JPS6032715B2 - Manufacturing method for surface-treated steel sheets - Google Patents

Description

Detailed Description of the Invention The present invention applies a phosphorous compound on the surface of a steel plate in order to form a phosphorous oxide film with good lubricating properties on the surface of the steel plate, and in order to suppress the moisture content in the atmosphere of the dawn anchor, the dew point is 000. In addition, in the case of a non-oxidizing gas containing hydrogen, the partial pressure ratio of hydrogen and water (PH20/P
The present invention relates to a method for manufacturing a surface-treated steel sheet, characterized in that H2) is 1.0 or less.

Regarding the method of forming a phosphorous oxide film by conventional heating, see Tokukotsu No. 49-109476 (Tokukotsu No. 51-37072).
Or Tokusai No. 50-3082, (Samurai Batsu 51-10
No. 5966), a method in which a water-soluble or insoluble neighboring compound is applied to the surface of a steel sheet and heated in a non-oxidizing atmosphere; A method is known in which the concentration of phosphorus on the surface of a steel sheet is increased by performing surface treatment with a phosphorus-containing compound that has no oxidizing properties and then performing non-oxidizing heat treatment.

Samurai Gan No. 49-109476 and No. 50-30822 disclose the above-mentioned method as a method for forming a phosphorous oxide film, but the characteristics of the film formed are not clear.
The heating conditions did not meet the necessary conditions. Furthermore, Machigao No. 44-54262 'is a method for forming a phosphorous-rich striped layer on the surface of a rolled steel sheet, which is completely contrary to the method for forming a phosphorous oxide film. The present inventors have investigated the problem of chapping, galling, abrasions, etc. (hereinafter referred to as surface damage) that occur when strong frictional phenomena occur between the processing tool and the material during line processing such as drawing, ironing, and rolling. In order to prevent this from occurring, it is best to prevent metal-to-metal contact from occurring on the friction surface, but we have discovered that for this purpose it is important to have a phosphorous oxide film that tightly adheres to the steel plate surface. , the present invention has been achieved.

Prevention of surface damage during cold working is indispensable for reducing processing jig maintenance costs, reducing work downtime associated with maintenance, and improving product quality. It is known that when a strong frictional phenomenon occurs during lining processing, the frictional surface is under high pressure conditions, and the heat generated by the friction raises the temperature.

Under such conditions, the presence of a solid film is important, as well as its adhesion to the steel plate surface. In the present invention, the total compound (P) is applied to the steel plate surface at a rate of 0.1 to 5.0 y/d and heated in a non-oxidizing atmosphere, but the reason for limiting the adhesion amount of neighboring compounds is that This is related to the film thickness, and the lower limit of 0.1 fence/d is the lower limit of the film thickness because it does not cause surface scratches, and it is the limit thickness that does not cause metal-to-metal contact. At the upper limit of coating amount of 5.0/d, it is a thick upper limit, but since it is an oxide film, the thicker it is, the more likely it is to break, and the film itself falls off from the steel plate surface.
The surface of the machining jig may build up, impeding lubricity, or
Since this may cause surface damage, the upper limit has been set.

A coating thickness of 9'd in the range of 0.1 to 5.0 corresponds to a coating thickness of about 0.01 to 0.5. Next, when heating a phosphorus compound after coating it on the surface of a steel plate, restrictions on the dew point of the heating atmosphere, heating temperature, and time are important.

First, atmospheric fog point constraints have important implications for film composition. Figure 1 shows the atmospheric dew point and the amount of oxygen in the film, and it is clear that as the fog point increases, the amount of oxygen in the film increases, and a rapid increase occurs above 0°C. It is. As the amount of oxygen in the film increases, the phosphorus oxide film becomes brittle and easily damaged, whereas those with low oxygen content are viscous and have good fluidity on friction surfaces under high pressure and temperature. , surface damage can be effectively prevented. Next, regarding the heating temperature, the phosphorous oxide film has poor adhesion even if it is simply applied to the surface of the steel plate, and it easily peels off and falls off on strong friction surfaces, so it cannot effectively exert its ability to prevent surface damage. be.

In order to eliminate this drawback, the adhesion of the phosphorus oxide film can be improved by allowing the phosphorus oxide to react with the surface of the steel sheet and intervening a phosphorus oxide layer containing iron as a reaction product. For this reason, the steel plate coated with phosphorous oxide needs to be heated to at least 200 qo or more, but dissolving the iron in the phosphorous oxide hardens the film itself and makes it brittle, so it is extremely difficult to improve adhesion. Thin layer. It only needs to react with iron.

Therefore, the heating temperature may be 20 mm or higher for a short time, that is, 3 minutes or less, preferably 3 $ec or less. By this heating, the phosphorus oxide film has a two-layer structure, with the upper layer being a thermal decomposition product of the scale compound and the lower layer being a reaction product film of iron and phosphorus compounds, which has an excellent ability to prevent surface damage. The reason why the heating atmosphere is non-oxidizing is to prevent the growth of iron oxide, and any gas such as nitrogen, argon, or a mixture of nitrogen and hydrogen may be used.

In the case of an atmosphere containing hydrogen, the higher the heating temperature, the more likely the phosphorus oxide is to be reduced, which may cause the oxide film to disappear, so it is necessary to increase the amount of deposition. As the reduction progresses, an iron-phosphorous alloy is formed, and this alloy is hard and brittle and has poor lubricity, so it is necessary to prevent the reduction of phosphorus oxides from proceeding as much as possible. Therefore, when the non-oxidizing atmosphere contains hydrogen, the partial pressure ratio of hydrogen and water (PQO
/PH2) must be 1.0 or less.

The reason for this is that the atmosphere changes from oxidizing to reducing depending on the partial pressure ratio. For example, at 700oo,
When PH20/PH2>5, iron oxidation (Fe+QO=Fe
○ If the conditions are such that 2) will also occur, healthy film formation cannot be expected. Elements that are more easily oxidized than iron are oxidized at lower partial pressure ratios. The present invention was achieved as a result of testing under various conditions to determine the conditions for forming a film that does not cause surface damage during lining processing, and is preferably PH20/PH2<1.0, preferably PH20/PH2<0.1. Examples of the present invention will be described below.

Example 1 After surface cleaning of a 0.3 mm steel plate after skin pass rolling, an aqueous ammonium phosphate solution was applied to the surface to give a coating weight of 1.5 mm and dried.

This steel plate was heated under the conditions shown in Table 1 to form a film. Thereafter, a load of 5k9 was applied to the steel balls on two sides using a Bowden friction tester, and changes in the coefficient of friction were measured when the same location (5 fence lengths) was repeatedly rubbed. In this case, lubricating oil was applied in advance to the surface of the steel plate using machine oil No. 1 9' and No. 2. The test results are shown in Table 1 and Figure 2, where the machine axis shows the number of repeated frictions, and the vertical axis shows the friction coefficient in that case.

As is clear from FIG. 2, samples ① and ② according to the present invention
, ■, ■, and ■ have extremely stable friction coefficients because the film does not break and metal-to-metal contact does not occur even when the number of times of friction increases.

On the other hand, it is clear that samples 2, 5, and 8 other than those of the present invention easily break down the film, and the coefficient of friction increases in a short time due to the occurrence of metal-to-metal contact. Example 2 After applying ammonium phosphate (as phosphorus) at 9/d of 1.0 on the surface of a clean steel plate after cold rolling on the 0.35 side, the steel plate was heated at 65,000 6%, d. p=-
The rest was heated at 25° C. (PH20/PH2=0.014) in an N2 atmosphere.

This steel plate was made into a disc with a diameter of 135 mm and was drawn twice to a diameter of 65 mm.
Make a cup with 5 ribs ◇, and process it 3 times to make it 0.35
→The side wall was stretched to 0.10 chest. The steel sheet with this phosphorous oxide film did not suffer any surface damage even if it was continuously formed on one or more sides, but the untreated material showed galling in 2 to 3 pieces and became hard at 10 to 2 q and could not be formed ( (in ironing process).

[Brief explanation of the drawing]

Figure 1 shows the relationship between the atmospheric dew point and the oxygen content in the film, and Figure 2 shows the massat coefficient (
This is a graph showing the test results for France) and Friction Islam. Many? Many diagrams

Claims (1)

[Claims] 1. A method for producing a surface-treated steel sheet in which ammonium phosphate is applied to the surface of the steel sheet and then heat-treated in a non-oxidizing gas atmosphere, wherein the dew point of the gas atmosphere is set to 0°C or less,
A method for producing a surface-treated steel sheet, comprising heating at 0° C. or higher for 3 minutes or less. 2 Contains hydrogen and has a partial pressure ratio of hydrogen and water (PH_2O
2. The method for producing a surface-treated steel sheet according to claim 1, wherein heating is performed in a non-oxidizing gas atmosphere in which /PH_2) is 1.0 or less.