JPS59189076A - Production of overlay clad steel - Google Patents

Abstract

PURPOSE:To prevent cracking by stripping in hydrogen environment at and under high temp. and high pressure by cladding pure iron on the surface of a base material consisting of carbon steel then cladding further an austenitic stainless steel thereon by build-up welding. CONSTITUTION:An intermediate layer 2 is clad between a base material 1 and a cladding material 3 in order to decrease the diffusion of C from the material 1 side and to prevent formation of a carburized layer which is a point for initiating cracking by bond stripping in the stage of a heat treatment after welding. The material of the layer 2 in this stage may be pure iron but if there is a need for taking erosion by hydrogen into consideration for the atmosphere to be used, a material composed of a low alloy steel in which the content of only the carbon is decreased is used together with the material 1. It is also possible to add Cr and Mo which are hydrogen resistant elements to the flux during welding in the case of incorporating a build-up welding method as a method for cladding the material 1 and the layer 2. There is no difference in thermal expansion at the boundary surface of the material 1 and the layer 2 as the surfaces thereof are both ferrite and since there is no abrupt change in hydrogen solubility, this part is free from cracking by stripping.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing overlay clad steel, and the present invention relates to the above method for preventing bond peeling cracking caused by hydrogen in overlay clad steel used in pressure vessels, etc. that handle extremely high temperature and high pressure hydrogen. It is about the method.

Pressure vessels used in high-temperature, high-pressure hydrogen environments, such as glue tanks for oil refining and coal liquefaction, are made of carbon steel or low-alloy steel, with austenitic stainless steel overlaid on the surface for corrosion protection. Welded parts are often used.

In these build-up clad steels, hydrogen gas permeates the stainless steel build-up layer by diffusion during operation and reaches the boundary between the build-up layer and carbon steel or low-alloy steel, and when shut down, the interface There is a problem that peel-like cracks occur.

This cracking is also called bond peeling cracking, and the cause is experimentally and empirically said to be delayed cracking caused by hydrogen. A factor that accelerates cracking is carbide precipitation on the stainless steel side due to carbon diffusion from the base metal.

That is, when these overlay clad steels are subjected to a long-term post-weld heat treatment at high temperatures, carbon in the base material migrates into the stainless steel, so that a carbide precipitate layer exists in a band shape along the boundary surface. Furthermore, continuous carbide precipitation is observed at the grain boundaries of the stainless steel. Bond peeling cracks propagate within this carbide layer or along austenite grain boundaries where carbides are precipitated.

There is still no established industrial method to prevent this cracking.

The present invention is applicable to the production of clad steel in which carbon steel or low alloy steel (base metal) pressure austenitic stainless steel is overlay welded.
This was done to prevent the occurrence of bond peeling cracks during use by reducing the migration of carbon from the base metal even if heat treatment is performed at high temperatures and for a long time after welding. .

That is, the present invention uses carbon steel or low alloy steel as a base material, and after cladding the surface of the base metal with pure iron or low carbon steel using various construction methods, further overlaying ordinary austenitic stainless steel. The present invention relates to a method for manufacturing overlay clad steel, which is characterized by cladding by welding.

The method of the present invention can be applied to all pressure vessels used in high-temperature, high-pressure hydrogen environments.

FIG. 1 is a diagram showing an example of an embodiment of the method of the present invention.
is the base material (carbon steel or low alloy steel), 2 is the intermediate layer (pure iron or low carbon steel), and 3 is the overlay weld (austenitic stainless steel). Cladding method (e.g. roll rolling, explosion welding, diffusion bonding, overlay rolling 2)
After cladding is performed by cladding (explosion rolling, cast rolling, diffusion rolling, etc.), ordinary austenitic stainless steel 3 for corrosion resistance is clad by overlay welding.

When a clad material of austenitic stainless steel and carbon steel or low alloy steel (hereinafter referred to as low alloy steel) is heated at high temperature, a carburized layer is formed on the stainless steel side of the interface.

That is, the diffusion rate of carbon in the austenite of stainless steel is lower than that in the ferrite of low alloy steel,
In addition, since stainless steel contains a large amount of Or, C that has migrated from low alloy steel is concentrated in the stainless steel boundary layer, and Or, C,
Forms a dense precipitated layer of carbide.

Bond peeling cracks then propagate through this carburized layer or the grain boundaries of the sensitized austenite.

In contrast, in the method of the present invention, the base material 1 (
From step 11ii, in order to reduce the diffusion of C and prevent the formation of a carburized layer that becomes the starting point for bond peeling cracks, the intermediate layer 2 is cladding between the sintered material 1 and the composite material 3.

The material for the intermediate layer 2 may be pure iron, but if the atmosphere in which it is used requires consideration of hydrogen corrosion, it is desirable to use a low-alloy steel of the same material as the base material 1, with only a reduced carbon content. In addition, when employing the overlay rolling method as the cladding method for the base material 1 and the intermediate layer 2, it is also possible to add hydrogen-resistant elements Or and No from 7 lux during welding.

In addition, since the cladding interface between the base material 1 and the intermediate layer 2 is both made of ferrite, there is no difference in thermal expansion, and there is no sudden change in hydrogen solubility, so peeling cracks do not occur at this portion.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an embodiment of the method of the present invention. Sub-agent: 1) Akira Sub-agent Ryo Hagi Hara - Figure 1

Claims (1)

[Claims] Carbon steel or low-alloy steel is used as a base material, and after cladding pure iron or low-carbon steel on the base metal surface using a moxibustion type method, ordinary austenitic stainless steel is further applied on top of that using an overlay welding method. A method for manufacturing overlay clad steel characterized by cladding.