JPH06240409A - Steel for bolt and nut excellent in refractioriness - Google Patents

Abstract

(57) [Abstract] [Purpose] Conventional high-strength hexagon bolt (F10T), hexagon nut (F1
0) A steel for bolts and nuts that has room temperature characteristics equivalent to those of steel and high-strength Torcia type bolt (F10T) steel, and has much higher temperature characteristics than these bolt and nut steels. [Constitution] C: 0.10 to 0.35%, Si: 1.2% or less, Mn: 0.
30 to 1.50%, Cr: 0.45 to 1.50%, Mo: 0.25 to 1.00
%, V: 0.01 to 0.25%, Nb: 0.001 to 0.050%, Al:
Steel for bolts and nuts containing 0.005 to 0.10% and N: 0.003 to 0.020%, the balance consisting of Fe and unavoidable impurities and having a quenched and tempered structure and excellent in fire resistance. In addition to the above ingredients, 0.0003-0.0050% B and 0.15%
One or more selected from the following Zr and / or 0.
One or more kinds selected from 01 to 0.60% Ni and 0.05 to 0.60% Cu may be contained. [Effect] Steel with a yield strength of 441 N / mm ² or higher even at a high temperature of 600 ° C, and can be used without a fireproof coating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bolt and nut steel used in a building structure. More specifically, it is a high strength hexagon bolt (F10T), hexagon nut (F10) (JIS B 118) at room temperature.
6) For bolts and nuts that show the same properties as steel and high-strength Torsian bolts (F10T) (JSS II 09) steel, and have a proof stress of 441 N / mm ² or higher at high temperatures, especially at 600 ° C It is about steel.

[0002]

2. Description of the Related Art Conventionally, JIS B has been used for fastening steel materials for building structures.
High strength hexagon bolt (F10T) and hexagon nut (F
10) and torcia bolts (F10T) specified in JSS II 09
However, even if a fire occurs in a building, the temperature of these steel materials will be 350 ° C even if a fire occurs in the building.
It is obligatory by law to apply a fireproof coating so as not to exceed the limit.

On the other hand, as a result of the comprehensive technical development project "Development of fire protection design method for buildings" carried out by the Ministry of Construction from 1976 to 1986, "stability at fire" was confirmed by numerical simulation and experiment. If this is done, it becomes possible to reduce the coating thickness of the refractory material and to use the steel frame without coating, and the degree of freedom in selecting the refractory construction method in steel frame construction has been greatly expanded compared to the conventional one. According to this new fireproof design method, it is possible to reduce or omit the fireproof coating required by law by using steel materials with excellent high temperature strength, and it is expected to reduce the construction cost and man-hours of steel frame construction. .

However, the well-known heat-resistant steel materials represented by stainless steel and alloy tool steels for hot molds are excellent in high temperature strength, but are too high in room temperature strength and poor in workability.
Since the price is also very high, it is difficult to apply as a steel for fireproof bolts and nuts of building structures from the economical aspect. In addition, the high temperature alloy steel bolt material specified in JIS G 4107 has the same room temperature characteristics as conventional high strength hexagon bolt (F10T), hexagon nut (F10) steel and high strength torcia type bolt (F10T) steel. Although it is shown, it does not have high temperature strength that can satisfy the new fireproof design method, and it is also difficult to apply it as a steel for fireproof bolts and nuts of building structures.

Japanese Unexamined Patent Publication (Kokai) No. 2-247355 proposes bolts and nuts having excellent high-temperature characteristics as a fastening member based on the new fireproof design method, and an economical manufacturing method thereof. However, even with the bolts and nuts of this invention, 600
The proof stress at ℃ is only about 351 N / mm ² at most, and it is hard to say that the high temperature proof stress is sufficient for the fireproof bolts and nuts for building structures that use the refractory coating at a minimum.

[0006]

DISCLOSURE OF THE INVENTION An object of the present invention is to improve the high-temperature yield strength of steel for bolts and nuts, and more specifically, to consolidate fire-resistant steel materials for construction based on the new fire-resistant design method. Hexagon bolt (F10T), hexagon nut (F10) steel, and high-strength torcia type bolt (F10T) steel show the same room temperature characteristics, and high temperature characteristics during fire are much higher than these bolt and nut steels. It is intended to provide steel for bolts and nuts having a proof stress of 441 N / mm ² or more at 600 ° C.

[0007]

Means for Solving the Problems The present invention includes the following (1)
The gist is the steel for bolts and nuts in (4). In addition,% indicating the content of the alloy component is% by weight.

(1) C: 0.10 to 0.35%, Si: 1.2% or less,
Mn: 0.30 to 1.50%, Cr: 0.45 to 1.50%, Mo: 0.25
~ 1.00%, V: 0.01 ~ 0.25%, Nb: 0.001 ~ 0.050%,
A steel for bolts and nuts containing Al: 0.005 to 0.10% and N: 0.003 to 0.020%, the balance being Fe and unavoidable impurities, and having a quenched and tempered structure and excellent in fire resistance.

(2) In addition to the components described in (1) above,
A steel for bolts and nuts which contains at least one of 0.0003 to 0.0050% B and 0.15% or less Zr and has a quenched and tempered structure and excellent in fire resistance.

(3) In addition to the components described in (1) above,
Steel for bolts and nuts containing 0.01 to 0.60% of Ni and 0.05 to 0.60% of Cu, and having a quenching and tempering structure and excellent in fire resistance.

(4) In addition to the components described in (1) above,
One or more of 0.0003 to 0.0050% B and 0.15% or less Zr, and 0.01 to 0.60% Ni and 0.05 to 0.
Steel for bolts and nuts containing at least one of 60% Cu and having a quenched and tempered structure and excellent in fire resistance.

[0012]

In the following, the reason for limiting the chemical composition and structure of steel in the present invention as described above will be explained together with the function and effect.

A) Chemical composition of steel C: C is added to secure a desired strength, but if the content is less than 0.10%, the strength is insufficient. On the other hand, F10T
Excellent toughness is indispensable for steel for class bolts and nuts, but the C content greatly affects this toughness, and C content is 0.35%.
If it exceeds, toughness will be seriously deteriorated. Therefore, the content of 0.10 to 0.35% is suitable.

Si: Si is an effective element for deoxidizing steel and increasing strength. However, if the content exceeds 1.2%, the toughness and cold workability deteriorate, so the content was made 1.2% or less.

Mn: Mn is used as a deoxidizer for steel,
It is an element effective in ensuring strength and toughness. However, if the content is less than 0.30%, the desired strength cannot be obtained, and if it exceeds 1.50%, the effect of improving the strength and toughness is saturated, and only the cost increases, so the content should be 0.30 to 1.50. %.

Cr: Cr has an effect of improving room temperature strength and high temperature strength. In particular, the combined addition of Mo, Nb and V significantly improves the high temperature strength, but if the content is less than 0.45% the desired effect is not obtained, and if it exceeds 1.50% the cold workability deteriorates. Therefore, the content is set to 0.45 to 1.50%.

Mo: Mo is an extremely effective element for improving the high temperature strength, and its effect is particularly remarkable when it is added in combination with Cr, Nb and V. However, if the content is less than 0.25%, the desired high-temperature strength cannot be obtained, and if it exceeds 1.00%, the above-mentioned effect is saturated, which is economically disadvantageous. And

V: V has the function of improving the room temperature strength and high temperature strength of steel. Its action is, in particular, Cr,
It is greatly exhibited by the combined addition of Mo, Nb and N.
However, if the content is less than 0.01%, the desired effect cannot be obtained, and if it exceeds 0.25%, not only the effect is saturated, but also the high temperature strength decreases, and the toughness deteriorates. The content was 0.01 to 0.25%.

Nb: Nb is one of the particularly important components in the steel of the present invention, and has a function of improving the high temperature strength when added in a trace amount. When added together with Cr, Mo, V and N, the high temperature strength is remarkably improved. To secure the effect, a content of 0.001% or more is required,
If the content exceeds 0.050%, not only the effect is saturated but also the hot workability and cold workability deteriorate, so the content was made 0.001 to 0.05%.

Al: Al is an element effective for stabilizing and homogenizing deoxidation of steel. However, if the content is less than 0.005%, the desired effect cannot be obtained, and
If it exceeds 10%, the effect is saturated, and conversely, the increase of inclusions causes flaws and deteriorates the toughness, so the content was made 0.005 to 0.10%.

N (nitrogen): N precipitates nitrides with V and Nb after tempering. This nitride (VN, Nb
N) contributes to refinement of crystal grains of steel, improves room temperature toughness, and helps secure high-temperature strength by increasing softening resistance at high temperatures. If N is less than 0.003%, such an effect is not sufficient. On the other hand, if the N content exceeds 0.020%, the toughness of the steel is rather reduced.

The steel for bolts and nuts of the present invention may further contain one or more of B and Zr or / and one or more of Ni and Cu in addition to the above components. The effects and desirable contents of these alloying elements are as follows.

B and Zr: Since B and Zr have the effect of further improving the hardenability of steel, one or more kinds may be added for the purpose of ensuring high strength, especially when the product size is large. However, in the case of B, if the content is less than 0.0003%, the desired effect cannot be obtained, and if it exceeds 0.0050%, the toughness and high temperature strength of the steel deteriorate. On the other hand, Zr
In the case of 0.1%, if not less than 0.15%, not only the above-mentioned action is saturated, but also the toughness and machinability of steel deteriorate. Therefore, when one or more of these alloy elements are added, B is
It is preferable that the content of 0.0003 to 0.0050% and the content of Zr be 0.15% or less.

Ni and Cu: Since Ni and Cu have the effect of improving strength and toughness, one or more of them may be added if necessary, especially when high strength and high toughness are required. However, in the case of Ni, if the content is less than 0.01%, the desired effect cannot be obtained, and if it exceeds 0.60%, the cold workability deteriorates. On the other hand, in the case of Cu,
If the content is less than 0.05%, the desired effect cannot be obtained, and 0.60%
If it exceeds, hot workability is deteriorated. Therefore, when one or more of these alloy elements are added, Ni is 0.01 to 0.
The content of 60% and Cu is preferably 0.05 to 0.60%. If necessary, one or more of Ni and Cu can be added. However, since Ni also has a function of preventing deterioration of hot workability due to Cu, when Ni is added, Ni is added.
Is also desirable to add at the same time.

B) Steel Microstructure Even if the steel has the above chemical composition, if the microstructure consists of so-called high temperature transformation products such as ferrite, pearlite and high temperature bainite, the desired room temperature strength and high temperature strength can be obtained. Absent. In order to have normal temperature strength equal to or higher than that of conventional bolt and nut steels, and high temperature strength, especially yield strength of 441 N / mm ² or more at 600 ° C, quenching and tempering is performed to quench the steel structure. A tempered structure is required. The quenching treatment may be carried out by a so-called direct quenching method in which the hot steel after hot working is rapidly cooled and quenched, and the hot steel after hot working is once cooled to room temperature and then reheated to quench. You may perform by the method.

[0026]

EXAMPLE Steels having the chemical compositions shown in (1) and (2) of Table 1 were melted by a usual method. In Table 1, steels A to O
Is a steel of the present invention, and steels P to W are comparative steels in which any of the components is out of the range of the content specified in the present invention.

Next, these steels of the present invention and comparative steels were made into steel slabs by a continuous casting method or an ingot-agglomeration method, heated to a temperature of 1200 to 1250 ° C., and then made into a round bar of 25 mm diameter. Hot-rolled, some hot-rolled, then 950-1020 ℃
Quenching was immediately performed from the temperature of. Others were hot-rolled, then once cooled to room temperature, reheated to a temperature of 920 to 1050 ° C and quenched. After that, 400 ~ for all round bars
Tempering was performed at a temperature of 650 ° C., and the structure was adjusted so as to be a quenched and tempered structure.

Test pieces were cut out from the round bar after quenching and tempering thus obtained, and the tensile properties at room temperature and 600 ° C. were investigated. The results are shown in (1) and (2) of Table 2 together with the quenching and tempering temperatures.

From Table 2 (1), the steel of the present invention has good characteristic values in both room temperature strength and high temperature strength, and is an excellent steel for fastening members (bolts, nuts) based on the new fireproof design method. I understand. On the other hand, the comparative steels in Table 2 (2) have almost the same room-temperature strength as the steels of the present invention, but their high-temperature strength is extremely low.

[0030]

[Table 1 (1)]

[0031]

[Table 1 (2)]

[0032]

[Table 2 (1)]

[0033]

[Table 2 (2)]

[0034]

EFFECTS OF THE INVENTION As is clear from the examples, since the steel of the present invention has significantly improved high-temperature properties and high room-temperature strength, it is suitable for fastening fire-resistant steel materials for construction based on the new fire-resistant design method. It is extremely useful as steel for bolts and nuts.

Claims (4)

[Claims] 1. By weight%, C: 0.10 to 0.35%, Si: 1.2%
Below, Mn: 0.30 to 1.50%, Cr: 0.45 to 1.50%, M
o: 0.25 to 1.00%, V: 0.01 to 0.25%, Nb: 0.001 to 0.
050%, Al: 0.005-0.10% and N: 0.003-0.020%
A steel for bolts and nuts containing iron, the balance of which is Fe and unavoidable impurities, and which has a quenched and tempered structure and has excellent fire resistance. 2. A refractory material having a quenched and tempered structure, containing, in addition to the components described in claim 1, at least one of 0.0003 to 0.0050% B and 0.15% or less Zr in weight%. Excellent steel for bolts and nuts. 3. A refractory having a quenched and tempered structure, containing, in addition to the components of claim 1, at least one of 0.01 to 0.60% Ni and 0.05 to 0.60% Cu in a weight percentage. Steel for bolts and nuts with excellent properties. 4. In addition to the components of claim 1, further comprising, by weight, one or more of 0.0003 to 0.0050% B and 0.15% or less Zr, and 0.01 to 0.60% Ni and 0.
Steel for bolts and nuts that contains at least one of 05 to 0.60% Cu and has a quenched and tempered structure and excellent in fire resistance.