RU1775256C - Method of resistance flash-butt welding of ferritic austenitic steels - Google Patents

Abstract

Usage: in flash butt welding by fusion of ferritic-austenitic steels. SUMMARY OF THE INVENTION: In flash butt welding by parts from ferritic-austenitic steels, the allowance for reflow is set equal to the thickness of the metal being welded. The precipitation is set to 1.0 ... 2.0 times less than the allowance for reflow, depending on the thickness of the metal. After welding, the welded joint is subjected to cooling at a speed of more than 25 ° C /. The choice of the optimal welding mode makes it possible to obtain a high-quality welded joint; welding technology is simple.

Description

FIELD OF THE INVENTION This invention relates to flash butt welding, mainly of parts made of ferritic-austenitic steels.

A known method of welding pipes for ferritic-austenitic stainless steels with reflow and draft to 1/4 of the thickness of the edges in an inert gas environment. After welding, the welded joint is subjected to heat treatment in order to increase the viscosity, ductility and corrosion resistance.

A disadvantage of the known method of welding pipes of ferritic-austenitic steels is the use of inert gas and additional heating of the joint after welding.

The aim of the invention is to simplify welding technology.

In the described method of flash butt welding in which parts of ferritic-austenitic steel are melted and deposited in air, the allowance for reflow

set equal to the thickness of the parts to be welded, the precipitation value is set to 1.0 ... 2.0 times less than the allowance for reflow depending on the thickness of the parts, and after welding, the connection is subjected to accelerated cooling at a speed of more than 25 ° C / s.

The amount of allowance for reflow is an indicator characterizing the temperature field at the welded ends of the parts. It has been found that when welding ferritic-austenitic steels, the optimum temperature field is formed when the allowance for reflow is equal to the thickness of the part. If the reflow allowance is less than the thickness of the metal, this can lead to the appearance of defects in the joint zone. If the allowance for reflow is increased above this value, the mechanical properties of the welded joint may be reduced.

A change in the limits of the precipitation value is 1.0 ... 2.0 times less than the allowance for glazing, due to the wide range of changes in the allowance. The melting depends on the welded thickness of austenitic ferritic steels, for example from 4 to 30 mm. For welding parts with a thickness of 4 mm, a factor of 1 is applied, and for parts with a thickness of 30 mm, a factor of 1.9-2 is applied. A decrease in coefficient leads to an excessive increase in the amount of draft and a decrease in the quality of the welded joint. An increase in the coefficient leads to a decrease in the amount of precipitation and the appearance of defects in the joint zone.

Fulfillment of these requirements for the flash butt welding of ferritic-asgenic steels allows one to obtain high quality of the welded joint and mechanical properties, including impact toughness at positive temperatures. However, when testing samples for impact strength at low temperatures, these values decrease.

The use of accelerated cooling of the welded joint after welding made it possible to increase the level of impact toughness at low temperatures to the required level by grinding grain in the joint zone.

The greatest effect of using accelerated cooling is observed at cooling rates above 25 ° C / s. A further increase in the cooling rate does not lead to a noticeable increase in toughness - but equipment for accelerated cooling of joints is complicated.

An example of a specific application of the flash butt welding method for the melting of parts from ferritic-austenitic steels is welding of pipes of 14 mm diameter with a wall thickness of 10 mm from 08X22H6T steel on a K584M welding machine.

The resistance welding method is implemented as follows. The pipes to be welded are prepared for welding, inserted into the clamps of the machine, clamped and, in accordance with the recommendations of the method, the following welding conditions are determined: allowance for reflow 10 mm; draft value - 7.7 mm, open circuit voltage 7 V; initial approach speed - 0.25 mm / s; the approach speed is final -2.7 mm / s; welding time 50 s.

After welding, an accelerated cooling of the joint is carried out at a rate of more than 25 ° C / s using a water-air mixture according to a linear law to a temperature of 300 ° C. Metallographic studies showed that there were no defects in the joint zone.

The mechanical properties of the welded pipe joints are at a high level, including impact strength at low temperatures.

The implementation of the method was monitored by recording the parameters of the welding mode and accelerated cooling.

Claims (1)

SUMMARY OF THE INVENTION Method of flash butt welding by fusion of parts made of ferritic-austenitic steels, in which the parts are melted and deposited in a specific medium, and then the welded joint is subjected to additional processing, with the exception of simplification of welding technology, parts are melted and deposited in air, the allowance for reflow is set equal to the thickness of the parts to be welded, the amount of precipitation is set 1-2 times less than the allowance for reflow the thickness of the parts, and after welding, the compound is subjected to accelerated cooling at a speed of more than 25 ° C / s.