturriza, powder metall. 46 (3) (2003), pp. 209218. 13 v. trabadelo, s. gimenez, t. gomez-acebo and i. iturriza, scripta mater. 53 (3) (2005), pp. 287292根据高速钢不同的加工条件t42冶金粉末烧结机制和微观结构的发展高速钢粉（ t42级）经单轴冷加压及随后的致密再通过不同烧结路线，包括： 超固相线烧结与液相烧结（ 液面压力 ）.在真空状态

29、下，不同的氮压力（ 0.2 ， 0.9和8个大气压） ，通过固相烧结（sss）由热等静压法(hip)， 当静压炉的温度低至850c能使材料充分致密（大于 98%理论密度）从而使平均粒径m6c和mc碳化物小于1 m而晶粒尺寸为3 m. 相对于真空烧结，在不同氮气压力下的烧结窗口，常温烧结（高达0.39wt%氮素吸收）使最佳烧结温度显著下降（大气外层空间）并日益突出显著.8个n2压烧结下，在美国科学技术局实验室里烧结温度得到进一步降低使得大量共晶结构连接在一起。因此sw判断是可以忽略不计。烧结反应的烧结材料，热处理，基本上是由碳量可在基体前淬火和晶粒尺寸来确定。最高硬度可达烧结条件评价范围700-

30、1100 hv2。在1100c时，奥氏体化后，油淬和多次回火保持在500-550 之间。工具钢服务于一个庞大的系统，包括热轧和冷轧工作金属和注塑成型的塑料或轻合金结构。高速钢（hss）是更多的作为切削工具和磨损零件。现在，这些材料在结构型上也有所应用。最显著的例子是客运车辆中高性能排气阀座的应用1。总体来讲，这些结构型的应用，结合强度高，耐磨性和硬度有一个值得称赞的韧性（相较于其他同类的材料应用）和抗疲劳是我们所需要的。从微观结构的角度来看，高速钢可以说是金属基复合材料，是一个黑色矩阵与色散指针的耐磨碳化物。该类型、大小、形态、分布和体积分数碳化物以及其特色的黑色矩阵取决于组成材料和制造过程

31、2 3 。高速钢的基本合金元素约有15-30wt%及硬质合金（cr, mo, w, v） 。有时co和足够的碳，能促进碳化物的形成。钨、钼、主要是有助于形成m6c和m2c碳化物，且钒是mc类型主要的组成部分。传统的制造工艺生产的组件与这些材料包括造成的冶金和粉末冶金（直接烧结和均衡加压热烧结法及热等静压法）。主要的生产步骤为变形处理的熔炼，铸造，热加工，机械加工和热处理。一般情况下，必要的大量热加工（面积减少90%）以达到驱散凝固过程中的铸锭中碳化物形成的网络。这个加热的工作过程生成各种碳化物，这是金属的各向异性性能2. 粉末冶金技术(pm)的初步形成得以克服这些问题。未经过加工的合金原料气体

32、或水微粒粉末，气体微粒粉是较清洁的微粒粉末，他们两个都是由于高冷却速率而自由偏析所形成的。气体微粒粉末是用于热等静压炉 4 和粉末注塑成型（pim ） 5 .热等静压炉是专门为总理优质的产品，未经加工的原料在实际致密经固态烧结（sss）处理。因此，纯净的和均匀分布的碳化物嵌入一孔隙游离亚铁基体，得到了重要的特殊性能。pim是最适合小元件与复杂几何形状元件凭借超固相线烧结及液相烧结（ 液面压力）机制 5 及 6 致密的直接烧结（即无压烧结）。水微粒粉末，通常处理的是直接烧结路线局部致密化，局部致密是实现由冷榨粉体与一个合适的压实润滑剂。随后，通过固相线液相烧结，以得到充分密度机制。对直接烧结路线

33、的固有优势而言，可实现的性能与加工成本和环境因素有关，以得到高效率的物质使用。在过去20年中，研究工作主要是针对在理解的物理和化学机制，在涉及致密途经的固相线液相烧结 7 与综合仿真系统 4 。此外，研究人员还侧重于微观结构发生的变化，在热处理得到预期的力学性能（如强度，韧性，耐磨，疲劳）主要来源于实际的应用 8 。以往的研究 9 ， 10 ， 11 及 12 已集中于优化的直接烧结路线，通过高钒高速钢的分级（主要是m35mhv ）了解影响烧结效应的因素。这种做法导致了烧结温度显著降低且能充分致密所需要的氮气的量。真空烧结：最佳烧结温度（ost）m35mhv下降至1220 c，真空烧结在114

34、0 c时，烧结中氮的浓度大小 3 及 10 。影响双方的烧结结果和合金的修改（即碳增补）已知的所使用的热力学计算（计算多元相图） 10 及 11 。此外，热力学计算和实验数据构成了一个初步步骤为合金设计新的高速钢成分 12 及 13 。本研究的目的是描述烧结行为的，控制 t42在不同级别氮压力下。这种材料已被选定并作调查，因为它是一个商业级含有适当数量的第五部微观结构设计，通过另外的途径。此外，优良的高温硬度t42是含有10.58%的wt，得到这种非常有趣的材料结构和摩擦学应用，结果令人满意。早先调查对烧结行为的t42，在n丰富大气压 9 应做一个更详细的调查，争取一个影响商业的的研究。在主要目标是微观设计时，高速钢通过致密的路线和热处理序列选定。广泛的一套不同的微观结构，已获得使用不同的烧结条件。影响了作为烧结的微观结构（主要是吸收氮含量和晶粒尺寸）对热处理（奥氏体+淬火+ 多次回火）进行讨论。参考文献1 h. kawata, k. hayashi,