CALCULATION OF PARAMETERS OF Mn-V FINE-GRAINED CONSTRUCTION STEEL MMA WELDING CONDITIONS

Dr. IOULI MAZEL, eng. GALINA POLISTCHUK and Dr. Yuri Kouskov

Mascow, Russia

Key words: Fine-grained construction steels, welding method, covered

electrodes, calculation, welding conditions, cracks, Theory of Heat

Conductivity, t criterion, welding heat input, low temperatures, preheating,

8/5

bead length.

Introduction

Low alloyed fine-grained Mn-V steels of 16 2A F type with nitrogen strengthening

G are widely used at manufacturing and assembling of different structures. Certain cracking and embrittlement susceptibility was revealed at welding of indicated steels, especially at low working temperatures. Due to this, the development of scientifically grounded improved technology for welding of the indicated and similar steels, also by using of MMA welding, is the task of the day.

The solution of this problem is complicated by the fact that the required operating properties of welded joints are to be achieved, asa rule, after welding without the additional heat treatment.

To calculate the welding condition parameters of construction steels it is expedient to use the Theory of Welding Heat Conductivity t_8/5criterion

indicating the welded joint cooling time within 800 -500°C (Fig.1) [2]. The use of t_8/5criterion allows to applya relatively easy technique for calculation of welding conditions using prominent relationships of the Theory of Welding Heat Conductivity [1,2].

It was experimentally established that for Mn-V steels with nitrogen strengthening the t criterion value should be within 6-15 seconds, as if t_8/5is less

8/5

than6 seconds the cold cracking develops, and if t_8/5is more than 15 seconds the grain growth and embrittlement develop, especially at low temperatures [2].

Depending on the accepted welding heat input pattern: surface point heat source (Fig.2a) or linear distributed heat source (Fig.2b), the calculation should be conducted according to the formula (1) or (2) respectively [2].

-1 -1

_8/5=(2 pl )^-1·E ·F [(500-T ) -(800-T ) ]; ................................. (1)

330 0 -12 2-2 -2 -2

_8/5=(4 plr c) ·h ·E ·d ·F [(500-T ) -(800-T ) ];..................... (2)

220 0

where

T₀the temperature of metal before welding, °C;

l -the arc thermal efficiency depending on the welding method (Table I);

E -welding heat input, J/cm; l -metal heat conductivity coefficient, J/s·cm·K;

r -metal density, g/cm ; c -metal heat capacity, J/g·K; d -metal thickness, cm.

TableI Relative thermal coefficient of arc burning, h for various welding methods [2]

No.	Welding method	Relative thermal coefficient of arc burning,h
1	Submerged arc welding	1,0
2	MMA welding by basic electrodes	0,8
3	MMA welding by rutile electrodes	0,9
4	Mechanized GMAW	0,8 – 0,9

F2 and F3 coefficients take into account the shape ofa welded joint (butt, fillet, T-joint, deposition on steel sheet) as well as the base metal thickness

Table IIF2 and F coefficients as function of welded joint shape [2].

Shape of welded joint	F2	F3
Deposition on sheet metal	1,0	1,0
Butt multilayer joint	0,9	0,9
Fillet joint	0,45 – 0,67	0,67
T-joint	0,45 – 0,67	0,67

Table III F coefficient as function of the base metal thickness [2].

(Table II, III). F and F3 values were obtained experimentally [2] for STE 460

steel, which approximately correspond to Russian Mn-V-N gr. 16 2

G AF steel.

While calculating it is necessary to consider the existence of the base metal critical thickness dcr (Formula 3). When d> dcr, the heat input valueE is calculated by formula (1) for the surface welding heat source, when d>d, the

heat input value is calculated by formula (2) for the linear heat source.

-1 -1

d =[h·E/2 rc· [(500-T ) +(800-T ) ] ]^1/2;............................... ( 3 )

cr 00

The following constant values were used at calculation of MMA conditions:

h = 0,8; t_8/5= 15 sec.(max); t =6 sec. (min.); r = 7,85 g/cm ; l = 0,27 J/s·cm·K;

8/5

c= 0,9 J/g·K.

The calculation of heat inputs at welding of 16 2

G AF steel butt (Tables IV, VI) and T-joint (Tables V,VII) welds were carried out within the base metal temperature range of T =-40-+200°C with simulation of welding at low

ambient temperatures (up to -40°C) as well.

Table IV The calculated ranges of heat inputE for welding of type 16 2

G AF steel butt joints at low temperatures.

TableV The calculated ranges of heat inputE for welding of type 16 2

G AF

steel T-joints at low temperatures.

Fig.3 and Fig.4 respectively show the developed diagrams for determination of permissible welding heat inputsE for butt (Fig.3) and T-joint welds preheated to 150°C.

Besides, the diagrams were made (Fig.5,6) for determination of optimal welding heat inputsE for 8,15 and ‡30 mm thick butt and T-joint welds considering that welding was supposed to be performed at low temperatures or with preheating.

Table VI The calculated ranges of heat inputE for welding of type 16 2

G AF

steel butt joints with preheating.

Table VII The calculated ranges of heat inputE for welding of type 16 2

G AF steel T-joints with preheating.

It is obvious that in order to provide the required heat input at welding by covered electrodes, it is necessary to know the electrode diameter, the welding current value I and the welding rateV which can be specified by the

length of the beadL deposited with one stick coated electrode, where:

Fig.3 Diagram for evaluation required welding heat input for butt joints.

Steel of gr.16 2A F Fig.6 The calculated range of heat inputE as function of To and d

L= I · U · t/E; where L = I · U · t/E , L = I · U · t/E_min

w w minw w maxmaxw w

where: I = the welding current, A;

U = the arc voltage, V;

t= arc burning time for one electrode, sec; E = welding heat input, kJ/cm

The calculated conditions of welding by ^yOH

13/55 stick electrodes, required for determination of the length of the bead deposited by one electrode, are shown in Table VIII..

Table VIII ^yOH

13/55 electrodes characteristics

Electrode diameter, mm	3,0	4,0	5,0
Electrode length, mm	350	450	450
Arc voltage, V	22	26	26
Welding current, A	95	145	180
Residual tail, mm	60	65	70
Electrode burning time, sec.	68,5	100	108

All the necessary data for engineering calculation of stick electrodes welding condition providing the high level of welded joints' service properties is obtained. Table IX (butt joints) and TableX (T-joints) indicate the results of calculation of optimal conditions specified using the welding current Iw and the bead length L for welding of fine-grained steel gr. 16 G2 AF butt and T-joints.

Fig.7 containsa diagram for selection of the welding speed for butt and T-joint welds by3 mm diameter ^yOH

13/55 electrodes, where, for the sake of convenience, the welding speed was calculated using the bead length L deposited by one electrode.

According to the suggested calculated welding conditions, the check tests of 16 2

G AF steel welded joints, made by

13/55 electrodes, were performed.

Table IX The calculated bead length L, deposited by one ^yOH electrode at type 16 2A F steel butt joints welding

t8/5 = 15 sec.(max); t =6 sec. (min.)

8/5

of gr. ^yOH

-13/55 of dia3 mm

13/55 electrode at type 16 2AF steel T-joints welding

t8/5 = 15 sec.(max); t =6 sec. (min.)

8/5

Table XI: The calculated type 16 2AF steel temperature before welding.

The results of the tests showeda sufficient level of technological strength and mechanicalproperties of welded joints.

Table XII Optimal heat inputsE (kJ/cm) values at 16 2A F steel butt

and T-joints welding.

T0, °C

Joint type

Welded metal thickness, mm

>30

15-20

Butt

7,7

12,2

14,2

22,8

17,6

44,1

T-joint

10,8

17,1

17,7

30,8

23,8

54,6

70-120

Butt

6,7

10,5

12,4

19,6

14,6

47,5

T-joint

9,4

14,8

15,4

26,8

19,6

47,5

150-200

Butt

4,7

7,5

8,3

14,0

8,3

20,8

T-joint

6,2

9,8

10,1

17,6

11,2

28,0

Table XIII Optimal conditions for 16 2

G AF steel butt and T-joints MMA welding by 3,4 and5 mm diameter yOH

13/55 electrodes.

Recommendations in technology of welding of type 16 2

G AF steel by covered electrodes were developed on the basis of the carried out research, the basic provisions of these recommendations are presented in Tables XI, XII, XIII.

Conclusions

The use of t8/5 criterion (formulas 1, 2, 3) allowed to calculate the optimal welding conditions for type 16 2
G AF steel including preheating and welding at low ambient temperatures.

Tables and diagrams were developed for prominent determination of permissible heat inputs for welding of type 16 2

G AF steel butt and T-joints depending on the metal thickness and the metal temperature before welding.

G AF steel with preheating

The range of heat inputs for MMA of type 16 2 up to 150°C was calculated depending on the joint type (butt, T-joint).

A diagram anda table for selection of MMA speed, setting by the bead length L deposited by one electrode, were developed for the sake of type 16 2
G AF steel welding conditions convenient application.

The scientifically proven conditions of welding by 3,4 and5 mm diameter ^yOH

13/55 electrodes were suggested on the basis of the conducted research.

References

Rykalin N.N. The calculation of thermal processes in welding, Mashgiz, 1951 (Russian).
Obering Karl Ebffer, Bischofshen Schweißen von hochfesten Feinkornbaustahlen für Stahlbauten // Schweißen und Schneiden 34 (1982), Heft9.

11-23-81 Part2 Engineering norms. Chapter 23. Steel structures. Moscow. Stroyizdat, 1982 (Russian).