JPS61149462A - Cored steel for of rock drill - Google Patents

Abstract

PURPOSE:To provide a cored steel for the rod of a rock drill fit well for use under the generation of heat to a high temp. by subjecting a steel contg. proper amounts of C, Si, Mn, Ni, Cr and Mo to induction hardening or carburization- hardening and tempering. CONSTITUTION:A steel consisting of 0.2-0.4% C, <=0.35% Si, <=2.0% Mn, <=3.0% Ni, <=2.0% Cr, 0.75-5.0% Mo and the balance Fe with impurities is forged, worked, and subjected to induction hardening or carburization-hardening and tempering to obtain a cored steel for the rod of a rock drill. The composition of the steel may further contain <=0.5% each of Al, Ti, Nb, Zr and V, and it is prepd. by changing the ratio in the composition of JIS SKC31 alloy. The cored steel can maintain high heat resistance even under conditions which cause the generation of heat to a high temp.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a hollow steel material for a rock drill rod, and more specifically, to a hollow steel material with further improved heat resistance strength. It is something.

[Conventional technique 11ir] Of the rods for rock drilling machines, those called joint rods are made by connecting several hollow steel members with threaded grooves on both ends with a coupling sleeve with threaded threads on the inner surface. used in conjunction. Conventional hollow steel materials for rods include:
The material used is one made by carburizing, quenching, and tempering JIS 5KC31, followed by shot peening. However, since rotational torque is applied to this steel material during drilling, the threaded portions of the seams at both ends generate heat. As a result, the surface hardness decreases, causing plastic deformation, and cracking occurs from this portion, resulting in damage. Furthermore, in the manufacturing process, products that have been carburized, quenched, and tempered undergo grain boundary oxidation during processing, which causes cracks to occur in those areas due to high-temperature heat generation, resulting in breakage. That is, when conventional hollow steel materials are used for rods of rock drilling machines, the threaded portions at the joints have poor heat resistance, which shortens the service life.

[Problems to be Solved by the Invention] In view of the above circumstances, the present invention provides a high-strength hollow steel material that can be used satisfactorily as a hollow steel material for rods even under high-temperature exothermic conditions. The purpose is to

Means for Solving the L Problem] As a result of various studies, the present inventors have found that the above problem can be solved by changing the content of alloy components specified in JTSSKC31. That is, the present invention provides carbon: 0.2 to 24% (indicates weight %, the same applies hereinafter), Si: 0.35% or less, Mn: 2.0% or less, Ni
: 3.0% or less, Cr: 2.0% or less, Mo: 0
．． The object is a hollow steel material for a rock drilling rod, which is characterized by containing 75% to 5.0%, the balance being composed of Fe and impurities, and having been subjected to induction treatment or carburizing and quenching and tempering. . The effects of each component of the above alloy and the reason for limiting the composition range are as follows.

C: Element that gives toughness to the base part, toughness is 012
If it is 5 or more, it is high, but if it exceeds 0.4%, it is rather low.

Sj: Contain 0.35% or less as a deoxidizing agent.

Incidentally, if the content is lowered to 0.15% or less, grain boundary oxidation during carburization can be prevented.

N1: As is well known, it is an element that provides high toughness. In the steel alloy of the present invention, the effect is saturated even if the content is 3% or more.

Cr: Improves hardenability, forms spherical carbides, and contributes to wear resistance. In the case of the alloy of the present invention, if the content is 2% or more, the carbides become reticulated and the wear resistance deteriorates.

MO: Contains 0.75% or more to improve high temperature strength. However, if it exceeds 5%, this effect is saturated, which is effective in preventing the deterioration of carburizing properties due to the presence of a Si and also in preventing the formation of network-like carbides.

Mn: Since it improves hardenability, Mn is contained in an amount of 230% or less. However, if it exceeds 2.0%, the toughness decreases.

Ai, Ti, Nb, Zr, ■=Crystal grain (7) 1 Prevents deterioration of toughness due to topography. However, this effect is saturated even if the content exceeds 0.5%.

To summarize the characteristics of the alloy composition in the present invention, by increasing the MO content, the core and surface layer hardness is ensured during high-temperature heat generation, and at the same time, special spherical carbides are formed to improve wear resistance. It is. Furthermore, the carburizing treatment is limited to a low Si content in order to prevent the occurrence of grain boundary oxidation.

Furthermore, if the treatment is carried out for a long time to increase the carburizing effect, there is a risk that the grains will become coarser and the toughness will decrease.
This can be significantly prevented by adding one or more of Ti, NbzZr, Al, and 21 or more to the above alloy components. Therefore, another preferred embodiment of the present invention is that, in addition to the above alloy components, Ti: 05% or less, Nb: 0.5% or less, helical content: 0.5% or less, Zr:
It is made of a material containing V: 0.5% or less and V: 0.5% or less.

The various steps of melting, forging, processing, carburizing, or quenching and tempering by high-frequency heating of the above composition for @1 manufacturing of the hollow steel material for rock drilling rod of the present invention are the same as the conventional manufacturing of this type of steel. It can be carried out according to the method used in the

[Effect J] As described above, the hollow steel material for rock drilling rods of the present invention has a new alloy composition in which the alloy composition ratio of the conventional JISSKC31 has been changed, and can maintain high heat-resistant strength even under high-temperature exothermic conditions. Therefore, it is suitable as a material for rock drill rondos, which require a long service life.

[Example] Steel having the composition shown in Table 1 (the remainder being substantially Fe) was melted.

Test pieces were taken from these materials, subjected to the following heat treatments, and various performance comparison tests were conducted. The results are shown in Table 2.

Heat treatment conditions (1) Carburizing, quenching, tempering Gas carburizing 920℃X13Hr A, C quenching 83
0℃xo, 5Hr A, C tempering 250℃x3Hr
A, C (2) Quenching, tempering, quenching 830℃×0.5HrA, C tempering 51
0℃X3l-1r A, C The following was found from the above test.

(1) All of the steels of the present invention containing a large amount of Mo have high high temperature tensile strength and excellent heat resistance strength.

(2) Low 3i content steel has less grain boundary oxidation after carburizing.

(3) The impact value is improved by adding V, Ti, Nb, etc.

(4) As a result of the above, the service life and performance of the rod are significantly improved.

Claims (1)

[Claims] 1 C: 0.2 to 0.4%, Si: 0.35% or less, M
n: 2.0% or less, Ni: 3.0% or less, Cr: 2.0
% or less, Mo: 0.75 to 5.0%, the balance being Fe
A hollow steel material for a rock drill rod, characterized in that the hollow steel material is composed of and impurities and is subjected to induction treatment or carburization quenching and tempering. 2. A hollow steel material for a rock drill rod according to claim 1, which contains 0.15% or less of Si, and is otherwise composed of the above-mentioned alloy components, and is carburized, quenched and tempered. 3 A rock drill containing 0.5% or less of each of Al, Ti, Nb, Zr, and V, and other than the alloy components described in the above item 1 or 2, which is subjected to induction treatment or carburizing and quenching and tempering. Hollow steel material for rods.