Produced by Robert J. Hall
THE
WORKING OF STEEL
ANNEALING, HEAT TREATING
AND
HARDENING OF CARBON AND ALLOY STEEL
BY
FRED H. COLVIN
Member American Society of Mechanical Engineers and Franklin Institute;
Editor of the _American Machinist_, Author of "_Machine Shop
Arithmetic_," "_Machine Shop Calculations_," "_American Machinists'
Hand Book_."
AND
K. A. JUTHE, M.E.
Chief Engineer, American Metallurgical Corp. Member American Society
Mechanical Engineers, American Society Testing Materials, Heat
Treatment Association, Etc.
SECOND EDITION
THIRD IMPRESSION
McGRAW-HILL BOOK COMPANY, Inc.
NEW YORK: 370 SEVENTH AVENUE
LONDON: 6 & 8 BOUVERIE ST., E. C. 4
PREFACE TO SECOND EDITION
Advantage has been taken of a reprinting to revise, extensively,
the portions of the book relating to the modern science of
metallography. Considerable of the matter relating to the influence
of chemical composition upon the properties of alloy steels has
been rewritten. Furthermore, opportunity has been taken to include
some brief notes on methods of physical testing--whereby the
metallurgist judges of the excellence of his metal in advance of
its actual performance in service.
NEW YORK, N. Y.,
_August, 1922._
PREFACE TO FIRST EDITION
The ever increasing uses of steel in all industries and the necessity
of securing the best results with the material used, make a knowledge
of the proper working of steel more important than ever before.
For it is not alone the quality of the steel itself or the alloys
used in its composition, but the proper working or treatment of
the steel which determines whether or not the best possible use
has been made of it.
With this in mind, the authors have drawn, not only from their
own experience but from the best sources available, information
as to the most approved methods of working the various kinds of
steel now in commercial use. These include low carbon, high carbon
and alloy steels of various kinds, and from a variety of industries.
The automotive field has done much to develop not only new alloys but
efficient methods of working them and has been drawn on liberally
so as to show the best practice. The practice in government arsenals
on steels used in fire arms is also given.
While not intended as a treatise on steel making or metallurgy in
any sense, it has seemed best to include a little information as
to the making of different steels and to give considerable general
information which it is believed will be helpful to those who desire
to become familiar with the most modern methods of working steel.
It is with the hope that this volume, which has endeavored to give
due credit to all sources of information, may prove of value to
its readers and through them to the industry at large.
_July_, 1921.
THE AUTHORS.
CONTENTS
PREFACE
INTRODUCTION
CHAPTER
I. STEEL MAKING
II. COMPOSITION AND PROPERTIES OF STEELS
III. ALLOYS AND THEIR EFFECT UPON STEEL
IV. APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY
V. THE FORGING OF STEEL
VI. ANNEALING
VII. CASE-HARDENING OR SURFACE-CARBURIZING
VIII. HEAT TREATMENT OF STEEL
IX. HARDENING CARBON STEEL FOR TOOLS
X. HIGH SPEED STEEL
XI. FURNACES
XII. PYROMETRY AND PYROMETERS
APPENDIX
INDEX
INTRODUCTION
THE ABC OF IRON AND STEEL
In spite of all that has been written about iron and steel there
are many hazy notions in the minds of many mechanics regarding
them. It is not always clear as to just what makes the difference
between iron and steel. We know that high-carbon steel makes a
better cutting tool than low-carbon steel. And yet carbon alone
does not make all the difference because we know that cast iron
has more carbon than tool steel and yet it does not make a good
cutting tool.
Pig iron or cast iron has from 3 to 5 per cent carbon, while good
tool steel rarely has more than 1-1/4 per cent of carbon, yet one
is soft and has a coarse grain, while the other has a fine grain
and can be hardened by heating and dipping in water. Most of the
carbon in cast iron is in a form like graphite, which is almost pure
carbon, and is therefore called graphitic carbon. The resemblance
can be seen by noting how cast-iron borings blacken the hands just
as does graphite, while steel turnings do not have the same effect.
The difference is due to the fact that the carbon in steel is not
in a graphitic form as well as because it is present in smaller
quantities.
In making steel in the old way the cast iron was melted and the
carbon and other impurities burned out of it, the melted iron being
stirred or "puddled," meanwhile. The resulting puddled iron, also
known as wrought iron, is very low in carbon; it is tough, and on
being broken appears to be made up of a bundle of long fibers.
Then the iron was heated to redness for several days in material
containing carbon (charcoal) until it absorbed the desired amount,
which made it steel, just as case-hardening iron or steel adds
carbon to the outer surface of the metal. The carbon absorbed by
the iron does not take on a graphitic form, however, as in the
case of cast iron, but enters into a chemical compound with the
iron, a hard brittle substance called "cementite" by metallurgists.
In fact, the difference between the hard, brittle cementite and
the soft, greasy graphite, accounts for many of the differences
between steel and gray cast iron. Wrought iron, which has very
little carbon of any sort in it, is fairly soft and tough. The
properties of wrought iron are the properties of pure iron. As
more and more carbon is introduced into the iron, it combines with
the iron and distributes itself throughout the metal in extremely
small crystals of cementite, and this brittle, hard substance lends
more and more hardness and strength to the steel, at the expense
of the original toughness of the iron. As more and more carbon is
contained in the alloy--for steel is a true alloy--it begins to
appear as graphite, and its properties counteract the remaining
brittle cementite. Eventually, in gray cast iron, we have properties
which would be expected of wrought iron, whose tough metallic texture
was shot through with flakes of slippery, weak graphite.
But to return to the methods of making steel tools in use 100 years
ago.
The iron bars, after heating in charcoal, were broken and the carbon
content judged by the fracture. Those which had been in the hottest
part of the furnace would have the deepest "case" and highest carbon.
So when the steel was graded, and separated into different piles,
a few bars of like kind were broken into short lengths, melted
in fire-clay crucibles at an intense white heat, cast carefully
into iron molds, and the resulting ingot forged into bars under
a crude trip hammer. This melting practice is still in use for
crucible steel, and will be described further on page 4.
THE WORKING OF STEEL
ANNEALING, HEAT TREATING AND HARDENING
OF
CARBON AND ALLOY STEEL
CHAPTER I
STEEL MAKING
There are four processes now used for the manufacture of steel.
These are: The Bessemer, Open Hearth, Crucible and Electric Furnace
Methods.
BESSEMER PROCESS
The bessemer process consists of charging molten pig iron into
a huge, brick-lined pot called the bessemer converter, and then
in blowing a current of air through holes in the bottom of the
vessel into the liquid metal.
The air blast burns the white hot metal, and the temperature increases.
The action is exactly similar to what happens in a fire box under
forced draft. And in both cases some parts of the material burn
easier and more quickly than others. Thus it is that some of the
impurities in the pig iron--including the carbon--burn first, and
if the blast is shut off when they are gone but little of the iron
is destroyed. Unfortunately sulphur, one of the most dangerous
impurities, is not expelled in the process.
A bessemer converter is shown in Fig. 1, while Fig. 2 shows the
details of its construction. This shows how the air blast is forced
in from one side, through the trunnion, and up through the metal.
Where the steel is finished the converter is tilted, or swung on
its trunnions, the blast turned off, and the steel poured out of
the top.
OPEN HEARTH PROCESS
The open hearth furnace consists of a big brick room with a low
arched roof. It is charged with pig iron and scrap through doors
in the side walls.
[Illustration: FIG. 1.--A typical Bessemer converter.]
Through openings at one end of the furnace come hot air and gas,
which burn in the furnace, producing sufficient heat to melt the
charge and refine it of its impurities. Lime and other nonmetallic
substances are put in the furnace. These melt, forming a "slag"
which floats on the metal and aids materially in the refining
operations.
In the bessemer process air is forced _through_ the metal. In the
open-hearth furnace the metal is protected from the flaming gases
by a slag covering. Therefore it is reasonable to suppose that
the final product will not contain so much gas.
[Illustration: FIG. 2.--Action of Bessemer converter.]
[Illustration: FIG. 3.--Regenerative open hearth furnace.]
A diagram of a modern regenerative furnace is shown in Fig. 3.
Air and gas enter the hearth through chambers loosely packed with
hot fire brick, burn, and exit to the chimney through another pair
of chambers, giving to them some of the heat which would otherwise
waste. The direction is reversed about every twenty minutes by
changing the position of the dampers.
CRUCIBLE STEEL
Crucible steel is still made by melting material in a clay or graphite
crucible. Each crucible contains about 40 lb. of best puddled iron,
40 lb. of clean "mill scrap"--ends trimmed from tool steel bars--and
sufficient rich alloys and charcoal to make the mixture conform to
the desired chemical analysis. The crucible is covered, lowered
into a melting hole (Fig. 4) and entirely surrounded by burning
coke. In about four hours the metal is converted into a quiet white
hot liquid. Several crucibles are then pulled out of the hole, and
their contents carefully poured into a metal mold, forming an ingot.
[Illustration: FIG. 4.--Typical crucible furnace.]
If modern high-speed steel is being made, the ingots are taken
out of the molds while still red hot and placed in a furnace which
keeps them at this temperature for some hours, an operation known
as annealing. After slow cooling any surface defects are ground
out. Ingots are then reheated to forging temperature, hammered
down into "billets" of about one-quarter size, and 10 to 20 per
cent of the length cut from the top. After reheating the billets
are hammered or rolled into bars of desired size. Finished bars are
packed with a little charcoal into large pipes, the ends sealed,
and annealed for two or three days. After careful inspection and
testing the steel is ready for market.
THE ELECTRIC PROCESS
The fourth method of manufacturing steel is by the electric furnace.
These furnaces are of various sizes and designs; their size may be
sufficient for only 100 lb. of metal--on the other hand electric
furnaces for making armor-plate steel will hold 40 tons of steel.
Designs vary widely according to the electrical principles used.
A popular furnace is the 6-ton Heroult furnace illustrated in Fig. 5.
It is seen to be a squat kettle, made of heavy sheet steel, with
a dished bottom and mounted so it can be tilted forward slightly
and completely drained. This kettle is lined with special fire
brick which will withstand most intense heat and resist the cutting
action of hot metal and slag. For a roof, a low dome of fire brick
is provided. The shell and lining is pierced in front for a pouring
spout, and on either side by doors, through which the raw material
is charged.
Two or three carbon "electrodes"--18-in. cylinders of specially
prepared coke or graphite--extend through holes in the roof. Electrical
connections are made to the upper ends, and a very high current
sent through them. This causes tremendous arcs to form between
the lower ends of the electrodes and the metal below, and these
electric arcs are the only source of heat in this style of furnace.
Electric furnaces can be used to do the same work as is done in
crucible furnaces--that is to say, merely melt a charge of carefully
selected pure raw materials. On the other hand it can be used to
produce very high-grade steel from cheap and impure metal, when
it acts more like an open-hearth furnace. It can push the refining
even further than the latter furnace does, for two reasons: first
the bath is not swept continuously by a flaming mass of gases;
second, the temperature can be run up higher, enabling the operator
to make up slags which are difficult to melt but very useful to
remove small traces of impurities from the metal.
Electric furnaces are widely used, not only in the iron industry,
but in brass, copper and aluminum works. It is a useful melter of
cold metal for making castings. It can be used to convert iron
into steel or vice versa. Its most useful sphere, however, is as a
refiner of metal, wherein it takes either cold steel or molten steel
from open hearth or bessemer furnaces, and gives it the finishing
touches.
[Illustration: FIG. 5.--"Slagging off" an electric furnace.]
[Illustration: FIG. 6.--Pouring the ingots.]
As an illustration of the furnace reactions that take place the
following schedule is given, showing the various stages in the
making of a heat of electric steel. The steel to be made was a
high-carbon chrome steel used for balls for ball bearings:
6-TON HEROULT FURNACE
11:50 A.M.--Material charged:
Boiler plate 5,980 lb.
Stampings 5,991 lb.
-----------
11,971 lb.
Limestone 700 lb.
12:29 P.M.--Completed charging (current switched on).
3:20 P.M.--Charge melted down.
Preliminary analysis under black slag.
Analysis:
Carbon Silicon Sulphur Phosphorus Manganese
0.06 0.014 0.032 0.009 0.08
Note the practical elimination of phosphorus.
3:40 P.M.--The oxidizing (black) slag is now poured and skimmed off as
clean as possible to prevent rephosphorizing and to permit of adding
carburizing materials. For this purpose carbon is added in the form
of powdered coke, ground electrodes or other forms of pure carbon.
The deoxidizing slag is now formed by additions of lime, coke and
fluorspar (and for some analyses ferrosilicon). The slag changes
from black to white as the metallic oxides are reduced by these
deoxidizing additions and the reduced metals return to the bath.
A good finishing slag is creamy white, porous and viscous. After
the slag becomes white, some time is necessary for the absorption
of the sulphur in the bath by the slag.
The white slag disintegrates to a powder when exposed to the atmosphere
and has a pronounced odor of acetylene when wet.
Further additions of recarburizing material are added as needed to
meet the analysis. The further reactions are shown by the following:
3:40 P.M.--Recarburizing material added:
130 lb. ground electrodes.
25 lb. ferromanganese.
Analysis:
Carbon Silicon Sulphur Phosphorus Manganese
0.76 0.011 0.030 0.008 0.26
To form white slag there was added:
225 lb. lime.
75 lb. powdered coke.
55 lb. fluorspar.
4:50 P.M.--
Analysis:
Carbon Silicon Sulphur Phosphorus Manganese
0.75 0.014 0.012 0.008 0.28
Note reduction of the sulphur content.
During the white-slag period the following alloying additions were
made:
500 lb. pig iron.
80 lb. ferrosilicon.
9 lb. ferromanganese.
146 lb. 6 per cent carbon ferrochrome.
The furnace was rotated forward to an inclined position and the
charge poured into the ladle, from which in turn it was poured
into molds.
5:40 P.M.--Heat poured.
Analysis:
Carbon Silicon Sulphur Phosphorus Manganese Chromium
0.97 0.25 0.014 0.013 0.33 0.70
Ingot weight poured 94.0 per cent
Scull 2.7 per cent
Loss 3.3 per cent
Total current consumption for the heat, 4,700 kW.-hr. or 710 kw.-hr.
per ton.
Electric steel, in fact, all fine steel, should be cast in big-end-up
molds with refractory hot tops to prevent any possibility of pipage
in the body of the ingot. In the further processing of the ingot,
whether in the rolling mill or forge, special precautions should
be taken in the heating, in the reduction of the metal and in the
cooling.
No attempt is made to compare the relative merits of open hearth
and electric steel; results in service, day in and day out, have,
however, thoroughly established the desirability of electric steel.
Ten years of experience indicate that electric steel is equal to
crucible steel and superior to open hearth.
The rare purity of the heat derived from the electric are, combined
with definite control of the slag in a neutral atmosphere, explains
in part the superiority of electric steel. Commenting on this recently
Dr. H. M. Howe stated that "in the open hearth process you have such
atmosphere and slag conditions as you can get, and in the electric
you have such atmosphere and slag conditions as you desire."
Another type of electric furnace is shown in Figs. 7 and 8. This
is the Ludlum furnace, the illustrations showing a 10-ton size.
Figure 7 shows it in normal, or melting position, while in Fig.
8 it is tilted for pouring. In melting, the electrodes first rest
on the charge of material in the furnace. After the current is
turned on they eat their way through, nearly to the bottom. By
this time there is a pool of molten metal beneath the electrode
and the charge is melted from the bottom up so that the roof is
not exposed to the high temperature radiating from the open arc.
The electrodes in this furnace are of graphite, 9 in. in diameter
and the current consumed is about 500 kw.-hr. per ton.
[Illustration: FIG. 7.--Ludlum electric furnace.]
[Illustration: FIG. S.--The furnace tilted for pouring.]
One of the things which sometimes confuse regarding the contents
of steel is the fact that the percentage of carbon and the other
alloys are usually designated in different ways. Carbon is usually
designated by "points" and the other alloys by percentages. The
point is one ten-thousandth while 1 per cent is one one-hundredth
of the whole. In other words, "one hundred point carbon" is steel
containing 1 per cent carbon. Twenty point carbon, such as is used
for carbonizing purposes is 0.20 per cent. Tool steel varies from
one hundred to one hundred and fifty points carbon, or from 1.00
to 1.50 per cent.
Nickel, chromium, etc., are always given in per cent, as a 3.5
per cent nickel, which means exactly what it says--3-1/2 parts in
100. Bearing this difference in mind all confusion will be avoided.
CLASSIFICATIONS OF STEEL
Among makers and sellers, carbon tool-steels are classed by "grade"
and "temper." The word grade is qualified by many adjectives of
more or less cryptic meaning, but in general they aim to denote
the process and care with which the steel is made.
_Temper_ of a steel refers to the carbon content. This should preferably
be noted by "points," as just explained; but unfortunately, a 53-point
steel (containing 0.53 per cent carbon) may locally be called something
like "No. 3 temper."
A widely used method of classifying steels was originated by the
Society of Automotive Engineers. Each specification is represented
by a number of 4 digits, the first figure indicating the class, the
second figure the approximate percentage of predominant alloying
element, and the last two the average carbon content in points.
Plain carbon steels are class 1, nickel steels are class 2,
nickel-chromium steels are class 3, chromium steels are class 5,
chromium-vanadium steels are class 6, and silico-manganese steels
are class 9. Thus by this system, steel 2340 would be a 3 per cent
nickel steel with 0.40 per cent carbon; or steel 1025 would be a
0.25 plain carbon steel.
Steel makers have no uniform classification for the various kinds
of steel or steels used for different purposes. The following list
shows the names used by some of the well-known makers:
Air-hardening steel Chrome-vanadium steel
Alloy steel Circular saw plates
Automobile steel Coal auger steel
Awl steel Coal mining pick or cutter steel
Axe and hatchet steel Coal wedge steel
Band knife steel Cone steel
Band saw steel Crucible cast steel
Butcher saw steel Crucible machinery steel
Chisel steel Cutlery steel
Chrome-nickel steel Drawing die steel (Wortle)
Drill rod steel Patent, bush or hammer steel
Facing and welding steel Pick steel
Fork steel Pivot steel
Gin saw steel Plane bit steel
Granite wedge steel Quarry steel
Gun barrel steel Razor steel
Hack saw steel Roll turning steel
High-speed tool steel Saw steel
Hot-rolled sheet steel Scythe steel
Lathe spindle steel Shear knife steel
Lawn mower knife steel Silico-manganese steel
Machine knife steel Spindle steel
Magnet steel Spring steel
Mining drill steel Tool holder steel
Nail die shapes Vanadium tool steel
Nickel-chrome steel Vanadium-chrome steel
Paper knife steel Wortle steel
Passing to the tonnage specifications, the following table from
Tiemann's excellent pocket book on "Iron and Steel," will give
an approximate idea of the ordinary designations now in use:
Approximate
Grades carbon range Common uses
Extra soft 0.08-0.18 Pipe, chain and other welding purposes;
(dead soft) case-hardening purposes; rivets; pressing
and stamping purposes.
Structural (soft) 0.15-0.25 Structural plates, shapes and bars for
(medium) bridges, buildings, cars, locomotives;
boiler (flange) steel; drop forgings; bolts.
Medium 0.20-0.35 Structural purposes (ships); shafting;
automobile parts; drop forgings.
Medium hard 0.35-0.60 Locomotive and similar large forgings; car
axles; rails.
Hard 0.60-0.85 Wrought steel wheels for steam and electric
railway service; locomotive tires; rails;
tools, such as sledges, hammers, pick points,
crowbars, etc.
Spring 0.85-1.05 Automobile and other vehicle springs; tools,
such as hot and cold chisels, rock drills
and shear blades.
Spring 0.90-1.15 Railway springs; general machine shop tools.