JPS581166B2 - Ferrite Austenite Stainless steel Seizouhouhou - Google Patents

Description

[Detailed Description of the Invention] In recent years, as pollution prevention equipment such as flue gas desulfurization equipment has become larger,
An economical steel suitable for this purpose is desired.

One of them is ferrite containing 20-30% Cr. Although it is an austenitic (α-γ) duplex stainless steel, there are still many problems that need to be solved in terms of manufacturing and properties.

Among these, the present invention aims to improve hot workability, toughness of the product, and stress corrosion cracking resistance particularly during production.

Generally, the γ phase of α-γ duplex stainless steel is already precipitated in the steel ingot stage, and particularly in the initial stage, it precipitates so as to cover the α grain boundaries.

After that, it also precipitates inside the grains, but the γ phase that precipitates at the beginning does not disappear easily even when subjected to subsequent heating and rolling such as blooming and thick plate rolling, and even the final product has special characteristics. be surpassed.

At the interface between the coarse γ phase and α phase, strain is particularly likely to concentrate during tensile deformation or impact deformation, and often becomes the starting point for cracking.

Therefore, edge cracking is likely to occur during manufacturing, causing a decrease in yield, and the stress corrosion cracking resistance and toughness of the finished product are also decreased.

The present invention aims to improve the properties described above by dividing the γ phase precipitated at the α grain boundaries and at the same time refining the α grains to create a uniform α-γ dual phase steel. It is.

The method is to hold the steel at 500-800°C in advance and apply warm working to make the α grains into elongated grains, while at the same time dividing the γ phase that has precipitated into elongated grains at the grain boundaries.
It is heated and held at ℃ for 1 to 20 hours to size the α grains and γ grains.

A more uniform microstructure can be obtained compared to the conventional method using only hot rolling.

This warm working and grain sizing treatment can be performed either before blooming or before plate rolling.

In that case, improvement in hot workability can also be expected.

It can also be carried out as a finishing treatment after rolling a thick plate.

Further, the processing method may be not only rolling but also forging.

Examples will be described below.

Example I C=0.03%, Si=0.6%, Mn=0.5%Ni
=6.0%, Cr=26.3%, Al=0.04%, N
= 1250 α-γ duplex stainless steel containing 0.05%
After heating to ℃ and hot rolling to a thickness of 40 mm,
It was reheated to 1050° C. and warm rolled to a final thickness of 13 mm, and then kept at 1050° C. for 2 hours.

On the other hand, as a comparison material, a material prepared by heating to 1250° C. and hot rolling to a thickness of 13 mm was used in the usual manner.

Figure 1 shows a comparison of microstructure photographs, and it shows that the γ phase (white island-like parts) of the product produced using the method of the present invention is also relatively round, the α grains in the base are also small, and the structure is uniform and fine throughout. I know that there is.

FIG. 2 shows the impact test results, and the fracture surface transition temperature is about 25 to 30° C. lower in the case of the present invention.

FIG. 3 shows the results of a stress corrosion cracking test in a boiling 43% MgCl2 aqueous solution.

Comparisons are made at loads of 0.6, 0.8, and 1.0 times the yield strength, and it can be seen that the stress corrosion cracking resistance of the method according to the present invention is superior.

Example 2 Same two types of structural steel as above (however, final plate thickness 25 mm)
A hot workability test was conducted using

The test method is shown in FIG. 4, and the results are shown in FIG.

Figure 4A shows a test piece, Figure 4B shows a test piece after rolling, where A shows the rolling direction and B shows edge cracking.

In Fig. 5, ↑ indicates that no cracks are observed.

This corresponds to using the method of the present invention before rolling a thick plate, but it can be seen that edge cracking does not occur regardless of the temperature and rolling reduction of the thick plate, and it is significantly superior to the conventional method.

Furthermore, it goes without saying that the present invention can be applied not only to hot-rolled products but also to cold-rolled steel plates.

As explained above, according to the method of the present invention, stainless steel with excellent hot workability, toughness, and stress corrosion cracking resistance can be obtained.

[Brief explanation of the drawing]

Figure 1 is an optical micrograph (200x magnification) comparing the structure of steel obtained by the conventional method and the method of the present invention, and Figure 2 is the same at 2 mmV.
Figure 3 is a chart comparing the Notchi impact test results.
A diagram comparing the stress corrosion cracking test results in a 3% boiling MgCl2 solution, Figure 4 A shows the test piece, Figure 4 mouth shows the test piece after rolling, and Figure 5 shows the test piece with hot workability. This is a chart comparing the results.

Claims (1)

[Claims] 1 Ferrite. In austenitic dual-phase stainless steel, the steel is held in a temperature range of 500 to 800°C and subjected to warm working, and then heated in a temperature range of 900 to 1100°C for 1 to 2 hours.
A ferrite characterized by being retained for 0 hours. A method for producing austenitic duplex stainless steel.