在曲柄压力机工作条件下对 VK20 硬质合金的疲劳试验外文文献翻译、中英文翻译、外文翻译.docx

1、EXCHANGE OF EXPERIENCE AND INFORMATIONFATIGUE TESTS ON VK20 HARD ALLOY* UNDERTHE CONDITIONS OF OPERATION OF A CRANK PRESSV. P. Smolyaninov and S. I. Spi rlnaUDC 669.018:620.178.3The fatigue limit, a property determined by tests on specimens or full-size components under controlled conditions, is a q

2、uantitative characteristic of resistance to fatigue. Fatigue tests give the best results when they are performed under conditions approximating as closely as possible those encountered in service. In such experiments, it is convenient to employ accelerated methods of testing for determining fatigue

3、strength.The woric described below was undertaken with the aim of studying the fatigue behavior of specimens of a WC Co hard alloy and examining the effectiveness of Dixon and Mood's "staircase" accelerated technique (1 as a method of determining the fatigue properties of brittle mater

4、ials of this type. The suitability of the "staircase" method for the testing of hard alloys was considered from two standpoints:a) determination of the fatigue characteristics of hard alloys under conditions simulating the loading in the operation of a hard alloy blanking tool (die or punc

5、h);b) study of the influence exerted upon the short fatigue limit of a hard alloy by one form of structural heterogeneity, namely, a system of residual interfacial stresses set up during the manufacture of a hard- alloy component.Tests on specimens were carried out in a special device mounted on the

6、 bolster plate of a K232B crank press operating at a speed of 120 strokes per minute. In certain testing machines and Installations, fatigue tests are carried out on specimens under conditions and in circumstances determined by specially designed mechanisms, various vibrators, pulsators, etc. (2, 3.

7、 The device used in our work was constructed so that it can be placed on the bolster plate of a crank press, and it is the operation of the latter that controls the magnitude of load and the duration of a cycle. The device enables specimens to be tested under conditions Identical with those prevaili

8、ng during the operation of a hard-alloy die set, involving the application of impact loads at the same frequency as the speed of the press. A specimen held in this device is subjected to "pure" bending in a pulsating load cycle, and this, too, is controlled by the press itself. A diagramma

9、tic representation of the testing device is shown In Fig. 1. The load applied to the specimen 1 is transmitted from the press ram 2 through the fine load adjustment mechanism 3 and the plunger 4. In the plunger is fitted the dynamometer 5 which measures the load. Before testing, the dynamometer is c

10、alibrated in the usual way. The mechanism 3 consists of two wedges which can be moved by means of screws in order to adjust the load according to experimental requirements. The specimen is held in the slides 6. These are rigidly attached to the base of the device, which in turn is fastened to the bo

11、lster plate of the press 7. The bending stress set up in the specimen during cyclic impacts is calculated with the familiar formula o-jj = M/W.All specimens were made of VK20 hard alloy by a powder metallurgy process consisting of pressing and sintering and were then machined on four faces. The fini

12、shed specimens were 5.0 x 6.0 x 35.0 mm in size. Grinding with an AS016-B1- 100 diamond wheel at V = 30 m/min, and Sj = 0.02 mm per double stroke ensured that their surface layers were free from any defects. Now the manufacturing process includes certain operations as a result of which hard alloys p

13、ossess, after sintering and diamond grinding, a characteristic structural heterogeneity in the form of permanent strains In the two phases (tungsten carbideA WC + 20% Co hard alloy 一 Translator.Kharkov Polytechnic Institute. Translated from Poroshkovaya Metallurgiya, No. 6 (150), pp. 102-105, June,

14、1975. Original article submitted March 27, 1974.© 1975Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, micro

15、filming, recording or otherwise, without written permission of the publisher. A copy of this article is available from the publisher for $15.00.Fig. 1. Diagram of specimen testing device. For description see text.crystals and cobalt layers). During cooling from the sintering temperature, internal ph

16、ase microstresses are set up in WC-Co alloys in consequence of the difference in thermal expansion between the tungsten carbide and cobalt components. Under these conditions, the cobalt skeleton is found to be in a state of compression and the cobalt layers in a state of tension 4. Subsequent machin

17、ing (diamond grinding) forms a thin surface layer, not more than 80-100 g thick, in which the carbide and cobalt phases exhibit compressive permanent strains 5The possible effects of this type of structural heterogeneity upon the strengE of WC-Co hard alloys does not appear to have been investigated

18、 as yet. Because of this, when considering ways of increasing the useful life of hard-alloy tools operating under cyclic loading conditions, an attempt should be made to allow for the influence of residual stresses upon the fatigue behavior of hard alloys.In investigations Into the effect of residua

19、l stresses upon fatigue strength, it is usual to employ results of comparative tests on annealed andunannealed specimens. Jn the present work, annealing as a stress-relieving operation was performed, on half of the specimens, according to the following schedule: a) heating up in a vacuum to 800°

20、;C in 3-4 h; b) soaking at 800°C for 4 h; c) cooling down with the furnace in not less than 4 h.According to existing information, such heat treatment induces no changes in the micrestructure and hardness of hard alloys. X-ray diffraction tests for residual strains showed that after annealing t

21、he phases were in an unstressed condition. Since, however, a layer not more than 1-4-gdeep can be examined by the x-ray diffraction technique, data are obtained indicating the absence of residual stress only in such thin surface layers of ground hard-alloy specimens. Thus, results of tests of this k

22、ind apply only to stresses in the surface layers of specimens. This enables us to choose a basis for our fatigue tests: The fatigue limit was taken as the stress at which the specimens withstood 1 ,105 cycles. Such a basis is shorter 比an that required for fatigue tests on brittle materials (5 106).

23、The choice was dictated by the following considerations.The testing basis selected was equal to the least life of hard-alloy blanking tools between two reg rinding operations. According to 5, the life of blanking tools for Soviet electrical steel sheets is up to 100,000 working cycles. Reg rinding r

24、emoves a surface layer 0.07-0.1-mm thick, so that the factor investigated 一 the presence of residual compressive stress at a depth of up to 0.1 mm 一 ceases to be operative. The part begins to operate once again with as it were a new surface layer, formed during the latest machining operation (regrin

25、ding). Thus, a system of residual stresses established at the surface can affect fatigue behavior only in the period between two reg rinding operations.In Fig. 2, the results of our tests are shown in the form of a chart of specimens which failed or did not fail at the stress levels investigated. Sh

26、ort fatigue limits and their rms deviations were determined, in accordance with 1, for specimens with residual stress set up in the course of fabrication and specimens with their residual stress relieved by annealing. Statistical processing of these data enables possible values of breaking stress to

27、 be determined with the degree of probability selected.TABLE 1.Test parameterVK20 hard alloy specimensafter diamond grindingafter diamond grinding and annealingNumber of speci mens tested2828Mean value of short fatigue limit for 95% probability, kg/mm2102.04 士 0.8471.2 ± 0.79Rms deviation of fa

28、tigue limit,1.451.33kg/mm2J, kg/mm?b Specimen No.Fig. 2Fig. 2. Chart of VK20 hard alloy specimens which failed or did not fail in consecutive tests: a) after diamond grinding; b) after diamond grinding and annealing at 800°C.Fig. 3. Fatigue curves for VK20 hard alloy specimens: a) after diamond

29、 grinding; b) after diamond grinding and annealing at 800°C.Our impact-load fatigue tests revealed that the specimens free from a system of residual stresses exhibited much lower fatigue strengths (Table 1). In Fig. 3, the results of the same tests are given in the form of fatigue curves plotte

30、d in semilogarlthmlc coordinates together with ranges of scatter for the mean values of short-fatigue limit.Thus, the technique developed by us for the fatigue testing of hard-alloy specimens under the conditions of operation of a crank press enables us to determine the effects of the residual inter

31、facial stresses set up in the course of processing upon the fatigue strength of such specimens. The results obtained show that the absence of residual stresses of this kind lowers the short-fatigue limit of VK20 hard alloy by almost 30 kg/mm2. The "staircase" accelerated fatigue-testing te

32、chnique can be successfully employed for evaluating the sensitivity of the fatigue strength of the brittle hard alloys to such a structural heterogeneity as fnterfacial residual stresses.LITERATURE CITED1. W. I. Dixon and A. M. Mood, J. Am. Statist. Assoc., 43, 109 (1948).2. L. G. Kuklin, Izv. Vyssh

33、lkh Uchebn. Zavedenii, Mashinostr., No, 7 66 (1963).3. M. G. Loshak. Tekhnol. 1 Organizatsiya Proizv., No. 6, 117 (1966).4. G. S. Kreimer, Strength of Hard Alloys in Russian, Metallurgiya, Moscow(1971).5. B. M Sverdlova et al., Fiz.-Khim. Mekhan, Mat., No. 4, 24 (1972).6. B. M. Kondrashov, Tekhnol.

34、Elektrotekhn. Proizv. No. 32, 43 (1971).在曲柄压力机工作条件下对VK20硬质合金的疲劳试验V. P. Smolyaninov and S. I. SpirinaUDC 669.018:620. 178.3疲劳极限是通过在受控条件下对试样或全尺寸部件进行试验而确定的一种 特性，是抗疲劳的一种定量特征。当疲劳试验在尽可能接近使用条件下进行时， 疲劳试验给出最佳结果。在这样的实验中，采用加速试验方法来测定疲劳强度是很 方便的。下述工作旨在研究碳化钙钻硬质合金试样的疲劳行为，并检验迪克森和莫德 的“阶梯"加速技术1作为确定这类脆性材料疲劳特性的方法的有

35、效性。从两 个角度考虑了 “阶梯”法对硬质合金测试的适用性：a）在模拟硬质合金冲裁工具（冲模或冲压机）操作载荷的条件下测定硬质合 金的疲劳特性；b）研究一种结构不均匀性对硬质合金短疲劳极限的影响，即在硬质合金部件 制造过程中建立的残余界面应力系统。试样试验在安装在K232B曲柄压力机垫板上的特殊装置中进行，该压力机以 每分钟120冲程的速度运行。在某些试验机和装置中，疲劳试验是在由特殊设计的 机构、各种振动器、脉动器等确定的条件和环境下对试样进行的。2, 3.我们工作 中所用的装置是这样构造的，它可以放在曲柄压力机的垫板上，而正是后者的操作控 制了载荷的大小和循环的持续时间。该装置使试样能够在

36、与硬质合金模具工作时相同 的条件下进行测试，包括以与压力机速度相同的频率施加冲击载荷。这个装置中的样 品在脉动载荷循环中受到“纯”弯曲，这也是由压力机本身控制的。如图1所示。施加到试样1上的载荷从压头2通过载荷微调机构3和柱塞4 传递。在柱塞中装有测量载荷的测力计5。测试前，测力计以通常的方式校准。 机构3由两个楔块组成，这两个楔块可以通过螺钉移动，以便根据实验要求调节 负载。样本被保持在载玻片6中。这些被刚性地连接到设备的基座上，该基座又 被紧固到压力机7的垫板上。用熟悉的公式计算了循环冲击过程中试样产生的弯曲 应力。所有样品都由VK20硬质合金通过粉末冶金工艺制成，包括压制和烧结，然 后在

37、四个面上加工。成品样品的尺寸为5. 0-6. 0-35. 0毫米。用AS016-B1- 100 金刚石砂轮在V = 30 m/rain和S2 = 0. 02mm/双冲程下研磨，确保其表面层无 任何缺陷。现在，制造过程包括某些操作，其结果是硬质合金在烧结和金刚石研磨 后，具有以两相（碳化铝晶体和钻层）。在从烧结温度冷却的过程中，由于碳化铝和 钻合金成分之间的热膨胀差异，在碳化钙-钻合金中形成了内部相微应力。在这些 条件下，发现钻骨架处于压缩状态，钻层处于拉伸状态4。随后的金刚石研磨（金 刚石研磨）形成-个不超过80-100 um厚的薄表面层，其中碳化物和钻相表现出 压缩永久应变5。这种结构不均匀

38、性对碳化钙钻硬质合金强度的可能影响似乎还没有被研究 过。因此，当考虑增加在循环载荷条件下工作的硬质合金工具的使用寿命时，应考 虑残余应力对硬质合金疲劳性能的影响。在研究残余应力对疲劳强度的影响时，通常采用退火和未退火试样的对比试验 结果。在目前的工作中，退火作为一种消除应力的操作，在一半的样品上进行，按照 下列时间表:a）在真空中加热到800 3-4小时；b）在800C浸泡4h； c）在不少于 4小时内用炉子冷却。根据现有资料，这种热处理不会引起硬质合金的显微组织和硬度的变化。残 余应变的x射线衍射测试表明，退火后各相处于无应力状态。然而，由于不超过1- 4-t 深的层可以用x射线衍射技术检测，获得的数据表明只有在研磨的硬质合金 样品的这种薄表层中