M 5| NHIHIHHI l 4 1! mg 03—} '-+ I _mma THE STRENGTH AND HARDNESS RELATIONSHIPS, AND CHARACTERESTIC PROPERTIES OF SINGLE HEAT~"1‘REATED PLAIN-CARBON BOLTS 'E‘husis for ht Degree of Med. E. MICHIGAN STATE COLLEGE A 12d?“ 6 I N. H cove-r 1939 . . . . - .. .. . wafi‘vv a»... L. L efifli .L THE STRENGTH AND HARDNESS RELATIONSHIPS, AND CHARACTERiSTIC PROPERTIES OF SINGLE HEAT-TREATED PLAIN-CARBON BOLTS. Thesis for degree of Net. E. Michigan State College Andrew Nelson Hoover ’5‘ -w. t.‘ II. Mechanical Engineering 1939 "rt-a 5:513 INTRODUCTION While working in the Heat Treat Department of the Olds Hotor Works Division of General Motors at Lansing, Kichigan, during the years 1954-1935, I first became interested in the subject of bolts. This interest grew in intensity-later when I transferred to the Metallurgical Laboratory in October of 1955. The country at that time was emerging from a bad depression, which had necessitated many improvements in the manufacture of steel as well as in the processes of forming products from the steel. The develonment of the bolt manu— facturing processes enabled the companies to furnish bolts which were superior to any heretofore made, without the use of the expensive alloys. In 1958 this enabled my company alone to use fifty different sizes and shapes of plain car- bon bolts as they were furnished by the bolt manufacturers. As the bolts, of the latest method of single heat treatment, have been on the market for only a short time, little or no data is available on their strength and hardness characteristics. So we in the laboratory are metallurgically interested in the bolts as they are used, and run routine checks on all bolts used, in the vital parts of the automobile. There seems to be a very wide disagreement between the strength of the bolt actually pull- ed in a tensile test and the strength as it could be aoproximated from a Brinell hardness test on the head. This apparent dis- 12.14198 crepancy challenged attention and a serious attempt has been made for the past fifteen months to analyze this, so as to reconcile the two sets of results, and to determine the best and most reliable routine test for plain carbon bolts. This thesis is the summation of the work done, the results observ- ed, and the conclusions reached. HISTORY The ordinary bolts, as one casually buys them in the nearest "dime store", have a very interesting historical record, as have many other articles we use today. There is no definite record of the first use of a bolt as this piece of machinery is used today, and it is generally con- ceded that bolts as such have been used for untold thousands of years. Prior to 1500 B. C., only six iron articles are definitely proven to have existed. Two of these were of meteoric iron. By 1000 B. C., iron was being made regularly anC used for various instruments of war and for or de_tools. There are various records of the advancement of the iron re- fining processes through the ages, among which are a cast chain used in a bridge in Japan, built 70 A. D. Casting processes continued to develOp slowly throughout the EurOpean countries, mainly through the pressure for the production of war materials, and iron utensils became common. In 1645 A. D., the first iron works, in what is now the United States, were established in Lynn, Hassachusetts. Less than one hundred years ago, the first machine-made bolt was turned out in this country. Previous to this time, nothing but strictly Land— forged bolts had been used anywhere. history shows that about the year 1550, the first screw threads were cut with an implement somewhat resembling our present day file. This method was greatly improved by having the shank of the bolt revolve and holding a thin, notched blade against it, thereby cutting the threads. About 1850 Thomas Oliver, of Staffordshire, England, developed a crude bolt- forging machine which has always been known to the industry as the "English Oliver", and occupies a conspicuous place in the history of bolt and nut making. His was strictly a hot forging process, the bellows being pumped by a boy hired for that purpose. The boy used up his spare time on the bel- lows by helping to Operate the forging machine. The American pioneer was Kicah Rugg, a country blacksmith. Hr. Rugg lived in the small village of Marion, Southington Township, Connecticut. His contribution consisted of a head- ing machine coupled with a machine for trimming the forged head. The patents on these machines were received from the United States Patent office by Mr. Rugg in 1842. Lical Rufig took into partnership one Kartin Barnes, to form the firm of Rugg & Barnes. In the year 1845 the first bolts and nuts manu- factured for trade in America, were turned out by this firm. As an improvement over the system as used by the "English Oliver", this firm used a Treadmill propelled by a strong bull to furnish its power for the bellows blowing to maintain the heat necessary for the forging Operation. With this power, six men were employed to produce on the average of five hundred bolts per day. (As time went on, other firms were formed, and many years later a considerable percentage of the bolt manufacturers could trace their lineage directly to the Southington Valley in Connecticut). The most common bolt of the period r as the 5/16 x 5 carria ge bolt which sold for S5 pe 1000 bolts.(l) Directly following this period, there came a deluge of inventions. Improved quality and workmanship were coupled with the new and ingenuous continuous headers, roll threaders, automatic screw machines, automatic tappers and threaders, and other improvements over a long period of years -— until in 1921 many plants in the United Stat es were pron Wucin over 1,000,000 bolts with nuts in one day's production. The same size bolts which formerly sold for S55 per 1000 now sold for S7.50 per 1000 (based on S12 steel).(2) Previous to the time of the Civil War, practically all of the bolts made were from square stock. The neck of the bolt was left intact, the head was forged, and the shank was rounded and threaded to the required leng h. Willia.m J. Cla ark, about 1860, brought to the public use a method of forging bolts from round stock. Up to this time apparently no effort had been made to standardize anv heat treating practises. Very few bolts were ieat trea ated and the local blacksmith did the work if heat treating was used. The use of alloys came in very slightly about this time, especially in the tool steels. In 1862 Siemens invented the Open hearth furnace; and with the start of the manufacturing of the soft Open hearth (1) As to the wages paid, about this time it was recorded that the average workman received One Dollar for twelve hours work. (2) At this time the av erag workman got for his days labor, from S6 to S8 for ten hours work. steel, came the deveIOpment of the process for cold heading of the smaller sizes of bolts. 1857 saw the firm of Russell, Burdsall & Ward begin the manufacturing of carriage bolts entirely by the cold forging process. They also introduced at this time the common stove bolts with shaved and slotted heads. Development of inventions was rapid after the Civil War. In the following years the manufacturer was taxed to the limit to supply for the designing engineer the intricate shapes and sizes which he desired. And the World War did much to complicate the problem of the manufacturer. In 1921 the Upson Works of the Bourne Fuller Co. had 50,000 different dies for forging, trimming, and threading, none of which were duplicates or were considered entirely obsolete. Until the year 1900 practically all of the larger sizes of bolts were made from wrought iron bars. During the period 1900 - 1922, there was a gradual change from wrought iron stock to the newer Open hearth steel. By 1922 practically all bolts, regardless of size, were made from steel rather than iron. The automobile industry greatly accelerated the purchases of bolts for widespread manufacturing use and let to a much greater demand upon the firms producing them. Thread—rolling machines came more and more into use to replace the much slower and more costly turning lathes. Previous to 1915 there were 240 thread rolling machines in use in tk United States plants. In 1925 there were in use 880 machines, or an increase of 5653. During this same period the thread cutting machines increase ‘0 ed from 2085 in 1915 to 2452 in 1925, or an increase of only 16.65. This shows the great trend to the more speedy and cheap— er processes. The deveIOpment of alloy steel for general use had much to do with the heat treated, high-strength, bolts we see in ‘ use today. These bolts were generally adOpted by the auto- mobile manufacturers because of their lightness of weight, for the strength produced, resistance to severe shock, their resistance to corrosion, their resistance to fatigue, and their susceptibility to heat treatment. At the present time practically all alloy bolts are heat treated. There are in the neighborhood of 550 bolts in every auto- mobile. Oldsmobile sent 185,000 cars or more off the end of the assembly line in one season. It will readily be seen that ample material has been available for this study and that such conclusions as have been reached are founded on many tests. Present Methods of hanufacture The modern method of cold heading practise was accelerated by the demand for smoother shanks, more accurately maintained, and free from scale, all secured by the methods to be described in the following pages. This fact seems to be rather well known; The greater the fineness of grain a structure possesses, the greater is the capacity for deformation of the metal. With the recent practise of controlling the grain size of steel sold, no risk is being taken by the bolt manufacturer as to whether the metal will cold work or not. The stock used by the bolt maker is standard hot-rolled bar, easily obtained to close spec- ifications: Chemical analysis, size, grain size, and freedom from surface defects. The wire as it is received passes through three distinct stages before it is formed into bolts. First, the wire is pickled in a solution of sulphuric acid to remove the hot-rolling scale. Secondly, it is washed in water, then dipped in a hot solution of slaked lime. Thirdly, the wire is drawn through cold-draw- ing dies to the desired size for further forming into bolts. These drawing dies are greased with various substances; notably, aluminum stearate, soluble oil, and grease. These dies reduce the diameter of the wire from 153 to 50%, depending on the size of bolt to be made. There are two main methods of manufacture in use at the present time, namely: Single extrusion double blow headed, and double extrusion, single blow headed. In the Kaufman Single Extrusion process, illustrated by the attached print, wire of the nominal diameter (instead of the pitch diameter) is pushed into the solid heading die and t "tulip" is formed, or coning as it is sometimes called. The head is upset in the usual manner and at the same time the shank is reduced to the pitch diameter for the thread section. By using wire of the nominal size instead of the pitch size, a considerably larger volume of stock may be upset; or for a given head size, less plastic flow of the metal is produced. Ex- perience has shown that the unsupported end, to be upset in double blow heading, should not exceed in length three and one half wire diameters. The double blow header is built so that the two dies which form the head are set in the same block and the block auto- matically shifts from one die to the other to make the forming a continuous process. With the later improvements and further developments of the single extrusion process, the double stroke header seems to have reached its limit as r gards the amount of stock upset. This, however, may be changed with the possibility of a more plastic stock. This method f bolt making was a great improvement over the hot forging and thread turning methods of the past. From plain carbon stock, with a single heat treatment, bolts could be made much cleaner, more free from die marks, and visibly stronger. §l§§£§.§i§5§PEQ_PCQELE 829w HEADED BOLT Steps in the Manufacture WIRE FIRET HEAD BLOW (Tuliping) \._)’ SECOND HEAD BLOW ' TRIMMING THE HEAD AND SHANK EXTRUSICN FINISHED BOLT COARSE ETCH ON D E D A E H 7W O L B E L B U 0 D SINGLE EXTRUDED, BOLT. Showing Work Lines. .86 X3 In the Double Extrusion Single Blow Headed process (DEX bolts) more recent deveIOpments have brought out the type of a machine known commercially as the Boltmaker. This is a multi-die, single stroke type of machine. It has a wider die space than the ordinary header and a series of dies ar— ranged in a horizontal plane in the bed of the machine, each die being Opposed by a heading tool in the slide. Each die is provided with a suitable kick-out pin. The machine is equipped with a transfer mechanism which grips each blank as it is eject- ed from the die and shifts it to the next die. In this manner a blaii is started, a blank is finished, and intermediate blanks are formed in a new die-hammer combination at each stroke. As a result of the deveIOpment of this machine we had the patent- ing, by Kaufman and others, of a process known as the "Double Extrusion” method of bolt making. In the double extrusion process the wire used for the manu— facturing is processed the same as that for the single extrusion method inasmuch as it is pickled, washed, and drawn. The wire used for the making of a given size of bolt is usually about one sixteenth of an inch larger in diameter tha the shank of the finished bolt. The shank portion is first pushed into an extrusion die and reduced to the nominal diameter. The portion remaining not extruded usually is not longer than two and one half wire diameters. In the next heading station this shank part is again extruded in part or to the length required to be . ___4 I Féva;q 0/4, .31 Féowfi Station I: The Wire Blank, from which the bolt is made, is larger in diameter than the Bolt Shank. Station II: The first Extrusion operation extrudes the Shank portion leaving only a short partof the larger diameter, which becomes slightly swelled during the operationo A J : h f 5% B Ola ml. g c ‘ ¥ + t ° . ‘4w ”5 ° ‘ \H “dd d % \lq> \ “fit \7 x w a D \ i Z I / [/7 “(lg ! Rock'B' 88 [ 364 o/A. I II Station Q55 43%] 6‘7'EPJ‘ //V 77/5 NANUFZCTUA’I L )3! E J” W 3o i r m'V- \22 Ram?” # ”6 . .329 HEAD/N6 '33 L/H/T' III Station III: ‘Uhile this Unextruded portion is hasoiDIA. ‘13 IV V Station V: The Bolt Blank is Pointed to Facilitate assembly. Headed in one blow without detri- mental Fracture of the Grain Structure, a part of the shank is Re-Extruded for the thread portion. Stati on IV: The Head of the Bolt Blank is Trimmed to desired size and shapeo The head cannot be knocked off the finished bolt Station VI: The Product will be finished after the thread is Rolled, holding the closest toleran- oee and having a perfect Iona. even thougm.Unannealed. Volumetric Analysis of the Operatiggg volume of A. .2h96 On. In. Volume of B . OQO ” " C .0116 " " D . 1&6: Total .2u99 On. In. volume of E .1036 Cu. In. ” " F .0807 ' ' 0 .0072 ' ” a .0578 Total .2h93 on. In. ll 1 04v threaded. The diameter is that pitch diameter of the desired 'thread. The head is upset from the larger end in a single blow and consequently experiences a minimum of cold-working. These steps, together with the dimensional analysis are found on the attached page. One print shows the process for a square headed bolt, the other for a common hex head bolt. I-'..va.H I1. .» . ..3J.V 3.... ..u ..4 Haywsuhrv .. I . .. .11“- . .\.I, It: \I 8. HQ N E o O L T s B L S S H W U 0 n e C O O B .l n T L D. W .1 E B B O L . .. E h 6 E E D D S k 8 S L E U r o R G D R O .3 A N A T W 6 I mm X x C S H E TESTS Bolt size-—— 3/8-24 x 1 3/8” Manufactured by Shngle Extrusion, Double Blow Heading process, all bolts had rolled threads. Chemical Analysis-— Carbon--- .20% Manganese-- .53% Grain Size (McQuaid-Ehn)-- 4-5 Tensile Test-- Pulled at the rate of .12 in. per Min. Pulled on a 30,000 lb. Machine. Heat treated-- A resistance type of electric furnace was used. Heat treated at the indicated temperatures, for 45 Min. (total time in the furnace). Hardness-- This was taken on all transverse sections as specified,. “it: 2.3....::t3:;-L;3:éa.3ié3?i:;:;::-“*%a:€?%.:::;?;i-:;;;;*=:;3:§;;: a .......... 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A . 11.,1 A.‘ , i , , _ . ,AA . .AAA . ..A A A. A ‘ A A AA A ‘ A A ‘A A vA AA A$AA . | _ A A A ..A.. .A .. ._‘,..A A: A AAA. ,‘. A ‘ ..A+. A. . J A; T, ill ,LJ‘ . . JA. . lA A I lAJ ., . .AAAAA A. . . A A. .. A A I ~LA~~~r;x.. a --" ”gleLin_thousa -hsiofwan-inch)livili;W;Hiilwlgi- i A r . , . ""‘l:i:':.:fi:_.“.. ' .. i . .'-‘;i - - 3 ' “ LT'TI" :‘ ;" ‘ A ' ' 21m 4' '. An l“ 1 A JV~ .. .... ....... ........ ...... .t.. ..... . ..... .. . ..E .....aE‘- .9...... . .. oa. . ... . ... . . . . ....q.. .. . .. ... . . . . ... ... . E . .. .. v .«4.1...« .2 PE ...E E_ . . er»r rEE » . .. L». y» . . » ., E» ..rE. »L y i. p E _ Cross Sectional Grainr X 750 Longitudinal Grain”~ X 750 gozo BOLT:_ HEADASECEION; Drawn ai~l§50U F: 19§9_§9923-§§§K§_3§§IIQE Drawn at 12503 F. Cross Sectional Grain X 750 Longitudinal Grain X 750 1020 BOLT: THREAD SEcTION Drawn at IEEEO-FT‘--_ Cross Sectional Grain X 750 Longitudinal Grain X 750 SUMMATICN CHART -“—-_“---_-_“ 5/8 -24 x 1 5/8” SINGLE EXTRUDED, DOUBLE BLOW HZADED IEEE- __ HA32§§§§__ _ _ IEEélL§-§I§E§§EE Dggw Brin- Rockwell "B" Yield Ultimate EE;___f§;;___2139;___§Dssk____lbzsss___----12§1____12§1_ None 216 105** 89 9k.5-193* 7000 8090 700 205 105.5 90.5 94 ~205 7100 8255 750 228 105.5 90.5 94 -205 7145 8240 800 225 105 91.5 94 -205 6950 8190 850 219 105 90.5 93 -200 6900 8085 900 216 105.5 90.5 95 -200 6700 7845 950 216 104 90 95.5-205 6500 7755 1000 205 101.5 88 90 -185 6275 7440 1050 195 80.5 86.5 87.5-174 6025 7255 1100 190 85.5 89 88.5-178 5900 7295 1150 144 80 85.5 87 -172 5250 6680 1200 157 80 84 87 -172 4800 6550 _1_2.5_0____1.I5_5_____Y 9 __ 82 £3 §}___15_9____ “3.299.---5225 * This is the Brinell equivalent of the Rockwell "3" hardness. ** This hardness is taken in the severely cold worked part of the bolt head by splitting the head in cross section. OTHER 1020 BOLTS TESTED 1020 Bolts 7/16- 20 x 1 3/8 SINGLE EXTRUDED, BCUBLE BLOW HEADED 2212- __§4321§§§_________-______ I§1§11§_§1351925 of Draw Brin- Rockwell "B" Yield Ultimate ell 32; HQ- 2152;___§§293___ID:222§___-__12§:_____lp§;-_ None 240 105.7** 100.5 101 -248* 10,642 13,367 500 255 - 101 102 -255 11,440 15,567 400, 255 - 101 101 -248 11,225 15,505 500 245 - 101.5 102 -255 12,045 15,890 600 260 109.5 103 105.5-266 12,047 14,257 650 255 109.5 102.8 102.7-260‘ 11,842 14,150 700 255 109.5 102.5 102.8-260 11,658 14,018 750 255 109 102.5 102.7-260 11,595 14,045 800 255 108.7 101.8 102.4-258 11,795 15,875 850 249 106.5 101.7 102.5-257 11,717 15,785 900 252 107 101.5 101.7-255 11,492 15,888 950 241 106.5 100.2 100 -240 11,055 15,202 1000 229 1C3.3 99.2 99.2-235 10,480 12,842 i105o 207 95.5 98 97.6-226 10,052 12,465 1100 174 90.7' 94.5 92.5-197 8,450 11,150 1150 174 91 94.7 88.7-179 7.633 10.553 1200 170 88-5 93.5 87 -172 7,455 10,545 * This is the Brinell equivalent of the Rockwell "B" hardness. ** This hardness is taken in the severely cold worked part of the bolt head by splitting the head in cross section. 19§9_§QLE§ 7/16-20 x 1 5/8" DOUBLE EXTRUDED, SINGLE BLOW BEADED TEES; ----------Eé§9fl§§ ___________ __ -T§E§lL§_§IBEEQTE- §§§Di of Brin- Rockwell "a" TES Draw ell Yield Ultimate EE;___§§:____%_§§:-__§§§EK_-_$§E§§§§______E§E _______ £22; _______ None 225 106*“ 102.5 102 -255* 15,550 15,290 20) 500 226 106 102.5 102 -255 15,500 15,168 400 251 106. 102.7 105.5-265 15,550 15,550 150 500 255 107.5 104 105-8-268 14,288 15,718 600 257 107 105.5 105 ~262 14,067 15,555 10° 650 241 107. 105.5 105.5-266 15,950 15,558 700 241 107.5 105.5 105.5-266 15,960 15,450 120 750 241 108 105.5 105.5-266 15,545 15,258 800 245 108 105.5 105.8-268 15,015 15,050 12° 850 252 107.5 102.8 105.5-265 12,670 14,970 900 251 106.5 102 102.8-261 12,410 14,760 17 0 950 225 105.5 101-5 102 -255 12,195 14,177 1000 220 104.5 100.5 101 -248 11,725 15,745 55° 1050 215 99.5 100 1;; -240 11,298 13,743 1100 192 92 97.5 95.5-212 9,598 11,958 1150 178 90 94 90 -185 8,045 11,115 1200 170 88.5 95 88.8-179 8,155 10,645 1250 157 87.5 92.8 87.8-175 7,553 10,298 -_a-. —--‘-‘-~‘---‘—_~ -—-—----.—--— ------—— ..- ‘-—___--. * This is the Brinell equivalent of the Rockwell "B" hardness. ** This hardness is taken in the severely cold worked part of the bolt head by splitting the head in cross section. IMO-0 arm—NI'II‘ $11 A Bolt Size 5/16-24 5/8 -24 1/2 -20 9/16-18 Note-~- AVERAGE 0F PRODUCTION 1020 BOLTS Ave. Ave Yield Ultimate 5,168 5,660 7.966 8.925 12,606 14,770 15,410 16,74l Averages were taken on 100 or over bolts. STRENGTHS 0F Minimum Ultimate 5,120 7.050 12,025 15,250 Maximum Ultimate 6.590 11.350 16,940 17.980 -. T .....‘.T. ...... I ..... I . L: I. 3:: ----- 1 ‘1". ‘ ; - r — 17 _---.11--_-.1_1 ‘1 1d ....... .L' __ A: iiII'IQLi ““““““ 1_.____- _____ , 1 a , _.__;-'_;1_, .__.__.-___._-_ a“. ‘1“; ___ . A“; . '6 ‘ 1‘ ..... -..-.O»:.-..l .. 7.11;. .1 ..... 1: 2:11.11 '1 :;' «“3 11‘11 12; ~ 11 - , .LJ. ‘1: 1LL11 11, ...... "‘1‘_ 1.1;: 1 7;: ........ 5 BE;; ;f - \I 1. 11 . ' -——«-. 1 1131.3? . 1134* 918%? - """"""""""""" r1 2H1? v t I ““‘”*““ --ilm ;. --——~-4 . 1 , _ f ‘12 i 1 i 1 i 1 1 I L ...... 1| -..—4 .05 .10 .L5 .20, 1‘ .25 “ELAN ARA (SC). in.) 1 ' ' i ': l ‘u 1 | ,._.._._.__1_. ___-_.___._ >—:-——-—--—---—- -—-——-————-———r- "—‘-°“"'H‘-f — »- __.___.__..___. —-——-~—~——~< The Mean Area is figrued rom the ave rage of the pitch and minor diameee PFATL 7?. """ ‘13.7 ..1. 1 1. .a “191'” 1 . 1 l 1 713- ‘ I i 4. SUMMATION —_‘--_‘-~~ In figuring the Tensile Strength of a bolt from the hardness, the Rockwell "B" is more accurate than the Brinell, especially in the smaller sizes of bolts, and if the Rockwell test is made on a“ transverse section of the threads. A Rockwell "B" hardness in the threads of from 85 to 100 is practicable. Recrystallization of the ferrite in the head is not necessary to insure good ductility, but a» draw treatment of from 950 to 1000 degrees F. should be used. This will guard against any brittleness if mixed stock is used or segregation is encountered. For strengths see Summation Charts and Curves. 1m -._ ..v—Q-n. ... - \ Ba . .. fit. 921‘“ n Y '7: . I 1 1', - 431 RUOM US ‘ . '? ILIIIIV ‘Il .4' 3'. 20‘- IIIIIII GNA NSTATE UNI IVERSI ITY Ll BR III IIIIW‘IIII .