Measurement of thermal cycles in the weld heat affected zone of mild steel

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CoA Note Mat. No. 13

m-'^-'U^ '!^OfS*'^f^^*. '^^in

THE COLLEGE OF AERONAUTICS

C R A N F I E L D

MEASUREMENT OF THERMAL CYCLES

IN THE WELD HEAT A F F E C T E D ZONE OF MILD S T E E L

by

CoA Note Mat. TIo. 13 September, I 9 6 7

THE_CO_LLEGE OF_AERqilAUTICS DEPARTUEI-IT 01'^ ilATERIALS

Measurement of t h e r m a l c y c l e s

i n the weld h e a t a f f e c t e d sonc of a i l d s t e e l by

-M.D. Coward and R . L . Apps

S U M M A R_Y

The thermal c y c l e s i n t h e mild s t e e l p a r e n t p l a t e a d j a c e n t t o a bead on p l a t e weld have been measured f o r h e a t i n p u t s of IO8, 5^ and tó l i j / i n c h , by means of embedded themiocouples c o n n e c t e d t o high r e s p o n s e a u t o m a t i c r e c o r d e r s . Tlie r e s u l t s sho^r t h a t d e c r e a s i n g the h e a t inrjut i n c r e a s e s the c o o l i n g r a t e and d e c r e a s e s the width of t h e h e a t a f f e c t e d z o n e .

For t h e r m a l c y c l e s i n which t h e peak temperratures r e a c h e d 900°C o r a b o v e , two p o i n t s of i n f l e c t i o n have been n o t e d i n the t e m p e r a t i t r e r a n g e s ifOO° - 600°C and 950° - 1200°C. The i n f l e c t i o n i n the lower t e m p e r a t u r e r a n g e , which h a s b e e n o b s e r v e d by o t h e r w o r k e r s , h a s been a t t r i b u t e d t o l a t e n t h e a t from t h e e x o t h e r m i c t r a n s f o r m a t i o n of a u s t e n i t e t o f c r r i t e . The h i g h e r i n f l e c t i o n p o i n t , n o t p r e v i o u s l y r e p o r t e d , h a s been t e n t a t i v e l y r e l a t e d t o the s o l i d i f i c a t i o n i n t h e weld pool and the r e l e a s e of the l a t e n t h e a t of f u s i o n .

Contents

Summary

1. Introduction 1

2. Experimental work 2 5. Results and discussion 5

k. References 6

5. Acknowledgements 7

Tables 8 Figures

1

-1 . Introduction

In the process of fusion welding an intense l o c a l i s e d heat source n e l t s some of the parent m a t e r i a l to form a pool of molten metal t o which a d d i t i o n a l f i l l e r metal nay be added. The parent material immediately adjacent to the molten zone i s subjected to extremely rapid changes in temperature over a r e l a t i v e l y small distance. In t h i s heat affected zone the combination of a wide raiige of theima]. cycles produces a whole s e r i e s of difTerent m e t a l l u r g i c a l s t r u c t u r e s with

accompanying v a r i a t i o n i n mechanical p r o p e r t i e s .

The temperature/tine r e l a t i o n s h i p s for points in the parent p l a t e a t various distances from, tlie f\.ision boundary are of p a r t i c u l a r

significance in the determination of the mechanical p r o p e r t i e s of the heat affected zone. The important parameters a r e the maximiun

temperature reached and the cooling r a t e thraLi.gh any p a r t i c u l a r temperatiure range. These allow us to p r e d i c t and control m e t a l l u r g i c a l n i c r o s t r u c t u r e and hence mechanical p r o p e r t i e s , and a l s o to p r e d i c t and control d i s t o r t i o n caused by the rapid heating and cooling cycle.

Tlie influence of mi crost nocture on mechanical p r o p e r t i e s i s w e l l known. Hardened and tempered s t e e l s develop the best conibination of

t e n s i l e strcngtii, d u c t i l i t y and notched-bar impact proiperties when t h e i r s t r u c t u r e s consist wholly of tempered m a r t e n s i t e . The presaice of f e r r i t e , p e a r l i t e or b a i n i t e usually lowers iiie values f o r proof s t r e s s , impact and fatigue s t r e n g t h . In welding, the limited time cycle during which the heat affected zone i s r a i s e d t o the maximum toiiperatuTe and then cooled again permits in many cases only a p a r t i a l degree of austen-i t austen-i s a t austen-i o n , and does not allow enough tausten-ime for complete dausten-iffusausten-ion of carbon and other alloying elements. Although the heat affected zone in mild s t e e l plate generally c o n s i s t s of f e r r i t e and carbide, other s t r u c t u r e s may be produced by changes in the r a t e of heating and cooling or by the use of plate of g r e a t e r h a r d e n a b i l i t y . Thus i t i s possible t h a t the heat

affected zone nay c o n s i s t of a range of mixed s t r u c t u r e s including martensite, b a i n i t e , p e a r l i t e and f e r r i t e , giving very d i f f e r e n t mechanical p r o p e r t i e s

to those of the -unwelded parent m a t e r i a l .

The use of continuous cooling transformation data has been applied for many years to the control and understanding of the heat treatment of alloy s t e e l s and, in a more q u a l i t a t i v e manner, t o the welding of such s t e e l s . The w e l d a b i l i t y of a s t e e l may be p a r t i a l l y a t t r i b u t e d to the l a r d e n a b i l i t y and the c r a c k - s e n s i t i v i t j ' ' of the heat affected zone and consequently the use of the C.C.T. diagrasi for inferring the striict^jral and the mechanical

p r o p e r t i e s of that zone offers a r e l i a b l e method of predicting the w e l d a b i l i t y of a s t e e l and for determining the welding conditions for a given s t e e l .

However, the transformation of a u s t e n i t e i s considerably influenced by the thermal condition of a u s t e n i t i s a t i o n ; therefore i t i s e s s e n t i a l ü i a t the C.C.T. diagraiii used for welding research be deteirnined under the exact conditions of h e a t i n g and cooling of regions in the heat affected zone. This has been achieved by the use of specially designed high speed d i l a -tometers ( l ) ( 2 ) . In t h i s way INAGAKI and h i s colleagxics (2) have drawn

2

-up a table for a s e r i e s of hif^i t e n s i l e s t e e l s shovring, together with t h e i r chemical composition, the l i m i t s of m a r t e n s i t e , b a i n i t e and p e a r l i t e corresponding to the various cooling r a t e s found in the regions of the h e a t affected zones.

The determination of weld heat affected zone thermal cycles i s

therefore of paramount importance i n deteimining the m-echanical p r o p e r t i e s of the welded j o i n t . The determination of these cycles was the f i r s t step in a programme of research cai'ried out at Cranf i e l d into the

i n v e s t i g a t i o n of the p r o p e r t i e s of the weld heat affected zone. Previoijs techniques used t o measure the taiiperature d i s t r i b u t i o n in materials have ranged from the use of temperature s e n s i t i v e lacquers (5)('+)which change colour when heated abo-'/e a c r i t i c a l temperature, th3X)ugh crayons and wax p e l l e t s which have fixed melting p o i n t s to theimocouples welded to the p l a t e and connected t o automatic recording instruments (5) (6) ( T ) .

The accuracy of the l a t t e r method i s considerably b e t t e r than the others which measure temperatures to only ± lOJo and are very s e n s i t i v e to change

in heating r a t e . For these reasons automatic recorders were used for t h i s work.

I n the second stage of the work a r i g was constructed to simulate exactly the measured thermal cycles in specimens of the parent p l a t e which were then t e s t e d t o determine the mechanical properties of the various regions of the heat affected zone. These r e s u l t s w i l l be published l a t e r . 2. Experimental Work

Heating and cooling thermal cycles in the parent p l a t e adjacent t o the weld were measured by means of thermocouples connected to high response, d i r e c t , continuous recording m i l l i v o l t m e t e r s . For t h e measuranent of

temperatures above 1,200°C the themocouples were constructed from O.OO5" diameter wire of pure platinum and an alloy of platinum - vyjo rhodium. For the measurement of temperatures below 1,200°C the thermocouples were

constructed from O.OO5" diameter wire of chromel (an a l l o y of ^Qffo nickel and lO^d chromium) and alumel (an a l l o y of 95^3 n i c k e l plus aluminium, s i l i c o n and manganese a d d i t i o n s ) . The thermocouple was constructed by feeding the separate wires through a two inch long twin bore alumina i n s u l a t o r , of outside diameter O.063", twisting the ends of the bare wires together and welding in a carbon arc to form a very small globule. Several of these

thermocouples, of both types, together with t h e i r cold junctions and conpensating leads wore c a l i b r a t e d against the meltirg points of standard pure s a l t s and metals using the thermal a r r e s t technique.

I n i t i a l t r i a l s were made with the thermocouples spot welded, by means

of a capacitor discharge u n i t , to the surface of the p l a t e at r e g u l a r i n t e r v a l s away from the region to be welded. This technique proved unsuccessful

since the thermocouples that were c l o s e s t t o the weld were detached from the p l a t e surface during weldirg by the turbulent molten flux . By d r i l l i n g holes about I/16" deep and spot welding thermocouples to the bases of tiie holes with subsequent peening of the edges of the hole around the j j i s u l a t o r ,

_ • ^

t h i s problem was overcome. However, the method was not acceptable for the following reasons: ( l ) The molten flux produced during the welding process caused a d d i t i o n a l heating of the thermocouple wires away from the hot junction and thus introduced e r r o r s in the HEasurasent of the p l a t e temperature; (2) Positioning the f i n i t e - s i z e d h o t - j u n c t i o n j u s t below the top sui'face of the p l a t e caused the hot junction to s t r a d d l e several isotherms, thus producing a l a r g e torijperature gradient across the hot j u n c t i o n . To avoid these e r r o r s i t was necessary to p o s i t i o n the hot junction along an isotherm, and t h i s was achieved by V7elding the thermocouple to the base of a hole d r i l l e d upwards from the ujiderside of the p l a t e , immediately underneath the weld bead where the temperature isotnemts were p a r a l l e l t o the p l a t e suurfaces.

For the a c t u a l measura'nent of the heat affected zone thermial cycles a bead on p l a t e weld was produced by an automatic submerged arc weldirg u n i t , vising 3/16" mild s t e e l f i l l e r w i r e , on a 1^' thick mild s t e e l

(B.S.15), p l a t e approximately 26" long and 12" wide. The com.position of the mild s t e e l i s given in Table I , whilst welding conditions for each heat input are l i s t e d in Table I I . The weld was then sectioned in

numerous p l a c e s , etched in lOfo N i t a l , and measurements made of the bead width, depth of p e n e t r a t i o n and width of tiie heat affected zone at the point of ma:^imuan p e n e t r a t i o n .

From t h i s information holes of O.O67 i n . diameter wore d r i l l e d i n t o another mild s t e e l p l a t e of i d e n t i c a l dimensions along the l o n g i t u d i n a l

centre l i n e to depths which on subsequent welding, under the same conditions, on the reverse side of the p l a t e , would take them i n t o various regions of the heat affected zone. The themocouples were then spot welded to the bottom of the d r i l l e d h o l e s . Tliis was achieved by connecting the p l a t e to one terminal of the capacitor discharge u n i t and the therm^ocouple wires to the o t h e r . By gently lowering the twin bore aluminium i n s u l a t o r dcr-.jn the d r i l l e d hole e l e c t r i c a l welding of the thermocouple to the base of the hole took place irmnediately i t touched the bottom. In order to produce a

s a t i s f a c t o r y weld i t was e s s e n t i a l to ensure t h a t the d r i l l e d hole did not contain any d i r t or g r e a s e . Also i t was necessary to ensure that the small lengtli of tliermiocouple i/ires emerging from the insulator to the hot junction globule did not touch the sides of the d r i l l e d hole during the lowering of the iherm.ocouple or else welding of the wire took place above

the base of the h o l e . F i n a l l y the twin bore alujaina i n s u l a t o r s were fixed in p o s i t i o n by cementing to the place surface with alumina p a s t e . The thermocouple cold junction was maintained at 0°C by m.eans of an ice/water mixture.

In order to avoid disturbance of the t h e m a l s t a t e of the p l a t e the holes were da-illed to as small a diameter as possible ( t h i s was l i m i t e d by the diaraeter of the smallest twin bore alumina i n s u l a t o r s m.anufactured) and the holes were spaced at not l e s s than one inch i n t e r v a l s .

Very fine thermocouple V7ires were used for t h r e e reasons; f i r s t l y , to produce a hot junction as small as possible in order to mxinimise the

k

-temperature gradient across the globule, i . e . t o miniiTiise the region of the heat affected zone whose thermal cycle was to be measured, secondly, to minimise conduction of heat from the solid and the e r r o r due to a temperature gradient along the wires, and t l i i r d l y , to keep the response time of the thermocouple to a minimum.

The thermocouples were connected v i a a multiple switch system t o four Sefram Graphispot high response, single channel, d i r e c t continuous recording m i l l i v o l t m e t e r s , e s p e c i a l l y designed for the measurement of low v o l t a g e s . The Graphispot recorded low p o t e n t i a l s by neans of an

immersed c o i l galvanometer which was i n s e n s i t i v e t o v i b r a t i o n and

consumed e s s e n t i a l l y zero c u r r e n t . A response time of -g- sec. was given for fiü-l scale d e f l e c t i o n , i . e . i t took V 4 s e c . to reach a temperature of 1,500°C. A t r o l l e y carried a pen giving i n s c r i p t i o n i n r e c t i l i n e a r c o - o r d i n a t e s , a s well as the photo e l e c t r i c r e c e i v e r serving as a detector for the l i g l i t spot. The current from t h i s d e t e c t o r was amplified and fed t o a servo motor which corrected any e r r o r i n p o s i t i o n between the l i g h t spot frcra the galvanometer and the d e t e c t o r . By c o r r e c t l y spacing the thermocouple holes in the p l a t e and by using a multiple switdiing system three therTüal cycles from three d i f f e r e n t couples could be recorded on a single Graphispot during the welding of the length of the p l a t e .

The technique for the a c t u a l temperatxare measurements consisted of f i r s t l i n i n g up the welding u n i t and adjusting to the correct conditions for welding on a run-on plate adjacent t o the p l a t e containing the thermo-couples. Wlien these conditions were obtained a l l the four Graphispot recorders wore switched on and tlie bead on plate weld was produced, using the multiple switching system a t the appropriate times to record a l l the thermal c y c l e s . The experim.ental arrangement i s shovm in F i g . 1.

After welding, the p l a t e was sectioned next to each thermocouple and small portions containing the thenaocouples carefully ground u n t i l the hole containing the thermocouple was v i s i b l e . This surface \jas then macro-etched in 10^ N i t a l s o l u t i o n for several minixtes t o show the heat affected zone and fusion boundary. The distance between the welded thermocouple and the fusion boundary was measured with a finely graduated s t e e l r u l e and a magnifying g l a s s to within 0.25 KU'ii' This region i s shavm in Fig. 2 .

I n order to determine possible e r r o r s in the measurement of the thermo-couple n i l l i v o l t a g e s a number of t e s t s were c a r r i e d out. For i n s t a n c e , Beevers(3)has shown t h a t one of üie major d i f f i c u l t i e s in the measurement of temperatures in welding by means of thermocouples i s the reduction of voltage pick-up from extraneous sources • To i n v e s t i g a t e the magnitude of t h i s problem, the welding power supplj' was switched ofY a t a p a r t i c u l a r point i n the thermal cycle of a t r i a l run and the inmiediate change in m i l l i v o l t a g e noted. The r e s u l t s of the t e s t shovjed that t h i s effect was n e g l i g i b l e . The c a l i b r a t i o n of both types of thermocouples was c a r r i e d out t o i n v e s t i g a t e e r r o r s due t o the c i r c u i t , ( i . e . connection wires to tiie cold junction and to the r e c o r d e r ) , and due to the Graphispot recorders and the appropriate c o r r e c t i o n s made . The r e s u l t s were used d i r e c t l y in the c o r r e l a t i o n of the m.easured temperature values .

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-5 . Resul-ts and Discussion

The r e s u l t s of the temperatiure - time measuraients for the various positions in the mild s t e e l parent p l a t e adjacent to t h e bead on iDlate weld for welding conditions giving three d i f f e r e n t heat inputs are sho\m

i n F i g . 3 , ^ and 5- The r e s u l t s show t h a t the heat Input has a

considerable effect on the coolirig r a t e , a s shown in F i g . 6. As would be expected decreasing the heat input increases the cooling r a t e and

markedly reduces the width of the v i s i b l e heat affected zone. The v a r i a t i o n s i n pealc temperatures >7ith d i s t a n c e from the fusion boundary for the d i f f e r e n t heat inputs are shovjn in F i g .

7-Of s p e c i a l i n t e r e s t i s the fact t h a t during cooling there are two regions which show a d e f i n i t e i n f l e c t i o n in cooling rate over a c e r t a i n temperature range. These temperature ranges are U00° 600°C and 1200° -950°C. The lower temperature i n f l e c t i o n depends on the heat input and peak temperature of the thermal c y c l e . This region has been reported by Calvo et al.V9)and i s thougtit to represent the temperature a t which the exothermic transforaiation of the a u s t e n i t e began during cooling. The

temperature a t which a u s t e n i t e transforms depends upon i t s homogeneity and grain s i z e and upon the cooling r a t e from the a u s t e n i t e range. To check t h i s the C.C.T. diagram for t h i s s t e e l was determined by means of high speed dilatometry at B.¥.R.A.(lO). i n t h i s t e s t the material was r a p i d l y heated t o 1525"C at a heat.ing r a t e siEiilar t o those found in the weld heat affected zones, held a t t h i s a u s t e n i t i s i n g tonperature for s e v e r a l seconds and then cooled a t various cooling r a t e s .

Tlie r e s u l t s are shown in Figure 8, with the cooling r a t e for a weld heat affected zone thermal cj'-cle, with a peak temperature of 15^7°C

super-imposed on the graph. From t h i s i t can be seen that transformation to f e r r i t e and p e a r l i t e s t a r t s at about 650°C for cooling r a t e s similar to those used in the present work. However, in the a c t u a l weld heat affected zone thermal cycle the material i s not held a t i t s peak temperature for any length of tine but immediately cooled and t h i s may not produce such complete homogenisation of the a u s t e n i t e , which may explain why there i s a difference of 50''C in the transformation s t a r t i n g temperatures.

The second i n f l e c t i o n has not been reported previously' in any of the papers on temiperature measurement in p l a t e s during welding. This i n f l e c t i o n occurs in the temperature range of about 1200-950°C again depending on the thermal cycle and heat input, and i t i s t e n t a t i v e l y suggested t h a t i t i s caused by the s o l i d i f i c a t i o n progression in weldirg .

Rabkin(ll)has studied the temperatures in the weld pool of automatically submerged arc welded aluminium. He showed t h a t in the welding pool there i s a powerfuJL flow of molten superheated metal forced from under the a r c , which flows to the r e a r part of the weld pool and produces a slower

cooling r a t e in the r e a r p a r t of the weld pool than in the forv/ard p a r t . This explains \7hy t h e molten pool shape is not e l l i p t i c a l , as predicated by heat flow theory,(l2^but includes an elongated t a i l .

6

-The shape of t h e molten weld pool f o r a bead on p l a t e weld i s shown i n F i g . 9^ from w h i d i i t m.ay be noted t h a t the m e l t i n g p o i n t i s o t h e r m i s v e r y n e a r l y p a r a l l e l t o t h e weld s u r f a c e a t t h e f r o n t of t h e p o o l , w i t h lower t e m p e r a t u r e i s o t h e r m s f o l l o w i n g a s i m i l a r p a t t e r n . Thus a therraocouple l o c a t e d i n tlie h e a t a f f e c t e d zone immediately below t h e arc would remain a t a h i g h t e m p e r a t u r e f o r a l o n g e r time t h a n would be p r e d i c t e d by h e a t flow t h e o r y or by t e m p e r a t u r e measureiiKnts i n a s t a t i c system (compare, for exaiuple, t h e r e s u l t s of Apps and M i l n e r 1 3 ) . Most of t h e l a t e n t h e a t of f u s i o n i s r e l e a s e d a t the end of the pool and

t r a n s f e r of t h i s h e a t c o u l d r e s u l t i n an i n f l e c t i o n i n t h e c o o l i n g c u r v e . No a t t e m p t h a s been made t o c o r r e l a t e t h e e x p e r i m e n t a l r e s u l t s w i t h h e a t flow t h e o r y s i n c e the s i z e of the p l a t e s used f o r t h e work was

i n s u f f i c i e n t t o e l i m i n a t e edge e f f e c t s . A d d i t i o n a l l y , the t h i c l i n e s s of t h e p l a t e s t o g e t h e r w i t h the h e a t i n p u t s used were such a s t o produce a h e a t flow p a t t e r n t h a t was n e i t h e r pure t w o d i m e n s i o n a l nor t h r e e

-d i m e n s i o n a l h e a t flo\-7 ( l U ) .

I t may be noted t h a t t h e widtii of the h e a t a f f e c t e d zone i n c r e a s e s markedly w i t h i n c r e a s e i n h e a t i n p u t , a l t h o u g h cooling r a t e s w i t i i i n t h e zone d e c r e a s e . The s i g n i f i c a n c e of h i ^ i c o o l i n g r a t e s i n mild and low a l l o y s t e e l s i s r e a d i l y a p p r e c i a t e d b u t t h e width of t h e h e a t a f f e c t e d zone c o u l d a l s o be i m p o r t a n t i n d e t e r r a i n i n g t h e p r o p e r t i e s of welded

s t r u c t u r e s . F u t u r e work may w e l l show the importance of s e l e c t i n g welding v a r i a b l e s such t h a t a c o r r e c t b a l a n c e i s m a i n t a i n e d between h e a t a f f e c t e d zone s t r u c t u r e and d i m e n s i o n s . k. R e f e r e n c e s 1 . T r e n l e t t , H . F . 2 . I n a g a k i , M. e t a l . 5 . Adams, C .M. J n r . h. Apps, R.L. and M i l n e r , D.R. 5 . H e s s , W.F. e t a l . 6 . N i p p e s , E . F . e t a l . 7 . B e l c h u k , G.A. 3 . B e e v e r s , A. 9 . C a l v o , F.A. e t a l . B.W.R.A. B u l l e t i n , Nov. I 9 6 1 , p . 9 . T r a n s . N a t . R e s . I n s t . M e t a l s ( 6 ) , 1964, p . 59-Welding J o u r n a l 2l> 195Ö, 2 1 0 - G B r i t i s h Weldirg J o u r n a l , 2 , 1955, ^75-Welding J o u r n a l 2 2 , 1 9 ^ 3 , 3 7 7 - ^ . Welding J o u r n a l m, 1955, 1 6 9 - s . Welding P r o d u c t i o n , 1959, 3 2 . B r i t i s h Welding J o u r n a l , 1 0 , 1 9 6 3 , 175-S t u d i e s of the welding m e t a l l u r g y of s t e e l s , B.W.R.A. p u b l i c a t i o n , I 9 6 3 .

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-10. Watkinson, F. 11. Rabkln, D.M. 12. Rosenthal, D. 13. Apps, R.L. and Milner, D.R. ik. J h a v e r i , P . , M o f f a t t , W.G., and Adams, C.M. 6 . Acknowledgements

The a u t h o r s wish t o t h a n k D r . E. Smith f o r h e l p f u l advice and d i s c u s s i o n t h r o u g h o u t t h e work. They a l s o w i s h t o acknowledge t h e f i n a n c i a l h e l p

of t h e Science Research Council w i t h o u t which the work c o u l d n o t have been u n d e r t a k e n . P r i v a t e Communication. B r i t i s h Welding J o u r ï i a l 6 , 1959, 1 3 2 . T r a n s . A.S.M.E. 6 8 , 1 9 t ó , 8^9. B r i t i s h Welding J o u r n a l , 1 0 , I 9 6 3 , 5 ^ . Welding J o u r n a l Ifl, I 9 6 2 , 12-rj.

8

-TABLE I: Composition of Parent Plate

Element C Mn S i S P Composition 'jo 0 . 2 1 0.39 0.065 0.050 O.Oij-0

TABLE II: Welding Conditions

Heat I n p u t k j / i n c h 103 5U 42 Welding C u r r e n t amps. 590 ± 10 390 ± 10 300 ± 10 Welding Voltage 30 ± 2 30 ± 2 30 ± 2 Welding Speed i n / m i n . • 6 | ± è 1 2 è - i 121 ± è Wire Diameter inches 7 l 6 7 l 6 7X6

n

FIG. 2. THERMOCOUPLE HOT JUNCTION IN THE HEAT AFFKTED ZONE.

FIG. I THE MEASUREMENT OF THE HEAT AFFECTED ZONE THERMAL CYCLES

1440 UJ a: UJ o. z UJ .- 1200 1080 960 840 720 600 480 360 240 120 60 70 e : TIME / SECS

FI6. 3, THERMAL CYCLES PRODUCED IN THE PARENT PLATE ADJACENT TO THE WELD FOR A HEAT INPUT OF 108 kJ/IN

1440 1320 UJ § 1200 < UJ I 1080 960 840 720 600 4S0 360 240 120

J

1

V

\

\

V

A

j

^ \ ^ \

s

d= Omr

k

^ \ • • n = l i mm

k"

^ mrn ^ r = ^ = :

ARC CURRENT 400amps ARC VOLTAGE 30 volts WELDING SPEED 13 in/min

1 1

10 20 30 40 50 60 70 80

TIME, SECS

FIG. L THERMAL CYCLES PRODUCED IN THE PARENT PLATE ADJACENT TO THE WELD FOR A HEAT INPUT OF 54 kJ/IN.

1440 f 1320 UJ (C Z) I 1200 UI Q. UI 1080 900 840 720 600 480 360 240 120 II

J

/

1

\ " ^ \

K\

\

i

• ^ M H rl n \ \ i= Imm ^ ^ d = 2 i m r T

s^

! ^ ^ O * ! 1 : : ^ ^ ^ j ^ _ _ ^ ^ ARC CURRENT 3 0 0 a m p s ARC VOLTAGE 30 volts WELDING SPEED 13 in/min

1

10 20 30 40 50 60 70 80

TIME, SECS

FIG. 5. THERMAL CYCLES PRODUCED IN THE PARENT PLATE ADJACENT TO THE WELD FOR A HEAT INPUT OF 4 2 k J / I N . •--'

k

\A\

w

-\

\u

W ^

! ' i

w

\ \ \ \ \

K^

~-\ i , '• ^*"""v..J08l<j/in ^ > J * SiKJ/in. i i

u

TÏ2kJIm~' i 0 10 20 30 40 50 50 70 60 TWE/SECS

1500 1250 ï 1000 750 500 250

i

a > \ . I __ —-\ , ^ • ^ 1 X HEAT INPUT of 54 k j / in D HEAT INPUT of 42 k j / i n " ^"^•.«^ O 3 6 9 12 15 18 Distance from Weld Fusion Boundary, mms.

FIG.7 VARIATION OF THERMAL CYCLE PEAK TEMPERATURE WITH DISTANCE FROM THE FUSION BOUNDARY FOR WELDS WITH HEAT INPUTS OF 1 0 8 k J / i n , 54 k j / i n and

4 2 k J / i n .

LIMIT OF WELD POOL |—ELECTRODE

PREDCTED THEORETCAaY DIRECTION OF WELDING \ /V"WELDING ARC PUTE SURfiftCE MaTEN WELD poa EMBEDDED THERMOOOUPIE IN PARENT PLATE / \

K

1000 800 U S- 600 UJ a: UJ CL iOO 200 \—T-\ i ^ 1 _{! I} 's

^w^

!

^ \f^

^ ' ^ 1 I 1 1 ; i ! _^ 1

i

1

i

S^

1 1 1 1 1 1 \ ' 1 1 i l l

- -COOLING RATE FOR THE WELD HEAT AFFECTED ZONE

\ \ \ \

4 398 ;228 ; t5s: 187, 187 10 10'

TIME TO COOL FROM 1000° C (SECS)

10'

K

K

FIG 8 C C I DIAGRAM FOR MILD STEEL AUSTENITISED AT 1325° C