JPH05345957A - Mast shape steel for fork lift excellent in wear resistance and weldability - Google Patents

Abstract

PURPOSE:To obtain the objective mast shape excellent in wear resistance and weldability by constituting the inside in contact with a roller of high carbon steel and the outside of low carbon steel into double layer steel. CONSTITUTION:In the axial section of other mast shape steel for a fork lift having flange parts (a) and (c), the chemical components of a layer in the range to the depth of 2/3 of the sheet thickness from the surface are specified, by weight, 0.3 to 0.9% C, 0.1 to 0.7% Si, 0.5 to 2.0% Mn, <=0.05% P and <=0.05% S. On the other hand, the chemical components on the outer face side 2 of the shape steel of at the other parts are specified to <=0.30% C, <=0.60% Si, <=1.50% Mn, <=0.05% P and <=0.05% S. By forming the structure of this shape steel into a double layer one of the high carbon steel good in wear resistance and the low carbon steel high in weldability, its weldability is improved while its wear resistance is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mast section steel for a forklift having excellent wear resistance and weldability.

[0002]

2. Description of the Related Art Forklifts, which play an important role in the field of industrial transportation equipment, are becoming larger and higher in performance year after year. Along with this, the mast section steel for forklifts that receives heavy loads has problems of wear from a practical point of view, and problems of weldability such as cracking when welding without preheating from a manufacturing point of view. Was there. Therefore, in order to solve these problems, the present inventors have
We systematically investigated various relationships such as the relationship between wear and weldability, the chemical composition of steel, the relationship with the structure, and the strength. As a result, the invention described in Japanese Patent Application Laid-Open No. 1-15318 was achieved. According to the invention described in this publication, the amount of carbon in steel, which is an element effective for wear resistance, was increased to about 0.30 to 0.50%, and remarkable wear resistance could be improved. However, on the other hand, since the carbon equivalent becomes large, the weldability deteriorates, cracks occur during welding, and preheating is required during welding, which has hindered manufacturing efficiency.

In order to solve the above problems, Japanese Unexamined Patent Publication No.
As disclosed in Japanese Patent Publication No. 2404062, there has been proposed a method of locally hardening the mast-shaped steel portion in contact with the roller by using the carbon steel S25C for machine structure having a relatively low carbon equivalent. As a result, a mast section steel having wear resistance and considerably improved weldability has appeared, but (1) the cost is high. (2) The technology is not suitable for mass production. (3) Although the carbon equivalent was low, occasionally welding cracks were occasionally found.

There are problems such as the above.

[0005]

In order to fundamentally solve the above problems, studies were conducted to increase the strength of the material by using, for example, TMCP technology. As a result, the wear resistance was improved. It was found that the carbon content in the steel is almost uniquely determined without much dependence on Of course, weldability is determined by the carbon equivalent. Therefore, the ideal mast shape steel that at the same time has good wearability while having wear resistance is
It was concluded that the part that comes into contact with the roller should be a steel with a high carbon content, which has good wear resistance, and the part that requires weldability should be a steel with a low carbon content. The mast section steel for forklift trucks has no welding points on the side that contacts the rollers, and there are welding points only on the side that does not contact the rollers. I tried first. As a result, in the mast-shaped steel shaft cross section, this problem is solved by making the portion in contact with the roller a double-layer steel with a component steel having a high carbon content as much as possible and the other portions with a component steel having a low carbon content as much as possible It was confirmed by experiments that this could be done. That is, an object of the present invention is to provide a mast section steel for forklift trucks, which is a two-layer steel having different composition of the inside and outside of the mast section steel and which has excellent wear resistance and weldability.

[0006]

The present invention has been made based on the above-mentioned findings in order to achieve the above object, and the gist of the present invention is to make contact with a roller in the axial cross section of a mast shaped steel for forklift truck. The range layer from the inner surface of the shaped steel to the depth of ⅔ of the plate thickness is C: 0.3 to 0.9%, Si: 0.1 to 0.7%, M in chemical composition wt%.
n: 0.5 to 2.0%, P: 0.05% or less, S: 0.
Steel with composition of less than 05%, other parts with chemical composition wt% C: 0.30% or less, Si: 0.60% or less,
Mn; 1.50% or less, P; 0.05% or less, S;
A mast-shaped steel for forklift trucks having excellent wear resistance and weldability, which is characterized by comprising a double-layered steel having a composition of not more than 05%.

The present invention will be described in detail below with reference to the drawings. 1 and 2 are axial sectional views of a mast section steel according to an embodiment of the present invention. FIG. 1 shows what is called an outer mast section steel for a forklift and FIG. 2 shows what is called an inner mast section steel. In these figures, the hatched portion 1 on the inner surface side of the shaped steel has a chemical composition wt%
C: 0.3-0.9%, Si: 0.1-0.7%, M
n: 0.5 to 2.0%, P: 0.05% or less, S: 0.
Steel with a composition of less than 05%. The outer surface side 2 of the shaped steel has a chemical composition wt% of C: 0.30% or less, Si: 0.60% or less, Mn; 1.50% or less, P; 0.05% or less, S;
Steel with a composition of 0.05% or less. 1 and 2
In the above, the a portion, the c portion and the d portion of the flange portion come into contact with the roller, and the wear resistance of the a portion and the c portion becomes a problem. In the present invention, the parts a and c in which wear resistance is a problem are steel composition systems characterized by a high carbon content, and the other parts where weldability is important are steel composition systems characterized by a low carbon content. I am trying.

The hatching portion 1 on the inner surface of the shaped steel is made to have a chemical composition
The reason why the carbon amount is limited to 0.30 to 0.90% in wt% is
It was found in the laboratory that wear resistance is uniquely determined by the carbon content in steel, and when the carbon content is 0.30% or less, the wear resistance is inferior to that of the current mast shaped steel. It is necessary to make the carbon content as high as possible for improvement, but if the carbon content is 0.90% or more, the material becomes brittle. If the amount of Si is limited to 0.1 to 0.7%, the amount of Si affects the strength, and to some extent also the wear resistance. And 0.7% or more causes problems such as flaws in manufacturing. Since the amount of Mn greatly affects the strength, the Mn content is limited to 0.5 to 2.0% in order to obtain a yield strength of 500 MPa or more and a tensile strength of 700 MPa or more. The amount of P and S is limited to 0.05 in order to reduce impurities as much as possible.
% Or less. The reason why these constituent steels are limited to the depth from the inner surface of the shaped steel to 2/3 of the plate thickness is that the heat effect inside the thickness causes cracking mainly due to welding performed from the outer surface of the shaped steel. This is to prevent it from occurring. That is, when the inner surface layer of the shaped steel with a high carbon equivalent is thick, the heat effect reaches the high carbon equivalent side due to welding from the outer surface side of the shaped steel,
This is because a martensite structure is easily generated and cracks are generated. It has been experimentally confirmed that the heat effect of fillet welding is within 1/3 of the plate thickness.

The reason for limiting the chemical composition of the outer surface 2 of the shaped steel is as follows.
This is basically to improve the weldability. That is,
The reason for limiting the carbon content to 0.30% or less is that when the carbon content is 0.30% or more, the weldability is deteriorated, cracking occurs during welding, and preheating is required during welding. The reason why the Si amount is limited to 0.60% or less is that the Si amount affects the strength as described above, so that the maximum 0.60% is necessary to secure the static strength of about 500 MPa. The content higher than that is because the weldability is deteriorated. The reason for limiting the Mn content to 1.50% or less is that Mn affects strength as well as Si. Therefore, a maximum of 1.50% is required to secure a static strength of about 500 MPa. The content depends on the deterioration of the weldability. The amount of P and S is limited to 0.05% or less in order to reduce impurities as much as possible.

As described above, the present invention having a two-layer structure of different component systems in the axial cross section of the mast-shaped steel has the following features: explosion-rolling, clad method, cast iron casting method, laminated dispersion casting method, multi-layer continuous casting method, etc. After the bloom or slab is manufactured by any method, it is manufactured into a mast shape steel by a normal hot forming rolling method. The mast shaped steel of the present invention produced in this way has sufficient wear resistance required for forklifts and has very good weldability. Also, it has static strength characteristics that are superior to those of the current mast section steel.

[0011]

EXAMPLES Next, examples of the present invention will be described. Abrasion tests were carried out using a real shaped steel and a real roller using three types of double-layered outer mast shaped steels of the present invention and two types of comparative outer mast shaped steels. Table 1 shows each chemical component, the thickness of the two-layer structure, and the like. Table 2 shows the wear test conditions and the wear test results of each shaped steel. Table 3 shows the maximum hardness of the HAZ portion (heat-affected zone) of the cross section of the shaped steel that was welded to the outer surface side of the shaped steel under the same conditions as the actual work. As is clear from Table 2,
The mast steel of the present invention has much better wear resistance than the current mast steel of the comparative material, and in the heat-affected zone of welding, the current mast steel has a maximum hardness exceeding Hv400 and the occurrence of a martensitic structure is recognized. However, in contrast to practically requiring welding preheating, the mast steel of the present invention has a low maximum heat-affected zone hardness, no martensitic structure is observed, and there is no risk of cracking even without welding preheating. ..

[Table 1]

[0012]

[Table 2]

[0013]

[Table 3]

[0014]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the inner surface side of the mast shape steel which requires wear resistance is a high carbon steel and the outer surface side of the mast shape steel which requires weldability is a low carbon steel. The layered structure is an epoch-making one that solves the contradictory characteristic that the weldability deteriorates on the contrary when the wear resistance is improved.

[Brief description of drawings]

FIG. 1 is a view showing an axial cross section of an outer mast section steel which is an embodiment of the present invention.

FIG. 2 is a view showing an axial cross section of an inner mast section steel which is another embodiment of the present invention.

[Explanation of symbols]

 1 shaped steel inner surface side 2 shaped steel outer surface side

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Uchino 1-1-1, Toibata-cho, Tobata-ku, Kitakyushu City, Kitakyushu, Fukuoka New Nippon Steel Corporation Yawata Works

Claims (1)

[Claims] 1. In the axial cross section of a mast section steel for forklift truck, a range layer from the inner surface of the section steel in contact with the roller to a depth of ⅔ of the plate thickness is C; 0.
3 to 0.9%, Si; 0.1 to 0.7%, Mn; 0.5
~ 2.0%, P: 0.05% or less, S: 0.05% or less of the composition, and the other parts are chemical components wt% C: 0.30% or less, Si: 0.60 % Or less, Mn;
1.50% or less, P; 0.05% or less, S; 0.05%
A mast section steel for forklift trucks having excellent wear resistance and weldability, characterized by comprising a double-layered steel having the following composition.