JPH0225977B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a low alloy steel having good seawater resistance, workability and hot-dip galvanizing properties. In recent years, as marine development has become more active, there has been a demand for steel materials that have excellent corrosion resistance in the harsh corrosive environment of the ocean, and various seawater-resistant steels have already been developed. By the way, depending on the purpose of steel materials, after hot rolling,
Often requires various types of cold working. Examples include cold rolling, cold drawing, cold extrusion, and cold forging. When cold-working hot-rolled steel, it is important to optimize the strength of the hot-rolled steel based on the equipment, process, and properties of the steel after processing. However, many conventional seawater-resistant steels are relatively high-strength hot-rolled steels that were developed primarily for structural purposes, and are not necessarily suitable for cold working as described above. Furthermore, conventional seawater-resistant steels suffer from significant plating burn when hot-dip galvanized, and are often unsuitable for hot-dip galvanizing for corrosion protection. The present invention was proposed to improve the drawbacks of conventional seawater resistant steel as described above.
Si: 0.03% or less, Mn: 0.20-0.50%, P: 0.025
~0.050%, Cu: 0.20~0.40%, Cr: 0.50~1.50%
It is a seawater-resistant low alloy steel characterized by containing Fe, with the balance essentially consisting of Fe, and this low alloy steel has significantly greater workability and hot-dip galvanizing properties than conventional seawater resistance. It has improved seawater resistance as well as improved seawater resistance. That is, the characteristics of the steel of the present invention are P in the above composition range,
Due to the combined action of Cu and Cr, it has excellent corrosion resistance in seawater and corrosive environments exposed to seawater spray and sea breeze, and has succeeded in maintaining workability and hot-dip galvanizing properties. bar wire,
It can be used for all steel materials such as shaped steel, steel plates, and steel pipes. Next, the reason for limiting the composition range of the steel of the present invention will be described. C: 0.10% or less C in the low alloy steel of the present invention is an effective element for ensuring strength, but since it deteriorates workability and corrosion resistance, it is limited to 0.10% or less. Si: 0.30% or less Si is effective as a deoxidizing agent in addition to increasing strength, but it cannot be said to be effective in terms of corrosion resistance.
If the Si content is too high, it will cause plating burns during hot-dip galvanizing, so it was limited to 0.30% or less. Mn: 0.20-0.50% Mn is effective as a deoxidizing agent in addition to increasing the strength of the seawater-resistant low-alloy steel of this invention, and at least 0.20% or more is necessary, but if it is too high, corrosion resistance will be reduced. This will cause deterioration, so set the upper limit to 0.50% or less.
The lower limit was set at 0.20%. P: 0.25~0.050% P is effective for corrosion resistance, at least 0.025%
% or more is necessary, but if it is too high, the toughness deteriorates, so it was limited to 0.050% or less. Cu: 0.20-0.40% Cu improves corrosion resistance and coexists with P to further increase its effect, so it is necessary to have at least 0.20%, but if it is too high, it will cause hot brittleness, so the lower limit was limited to 0.20%, and the upper limit was limited to 0.40%. Cr: 0.50 to 1.50% Cr improves corrosion resistance and coexists with Cu to further increase the effect, so at least 0.50% or more is required, but if it is too high it may cause local corrosion, so the upper limit should be set. 1.50% or less, with the lower limit set at 0.50%. Examples Examples in which the steel of the present invention is applied to wire rods will be described below. Low alloy steel and comparative steel having the compositions shown in Table 1 were produced. Comparative steel No. 1 is a conventionally used mild steel, and No. 2 and No. 3 are steels of the present invention, each of which was used for comparison. Table 1 shows the chemical composition and tensile strength test results of the sample materials.

[Table] The low alloy steel and mild steel (comparative steel) of the present invention having the compositions shown in Table 1 were melted, hot rolled into wire rods with a diameter of 5.5 mm, and then drawn into wire rods with a diameter of 3.2 mm. The tensile test values are shown in Table 1. Further, a drawn wire with a diameter of 3.2 mm was immersed in actual seawater as a bare wire, and hot-dip galvanized with a zinc coating amount of 44 g/m ² to measure the corrosion loss. Figure 1 shows the corrosion test results of bare wires in actual seawater.
Figure 2 shows the results of a corrosion test of hot-dip galvanized wire in actual seawater. As shown in Fig. 1, comparative steel No. 1, which is a conventionally used mild steel, breaks after 18 months in the case of bare wires, whereas invention steel No. 2 and No. 3 break after 18 months.
has been used for more than 24 months. In addition, as shown in Fig. 2, hot-dip galvanized wires can also be used with the invention steel No. 2 and
No. 3 has less corrosion loss than comparative steel No. 1, and has excellent corrosion resistance. As described above, the steels of the present invention No. 2 and No. 3 are superior to the comparative steel No. 2 in both bare wire and hot-dip galvanized wire.
It exhibits superior corrosion resistance to seawater, and is suitable as a steel wire rod used in aquaculture cages, gabions, futon cages, and other corrosive environments exposed to seawater, seawater spray, and sea breeze.

[Brief explanation of drawings]

Figure 1 shows the results of a corrosion test in actual seawater for bare wires made of the invention steel and comparison steel (mild steel), and Figure 2 shows the hot-dip galvanized wires made of the invention steel and comparison steel. A diagram showing the results of a corrosion test in actual seawater.

Claims (1)

[Claims] 1 C: 0.10% or less, Si: 0.30% or less, Mn: 0.20
~0.50%, P: 0.025~0.050%, Cu: 0.20~0.40
%, Cr: 0.50 to 1.50%, the remainder being substantially
Seawater resistant low alloy steel characterized by being composed of Fe.