JPH06328125A - Manufacture of two phase stainless steel seamless tube - Google Patents

Abstract

PURPOSE:To provide a method low in generation of inside flaws in manufacture of a seamless steel tube of ferritic and austenitic two phases by hot extrusion processing CONSTITUTION:When a two phase stainless steel seamless tube is extruded at a high temperature, the inside of a hollow billet is coated with more than 0.15g/cm<2> of glass lubricant to improve heat insulation of the billet and a mandrel to refrain the generation rate of the rough surface of the inside by excessive lubrication within the allowable limit. Consequently, the generation rate of the inside flaws of the stainless steel seamless pipe is reduced to enable a high yield manufacture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferrite-austenite duplex stainless steel seamless steel pipe by a hot extrusion method.

[0002]

2. Description of the Related Art The hot extrusion method is suitable for processing materials having low hot workability, and is used for producing seamless pipes such as stainless steel and high Ni alloys. The advantage of this processing method is that compared to other hot working methods for steel pipes such as the inclined rolling method, the material does not have an excessive tensile force, and due to the good lubricating action of the glass lubricant, defects occur. It is difficult to do. Further, since a glass lubricant is used, the heat insulating effect by this is also effective in obtaining a product with few defects.

[0003]

In the hot extrusion of a ferrite-austenite duplex stainless steel pipe, the hot workability of the steel is inferior to that of other materials such as austenite stainless steel, and the optimum working temperature range is obtained. However, the inner surface properties after hot extrusion were not always good. This is because the ferrite-austenite duplex stainless steel has a mixed structure of a ferrite phase and an austenite phase, which have different ductility and strength at high temperature, and the deformation is likely to concentrate in the low strength ferrite phase. Furthermore, the ratio of this phase depends on the temperature. This is because the change in the deformability at high temperature and the change in the deformation resistance due to the change and the change in the phase ratio make it difficult to determine the optimum working conditions for this steel.

Since the hot extrusion method is originally intended for processing materials having low hot workability, it is used as a glass lubricant for materials having poor hot workability such as austenitic stainless steel. It is not always easy to find the optimum value such as what kind of glass to use, how much the coating amount should be, what range the processing temperature of the material should be, and what range the processing degree should be. . As a result, the occurrence of cracks due to insufficient lubrication and heat insulation due to an inadequate amount of glass is significant compared to other steel types, and the resulting scratches need to be removed with a grinder or the like. This caused a great deal of man-hours and a decrease in yield.

The present invention was devised for the purpose of solving such a situation, and when a ferrite-austenite duplex stainless steel seamless steel pipe is manufactured by the hot extrusion method, the inner surface of the steel pipe is roughened or cracked. It is an object of the present invention to provide a manufacturing method for suppressing the occurrence of flaws and the like.

[0006]

[Means for Solving the Problems] The above object is to provide a glass lubricant on the inner surface of a hollow billet in an amount of 0.15 g / cm ² or more and 0.28 or more.
This is achieved by a method for producing a ferrite-austenite duplex stainless steel seamless steel pipe, which is characterized in that coating is performed in a range of g / cm ² or less and hot extrusion processing is performed.

[0007]

The inventors of the present invention have conducted an earnest test, and as a result, in the production of a ferrite-austenite duplex stainless steel seamless steel pipe, by applying a glass lubricant of 0.15 g / cm ² or more, a sufficient heat insulating effect can be obtained. It has been found that it is possible to work and prevent the occurrence of internal lateral cracks due to temperature decrease.

It has been considered that excessive application of the glass lubricant causes a partial accumulation of glass, which causes avatar scratches. Ferrite-austenite 2
It has been discovered that, in the case of duplex stainless steel, even if the coating amount is within the range where avatar scratches are conventionally generated, it does not occur within a range not exceeding 0.28 g / cm ² .
The reason for this is considered to be that in the ferritic-austenitic duplex stainless steel, phases having different deformation strengths exist at minute intervals, so that the glass pool is minutely dispersed.

[0009]

EXAMPLES FIG. 1 and Table 2 show that in the steels whose components are shown in Table 1, the coating amount of the inner surface glass lubricant on the billet and the flaw generation after hot extrusion of the ferrite-austenite duplex stainless steel pipe It shows the relationship with the rate.

[0010]

[Table 1]

[0011]

[Table 2]

The billet size is 220 mmφ, the heating temperature during extrusion is 1180 ° C., and the extrusion ratio is 18-21. Viscosity of glass lubricant is 900 at 1180 ℃
It was ~ 1100 poise. In the hot extrusion process with a high processing rate, the ferrite phase with low strength is largely deformed, whereas the deformation of the austenite phase is small, and excessive processing is applied to the ferrite phase, causing cracks, which causes the internal surface Cracks occur. In order to avoid this, it is necessary to keep the hot working temperature as high as 1150 ° C. to 1190 ° C., to increase the ferrite phase at the time of working, and further to minimize the heat removal by the mandrel and the die.

When the coating amount of the inner surface glass lubricant is increased, as shown in FIG. 1 and Table 2, the adiabatic function works effectively, so that the flaw occurrence rate of the inner surface lateral cracks is reduced and the coating amount is 0. 0.10 g / cm ² less than 10%, 0.20 g / cm ²
When it exceeds cm ² , it becomes a low level of 5% or less. On the other hand, the inner surface avatar generation rate increases with an increase in the amount of the inner surface glass lubricant applied, and in particular, the inner surface glass lubricant application amount is 0.28 g / cm ²
If it exceeds, it will increase rapidly and exceed 10%. Therefore, the coating amount of inner surface glass lubrication exceeds 0.15 g / cm ² and is 0.28 g / cm ^2.
It can be seen that the range should not exceed ² .

[0014]

EFFECTS OF THE INVENTION By appropriately controlling the coating amount of the inner surface glass lubricant according to the present invention, it is possible to carry out hot extrusion of a ferrite-austenite duplex stainless steel seamless steel tube with less occurrence of inner surface defects.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a relationship between a coating amount of a glass lubricant on a billet inner surface and a defect occurrence rate of a product in a graph.

Claims (1)

[Claims] The inner surface of the 1. A hollow billet, the glass lubricant was applied at 0.15 g / cm ² or more 0.28 g / cm ² or less in the range, and performing a hot extrusion ferrite - austenite 2 Method for producing duplex stainless steel seamless steel pipe