Mar., 1916
T H E JOURiVAL O F I N D U S T R I A L AhTD E N G I N E E R I N G C H E M I S T R Y
209
ORIGINAL PAPERS RESEARCH ON THE CORROSION RESISTANCE OF COPPER STEEL By D. M. BUCK^
AND
J. 0. H A N D Y %
Received January 22, 1916
I n order t o obtain further definite information relative t o t h e influence of varying amounts of copper and other elements when alloyed with steel, an extended series of service tests was undertaken b y t h e authors in t h e spring of 1914. Following work which had been done b y one of US,^ we continued t h e practice of conducting the tests on full size, uncoated sheets, under exact service conditions, extreme care being taken so t o plan t h e work t h a t those differences found in the various grades of steel used could be safely ascribed t o the influence of t h e particular element which had been added. I n addition t o repeating work which had already been done on t h e effect of t h e addition of approximately 0 . 2 5 per cent copper, we have included in this test steels with a copper content as low as 0.04 per cent, as well as steels with higher amounts up to and including z per cent copper. -4s will be seen from Tables I t o 111, we also made additions of phosphorus, silicon, aluminum, sulfur, roll scale, and, following a suggestion b y a colleague* t h a t t h e addition of cold steel t o t h e middle ingots of t h e heat would cause t h e m t o outlast t h e first poured ingots, a similar amount of cold steel turnings was added t o one of t h e ingots in exactly the same manner in which t h e copper had been added t o t h e others. Some work has also been done on the influence of annealing temperatures higher t h a n t h e average practice, and we have kept careful records of inside and outside sheets of t h e pack,S and of t h e presence or absence of mill scale on t h e surface of t h e sheets at t h e time of exposure, t o determine whether or not these differences in initial protection affected t h e ultimate time of failure of t h e sheets. S T E E L S USED
Ik T E S T S
Several heats of open-hearth a n d Bessemer steel were used in t h e tests. Table I gives the additions as they were made: t h e grade numbers given here are those used throughout this paper. .It will be noted t h a t in one instance ten ingots were used from a single heat, and t h a t they differed one from the other only in t h e amount and kind of element which was added. I n Tables I1 and I11 appear the final analyses of t h e sheets rolled from these ingots. I n t h e manufacture of basic open-hearth heat No. 1 Metallurgical Engineer, American Sheet and Tin Plate Company, Pittsburgh, Pa. Director of Laboratories of the Pittsburgh Testing Laboratory, Pittsburgh, Pa. THIS JOURNAL,6 (19131, 447; Iron Age, June 3, 1915; I r o n Trade Reniew, June IO, 1915. Institute of Industrial Research, Bull. 6. 3 Sheets are rolled in packs and the two outside sheets of the pack always carry on their surfaces much more mill scale (magnetic oxide of iron) than do the inside sheets.
7 7 j 0 , a n effort was made t o produce a wild, oxidized heat. The steel was melted “hot;” ore was fe.d faster t h a n usual and continued even after carbon had been reduced t o 0 . 1 2 per cent. Silica sand was added instead of dolomite. The heat had a very wild appearance, rose strongly in the moulds, and in addition, we had a running stopper in t h e ladle giving a divided stream, which of course favored oxidation. Analyses of t h e sheets from this heat b y the Ledebuhr method showed a n oxygen content averaging only 0.03 per cent, which is no higher t h a n t h a t in normal open-hearth steel Basic open-hearth heat S o . 88j7 was made without TABLE I-STEELS USEDIS TESTS A N D ADDITIONS MADE TO MODIFYTHEM BASIC OPEX-HEARTH HEAT HEAT No. HEAT No. 6807 8805(a) Ingot ADDITIONS KO. MATERIAL AMOUNT Grade Grade 1 . . Xone .. 2 2 2 Copper 3 3 3 Copper 4 4 4 Copper 5 5 5 Copper 6 None 6 7 Phosphorus 8 Si1icon 9 9 Aluminum 9 10 10 Sulfur 10 11 11 11 Cold steel HEAT KO. HEAT No. Ingot 8815 /699(b) Xo. Grade Grade 12 12x 2 Copper t o ladle 0 , 2 5% ( d ) 13 13x 2 Copper t o mould 0 , 2 5 yG( d ) 14 14X 3 None .... HEAT KO. 7750 Ingot h70. Grade 19 4 Copper 20 6 20,&pS”1e 21 7 Roll scale 22 8 Silicon 23 9 Phosphorus 24 3 None HEAT No. 8857 Ingot Grade KO. 25 2 None .... 26 3 Copper 0.35%(d) HIGH SULFURBESSEMERHEAT /RESIDUAL(A‘oT ADDED)SULFUR] Ingot Grade h70. 15 (C) Copper 0,25%(d) 16 (6) None .... X O R Y A LBESSEYSR HSAT Ingot Grade iio. 17 (L) Copper 0,25%(d) 18 (6) None .... ( a ) About 0.04 per cent residual copper. (c) See test. ( b ) About 0.05 per cent residual copper. ( d ) Aimed a t .
6
A
A
{
t h e addition of manganese or other deoxidizer a t a n y stage. Basic open-hearth heat KO. 8 8 0 j corresponds t o heat No. 6807 (grades 2 t o 11 inclusive) and t h e same additions were made in exactly t h e same way and in t h e same order. The composition is quite similar t o X o . 6807 except t h a t the c o p p e r ( r e s i d u a l ) is about 0.04 per cent in all grades except those t o which copper was added. Comparison of t h e results on sheets from these two heats affords information relative t o the influence of comparatively small copper contents. The grade numbers for heat No. 8 8 0 5 are the same as for S o . 6807 except t h a t a n “ X ” has been added t o each. Basic open-hearth heat No. 7699 corresponds t o
THE J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
2 IO
heat S o . 8 8 1 j and t h e additions were t h e same. T h i s heat, howeoev, contained 0.05 pev cent residual copper. S H E E T M A N U F A C T U R E AKD E X P O S U R E O F TEST P I E C E S
All of the operations of blooming, rolling, sheet rolling, etc., were conducted according t o regular mill practice and were under the personal supervision of the authors. Enough sheet bars were taken from t h e
1701. 8,
No. 3
required for our tests were taken a t regular intervals from the piles, a n average product being thus obtained. Each sheet was stamped with a distinguishing mark, and they were numbered consecutively from I t o 2 4 . In the case of the grades 2 X to 1 4 X inclusive, and also grades 2 5 and 2 6 , six sheets of each were selected
OUNCESPER SQUARE FOOTPER MONTH FOR EACH PERIOO OF EXFOSCRE I N TESTSAT SCOTTOALE A N D MCKEESPORT, PENNSYLVANIA PERCEXTAGES PRESENT Annealing SCOTTDALE TESTS MCKEESPORT TESTS RANK _.___temp. 6.5 9.53 8.2 10 9 GRAND See ELEMENT Mn S P Si Cu OF. mo. mo. Av. mo. mo. Av. Av. Text ADDED GRADEC
TABLE 11-Loss
IX
_-
___-
2
0.06
0.41
0.039
0,032
3
0.06
0.43
0.045 0.041
0 , 0 0 4 0,272 0.004
0.549
4
0.07
0.43
0.039
0.036
0.004
1.085
5
0.06
0.42
0.042
0.040
0.004
2.180
6
0.06
0.45
0,047
0.035
0.004
0.018
7
0.06
0.44
0,047
0.089
0.009
0,016
8
0.06
0.41
0.045
0.034
0,319
0.016
9
0.06
0.43
0.047
0.036
0.007
0.017
10
0.06
0.43
0.075
0.028
0.008
0.019
11
0.05
0.44
0.037
0.030
0.003
0.014
12
0.06
0.46
0.028
0.035
0.003
0.242
13
0.06
0.56
0.034
0.033
0.010
0.266
14
0.08
0.60 0.035 0.032
0.006
0.014
15 16 17 18 19 20 21 22 23 24 50
0.06 0.06 0.07 0.07 0.07 0.06 0.06 0.06 0.06 0.06 0.02
0.50 0.47 0.48 0.49 0.29 0.31 0.26 0.29 0.29 0.30 0.03
0.140 0. I42 0.048 0.052 0.029 0.039 0.030 0.033 0.035 0.027 0.031
0.006
0.093 0.096 0.112 0.llL 0.010 0.018 0.017 0,018 0.068 0.016 0.005
0.256 0.004 0.008 0.012 0.260 5.010 0.004 0.009 0.265 0.005 0.102 0.005 0.014 0.123 0.016 0 , 0 0 6 0.015 0.004 0.014 0 , 0 0 2 0.041
1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1600 1400 1400 1400 1400 1400 1400 1400 1400 1400 1400 1400
0,1411 0.1405 0.1423 0.1374 0.1389 0.1375 0.1314 0.1332 0,3723 0.2632 0,3040 0.2692 0.3521 0.3186 0,3764 0.3591 0,4327 0.4211 0,3746 0.3023 0.1386 0.1406 0,1388 0.1431 0.3344 0.2729 0.1332 0.4221 0.1280 0.3301 0.1403 0.1469 0.2849 0.3026 0.2366 0.2752 0.1588
0,1361 0.1382 0.1345 0.1338 0,1319 0.1353 0.1294 0.1303 0,4202 0.3831 0,3564 0.3258 0.4747 0.3909 0,4732 0,4758 0,5144 0,5206 0,4538 0.3693 0.1381 0.1394 0,1401 0.1377 0.3477 0.3104 0.1458 0.5018 0.1358 0.3911 0.1366 0.1478 0.2984 0.3342 0.2571 0.2939 0.1577
product of each ingot t o give us a large excess of sheets for our tests. T h e bars were taken from the piles at such points as t o represent the whole ingot from t o p t o bottom, thus securing t h e average product of t h e ingot. All grades were given exactly t h e same treatment in all of t h e manufacturing operations, a n d each sheet received the customary one (straightening) pass through t h e cold rolls. All sheets (except those annealed a t higher temperature) were annealed a t one time in the same furnace, thus securing uniform heat treatment. To determine t h e possible influence of higher annealing temperature, one-half of t h e sheets of grades 2 t o 14, inclusive, were annealed a t a temperature about TABLE111-Loss
OULCESPER SQUARE FOOTPER MONTHFOR EACH PERIOD O F EXPOSCRE PERCENTAGES PRESENT MCKEESPORT TESTS
GRADEC Mn
IN
S
P
Si
Cu
8.2 mo
10.9 mo.
ELEMENT
Av.
ADDED Copper Copper Copper Copper None Phosphorus Silicon Aluminum Sulfur Steel Copper Copper Xone hTone Copper
zoo’ F. higher t h a n t h e normal temperature for sheets. The remainder of t h e sheets of these grades and all other grades were annealed a t t h e usual temperature (1400’F.). After t h e annealing process t h e sheets were laid out in piles and t h e twenty-four ( 2 4 ) sheets
0.1386 0.1134 0.1393 0.1041 0.1384 0,1089 0.1356 0.1043 o 11.54 n 1039 ~~~. 0.1364 0.099i 0,1005 0.1304 0.0966 0.1317 0,3962 0.1843 0.3231 0.1634 0.1589 0.3302 0.1460 0.2975 0.2016 0.4134 0.1527 0.3547 0,4248 0.2103 0.4174 0.1932 0.2341 0.4735 0.1960 0.4708 0.4142 0.1923 0.1383 0.1400 0.1394 0.1404 0.3410 0.2916
o.im
0.4619 0.1319 0.3606 0.1384 0.1473 0.2916
n
RIM
0.2468 0.2845 0,1582
0.1095 0.1043 0,1068 0.1002 n 1007 o 102.3 0.0962 0.0976 0.0941 0.0973 0.0905 0.0935 0,.2215 0.2029 0.2007 0.1820 0.1682 0.1635 0.1620 0.1540 0.2027 0.2021 0.1656 0.1593 0.2335 0.2219 0.1890 0.1911 0.2926 0.2633 0.2464 0.2212 0.2204 0.2063 0.1057 0.1045 0,1047 0.0961
0.1241 0.1218 0.1226 0.1179 o 1188 0.1170 0.1138 0.1126 0.2996 0.2526 0.2469 0.2257 0.3078 0.2569 0.3233 0.3043 0.3684 0.3460 0.3103 ~~~~
0:ioii 0:iOio 0.iosi 0iizi7
0,1107 0,1043 0.1079 0.1785 0.1788 0.1022 0.2547 0.1028 0.1895 0.1074 0.1155 0.1649 n...... 1604 0.1406 0.1677 0,1156
0.1056 0.1064 0.1073 0.1745 0.1914 0.1020 0.2353 0.0963 0.1922 0.1037 0.1125 0.1711 n. .1606 . ~ 0.1476 0.1684 0,1178
0.1081 0.1053 0.1076 0.1765 0.1851 0.1021 0.2450 0.0995 0.1908 0.1055 0.1140 0.1680
0.1241 0.1224 0.1240 0.2588 0.2384 0.1208 0.3535 0.1157 0.2757 0.1220 0.1307 0.2298 0.2394 .0.1605 ~.~~~~ ~ 0.1955 0.1441 0.2263 0,1680 0.1167 0,1375
9
8 R
1 19 16 20 22 24 21
5 7 17 4 23 2 18 6 10 14 15 12 13 11
Copper Copper Copper Comer CoDDer Copper Copper Copper None Xone Phosphorus Phosphorus Silicon Aluminum Silicon Aluminum Sulfur Sulfur Steel Copper Copper Copper Copper None None Copper None Copper None Copper Copper a n d scale Scale Si1icon Phosphorus .None
--
in the same manner as above, and were numbered from I t o 6. All sheets were 26 gauge, 2 6 in. X 96 in. A strip 2 in. wide was cut lengthwise from each sheet, and these strips were given t h e same distinguishing numbers as the sheets from which they were cut, and were sent t o t h e laboratories, where each one was carefully analyzed. As soon as this work had been completed, a n d we were thus assured t h a t no mistakes had been made in marking t h e sheets, they were corrugated and forwarded t o Scottdale and McKeesport, Pennsylvania. Twelve ( I 2 ) sheets of each grade, 2 t o 24 inclusive, were exposed a t each station, while t h e other grades 2X t o 14X, 2 5 and 26 were exposed at McKeesport only. Meanwhile, there had been obtained in the open market, from three different sources, three lots of one of the so-called “pure irons,’’ which on analysis proved t o have a copper content of 0.041 per cent. Several sheets of each lot were exposed exactly as received, without pickling or cleaning of a n y kind (this has been t h e invariable practice on all corrugated sheets of all grades in this test a n d in all previous tests made by one of us). All of the grades above mentioned, including t h e so-called “pure iron” (grade s o ) , were exposed as roof panels a t McKeesport on July 7, 1914,and a t Scottdale on July 9, 1914. At approximately t h e same time t h a t the full size sheets were exposed, a series of 2 in. x 4 in. test pieces cut from t h e 2 in. strips before mentioned, and consisting of one piece from each sheet (636 in all), was exposed. These
Mar., 1916
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
test pieces were cleaned by a very light wash of sulfuric acid, dipped in ammonia water t o neutralize all acid, then thoroughly washed, dried, weighed and arranged in wooden racks in such a manner as t o afford all free a n d equal exposure t o t h e weather. The method of removing, cleaning a n d weighing these test pieces will be discussed later. The results obtained are given in Tables I1 and 111. INSPECTION O F EXPOSED SHEETS
At t h e time of exposure of the full size corrugated sheets careful notes were taken concerning t h e physical appearance of t h e sheets as affected by t h e amount of mill scale which was present, and as t o whether they were outside or inside sheets of t h e packs. During t h e progress of t h e test, this feature was carefully watched, a n d t h e time of ultimate.failure of sheets whose surfaces were comparatively free from mill scale was compared with others of t h e same grade, whose surfaces were well covered with mill scale. From these observations, we concluded t h a t t h e influence of this original surface oxide is slight, and is lost in t h e early stages of rusting, for no difference in final failure could be noticed. The photographs shown on pages 2 1 2 and 2 1 3 were taken from time t o time during t h e tests, and show in a graphic manner t h e progress of t h e corrosion a t various stages. Careful inspections of t h e sheets were made approximately once every two months. At t h e first inspection, distinct differences were noticed in t h e physical conditions of t h e various panels: t h e corrosive action of t h e atmosphere had produced a decided difference in color, t h e steels with a copper content of 0.25 per cent or more being distinctly darker t h a n t h e others which contained only a trace of copper; a t t h e same time, these dark brown panels were smoother to t h e touch t h a n t h e others, and t h e rust was denser a n d more adherent. Inasmuch as this same phenomenon had been noticed in former tests, i t was t h u s indicated, even a t this early stage, which steels would be the most resistant. It was also noted t h a t several of t h e panels t o which ingredients other t h a n copper had been added, e. g., sulfur and aluminum, gave indications t h a t t h e rate of corrosion was proceeding even faster t h a n with those steels t o which no additions had been made. The fact t h a t such early inspections are valuable, and t h a t t h e relative merits of t h e various steels a n d irons can be predicted with fair accuracy, is borne out by t h e results of later inspections, and by t h e order of failure of t h e various panels. T h e peculiar piebald appearance of t h e sheets (photographs were taken immediately after exposure of t h e sheets) in Cuts A-I,2, and 3, is caused b y t h e irregular distribution of mill scale. The outside sheets show a uniform dark color while t h e inside sheets are light in t h e areas where mill scale was absent a n d vice versa. It will be noted t h a t t h e twelve ( 1 2 ) sheet panels have been divided into two panels of six (6) sheets each. I n t h e cases of Grades 2 to 14 inclusive t h e left half of these consists of sheets annealed at 1400°,
211
while those in t h e right half were annealed a t 1 6 0 0 ~ . I n all other cases t h e two halves received identical treatment. Referring t o Cuts E-I, 2 a n d 3, a n unusually severe wind storm occurred at Scottdale on Nov. 18, 1915, which blew away all fragments of sheets which were hanging by one end, only those sheets remaining which were in good condition and which still contained a considerable amount of uncorroded metal. The rate of corrosion of t h e various grades may be observed by studying Photographs A, B, C, D and E, of t h e Scottdale test, and F, G, H and I , of t h e McKeesport test. While t h e corrosion a t McKeesport was somewhat slower t h a n at Scottdale, yet b y a study of t h e photographs and tables, i t will be seen t h a t t h e relations between t h e various grades are approximately t h e same. We call particular attention t o t h e photograph of the Scottdale test taken December I, 1915, 1 7 months after t h e test was erected. At this time all of t h e non-copper steels a n d the “pure iron” h a d completely failed, while every panel t o which copper had been added was intact. R E L I A B I L I T Y O F T E S T S OK S X A L L P I E C E S
It has been claimed’ t h a t tests made by determining t h e losses in weight on exposure of comparatively small test pieces are inaccurate and misleading. A study of t h e tables which we present herewith, showing the weight losses due t o corrosion of t h e various grades of steel and iron, in t h e shape of 2 in. X 4 in. test pieces, together with t h e photographs showing the conditions of t h e large size sheets, will prove t h a t t h e results accord remarkably, and t h a t t h e weight losses correspond t o t h e relative endurances of t h e large sheets. I n these experiments, we adopted t h e practice of removing and cleaning one-half of t h e small test pieces after t h e lapse of several months, allowing the others t o remain exposed for some time longer. This was done in an effort t o determine if there was any tendency of t h e rust film t o behave differently on different sheets. It was thought t h a t the sponge-like rust which is normally formed on non-copper steels might accelerate corrosion more t h a n t h e dense adherent film on copper steels. T h a t this idea was correct, is shown by the results (discussed below). C L E A N I N G O F SMALL T E S T P I E C E S
T o clean the rust from t h e test pieces before final weighing, we used a n ammoniacal solution of ammonium citrate. This solution completely removes t h e rust in about I 2 hours, with t h e minimum attack upon t h e underlying metal. Careful experiments show t h a t t h e attack on bare iron and steel by this solution is practically nil. On rusted pieces, due no doubt t o electrolysis, i t is a little greater, b u t still negligible compared with t h e total losses obtained. Furthermore i t is approximately t h e same on all grades used in this test. This is further substantiated by t h e fact t h a t t h e order of final failure of t h e large sheets coincided almost exactly with the. weight losses obtained on t h e small pieces by this method. 1
Cushman. Proc A m I r o n and Steel Instifute, 1916.
II !
I
I
I
/
214
T H E JOliRNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY
This report does not include details of t h e various inspections nor detailed tables showing losses of individual test pieces, b u t presents tables of summaries giving average results. The losses are in each case expressed in ounces per square foot of exposed surface per month, and the results are averages of from six to twelve determinations in each case. Complete detailed notes may be found a t the authors’ offices, and are available t o anyone who wishes t o study them. RESISTANCE T O C O R X O S I O N O F V A R I O U S G R A D E S
Table I1 summarizes t h e results on all grades which were exposed in both locations, and compares losses during each entire period of exposure, and also grand averages. The column headed “ R A N K ” gives the order of resistance t o corrosion of t h e various grades-1 being best, and 24 poorest. I n this ranking we have compared only those grades annealed at 1400’ F. I n this list there are t e n grades t o which copper was added in amounts from 0.25 to 2 . 0 0 per cent.l These have taken t h e ten highest positions, and there is a remarkable uniformity in corrosion rate among them, t h e greatest loss being 0.1307 a n d t h e lowest 0.1138. Higher amounts t h a n 0 . 2 j per cent copper give slightly better results, b u t t h e differences are so small as t o be negligible, especially when considering t h e added cost. The so-called “pure iron” with a copper content of 0.041 per cent takes 11th place, while t h e other
Vol. 8, No. 3
(Table I I ) , we find t h a t as low a copper content as 0.04 seems t o have materially lessened corrosion -compare 6 X with 6, 14X with 14, a n d IOX with I O , etc.: from t h e latter we learn t h a t 0.04 per cent copper partially neutralizes t h e influence of as much as 0.082 per cent sulfur. Panel 2 j , from a heat t o which no deoxidizer was added, and which was comparatively low in manganese, shows a corrosion rate greater t h a n t h a t of normal basic open-hearth steels, indicating no benefit because of lower manganese b u t a possible detriment, from t h e steel not having been deoxidized. Panel 26 from t h e same heat, with copper addition, is quite t h e equal of other steels t o which copper was added. Table IV(A) indicates t h e relative rates of corrosion in t h e two different atmospheres, of all varieties of steel tested. On plain steels we find t h a t t h e corrosion in t h e coke regions, t h a t is, a t Scottdale, is nearly twice as great as t h a t at McKeesport in a normal mill district. The difference is very much less when considering copper-bearing steels, t h e ratio being approximately as follows: 811 steels: 100 a t McKeesport t o 173 a t Scottdale Copper steels: 100 a t McKeesport t o 133 a t Scottdale Plain steels: 100 a t McKeesport t o 190 a t Scottdale
From Table IV(B) we learn t h a t t h e benefit of higher annealing temperatures in t h e case of plain steels is approximately 1 2 per cent greater endurance, while for copper steels i t is practically negligible.
TABLEIV-AVERAGE CORROSION PER MONTH(PROM TABLEI): RESULTSIN O u a c ~ sPER SQUAREFOOT (B) FROM ( c ) GRADES2 TO 24 (A) Scottdale McKeesport BOTH TEMPERATURES GRANDA V E R A G ~ 1400’ 1600 1st period 2nd period 1st period 2nd period Scottdale McKeesport STEELSAVERAGED .... .... .... .... .... Grades 2 t o 50.. ....................... 0.2596 0.1502 .... Copper steels., ........................ 0.1376 0.1037 0.1206 0.1196 0.1379 0.1369 0.1066 0.0917 0.3021 0.2686 0.3383 0.5122 0.1875 0.2343 0.3528 0.1857 Allothers.. ...........................
grades which have only t h e usual traces of copper take positions from 12 t o 24, t h e poorest being those t o which sulfur was added (No. IO) a n d which contained high sulfur residually (KO.16), t h e latter showing losses approximately three times as great as t h e copper steels. . T h e addition of aluminum, silicon and cold steel in each case has slightly increased t h e corrosion rate (compare Nos. 9, 8 a n d 11 with KO. 6). A phosphorus addition has somewhat lessened t h e corrosion (compare No. 7 with No. 6 and No. 23 with KO. 24): this is in line with some of our previous work. Grades 19 t o 24, although from a heat which was supposed t o be highly oxidized, have shown somewhat lower losses t h a n the other heats. From other work we have done, we ascribe this t o t h e somewhat lower sulfur content (compare Kos. 6 and 14 with No. 24). I n studying t h e results on Grades ~ j 16, , 1 7 and 18 (Bessemer), we note t h e accelerating effect of very high sulfur, At t h e same time, t h e addition of 0.25 per cent copper t o t h e same steel has entirely neutralized this influence and t h e results are quite comparable t o those obtained with normal copper steels. Considering Table 111, Grades 2X t o 14X, t o which t h e same additions were made as t o Nos. 2 t o I 4 1
In grade No. 20, the steel was so wild that i t was very difficult t o add
t h e copper properly, and some was lost.
I n determining t h e losses of t h e weighed test pieces, the authors adopted t h e practice of removing them from t h e racks at different periods. , A t t h e end of these periods, which were 6.5 and 8.2 months, respectively, we removed one-half of t h e test pieces a n d cleaned and weighed them. The remaining half we left exposed for approximately 3 months longer, a t t h e end of which time they also were taken down, cleaned a n d weighed. Various conclusions may be drawn from a study of corrosion rates during these two periods of exposure. I n Table IV(C) in t h e Scottdale test we notice t h a t in the first period t h e rate of corrosion of copper steels was 0,1379 a n d of t h e same steels in the second period, 0.1369, showing t h a t t h e corrosion rate does not increase for successive periods of exposure, while with t h e plain steels, we find a decided increase in t h e second period over t h e first, uiz,, 0.3383 in t h e first t o 0.5122 in t h e second, a 51 per cent increase in corrosion rate. Similar results were obtained in t h e McKeesport test. TABLE V-COMPARISON OF COPPERSTEELSOF NORMALANALYSISWITH OTHER STEELS TO WHICH N O ADDITIONS WERE M A D E : (FROM TABLES I A N D 11) “Pure Low copper Plain Copper steels Iron” steels steels 0.25% Cu TEST Period (2-12-13-17) (6-14-18) (50) (6X) (14X) Scottdale 1st 0,1366 0.3456 0,1588 .... .... 2nd 0.1394 0.4737 0.1554 .... McKeesport 1st 0.1069 0,1841 0.1156 0.1293 0.1173 2nd 0.0905 0,2325 0,1244 0.1307 0.1147
....
Mar.,
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
1916
I n Table V, we have set a p a r t t h e copper steels which agree in copper content with t h e amount used in t h e average material which is placed on t h e market, t h a t is, 0.25 per cent, and we have compared these with plain steels t o which n o additions have been made, a n d also with so-called “pure iron.” Such comparisons have been made both in t h e Scottdale test a n d in t h e McKeesport test. We find again t h a t with copper steels, as in Table IV(C), t h e corrosion rate does not accelerate in t h e second period of exposure, whereas with plain steels, t h e reverse is true, t h e corrosion ratio being IOO : 1 7 7 . T h e pure open-hearth iron containing 0.04 per cent copper has shown greater total corrosion loss t h a n t h e copper steels, yet, probably due t o its copper content, i t ranges itself with t h e copper steels, in t h a t t h e corrosion rate is not increased in t h e second period. T h e same statement applies t o t h e normal open-hearth steels containing 0.04 per cent copper, a s will be noted b y t h e results o n Panels 6X a n d 14X. It will also be noted t h a t Grade 6X, a normal open-hearth steel with 0.041 per cent copper is nearly as good a s No. 50 (pure iron with 0.041 per cent copper), while Grade I ~ X with 0.05 per cent copper is better t h a n No. 50. (The test roofs have been shown at t h e different stages of rusting t o many parties of metallurgists and other investigators of corrosion problems.) ADDITIONAL “PURE IRON”
TESTS
I n addition t o the tests reported above, one, of t h e authors1 has conducted some tests, t h e results of which give further corroborative evidence o n t h e behavior of low copper “pure irons” under atmospheric in-
I
I
215
atmosphere, under t h e same conditions, with copperbearing steels and plain steels. T h e sheets were of 26 gauge, except in t h e case of Type A, 1st lot, which had a thickness of 0.022 in. instead of 0.0185 in. They were first exposed on July 16, 1914, November 7, 1914 and August 5, 1914, respectively. T h e analyses of t h e “pure iron” sheets were a s follows: Type A: Low-wppa 2nd lot 0.020 0.094 Phorphorur ............ 0.004 0.005 Sulfur ................. 0,030 0.018 Silicon ................ 0.002 0.002 Copper ............:. .. 0.027 0.020 Oxygen ............... 0.031 ... Aluminum ............. 0.005 ... PBRCBNTADBS
Type B 0.04 t o 0.05% C“
1st lot
...............0.013 Manganerc ............ 0.04 Carbon
0.014 0.049 0.003 0.033
0:045
TYPE A, IST LoT4bservations showed that in less than I month this lot was rusting badly and the rust had the light brown color which had been found to be characteristic of the more rapidly corroding steels; in less than 2 months the same sheet had become very rough, resembling in this respect the most rapidly rusting steels containing added sulfur and siliwn; in 9 months it had become as thin as paper a t the edges; in 12 months it had frayed and broken at the bottom, but did not break transversely when pressed; in 15 months it had broken through near the bottom, though fairly strong a t the upper end; after 18 months, one square. foot of it had rusted away at the bottom, and it was cracked half way up; it cracked transversely when lightly pressed near the top. TYPE A. ZND LOT showed a thick, light brawn rust after ahout 2 months’ exposure; after 4 months, there was a thick, light brown scale; after 6 months, the sheets were thin at the bottom, but could not then be broken by light pressure; after 9 months, the sheets were rusted away a t the hottom-me sheet was full of holes in the lower half and the rusting had praceeded further than in the case of the 1st lot at this period; after 12 months the sheets had become detached and were rusted so badly that they could be broken easily by hand in any part.
T h e more rapid corrosion of t h e second lot of this “pure iron” is believed t o be due t o t h e lower copper content.
fluences, and also on t h e progress of rusting during successive periods of exposure. A description of these tests follows: At the request of one of t h e authors, two mannfacturers of “pure iron” furnished sheets of their material, which were analyzed, corrugated a n d included in t h e weather exposure tests at McKeesport. Test pieces were also cut from t h e sheets a n d the losses of weight determined b y exposure, in t h e Pittsburgh Mr. H - 4 .
TYPE B-It will be noticed that this type of “pure iron” contained more than twice as much copper as the “pure iron” of Type A. The percentages of wpper in the different sheets were 0.043. 0.044 and 0.048, which places it in the class with the “pure iron” in the main test and with the sheets 6X and I&, already described as being far more durable than plain steel or “pure iron” of Type A, especially in the 2nd lot. After 6 months, they were graded as showing no more corrosion than the copper-bearing steels which had been exposed for 7 months; after 8 months they were graded as being no longer as resistant to corrosion as the copper-hearing steels containing approximately 0.25 per cent copper-the rust was quite rough, resembling 7X, i q X and the “pure iron” in the main test; after I I months, while the rust was rough and deep, there was no perceptible thinning at the edges and no sagging; after 14 months, one sheet brake when lightly pressed; after 17 months, one sheet was perforated and cracked-the second sheet was cracked and had a small perforation while the third sheet was not then broken through.
QUANTITATIVE WEIGHT LOSSES of t h e test pieces exposed for approximately equal periods, though at slightly different seasons, in t h e Pittsburgh atmosphere were as follows: Time Type A. 1st lot Type A. 2nd lot Type B.
6 mo. (Oet. to Apr.) 5 % mo. (No“. to Apr.) 5’/r mo. (Oet. t o Apr.)
LOSS
in ounces p a ’9. ft. 2.70 2.34 1.64
T H E J O C R A V A L O F I N D C S T R I A L A X D ENGI-VEERIi\TG C H E M I S T R Y
216
Tol. 8,N O 3
The test pieces, of which there were three in each case, were, after cleaning with ammonium citrate solution and weighing, exposed for three months longer.
steels after the fourth month: the rust had formed an efficient protective coating.
Time, 3 mo ( M a y t o Aug ) Loss in o z per sq f t T y p e 4 , 1st l o t . . . . . . . . . . . . . . . . . 1 . 2 6 Type A , 2nd l o t . . . . . . . . . . . . . . . 1 . 6 6 T y p e B . . . . . . . . . . . . . . . . . . . 0.99
Sheet steel or iron containing C O P P E R shows greatly increased corrosion resistance when exposed t o atmospheric conditions. The most effective amount of copper to be used for this purpose is approximately Smaller amounts of copper down t o as 0 . 2 j per cent. little as 0.04 per cent have a considerable influence in lessening corrosion, b u t t h e results are not as good as with the higher amount mentioned above. Work previously done by one of us has indicated t h a t 0.1; per cent copper is in nearly all cases as efficient as 0.25 per cent. Higher amounts of copper, up t o 2 per cent, give little or no added benefit. Copper is as necessary in t h e so-called “pure irons” t o insure corrosion resistance as it is in normal open-hearth and Bessemer steels. P H O S P H O R C S added t o open-hearth steel slightly lowers t h e corrosion rate. SILICON, while probably without effect in the amounts normally present in openhearth and Bessemer steels, accelerates corrosion when added in amounts from 0 . 1 0 t o 0.30 per cent. The addition of small amounts of A L L X I K U Y p.robably has little influence on corrosion: the above tests indicate it t o be harmful rather t h a n beneficial. T h e addition of S U L F U R t o steel greatly increases the corrosion rate and when residually present in abnormal amounts, it is probably also detrimental from a corrosion standpoint. The addition of C O L D S T E E L t o molten steel does not lower t h e corrosion rate, b u t , if it has a n y influence a t all, it is t o increase t h e corrosion.
Copper percentage 0 027 0.019 0.045
I t will be seen t h a t . when exposed under exactly t h e same conditions, t h e losses of weight were inversely proportional t o t h e small and slightly varying copper percent ages. T h e following experiment shows the comparison between weight losses during one, two and three months’ exposures of s e p a r a t e test pieces of “pure iron,” Type A , 2nd lot. Loss in oz. per sq. f t . June 1st t o July 1st.. . . . . . . . . . . . . . . . . . . . . . . . . 0.74 . . . . . . . . . . . . . . . . . 1.42 Augustlst. “ “ “September 1 s t . . . . . . . . . . . . . . . . . . 2 . 2 7 I‘
‘
I
,
,
I t had been noticed in other experiments t h a t the copper-bearing steels showed less loss of weight for equal periods of exposure. after the first dense rust coating had formed. These experiments show t h a t the nearly equal corrosion loss during the second month and the greater corrosion loss during t h e third month place this low copper “pure iron” in the same class of inferior weather-resisting material with plain steel free from copper. C O R R O S I O N LOSSES ISC
(oz.
P E R S Q . FT.) O F
COPPER-BEAR-
S T E E L , p r A A I s S T E E L A K D ( ‘ P U R E IRON”
Test pieces were exposed in racks for oize-nzoiztlz p e r i o d s in the Pittsburgh atmosphere. The results in the following table do not represent progressive rusting. a new test piece having been exposed on the first of each month. Copper-bearing steel LOSS n 2 ~ cu7 ~ M a y . . . . . . . . . . . . . 0 52 J u n e . . . . . . . . . . . . . .0 . 3 8 July.. . . . . . . . . . . . . 0.56 August.. . . . . . . . . . . 0 . 5 4
CORROSIOX
Plain steel 0.90 0.65 0.95 o.i5
“Pure iron” 0 045% Cu 0.64 0.49 0.i6
0.68
Test pieces were exposed for from I - t o ;-month periods in t h e Pittsburgh atmosphere with the following results. These results represent progressive losses, six (6) pieces having been exposed a t the start and one taken down a t a time a t the end of each month. Copper-bearing steel Period exposed 0 2 5 % cu Months l . . . . . . . . . . . . . . . 0.52
Plain steel
“Pure iron” 0 04570 Cu
n on
0.64
( a ) This piece of plain steel was a t this time reduced from an original weight of 18.3 grams to 0.9 gram, and was wholly disintegrated.
From t h e above tables, il; mill be noticed that the progress in rusting under t h e original rust coat is much more rapid in t h e case of the plain steel t h a n in t h e case of t h e copper-bearing steel, and materially less rapid in the case of the copper-bearing steel t h a n in t h e case of the “pure iron.” However, this “pure iron” contains enough copper t o account for its approximating in corrosion resistance t h e copper-bearing steel. I t is of great interest t o note t h a t corrosion practically stopped in the case of t h e copper-bearing
SUM hI A R T
LOSS
IN
WEIGHT
DETERMINATIONS
Oh-
SlZIALL
are found t o be accurate and valuable when determining t h e relative corrosion resistance of various sheet metals. The method of cleaning such test pieces with ammoniacal ammonium citrate solution is found t o be the most convenient and accurate thus far investigated. T E S T PIECES
C 0 N C L US1 0 N S
I-Copper increases t h e resistance of steel and iron t o atmospheric corrosion: I-Its influence is apparent when the copper content reaches only 0.03 per cent. 2-Its effect is almost a t a maximum n h e n the copper reaches 0 . O j per cent. 3-The best amount of copper for commercial steel has been found t o be 0 . 2 j per cent. 11-Steel containing 0 . 2 j per cent copper outlasts “pure iron” containing 0.04 per cent copper. 111-Steel containing o . o j per cent copper lasts as long as “pure iron” containing 0.04 per cent copper. IT-Sulfur in steel accelerates corrosion very markedly. T-Sulfur oxides in the air accelerate the corrosion of steel. VI-Copper in steel counteracts or retards both t h e corroding influence; noted ;n IT’’ and V. PITTSBURGH
