JPH08209392A - Chromium plated steel sheet excellent in high speed continuous weldability - Google Patents

Abstract

PURPOSE: To produce a chromium plated steel sheet for cylindrical can body, excellent in high speed continuous weldability, by laminating a metallic chromium layer having projections and a chromium hydrated oxide layer on the surface of a steel sheet under respectively specified conditions. CONSTITUTION: A metallic chromium layer of (25 to 200)mg/m<2> is formed on the surface of a steel sheet, and a chromium hydrated oxide layer of (2.5 to 20)mg/m<2> expressed in terms of metallic chromium is formed on the above layer. At this time, the metallic chromium layer is applied so that it is partly formed into projections while continuously coating a substrate Fe layer, and further, the diameter of the base of a projection, the height of the projection from the base, and the existense density of the projections are regulated to 30-50nm, >=10nm, and (1×10<12> to 1×10<15> ) pieces/m<2> , respectively. Moreover, in the region from the outermost surface of the steel sheet as a plating substrate to the position at a depth of 20μm from the outermost surface, C and Mn are incorporated by 0.001-0.18% and 0.10-0.6%, respectively, by average weight percentages. By setting the heat generating velocity in the interface between the sheets at the time of welding to a desirable value, welding operations can be performed in high efficiency, at the time of forming a cylindrical can body by using the chromium plated steel sheet produced by this method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a cylindrical can body by forming a rectangular blank into a cylinder using a mash seam welding machine for can body welding, and then seam welding by laminating two opposite sides. In this case, the present invention relates to a chrome-plated steel sheet used as a can body material, and particularly to a chrome-plated steel sheet having excellent high-speed continuous weldability.

[0002]

2. Description of the Related Art Generally, the weldability of a can material is a control range of a welding current value necessary for obtaining a sound weld, that is, a maximum limiting current value at which a so-called splash of molten metal due to overheating of the weld does not occur. , The weldable current range (hereinafter referred to as ACR) defined by the difference between the minimum limiting current values at which sufficient welding strength is obtained. Then, it is necessary to fit the allowable range of the welding condition with the dispersion of the welding resistance value of the material into this ACR.

Conventionally, regarding this ACR, Japanese Patent Publication No. 63-
In Japanese Patent No. 26200, there is known a method of improving continuous weldability by forming granular projections on a chromium plating layer and controlling the amount of chromium hydrate oxide adhered to a certain range. This technology is used for normal TFS (Tin Free).
Steel), which utilizes the effect of suppressing the splash that occurs when the welded portion is overheated by the welding current because the static contact resistance increases due to the insulating chromium hydrated oxide layer existing on the outermost surface. Is. In other words, the above-mentioned known technique increases the welding upper limit current in order to increase the ACR.

However, the present inventors have found that even in the case of a chromium-plated steel sheet having the same amount of deposit and the same fine structure, the lower limit of the welding current actually varies depending on the production lot. In other words, this change in welding resistance is made possible by aligning welding conditions such as electrode pressure, overlap width, coating baking temperature and baking time, and plate thickness, roughness, metal chromium and chromium hydrate oxide adhesion amount, chromium plating. It exists even if the material conditions such as the layer microstructure are aligned.

Conventionally, it is assumed that this variation in welding resistance is unavoidable, and by conducting a welding condition investigation for each lot change in the welding process and adjusting the welding current and welding speed, a sound can body is manufactured. However, the stoppage of the equipment required for this adjustment greatly hinders productivity.

[0006]

DISCLOSURE OF THE INVENTION The present invention reduces the variation in the lower limit of the welding current of chromium-plated steel sheets, which has been considered inevitable in the past, depending on the lot, and reduces the plate / plate interface heat generation rate. It is an object of the present invention to provide a chrome-plated steel sheet which is excellent in high-speed continuous weldability and which can enhance the control of the welding current in the can body welding equipment.

[0007]

The present invention is a chrome-plated steel sheet formed on a welded can body by lap seam welding using a can body welding machine, wherein the surface of the steel plate is 25 to 200 mg /
m ² metallic chrome layer and further on it in terms of metallic chrome 2.
5 to 200 mg / m ² of a hydrated chromium oxide layer, the metallic chrome layer has a part thereof protruding while continuously covering the underlying Fe layer, and the base diameter of the protruding portion is 30 to 50 nm, Height from the base is 10 nm or more, and the density of protrusions is 1 × 10 ¹² to 1 × 10
¹⁵ pieces / m ^2, which is C0.00 as an average weight percentage in the region from the outermost surface of the steel plate as a plating base to a depth of 20 μm.
It is a chromium-plated steel sheet excellent in high-speed continuous weldability, characterized by containing 1 to 0.18% and Mn 0.10 to 0.6%.

[0008]

The present inventors discovered the relationship between the steel plate composition and the increase rate of the interfacial welding resistance by studying the behavior of the plate / plate interfacial welding resistance during welding of chrome-plated steel plates, and made the present invention. I arrived. In FIG. 1, the plate thickness is 0.32 mm, the steel type is the same, the roughness is the same, the amount of metal chromium deposited is 100 mg / m ² , and the metal chromium layer continuously covers the underlying Fe layer, and a part of it protrudes, The average base diameter of the protrusions is 200 nm, the average height from the base is 100 nm or more, and the density of protrusions is 2 × 10 ¹³ /
m ² and chromium hydrate oxide adhesion amount are 2.5 mg / m ² , 10 mg / m ² and 25 mg / m ² respectively in terms of metallic chromium.
m ² and C: 0 with an average composition in the range of 20 μm from the outermost layer of the original plate.
The welding resistance (dynamic contact resistance) of the plate / plate interface of the material measured by the dynamic contact resistance measuring method for the plated steel sheet with 02% and Mn: 0.3% is shown. The dynamic contact resistance was measured according to the method disclosed by the present inventors in “Materials and Processes”, Volume 4, page 1616, published by the Iron and Steel Institute of Japan. Specifically, this measurement method controls the current discharged from the capacitor with a power transistor to obtain a DC pulse for an extremely short time, and uses it as the welding current to change the welding resistance with time when performing micro spot welding. It is possible to directly measure the change in the interfacial resistance of the material to be welded in the time range equivalent to the formation time of a single weld nugget in mash seam welding, and to measure the initial welding resistance and the resistance value at the completion of welding. The continuous weldability of materials can be determined by comparison. The continuous weldability is better as the initial resistance is lower than the welding completion resistance and the resistance increase gradient with the progress of welding is gentle.

Looking at the initial resistance of welding, the smaller the amount of hydrated chromium oxide deposited, the smaller it becomes. The resistance in the vicinity of the welding end point in FIG. 1 is the bulk resistance of high-temperature iron that has completed welding, and the initial resistance represents the interfacial contact resistance of the low-temperature material. Considering the electrical resistance distribution in the vicinity of the weld nugget formation part of the joint interface of the material immediately below, the welding current in the can body is an AC wave, so the nugget is formed intermittently, but in Figure 1 the initial resistance is welded The lower the material's resistance is, the lower the resistance of the unwelded interface that is newly bitten by the roller compared to the preceding previous nugget, and the welding current flows in that area, creating a new nugget. It can be easily inferred that the layers are sequentially formed. On the contrary, if the initial welding resistance in FIG. 2 is higher than the resistance at the time of completion of welding, in actual welding, the welding current flows to the preceding nugget with the lowest resistance, so the preceding nugget forms a blowhole due to overheating, which is originally new. The part where the nugget should be formed remains as a cold spot. At the next welding current peak, a weld nugget is formed in the area between the cold spot and the new bite due to the resistance distribution between the cold spot and the new bite portion, but at the next peak, a welding defect occurs similarly to the above, and sound welding is performed. Is difficult.

For the above-mentioned reason, the upper limit of the amount of hydrated chromium oxide of the present invention is limited to 20 mg / m ² in terms of metallic chromium, which ensures the continuous weldability of the nugget, but does not increase ACR. The above-mentioned resistance distribution is not the only determining factor. There are two methods for increasing the ACR: increasing the upper limit value of the welding current or lowering the lower limit value. In Sn-plated steel sheets, the welding current path cross-sectional area increases when the Sn layer melts during welding, and the welding resistance decreases, preventing overheating and increasing the welding upper limit current. On the other hand, the present inventors have earnestly studied the factors that determine the lower limit value of the welding current, and completed the present invention.

FIG. 2 shows that the plate thickness is 0.32 mm, the steel type and the roughness are the same,
The amount of metallic chromium deposited is 100 mg / m ² , and the metallic chromium layer continuously covers the underlying Fe layer and a part of it is protruding,
Average base diameter of protrusions is 200 nm, average height from the base is 100 nm or more, density of protrusions is 2 × 10 ¹³ pieces / m ² , and chromium hydrate oxide adhesion is 7 mg / m in terms of metallic chromium. ^In Table 2, the results of measuring the dynamic contact resistance of the chromium-plated steel sheet having an average composition in the range of 20 μm from the surface of the original sheet as shown in Table 1 under the same conditions as in FIG. 1 are shown.

[0012]

[Table 1]

With the increase of C and Mn in the composition of the original plate,
It can be seen that the increasing gradient of welding resistance increases. In the case of a chrome-plated steel sheet, if the oxide film thickness and the metallic chromium ridge structure are the same, the reduction rate of the welding resistance that occurs as a result of the change in the welding current path cross-sectional area due to oxide film destruction can be regarded as the same. It is considered that the increase in γ reflects the increase in resistance due to the increase in the temperature of chromium and base iron in the plating layer. From this, it is understood that the heat generation rate during welding can be controlled by the C and Mn concentrations of the steel sheet surface layer.

However, according to the Iron and Steel Handbook, 3rd Edition, Volume 1, Page 311, the specific resistance of steel due to trace elements in ordinary steel is ρ = ρ
₀ + αC {ρ ₀ : electrical resistivity of pure substance, C: atomic percentage of impurities, α: 5.9 μΩcm (Mn)}. Here, even if the Mn content changes to 0.4 wt% and 0.2 wt% for pure iron having an electric resistivity of 25 μΩcm at the temperature during welding, for example, 505.1 K, it can be regarded as atomic percentage ≒ weight percentage in the trace amount. Therefore, the electrical resistivity is {(5.9 × 0.2 / 100) /
25} × 100 = 0.047% only, and the same applies to the C concentration, which cannot be the cause of the difference in the resistance increase rate gradient of each sample in FIG.

That is, the inventors of the present invention have discovered the influence of C and Mn in steel, which has not hitherto been known, on the plate / plate interface welding resistance. The present inventors have obtained the following findings as a result of investigating the influence of the components in the steel on the welding resistance. That is, in order to increase the interfacial resistance at the time of welding, C0.001 to 0.18% as the average weight percentage in the region from the outermost surface of the steel sheet as the plating base to 20 μm, Mn0.
It is necessary to contain 10 to 0.6%. Even if the above elements are in the above range as the average composition of steel, if the average weight percentage in the region from the outermost surface of the steel sheet to a depth of 20 μm deviates from the above range, the above effects cannot be obtained. If the average composition does not satisfy the above range in the region from the outermost surface of the steel sheet to a depth of 20 μm, increase in heat generation rate due to increase in welding resistance cannot be obtained. Further, even if it exceeds the above range, the effect is saturated. The cause of this phenomenon is not clear, but it is considered that the interface resistance changes due to the steel composition that concentrates on the surface. In any case, it can be seen from this that by controlling the content of Mn together with C in the steel, the rate of increase in welding resistance at the plate / plate interface, that is, the rate of temperature rise can be controlled.

The chromium-plated steel sheet of the present invention is a chromium-plated steel sheet which cannot be controlled by the conventional method with respect to the welding resistance conventionally controlled by adjusting the amount of hydrated chromium oxide and the fine surface structure of metallic chromium. Focusing on dispersion by manufacturing lot, for chromium-plated steel sheets with a coating layer adhesion amount and plating layer structure within a certain range, by controlling the C and Mn contents in the steel sheet within a certain range, one weld nugget The rate of increase in the welding current resistance value at the interface during formation is controlled. Thereby, the heat generation rate of the plate / plate interface during welding can be set to a desired value, and the above-mentioned lower limit current value and upper limit current value can be set by material design.

The chrome-plated steel sheet of the present invention has
25 to 200 mg / m ² of metallic chromium layer and further reckoned as metal chromium thereon of 2.5 to 20 mg / m ² has a hydrated chromium oxide layer,
The metal chrome layer has a part thereof protruding while continuously covering the underlying Fe layer, and the base diameter of the protruding part is 30 to 500 nm,
Height from the base is 10 nm or more, and the density of protrusions is 1 x 1
0 ¹² to 1 × 10 ¹⁵ pieces / m ² and contains C0.001 to 0.18% and Mn0.10 to 0.6% as an average weight percentage in the region from the outermost surface of the steel sheet as a plating base to a depth of 20 μm. It is a chrome-plated steel sheet with excellent high-speed continuous weldability.

If the amount of metallic chromium deposited is less than 25 mg / m ² , the underlying coating with metallic chromium is not sufficient, and the rust resistance and paint adhesion are insufficient. On the other hand, if it exceeds 200 mg / m ² , further improvement in paint adhesion cannot be expected, and there is no point in producing too much production equipment. If the amount of chromium hydrate oxide adhered is less than 2.5 mg / m ^{2 in} terms of metal chromium, the paint adhesion is insufficient, and if it exceeds 20 mg / m ² , the initial welding resistance becomes too high and weldability is impaired. Not preferable. Even if the diameter of the base of the protrusion of the metal chromium plating layer is less than 30 nm, and the height thereof is less than 10 nm, the density of protrusions is 1 ×.
Even if it is less than 10 ¹² pieces / m ² , the effect of reducing the welding resistance due to the destruction of the oxide film during welding is insufficient. Even if the diameter of the base exceeds 500 nm and the density of protrusions exceeds 1 × 10 ¹⁵ pieces / m ² , the effect of reducing the welding resistance due to the destruction of the oxide film during welding is saturated, and the surface It is not preferable because the color tone becomes dark.

The C content and Mn content in the steel are C as the average weight percentage in the region from the outermost surface of the steel sheet to a depth of 20 μm.
It is limited to 0.001 to 0.18% and Mn 0.10 to 0.6%. If these elements are less than the lower limits, they are insufficient to contribute to the control of interfacial welding resistance. Further, even if these elements exceed the upper limit, the effect of controlling the weld interface resistance is saturated, and when imparting the mechanical properties normally required for steel sheet for cans, there are restrictions on the heat treatment time, rolling reduction, etc. It is not preferable.

Further, in the present invention, an organic coating may be appropriately applied as the outermost layer on the chrome-plated layer of the chrome-plated steel sheet for rust prevention or lubrication.

[0021]

EXAMPLES Specific examples of the present invention will be shown below together with comparative examples. [Examples 1 to 4 and Comparative Examples 1 to 4] Regarding the steel plates having the plate thickness, roughness, chrome plating adhesion amount, C in steel and Mn amount shown in Table 2, after heat treatment at 210 ° C. for 20 minutes, The dynamic contact resistance was measured with a dynamic contact resistance measuring device.

Welding current is 3kA, square wave pulse of 6msec,
The electrode diameter was 1.2 mm and the electrode pressure was 60 kgf. In each of the chrome-plated steel sheets of the examples, by controlling the average Mn and C concentrations of the outermost layer 20 μm in the steel within the fixed range of the present invention,
The plate / plate interface welding resistance increase rate is higher than that of each comparative example.

[0023]

[Table 2]

[0024]

According to the present invention, when a rectangular blank is formed into a cylinder by using a mash seam welding machine for can body welding and the like, and two opposite sides are overlapped and seam welded to form a cylindrical can body. In addition, for chrome-plated steel sheets used as can body materials, the heat generation rate at the plate / plate interface during welding can be set to a desirable value, and the welding current can be set easily by reducing the dispersion of welding resistance. , The efficiency of welding work is achieved.

[Brief description of drawings]

FIG. 1 is a graph showing measurement results of dynamic contact resistance at a plate / plate interface.

FIG. 2 is a graph showing the measurement results of the dynamic contact resistance at the plate / plate interface.

Claims (1)

[Claims] 1. A chrome-plated steel sheet formed on a welding can body by lap seam welding using a can body welding machine, wherein a metal chrome layer of 25 to 200 mg / m ² is formed on the surface of the steel plate, and further thereon. It has a hydrated chromium oxide layer of 2.5 to 20 mg / m ^{2 in} terms of metallic chromium, and the metallic chromium layer continuously covers the underlying Fe layer and partially protrudes. 30 to 50 nm, the height from the base is 10 nm or more, the density of protrusions is 1 × 10 ¹² to 1 × 10 ¹⁵ pieces / m ² , and the depth from the outermost surface of the steel sheet as a plating base to 20 μm C0.001 to 0.18%, Mn0.10 to 0.6 as the average weight percentage in the region
%, A chrome-plated steel sheet with excellent high-speed continuous weldability.