NBSIR 82-2618 (A)

PROCESS CONTROL SENSORS

FOR THE STEEL INDUSTRY

Report of Workshop

Edited by

R. Mehrabian

R.L. Whitely

E.C. vanRsuth

H.N.G. Wadley

Sponsored by:

American iron and Steel institute

Defense Advanced Research Projects Agency

National Bureau of Standards

Hosted by:

- National Measurement Laboratory

National Bureau of Standards

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PROCESS CONTROL SENSORS

FOR THE

STEEL INDUSTRY

Report of Workshop

NATIONAL BUREAU OF STANDARDS

GAITHERSBURG MARYLAND

July 27-28, 1982

Contents

Process Control Sensors for the Steel Industry Briefing/ iv

Workshop Coordinating Committee

Introduction 1

Q Automatic Detection of Pipe and Gross Porosity in Hot Steel 4

Billets, Blooms or Slabs

On-Line Inspection for Surface Defects on Hot and Cold Strip 14

Rapid In-Process Analysis of Molten Metal 26

Rapid Measurement of Temperature Distribution within a Solid 32

or Solidifying Body of Hot Steel

i i i
Process Control Sensors for the Steel Industry Briefing/

Workshop Coordinating Committee

Process Control Sensors For the Steel Industry

Briefing/Workshop Coordinating Committee

Chairman: R. L. Whiteley, Bethlehem Steel Corporation,

Bethlehem, PA

Members: F. A. Achey, Bethlehem Steel Corporation,

Bethlehem, PA

W. E. Dennis, American Iron and Steel Institute,

Washington, DC

R. Mehrabian, National Bureau of Standards,

Washington, DC

J. B. Morgan, Allegheny Ludlum Steel Corporation,

Brackenridge, PA

C. D. Rogers, United States Steel Corporation,

Monroeville, PA

E. C. van Reuth, Defense Advanced Research Projects

Agency, Washington, DC

R. G. Watson, Republic Steel Corporation,

Cleveland, OH
Introduction

A Briefing/Workshop on Process Control Sensors for the

Steel Industry was convened and attended by 160 people

on July 27-28, 1982 at the National Bureau of Standards,

Gaithersburg, Maryland. It was sponsored by the American

Iron and Steel Institute (AISI), the Defense Advanced

Research Projects Agency (DARPA) and the National Bureau

of Standards (NBS). The aim of the Briefing/Workshop

was to first provide scientists and engineers in

industry, universities and government with specific

Process Control Sensor needs of the Steel Industry and

second, to seek immediate input and future research and

development involvement from a broad spectrum of

disciplines to facilitate development of sensors. This

report is the proceedings of the deliberations from the

Workshop portion of the meeting. The material was obtained from detailed notes and summaries given to us by the Recorders and Moderators of the four different

Workshop Task Groups.

The General Research Committee of the American Iron and

Steel Institute has identified the development of

Process Control Sensors as an area of research that

would have substantial impact toward improving productivity

and quality in the steel industry. On March 11, 1980,

the Committee directed the establishment of a Task

Group to formulate a plan of research and development

relevant to "process control and sensor development"

for the steel industry. The purpose of the plan was to

provide a basis for discussion with appropriate

organizations aimed at getting development and basic

research started on projects of interest. The Task

Group was established with representatives from thirteen

member companies.

1
On January 8, 1981, the Task Group issued a draft report

entitled "Steel Industry Priorities for Process Control

and Sensor Development". In this report they critically

evaluated sensor applications and needs across the

entire steel industry, and categorized then by type of

application relative to control and by their commercial

and technical availablity, and then prioritized them on the basis of need, significance and interest. In the

analysis, 35 steel processes were studied and 537

process control sensor needs were identified. Individual

member companies were asked to rank these needs as to

present availability, level of interest, and significance

for current and future operations. This ranking process

reduced the number of research needs to a list of 18

potential process control sensors that were considered

most significant. Of these, the AISI assigned top

priority to four specific sensor needs.

The four sensor needs established were:

I. Automatic Detection of Pipe and Gross Porosity in

Hot Steel Billets, Blooms or Slabs

II. On-Line Inspection of Surface Defects on Hot and

Cold Strip

III. Rapid In-Process Analysis of Molten Metal

IV. Rapid Measurement of Temperature Distribution Within

a Solid or Solidifying Body of Hot Steel

In August 1981, AISI Task Force Units were established

with the responsibility to start research work that

ultimately would lead to development of each sensor.

This resulted in the Briefing/Workshop reported here.

During the first day of the meeting, coordinated

briefings were given on the sensor needs of the steel

industry, the available technology, benefits and

information pertinent to relevant research. A

2
Workshop /Task Group format, organized by each of the

four task groups responsible for a specific sensor

need, took place in the late afternoon of the first day

and the morning of the second day to permit a wide

range of inputs from the attendees.

Two moderators and two recorders were assigned to each

Workshop Task Group. Each Task Group had previously

prepared a list of questions for the Workshop and

speakers had been assigned to initiate discussion on each question with a five to ten minute presentation,

thus opening avenues for further deliberations. At the

end of the apportioned time for each question, the

Moderators summarized the conclusions and recommendations

emanating from the discussion and moved onto a new subject.

s>

3
Automatic Detection of Pipe and Gross Porosity in

Hot Steel Billets, Blooms or Slabs

The objective is the detection of primary pipe, gross

porosity and fishtailing in hot primary rolled materials

and to provide a map showing such anomalies for use during cropping.

Moderators:

Recorders:

Speakers:

R. C. Booth, Bethlehem Steel Corp.

R. E. Green, Jr., Defense Advanced Research

Projects Agency

M. Rosen, Johns Hopkins University and

National Bureau of Standards

E. A. Upton, Jones & Laughlin Steel Corp.

J. M. Lude, Inland Steel Co.

R. C. Booth, Bethlehem Steel Corp.

B. Maxfield, MEA California Ltd.

C. M. Fortunko, National Bureau of Standards

R. Hyatt, Battel le Columbus Labs.

G. A. Alers, Magnasonics Inc.

R. E. Green, Jr., Defense Advanced Research

Projects Agency

4
1. What form does pipe take in ingot cast materials

vs. porosity or secondary pipe? What are other

characteristics of hot blooms and slabs that may

influence a test for internal discontinuities?

• Primary pipe is formed at the top of an ingot due

to solidification shrinkage. Its surfaces are frequently oxidized and do not weld on rolling.

This pipe must be cropped from a bloom.

• Voids can also be generated by shrinkage deep

within the ingot. This is termed secondary pipe.

It is not exposed to oxygen and welds shut on

rol ling.J a

• Molten steel contains dissolved oxygen which

combines with carbon forming CO and porous zones,

often at the top of an ingot, on solidification.

If the surfaces of the pores are unoxidized they

weld shut on rolling. The gas content of molten

steels is much less in semi -killed or killed steels

compared with rimmed or mechanically capped product.

• During rolling, the outer surfaces of the slab

deform more than the center, forming a defect

known as mechanical pipe or fishtail. This defect

has to be cropped prior to further processing.

t A sensor system must be able to identify pipe and

fishtail and locate its position to within 1" in

slabs up to 12" thick. It should also be capable

of locating pores greater than 3/8". Inspection

should take less than 30 seconds and the technique

must be able to work on material at a temperature

of 1900 - 2500°F.

5
2. What are the likely benefits and/or possible

shortcomings of each "contact" method?

• With an ultrasonic sensor, elastic waves introduced

into a slab or bloom are reflected from pipe and are detected as echoes that arrive back at the

sensor before the echo from the backside of the

slab or bloom. The echo signal may be weak, and

could be obscured when the grain size is comparable

with the wavelength of the elastic waves because

of grain scattering. Signal to noise might be

improved by working at low frequency (longer

wavelength, but this reduces resolution), or by

delaying inspection until after primary rolling

when the coarse cast structure h*as been broken down.

• The most critical problem with using ultrasonic

techniques is coupling a transducer (that must

remain cool) to a hot steel bloom or slab. Attempts

have been made to use momentary (or rolling)

contact in a number of steel mills in the U.S.

and abroad.

• Poor coupling efficiency, due to surface roughness,

can be overcome by the application of a high

pressure to the transducer. The amount of pressure

required will vary with steel temperature and

grade. Some denting of the surface is likely to occur but provided dents are shallow (< 1/8") they

should pose no problem. Further coupling efficiency

increases and vital thermal protection of the

sensor (to provide mechanical reliability) can be

achieved by using a water or liquid spray couplant.

However, this may be detrimental to steel quality.

6
• The requirement that a substantial portion of the

product area must be tested to both identify pipe

or porosity and to determine a cropping point is

not compatible with the discontinuous nature of

the contact test. Using the momentary contact

method, the transducers ) (or product) need to be

moved rapidly betwen pulses and a large number of

pulses might be necessary. Developing a mechanical

system that is reliable and rugged to provide the

transducer scanning required is expected to be

difficult.

7
3. Electromagnetic acoustic transducer (EMAT) technology

seems to offer potential for noncontact testinq

of hot products, but present techniques require

the transducer to be relatively close to the

surface. What can be done to improve signal -to-noi se ratios and get the transducers further from the

surface? What are the fundamental limitations

affecting transducer positioning? What techniques

night be employed to help an EMAT survive in the

hot inspection environment? Are there safety

considerations if high power is involved? How

does steel grade influence test sensitivity?

• The si gnal -to-noise ratio nay be improved by:

inpedance matching, reducing bandwidth, increasing,

magnetic field strengths (to 6-10 kG), increasing

the number of coil turns (but this could result in

higher voltage levels) and increasing the drive

current. Surface roughness decreases the efficiency.

Signal averaging should also improve S:N.

• Sensitivity decrease due to lift-off from the

specimen, can be compensated for by increased EMAT

size, a higher drive current and a restricted bandwidth.

• The EMAT may not be as intense a source of elastic

waves as say thermoelastic generation with the

pulsed laser, but its sensitivity as a detector

may be greater than that of a laser interferometer.

• EMATs can be used at tenperatures up to 1000°F with

minimal shielding. Higher temperature operation

would require development of radiation shields.

• A practical system utilizing a single scanned

transducer is likely to cost Si 00,000.

8
4. EMA transducers typically are not "pure-node"

devices in that both shear and longitudinal waves

nay be generated with various angles of incidence.

Is that a serious problem? Can it be overcome in

a practical inspection system?

• EMA transducers generate both longitudinal and

shear waves. The theory of generation is now fairly well established and a design could be made

that was optimal for a particular application.

The generation of both wave types is thus not a liniting problem and it can be overcome through

sensor design.

• Departure of EMA transducers from ttfeir theoretical

characteristics can be caused by non-ideal magnetic

field patterns. For a high temperature transducer

it is likely the magnets would be pulsed electromagnets. The resulting pulsed fields would further

contribute to variations in magnetic field patterns

and to loss in predictability of transducer

performance.

• Higher electrical resistivity of steel at elevated

temperature will lower EMAT sensitivity because of

decreased eddy current flow.

9
5. Lasers are reportedly being used for both remote

generation and reception of ultrasonic signals.

What are seen as the limitations of this technology

in terms of power levels needed and resolution to

detect small flaws in a relatively large product

as is being discussed here? What are the limitations

in pulsing rate and how will this affect the time

required to complete testing on each bloom/slab?

• The amplitude of the elastic waves generated by a pulsed laser increases with flux. For a given

flux, the amplitude decreases approximately as 1/r

because the source radiates spherically. The flux

required will therefore depend on:

a. The smallest signal detectable with a detector.

b. ' The size defect to be detected.

c. The distance travelled by the elastic wave

from source to defect to detector.

• For moderately sensitive detectors and large

defects up to several inches within a plate a flux

of 1-10 MWcm“2 i s probably sufficient. This

translates into a laser pulse of 200 mJ deposited

onto an area of 0.5 cm^ in a time of 20 x 10 _9

s assuming a reflection coefficient of 0.5.

• For practical applications pulsed solid state

(such as Neodymium YAG or glass) or gas (such as CO2 ) lasers have adequate energies. They are able

to be pulsed with repetition rates of 10-20 pulses

per second and their energy can be varied

continuously.

10
• Laser interferometers are being developed in many

different forms and with gradually improving

sensitivity. Krautkramer* (Germany) has developed

a laser i nterferometer that might be able to cope

with the steel mill environment and because of

this, remote positioning nay be preferable to an EMAT detector.

• Problems that must be addressed with the laser

approach are dust and water vapor in the optical

path, safety, laser reliability, surface effects

and engineering for implementation.

• Krautkramer has developed a laser pulsinq/i nterferometric receiving system intended for use on hot steel. They use an 80 MW power YAG laser

pulsing at 50Hz. Although no problems have been

encountered with dust and water vapor in the area near the product to be tested, they stress the

need to keep the system optics clean. Also problems

could be encountered in laser reliability and cost

due to the high power used.

*See note of disclaimer on last page.

11
6. To increase EMAT sensitivity, it nay be useful to

cool the hot surface to just below the Curie

temperature. What are the implications of this

technique?

• The magnetostriction effect (which only occurs

below the Curie temperature) can be used to enhance

the efficiency of an EMAT.

• To use this approach, the French have used water

cooling to reduce surface temperatures to just

t below the Curie temperature (~1100°F). Such

cooling could create material problems and the

steel industry would probably prefer a device that

operated satisfactorily between 1900-2500°F.

12
7. What techniques, other than those discussed, might

be considered for detecting pipe or gross porosity

in hot steel?

• Penetrating radiation, such as neutrons or x-rays,

could be used for radiography or CAT scanning.

They pose very significant safety problems however.

t General Electric (GE)* has developed a laser based

acoustic emission system for detecting acoustic

emission events in electric power turbine rotors.

The GE system uses a split laser beam which is

reconverged optically on the detection surface.

Speckle patterns resulting from (a) surface

roughness and (b) surface movement caused by

ultrasonic vihrations are detected by a photo

detector. Doppler shifts are used to detect

ultrasonic signals.

• The GE system is useful on rough surfaces and

could therefore be readily used on primary steel

products. Detection capability is reported to be

5-1 OA displacement. To put such numbers into

context, the Krautkramer pulsed laser is capable of

creating a 100A displacement back wall echo at

the detection surface.

• J. L. Morgan (Scientific Measurement Systems,

Inc.*) described a y tonography technique that has

the potential to detect 0.02" defects through 12"

steel slab/bloom in about 10 s. It would cost

about $500,000 to implement. The system uses a fan beam of y rays up to 90° wide with an array of

2 mm wide plastic scintillation counters as detectors.

*See note of disclaimer on last page.

13
On-Line Inspection for Surface Defects on Hot and

Cold Strip

The objective is the detection, characterization and

classification of surface defects on hot or cold strip

for quality control during processing operations. The

sensor system must:

a) Have a high speed sensing capability because

strip speeds of up to 6000 fpm are possible.

b) Be capable of better defect classification

than is presently available.

c) Be able to handle very large quantities of

data and reduce them for on-line decision making.

d) Operate in the severe mill environment with

variable production conditions.

e) J3e economically justifiable, cost less than

$0.1 - 0.2M per line.

Moderators

:

Recorders:

Speakers:

R. A. Sylvester, Jones & Laughlin Steel

Corp.

H. T. Yolken, National Bureau of Standards

R. B. Clough, National Bureau of Standards

S. Moore, Empi re-Detroit Steel Division

M. Conrad, U. S. Steel Corp.

D. Watanopongse, Inland Steel Corp.

T. W. Judd, Republic Steel Corp.

G. L. Neiheisel, Armco, Inc.

W. A. Wilson, National Steel Corp.

14
1 To what extent is it necessary to characterize

defects (identify as seam or scab, length, width,

depth; raised or sunken in strip) and to outline

the defect boundary?

• Whether a defect is detrimental or not depends on the sheet's intended use. On-line inspection for

surface imperfections must be performed early

enough in the processing route to classify the

product for a particular end use. Diversion of

less than prime product or misdirection of

incorrectly classified product directly affects

product yield and steel processing costs.

• Surface imperfections must be defined and

characterized before a method or equipment capable

of detecting, characterizi ng and classifying surface

imperfections can be developed.

• There are basically three classifications of

surface defect:

a) Linear

b) Area

c) Miscellaneous and intermediary

Linear defects are narrow and long, the width

dimension being as small as 0.03" and the length

extending several feet in some cases. Examples

would be scratches, roll marks and seams. Area

defects may be either single or occur in groups of

the same type of imperfection. A single defect

may be as small as 0.03" in diameter, but groups

may extend over several square inches of surface

or even several square feet. Examples would be

slivers, laps, scabs, holes and scale. Miscellaneous

and intermediary types of defects include those

15
caused by Mechanical damage, edge defects (cracked,

wavy, damaged and breaks) and gouges. In general,

although they are gross defects, their detection nay be

complicated by their location.

• It is desirable to detect defects as early, during

processing, as possible consistent with accessibility

to the sheet. The lower limit for detection should

be about 0.03'', but may be limited by factors such

as sheet velocity.

• Classification of defects should distinguish

anomalies (e.g. liquid drops) from true defects.

Pattern recognition nay be used to develop decisionmaking rules and deduction of defect origin for

feedback control of processing variables. At the

very least, a system should give a go, no-go

decision.

16
2. How well nust the defect be located?

• Briefly, a desirable requirement would be to

locate a 30 mil defect to ± 1/4" in the width

direction and ± 12" in the length direction on

a 5 mile coil processed at 6000 feet per minute.

The sheet width could be 20-80" and thickness 1/4"

(hot rolled) to 0.006" (cold rolled).

t Defect location is important in:

a) Slitting

b) Diversion of defective strip portions

c) Correction of processing to eliminate future

defects (e.g. roll defects)

9 In practice it would be desirable to locate all

defects but it is likely only a part of the

information would be used for each particular

operation.

• Consumers currently tend to inspect the first 150

feet of rolled sheet coil and reject the entire

roll if this front end is defective enough.

17
3. How important is it that inspection results be

obtained in real-time?

• The advantages of real-time inspection are:

a) Diversion of products with unacceptable defect

concentrations can be used to avoid subsequent

processing costs and minimize bottle necks.

b) Implementation of immediate corrective actions

to processing procedures to eliminate further

defects.

c) Reinspection either manually or at a slow

speed to accurately characterize defects.

d) An aid to production scheduling so costly

inventories can be kept to a minimum.

• It is imperative that inspection results be in

real-time to allow immediate decision makinq by the

mill operator.

• If signal processing speed is a limiting factor in

providing real-time information, then it would be

desirable that some immediate indication of a defect

be provided to the operator, followed, up to a few

minutes later, with the detailed characterization

(type, size, location,...). Finally, a hard-copy

of the inspection results is certainly required,

though not in real-time.

• The minimum information for decision making should

be supplied to a mill operator. His experience

may enable quicker judgements to be made than would be

made by relying entirely on computer-based decisions.

It is not clear what information should be given.

Perhaps a percentage of the width with defects, or some visual display. The latter might be particluarly

useful since one of the most effective current

18
methods is to use the eye of an operator and some

TV display.

• The sensor system can be verified and calibrated

by running a standard sheet of known defects

through the system.

19
4. What constitutes an undesirable defect? How do

you distinguish it from conditions that are not

detrimental?

• There are no industry-wide standards and one of

the major problems with current process NDE is to

distinguish detrimental and harmless defects. This

categorization depends both on the ultimate

application for sheet product and the economics of

product over-rejection.

• Harmless defects include drops of water, light

stains, grease and residual rolling lubricant.

They are difficult to distinguish between detrimental

and harmful defects at present. When an imperfection

becomes severe enough to degrade the end use of

the product, then it is considered a defect.

Since the defect criterion is one of the product

suitability, it is product dependent. Therefore,

a condition which may be a defect on cold rolled

strip may not be a defect on hot rolled material.

t Novel NDE approaches worth considering for defect

characterization are ultrasonics and acoustic

emission utilizing EMAT's or laser i nterferometers.

Optical methods (particularly, laser scanning) are probably the most effective presently. Some hybrid

approach may give’ the best defect categorization

ultimately, particularly in combination with

adaptive learning.

20
5. Can inspection locations be limited in order to

minimize environmental, temperature, speed, etc.

requi rements?

• Inspection locations can be limited to minimize

environmental, temperature, speed and stress

requirements. Many, if not most, of the defects

probably originate in the melt and during

solidification. It would be highly beneficial to

detect them at this point. Also, since strip

speed increases as it passes through the mill,

there might be both economic (less wasted processing)

and practical advantages to early location of defects.

• Pfobably the most desirable location from an economic standpoint is at the temper mill. This

is the last operation for uncoated low carbon

steel and is the last opportunity to prevent defects

from entering the customer's plant. There are environmental problems associated with this line:

very high line speed (e.g. 30 m per second), limited

space and danger from wrecks. However, because of

the economic implications, this is a must location

for some kind of inspection device.

21
6. Are separate inspection techniques or systems

required to evaluate the different surfaces

encountered in steel processing (such as dull,

bright or roughness variation)?

• Background reflectivity conditions represent a serious consideration in the design of an optimum

surface inspection system. Dull surfaces scatter

light in a diffuse or non-specular manner. Polished

surfaces however, give specular reflection. These

result in different intensity light source

requirements and variations in the optimal angle

of observation.

• Alternative techniques suoh as holography might be

difficult to implement because the sheet is moving,

vibrates and is in an extreme environment. The

ultrasonic method utilizing scanning lasers and

interferometric detectors or acoustic emission also

must overcome these problems.

7. Is inspection of both surfaces of the strip necessary?

• Generally speaking, inspection on both sides of

the strip is desirable. However ultimately the

question is determined by accessibility, economics

and ultimate product use.

22
8. What is the importance of economics in considering

an inspection system?

• NDE systems in rolling mills have to pay for

themselves. They do this by minimizing the amount

of material that must be reprocessed and the

elimination of excess trimming. A third consideration

is customer claims and buyer confidence.

• It is impossible to ascertain the loss due to

creation of poor business relations caused by the

selling of a product which is anything but "zero

defect". Typical penalties of $60,000 per month

are encountered for cold rolled product shipped

with surface defects and slivers. It has been

estimated that $50 million in annual savings

(through increased productivity and reduced cost)

could result if suitable sensors were developed.

• Consider an example problem occurring at all tandem

mills. Specifically, the surface inspection system

is to detect repetitive mi 11 -produced surface

defects. These flaws will occur for a time with

some periodicity related to roll circumference.

The surface inspection system logic will indicate

the stand containing the damaged roll to facilitate

the elimination of the problem. The alternative

to this automatic detector is to take every third

coil leaving the mill, unwrap the coil, and visually

inspect for repetitive defects. With this manual

inspection, as many as three coils are affected

whenever a mi 11 -produced defect is found.

A principal example of financial rewards by

eliminating costly further processing of defective

material is surface inspection at the exit of a pickle line. This example is based upon typical

23
data taken during a six-month period in the year 1967.

Obviously, the savings based upon present operating

cost is significantly higher. The analysis is

restricted to the savings obtained by diverting

coils from a tinplate product to a galvanized

product due to surface imperfections.

Coils are visually inspected on both surfaces with

the assistance of mirrors as they leave the pickle

line. This visual inspection is somewhat effective

with regard to gross surface defects. However,

present-day pickle line speeds make it difficult

to detect minor surface defects which may also be

indicative of major sub-surface defects.

Coils which are rejected for defects at pickle

line inspection are diverted to galvanized orders

and scheduled through the proper tandem cold

rolling mills to achieve the desired galvanized

gauges. Experience has shown that coils with

surface defects which would result in unacceptable

tinplate products produce acceptable prime galvanized

coils or sheets.

The difficulties mentioned with regard to line

speed and surface defects result in rejections at

inspection at the end of the electroplater.

"Lines" and "slivers" produce unacceptable surface

quality and result in the rejection of a substantial

number of coils and units.

For the six-month period of 1967, an average of

1,000 tons per month of tinplate products were rejected for steel defects. This tonnage would

have been diverted at the pickle line to prime

galvanized coils if these defects had been detected.

24
Savings of $100,000 per nonth would have accrued

from:

a) The cost differential between processing

these coils through the tin line versus the

galvanizing line.

b) The selling price differential between

galvanized prime coils and reject tinplate.

c) Profit on additional yield from the tin line

by replacing the diverted coils with prime

tinplate coils.

An additional $25,000 per month from reductions in

lost tine and roll shop costs would have brought

the total DOtential savings to $125,000 per nonth.

25
Rapid In-Process Analysis of Molten Metal

The objective is develoDnent of a system for the rapid,

in-process chemical analysis of molten iron and steel

for compositional control during ooerations such as: refining in BOF vessels, and ladles, melting in elecric

furnaces and casting. Elements to be analyzed include

carbon, nanganese, phosohorous, sulfur, aluminum, silicon,

copper, nickel and chromium. When develooed, the

instrumentation could be used to:

0 Provide continuous iron conDOsition during blast

furnace casting.

0 Provide rapid analysis of the steel bath during

the refining process.

0 Monitor sulfur removal and avoid overtreatnent

during desulfurization of liquid iron and steel.

0 Assure neetinq Requirements for ladle treatment processes.

0 Optimize trim additions in the ladle.

0 Make ladle tests while ingot teeming.

0 Monitor the composition of metal going into the

continuous caster.

0 ODtinize alloy additions in vacuum deaassinq.

Moderators: H. C. Oil worth, Amco, Inc.

Recorders

P. A. Stoll, U.S. Steel Corp.

T. J. Ribble, Inland Steel Co.

Soeakers:

?. J. Blau, National Bureau of Standards

R. J. King, U.S. Steel Corp.

H. C. Hardee, Sandia National Lab

J. S. Beaty, Fisher Scientific Co.

C. L. Herzenberg, Argonne National Lab

J. Devoe, National Bureau of Standards

26
1. What restraints are imposed by the steel nakinq

environment upon in-process chemical analysis?

• The interval between analyses during compositional

adjustment ideally should be about one minute.

This could be most critical for carbon adjustment

toward the end of an oxygen blow using the BOF

technique.

• The analysis must be made in the hostile environment

of a turbulent molten steel pool where temperatures

of 3500-3800°F are encountered. If some kind of

probe is used, it must be efficiently cooled.

i • Large concentration gradients can occur in the

melt. The technique should be able to account *or

these.

• The "off-gas" chemical analysis technique has

already been demonstrated inadequate for this

problem.
2.

What instrumental designs are required for a sensor

to survive high temperatures and hostile environments?

• Four basic approaches are available:

1. Transient techniques which take samples (for

off-line analysis) using cheap, destructable

probes.

2. Active probe cooling using water or gas.

3. Thermal insulation of the probe.

4. The use of ceramic probes able to withstand

high temperature.

•

' Disposable cardboard shielded probes are in use today and give reasonable performance. Disposable

probes should cost $15-20 each to ensure cost effectiveness.

• There may be problems of poor thermal shock

resistance with ceramic probes although a watercooled steel probe with alumina lining is currently

being evaluated at Lehigh University.

• The least hostile environment where a chemical

analysis sensor would be useful is ladle metallurgy

process control and there might be some merit in

tackling this problem first.

28
3. How can a molten steel bath be analyzed by emission

spectrochemi cal methods?

• Because of the extremely hostile, corrosive, high

temperature and mechanically violent environment,

and because in the BOF slag is emulsified with the

steel, sampling is a fundamental problem that must

be addressed.

• The spark discharge technique may be difficult to

implement directly into the furnace due to likely

variations of the spark-source gap and optical

component fragility.

• Generation and transport of an aerosol is a more

encouraging approach. Aerosols representati ve of

bulk composition have been produced and transported

as far as 100 ft. A problem here, however, is the

time lag in making an analysis, particularly

critical for the BOF technique.

• Analysis precision depends upon effective elimination

of slag contributions to spectra (less of a problem

for ladle composition control), careful instrument

calibration and the development of predictive

models to minimize time lag effects.

29
4. Are nuclear techniques useful for analyzing molten

metal durinq processing: What are their advantages

and limitations?

• A great variety of nuclear techniques are now available for determining the concentration of

elements such as C, Mn, P, S, Si, etc. A combination

of these could, in principle, be used to deduce

the composition of a sample of steel.

• Analysis, using existing methods, would take about

5-10 minutes. This is controlled by counting

statistics and therefore depends upon source

intensity and element concentration.

• Transportable radiation sources, such as Californium,

are available, though expensive. Detectors, such

as cryogenical ly cooled Ge, each cost upwards of

$50,000.

• These techniques pose a significant safety hazard.

It is unclear if the precautions needed to guarantee

safety would exclude application of these methods.
5. What are the possible applications of laser

technology to in-process analysis of molten metal?

t A short duration (10-20 ns) laser pulse with an intensity of 10^-10^ Wcrr^ wi 1 1 evaporate (ablate)

the surface of a metal. The vaporized metal could

then be analyzed.

t Further laser radiation of the metal vapor could

excite x-ray emissions whose energy are characteristic

of the elemental composition.

t High background, near a molten metal surface,

would preclude direct analysis, but Ar or He streams

could be used to transport the vapor to a more

suitable analysis location.

• An exploratory study to establish feasibility is

required. Additional problems to be addressed

include the susceptibility of laser optical

components to vibration and the safety hazard

associated with class IV laser systems.

31
Rapid Measurement of Temperature Distribution

within a Solid or Solidifying Body of Hot Steel

The objective is the development of a system for the rapid,

direct measurement of temperature and temperature distribution

within a solid or solidifying body of hot steel. The sensor

should ultimately be capable of measurements in the hostile

environments associated with a variety of production facilities

such as continuous casters, reheat furnaces, ingot soaking pits

and annealing furnaces.

The "ideal" sensor would measure temperature within ±10 C over

a temperature range of BOO to 1350 C without the need to

physically contact the sample. It should also take only a few

seconds to provide the temperature distribution and be insensitive

to the presence of combustion gas products or* of nearby sources

of heat greater than the temperature being measured. Sensors

for "specific" applications might not have to match all

the specifications of the "ideal" sensor.

Moderators: V. V. Horvath, Bethlehem Steel Corporation

* K. G. Kreider, National Bureau of Standards

Recorders: R. G. Rudolph, IJ. S. Steel Corporatin

H. N. G. Wadley, University of Maryland/National

Bureau of Standards

Speakers: H. Pielet, Inland Steel Corporation

D. P. DeWitt, Purdue University

J. R. Cook, Armco Steel Corporation

H. N. G. Wadley, University of Mary land/National

Bureau of Standards

K. G. Kreider, National Bureau of Standards

.J. W. Chang, The Foxboro Company

R. G. Watson, Republic Steel Corporation

32
1. How might the internal temperature distribution

sensor be applied in various steel processing

operations?

• During continuous casting, liquid metal breakouts

can arise should the partially solidified stand be

withdrawn too rapidly. Normal variations in a number of other casting parameters make low casting

speeds necessary. Casting problems can also occur

due to irregular solidification within a strand.

If sensors were available to measure temperature

distribution within the solidifying strand, it

would enable the shell thickness and heat removal

rate to be continuously monitored and used for

feedback control. .The sensors would have to

withstand an extremely hostile environment with

hot steam, high temperature and occasional sprays

of molten steel.

• In a reheat furnace, steel slabs with unknown

initial temperature states are heated for rolling.

Extended soaking to insure a uniform heat condition

is wasteful of time and energy. A sensor to

measure temperature distributions before, during

and after heating would provide needed information

permitting savings in both areas. A contacting

sensor must survive the hostile environment of the

furnace and be insenstitive to oxide layers. A

noncontacting sensor must additionally be unaffected

by dust and flames within the furnace.

• The spatial resolution needed will depend upon the

particular application. For control of continuous

casting, a resolution of ±2 mm and ±10 C would

be advantageous, whereas for a reheat furnace, a reading of the minimum internal temperature could

be sufficient.

33
• The needed frequency with which temperature

distribution is measured (temporal resolution)

reflects the application. In continuous casting,

a continuous observation of temperature distribution

is desirable; in the reheat furnace, periodic

measurements would be sufficient.

• The use of computer models to predict temperature

distributions have been only partially successful.

Direct measurement of temperature distribution,

even at a coarse resolution, would greatly aid in

adjusting heating models to changes in the heating

situation.

34
2. What are the capabilities and limitations of

conventional methods for measuring the temperature

of solids at their surfaces and within their

i nterior?

• Thermocouples have been used both for surface and

limited interior temperature measurement. They

have unsatisfactory resolution, are mechanically

fragile and require elaborate precautions to

survive the reheat furnace environment.

t The absence of a well-defined set of emissivities

for hot steels is one problem with radiation

thermometry. The emissivity of clean steel is

• typically 0.4 - 0.5 depending upon composition.

This rapidly increases to 0.8 when a thin oxide

layer forms. Further increases with increasing

thickness are then small until surface roughness

develops when the emissivity increases towards

0.95.

t Loose surface scale poses an additional problem

because of its poor thermal coupling to the

substrate. Thus, it undercools or superheats

during cooling/heating treatments leading to gross

error in deduced substrate (surface) temperature.

• Reflected radiation from furnace walls and

atmospheric absorption associated with combustion

fuels are additional sources of i naccuracy . wi th the

radiation thermometry technique.

• Radiation thermometry only measures surface

temperature. However, it may be possible to

measure the rate of change of surface temperature

to deduce a thermal profile. In essence this is

the solution of the thermal diffusion equation

using the surface temperature, and rate of change

of temperature as boundary conditions. Unambiguous

solutions probably also require the (unknown)

thermal history.

35
3. To what extent can these techniques, in combination

with computer models, be used to infer temperature?

• Experience has indicated models based upon physical

insight give the best results.

• Models alone, however, are not sufficient due to

lack of knowledge of the extent of changes in

heating variables. A more powerful approach is to

combine computer models with actual measurements.

• The combined approach could be improved with better

high temperature (> 1800 F) thermal property data

(thermal conduction, heat capacity and heat of

fusion), improved values for heat transfer

coefficients and more accurate surface temperature

measurements.

• The computer models now being used are constructed

from a set of assumptions and often supported by

few actual temperature measurements. Using sensors,

the fewer the assumptions and the better will be

the precision of predictive computations. Even a sensor capable of average temperature measurement

could provide a useful check on model predictions.

36
4. What principle phenomena and/or material properties

of steel undergo a change with temperature? What

techniques are available for monitoring these changes?

t While many physical properties are temperature

dependent, it is worthwhile to concentrate upon

those for which nondestructive, hopefully

noncontacting measurements in hostile environments

can be made. Three basic phenomena can be

considered:

a. Change of elastic constants

b. Thermal expansion

c. Change of phonon distribution

• Elastic constant changes can be measured by

monitoring ultrasonic velocity. This could give

the surface temperature (longitudinal/transverse

waves) and the temperature field using computerized

tomography.

• Ultrasonic velocity can, in the laboratory at least,

be measured using noncontacting laser generation/detection

and EMAT techniques. The effect of surface oxide

layers is one problem that must be addressed if

these approaches were attempted in the mill.

t Thermal expansions can be measured directly as lattice parameter changes using X-rays (or laser

interferometry or holography) or indirectly, as density changes, using y or neutron radiography,

to give average temperature.

0 Changes in phonon distribution could possibly be detected

by measuring the energy distribution of thermal neutrons

that have traversed a hot steel body (provided the

capture cross section is not too high) or by

measurement of electrical resistivity using eddy

current methods, to give average temperature.

37
A

J

5. What are the relative merits and prospects for the

various technologies that have been considered?

)

t Acoustic velocity measurements are advantageous

for the measurement of temperature profile because

of the penetrating nature of elastic waves, the

ability to use tomography to deduce temperature

distributions and the availability of EMATs and

laser techniques to generate and detect the elastic ") waves.

• Further work on the acoustic velocity technique is

required to provide basic information about velocity

changes due to microstructure, preferred orientation

and residual stress as a function of temperature.

• Unresolved issues are the durability of acoustic

velocity sensors, their resolution due to scattering

by microstructure and scale and the influence of

phase transformations ( y a ).

• Thermal expansion coefficients can be measured by

laser techniques with considerable precision and

this could provide a noncontacting rapid method

for deducing average temperature. Density

determinations using x or y-ray radiography

suffers from severe safety hazards.

• Electrical conductivity techniques are basically

near surface techniques (within a few inches).

Multifrequency techniques have been used to deduce

profiles down to 4" and have been applied to

continuous casting.

• At high temperatures (above 1500 C), resistivity

is, in the main, dominated by phonon scattering

and compositional differences are not too important

38
until one gets to very high alloy concentrations

(of the order to 30%). At lower temperatures,

resistivity is very sensitive to microstructure

and, indeed, has been used to monitor precipitation

of intermetal 1 ic phases (e.g. , the sensitization

of austenitic stainless steels can be observed).

• If only the position of a liquid-solid interface

is required (and no temperature data), for example,

during continuous casting, pulse echo ultrasonics

and y radiography show much promise.

• Battel le Northwest, under DoE funding, has reviewed

various approaches to measurement of thermal state.

Because they were interpreted in a longer term basic

study that would have generic benefits, they have

recommended the laser generation of ultrasound

coupled with computer tomography as the best choice

for a temperature distribution sensor.

39
6. What other applications outside the steel industry

are there for an internal temperature sensor?

• The most obvious application might be to the

processing of nonferrous alloys. Other applications

might be the manufacture of cement, semiconductor

crystal growth, hot isostatic pressing and, perhaps,

during the manufacture of glass. However, in none

of these applications is the sensor likely to make

such a revolutionary impact as in the steel industry.

7. What steps should be taken to stimulate the

development of a sensor to measure internal

temperature?

• There is a clear financial incentive (productivity

improvements valued at $275 million annually) for

the development of a thermal distribution sensor. Laboratory studies are required to establish

correlations between physical properties and

temperature and to demonstrate the feasibility of

internal temperature measurement.

• AISI seeks to develop a research program and

therefore solicits research proposals. These

should be no more than two pages in length and

contain brief statements, on the approach to the

problem, background information, work proposed,

time required and funding needs. They should be

sent to AISI headquarters irl Washington to the

attention of W. E. Dennis.

40
DISCLAIMER: Certain trade names and company products are mentioned in the text in order to adequately specify

the experimental procedure and equipment used. In no case does such indentification imply a recommendation

or endorsement by the National Bureau of Standards, nor

does it imply that the products are necessarily the

best available for the purpose.