in-situ m'graphy-a technique_090814 (f)

8/11/2019 In-situ M'Graphy-A Technique_090814 (F)

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sta e. ne can %oresee correcti'e measures )ased on the result o% in&situ metallo raphy andhence it is an important tool %or continual impro'ement o% %or ed roll


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Bepth o% hardenin depends on the usa)le diameter o% the roll. I% it is more than usual, rollmay %ail trans'ersely into multiple pieces. :ardenin parameter should )e okay %or the si+e o% the roll and the pyrometers should )e ell cali)rated to a'oid this kind o% %ailure. To 'eri%ydepth o% hardness Tayo occasionally does step )y step machinin on a test roll to esta)lish ahardness pro%ile and the hardenin parameters. 7d e crackin ? spallin o% a %or ed roll durin

hardenin process is also a common phenomenon i% steel is not clean or there is machininmarks at )arrel ed es not remo'ed.

hen a %or ed roll is hardened and tempered ithout any pro)lem (i.e. no crack? spall? )urstin $, there may )e issues ith the le'el o% hardness achie'ed. hardenin mana er al ays puts his e%%ort to achie'e ma-imum hardness durin induction hardenin processirrespecti'e o% hardness speci%ication o% the customer. *inimum temperin temperatureensures release o% stress ithout sacri%icin the hardness. Temperin temperature can )eincreased to adCust the hardness as per the customer s re


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Ta)le&5

A *n / 8 /i l Ar Gi :2H 2H

/87A 0. 0

0.9!

0.20

0.!0

0.050

*a-

0.020

*a-

0.20

0.!0

0.05

ma-

2.9!

".!0

0.#0

ma-

2

ma-

20

ma-TestRoll

0.# 0.2! 0.009 0.050 0."# 0.009 "."0 0.55 5. 5

H In ppm

".2 In&/itu metallo raphy Test

In&/itu metallo raphy is carried out on roll )arrel a%ter localised rindin ith di%%erent rit papers, %ollo ed )y diamond paste (0.!micron$ polishin %or mirror %inish as re


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i . 5 *icro&photo (-500 D -400$ o% In&/itu metallo raphy done on the )arrel sur%aceith lo hardness roll

In&/itu as done on adCacent Cournal area (outside hardenin area$ o% the same roll toin'esti ate the pre&induction hardened micro&structure. The comparati'e o% pre&hardeninmicro&structure o% lo hardness roll and that o% hi h hardness roll is sho n in i &2.

i . 2 *icro&photo (-400$ o% In&/itu metallo raphy done on )arrel step (7tchant 2; Gital$o% hi h hardness and lo hardness roll.

nother lo hardness roll as in'esti ated ith In&/itu metallo raphy here the micro&structure sho in coarse rain and coarse martensite. *icro&photo raph o% the same issho n in i .".

4igh hardness roll 2o5 4ardness roll

.

!

ine car)ides(0." &5.!micron$

uni%ormly distri)uted

Fery coarse car)ide( 2 micron$ non&

uni%ormly distri)uted


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i . " *icro&photo (K400$ o% In&/itu metallo raphy done on )arrel (7tchant 2; Gital$ o%

lo hardness roll.

or the a)o'e case, retained austenite also as relati'ely on hi her side. The retainedaustenite as measured )y Ri aku */ &"* K&ray /tress naly+er and the 'alue as !.9!;.

!ase-):or identi%ication o% ne-t le'el route cause o% coarse martensite cases, the +one ise Time&

Temperature matri- (Ta)le&2$ o% pre&induction normalisin treatment cycle as studied and%ound a maCor de'iation. Eoth +one ise and contact thermocouple temperature are "0&!0 oAhi her (hi hli hted in Ta)le 2$ o'er the speci%ied ran e.

Ta)le&2 one ise Time&Temperature *atri- o% Gormalisin soakin temperature.

Time

5 2 " 4 AT5 AT25st ! hrs # #0 # 0&950 67.-8)9 669-8/9 ##0&90 6.9-639

2nd !hrs #!0 0 #90&950 #90&90! 8.9-8/9 ##9&900 639-63

Ge-t !hrs # 0&900 900&92 900&90! 8)/-8.8 689-8/9 # 0Z

Last !hrs 8).-8.. 8.7-8/ 904&90! 8.6-8/9 8/ -83) # 9 4

/peci%ied temperature # 0&900 0A5 to 4 one temperature, AT5 D AT2 Aontact Thermocouple Temperature

!ase-.:In most o% the cases o% lo hardness roll, coarser car)ides on matri- ere seen.

or lo hardness rolls, hardenin parameter checked ith actual temperature pro%ile recorded )y the hardenin machine 8LA system. Fariation o% temperature as around !&50 oA ( i .4$

hich is normal and also seen %or ood hardness roll. Aali)ration o% temperature sensors eredone ith respect to )lack )ody %urnace and no anomaly o)ser'ed.

Coarse Grain ASTM 5-6

CoarseMartensite


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i .4 Temperature pro%ile alon )arrel durin induction hardenin

6ood hardness area sho s %ine car)ides ith %ine martensitic matri-. 6rains si+e is %ound 9or 50 as per /T* 7552. In&/itu test as done on many rolls ()oth ha'in hi h and lohardness$ and it as o)ser'ed that the pre&induction microstructure as not consistent. sthere is no di%%erence in chemistry or hardenin parameter, di%%erence in pre&hardenin micro&structure as identi%ied as a pro)a)le cause o% the 'ariation in hardness.

*icro&structure sho s non&uni%orm an ular coarse car)ides indicatin poor homo eni+ationand dissolution o% as cast primary car)ides. It happens due to improper thermo&mechanicaltreatment durin %or in and primary heat treatment operation. Impro'ement o% pre&inductionmicrostructure is o% prime importance to et a desired result durin induction hardenin .

,esign of e;peri


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E7 R7 T7R

i .! *icro&photo (-400$ o% )e%ore and a%ter modi%ied Aycle (7tchant 2; Gital$

s a process control micro structural study o% samples in as %or ed heat treated conditionhas )een incorporated to take necessary correcti'e measures in hardenin parameters

)e%ore induction hardenin .

Roll stackin pattern durin normalisin treatment as also modi%ied %or )etter temperature uni%ormity and contact thermocouples at top layer and )ottom layer is madecompulsory. ( i . $

i . Roll stackin arran ement and thermocouple position o% )e%ore and a%ter.

Test Bata Roll reprocess cases due to lo hardness )ecame ne li i)le and the trend analysisdepicted in i . .

i . month ise lo hardness issue trend analysis !+*!2 SI+*S

#


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5. M8re&induction hardened microstructure as the main 'aria)le causin this lo hardnessissue a%ter induction hardenin operation. Eesides the matri- car)ide si+e, shape anddistri)ution also play maCor role in the %inal hardness.

2. or route cause analysis o% hardness 'ariation pro)lem a%ter induction hardenin , in&situ

metallo raphy techni

in-situ m'graphy-a technique_090814 (f)

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