Technical field

The present disclosure relates to a laying head pipe comprising a specific ferritic- austenitic (duplex) stainless steel. The present disclosure also relates to the use of the specific duplex stainless steel as a laying head pipe, either as a whole pipe or as an inner tube and to a method of manufacturing an object, such as a wire rod, wherein said method comprises the step of providing a laying head pipe containing the specific duplex stainless steel.

Background

In a typical wire rod rolling mill, wire rod is formed by hot rolling wire rod billets and the finished wire rod is then directed into a laying head pipe, mounted in a rotating laying head, which lays the wire rod in an ordered coil (ring) pattern onto a continuously moving cooling lane (conveyor) behind the laying head. During laying, the wire rod is running at very high speed inside the rotating laying head pipe, thereby exerting the inside surface of the laying head pipe to high levels of wear. As can be understood, the exposure to high wear in combination with high temperature is a problem because tubes will have to be replaced when they have run out due to wear or cracks.

There have been attempts to reduce the wear by for example carburizing the interior pipe surfaces in order to increase hardness and resistance to wear. However, the carburizing process requires a drastic quenching from elevated processing temperatures, which can distort the pipe curvature. The carburized layer has also been found to be relatively brittle. There have also been attempts to have a wearing layer on the surface of the inner pipe, but those attempts have not been successful.

Duplex stainless steels have been suggested to be used as laying head pipes and tests performed have shown that these steels will provide improvements in wear resistance compared to, for example, carbon steels. Even though said duplex stainless steels are working in today's machines there is a demand for a material which will work in even more demanding environment.

It is therefore a need for a new type of material which will withstand the wear.

Summary

The aspect of the present disclosure is to provide a solution to or to reduce the problems mentioned above by providing an improved laying head pipe with improved wear resistance compared with for example a carbon steel laying head pipe.

The present disclosure therefore relates to a laying head pipe comprising a specific ferritic-austenitic (duplex) stainless steel.

Furthermore, the present disclosure also relates to the use of the specific duplex stainless steel as a laying head pipe in a method for manufacturing a wire rod, which may be used to form coils (rings).

Additionally, the present disclosure also relates to a method of manufacturing a wire rod, in the form of rings, wherein said method comprises the step of providing a laying head pipe containing the specific duplex stainless steel.

According to the present disclosure, a laying head pipe is configured for rotation around an axis in a rolling mill laying head. The laying head pipe includes an inlet part, a curved part and an outlet part. Furthermore, in the present disclosure, the terms’’pipe” and’’tube” are used interchangeably.

Brief description of the Figures

Figure 1 A shows the front view of a laying head pipe;

Figure IB shows the side view of a laying head pipe.

Detailed description The present disclosure relates to a laying head pipe comprising a duplex stainless steel having the following composition in weight%:

Cr 28 to 30;

Ni 5 to 8;

Mo 1 to 3;

Mn 0.5 to 2.0;

Cu 0 to 0.8;

N 0.1 to 0.5;

Si 0 to 0.5;

C 0 to 0.03;

P 0 to 0.03;

S 0 to 0.03;

Balance Fe and unavoidable impurities.

Rolling small-diameter hot wire rods at high wire rod speeds with conventional laying head pipes will wear the pipe out and have an impact on the quality and consistency of the final product. The present duplex stainless steel will enable higher wear resistance and thereby improve the quality of the product and increase the productivity in the wire rod mills because there will be fewer shutdowns due to changing of worn pipes. As stated above, figure 1 shows a laying head pipe having an inlet part 1, a curved part 3 and outlet part 2. The wire rod is passed into the inlet part and continue in the curved part and is then passed through the outlet part where after it is coiled is allowed to cool.

According to one embodiment, the laying head pipe comprises a duplex stainless steel having the following composition in weight%:

Cr 28 to 30;

Ni 6 to 8;

Mo 2 to 3;

Mn 0.5 to 1.5;

Cu 0 to 0.8;

N 0.3 to 0.4; Si 0.2 to 0.4;

P 0 to 0.03;

S 0 to 0.03;

Balance Fe and unavoidable impurities.

It is very surprising that the present duplex stainless steel would work as a laying head pipe because the working temperature during operation is higher than recommended for the present duplex stainless steel. Hence, the present duplex stainless steel should not withstand the erosion it is exposed to during the operation. However, the present duplex stainless steel did work excellent and without being bound to any theory it is believed that it is due to the kinetics of the sigma phase transition.

According to another embodiment, the whole laying head pipe is composed of the duplex stainless steel as defined hereinabove or hereinafter. According to another embodiment, the whole laying head pipe consists of the duplex stainless steel as defined hereinabove or hereinafter.

According to another embodiment, the laying head pipe is a composure of an inner tube and an outer tube and the inner tube comprises the duplex stainless steel as defined hereinabove or hereinafter. According to one embodiment, the inner tube consists of the duplex stainless steel as defined hereinabove or hereinafter.

Another aspect of the present disclosure relates to a use of a pipe comprising the duplex stainless steel as defined hereinabove or hereinafter as a laying head pipe. As described above, the laying head pipe may be composed or may consist of the duplex stainless steel as defined hereinabove or hereinafter and the laying head pipe may comprise or consist of the duplex stainless steel as defined hereinabove or hereinafter.

Yet another aspect of the present disclosure relates to a method of manufacturing a wire rod comprising the step of:

Providing a pipe comprising the duplex stainless steel as defined hereinabove or hereinafter; Inserting the pipe in a wire rod mill as a laying head pipe.

As described above, the laying head pipe may be composed or may consist of the duplex stainless steel as defined hereinabove or hereinafter and the laying head pipe may have an inner tube comprising or consisting of the duplex stainless steel and defined hereinabove or hereinafter. By using a laying head pipe composed of duplex stainless steel as defined hereinabove or hereinafter, in the present method, the severe wear at the inner surface of the laying head pipe caused by abrasion will be reduced as the present duplex stainless steel will be able to withstand the high wear between the hot wire rod and the laying head pipe inside surface at high wire rod speeds. Furthermore, by using the present duplex stainless steel, the production of the wire rods is increased as higher wire rod speeds are combined with rising production output per day.