Elongated member and a steel for percussion boring

FIELD: metallurgy and mechanical engineering.

SUBSTANCE: the invention is pertaining to the field of metallurgy and mechanical engineering, in particular, to development of the corrosion-resistant steel for percussion boring with improved properties concerning resistance to the corrosive fatigue. These properties are realized in the in the elongated member for the percussion boring, which has a threading and a flushing channel. The corrosion-resistant steel used for production of the boring equipment has the martensite structure with the share of the martensite from more than 50 and up to less than 100 mass % and contains Cr ≥11÷ mass % and 0.1 mass % ≤ C + N 0.8 mass %. The steel may additionally contain Mo ≤5 mass %, W ≤5 mass % and Cu ≤ 2 mass %. The composition of the steel meets the value of the index of the equivalent of resistance to a pitting corrosion (ERPC) > 10, determined according to the formula: ERPC = Cr + 3.3 (Mo + W) + 16 N, where Cr, Mo, W and N correspond to the contents of the indicated elements (in mass percents). The content of the martensite in the steel makes from 75 up to 98 mass %. The standard service life of the drill rods used for the core drilling at boring a rock - mainly from granite has increased up to 2189÷3299 drilled meters.

EFFECT: the invention ensures significantly increased standard service life of the drill rods used for the core drilling at boring a rock - mainly from granite(in drilled meters).

8 cl, 2 dwg, 1 ex

 

The purpose of the invention

The invention relates to martensitic corrosion-resistant steels for drilling with new and improved properties, particularly in relation to resistance to corrosion fatigue.

The level of technology

During percussion drilling of the shock wave and the rotation is transmitted from the equipment through one or more rods or pipes to the drill head, with a hard alloy. Drilling steel, i.e. the material of the drill heads, rods, tubes, couplings and tail holders, when drilling is exposed to corrosion. This applies in particular to underground drilling, where washing water is used and where the environment is mostly wet. Corrosion effects, particularly serious on the most loaded areas, i.e. hollows and gaps in the thread. In combination with pulsating stresses caused by bending and above shock waves, a so-called corrosion fatigue (see figure 1). This is a common cause of the destruction of the drill steel.

When drilling is typically used low 'case-hardened steel. The reason for this is that the durability was limited to the abrasive action on the threaded part and wear. As the equipment and tools become more efficient, these problems have decreased and the limiting factor was corrosion is starosti. Cementing causes compressive stresses on the surface that gives a certain slowing effect in relation to fatigue.

U.S. patent 5496421 relates to high-strength martensitic stainless steel. This steel contains 0.06 wt.% or less, 12-16 wt.% CR, 1 wt.% or less Si, 2 wt.% or less MP, 0.5 to 8 wt.% Ni, 0.1 to 2.5 wt.% Mo, 0.3 to 4 wt.% Si, 0.05 wt.% or less N, and the rest Fe and inevitable impurities, and has a maximum area of Delta-ferrite phase 10%. This steel is designed to solve stress corrosion caused by the acid environment.

The closest analogue of the present invention is the application of Japan JP06-099354 AND in which is described an elongated element for drilling (pipe thread), made of corrosion-resistant (stainless) steel.

The invention

One object of the invention is the creation of the elongated element for percussive drilling, providing a further increase in efficiency of modern mining operations.

Another object of the invention is the creation of the elongated element for percussion drilling with increased durability.

Another objective of the invention is to provide a drill steel with a reduced rate of corrosion.

Another objective of the invention is to provide a drill steel with reduced sensitivity to corrosion ostalos is I.

These problems are solved by the present invention, by creating a composition of steel for drilling, made in the form of corrosion-resistant alloy with a martensite basis, in which corrosion resistance is achieved by additions of CR and Mo, W, si and/or n Due to the martensitic structure is achieved the necessary strength and core hardness. Preferably the content of martensite is > 50 wt.%, but <100 wt.%, preferably >75 wt.%, but less than 98 wt.%. The ultimate tensile strength should be >800 MPa, preferably 1300-3000 MPa.

When performing the drill steel in the form of a corrosion-resistant alloy due to additives of chromium on the surface of the passive layer occurs, which prevents corrosion or reduces its speed and thereby affect corrosion fatigue, especially in the hollows of the thread. For drilling steel in accordance with the invention have sufficient corrosion resistance, the desired chromium content is at least 11%. The total content of carbon and nitrogen should be ≥0.1% ≤0,8%. Additional additives Mo and W should not exceed 5 wt.%, Si - 2 wt.%.

The alloy according to the invention has the index value of ESD > 10, preferably > 12-17. ASTC means the Equivalent Resistance Pitting and characterizes the resistance of the alloy is ochechnogo corrosion. ESTK is determined in accordance with the formula

ESTK=CR+3,3(Mo+W)+16N,

where CR, Mo, W and N correspond to the content of elements in weight percent.

Steel in accordance with the invention has a surface hardness of > 400 Vickers, preferably 500-800 Vickers, to increase its resistance to abrasion caused by, for example, movements in the threaded connection, destroyed the breed and contact with the surrounding rock (wall framing). Preferably, the steel has a surface layer with increased hardness thickness of 0.5-2 mm.

Drilling began in accordance with the invention are subjected to conventional processing to produce a steel rod and machine processing. To obtain the desired martensitic structure steel subjected to quenching or cold treatment. The wear resistance can be further improved by means of induction hardening or the application of surface treatments, such as carburization or nitriding.

The invention also relates to the use of steel in accordance with the invention for the manufacture of an elongated element for percussion drilling with the thread and the flushing channel.

One or both of the threaded end of the element can be made of steel in accordance with the invention and is welded or otherwise attached to a rod or pipe of drugog the material.

Brief description of drawings

Figure 1 with increasing 25x shown cracks in the hollow thread-alloy steel.

Figure 2 at 500x magnification shows the structure of the drill steel in accordance with the invention.

Example

When the so-called core drilling used a rod with a length of about 4 m Critical sections of the rods were hollow covered threads, such as shown in figure 1, in which the effects of wash water and pulsating stresses caused the development of corrosion fatigue, which often led to the destruction.

Rods for core drilling have been completed of the three alloys with the following composition:

Test%%Cr%Ni%Mo%W%Cu%N%FeThe content of martensite
1-40,18the 13.40,30,020,010,120,012Rest98%
5-80,5014,30,150,020,010,060,011Rest89%
9-120,3511,90,22 1,050,010,060,013Rest95%

Drilling was carried out continuously on the equipment for core drilling up to failure due to the failure or wear. Below is the relevant achieved longevity in passed away:

Test # 123456
Passed away329929043030287628933121

Test # 789101112
Passed away297626562628218932222929

Normal durability rods for drilling conventional type, i.e. of low-alloyed case-hardened steel, in the test conditions, when the breed consisted mainly of granite, is about 2000 m. This shows that the use of drilling steels in accordance with the invention gives a significant improvement.

1. Corrosion-resistant steel for fabricated what I drilling equipment, having martensitic structure containing martensite more than 50 and less than 100 wt.% and containing Cr11 wt.% and 0.1 wt.%C+N0.8 wt.%.

2. The steel according to claim 1, the composition of which corresponds to the value of equivalent resistance to pitting corrosion (ASTC)>10, defined in accordance with the formula ESTK=CR+3,3(Mo+W)+16N, where CR, Mo, W and N correspond to the content of selected elements in weight percent.

3. The steel according to claim 1, in which the content of martensite is more than 75 wt.%.

4. The steel according to claim 3, in which the content of martensite is from 75 to 98 wt.%.

5. The steel according to claim 1, characterized in that it further contains Mo5 wt.%, W5 wt.% and si2 wt.%.

6. An elongated element for percussion drilling with the thread and the flushing channel, in which at least the thread is made of corrosion-resistant steel having a martensitic structure containing martensite more than 50 wt.% and less than 100 wt.% and containing Cr11 wt.% and 0.1 wt.%C+N0.8 wt.%.

7. The element according to claim 6, in which the content of martensite is more than 75 wt.%.

8. The element according to claim 7, in which the content of martensite faced the t from 75 to 98 wt.%.



 

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