a “2 2 l | | Sa MMi THESIS A DETERMINATION OF BEST PROPORTION OF OLD AND NEW CARBONIZERS FOR CASE HARDENING STEEL ca F. G. MILLARD eee, AA | 585 0304. | lh ri | | C1. we“ =e « To Determine the Best Proportion of 01d and New Carbeniszers for Case Hardening Steel A Thesia Submitted to The Faculty of MICHIGAN AGRICULTURAL OOLLEGE F. G. Milleré Candidate for the Degree of Baehelor of Seience June, 1919. Im this theeis I have endeavored to determine the best prepertion ef 614 and new earbonisers for ease hardening of steel, taking into consideration only the eost ef gas ecneumed and the earbeniser used, te obtain @ certain depth ef ease with different proportions of carbonisers. fhe work was done by practical tests under ~~ eenditions which were anslogous to those in modern shops. In the theoretical work I used the following books and articles as references: Factors in Case Hardening Steel, by John A. Matthews and Heward J. Stragg, dr. Heat Treatment of Steel in Gas Purneees, by Garnet W. MNeGee. Neat Treatment of Steel. and Pyrometers, by Hereeus Le Chatelier. - Metallography of Iron and Steel, by Sauveur. 102689 de Part I Deseription of apparatus and method of running the test. Part ITI Resulting ourvesg and their analysis. Part III Heat treatment in ease hardened steel. DESCRIPTIVE APPARATUS AND METHOD OF RUNNING TEST. Im the past few years great advancement has been made in the process of case carburising of steel. In this efvancement the chemical and metallurgical iaberateries have played no small part. During this time, a study of the carbenising material at hand has mot been complete, and in many cases has been neglected er not considered. The objeat of case hardening is the production of a hard wearing surface (the “case") on low earbon steel, and at the same time to increase the toughness ef the “eore™ of the metal. The process may be roughly Givided into two different periods. First, the earburisation of the surface to make the steel capable of taking on great surface hardness. Second, suitabie heat treatment whieh shall develope the properties both ef ease and core. Recent investigations have made it evident thet transfer of carbon from the packing material to the metal is agcomplished chiefly by means of some gases formed during the treatment. It is certain that the carbon must first be volatilised before coming very aetive as a carbonising agent in the gementation ana ease hardening treatments. It has been found that carbon monoxide (CO) is a gas which seems most effective. The carbon monoxide is derived from a partial combustion ef the carbon of the carboniser end oxygen of the air. It may be assuned that carbon monoxide once formed gives up its earbon to iron according to this reaction, 200 + 3 Fe = Fes + 00, The resulting FegO or cementite being dissolved by the anstenite, and the CO, again reduced to 00 om coming in contact with fresh carbon, COg + C = 2 CO The requirements or main factors which mst be considered in case carburising of steel are: first, the solvent or steel, second, the carbonising material, or the compound capable of delivering the carbon, third, the temperature, and fourth, the time of contact between the steel and carbonising agent. In this test I considered only the carbonising material, although the other requirements entered in. It is known in practice that it is not at ali necessary to use entirely new carbonising material to case harden steel. While same results may be obtained by using 8 mixture of new sarbenizer and carbenizer that has been used befere. Bat as far es I have been able te learn it has net beam determined at whieh pereentages of "old" and “new” earbonisera may be used to the best aéventage. This is what I am trying te determine in the following test. fhe following apperatus was used. Hot rolled mild steel that ecntained .22% carbon was cut inte pieces 3/4" x 1/4" - 3° long. ‘The same grade of steel was used for all tests. Some of the pieces were used for samples and others for plugs, to determine the depth of ease at any desired time. In those used for plugs a 3/6" hold was bored im the ends. A wire was inserted and wound to projest far enough ontside the boxes so that it made it possible te pull the plugs from the boxes easily. These plugs were pulled from the packing bexes at the end of each hour, quenched in water, and broke by Placing them in the vice and striking with a hammer. The depth of case was easily identified and measured te the nearest 1/100 of inch with a scale and magnifying Glass. These plugs were net re-inserted for enough pluge were placed in the bex at the beginning of the test so that gt was pesaible te pull encther at the end ef each hour. The packing boxes and covers were of cast iron, The dimensions of the boxes were (18° x ox 3*) and the covers were 1/4” thick and ground $e fit in side. The bexes were numbered “one” and "two" alsp the eevers to correspond. In one end of eagh bex three oe holes were bored, (7/8" x 3/6" thru whieh tae plugs were pushed efter the boxes were packed. ‘Thru the center and ends of the covers of the boxes small heles were bored se that wires soulé be pushed to the bottom of the boxes and extend out at the tep. These wires were pulled from the bexes at the start of a run to determine when the box was heated uniformly thrnuout. The method of packing the boxes consisted in putting a layer of abont an inoh of carburising materiel on the bottom and then putting in a iayer of steel. Hone of the pieces were allowed to tough eseh other or the sides of the boxes. A layer of earburising material was Placed around ané on top of this layer of steel and deep enough to held the next layer from toueshing the first one. Another layer of steel was placed in the bex, as wes the first and se on witil the box was filled. .fhe Prankfort Gas Furnace number 7 was used, which burned city gas and was controled by hand cperation of air anf gas valves. The temperature was held constant at 1650°F, a little above the critical temperature of the steel, and indieated by a Leeds and Nerthrup Potentioneter. Two pyrometers, come placed to the rear of furnace and the other to the front making it possible to regulate the furnees te a constant temperature thruont, were eheckea against a Le Chatelier Pyrometer having sa Platinum and platinum-rhodium thermocouple. Both pyrometers whose eouples were made from iron and eonetantan wire were verified as being correct.with this standard pyrometer. The two carbenisers usea were Hlaichs and Woodsides (fype E), whieh are used extensively in con- mercial lines. Other apparatus used was longhandied tongs, pair seales weighing to the nearest eunee, special pair tengs to fit the bexes, gas meter in the line, bod stick, and mixture of half and half fire olay end core sand with water. fhe follewing method was used thrucut the test; The furmace was started and heated te a constant temperature, 1650°F, at the start of each run. The first run, a preliminary to the experinent, was made so that the bexes and their covers would be case hardened, thereby preventing any serious loss of carbon during the experiment. When the boxes were filled and placed im the furnace they always contained the same kind of ocarboniser ané put in the same place. Number one box containing Woodsides earbeniser and the required steel was placed to the Left in the furnace. Number two box containing Biliachs earboniser was placed to the right in the furnace. fhe first question te be determined waz, what is the life of the earbvonisers, or how many tines it ean be used to be of commercial value. It is known that after the carboniser has been used to a certain extent it loses its strength. That is it gives up its carbon content and also the chemieals or energisers now added to the carbonaceous elements so as to increase the depth ef penetration, ioses its qualities. so { determined how many times these earbonisers could be used to be of value. fhe bexes were packed with their respective carbonisers and the same amount ef steel each tins. After plaeing the boxes in the furnace, heated to 1650°F, the gas meter was reed and the time recorded. When 1/32" depth of ease was obtained to the nearest 1/100 of an inch, the gas meter was read and the tine recorded again. A second run was made in a sinilar way except the earbonizer used in the previous run was freed frem dust and used in this. The dust was removed by allowing the carboniser te fall thru « blast ef air. In this way the lighter foreign material and dust which ia of mo vaine in the sarbonizer was separated from the reeidue material. The time te reach 1/32" case and the amount of gas used were determined. The third rum was made by using the sarbeniser left from the second run. fhe time and amount of gas eonsumed during this run was so high that it was desided that carboniser used the seconé time was the oldest one that is practical. The fellowing methed of procedure is the way I determined the best preporticns of old and new carbenisers. In this run 100% new carboniser was used thra out. Rxtra bexes, other than those I used in eonnectSion with the experiment, were packed sone with Weodstdes (Type EB) carbonizer and some with Blaichs; and placed in the furnace so as to have an ample supply of 014 earboniser for future use. Zam boxes Fo. 1 and No. 2 a pound of Woodsides and Kiaichs, 100% new earbenising mterial was used respectively. Care was teken each time that the sample im one end of the box and the plugs in the other were at least ene inch from any other metal, thereby making sure that an ample supply of earbonizer was at hand. The covers were placed om and all ernacks around the sovers and the heles in the ends were sealed tightly with a mixture ef fire elay and cere sand, preventing the loss of gases as mach as possible. The boxes were then placed in the furnace, heated to 1650°F. in their respective places. The gas meter was immediately read and the time recorded. At the end of each hour plugs were pulled from each box and quenched in water to obtain the mximum hardness. They were then broken in the vice with a hammer and the depth of case measured to the nearest 1/100 of an inch with a scale and magnifying glass. When 1/32" case was obtained the furnace was shut off and the boxes were allowed to cool or anneal in the furnace. The gas moter was read and the time recorded. The samples of steel used during the experi- ment were marked so that one would know under what conditions it had been esse hardened. In the first run or the one just deseribed, the samples were marked with a sub-sero after the letters “W" and "3". The steel marked “W¥," was case hardened with Woodsides (Type EB) carbonisér while that mrked "Bo" was with Blaichs. During each successive run an inorement of one- eighth by weight old carboniser was added to eash box until one hundred percent 014 carboniser had been used. The items that remained eonstant during each run were, depth of case obtained, 1/32", weight of carboniszer, ene peund, and temperature of furnace, 1650°F. The items that varied were percent of old earboniser, time or run, and eubio feet of gas consumed. LO RESULTING CURVES AND THEIR ANALYSIS. Im plotting the fellewing curves the resualts obtained by the experiments, pereent of o]4 sarbeniszer were pletted againat ecat of gas and earbonisers. Az analysis of the curves is interesting in Pig. 1, Ne. 1 anf No. 2 curves describe the relation of Weoésides and Blaiehs carbonisers respectively. It is easily noted thet 62 1/24 o¥4 carboniser with 37 1/2% new sarboniser is the mst economical percentages that ean be obtained with either Blaichs or Woodsides earbonisers. From the results shown end the curves, it will be noted that the price of the carbenizser eheapens and the ameunt ef gas consumed remains constant antil 75% 014 carboniser is used. hen the osst rises rapidly, due to great depreeiatien ef life ef the carbonizser ené the inereased sost of the gaa. In such an experiment as this one, I would think that cost of labor and power would be two bit items to consider. The above results go to show that with these earbonisers they do not enter into consideration. It takes just as long to case harden steel with 62 1/24 old earboniser as it does with 100% new carboniser at a constant temperature. The results show that a saving of $0.028 is ade with Woodsides and $0.024 with Blaichs, on a pound of 22 LZ earbonizer used at this proportion, 62 1/2% eld and SY 1/24 new. On a thousand pounds of cerboniser used @ saving from $24.00 te $28.00 would be made with exactly the same resuits and in the same tine as if 100% new earhoniser waa used. With the two earbonisers used it is evident that Blaichs is the better. For although the results of the above experiment prove to be the same with both carbonizsers the initial cest of Blaichs is the least. Also the results show that there was less dust end other material of no value after each run, in Blaiehs. It was interesting to note from the results that the depth of case after first hours run was greater than any hour thereafter. HEA? PRRATMENT OF CASE HARDENED STEEL. Im order to refine the structure of the core whieh has been eosrsened by a long exposure to a high temperature the metal was reheated slightly above the eritical temperature of the core (1600°F). The finer etructure thus imparted to the eore was retained most effectively by quenching the metal in water. By such @ treatment, however, the ense, although hardened, was relatively esarse since its quenching wae effected at a temperature considerably exeseding its eritienl range. ‘fhe ease obtained, probably had a earben content of 0.9%, a higher percentage tham that of the cere, making it pessible te harden the case, by reheating to a little above the eritical temperature (1200°) and queneghing in oil. By thie double treatment I herdened the case as well as making the core of the finest structure. is RESULTS, OBTAINED | MAr'c ‘on a fel herd Geer aera a | | steel in a we ry | C@2bonizen gas and E ie] carbonizer | ® | used carbonizer|- ie an | ae Bs Aly | 3 a 4 e s & is ‘ R (ry 5 wa] se Aly 8 See ; car Cee cs ae ome) 8 ae es eS rm art ees?) Mee aed ee ec a Se ee on ae bee lee ee Pe iene: Fel —— 7 Fe] a al MN ec Oecd a By’ | .035] 1602 0449}0350 |$.345/$.333/ 3 | 240 | 4.30/1650 By | do,| do, 939540333] .339| 13331 3 | 240! .30| ao, B> | do.| ao, $0337-0285) .334) .328 3 | 240 | “301 ao, Bs | do.| ao, }028140237| .528/ .324 3 | 2401 30] ao, Bg | 40,1 do. 02250190) .322) .319 3 | 240] .30] ao, Bs | do,| do, O169.0142) 517} 13144 3. | osc] 130! ao, ye a oe 0114.0095/ 4361] .359 31/2 200| 135] ao. Ean PCP CY Ve ore: Aer vd ee oe Co) BB | doo] do. == {== | .50] .50] 5° | 400] .50] ao, RESULTS OBTAING rae a rue oe) peal R=} ChDe ach aed Bas Se wy © On Ei 4: S | : rv ee ® — BOPTE poo, Td = | " : is = : ‘ i r ee ; POA ‘BtoTeTe DS A mc “8 8 i I re oe | a a shine Teeter. RY Ey 7 hb Sih te, ee i ce) = : he poker 3 al 4 ce} ne ae om RLS o atqng | mK “i Sioa he iN aye Leen SRL Teas || SUOTeT Bey es oe OTT E oe Ed 9 hs a5 aI ; ey a ES : ~ 7 OF ~ | 4 : Ld Se a ee CES ae ttre cer toh i on ey Boe ol oihet ee seus fae RESULTS OBTAINED Aric on ft Cost of Cost of ea Sitios ABs = rf Carbonizen gas anda Fe Le] Carbonize “4 , o Fekeye4 carbonizer Ff i a aw! 5 3 b* amo a i a eee ee 5 2 Olo . : Pare LSE A i ra as! ONS Qn] sc ‘ or] ar Pe) aa a aes Bal 8 ia cared te 5 te aa ae E ee kee ee eae en Pe ‘e oF a ‘ A j®alesi2sjas) g]a | s 8 ss 2/e8 .035!1 1607/0 0449} 0350 |$.345/3.333/ 3 do,| do. | 121/2,039310333] .339] 333 3 do.| dc. | 25 . Loz37h0285| .334] 308 5) do.! do, | 371/2,0281,0237] .328} .304) 3 dO.) do. 150 [02250190] .32a! 319) 35 d0.] do, | 621/2,0169.0142] .317] 314) 5 ao, fo ka 75 ahr Poke Iay Pei PB Io @o.| do. | 871/a,0054.0047] F405! , 40 odd. pesehe! 0501. .50 CO,| do, | 100 ROOM USE ONLY MICHIGAN STAT IIH 31293005850 TT hes : aps : | a 4 op ll - { ; “ oe , Sag =~, ig a = — * aad , i a - 7 ° ae : —— = — SSS a en x : ae . _ = i any AW. L . tia atl eel