JPH03229819A - Production of clad steel plate excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain the clad steel plate combining the adhesive strength with the corrosion resistance of steel plate by continuously casting a duplex layer cast slab in which the surface layer part is composed of high alloy steel and the inner part is composed of low alloy steel with proscribed composition, heating this cast slab up to the prescribed temp., hot-rolling the cast slab at a specific finishing temp. or above, and then performing air cooling or water cooling. CONSTITUTION:A duplex layer cast slab in which the surface layer part is composed of high alloy steel and the inner part is composed of a low alloy steel having a composition containing, by weight, <=0.06% C, <=0.80% Si, 0.80-1.50% Mn, 0.005-0.05% Nb, <=0.06% Al, 0.005-0.03% Ti, and 0.005% N is continuously cast. Subsequently, this cast slab is heated up to a relatively low temp., 1100-1300 deg.C, and hot-rolled at >=650 deg.C finishing temp. Then, the above cast slab after hot rolling is subjected to air cooling or to water cooling (accelerated cooling), by which the clad steel plate having the above characteristic and excellent in corrosion resistance can be obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method of manufacturing a composite steel plate with excellent corrosion resistance, and in particular, to a method of manufacturing a composite steel plate with excellent corrosion resistance, in which the surface layer is made of high alloy steel and the inner part is made of ordinary steel or low alloy steel. The present invention relates to a method for manufacturing composite steel sheets.

(Prior Art) The operating conditions for oil and natural gas transport pipes have become increasingly severe in recent years. For example, when transporting fluids that contain large amounts of hydrogen sulfide and carbon dioxide gas and have a harsh pH, line pipes must have sufficient corrosion resistance and toughness to withstand such usage conditions in terms of operational stability and safety. There is an increasing demand for steel pipes that have the characteristics required for transportation steel pipes for line pipes, such as steel pipes, strength, and other properties.

Due to these demands, there is a tendency to use high-alloy steel instead of the conventionally used ordinary steel or low-alloy steel, but manufacturing steel pipes only from high-alloy steel is economically disadvantageous. Become.

Therefore, we decided to use relatively inexpensive ordinary steel or low alloy steel as the base material.
Clad steel pipes made of expensive stainless steel or other highly corrosion-resistant, high-metallic copper have been developed and are now in use.

This method of manufacturing rad steel pipes was developed in the 1980s.
There are rolling methods, explosion bonding methods, casting methods, diffusion methods, thermal spraying methods, etc. as shown in Japanese Patent No. 138. For example, in the rolling method, in order to ensure adhesion between the base material and the composite material, considerations such as surface polishing of the adhesion surface, four-circle welding and vacuuming to prevent oxidation during heating and rolling are required. Necessary when assembling slabs.

However, these operations have cost problems,
In addition, there was a problem in ensuring adhesion of the entire contact surface.

Similar problems exist in other manufacturing methods such as the explosion bonding method and the casting method, and reducing manufacturing costs and ensuring stable adhesion between the base material and the composite material are major issues in manufacturing composite steel sheets. It became.

Recently, a method of manufacturing a multi-layer slab whose surface layer and interior are made of different metals using a continuous casting method has been proposed, for example, in Japanese Patent Application Laid-Open No. 83-108947.

(Problems to be Solved by the Invention) The present inventors have devised a method of manufacturing a composite steel plate with excellent corrosion resistance by manufacturing a multi-layer slab using a continuous casting method and rolling forming the same. It has been discovered that this clad steel plate not only has excellent adhesion between the base material and the laminated material, but also has excellent corrosion resistance, and can be processed and formed into steel pipes and the like.

(Means for Solving the Problems) The gist of the present invention is that the surface layer is made of high alloy steel, the inside is made of C: 0.06% or less, S j: 0.80% or less, Mn: 0. .8 (1-1.50%, Nb: [
1,005 to 0.05%, A, 77: 0.06% or less,
Ti: 0.005-0.03%, N: 0.005
% or less, the balance being iron and unavoidable impurities, is produced by continuous casting. The slab is heated to 1100 to 1300°C, then hot rolled at a finishing temperature of 650°C or higher, and then air cooled. Or, a method for manufacturing a composite steel plate with excellent corrosion resistance characterized by water cooling and continuous casting, in which the surface layer is made of high-alloy steel and the interior is made of high-alloy steel and the inside is made of c: o, oe% or less, s.
i: 0.80% or less, Mn: 0.80 to 1.50%, N
b: 0.005 to 0.05%, AI: 0.06% or less,
T: 005-0.03%, N: 0.005% or less, Ca: 0.001-0.006%, Cu: 0.
05-0.5%, Ni: 0.1) 5-0.5%,
V: 0. (II-0.10%, Mo: 0.05-0
．． A multi-layer slab containing 30% of one or more of the above and the remainder consisting of iron and unavoidable impurities is produced, the slab is heated to 1100-1300°C, and then hot rolled at a finishing temperature of 650°C. This is a method for producing a composite steel sheet with excellent corrosion resistance, which is characterized by carrying out the process at a temperature of 0.degree. C. or higher, followed by air cooling or water cooling.

(for production) The present invention will be explained below.

(1) Laminating material (surface layer material) As the laminating material, a high alloy steel component with excellent corrosion resistance is used. High alloy steels with excellent corrosion resistance include stainless steels such as austenitic stainless steels and duplex stainless steels, as well as high N steels such as Incoloy and Inconel.
i means a metal or alloy with excellent corrosion resistance such as high alloy steel, titanium, or cupronickel, and the selection should be determined depending on the usage environment.

(2) Base material (inner layer material) C: The amount of C in the inner layer material has the most important meaning in the production of composite steel sheets by continuous casting. That is, when manufacturing a multilayer slab by continuous casting, a transition layer is inevitably generated at the interface between the surface layer and the inner layer. The authors' research has revealed that when high-alloy steel components are used in the surface layer, if the C content in the internal base material component is high, martensite is likely to form in this transition layer, causing internal cracks. .

That is, if the C content exceeds 0.06%, internal cracks in the transition layer become noticeable, so the upper limit needs to be set to 0.06%. Note that, depending on the amount of C in the laminated material, it is desirable that the amount of C in the base material is equal to or less than the amount of C in the laminated material.

Si: Si is an element contained in deoxidized steel, and its excessive addition inhibits weldability and HAZ toughness.

Therefore, the upper limit is set at 0.8%.

Mn: Mn is a useful element for ensuring strength, toughness, and hardenability, and must be added in an amount of 0.8% or more.

However, too much Mnff1 causes deterioration of weldability and HAZ toughness, so the upper limit was set at 1.5%.

Nb: The reason why the lower limit is set to 0.005% is to obtain strength through the precipitation effect of Nb. Furthermore, when heated to the solution temperature, it has the effect of preventing coarsening of austenite grains, that is, the effect of finely and uniformly dispersing Nb (CN) in the base material.

On the other hand, if it exceeds 0.05%, the toughness deteriorates.

Therefore, the upper limit was set at 0.05%.

Al: A and Q are generally elements contained in deoxidized steel, but since deoxidation is also performed by Si, Mn, or Ti, the present invention does not limit the lower limit of Al.

However, if ANffl increases, the cleanliness of the steel deteriorates and the HAZ toughness deteriorates, so the upper limit was set at 0.06%.

Ti: Ti is effective in refining austenite grains,
From the viewpoint of ensuring toughness, it is necessary to add 0.005% or more. On the other hand, if it exceeds 0.03%, it causes deterioration of weldability, which is not preferable, so the upper limit was set at 0.03%.

N: Since N inevitably mixes into molten steel and deteriorates the toughness of the steel, its upper limit was set at 0.005%.

P, S: P and S are contained in steel as inevitable impurities. In the present invention, the upper limit is not intentionally limited, but since these deteriorate the toughness of the base metal and the welded part, it is preferable to reduce the amount as much as possible.

In the steel of the present invention, if necessary, Ca: 0.00
1-0.006%, Cu: 0.05-0.5%, Ni:
0.05-05%, V: 0.01-0.10%, M
o + Any one or two of 0.05 to 0.30%
Contain more than seeds.

The main purpose of adding these elements is to improve various properties such as strength and toughness without impairing the excellent characteristics of the steel of the present invention. Therefore, the amount added must be limited.

Ca: Ca controls the morphology of sulfides, increases Charpy absorbed energy, and improves low temperature toughness. However, C
If the amount of a is less than 0.001%, there is no practical effect, and
If it exceeds o, ooe%, large inclusions such as CaS and CaO occur, so the upper limit was set at 0.006%.

Nj: Ni has the property of improving the strength and toughness of the base material without adversely affecting HAZ hardenability and toughness, and
．． It is necessary to add 0.05% or more.

In addition, if it exceeds 0.5%, it is unfavorable in terms of hardenability and toughness of the HAZ, so the upper limit was set to 0.5%.

Cu: Cu has almost the same effect as Ni, 0.05
% addition is necessary. However, if it exceeds 0.5%, hot workability deteriorates, so the upper limit was set at 0.5%.

Although V=V is effective for the precipitation effect, it has no effect unless it is added in an amount of 0.01% or more. Moreover, if it exceeds 0.10%, weldability deteriorates, which is undesirable, so the upper limit should be set at 0.10%.
It was set at 10%.

Mo: Mo is an element that improves both the strength and toughness of the base material, but it has no effect unless it is added in an amount of 0.05% or more. In addition, if it exceeds 0.30%, the weld toughness and weldability will deteriorate, which is undesirable, so the upper limit should be set at 0.30%.
%.

(3) Production method Since multi-layer slabs are manufactured by continuous casting and the slabs are hot rolled, there is no difference in process from the conventional manufacturing method of large steel plates, and the preparation process when manufacturing clad steel plates is simplified. It is advantageous in terms of mass production and economy as there is no need to apply the same.

The reason for limiting the manufacturing method after hot rolling will be described below.

First, regarding the heating temperature, from the point of view of ensuring the toughness of the base material, it is better if the initial austenite grains are finer. Therefore, it is desirable that the heating temperature of the multilayer slab be lower. Heating temperature is 1
If the temperature exceeds 300°C, the austenite grains become coarse and the toughness deteriorates, so the upper limit of the heating temperature was set at 1300°C. On the other hand, from the viewpoint of solution treatment of high alloy steel, the lower limit is 1
It is necessary to raise the temperature to 100°C or higher.

If the finishing temperature was less than 650°C, the ferrite in the structure of the high-alloy steel plywood would be processed and the toughness would deteriorate, so the lower limit of the finishing temperature in the rolling process was set at 650°C. Furthermore, for cooling after rolling, either air cooling or water cooling (accelerated cooling) may be applied.

The present invention can be applied to various steel plates, and is preferably applied mainly to thick steel plates, hot-rolled steel plates, and steel pipes produced by cold or hot working these.

(Example) A multilayer slab manufactured by continuous casting having the chemical components shown in Table 1 was hot rolled according to the rolling conditions shown in Table 2.

A test piece was cut from the base metal portion of the composite steel plate A-J manufactured in this way, and a tensile test and a Charpy test were conducted.

Furthermore, pitting corrosion tests and side bending tests were conducted using these composite steel plates.

These results are also shown in Table 2.

As a result, for Comparative Example I, the amount of C in the inner layer was 0.0
Since the C content was 98%, which was higher than the C content in the surface layer, the adhesion was deteriorated. Furthermore, regarding Comparative Example J, the pitting corrosion resistance deteriorated due to insufficient solution treatment, and the toughness also deteriorated due to the low finishing temperature. In contrast, with the method of the present invention, pitting corrosion did not occur, adhesion was good, and appropriate strength and toughness were obtained.

As explained above, according to the present invention, the laminated material portion has excellent corrosion resistance. Composite steel plates with excellent corrosion resistance can be manufactured by hot rolling multilayer slabs.

(Effect of the invention) According to the method of manufacturing a composite steel plate with excellent corrosion resistance of the present invention,
A composite steel plate that has both the adhesion and corrosion resistance of a steel plate can be easily and inexpensively manufactured.

teenager Reason Man

Claims (1)

[Claims] 1. The surface layer is made of high-alloy steel, and the inside is made of C: 0.06% or less, Si: 0.80% or less, Mn: 0.80-1.50%, Nb: 0.005-0.005% or less. 0.0
5% Al: 0.06% or less Ti: 0.005 to 0.03
%N: 0.005% or less A multilayer slab with the balance consisting of iron and unavoidable impurities is manufactured by continuous casting, and the slab is heated to 1100 to 1300 ° C.
A method for producing a composite steel sheet with excellent corrosion resistance, which comprises hot rolling at a finishing temperature of 650° C. or higher, followed by air cooling or water cooling. 2. Inside is Ca: 0.001-0.006% Cu: 0.05-0.
5%Ni: 0.05-0.5%V: 0.01-0.10
%Mo: 0.05 to 0.30%, and the remaining part is iron and inevitable impurities. Method.