Page 13 - SSAB Welding Handbook Edition 2

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Welding handbook 3.0 The thermal cycle of a welding performance

3.0 The thermal cycle of a welding performance
©SSAB

The welding process subjects a joint to a localized k x U x I x 60
thermal heat treatment wherein the joint attains Q =
v x 1000
mechanical properties and microstructures that are Q = Heat input [kJ/mm]
different compared to that of the unaffected parent U = Voltage [V]
metal. I = Current [A]
v = Welding speed [mm/min]
Welding properties are of vital concern for SSAB k = Thermal efficiency [dimensionless]
during the development of the Hardox and Strenx
grades. As a result, these steels can achieve favorable Recommended heat inputs for welding the Strenx and
properties in the joint.
the Hardox grades are found in chapter 5.

The principal purpose of this chapter is to describe 3.2 The heat-affected zone
which parameters affect the thermal heat treatment
in the joint. The complete part of the parent metal that is influenced
by the thermal cycle of the welding procedure is called
the heat-affected zone (HAZ). The other main areas in
3.1 The heat input the joint are the unaffected parent metal and the weld
metal, see fig. 3.1.
The heat input from a welding method depends on the
applied current, voltage and speed and it describes the
delivered energy/ length of the joint.

During welding there is loss of energy in the arc. The
thermal efficiency factor (k) expresses that part of 1. Unaffected parent metal
the heat input that is transferred to the joint during 2. Heat affected zone, HAZ
3. Weld metal
the welding process. This parameter depends on the
welding process being used and the specific welding Fig. 3.1: The principal parts of the joint
conditions. Approximate values for different welding
methods are according to table 3.1. The characteristics of the thermal heat treatment from
welding are of crucial importance for the mechanical
Thermal efficiency k [dimensionless] properties and microstructures in the HAZ. Its outcome
MMA 0.8 depends primarily on:
MAG, all types 0.8 4 The position in the joint
SAW 1.0
TIG 0.6 4 The level of heat input
4 The plate thicknesses in the joint
Table 3.1: The thermal efficiency factors for different welding methods.
4 The type of joint
4 The preheat temperature, when applicable
The heat input that is transmitted to the joint can be
calculated according to the following formula.

This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications. 13
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.