机床英语

7..22 1,95
22753
0.17 0.16 0.16
1,00 1.77 2.22 1.12
168 161
0.46 0.46
0.053 0.31 0.31 0.32
378
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220
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1
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12
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1.02 0.94 1.00 0.92 0.54 1.44 1.30 1.38
i.61 1.I2 0.20 0.22 0.43 0.88 0.90 091
0.020 0.024 0.001 0.024 0.020 0.035 0.034 0.031
0.025 0.028 0.010 0.025 0.018 0.027 0.024 1.027
Table 1 C h e m i c a l Composition of Experimental Steels
Melt I designa tion A B C D E F G H
Chemical anal/sis, % by wt. Mn Ni Cr Mo
0.39 0.58 0,56 0,58 0.43 0,21 0.27 0.41
UDC 620.197 E F F E C T OF T H E R M O M E C H A N I C A L TREATMENT P R O P E R T I E S OF S T R U C T U R A L STEELS L. Hyspeckg and K. Mazanec Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 4, No. 5, pp. 517-524, 1968 The m e c h a n i c a l properties of ordinary and v a c u u m - s m e l t e d steels subjected to t h e r m o m e c h a n i c a l and thermal treatments were studied. It was shown that the long-term strength of freshly-quenched F e - N i - C alloy is affected by t h e r m o m e c h a n i c a l t r e a t m e n t . Comparative data were obtained on the fatigue strength of three steels with different carbon contents after thermal and t h e r m o m e c h a n i c a l treatments. T h e r m o m e c h a n i c a l treatment ( T M T ) i m p r o v e s the m e c h a n i c a l properties of steel [ 1 - 3 ] . It has been studied for many years, the results of the most recent investigations being reported in [ 4 - 6 ] . The aim of this investigation was to elucidate certain less extensively studied aspects of the influence of TMT on the m e c h a n i c a l properties of steel (deIayed fracture, fatigue strength) and of the role of m e t a l l u r g i c a l factors in a TMT-induced increase in the strength of steel. The last part of this article is devoted to a discussion of the nature of the TMT-induced increase in strength with p a r t i c ular reference to concepts of the dynamic effects accompanying the formation of martensite platelets [7-10]. Experimental materials and techniques. The experiments were carried out on several alloy steels ( T a b l e 1 ) s m e l t ed in a small (40 kg) laboratory hf induction furnace using a standard charge; a v a c u u m - s m e l t e d steel ( m e l t C) made from superpure materials was also studied. The h i g h - t e m p e r a t u r e t h e r m o m e c h a n i c a l treatment (HTMT) involving a total deformation of 80-85% was carried out on a semi-industrial "duo" rolling m i l l . The deformation temperature was 900 ~ C in every case. The quenching in water or oil (depending on the carbon content in the steel) was done 2 - 4 sec after rolling. A detailed description of HTMT was previously given in [7,8, 11]. Control specimens (subjected to conventional quench-hardening treatment) were held for 1.0 hr at the temperature before quenching. The tempering treatment lasted 4 hr in every case. Specimens for static and fatigue strength tests were made from 3 - m m - t h i c k ground strip. The fatigue tests in plane bending were carried out on a Shenck-Plateau machine at a frequency of 1500 c p m . The retarded fracture was studied on a model a h o y F e - N i - C ( m e l t E, Table 1). In this case, HTMT was applied after preliminary deformation of austenite by drawing at room temperature (25% reduction). Specimens of this alloy were given a double austenitizing treatment at 1050 ~ C followed by water-quenching. The quenching after HTMT was done in liquid nitrogen which ensured intense transformation and a low ( 5 - 8 % ) r e s i d u a l austenite content. The m a r t e n sitic transformation tem~ crature of this alloy is - 3 5 ~ C. The retarded fracture tests were carried out on untempered specimens. Experimental results. The effect of tempering temperature on the UTS and elongation of an alloy steel with 0.39% C is illustrated in Fig. 1; as previously shown [11], this carbon content ensures the m a x i m u m strength of steel after quenching and tempering at 100 ~ C. The corresponding data for a steel with a higher carbon content (0.58%) are shown in Fig. l b . In this case the difference in the strength of tempered specimens is larger. Quench-hardened steels tempered at a low temperature have a reduced ductility and their fracture is predominantly intercrystalline in character. After ON M E C H A N I C A L
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Fig. 1.
Effect of HTMT on the strength and ductility of steel, a) Melt a; b) melt g; Q) HTMT; 9 conventional heat treatment.
HTMT and low-temperature tempering, the proportion of intercrystalline fracture is sharply reduced. Only after t e m p e r ing at temperatures higher than 200 ~ C does the character of fracture become the same ( i . e . , predominantly transcrystalline) though there are some differences in the "granularity" of fractures associated with structural changes after HTMT [11,12]. Especially interesting are the results of tests on a v a c u u m - s t o c k e d steel made from very pure materials (Fig. 2). In this case, in contrast to an ordinary steel with the same carbon content, there was no large difference in the strength and ductility of specimens subjected to HTMT and those given a conventional heat treatment (even in the case of specimens tempered at the very lowest temperature). We studied also the effect of austenite grain size on the martensite strength and character of fracture of steel after HTMT and conventional heat t r e a t m e n t . The experiments were carried out on a m o l y b d e n u m - f r e e steel alloy which made it possible to reveal austenite grain boundaries by etching. As shown in Fig. 3, "premature" fracture ( p r e d o m i n a n t ly intercrystalline in character) takes place when the austenite grain size is larger than a certain critical value (d 1/2 22). As the austenite grain size decreases below this value, the fracture becomes more transcrystalline in character,