JPS59107064A - Corrosion-resistant steel material - Google Patents

Abstract

PURPOSE:To provide a corrosion-resistant steel material which improves remarkably the pitting resistance of a weather and sea water-resistant steel material to be used in land and ocean environment by composing the same of C, Si, Mn, Cu, P, S, Al, Ca, Ce, and iron, etc. and of a specific compsn. CONSTITUTION:A titlted corrosion-resistant steel material contains 0.001-1.0% C, 0.005-1.0% Si, 0.01-2.0% Mn, 0.01-0.5% Cu, 0.06-0.15% P, <=0.002% S, 0.001-0.1% Al, 0.0002-0.05% Ca and Ce (a small amt. of La may be incorporated) added in combination, and further contains 0.01-0.2% Nb, Ti, V, Mo, B alone or in combination or 0.01-1.0% Ni, Cr according to need and consists of the balance iron with unavoidable impurities, wherein the amt. of the S composed therein is decreased and Ce is added to improve pitting resistance. Nb, etc. are added to improve the strength of the steel material and Ni, etc. are added respectively according to need in order to improve the strength and toughness.

Description

[Detailed Description of the Invention] This is a corrosion-resistant steel material that has significantly improved pitting corrosion resistance compared to steel and seawater-resistant steel materials.

The essence of the present invention was discovered by the present inventors, and a patent application was filed in Tokuko Sho J, 2-9! Guj No. 3, U.S. Patent No. 3? Gu7! However, with subsequent improvements in smelting technology, the amount of S in steel was reduced to θθθ. ．． Even if the amount of P is increased to θθ6 or more as it becomes possible to reduce it to 2oII or less, C
A dramatic improvement in rust resistance and pitting corrosion resistance was observed with the addition of e alone. Therefore, Ce is basically added to materials with a significantly reduced S content.

Now, corrosion of steel is caused by sulfide α (Mn, Fe
)・S dissolves in dew or seawater that comes into contact with the steel surface, and is generated by the oxygen dissolved in these.γ・Mn203
・(Mn304) acts as a trigger to form red rusty γ・FeSO
Generate H. Pitting corrosion is likely to occur from this sulfide portion. Therefore, in order to reduce and suppress the occurrence of pitting corrosion, it is necessary to reduce the amount of KS as much as possible in order to lower α・(Mn,Fe)・S, which is the starting point of corrosion, or to change the properties of sulfides in water. It is necessary to convert it into something insoluble. This first thing.
These are disclosed in Tokuko Sho S, No. 2-YG S, U.S. Patent No. 3. As described in Bug 7.2, with the refining technology at the time of filing, the entire S view θθθ,...? It was difficult to reduce the Therefore, for rust resistance 1 and pitting corrosion resistance α・
(Mn, Fe)・S is insoluble in water (Ce sulfide, Ce
Composite sulfide! It is impossible to simultaneously reduce the amount of KP to 9041% or less when adding KCe.

On the other hand, in the present invention, it has been found that outstanding rust resistance and pitting corrosion resistance can be achieved even when P is increased to θθ6 to θ/S as it becomes possible to reduce S to θθθ2 or less. This is what happened.

The basic component of the present invention is Cθθθ/~/θθS10θθS
~10 ratio, Mnθθ/~βθ ratio, Cuθθ/~θ5 ratio,
Pθθot~θ/, 5%, Sθθθ, 2% or less, htθ
θθ/~0/%, Ca.

It contains 68,862 to 685% of Ce as a composite addition, and the balance consists of iron and inevitable impurities. Further, the second invention is characterized in that this basic component is a carbide- or nitride-forming element of N.
The aim is to improve the strength of steel materials by adding b, Ti, v, Mo, and B as selective elements. Ni again.

The purpose of adding Cr is to improve strength and toughness.

The details will be described below, and the reason why the composition range of the steel material of the present invention was determined as described above will be explained.

C is the easiest element to obtain the strength of steel, but θ
When the ratio is less than θθ, sufficient strength cannot be obtained, and when the ratio exceeds θθ, it becomes brittle. Therefore, the lower limit is defined as θθθ/q42 limit/θchi(((defined).

Si and Mn are necessary as deoxidizing elements in steelmaking work, and each requires an amount of 660.5%, 667% or more. Furthermore, although Si and Mn are metals that are easy to obtain the strength of steel, if Si is added in an amount exceeding /θ% and Mn is added in an amount exceeding Ωθ, there is a possibility of causing embrittlement of steel. Therefore, Si
The lower limit of θθθ5% and the upper limit (d/θ%).
The lower limit of Mn is θθ/chi, and the upper limit is! It is specified in relation to θ. Cu
is added to improve weather resistance and seawater resistance; if it is less than 907%, no effect will be observed, and if it exceeds 85%, it will cause embrittlement. Therefore, the lower limit is θθ/the upper limit is 9
limited to 5%]7.

Although P has a remarkable effect in terms of weather resistance and seawater resistance, it is more desirable to reduce the amount of P in terms of rust resistance. In the present invention, by reducing St-θθθ to 2% or less and fixing this S with Ce, the rust resistance does not deteriorate even if the amount of P is increased. However, if the amount of P exceeds the θ/S ratio, the rust resistance will be adversely affected. Therefore, in order to simultaneously satisfy a wide range of weather resistance, rust resistance, and corrosion resistance, the P amount was limited to 696 to 975%.

At is used as a deoxidizing element, but when fixing S in steel with KCe as in this case, A
The method of adding t and the setting of the amount added are important. At amount θθ
When the kt amount is less than θ/%, deoxidation is insufficient, and when the kt amount exceeds θ/%, there is a risk of At203 cluster formation which causes surface defects. Therefore, the lower limit of At is θθθ/chi, and the upper limit is θ
/%.

Next, Ca is an essential element to reduce S in steel to 6962% or less, but in order to generate water-insoluble sulfides, it is necessary to reduce the amount of Ca mixed in sulfides as much as possible. is desirable. Therefore, taking into consideration the amount of Ca remaining in the steel, the lower limit of the combined amount of Ca and Ce added was set to θθθθ2.

Ce (which may be accompanied by a small amount of La) is the heaviest element, but since the amount of S in the steel is reduced to θθθ−2% or less, an upper limit of around 665% is sufficient. Therefore, when reducing S, in addition to Ca included, Ce and C
The upper limit was set to 605% for both a.

The addition of KNb, Ti, V, Mo, and B was aimed at increasing the strength of the above corrosion-resistant steel materials.88697
If the coefficient is less than 2%, no effect will be observed, and if the coefficient of θ exceeds 2, embrittlement will occur.

・The lower limit was set at 99887%, and the upper limit was set as the vanguard.

In addition, Cr and Ni are used when strength and toughness are required (
No effect is observed below 0θ/value when added at
If the number exceeds 10, the call economy deteriorates. Therefore, the lower limit is θθ
The upper limit was defined as /θ.

According to the present invention, the steel composed of the above-mentioned chemical components is melted in a converter, electric furnace, etc., and is hot-rolled into steel sheets using a continuous casting method or a normal ingot-forming method, using vacuum degassing as necessary. Manufactured as. If necessary, it can be manufactured as a billet during casting.

Furthermore, after hot rolling according to the required C, standard or annealing or f/
-i Manufactured as a steel plate by cold rolling or cold rolling followed by annealing.

Furthermore, the steel sheet of the present invention can also be used as a surface-treated steel sheet.

Examples of the present invention are described below.

Table 1 shows the chemical compositions of the comparative steel and the steel of the present invention.

Both are melted in a converter, and after ingot formation, hot rolling 1. To conclude, Table 3 shows the results of the pitting corrosion resistance test and the rust resistance test.A in Table 2 shows the results of the hot-rolled sheet after descaling and exposing it outdoors for 6 months to remove the rust. The maximum depth of pitting corrosion measured with a micrometer is shown as /θθ for the comparative steel.Also, A2 is the maximum depth of pitting corrosion after salt water spraying for θdays. Similarly, A3 is a hot-rolled sheet specimen after puff polishing using a QC panel tester (inner surface 3
2℃, outside! θ°C) K/hr exposure to promote rust formation, and the results are shown in terms of rust generation area. From Table 3, it can be seen that the steel of the present invention has multifunctional corrosion resistance and is completely ν stiffer than the conventional steel.

Claims (1)

[Claims] fllc; θθθ/~/θ%, Si: θθθj~/
θ ratio, Mn: θθ/~ノθ%, Cu: 00/~03 ratio,
P: 666-975%, S: θθ0.2% or less ht: θ
Corrosion-resistant steel material containing 69,663 to 085% by composite addition of θθ/~θ/%, Ca, and Ce (sometimes accompanied by a small amount of Laf), with the balance consisting of iron and inevitable impurities. +2+C; θθθ/~/θ ratio, Sl; θθθj~/θ%
, Mn; θθ/~2θ salary, Cu; θθ/~θj%,
P; θθ Oto ~ θ/j, S; θθθ, 2 or less, At;
θθθ/~θ/chi, Ca. Ce (sometimes accompanied by a small amount of La) is added in combination to contain θθθθ ~ θθj%, and V, Mo, B, Ni, and Cr are added singly or in combination to contain Nb, Ti, V. Mo, B are θθ/~θ, 2q6, Ni, Cr are θθ/
A corrosion-resistant steel material containing ~/θchi with the balance consisting of iron and inevitable impurities.