JP2859698B2 - Hot-rolled steel with excellent high-temperature strength properties and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot-rolled steel material having high strength at a high temperature and a method for producing the same.

(Prior Art) As a heat-resistant material, there is a high-strength steel sheet for high temperature containing Cr, Mo, V or Nb for the purpose of enhancing high-temperature strength or oxidation resistance. For example, Japanese Patent Application Laid-Open No. 57-35623 discloses that a steel structure is made into ferrite + pearlite or ferrite + pearlite + bainite by adding Mo, Cr, V or Nb, and then gradually cooling after hot rolling. It has been proposed to obtain a steel sheet having excellent high-temperature strength.

It is already well known that a heat-resistant material having excellent high-temperature strength can be obtained without performing heat treatment after hot rolling.

By the way, due to the revision of the Building Standard Law in 1987, the strength of building steel at high temperatures has been required more,
In addition, since there is a strong demand for high-rise buildings, it is necessary to further improve high-temperature strength from the viewpoint of ensuring safety.

(Problems to be Solved by the Invention) Generally, even though it is a heat-resistant steel material, its strength is, for example, high temperature.
When the temperature is 600 ° C. or higher, the temperature decreases, and the strength of the steel material at normal temperature is higher at a higher temperature. Therefore, in order to satisfy the above-mentioned requirements, it is necessary to develop a steel material with less of these phenomena.

In order to obtain high-temperature strength, it is conceivable to increase the amount of alloying elements such as Mo, Cr, V, and Nb.However, such an increase in the amount of alloying elements deteriorates weldability and toughness. There is a problem that the cost is increased again.

An object of the present invention is to provide a hot-rolled steel material having a small amount of alloying elements, excellent high-strength properties, and low softening at high temperature for high strength, and good weldability. .

(Means for Solving the Problems) The present inventors have conducted experiments and studies in order to achieve the above object, and as a result, when Ti, Mo, and B are compounded, a synergistic effect occurs.
In addition, it has been found that a hot-rolled steel material having particularly excellent high-temperature strength characteristics can be obtained even if the amount of each addition is small.

The present invention is based on such findings, and the gist of the present invention is that, in weight%, C: more than 0.01 to 0.13%, Mn: 0.40% or less, Al: 0.01 to 0.10%, Ti: 0.01 ~ 0.15%, B: 0.0004 ~ 0.005%, Mo: 0.005 ~ 0.50%, and the balance consists of iron and inevitable impurities. In the production, a slab consisting of the above components was
It is characterized by performing hot rolling after heating to a temperature of at least ℃.

 Next, the present invention will be described in detail.

 First, the reasons for limiting the steel components of the present invention will be described.

If the content of C is small, it becomes difficult to generate carbide for effectively acting the added alloy element, so it is necessary to exceed 0.01%. On the other hand, if the content increases, the strength at room temperature increases and the moldability deteriorates.
0.13% or less.

Mn is contained in order to prevent hot brittleness due to inevitably contained S. However, if the amount is too large, the room temperature strength becomes too high as a building steel material, and the formability is deteriorated.
% Or less.

Al is used in order to deoxidize molten steel and improve the yield of added alloy elements.
The content is made 01% or more. On the other hand, when the content is increased, the amount of oxide-based inclusions is increased, and the above-mentioned effect is saturated.

In the present invention, in order to enhance the strength characteristics under high temperature, Ti,
B and Mo are mixed and contained. This complex content will be described with reference to experimental results. Fig. 1 shows C: 0.03%, Al: 0.02%
The results of measurement of tensile strength at room temperature and 600 ° C. are shown for a hot rolled steel material containing Ti, Mo, and B alone and a steel material containing Ti, Mo, and B in a steel-containing steel.
As can be seen from this figure, the steel material in which Ti, Mo, and B are compounded has a small decrease in strength due to a rise in temperature, and has a high high-temperature strength. Also, the strength at room temperature is large. This composite content effect is much greater than the effect of increasing the strength due to the single content of Ti, Mo, and B.

It is considered that the increase in strength when Ti alone is added is due to precipitation strengthening by TiC, the increase in strength when only Mo is added is solid solution strengthening and slight precipitation strengthening, and the increase in strength when only B is added is due to microstructure refinement. However, when these are compounded, Mo also works as a B-element with a fine structure, and this fine structure contributes to fine precipitation of TiC due to the inclusion of Ti, and exhibits a large precipitation strength. Further, fine TiC, solid solution Mo, and B suppress dislocations and movement of grain boundaries in steel, and prevent softening at high temperatures. To achieve such effects, Ti needs to be 0.01% or more, Mo needs to be 0.005% or more, and B needs to be 0.0004% or more. On the other hand, if the content of these increases, the strength at room temperature becomes too high, the formability is deteriorated, the weldability is reduced, and the cost is increased.
%, Mo is 0.50%, and B is 0.005%, respectively.

The steel material of the present invention comprises the above composition and the balance of iron and unavoidable impurities.

In the production of the hot-rolled steel material of the present invention, a slab having the above-mentioned composition is heated prior to hot rolling, but fine TiC for securing high-temperature strength and 115 for finer microstructure are required.
Heat to a temperature above 0 ° C.

Although there is no particular need for hot rolling after heating, it is preferable that the finishing temperature be Ar ₃ or higher in order to maintain high-temperature strength characteristics as it is and to obtain good formability. The winding temperature in the hot rolling is not particularly required and is optional.

After hot rolling, various platings or paints can be applied except for the oxide scale on the surface of the steel sheet.

Example Next, an example will be described.

Table 1 shows the steel composition and production conditions of the test materials. The tensile strength (TS) and the yield strength (PS) of the obtained hot-rolled steel sheet at room temperature (30 ° C.) and 600 ° C. were measured, and the results are shown in Table 2.

As can be seen from this example, 60
The strength at 0 ° C. is high for all the samples, and it is clear that the high-temperature strength characteristics are excellent.

(Effects of the Invention) As described above, according to the present invention, a hot-rolled steel material having high high-temperature strength characteristics with a small addition amount of a small amount of alloying elements and excellent weldability can be obtained extremely economically.

[Brief description of the drawings]

The drawing is a graph showing the relationship between the addition of alloy elements and the yield strength (PS).

Claims (2)

(57) [Claims] (1) C: over 0.01 to 0.13%, Mn: 0.40% or less, Al: 0.01 to 0.10%, Ti: 0.01 to 0.15%, B: 0.0004 to 0.005%, Mo: 0.005 to 0.50% by weight% A hot-rolled steel material having excellent high-temperature strength characteristics, including a balance of iron and unavoidable impurities. 2. In% by weight, C: more than 0.01 to 0.13%, Mn: 0.40% or less, Al: 0.01 to 0.10%, Ti: 0.01 to 0.15%, B: 0.0004 to 0.005%, Mo: 0.005 to 0.50% Steel slabs, including iron and unavoidable impurities,
A method for producing a hot-rolled steel material having excellent high-temperature strength characteristics, wherein the material is heated to a temperature of 1150 ° C. or more and then hot-rolled.