Effect of Cooling Rate on the Structure of the Weld Metal and Heat Affected Zone

high rate of cooling after welding is observed

Effect of cooling rate on the structure of the weld metal and heat affected zone.


In the case of low cooling rates in the area and pig-iron weld heat-affected zone can be ensured the preservation of gray cast iron structure with a certain part of it.

At high cooling rate in almost any part of iron in the weld and the HAZ region 2 will take place whitening. Welding cast iron is heated. (300-400 ° C) reduces the rate of cooling. At this temperature, the heat in the weld and the HAZ region 2, depending on the number of grafitizatorov can be obtained either white or gray cast iron.

At high heating (600-650 ° C) cooling rate at the eutectic temperature is very low, bleaching is not happening. Slowing down the cooling leads to the disintegration of austenite to ferrite or pearlite formation ferrite-metal base.

Thus, the most effective means to prevent bleaching of the weld metal and heat affected zone of high land, as well as a sharp hardening of HAZ in the area - a high pre-heated cast iron or collateral to a temperature of 600-650 ° C. The welding is called with the heated hot welding cast iron. High heating and cooling also contribute to the slow elimination of cracks and voids due to increase in the lifetime of the bath and the degassing of the best, and to reduce the temperature gradient, thermal stresses.

Welding is heated to temperatures of 300-400 ° C called for semi, and without pre-heating - cold welding of cast iron. If for semi and cold welding of cast iron is widely used metallurgical and technological means of exposure to the metal in order to improve the quality of welded joints. Among them are:

- Weld metal alloying elements - so that at a given cooling rate obtained in the joint structure of gray cast iron;

- Weld metal alloying elements such as would allow for the seam in the pearlite-ferritic structure characteristic of low-carbon steel, by binding to excess carbon in the carbides are more stable than cementite, and uniformly distributed in the metal;

introduction of oxygen-containing components of welding consumables in order to maximize carbon oxidation (burning it) and get in the weld metal of low carbon steel;

application of welding materials, providing in the weld metal to obtain the various non-ferrous metals: copper-nickel, copper and iron, iron-nickel, etc., with high plasticity and having a melting point close to the melting point of iron.

Hot welding of cast iron

The most radical way to combat the formation of bleached and hardened parts of the weld and heat affected zone and the formation of pores and cracks is heated to a temperature of product 600-650 ° C and slow cooling after welding it.

See also:
Welding of Cast Iron
Composition and Properties of Iron
Marking of Iron
Basic Information on Weldability and Technological Advice
Structural Transformations in the Heat Affected Zone during Welding of Cast Iron
Effect of Cooling Rate on the Structure of the Weld Metal and Heat Affected Zone
The Technological Process of Hot Welding
Cold Welding of Cast Iron with Simple Electrodes
Cold Welding Electrodes, Cast Iron, Providing the Receipt of the Weld Metal Color