4th Annual Snmmer Symposium-Standards
interplant Standardization in the Steel Industry .\RE4 €I. THOMAS
AND
CHARLES S. MILLS, Armco Steel Corp., Middletown, Ohio
Details are given of the procedure used by the Armco S tee1 Corp. for the preparation and standardization of standard steel samples. Also described is the system used for the check analysis of the values reported by the Divisional Control Laboratories in the routine analysis of steel and iron samples. The analytical tolerances observed are shown and discussed. Finally, the development and standardization of the analytical methods used by all the Armco laboratories are described. All these functions have as their purpose the establishment of as high a degree of analytical accuracy as it is possible or practical to attain in both the control and resear& laboratories. Typical check analysis reports are shown as an indication that this goal essentially has been achieved. Other laboratories may find a similar program of equal value.
A
RlONG the important functions of the Analytical Section
of the Armco Research Laboratories are those which have as their purpose the maintaining of the analytical standards of the Operating Division Control Laboratories a t the highest practical level. These functions are: Development and standardization of the analytical methods used by the various Armco laboratories. Preparation and standardization of steel and iron samples to eupplement these available from the National Bureau of Standards. Check analyses made on the values reported by the various operating division laboratories in the routine analysis of heats and casts. Together these three functions constitute the standardization program of the Research Analytical Section. Each is discussed in some detail in thr follo\ving sections. DEVELOPMENT AND STANDARDIZATION OF METHODS
Thc standardization of methods is basically the most important of the three functions, for without this there could be no common basis on which to judge the accuracy of the analytical values reported. Of course, this assumes that the methods, as established, yield values that represent the true values as nearly as it is practical to do so. The responsibility for this rests on the Research Analytical Section. I n order to give this responsibility the attention it deserves, one chemist has been assigned full time to the development of methods. He also supervises any work on method investigation that the other chemists and analysts are ab]? t o handle along with their regular work. In determining what method or methods are to be developed, the need8 of the operating division laboratories receive f i s t consideration. Usually notice is received of the need for a new procedure somen hat in advance, so that the developmental work can be completed by the time the method is required. However, there are occasions, emergency in nature, when little or no advance warning is given. I n such cases the combined efforts of several analysts often are required to obtain a quick solution to the analytical problem a t hand. Frequently, the method so developed is only temporary in nature and final development of the procedure follows later. In addition t o the development of new methods, work is continually in progress on improvement of methods already in estnhlished use. These developments have as their goals im-
proved accuracy, increased speed, or both. I n developing a new procedure or in improving one already established, three sources of information are drawn upon: Information obtained from the literature Suggestions made by the operating division laboratories Original ideas obtained from members of the research analytical staff and occasionally from the research engineers and metallurgists Once the details of a method have been established to the satisfaction of the chemist in charge of method development and his supervisors, the method is written up io tentative standard form, reproduced by ditto, and circulated to the division chemists of all the operating division laboratories. After trial for a reasonable time, the division chemist either advises the Research Bnnlytical Section that the method is satisfactory as written or submits a list of its shortcomings together with any changes he feels are necessary. These points are investigated and any suggested changes that are found desirable are incorporated in a rrvised tentative procedure. Once the method has been accepted, it is issued in the tentative form for a period of about one year. If no additional changes appear necessary after this extended period of use, the method is then printed and issued as an official Armco standard method. Whether in tentative or standard form, it is the responsibility of the division chemists to see that the methods are used as written. PREPARATIOY 4 N D ST4YDARDIZATION O F S T E E L A h D I R O 8 SAMPLES
In order to provide a check on the accuracy of the est,ahlished standard methods and on the analytical technique of the individual analysts, it is necessary to provide suitable standard samples. I n many capes those available from the Sational Bureau of Standards are satisfactory and are used regularly. However, in some instances the specialized grades of steel produced a t A4rmcohave no counterpart among the samples provided by the bureau. I n other cases, it has been more economical to prepare standards, especially of types of steel which require daily use by the operating division laboratories. I n preparing a standard steel sample a t Armco much the same pi ocedure is followed as a t the Bureau of Standards. % . 300- to 500-pound section of a hot rolled slab is obtained from one of the plants. A slab from the bottom section of the ingot is always specified, as there is less danger of segregation effects from this portion of the ingot. Before shipping to Research the surface of the slab is cleaned by scarfing or grinding and the slab is sawed into pieces of a size that can be handled by the milling machines. These are about 3 inches thick X 6 X 10 inches. At Research these sections are acid pickled and milled by a cutter with the cutting edges notched a t intervals of about 0.5 inch, in order to avoid e~cessivelylong millings. The millings are stored in large closed metal cans until the entire sample has been milled, after which they are thoroughly mixed in a small concrete mixer, and screened through 50- and 20-mesh sieves. The -50 and +20 portions are discarded and the remainder is bottled in clean 5-pint acid bottles. For standardization, a 4-ounce bottle of millings is taken from each 5-pint bottle. From 3 to 5 of these 4-ounce bottles are sent to each of the four operating division laboratories and a like number are retained a t Research. By analyzing a portion of the millings from each of 20 to 25 large bottles, any evidence of segregation is easily detected. Each bottle is assigned to a different analyst, who determines the desired constituents. Analyses are made a t least in triplicate. All individual values obtained are transmitted to Research, where they are carefully inspected. If the values reported by a particular analyst or 1553
ANALYTICAL CHEMISTRY
1554 laboratory appear out of line with those reported by the others, checks are requested. When satisfactory agreement is reached for all constituents, the values are averaged and labels printed showing the official values. The standard sample is then available to the operating division laboratories for use as needed. Table I illustrates the range of values obtained by the individual analysts on a typical Armco standard sample, a nickelmolybdenum alloy steel. Figure 1 shows the printed label for this standard. The elements shown in bold-faced type are those for which the standard is primarily intended to be used. CHECK ANALYSIS SYSTEM
of the other operating division laboratories for a referee analysis. As a basis for determining when a particular value reported by an operating division laboratory is in error, a table of standard analytical tolerances has been established. Typical sections of this table are shown in Table 11. The tolerance permitted varies with the element concerned, the percentage present, and the type of steel or iron involved. For example, the tolerances permitted for alloy steel analysis are somewhat greater than those
Table 11.
I n order to determine the accuracy of the values reported by the operating division laboIatories, a check analysis program was initiated a t Ariiico about 15 years ago. The present system involves monthly check analyses by Research of selected determinations from an entire day's production of heats and casts from each of the four Armco divisions. The day for the check analyses is selected by Research and is varied from month to month. Requests for the samples of the heats and casts are made throughout the month, so that samples from each of the four divisions are spaced about a week apart. By so doing, the check analyses for each division can be made n ithout undue delay. I n selecting the determinations to be checked, an equal number from each of the three work shifts are chosen, so that all the analysts a t work on that particular day are covered, So far as possible, a variety of the different grades of steel are selected. As soon as the check analyses are completed, the laboratory concerned is advised by telephone or wire of those determinations on which their reported values were outside of the Armco standard analytical tolerances. Check analyses then are made by the operating division laboratory and the values are reported to Research. Occasionally a determination will be encountered on \Thich agreement betwecn Research and the operating division laboratory cannot be reached, I n such cases the sample is submitted to one
Standard Analytical Tolerances for Armco Analytical Laboratories Range,
Grade Plain steel
Element Carbon
Plain steel
Silicon
t
C (O.ll)a
,.
..
.. .. .. ..
..
, .
..
... ...
O.1RU
0.186
..
..
..
...
...
Sn
Pb
... ... ... ...
... ... ... ...
0.016b 0.0146
O.OOBb
...
...
0,5ga
12.38 12.36
.,
.. , . .. .. .. , . ..
.. .. .. ..
,..
...
0.16C
..
Cb 0.52" 0.53O 0.56O
1\10
0.38 0.38 0.51 0.50
0.15a
... ...
. .. ..
Cr 18.39 18.38
...
0 14" 0.185,c
..
...
,
Xi 10.59 10.59
10,14) . .
...
O.O!J8 0.095
.. .. .. ..
, . .
0 226L 0.22Q
1.75 1.73
..
Co
.. .. ..
..
0.024 0.024
...
Cii
...
... ...
,..
..
Si ..
0.28
..
,.
1555
..
..
...
..
.. ..
..
0.0026
..
... ...
... ...
..
... ...
... ... ... ...
.. ..
... ...
.. ..
..
...
..
..
Ta 0. loa 0.08b
.. ..
.. ..
0.010b 0.011b
O.OO?a
..
..
0.0246 0.0'746
0.006b
, .
O.OO4b
, .
..
0.0135
0.001b 0 0015
..
..
0.0026
,.
,..
.. .. ..
.. ..
..
0.0146
,.
Rating. 0 3 . 8 % Wet chemical b Spectrographic. Values o u t s i d e analytical tolerances perinitted.
a
Check r a l w s in parentheses
for plain carbon steel. The value report,ed by the operating division lahoratory is called in error if it is not in agreement with the research value n-ithin the established tolerance limit. A4sthe final step in the check analysis program, a monthly rcport, is issued showing the research and operating division values for all the detcrmiriations checked. Each laboratory is given a straight percentage rating obtained by dividing the number of correct valurs-i.e., those within the tolerance h i t s tiy the total number of determinations checked. Typical pages from one of these reports are shovin in Tables 111,IT, and ,V. Recently a revision of the grading system has been pro'posed in which the degree of accuracy is taken into account. I n this system a credit of 100 would be given for each determination within tolerance and a credit of 0 for those in n-hich the differences are twice or more the standard t,olerance limits. Partial credit would be given for those between one and two times the standard tolerance limits. The total of all the credits, divided by the number of determinations, would yield t h e percentage rating. An example of how this system would work is shown in STANDARD - SAMPLE a Table VI. As can N o . IU be seen, the proNi-Mo STEEL Dosed svstem would result in somewhat 01 /o higher percentage c . . . . . . . . . . . . . . . . . . . . . . . . . .174 ratings than does Mn . . . . . . . . . . . . . . . . . . . . . . . . 547 the present system, P . . . . . . . . . . . . . . . . . . . . . . . . . .014 but it may be that S (Comb.) . . . . . . . . . . . . . . . . .019 a truer and more Si . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 6 realistic picture of Cu . . . . . . . . . . . . . . . . . . . . . . . . .066 the accuracy of the Ni.. *. 3.98 operating division laboratories would Mo .381 bc ohtained. AdopARMCO RESEARCH LABORATORIES tion of this or a MIDDLETOWN. OHIO similar system is being considered. Figure 1. Standard Label
_.
~~
...... ...... ..............
Table VI. Proposed Revision of Check Analysis Grading System D. C.
Deviation of reported value from Research value. Credit allowed.
100 50 0
0.002 0.003 0,004 *0.005
D 0.005 0.006 0.007 0.008
0,009
0.003 0.004 0,003 0,006
-
c, % 100 80 60 40 20 0
100
0.10
67 33 0
0.11 0.12 0.13 0.14 0 . 13 0 16 0 17 0.18 0.19 0.20
+0.04
D 0.04 0.05 0.06 0.07 0.08
c, %
.
100
75 50 25 0
0,010 ExAwLE I d determinations within tolerance limits 2 determinations outside double tolerance limit 1 determination partial credit 1 determination partial credit 1 determination partial credit
-
20 total determinations
Rating
Rating b y present system:
2
'
100 90 80 70 60 50 40 30 20 10 0
1500 0 50 70 30
-_
20' 16.50 82 5So
X 100 = 75.070
Based on fifteen years' experience, it is felt that the check analysis system has contributed materially in maintaining a t a high level the analytical standards of thc operating division laboratories. For example, during the year 1950 the four Armco division laboratories had average ratings between 84 and 94%. I n evaluting thePe percrntage ratings it should be remembered thax the values reported b y the operating division laboratories represent single dc,terniinations made under conditions requiring high speed of analysis. I n view of this, and of the rather strict tolerances observed, these percentage ratings are considered satisfactory evidence that the standard methods are being folIon-cd as n ritten and the anal\-tical technique used is good. Contributing greatly t o the success of this program has been the Ftandardization of the methods used and the frequent use of standard samples. Other laboratories map find that a program of the type described will have similar beneficial results. RECEIVED June '20, 1951.
