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					                 THE BASIC OXYGEN STEELMAKING (BOS) PROCESS
                             By John Stubbles, Steel Industry Consultant


I INTRODUCTION
Accounting for 60% of the world's total output of crude steel, the Basic Oxygen Steelmaking (B
process is the dominant steelmaking technology. In the U.S., that figure is 54% and slowly dec
due primarily to the advent of the "Greenfield" electric arc furnace (EAF) flat-rolled mills. Howe
elsewhere its use is growing.

                                                                                           Figure
                                                                                           Charg
                                                                                           aisle o
                                                                                           Basic
                                                                                           Oxyge
                                                                                           Steelm
                                                                                           Plant
                                                                                           showin
                                                                                           scrap
                                                                                           charge
                                                                                           the BO
                                                                                           vessel
                                                                                           ladle f
                                                                                           hot m
                                                                                           seen t
                                                                                           right.




There exist several variations on the BOS process: top blowing, bottom blowing, and a combina
of the two. This study will focus only on the top blowing variation.

The Basic Oxygen Steelmaking process differs from the EAF in that it is autogenous, or self-suf
in energy. The primary raw materials for the BOP are 70-80% liquid hot metal from the blast fu
and the balance is steel scrap. These are charged into the Basic Oxygen Furnace (BOF) vessel.
Oxygen (>99.5% pure) is "blown" into the BOF at supersonic velocities. It oxidizes the carbon a
silicon contained in the hot metal liberating great quantities of heat which melts the scrap. Ther
lesser energy contributions from the oxidation of iron, manganese, and phosphorus. The post
combustion of carbon monoxide as it exits the vessel also transmits heat back to the bath.

The product of the BOS is molten steel with a specified chemical anlaysis at 2900°F-3000°F. Fr
here it may undergo further refining in a secondary refining process or be sent directly to the
continuous caster where it is solidified into semifinished shapes: blooms, billets, or slabs.

Basic refers to the magnesia (MgO) refractory lining which wears through contact with hot, bas
slags. These slags are required to remove phosphorus and sulfur from the molten charge.

BOF heat sizes in the U.S. are typically around 250 tons, and tap-to-tap times are about 40 min
of which 50% is "blowing time". This rate of production made the process compatible with the
continuous casting of slabs, which in turn had an enormous beneficial impact on yields from cru
steel to shipped product, and on downstream flat-rolled quality.

II BASIC OPERATION
BOS process replaced open hearth steelmaking. The process predated continuous casting. As a
consequence, ladle sizes remained unchanged in the renovated open hearth shops and ingot po
aisles were built in the new shops. Six-story buildings are needed to house the Basic Oxygen Fu
(BOF) vessels to accommodate the long oxygen lances that are lowered and raised from the BO
vessel and the elevated alloy and flux bins. Since the BOS process increases productivity by alm
an order of magnitude, generally only two BOFs were required to replace a dozen open hearth
furnaces.

Some dimensions of a typical 250 ton BOF vessel in the U.S. are: height 34 feet, outside diame
feet, barrel lining thickness 3 feet, and working volume 8000 cubic feet. A control pulpit is usua
located between the vessels. Unlike the open hearth, the BOF operation is conducted almost "in
dark" using mimics and screens to determine vessel inclination, additions, lance height, oxygen
etc.

Once the hot metal temperature and chemical analaysis of the blast furnace hot metal are know
computer charge models determine the optimum proportions of scrap and hot metal, flux addit
lance height and oxygen blowing time.




                                                                             2
                                                            Figure 2: BOF Vessel in Its Operati
                                                            Positions. (Ref: Making, Shaping, and Treati
                                                            Steel, 11th Edition, Steelmaking And Refining V
                                                            AISE Steel Foundation, 1998, Pittsburgh PA)




A "heat" begins when the BOF vessel is tilted about 45 degrees towards the charging aisle and
charge (about 25 to 30% of the heat weight) is dumped from a charging box into the mouth of
cylindrical BOF. The hot metal is immediately poured directly onto the scrap from a transfer lad
Fumes and kish (graphite flakes from the carbon saturated hot metal) are emitted from the ves
mouth and collected by the pollution control system. Charging takes a couple of minutes. Then
vessel is rotated back to the vertical position and lime/dolomite fluxes are dropped onto the cha
from overhead bins while the lance is lowered to a few feet above the bottom of the vessel. The
is water-cooled with a multi-hole copper tip. Through this lance, oxygen of greater than 99.5%
is blown into the mix. If the oxygen is lower in purity, nitrogen levels at tap become unaccepta



                                                                                 3
As blowing begins, an ear-piercing shriek is heard. This is soon muffled as silicon from the hot m
is oxidized forming silica, SiO2, which reacts with the basic fluxes to form a gassy molten slag t
envelops the lance. The gas is primarily carbon monoxide (CO) from the carbon in the hot meta
rate of gas evolution is many times the volume of the vessel and it is common to see slag slopp
over the lip of the vessel, especially if the slag is too viscous. Blowing continues for a predeterm
time based on the metallic charge chemistry and the melt specification. This is typically 15 to 2
minutes, and the lance is generally preprogrammed to move to different heights during the blo
period. The lance is then raised so that the vessel can be turned down towards the charging ais
sampling and temperature tests. Static charge models however do not ensure consistent turndo
the specified carbon and temperature because the hot metal analysis and metallic charge weigh
not known precisely. Furthermore, below 0.2% C, the highly exothermic oxidation of iron takes
to a variable degree along with decarburization. The "drop" in the flame at the mouth of the ve
signals low carbon, but temperature at turndown can be off by +/- 100°F.
                                                                                              Figure
                                                                                              Sectio
                                                                                              throug
                                                                                              BOF v
                                                                                              during
                                                                                              oxyge
                                                                                              blowin
                                                                                              (Ref:
                                                                                              Makin
                                                                                              Shapin
                                                                                              and Tr
                                                                                              of Ste
                                                                                              11th E
                                                                                              Steelm
                                                                                              And R
                                                                                              Volum
                                                                                              AISE S
                                                                                              Found
                                                                                              1998,
                                                                                              Pittsbu
                                                                                              PA)




In the past, this meant delays for reblowing or adding coolants. Today, with more operating



                                                                               4
experience, better computer models, more attention to metallic input quality, and the availabili
ladle furnaces that adjust for temperature, turndown control is more consistent. In some shops
sublances provide a temperature-carbon check about two minutes before the scheduled end of
blow. This information permits an "in course" correction during the final two minutes and better
down performance. However, operation of sublances is costly, and the required information is n
always obtained due to malfunctioning of the sensors.

Once the heat is ready for tapping and the preheated ladle is positioned in the ladle car under t
furnace, the vessel is tilted towards the tapping aisle, and steel emerges from the taphole in th
upper "cone" section of the vessel. The taphole is generally plugged with material that prevents
entering the ladle as the vessel turns down. Steel burns through the plug immediately. To mini
slag carryover into the ladle at the end of tapping, various "slag stoppers" have been designed.
These work in conjunction with melter's eyeballs, which remain the dominant control device. Sl
the ladle results in phosphorus reversion, retarded desulfurization, and possibly "dirty steel". La
additives are available to reduce the iron oxide level in the slag but nothing can be done to alte
phosphorus.


                                                                                            Figure
                                                                                            ladle o
                                                                                            molten
                                                                                            leavin
                                                                                            the lad
                                                                                            metall
                                                                                            facility
                                                                                            caster




After tapping steel into the ladle, and turning the vessel upside down and tapping the remainin
into the "slag pot", the vessel is returned to the upright position. In many shops residual slag is
blown with nitrogen to coat the barrel and trunion areas of the vessel. This process is known as
splashing". Near the end of a campaign, gunning with refractory materials in high wear areas m
also be necessary. Once vessel maintenance is complete the vessel is ready to receive the next



                                                                              5
charge.


III BASIC CHEMISTRY AND HEAT BALANCE
A heat size of 250 tons is used as the basis for the following calculations. This is close to the av
heat size for the 50 BOFs which were operable in the U.S. in 1999. The following charge chemis
assumed:
               %C      %Si %Mn %S %P %Al                   Residuals
Hot metal       4.5    .75      1.0   .01 .05       0          0
Scrap           .05    .05       .4  .015 .01      .03        0.1
Table 1 illustrates the heat balance PER TON OF HOT METAL. It assumes a 75% hot metal in a
charge of 275 tons which yields 250 tons of liquid steel (without alloys). If the oxygen were sup
as air, the heat required to take N2 from room temperature to 2900°F would be about 500,000
per NTHM, which illustrates that the BOS is a Bessemer process with cold scrap substituted for
nitrogen. (NTHM one short ton or 2000 pounds of hot metal).

TABLE I. HEAT BALANCE PER NET TON OF HOT METAL
75% HOT METAL IN CHARGE
     HEAT                Btu                                  Btu
                                    HEAT REQUIRED
   AVAILABLE           (000's)                              (000's)
                                    H.M 2400—>2900 F
     C —> CO             366                                    220
                                            _
    Si —> SiO2           204        FLUXES —>2900 F             110
    Mn —> MnO             60           O2 —>2900 F              120
    P —>P2O5              10           HEAT LOSSES              50
     Fe—>FeO             110         SCRAP —>2900 F             415
    CO—>CO2              130
 SLAG FORMATION           35
      TOTAL              915                                    915

The actual percentage of hot metal in the charge is very sensitive to the silicon content and
temperature of the hot metal and obviously increases as these decrease.

The oxygen required per heat is shown in Table II, as #/NTHM and as a percentage for the vari
reactions. 181#/NTHM corresponds to about 18.6 tons/per heat or 1800 scf/tapped ton. Oxyge
consumption increases if end-point control is poor and reblows are necessary.

TABLE II. OXYGEN REQUIREMENTS PER NTHM
          REACTION                  #/NTHM           % OF TOTAL
            C —>CO                     120                 66
           Si—>SiO2                     17                  9
       Fe—>FeO (SLAG)                   16                  9
           CO—>CO2                      12                  7
       Fe—>FeO (FUME)                   8                   4
       Mn,P—>MnO,P2O5                   7                   4




                                                                               6
     DISSOLVED OXYGEN                   1                   1
                                       181                 100

The final calculation for yield losses is shown in TABLE III. The metalloids and Mn are oxidized o
the hot metal, the scrap is often coated with Zn which volatilizes, and iron units are lost to the
fume, and slopping. To tap 250 tons of liquid steel, 250/0.91 or 275 charge tons are required, o
which 206 will be hot metal, and the balance scrap.

TABLE III YIELD LOSSES IN A BOF HEAT
                    LOSS                         % CHARGE
         METALLOIDS IN HM (6.3%)                     4.7
   DEBRIS,COATINGS ON SCRAP ( 2.5 %)                 0.6
                IRON TO SLAG                         2.2
                IRON TO FUME                          1
             IRON TO SLOPPING                        0.5
                    TOTAL                             9

IV RAW MATERIALS
i) HOT METAL

Hot metal is liquid iron from the blast furnace saturated with up to 4.3% carbon and containing
or less silicon, Si. It is transported to the BOF shop either in torpedo cars or ladles. The hot me
chemistry depends on how the blast furnace is operated and what burden (iron-bearing) mater
are charged to it. The trend today is to run at high productivity with low slag volumes and fuel
leading to lower silicon and higher sulfur levels in the hot metal. If BOF slag is recycled, P and M
levels rise sharply since they report almost 100% to the hot metal. U.S. iron ores are low in bo
elements.

The sulfur level from the blast furnace can be 0.05% but an efficient hot metal desulfurizing fac
ahead of the BOF will reduce this to below .01%. The most common desulfurizing reagents, lim
calcium carbide and magnesium - used alone or in combination - are injected into the hot meta
through a lance. The sulfur containing compounds report to the slag; however, unless the sulfu
slag is skimmed before the hot metal is poured into the BOF, the sulfur actually charged will be
above the level expected from the metal analysis.

ii) SCRAP

In autogenous BOS operation, scrap is by far the largest heat sink. At 20 - 25% of the charge i
one of the most important and costly components of the charge.

Steel scrap is available in many forms. The major categories are "home scrap", generated withi
plant. With the advent of continuous casting, the quantity of home scrap has diminished and it
necessary for integrated mills to buy scrap on the market. Flat rolled scrap is generally of good
quality and it's impact on the chemistry of BOF operations can almost be ignored. There is a yie
loss of about 2% due to the zinc coating on galvanized scrap. "Prompt scrap" is generated durin
manufacturing of steel products. It finds its way into the recycling stream very quickly. Many st
mills have agreements with manufacturers to buy their prompt scrap. "Obsolete" or "post consu
scrap returns to the market after a product has ended its useful life. Cans return to the market
quickly but autos have an average life of 12 years.




                                                                              7
Scrap also comes in many sizes, varying chemical analyses and a variety of prices. All of which
makes the purchase and melting of scrap a very complex issue. Very large pieces of scrap can
difficult to melt and may damage the vessel when charged. Some scrap may contain oil or surfa
oxidation. Obsolete scrap may contain a variety of other objects which could be hazardous or
explosive. Obviously the chemical analysis of obsolete scrap is imprecise.

Scrap selection is further complicated by the wide variety of steel products. Deep drawing steel
the maximum residual (%Cu +%Sn + %Ni +%Cr +%Mo) content to less than 0.13%. While ot
products allow this to range as high as 0.80%. Since these elements cannot be oxidized from th
steel, their content in the final product can only be reduced by dilution with very high purity scr
hot metal. The use of low residual hot metal in the BOS, with its inherent dilution effect, is one
features that distinguish BOF from EAF steelmaking.

iii) FLUXES

Fluxes serve two important purposes. First they combine with SiO2 which is oxidized from the h
metal to form a "basic" slag that is fluid at steelmaking temperatures. This slag absorbs and re
sulfur and phosphorus from the hot metal.

Lime (95+% CaO) and dolomite (58%CaO, 39% MgO) are the two primary fluxes. They are ob
by calcining the carbonate minerals, generally offsite in rotary kilns. Calcining CaCO 3 and MgCO
liberates CO2 leaving CaO or MgO. Two types, "soft" and "hard" burned lime, are available. A lu
soft burned lime dissolves quickly in a cup of water liberating heat. Hard burned material just s
there. Soft burned fluxes form slag more quickly than hard-burned, and in the short blowing cy
this is critical for effective sulfur and phosphorus removal. The amount of lime charged depends
the Si content of the hot metal.

In BOS steelmaking a high CaO/SiO2 ratio in the slag is desirable, e.g. 3. A rule of thumb is 6 X
weight of Si charged. The MgO addition is designed to be about 8 to 10% of the final slag weigh
This saturates the slag with MgO, thus reducing chemical erosion of the MgO vessel lining.

iv) COOLANTS

Limestone, scrap, and sponge iron are all potential coolants that can be added to a heat that ha
been overblown and is excessively hot. The economics and handling facilities dictate the selecti
each shop.

v) ALLOYS

Bulk alloys are charged from overhead bins into the ladle. The common alloys are ferromangan
(80%Mn, 6%C, balance Fe), silicomanganese (66%Mn, 16%Si, 2%C, balance Fe), and ferrosilic
(75% Si, balance Fe). Aluminum can be added as shapes and/or injected as rod. Sulfur, carbon
calcium, and special elements like boron and titanium are fed at the ladle furnace as powders
sheathed in a mild steel casing about 1/2 inch in diameter.

V REFRACTORIES
The basis for most refractory bricks for oxygen steelmaking vessels in the U.S. today is magnes
MgO, which can be obtained from minerals or seawater. Only one dolomite (MgO + CaO) depos
worked in the U.S (near Reading, PA). For magnesia, the lower the boron oxide content, and th
lower the impurity levels (but with a CaO/SiO2 ratio above 2 to avoid low melting point intergra
phases), the greater the hot strength of the brick. Carbon is added as pitch (tar) or graphite.




                                                                              8
The magnesia lime type refractories used in lining oxygen steelmaking vessels are selected ma
their compatibility with the highly basic finishing slags required to remove and retain phosphoru
solution. During refining, the refractories are exposed to a variety of slag conditions ranging fro
to 4 basicity as silicon is oxidizes from the bath and combines with lime. The iron oxide, FeO, co
of the bath increases with blowing time especially as the carbon in the steel falls below 0.2 % a
is oxidized. Although all refractory materials are dissolved by FeO, MgO forms a solid solution w
FeO, meaning they coexist as solids within a certain temperature range. The high concentration
FeO formed late in the blow, however, will oxidize the carbon in the brick.

The original bricks were tar bonded, where the MgO grains were coated with tar and pressed w
represented a great step forward for the BOS process. Tempering removed volatiles. In service
tar was coked and the residual intergranular carbon resisted slag wetting and attack by FeO. In
addition, as the tar softened during vessel heat-up, the lining was relieved of expansive stresse
strength was increased by sintering bricks made from pure MgO grains at a high temperature a
then impregnating them with tar under a vacuum. However, for environmental reasons these ty
of bricks are no longer used in oxygen steelmaking.

Today's working lining refractories are primarily resin-bonded magnesia-carbon bricks made wi
high quality sintered magnesite and high purity flake graphite. Resin-bonded brick are unfired a
contain 5% to 25% high purity flake graphite and one or more powdered metals. These brick re
a simple curing step at 350 to 400°F to "thermoset" the resin that makes them very strong and
therefore easily handled during installation. Further refinements include using prefused grains i
mix. Small additions of metal additives (Si, Al, and Mg) protect the graphite from oxidation bec
they are preferentially oxidized. Metallic carbides, nitrides, and magnesium-aluminate spinel fo
service at the hot face of the brick filling voids, and adding strength and resistance to slag attac

The rate of solution of a refractory by the slag is dependent on its properties. These properties
directly related to the purity and crystal sizes of the starting ingredients as well as the manufac
process. Additions of up to 15% high purity graphite to MgO-carbon refractories provide increas
corrosion resistance. Beyond 15% this trend is reversed due to the lower density of the brick.
Ultimately, the cost per ton of steel for brick and gunning repair materials, coupled with the nee
vessel availability, dictate the choice of lining.

The penetration of slag and metal between the refractory grains, mechanical erosion by liquid
movement, and chemical attack by slags all contribute to loss of lining material. Over the years
there have been numerous operating developments designed to counteract this lining wear:
i) Critical wear zones (impact and tap pads, turndown slag lines, and trunion areas) in furnaces
been zoned with bricks of the highest quality.

ii) "Slag splashing" whereby residual liquid slag remaining after the tap is splashed onto the lini
with high pressure nitrogen blown through the oxygen lance. This seemingly simple practice ha
increased lining life beyond all expectations, from a few thousand to over 20,000 heats per
campaign.

iii) Instruments are now available to measure lining contours in a short time period, to maximiz
gunning effectiveness using MgO slurries.

iv) Dolomite (40%MgO) is added to the flux addition to create slags with about 8% MgO, which
close to the MgO saturation level of the slag.

v) Improved end-point control resulting in lower FeO levels and shorter oxygen-off to charge
intervals have reduced refractory deterioration.



                                                                               9
None of the above would be significant however, without the improvements in quality and type
basic brick available to the industry.

Today, the refractory industry is undergoing major structural changes. Companies are being
continually acquired and the total number of North American suppliers is greatly reduced. A ver
percentage of refractory materials are being produced off shore, with China being the most
significant newcomer.

VI ENVIRONMENTAL ISSUES
Environmental challenges at BOS shops include: (1) the capture and removal of contaminants i
hot and dirty primary off-gas from the converter; (2) secondary emissions associated with char
and tapping the furnaces; (3) control of emissions from ancillary operations such as hot metal
transfer, desulfurization, or ladle metallurgy operations; (4) the recycling and/or disposal of col
oxide dusts or sludges; and (5) the disposition of slag.

In the U.S., most BOF primary gas handling systems are designed to generate plant steam from
water-cooled hood serving the primary system. About half of the systems are open combustion
designs where excess air is induced at the mouth of the hood to completely burn the carbon
monoxide. The gases are then cooled and cleaned either in a wet scrubber or a dry electrostatic
precipitator. The remainder of U.S. systems are suppressed combustion systems where gases a
handled in an uncombusted state and cleaned in a wet scrubber before being ignited prior to
discharge. In both cases, the cleaned gases must meet EPA-mandated levels for particulate ma

Suppressed combustion systems offer the potential for recovery of energy, a practice that is mo
prevalent in Europe and Japan. However, in the U.S., other than steam generation, no attempt
made to capture the chemical or sensible heat in the off-gas leaving the vessel. While this repr
the loss of a considerable amount of energy (about 0.7 million Btu/ton), the pay-back on capita
required, either for the conversion of open combustion to suppressed combustion systems or th
addition of necessary gas collection facilities for suppressed combustion systems, is over 10 yea
addition, the necessity of taking shops out of service to make these changes is not practical. M
BOF shops in the U.S. pre-date the energy crises of the 1970s, and even today, energy in the U
relatively less expensive than it is abroad.

Secondary fugitive emissions associated with charging and tapping the BOF vessel, or emission
escaping the main hood during oxygen blowing, may be captured by exhaust systems serving l
hoods or high canopy hoods located in the trusses of the shop or both. Typically a fabric collect
baghouse, is use for the collection of these fugitive emissions. Similarly, ancillary operations su
hot metal transfer stations, desulfurization, or ladle metallurgy operations are usually served by
hood systems exhausted to fabric filters.

The particulate matter captured in the primary system, whether in the form of sludge from wet
scrubbers or dry dust from precipitators, must be processed before recycling. Sludge from wet
scrubbers requires an extra drying step. Unlike EAF dust, BOF dust or sludge is not a listed haz
waste. If the zinc content is low enough, it can be recycled to the blast furnace or BOF vessel a
briquetting or pelletizing. Numerous processes for recycling the particulate are in use or under
development.

BOF slag typically contains about 5% MnO and 1% P2O5 and are often can be recycled through
blast furnace. Because lime in steel slag absorbs moisture and expands on weathering, its use a
aggregate material is limited, but other commercial uses are being developed to minimize the
amount that must be disposed.




                                                                             10
VII CONCLUSION
The BOS has been a pivotal process in the transformation of the U.S. steel industry since World
II. Although it was not recognized at the time, the process made it possible to couple melting w
continuous casting. The result has been that melt shop process and finishing mill quality and yi
improved several percent, such that the quantity of raw steel required per ton of product decre
significantly.

The future of the BOS depends on the availability of hot metal, which in turn depends on the co
availability of coke. Although it is possible to operate BOFs with reduced hot metal charges, i.e.
70%, there are productivity penalties and costs associated with the supply of auxiliary fuels.
Processes to replace the blast furnace are being constantly being unveiled, and the concept of a
hybrid BOF-EAF is already a reality at the Saldahna Works in South Africa. However, it appears
the blast furnace and the BOS will be with us for many decades into the future.

The American Iron and Steel Institute acknowledges, with thanks, the contributions of Teresa M
Speiran, Senior Research Engineer, Refractories and Bruce A. Steiner, Senior Environmental Ad
Collier Shannon Scott PLLC.


ADDENDUM

HISTORY OF THE BASIC OXYGEN STEELMAKING PROCESS

Basic Oxygen Steelmaking is unquestionably the "son of Bessemer", the original pneumatic pro
patented by Sir Henry Bessemer in 1856. Because oxygen was not available commercially in th
days, air was the oxidant. It was blown through tuyeres in the bottom of the pear shaped vesse
Since air is 80% inert nitrogen, which entered the vessel cold but exited hot, removed so much
from the process that the charge had to be almost 100% hot metal for it to be autogenous. The
inability of the Bessemer process to melt significant quantities of scrap became an economic
handicap as steel scrap accumulated. Bessemer production peaked in the U.S. in 1906 and ling
until the 1960s.

There are two interesting historical footnotes to the original Bessemer story:

William Kelly was awarded the original U.S. patent for pneumatic steelmaking over Bessemer in
1857. However, it is clear that Kelly's "air boiling" process was conducted at such low blowing r
that the heat generation barely offset the heat losses. He never developed a commercial proces
making steel consistently.

Most European iron ores and therefore hot metal was high in sulfur and phosphorus and no pro
to remove these from steel had been developed in the 1860s. As a result, Bessemer's steel suff
from both "hot shortness" (due to sulfur) and "cold shortness" (due to phosphorus) that render
unrollable. For his first commercial plant in Sheffield, 1866, Bessemer remelted cold pig iron
imported from Sweden as the raw material for his hot metal. This charcoal derived pig iron was
in phosphorus and sulfur, and (fortuitously) high in manganese which acted as a deoxidant. In
contrast the U.S. pig iron was produced using low sulfur charcoal and low phosphorus domestic
Therefore, thanks to the engineering genius of Alexander Holley, two Bessemer plants were in
operation by 1866. However, the daily output of remotely located charcoal blast furnaces was v
low. Therefore, hot metal was produced by remelting pig iron in cupolas and gravity feeding it t
5 ton Bessemer vessels.




                                                                            11
The real breakthrough for Bessemer occurred in 1879 when Sidney Thomas, a young clerk from
London police court, shocked the metallurgical establishment by presenting data on a process t
remove phosphorus (and also sulfur) from Bessemer's steel. He developed basic linings produc
from tar-bonded dolomite bricks. These were eroded to form a basic slag that absorbed phosph
and sulfur, although the amounts remained high by modern standards. The Europeans quickly
the "Thomas Process" because of their very high-phosphorus hot metal, and as a bonus, granu
the phosphorus-rich molten slag in water to create a fertilizer. In the U.S., Andrew Carnegie, w
was present when Thomas presented his paper in London, befriended the young man and cleve
acquired the U.S. license, which squelched any steelmaking developments in the South where h
phosphorus ores are located.

Although Bessemer's father had jokingly suggested using pure oxygen instead of air (U.K.paten
2207, Oct 5,1858), this possibility was to remain a dream until "tonnage oxygen" became avail
at a reasonable cost. A 250 ton BOF today needs about 20 tons of pure oxygen every 40 minut
Despite its high cost, oxygen was used in Europe to a limited extent in the 1930's to enrich the
blast for blast furnaces and Thomas converters. It was also used in the U.S for scarfing, and we

The production of low cost tonnage oxygen was stimulated in World War II by the German V2 r
program. After the war, the Germans were denied the right to manufacture tonnage oxygen, bu
oxygen plants were shipped to other countries. The bottom tuyeres used in the Bessemer and
Thomas processes could not withstand even oxygen-enriched air, let alone pure oxygen. In the
1940s, Professor Durrer in Switzerland pursued his prewar idea of injecting pure oxygen throug
top of the vessel. Development now moved to neighboring Austria where developers wanted to
produce low nitrogen, flat-rolled sheet, but a shortage of scrap precluded open hearth operatio
Following pilot plant trials at Linz and Donawitz, a top blown pneumatic process for a 35 ton ve
using pure oxygen was commercialized by Voest at Linz in 1952. The nearby Dolomite Mountain
provided an ideal source of material for basic refractories.

The new process was officially dubbed the "LD Process" and because of its high productivity wa
globally as a viable, low capital process by which the war torn countries of Europe could rebuild
steel industries. Japan switched from a rebuilding plan based on open hearths to evaluate the L
and installed their first unit at Yawata in 1957.

Two small North American installations started at Dofasco and McLouth in 1954. However, with
know-how and capital invested in 130 million tons of open hearth capacity, plans for additional
hearth capacity well along, cheap energy, and heat sizes greater by an order of magnitude (300
versus 30 tons), the incentive to install this untested, small-scale process in North America was
lacking. The process was acknowledged as a breakthrough technically but the timing, scale, and
economics were wrong for the time. The U.S., which manufactured about 50% of the world's to
steel output, needed steel for a booming post-war economy.

There were also acrimonious legal actions over patent rights to the process and the supersonic
design, which was now multihole rather than single hole. Kaiser Industries held the U.S. patent
but in the end, the U.S. Supreme Court supported lower court decisions that considered the pat
be invalid.

Nevertheless, the appeal of lower energy, labor, and refractory costs for the LD process could n
denied and although oxygen usage in the open hearth delayed the transition to the new proces
the U.S., oxygen steelmaking tonnage grew steadily in the 1960's. By 1969, it exceeded that o
open hearth for the first time and has never relinquished its position as the dominant steelmak
process in the U.S. but the name LD never caught on in the U.S.




                                                                            12
Technical developments over the years include improved computer models and instrumentation
improved turn-down control, external hot metal desulfurization, bottom blowing and stirring wit
variety of gases and tuyeres, slag splashing, and improved refractories.




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