钢制夹紧液压缸支架.pdf

UDC 669.14.018.298:621.226 STEEL FOR CRAMPS OF HYDRAULIC PRESS CRADLES I. A. Borisov1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 24 26, May, 2001. INTRODUCTION Creation of installations with a high unit power is ac- companied by growth of their sizes and the mass of the prin- cipal parts. This raises the requirements to the steels used for the production of heavy-duty parts for such installations. In the present work we solved the problem of the choice of steel for making large-size welded cradle cramps that are highly loaded components of hydraulic presses and can de- velop, for example, a force of 650 MN. The design of a cradle includes twenty welded cramps. The length of each cramp is 30 m, the width is 1.5 4 m, and the thickness is 0.28 0.32 m. A cramp weighs 160 tons. It should be noted that the maximum thickness of the sheets used for fabricating such cramps is 0.36 m with the process allowance. Based on the data contained in native handbooks of steel grades and special specifications 1 3 and the experience of plants producing rolled sheets, we analyzed 10 carbon and low-alloy steels, namely, 25, 30, 16GS, 20GS, 25GS, 09G2S, 22K, 20Kh2MA, ITs-14, and 16GNMA. It turned out that only grades ITs-14 and 16GNMA of the list fully satisfy the requirements of the specifications. We did not know of any experience of their use for the production of parts with a thickness of 0.36 m. Steel 30 used for plates up to 0.5 m thick was the only exception, since it met the requirements of the TU with respect to the level of mechanical properties. Steels ITs-14 and 16GNMA have a quite high adaptabi- lity to manufacture and are widely used in the industry for the production of rolled sheets possessing a high strength and ductility and a twice-higher impact toughness than is re- quired by the TU. The steels are satisfactorily weldable in large cross sections. Taking these properties into account we chose steel 16GNMA used for fabricating boiler drums with high steam parameters as a prototype for our study. METHODS OF STUDY The specified mechanical properties of cramp steels are as follows: ?0.2? 225 MPa, ?r? 450 MPa, ? ? 18%, KCU ? 0.4 MJ?m2. The chemical composition of steel 16GNMA was cor- rected for the production of plates with respect to the main alloying elements. In particular, the lower carbon limit was widened by 0.1%, the content of manganese was diminished by 0.1%, and modification with vanadium and titanium (0.05% Ti and 0.07% V) was undertaken in order to preserve the strength. These changes were directed at improving the fabricability of the steel and obtaining a steady level of its mechanical properties. As a result, the steel has become po- pular in the production of power components of heavy hy- draulic presses under the name of ITs-1M. We also tried steel 30A as the simplest and economically expedient variant (Table 1). The test steels were molten in 100-ton open-hearth fur- naces by the scrap process and cast into 68- and 82-ton molds. The ingots were forged with and without preliminary upsetting. The forged plates were subjected to a single an- nealing (with full recrystallization) at 860C (steel 30A) and Metal Science and Heat TreatmentVol. 43, Nos. 5 6, 2001 199 0026-0673/01/0506-0199$25.00 2001 Plenum Publishing Corporation 1 TsNIITMASh Research and Production Association, Moscow, Russia. TABLE 1. Chemical Composition of the Studied Steels Steel Content of alloying elements, %Content of admixtures, % CSiMnNiMo CrNiCuSP at most 30A0.26 0.32 0.17 0.37 0.50 0.800.250.250.0200.020 ITs-1M0.12 0.18 0.17 0.37 0.70 1.001.0 1.30.45 0.550.300.300.0200.020 910C (steel ITs-1M) and to a single (steel 30A) or double annealing (steel ITs-1M) at 650C with subsequent cooling with the furnace. Four forgings for pilot plates were pro- duced from each grade of steel. The ultrasonic check of the plates was performed with adjustment of the device for a standard opening 2 mm in diameter. Templates with a thickness of 200 mm were cut from the plates on the sides of the crop and the butt of the ingot after cutting the recrement 200 400 mm wide. They were used to study the macro- and microstructure of the metal of the forging, take sulfur imprints, and perform additional ultra- sonic check if necessary. The final heat treatment consisted of “soft” normaliza- tion and subsequent annealing. For this purpose preforms 20 mmthick,200 mmwide,and 380 mm high taken from the templates were subjected to a final heat treat- ment by the following regime: 2-h austenization at 920C, cooling at a rate of 150 K?h to 600C and then in air (imitation of the regime of norma- lization of plates), and annealing at 650C for 10 h. The mechanical pro- perties were determined on transverse andlongitudinalspecimens.The transverse specimens were taken from the surface zones of the plates and at a depth of 1?3 and 1?2 of the thickness of the plate. The vertical specimens were taken from the surface and central (with respect to the thickness) zones of the plate. RESULTS AND DISCUSSION The study of the metal of the plates fabricated from steel 30A showed that it fully meets the requirements of the speci- fications to the mechanical properties, the microstructure, and the sulfur content. For example, the level of the proper- ties of plates with a chemical composition including 0.32% C, 0.37% Si, 0.71% Mn, 0.25% Cr, 0.23% Ni, 0.15% Cu, 0.017% S, and 0.008% P exceeded the specified values even after a preliminary heat treatment, namely, ?0.2= 240 MPa, ?r= 460 MPa, ? = 33.6%, ? = 59%, and KCU = 1.0 MJ?m2. However, the ultrasonic control of all the pilot plates showed that they possessed defective zones at a distance of 130 150 mm from the surface, which stretched from the padding to the butt of the plates. Therefore, three plates of the four ones subjected to this kind of check were rejected. Another four pilot plates were produced from steel ITs-1M. The chemical composition of the pilot plates is pre- sented in Table 2; the method of casting and the mass of the ingots and the forgings are presented in Table 3. The level of mechanical properties of the pilot plates af- ter the preliminary heat treatment and the points of the sulfur imprints are presented in Table 4. Analyzing the data of Tables 2 4 we can see that steel ITs-1M meets the requirements of the specifications even in the state of annealing, and its characteristics of ductility and impact toughness are even much higher. The inconsiderable difference in the properties of the metal of the four heats that differ in the chemical compositions but correspond to the specifications indicates that the specified composition of steel ITs-1M is balanced. The close levels of the metal taken from the crop and butt of an ingot show that the steel is appli- cable for large forgings due to its high fabricability. Control of the macrostructure showed the absence of de- fects. The points of the sulfur imprints in the crop and butt parts of the ingot satisfied the requirements of the specifica- tions (Table 4). Individual defects with the size of the stan- dard opening (? 2 mm) were detected by ultrasonic check only in the central part of a plate fabricated from heat 3 at a 200I. A. Borisov TABLE 3. MassofIngotsandForgingsfromsteelITs-1M Heat Casting technique Mass, tons ingotforging 1Degassed82.053.5 268.036.6 3Not degassed68.036.6 482.053.5 TABLE 2. Chemical Composition of Steel ITS-1M Heat Content of alloying elements, %Content of admixtures, % CMnSiNiMoCrCuSP 10.170.750.301.20.490.260.120.0160.008 20.160.850.241.130.520.290.150.0180.010 30.130.710.231.170.500.250.120.0170.008 40.130.850.251.080.550.300.150.0180.008 TABLE 4. Mechanical Properties and Points of Sulfur Imprint of Plates from Steel ITs-1 after Preliminary Heat Treatment Heat ?0.2, MPa ?r, MPa ?, %?, % KCU, MJ?m2 Points of sulfur imprint 1 280 300 480 480 314 306 . . 710 680 . . 13 12 . . 2 1 2 320 330 500 480 304 300 . . 730 730 . . 17 16 . . 2 1 3 280 300 450 455 320 308 . . 650 690 . . 15 14 . . 2 1 4 335 325 520 510 246 300 . . 460 640 . . 08 09 . . 2 1 Notes. 1. The numerators present the properties determined for specimens cut from the crops of the ingots; the denominators present the properties of specimens cut from their butts. 2. The scale of points of the sulfur imprint consisted of four points (the fourth point corresponded to rejection). depth of 100 260 mm. The other three pilot plates had no defects. This circumstance was decisive for choosing steel ITs-1M for the production of commercial cramps for press cradles. In order to obtain an all-sided picture of the quality of the metal of the pilot plates we performed a laboratory study im- itating the regime of normalizing and annealing of actual plates. Templates subjected to such a treatment were used to cut transverse and longitudinal preforms for specimens for mechanical tests. The preforms were cut in these directions in order to estimate the suitability of steel ITs-1M for the production of thick sheets, because these directions are not only the worst but the most indicative from the standpoint of the quality of the plate metal (Table 5). The performed study showed that the mechanical proper- ties of the pilot plates in the normalized and annealed states exceeded the requirements of the specifications quite sub- stantially even in tests of the specimens cut in unfavorable directions. It should be stressed that no deviation from the re- quirements was detected in the course of the tests, which is a very rare case for the metal of large preforms. The level of the mechanical properties was close over the thickness and in various zones of the forgings, as well as in individual forgings. This means that the metal is highly isotropic and confirms the correctness of the choice of the chemical com- position for steel ITs-1M and the production process for the plates. CONCLUSIONS 1. We recommend steel ITs-1M of the following chemi- cal composition: 0.12 0.18% C, 0.17 0.37% Si, 0.7 1.0% Mn, 1.0 1.2% Ni, 0.45 0.55% Mo, ? 0.30% Cr, ? 0.30% Cu, ? 0.020% S, ? 0.020% P for the production of cradle cramps of high-capacity presses in the form of forged and rolled plates. 2. The mechanical properties of the plates after the pre- liminary heat treatment (?0.2= 280 335 MPa, ?r= 450 520 MPa, ? = 24.6 31.4%, KCU = 0.8 1.6 MJ?m2) and afterthefinalheattreatment(?0.2= 350 460 MPa, ?r= 490 620 MPa,? = 22.3 32.7%,andKCU = 0.8 1.8 MJ?m2) substantially exceed the requirements of the specifications(?0.2? 225 MPa,?r? 450 MPa,? ? 18%, KCU ? 0.4 MJ?m2). 3. It has been shown that low-carbon compositions of Mn Ni Mo steels in the form of a thick forged and rolled plate are suitable for heavy-duty parts after normalization and annealing. REFERENCES 1. A Handbook of Grades of Steels and Alloys in Russian, TsNIITMASh, Moscow (1971). 2. V. N. Zhuravlev and O. I. Nikolaeva, Steels