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H..f:.u+:wtrsl ".2. . ‘ PART I, COMBINED CARBON CONTROL IN HOLY-GRAPHITIO STEEL ' PART II ET- SURFACE CONDITIONS OF DOWETAL G ALLOY 13(1le SOLUTION AND PRECIPITATION HEAT TREATMENTS Denton DzjggGredy A Theeie Submitted in Partial Fulfilment 0f the Requirements for the Degree MASTER OF SCIENCE In the Graduate School Michigan Stete College // Department of Chemical Engineering r a!“ M flq \ June 1939 02‘}, G bl (I, 'h I. II. III 0' IV. V. I. II. III. IV. V. VI. TABLE OF CONTENTS Part I Introduction ............................ Experimental Methods .................... Discussion of Results ................... Conclueione ............................. Ab.tr‘°t. .00..OOOOOOOOOOOOOOQO0.00.00... Part II Introduction ............................ Experimental work and Afiparatue ......... Diecueeion of Results ...............;... Summary ................................. Conclueione ............................. Ab.tr‘ct. O....00...OOOOOOOOOOOOOOOOOOOO. 121473 Page 26 27 33 36 48 80 85 87 Acknowledgements The advice and guidance of Professor H. E. Publow is gratefully acknowledged. The Holy-Graphitic Steel samples were furnished by the Timken Steel and Tube Company, Canton, Ohio. The samples of Dometal G alloy used herein were available through courtesy of the Dow Chemical Company, Iidland, Ii chigan. -4- PART I COMBINED CARBON CONTROL IN HOLY—GRAPHITIC STEEL INTRODUCTION The molybdenum alloy graphitie steel used in this study was from heat number 18047 and had the following chemical analysis. The steel is specified to the trade as "Graph-mo". - “K Carbon ......... 1.47 Silicon 0.0.0... 0.9? ‘Hanganese ...... 0.42 Molybdenum ..... 0.21 Phosphorus ..... 0.015 sulfur 0.0.0.... 00014 The investigation of this type of steel centered around the possibility of altering the relative amounts of combined and graphitie carbon by simple heat treatment. *Graphitic steel is an electric furnace product. It is made under rigid control. It combines the easy machining qualities, high resistance to wear, and good frictional properties of cast iron together with the uniformity, ease of hot or cold work, ready response to heat treatment, and good physical properties of steel, to form a.material which can‘be utilized to advantage in many fields, particularly the die industry. *For water-hardening uses a type of graphitie steel known as 'Graph-sil', containing no molybdenwm, is used. -6... If special toughness and freedom from distortion is desired, the oil-hardening "Graph-mo", which contains approximately 0.25% molybdenum, is used. Preliminary and final heat treatments are dependent upon the par- ticular application for which the steel is to be used. *, Literature - Timken Steel and Tube Company, Canton, Ohio. - 7 - EXPERIMENTAL'METHODS In order to study the reaction of moly-graphitic steel to various heat treatments, samples of 5/8 inch round about 6 inches in length were secured, heated in closed pipe bombs for varying lengths of time at diff- erent temperatures, and subsequently cooled through the critical range at varying rates. The effect of each of these factors on the structure of the steel was deter- mined by metallographic methods. Dilatometer curves (abstract 3, page 28) show that the critical temperature on heating is about 1400 deg. F., and on cooling about 1300 deg. F. The presence of graphite in the steel complicates the procedure necessarily used to prepare the specimen for metallographic examination. Unless great care is employed in all of the polishing steps, the abrasives will tend to tear out the graphite inclusions and leave only exaggerated holes. Buffing action.must also be avoided. Rouge, used on a slightly dampened wheel revolving at a fairly slow speed, was found to be the most satis- factory of available methods for the final stage of polishing. The rouge must be thoroughly removed from -8... the polished surface to prevent misleading observations. Picric acid of some 3-4% strength, mixed with a small amount of 2% nital and a trace of HCl, was perhaps the best etchant found, particularly for bringing out the grain boundries in the ferrite. Picric acid alone was used on samples having a tendency to stain readily. In all cases it was difficult to secure sharp grain boundries (when present) and at the same time preserve the detail of the pearlite and other constit- uents present. DISCUSSION OF RESULTS The samples used were taken from.§/B inch round bars of moly-graphitic steel. The bars were received in mill lengths in the hot rolled condition. Figures 1, 2, 3, and 4 are photomicrogrsphs of the steel in the as-received condition. Figures 5 and 6 show grains of ferrite resulting from a slow cool of 1 deg. F./min. after the sample has been held at 1400 deg. F. for 48 hours. The difference in structure resulting from.more rapid cooling through the critical range is illustrated by comparing Figures 5 and 6 with Figures 7, 8, and 9. Figure 7 shows a sample held at 1400 deg. F. for 48 hours and cooled at 6 to 8 deg. F. per minute. Figure 8 was taken fron.a sample held at 1400 deg. F. only 2 hours and cooled at 3 deg. F./minute. The sample in Figure 9 was held at temperature only 15 minutes and than furnace cooled. a photomicrograph of a sample held at 1400 deg. F. for 60 hours and cooled at 1 deg. F./min. through the critical range is shown in Figure 10. Figures 11 and 12 are the same as Figure 10 except the sample was held at temperature only 2 hours. Two sample were photographed that had been held at 1800 deg. F. for 48 hours and 2 hours respectively, and which had been cooled together at 1 deg. F./min. from 1400 deg. to 1200 deg. F. Figure 13 shows the 48 hour sample, and Figure 14 the 2 hour sample. Ferrite grains are present in both these samples. Figure 13 shows, apparently, a pearlite area in the late stages of disin- tegration or diffusion. A portion of the above 2 hour sample shown in Figure 14 was taken and heated to 1800 deg. F. again for a 2 hour period, but this time it was cooled rapidly in air to room.temperature - resulting in the structure shown in Figure 15. Since the structure in Figure 15 is quite different from the original, it would indicate the possi- bility of changing some of the graphitised carbon back into the combined form. It may be noted at this point that the samples held at 1400 deg. F., which is very close to the critical temperature, did not produce consistent results. This was occasioned, perhaps, by the possible variation between indicated and actual sample temperatures. - ll - Fig. l 'Moly Graphitic Steel As Received Picral - Vital etch 1000x - 12 - Fig. 2 Holy Graphitic Steel As Received Picral etch - same area as Fig. l 3000x 13 - 3 Fig. Steel Moly Graphitic As Received Picral etch 2000x - 14 - Fig. 4 Holy Graphitic Steel As Received Picral etch .3000x - 15 - Fig. 5 As received sample of Moly Graphitic steel held at 1400 deg. F. for 48 hrs. and then slow cooled at l deg./min. Picral - Nital - HCl etchant 1500x ‘ w n 4 ‘ ‘ u ' Fig. 6 Same as Fig. 5 except at 2000x -17- Fig. 7 As received sample of Holy Graphitic steel held at 1400 deg. F. for 48 hrs. and then cooled at 6 to 8 deg. F./min. Picral - Nital - HCl etchant ‘2000x - 18 - Fig. 8 As received sample of Moly Graphitic steel held at 1400 deg. F. for 2 hrs. and oven cooled at 2 to :5 deg. F./min. over the range 1400 - 1000 deg. F. P - N'- HCl etch 2000x - 19 - Fig. 9 As received sample of Holy Graphitic steel heated to 1450 deg. F. for 15 minutes and then oven cooled. Picral etch 2000x I F 4.1” . k C 5 J ’ ( {3/545 [Oil'frfiw a Fig. 10 As received sample of Moly Graphitic steel heated to 1400 deg. F. for 60 hrs. and then cooled at 1 deg. F./min. from 1400 deg. F. to 1000 deg. F. P - N; HCl etch 2000x -21- 1g. 11 F 10 except held at Fig. Same as 1400 deg. F. only 2 hrs. P - N - H01 etch 2000x v,‘ A . O \T“ . Q’)'— ‘. .«f Mn “’2 \ {I‘M/£24- . Fig. 12 Same as Fig. 11 except another spot on sample. ZOOOX 23 - Fig. 13 As received sample of Holy Graphitic for 48 hrs. steel held at 1800 deg. F. and then cooled at 1 deg. F./min. from to 1200 deg. F. 1400 deg. - HCl etch N P- 2000x Same as Fig. 13 except held only 2 hrs. at 1800 deg. F. P-N;HCI etch 2000x -25.. Fig. 15 Startirg with Fig. 14 (sample No. 15) and held at 1800 deg. F. for 2 hrs. and then rapidly cooled in air to room.temperature. Picral etch 2000x -26- CONCLUSIONS 1. It was found possible, apparently, to graphitize lost of the carbon in the steel, and to have left, conse- quently, large grains of ferrite, some small amount of pearlite, and large inclusions of graphite. 2. 0n the basis of the evidence at hand, the rate of cooling through the critical temperature range seems to be the major determining factor in this phenomena. 3. When the samples were held at a temperature of 1800 deg. F., the length of time at temperature did not produce any marked difference in observed structure. -27- .ABSTRACTS OF THE THESIS AND PROBLEM WORK. ON'GRAPHITIC STEEL AT MICHIGAN STATE COLLEGE Year Author Title (1.) 1933 Adler, o. Graphitic Steel Rakas, N. (problem report) An investigation of plain carbon graphitie steel. Dilatometer curves on (1) furnace cooled sample, and (2) quenched sample. Brief history, introduction, and explanation of special properties of graphitie steel. Chemical analysis of the steel given. Data on physical properties as determined by the University cf‘Michigan. Suggsations for possible uses of graphitie steel. Effects of quenching from different temperatures. Notations on changes from.spheroida1 to lemmellar pearlite. (2.) 1934 Barry, J.C. Heat Treatment of Shotwell, F.C. Graphitic Steel Tallefson, W.T. (problem report) A continuation of the investigation of plain carbon graphitie steel. General statement of history and prop- erties. Effects of cooling rates on hardness and combined carbon is discussed. Dilatometer curves on (1) and (2), slcw'heating and cooling; (3), (4), and (5), fast heating and cooling; (6), quenching, and (7), standard eutectoid steel dilatometer curve for comparison. Data published by the University of‘Michigan and Timken Company partially verified. ' -28... (3.) 193? Pfefferle, P.R. An Investigation of inoehring, WtE. Alloy Graphitic Steel (B.S. Thesis) An investigation of “Holy-Graphitic” and 'Ni-Moly-C Graphitic” steel. Discussion of problems of polishing and etching. Effect of time at temperature above critical on hardness. Dilation curves (1) and (2) on‘Moly-graphitic steel; and (3) and (4) on Ni-moly-graphitic steel with slow heating and cooling. Photomicrographs. ‘Macrograph of fracture. (4.) 1937 licGrady, 13.1). Graphitic Steel Chapman, R.D. (problem report) A study of combined carbon control by simple heat treatment in ”graph-mo" or moly-graphitic steel. The effect of maximum temperature, time at temperature, and cooling rate through the critical temperature range was studied. Discussion of theory, experimental procedure, and results. Polishing and etching methods considered. Photomicrographs. Conclusions: (1) The cooling rate through the critical temperature range is the main factor in combined carbon control, and (2) the length of time at a temperature of 1800 deg. F. has no appreciable effect. Chemical analysis given. - 29 - (5.) 1938 Reyes, JIM. Effect of Nitriding Packowski, G.W. on Graphitic Steel (B.S. Thesis) A study of the effect of nitriding on moly-graphitic and Ni-moly-graphitic steels. Discussion of apparatus design and arrangement. Ammonia gas used at 1400 deg. F. and under 2 inches of mercury pressure for time periods of 30 and 60 hours. General discussion of nitriding. Experimental procedure outlined. Chemical analysis of sample given. Hardness results stated. Photomicrographs. Conclusions. General bibliography. (6.) 1938 Reid, 13.3. Alloy Graphitic Huff, F. Steel (3.8. Thesis) A study of combined carbon control in moly-graphitic steel. Extensive introductory quotation from.Timken Roller Bearing Company summarizing the various properties, and control of properties of ”graph-ail“ steel. Determin- ation of combined and graphitie carbon, with comparison of chemical and metallographic methods. Discussion of laboratory procedure and apparatus. Conclusions. - 3O - General Information About Graphitic Steel Samples Available at Michigan State College. The following quotation is from.a letter dated Dec. 4, 1936 and written by Mr. F. R. Boats of the Timken Steel and Tube Company, Canton, Ohio. ... We are sending .."six'bars of 5/8 inch round in mill lengths in the three grades of graphitic steel which we now produce. These three grades are, the Carbon Silicon analysis, the Carbon Silicon Molybdenum analysis, and the Carbon Silicon, Nickel molybdenum analysis. The material will be shipped to you in the hot rolled condition together with the heat analysis...” The following graphitie steel samples are on hand as of June 1, 1939. (1) Received Dec. 14, 1936. - 2 bars each 1 ft. in length of heat number 16626, plain graphitie, the same material as used in previous dilatometer tests. Chemical analysis; Carbon 1.46% Manganese 0.40% Phos&Su1 0.017 Silicon 0.85 (2) Received Dec. 15, 1936. Six mill lengths of 5/8 inch round. (Now cut into 1 ft. lengths) “Graph-mo" or molybgraphitio. Heat number 18047. Hot rolled as - 31 - received. Chemical analysis as follows: (Heat No. 18047) Carbon 1.47 Manganese 0.42 Phos. 0.015 Sulfur 0.014 Silicon 0.97 Molybdenum 0.21 (3) Received Dec. 30, 1936. Six mill lengths of 5/8 inch round. (flow out into 1 ft. lengths) Hot rolled as received. Heat number 13136 - NiAMoly- Graphitic. Chemical analysis not given. -32- PART II ETCHED SURFACE CONDITIONS OF DOWMETAL G ALLOY DURIN} SOLUTION AND PRECIPITATION HEAT TREATMENTS -33.. INTRODUCTION Dowmetal G is an alloy of magnesium and aluminum, and exhibits typical solution and precipitation reactions. Figure 16 is designed to illustrate the completely rever- sible precipitation and solution reaction studied herein. The background for this work on Dowmetal may be traced to previous investigations along similar lines carried out in this department. (See abstracts - page 87). The previous studies were concerned with the reactions of plain carbon steels under vacuum heat treatment. However, the higher temperatures necessary, and the nature of the steel itself, introduce many experimental complications. Since the precipitation and solution reactions of Dowmetal G occur at much lower temperatures than could be used with steal, it was thought advisable to study this material. By way of introductory explanation, the following quotation is included. The quotation is from a letter written by Mr. F. L. Reynolds of the Dow Chemical Company, Midland,‘Michigan. ”... These Dowmetal G cast test bars have had a solution heat treatment which we designate as heat treat- ment Nb. 1. The heat treatment is 16 hours at 780 deg. F. AuH.o omossmns: .uoa sodassa< .mm.mm soauonwsm ”mauhasn