JPH0249383B2 - KOSHITSUJIBANUCHIKOMIPAIRUYOKOZAI - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a steel material for piles driven into hard ground (used as piles such as sheet piles and pipe piles). Previously, the tip was hardened by carburizing or nitriding, or high-hardness steel was spliced by welding, but now we have developed a steel material for piles that eliminates this complicated welding process and has sufficient wear resistance as a pile tip. is intended to provide. In recent years, with the diversification of civil engineering and construction work such as dredging work and the location conditions of structures, strict performance has become required of the steel piles used. In particular, piles driven into hard ground such as bedrock often require abrasion resistance and deformation (flipping) resistance at the tips. Taking pipe piles as an example, conventionally carbon steel pipes for general structures (e.g.
Only the tip of JIS G344STK51) is carburized or nitrided to make it hard, or the tip of the steel pipe is made of high C-high Mn (Hadfield steel) with good wear resistance, 80kg class tempered steel, cast steel, etc. around the circumference. It was welded and used. However, when circumferentially welding steel pipes of different steel types to general carbon steel pipes, it is difficult to select welding materials and welding conditions to obtain a sound bead without defects because the joints are of different types, and it is difficult to select the welding conditions to obtain a defect-free bead. There were problems such as the need for a large amount of material and the relatively high cost of these materials. Further, even when using a method of carburizing and nitriding only the tip to harden it, high heat treatment costs are required, making it unsuitable for mass production of large steel materials. Conversely, if ordinary carbon steel (e.g. STK55) is used for rock piles without such a method, the wear resistance will be poor due to insufficient hardness, and the tip will curl up during boring, making it difficult to use. It is easy to infer that people will not be able to withstand it. As a result of various studies in view of the above-mentioned problems, the inventors of the present invention have made it possible to use a relatively inexpensive material of the STK51 class and make only the tip hard, so that it can be used even in the event of a collision with rock. We have successfully developed a steel material for piles driven into hard ground that does not curl up and suffers little wear. The present invention has the following features: (1) The main body (from the tip to the rear end) has a C of 0.10 to 0.50%,
Contains less than 0.80% Si, 0.50~2.0% Mn, and the balance is Fe
and has a uniform composition consisting of unavoidable impurities, and the surface hardness of at least one surface layer of the inner and outer surfaces from the tip to a length of at least 50 mm is Hv (load 10 kg) 400 or more. A steel material for piles driven into hard ground, characterized by the following: (2) Body (from tip to back) C0.10~0.50%,
Si0.80% or less, Mn0.50-2.0%, and Cu0.5
% or less, Ni0.5% or less, Cr0.5% or less, Mo0.5%
Below, Nb 0.06% or less, V 0.10% or less, Ti 0.05%
Hereinafter, a portion containing one or more types of B0.0008 to 0.0030%, with the remainder having a uniform composition consisting of Fe and unavoidable impurities, and extending from the tip to a length of at least 50 mm, and The surface hardness of at least one of the inner and outer surfaces is Hv (load
This is a steel material for piles driven into hard ground, characterized by a weight of 10Kg) 400 or more. In the present invention, the main body (from the tip to the rear end) is made of a steel material having the above-mentioned specific uniform composition. Moreover, this is because there is no weld between this tip and the other main body parts, and there is no composition due to decarburization, nitriding, etc. not only in the length direction of the steel material but also in the thickness direction. This means that there is no major change.
Of course, in this case, the decarburized layer that occurs on the surface of the steel material during normal processes such as rolling and heat treatment of the steel material is not considered a problem. Next, the reasons for limiting the steel composition in the present invention will be explained. In the present invention, the composition must be such that the tip of the steel material can secure a hardness of Hv (load: 10 kg) of 400 or more, which is necessary for a pile driven into hard ground, after hardening from ₃ or more points of Ac. From this point of view, the composition and A lower limit was set. C is an essential element to increase hardenability, but if it exceeds 0.5%, hardenability increases but ductility decreases, or in the case of welded pipes where the pipe pile itself has a straight or helical weld. ,
Since weldability problems such as cracks in the weld zone may occur, this is the upper limit.On the other hand, if it reaches 0.10%, Hv
Since it would be difficult to secure over 400 kg), this was set as the lower limit. Although Si has a deoxidizing effect, if it exceeds 0.80%, ductility and toughness decrease, so this was set as the upper limit. Mn is an element that improves hardenability like C,
The amount is determined by the balance with C, and when the amount of C is small, it is better to increase it in order to ensure hardness, but if it exceeds 2.0%, weldability will deteriorate, so this is the upper limit.On the other hand, if it is less than 0.5% This was set as the lower limit because the toughness deteriorates. In addition, in the steel material of the present invention, if necessary,
Although one or more of Cu, Ni, Cr, Mo, Nb, V, Ti, and B are added, the reasons for limiting these components are as follows. Although Cu increases strength, too much added impairs hot workability, so the upper limit of Cu was set at 0.5%. Although Ni is an effective element for obtaining strength and toughness, the upper limit was set at 0.5% due to cost considerations. Cr is an element that increases strength and wear resistance, but if it is contained in a large amount, the cost will increase and the ductility will also decrease, so the upper limit must be set.
It was set at 0.5%. Although Mo is an effective element for improving hardenability and wear resistance, adding a large amount increases cost and adversely affects toughness, so the upper limit was set at 0.5%. Nb, V, and Ti increase the strength when they are dissolved in solid solution and the fine carbonitrides are uniformly and finely dispersed through subsequent heat treatment, and although inferior to C, they improve wear resistance, so the upper limit is 0.06% each
0.10% and 0.05%. Although B has the effect of increasing hardenability when in a solid solution state in the austenite region, the amount added to effectively exhibit this effect is limited to N, Al,
Since it is greatly affected by the amount of Ti, it was set in the range of 0.0008 to 0.0030% to avoid this. Although there are no particular limitations on the production of the steel material of the present invention, only the specified tip portion described above can be manufactured using Ac ₃
Hard parts can be easily manufactured by heating the part above a point and then cooling it with water.Adding a tempering process after water cooling not only complicates the manufacturing process, but also reduces the quality of the pile material. This is undesirable because it reduces the wear resistance of the material. The hard part mentioned above must be at least 50mm long from the tip of the steel material, but
It is not necessarily necessary to make the entire length hard, 50 to 500
If the length is mm, the effect can be sufficiently exhibited, so it is advantageous from the viewpoint of manufacturing to keep the length within this range. Also, although it is preferable that this hard part be as hard as possible down to the center of the thickness of the steel material, if the surface part that comes into contact with the hard ground of the driving ground and wears out has a certain hardness, then this hard part will be hard enough to surround the surface. There is no problem even if the endoplasmic part is considerably softer than this. It goes without saying that even if the surface having a certain hardness is the outer surface of a sheet pile or the inner surface of a pipe pile, it will have a certain effect. The heating and cooling to obtain this hard part is preferably performed on both sides of the tip of the steel material, but is not necessarily limited to this, and may be performed in various ways such as single-sided heating → double-sided cooling, double-sided heating → single-sided cooling, etc. can. Note that mist, spray, water jet, laminar flow, accompanying cooling, etc. are used for cooling. The heating temperature for quenching is preferably set to Ac ₃ or higher so that the structure during heating becomes uniform austenite and quenching is completed. Although the heating method prior to this hardening is not particularly limited, industrially, short-time heat treatment by induction heating is desirable from the viewpoint of efficiency. Furthermore, although it is known that the harder the steel is, the better the wear resistance of the steel material is.
(Load: 10Kg) The reason why it is 400 or more is because the Hv (load: 10Kg) of general steel pipe piles, for example, JISG3444STK51.
is approximately 170, which makes it unusable for piles driven into hard ground. Therefore, as already explained, a steel pipe for piles driven into hard ground is being considered, in which dissimilar materials are welded only at the tip. Figure 1 shows the case where such dissimilar materials are welded to the tip of a steel pipe, where 1 is a steel pipe, 2
3 indicates a welded portion, and 4 indicates a location where the hardness of the surface thereof is measured. Table 1 below shows the Hv (load: 10 kg) of the outer surface layer when different materials are welded and when the above STK50 is carburized and quenched.

[Table] As is clear from Table 1, the hardness of the outer surface layer at the tip of the steel pipe is approximately 300 to 600 Hv (load 10 kg).
In view of the current situation where Hv300 products do not have sufficient wear resistance, the present invention has developed at least Hv (load 10
Kg) 400 or more. Examples of the present invention are shown in Table 2 below.

【table】

[Table] * Position 1mm from the surface Steel materials No. 1 to 4 are for C-Si-Mn system,
Steel materials No. 5 to 7 are cases in which some alloy is added. For example, in steel pipes such as steel material No. 2 that are water-cooled only from the outside, only the outside surface is hardened to provide wear resistance and curling resistance, and the inner surface layer, which has a relatively low hardness, has toughness. It is also possible to have it provided. Incidentally, the following Table 3 shows a comparison of the toughness values of steel materials No. 1 and 2.

[Table] As is clear from Tables 2 and 3, in the case of hardening the inner and outer surfaces, a hard product is obtained, while in the case of single-sided hardening, a product with a good toughness value is obtained, although the hardness is slightly inferior. It is necessary to use both types depending on the conditions of use. FIG. 2 shows the hardness of the surface layer of the steel pipes according to the embodiments of the present invention shown in Table 2 above and the conventionally used steel pipes shown in Table 1. As is clear from this figure, the steel pipe according to the present invention has the same hardness as conventional piles driven into hard ground (excluding STK50 general purpose piles), and can not be circumferentially welded as conventionally. Since this is not necessary, the cost can be reduced.
Of course, the steel pipe according to the present invention is not used for pile driving, but can be buried as is, or in cases where the ground is deep, it can be easily added and used. The steel material for piles driven into hard ground according to the present invention has the following advantages over conventional ones. (i) Only the tip of the steel pipe is heat treated to harden it.
It is possible to omit the welding process that requires a large amount of man-hours and technology as in the conventional type. (ii) In particular, since the first aspect of the present invention does not use expensive alloy components, it is possible to provide the same performance as conventional products at low cost. (iii) As mentioned in item (ii) above, since it is low cost, it can be directly embedded as a steel pile without having to be used many times for pile driving. (iv) Because only the quenching process is required, the heat treatment time is shorter than that of conventional QT.
It is shorter compared to etc. (v) Of course, if the ground is deep, it is possible to easily add more.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the external appearance of a steel pipe pile with a tip added by conventional welding, and FIG. 2 is a graph comparing the hardness of an embodiment of the present invention and a conventional steel pipe.

Claims (1)

[Claims] 1. The main body (from the tip to the rear end) has a C of 0.10 to 0.50%,
It has a uniform composition containing 0.80% or less of Si, 0.50 to 2.0% of Mn, and the remainder consists of Fe and unavoidable impurities, and has a length of at least 50 mm from the tip, and has an inner and outer surface layer. A steel material for piles driven into hard ground, characterized in that the surface hardness of at least one surface layer of the material is Hv (load 10 kg) 400 or more. 2 The main body (from the tip to the rear end) is C0.10-0.50%,
Si 0.80% or less, Mn 0.50-2.0%, and Cu 0.5%
One or two of the following: Ni 0.5% or less, Cr 0.5% or less, Mo 0.5% or less, Nb 0.06% or less, V 0.10% or less, Ti 0.05% or less, B 0.0008 to 0.0030%. Including the above, the remainder has a uniform composition consisting of Fe and unavoidable impurities, and the surface hardness of at least one of the inner and outer surfaces is Hv (load 10Kg) Steel material for piles driven into hard ground, characterized by a weight of 400 or more.