JPH0448046A - Hot rolled steel excellent in high temperature strength and its manufacture - Google Patents

Abstract

PURPOSE:To improve the high temp. strength of a hot rolled steel and to make better its workability and weldability by compositely adding Ti, Mo and B to an Mn-Al contg. steel and specifying its heating and hot rolling conditions. CONSTITUTION:A steel constituted of, by weight, <=0.01% C, <0.60% Mn, 0.01 to 0.10% Al, 0.05 to 0.25% Ti, 0.0004 to 0.005% B, 0.005 to 1.50% Mo and the balance Fe with inevitable impurities is manufactured. This slab is heated to >=1,050 deg.C and is hot-rolled at >=Ar3 or Ar3 to Ar1 finishing temp. Its coiling temp. is optionally regulated. In this hot rolled steel, the content of carbon is reduced and Ti, Mo and V are compositely incorporated, so that it has excel lent high temp. strength, good workability and weldability and high industrial effect.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hot-rolled steel material with excellent high-temperature strength properties and workability, and a method for producing the same.

(Prior Art) As heat-resistant materials, there are high-strength steel plates for high temperature use that contain Cr, Mo, V, or Nb for the purpose of increasing high-temperature strength or oxidation resistance. For example, in JP-A-57-35823, Mo, Cr, V or Nb is added, and after hot rolling, the steel structure is changed to ferrite+pearlite or ferrite+pearlite. A method has been proposed in which steel sheets with excellent high-temperature strength can be obtained as hot-rolled steel sheets using bainite.

According to this method, there is an effect that a heat-resistant material with excellent high-temperature strength can be obtained without performing heat treatment after hot rolling.

By the way, due to the revision of the Building Standards Act in 1986, higher strength at high temperatures was required for architectural steel materials.
Furthermore, as there is a strong demand for buildings to become taller, it is necessary to further improve high-temperature strength from the perspective of ensuring safety. Further, steel materials for construction are desired to have good workability, and steel materials with good strength characteristics, high-temperature strength characteristics, and good workability are desired.

(Problems to be Solved by the Invention) Regarding the strength at high temperatures of steel materials, that is, the high temperature strength of steel materials, steel materials with high strength at room temperature have a large decrease in strength at high temperatures, and the above-mentioned Cr and Mo are used to reduce this phenomenon.

(2) Alternatively, Nb is added or the steel structure is refined. On the other hand, as the amount of these additive elements increases, the strength at room temperature increases, and for example, the workability in construction and construction deteriorates, making it difficult to process. In addition, if weldability is adversely affected, the welded area may change in material quality.

The object of the present invention is to obtain a hot-rolled steel material that has excellent high-temperature strength characteristics, good workability, is easy to process in construction and construction, and has good weldability and is suitable for construction.

(Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention have conducted experiments and research to reduce the carbon content and use Ti, Mo, and B as additive elements.
It has been found that when these are contained in combination, a synergistic effect occurs, and a hot-rolled steel material with excellent high-temperature strength properties, good workability, and good weldability can be obtained even though the amounts of each of these are small.

The gist of the present invention is, in weight %, c: o, oi% or less,
Mn: less than 0.00%, AN: 0.01-0.10
%, TI+0.05-0.25%, B: 0.00
The hot-rolled steel material has excellent high-temperature strength characteristics and workability, and is characterized by containing 0.04 to 0.005%, Mo2 and 0.005 to 0.50%, with the remainder consisting of iron and inevitable impurities. In addition, another gist is that 1 piece of steel consisting of the above components is used.
After heating to a temperature of 050°C or higher, the finishing temperature is set to A r
The manufacturing method is characterized in that hot rolling is carried out at a point of A or more or between A r 3 and A r 1 point.

Next, the present invention will be explained in detail.

The reason for limiting the steel composition will be explained.

When the content of C increases, the processability at room temperature deteriorates,
Also, since weldability deteriorates, the content should be 0.01% or less.

Mn is included to prevent hot embrittlement due to the unavoidably contained S, but if the amount is too large, the room temperature strength becomes too high for architectural steel and the workability deteriorates, so 0.60
less than %.

1) is 0 to deoxidize molten steel and improve the yield of added alloying elements.
．． The content should be 0.1% or more, but on the other hand, if the content increases, oxide inclusions will increase, and the above-mentioned effect will be saturated, so the content should be 0.10% or less.

In the present invention, Ti, B, and Mo are contained in a composite manner in order to reduce the decrease in strength at high temperatures and obtain high-temperature strength characteristics. Even if these elements are contained alone, there is little increase in strength, but when they are added together, the high temperature strength properties are excellent.
High strength can be obtained even at temperatures above ℃.

To obtain this effect, T1 is 0.05% or more, M.

is 0. (105% or more, B needs to be 0.0004% or more.

On the other hand, if these contents increase, the strength at room temperature becomes too high, the effect of improving high temperature strength properties is saturated, and the cost increases, so Ti is 0.25%, MO is 1.5%, and B is 0. The upper limit is .005%.

The effects of the composite inclusion of Ti, B, and Mo are as follows:
, B work together as structure-refining elements to refine the structure, and the structure refinement contributes to the fine precipitation of TiC, resulting in large precipitation strengthening. It is thought that this suppresses the movement of dislocations and grain boundaries inside, preventing softening due to high temperatures.

The steel composition of the present invention includes the above-mentioned components, with the remainder consisting of iron and inevitable impurities.

In the production of the hot-rolled steel material of the present invention, a steel piece having the above-mentioned composition is heated prior to hot rolling.
Heat to a temperature of 0.050°C or higher.

Hot rolling after heating is carried out at a finishing temperature of Ar or above, or between A r s and A r in order to maintain high temperature strength properties as rolled and to obtain good workability. If the finishing temperature is preferably between Ar3 and Ar1, the strength will be even higher.

The winding temperature in hot rolling does not need to be specified and can be set arbitrarily.

In addition, the cooling rate after finish hot rolling is
There is no need for gradual cooling as in the 5623 publication. Further, after hot rolling, various plating or paints can be applied to remove oxidized scale on the surface of the steel sheet.

(Example) Table 1 shows the steel composition and manufacturing conditions of the sample materials.

The thickness of the hot-rolled steel sheets produced was 4.5 mm, and the tensile strength (TS) and yield strength (PS) of these hot-rolled steel sheets were measured at room temperature (30°C) and 600°C, and the results were Shown in Table 2.

In addition, a bending test was conducted with a minimum bending radius of 0.5 degrees, and 160 degree bending was performed at room temperature (30° C.), and the presence or absence of cracks was investigated. The results are also shown in Table 2.

2nd table Normal temperature strength 600℃ strength Bending test PS TS
PS TS Occurrence 1 35.2 4B, 9
22.8 28.5 None Invention 2 35.1
47.3 23.3 29.1 None Invention 3 33.3 45.7 22.1 27.7 None Invention 4 32.9 45.2 21.6 27
．． 3 None Invention 5 2B, 7 35.8 1
2.4 15.2 None Comparative example 6 36.9
47.4 21.8 28.8 None Invention 7
37.3 48J 20.9 29.3 None Invention 8 28.3 3B, 1 10°5 16.
2 None Comparative Example 9 27.5 35.9 12
．． 8 15.9 None Comparative example 10 27.9
36.5 13.1 18.3 None Comparative example (
Note) PS: Yield strength, TS: Tensile strength As recognized from this example, the present invention demonstrated high strength at 600°C and excellent high-temperature strength properties. Furthermore, although it has high strength, cracks do not occur even when bent at a radius of 0.5 radius, as in the case of low strength, and it is clear that the workability is good.

(Effects of the Invention) The present invention has a low carbon content and contains a composite of Ti, Mo, and B, so a hot-rolled steel material with excellent high-temperature strength, good workability, and weldability can be obtained, and has industrial effects. is large.

Claims (1)

[Claims] 1. In weight%, C: 0.01% or less Mn: less than 0.60% Al: 0.01 to 0.10% Ti: 0.05 to 0.25% B: 0. 0004-0.005% Mo: 0.005-1.50% A hot-rolled steel wire with excellent high-temperature strength characteristics, characterized in that the balance consists of iron and unavoidable impurities. 2. In weight%, C: 0.01% or less Mn: less than 0.60% Al: 0.01-0.10% Ti: 0.05-0.25% B: 0.0004-0.005% Mo: 0.005 to 1.50% A steel billet, the balance of which is iron and unavoidable impurities, is heated to 105%
A method for producing a hot-rolled steel material with excellent high-temperature strength properties, which comprises heating to a temperature of 0° C. or higher and then hot rolling at a finishing temperature of Ar_3 or higher or Ar_3 to Ar_1.