CN115552051A

CN115552051A - Novel bainite steel

Info

Publication number: CN115552051A
Application number: CN202180033253.7A
Authority: CN
Inventors: 扬·哈拉德逊; 拉尔斯·尼洛夫; 索菲亚·维斯特霍姆
Original assignee: Herui Mai Rock Drilling Steel Co ltd
Current assignee: Herui Mai Rock Drilling Steel Co ltd
Priority date: 2020-05-06
Filing date: 2021-05-06
Publication date: 2022-12-30
Also published as: WO2021224423A1; EP4146838A1; JP2023525516A; BR112022022553A2

Abstract

The present disclosure relates to a novel bainite steel for use in the manufacture of drill tool components, such as drill rods, or in any other component where such a steel is useful. The disclosure further relates to a drill component comprising the bainite steel. The bainitic steel comprises the following composition in weight%: c0.33 to 0.40; si 0.60 to 1.45; mn is 0.25 to less than or equal to 0.80; p is less than or equal to 0.03; s is less than or equal to 0.03; cr 1.00 to 1.50; 0.10 to 0.60 of Ni; mo 0.40 to 0.80; n is less than or equal to 0.020; al is less than or equal to 0.05; the balance Fe and inevitable impurities.

Description

Novel bainite steel

Technical Field

The present disclosure relates to a novel bainitic steel for use in the manufacture of drill tool components, such as drill rods, or in any other component where such a steel is useful. The present disclosure further relates to a drill component comprising said bainitic steel.

Background

During rock drilling, shock waves and rotation are transmitted to a drill bit equipped with cemented carbide via more than one rod or tube, which means that the drill rod will be subjected to severe mechanical loads. One problem associated with drill rods is therefore that they are exposed to extensive wear, deformation, fatigue and chipping, resulting in a relatively short service life, which requires replacement of the drill rods at repeated intervals during drilling, and which will have a direct impact on the overall cost of the drilling operation. Another problem is accidental breakage of the drill rod during drilling, as it may take a considerable time to retrieve the broken drill rod from the drilled hole. Therefore, the hardness, tensile strength and impact toughness of the drill pipe are particularly important.

Accordingly, it is an aspect of the present disclosure to solve or at least reduce the above-mentioned problems. In particular, it is an aspect of the present disclosure to provide an improved bainitic steel composition that will enable the manufacture of drill rods having a microstructure that will provide well-balanced and optimized mechanical properties for the bainitic steel, resulting in drill rods having an extended and predictable service life. Another aspect of the present disclosure is to obtain a cost-effective drill component. In addition, a further aspect of the present disclosure relates to the use of an improved bainite steel in rock drilling components.

Disclosure of Invention

Accordingly, the present disclosure relates to a bainitic steel comprising the following composition in weight% (wt%):

c0.33 to 0.40;

si 0.60 to 1.45;

mn is 0.25 to less than or equal to 0.80;

P ≤0.03；

S ≤0.03；

cr 1.00 to 1.50;

0.10 to 0.60 of Ni;

mo 0.40 to 0.80;

N ≤0.020；

Al ≤0.05；

the balance Fe and unavoidable impurities.

The steel of the present invention will have a bainitic microstructure, meaning that the microstructure will consist essentially of dislocation-rich ferrite and cementite formed during bainitic transformation, and retained austenite. Furthermore, the steel of the invention may also contain small amounts of pro-eutectoid ferrite and/or martensite, but it is important to keep these amounts low in order to avoid too low strength and hardness or too high brittleness, respectively.

Thus, due to the composition and the specific microstructure of the present invention, the bainitic steel of the present invention will resist wear and reduce brittleness in drilling applications. Furthermore, both fatigue cracking and plastic deformation will also be reduced, especially during load peaks. In addition, the bainitic steel of the invention will also have good resistance to softening due to overheating, due to its temper resistance (i.e. the extent to which the steel will retain its hardness at elevated service temperatures). Accordingly, a bainitic steel as defined above or below will have a unique combination of desirable characteristics for drilling applications, thereby overcoming or at least reducing the above-mentioned problems.

The present disclosure also relates to the use of a bainite steel as defined above or below for the manufacture of a drill tool component, for example a drill rod, such as a top hammer drill rod, or any other drill tool component comprising the bainite steel.

Detailed Description

The present disclosure relates to a bainitic steel for drilling applications comprising the following elements in weight% (wt%):

c0.33 to 0.40;

si 0.60 to 1.45;

mn is 0.25 to less than or equal to 0.80;

P ≤0.03；

S ≤0.03；

cr 1.00 to 1.50;

0.10 to 0.60 of Ni;

mo 0.40 to 0.80;

N ≤0.020；

Al ≤0.05；

the balance Fe and unavoidable impurities.

Thus, the inventors have surprisingly found that a bainite steel having alloying elements within the ranges as defined above or below will have a combination of suitable mechanical properties for drilling applications, which will provide the bainite steel of the invention with a combination of good hardness, good yield strength, good ultimate tensile strength, good impact toughness and good tempering resistance, such that it will be able to withstand wear, plastic deformation, load change, embrittlement and softening at elevated service temperatures.

The alloying elements of the steel according to the present disclosure will now be described. The terms "wt%" and "wt%" are used interchangeably. Also, the list of properties or contributions mentioned for a particular element should not be considered exhaustive.

Carbon (C): 0.33 to 0.40% by weight

Carbon is included in the bainitic steel of the present invention for increasing strength and hardness, and for controlling a desired microstructure of the steel, which will be formed during continuous air cooling after a final hot rolling operation. For example, C will slow the formation of pro-eutectoid ferrite on cooling, which otherwise may have an effect on bainite formation at lower temperatures. Furthermore, C will provide improved mechanical properties in the bainitic structure due to extended interstitial solid solution strengthening and due to precipitation hardening and due to inhibition of the Bs temperature. The Bs temperature is the transition temperature at which bainite begins to form on cooling. Inhibition of bainite formation results in a finer bainite microstructure, as both bainite nucleation and bainite growth rate will be affected.

Therefore, too low a content of carbon will result in poor mechanical properties of the bainite microstructure. However, too high a content of C will increase the hardenability too much and result in a high martensite content during air cooling since the Bs temperature will be suppressed too much. This will result in an incomplete bainite transformation, whereby a microstructure with impaired mechanical properties, such as reduced ductility and reduced impact toughness, will be formed. Accordingly, the content of C in the bainitic steel of the present invention is between 0.33 and 0.40 wt%. According to one embodiment and in order to have optimal mechanical properties, the content of C is between 0.35 and 0.39 wt%.

Silicon (Si): 0.60 to 1.45% by weight

Silicon is used as a deoxidizing element during the manufacturing process, so a certain amount of silicon is always present in the steel of the invention. In addition, silicon has an important role because it is a solid solution strengthening element and will significantly improve the strength of the bainite microstructure. It has been shown that Si is particularly important for improving the mechanical properties of the inventive steel, such as the ductility and impact toughness of the inventive steel, by delaying the formation of cementite during cooling, thereby increasing the amount of retained austenite in the bainite microstructure. In order to have any desired effect, the content of Si must be at least 0.60 wt%.

However, si will stabilize proeutectoid ferrite on cooling and since the steel of the invention should have a microstructure that is mainly bainitic, too high amounts of Si will result in too much proeutectoid ferrite being formed during air cooling. This may also result in a reduction in hardness and strength because proeutectoid ferrite has inferior mechanical properties compared to the bainite microstructure.

Therefore, it is very important to carefully select the range of Si for the steel of the present invention, and thus, the amount of silicon is selected to be 0.60 wt% to 1.45 wt%. According to an embodiment and in order to have an optimal hardness and strength, the content of silicon is 1.00 to 1.45 wt.%.

Manganese (Mn): 0.25 to less than or equal to 0.80 percent by weight

Mn is mainly contained in the steel of the invention to reduce thermal cracking by forming MnS with sulphur, which will avoid detrimental FeS formation. Therefore, in order to secure the MnS-type sulfide, the content of Mn should be at least 0.25 wt%. Furthermore, mn has a positive influence on the mechanical properties of the steel according to the invention, since it will contribute to the solid solution strengthening of the bainite microstructure. Mn also lowers the Bs temperature and therefore favors the formation of a finer bainite microstructure, which improves both strength and ductility.

However, mn will lower the austenitizing temperature, thereby reducing the austenite grain size during hot rolling. Thus, mn, although a hardenability element, will also promote pearlite formation upon cooling, at the expense of subsequent bainite formation. Mn will also increase work hardening and have a negative effect on the general sensitivity of embrittlement, especially of temper embrittlement. In addition, mn may increase softening of the steel when exposed to elevated service temperatures, which compromises hardness and strength.

Mn already has a strong hardening effect at low amounts, and too high amounts of manganese will result in too high hardenability, which leads to the formation of high martensite content during air cooling and thus to a reduction in ductility and impact toughness.

Due to these drawbacks, in the steel of the invention it has been found that it is crucial to limit the amount of Mn in order to enable a larger addition of other alloying elements in order to avoid too high hardenability. It is very important to carefully select the range of Mn, and therefore the content of Mn is 0.80 wt% or less. In one embodiment, mn is 0.70 wt.% or less.

Chromium (Cr): 1.00 to 1.50% by weight

Cr will contribute to the solid solution strengthening of the bainite microstructure and will therefore improve the mechanical properties of the steel according to the invention. It will also increase hardenability and inhibit the Bs temperature. The suppressed Bs temperature will improve the mechanical properties, especially the strength and ductility properties.

In the steel of the present invention, it has been found that Cr is a more important alloying element than the alloying elements Mn, ni and Si. Although Cr is a hardenability element, it has been found that Cr has a much weaker hardenability effect at lower temperatures compared to higher temperatures and will therefore retard the formation of pearlite, but the same limitation of bainite formation will be avoided if compared to Mn and Ni. It was also found that Cr would increase the strength of the bainitic microstructure more than Ni and would not promote the formation of proeutectoid ferrite like Si.

However, excessive chromium may increase hardenability too much, which will result in high martensite content being formed during air cooling and the microstructure having impaired mechanical properties such as reduced ductility and reduced impact toughness. Too high Cr content may further increase the risk of grain boundary carbides precipitating upon cooling, which has a negative effect on ductility. On the other hand, too low a Cr content will result in a poor mechanical properties of the bainite microstructure. The Cr content is 1.00 wt% to 1.50 wt%. Furthermore, the Cr content may be between 1.10 wt% and 1.50 wt% in order to have optimal mechanical properties.

Nickel (Ni): 0.10 to 0.60% by weight

Nickel increases the hardenability of the steel and results in a solid solution strengthening effect, which improves the strength of the bainite microstructure, but above all has a strong toughening effect. The toughening effect will increase the impact strength, especially at low use temperatures. In order to ensure sufficient impact strength of the steel, the Ni content should be at least 0.10 wt.%. On the other hand, however, too high a content of Ni may result in too high an amount of retained austenite, resulting in reduced hardness and strength. At elevated service temperatures, high Ni content may also impair tempering resistance, whereby the hardness and strength of the steel will decrease over time. Too high Ni content may also increase hardenability too much, resulting in high martensite content during air cooling and a microstructure with impaired mechanical properties such as reduced ductility and reduced impact toughness. Therefore, in the steel of the present invention, the Ni content should be limited to 0.60 wt%. Ni is also an expensive alloying element and should therefore be added in as low and well-balanced amounts as possible. According to an embodiment, the content of Ni may be 0.10 to 0.50 wt%.

Molybdenum (Mo): 0.40 to 0.80% by weight

Molybdenum will improve the strength of the bainite microstructure through solid solution strengthening and precipitation hardening. Mo is very effective in retarding the formation of pearlite during cooling, and also suppresses temper embrittlement that may occur during slow cooling. Mo is particularly advantageous in reducing softening during use when the steel is exposed to high temperatures, i.e. improving tempering resistance, and will therefore help to maintain hardness and strength. However, mo is also an expensive element, and therefore is preferably kept as small as possible, but is still added in an amount that has an influence on the characteristics. To ensure that Mo has these positive effects, the amount of Mo is at least 0.40 wt% and the upper limit of molybdenum is 0.80 wt%.

Nitrogen (N): less than or equal to 0.020 percent by weight

N may be added to the steel of the present invention because it has both an interstitial solid solution strengthening effect and a precipitation hardening effect, which improves the strength, especially the yield strength, of the steel. N may contribute to grain refinement as a nitride, thereby further improving the mechanical properties of the steel. However, N is generally regarded as an undesirable impurity in the steel, since it causes embrittlement and strain ageing effects, which are particularly detrimental to ductility, formability and impact toughness at room temperature. Too high a content of N may also reduce hot working characteristics during forging and rolling. Therefore, the upper limit is set to 0.020% by weight or less. If added, the N content is set to 0.005 to 0.020% by weight.

Phosphorus (P): less than or equal to 0.03 percent by weight

P is an optional element and is generally considered to be a harmful element due to its embrittlement effect and is therefore considered to be an impurity. Therefore, it is desirable to have P less than or equal to 0.03 wt%.

Sulfur (S): less than or equal to 0.03 percent by weight

S is an optional element, but may be included to improve processability. However, S is generally considered as an impurity since it may form grain boundary segregation and inclusions, and thus will limit hot working characteristics as well as mechanical characteristics, resulting in an increase in anisotropic behavior. Therefore, the S content should be 0.03 wt.% or less. If added, the S content is set to 0.01 to 0.03% by weight.

Aluminum (Al): less than or equal to 0.05 percent by weight

Al may be used as a deoxidizer, but may also be added for grain refinement because it readily combines with nitrogen to form stable AlN precipitates, which promote toughness, especially at low temperatures. However, too high content of Al may degrade mechanical properties by reducing ductility. If added, the content of Al is set to 0.01 to 0.05 wt%.

Optionally, small amounts of other alloying elements may be added to the bainitic steel of the invention as defined above or below in order to improve, for example, workability or hot workability characteristics such as hot ductility. Examples of such elements, but not limited to, are Ca, mg, B, pb and/or Ce. The amount of one or more of these elements is at most 0.05% by weight, with the exception of B, which is present in an amount of at most 0.005% by weight.

The bainitic steel of the invention may contain trace elements such as tungsten (W), cobalt (Co), copper (Cu), titanium (Ti) and tantalum (Ta), vanadium (V) and/or niobium (Nb). Such trace elements will be considered impurities, i.e. not intentionally added, which means that they are allowed to be present in the steel, but only in amounts that do not affect the final properties of the steel. Thus, impurities are elements and/or compounds which are not purposefully added but cannot be completely avoided, since they are usually present as impurities, for example, in the starting materials.

When the term "maximum" or "≦" is used, the skilled artisan will appreciate that the lower limit of the range is 0 wt% unless otherwise stated.

The balance of the elements of the steel as defined above or below are iron (Fe) and impurities typically present as discussed above.

The inventors have therefore surprisingly found that by a particular elemental composition of the present disclosure, a bainitic steel will be obtained that will provide wear resistance and embrittlement resistance. Furthermore, the bainitic steel composition of the present invention will provide a reduction in fatigue cracking and plastic deformation. The composition of the alloying elements is thus carefully adjusted so that the body consisting of the bainitic steel according to the invention will have the desired bainite content, i.e. the equilibrium content of ductile phase, and as low a content as possible of brittle or mechanically weak phase. Thus, the bainitic steel of the present invention will be suitable for drilling applications.

According to one embodiment, the bainitic steel of the invention consists of or comprises all of the elements described herein and within the different ranges as described herein.

According to an embodiment, the bainitic steel comprises or consists of, in weight%:

element(s)	Embodiment mode 1	Embodiment mode 2	Embodiment 3
				C	0.33 to 0.40	0.35 to 0.39	0.35 to 0.39
Si	0.60 to 1.45	0.60 to 1.45	1.00 to 1.45
				Mn	0.25 to less than or equal to 0.80	0.25 to less than or equal to 0.70	0.25 to less than or equal to 0.70
P	≤0.03	≤0.03	≤0.03
				S	≤0.03	≤0.03	≤0.03
Cr	1.00 to 1.50	1.00 to 1.50	1.10 to 1.50
				Ni	0.10 to 0.60	0.10 to 0.60	0.10 to 0.50
Mo	0.40 to 0.80	0.40 to 0.80	0.40 to 0.80
				N	≤0.020	≤0.020	≤0.020
Al	≤0.05	≤0.05	≤0.05

The balance being Fe and unavoidable impurities and optional elements as described above. In addition, as described above, S, al, and N may be purposefully added.

According to embodiments, it has also been found that if the steel of the invention also fulfils a chromium equivalent (Cr) of at least 2.70 _eq ) Will ensure that the desired bainitic microstructure will be obtained, and the steel of the invention will have good strength (R) _p0.2 ) Good ductility, good impact toughness and good hardness (hardness 3). Chromium equivalent (Cr) _eq ) Calculated according to the Schaeffler's formula (Schaeffler's formula), where the values are in weight%:

Cr _eq ＝Cr+(1.5*Si)+(1*Mo)+(0.5*Nb)。

according to one embodiment, the alloy of the invention as defined above or below has a Ni content of 0.10 to 0.40 wt.%, a Mn content of 0.25 to 0.55 wt.% and a Mo content of 0.55 to 0.80 wt.%. According to another embodiment, the content of Si is 1.00 wt% to 1.45 wt%.

According to an embodiment, for an as-received drill rod sample, the bainitic steel as defined above or below has a yield strength (R) of ≧ 1000MPa _p0.2 ). The term "as is" means that the drill rod has been hot rolled and straightened.

According to an embodiment, the bainitic steel as defined above or below has a tensile strength (Rm) of ≧ 1400MPa for the as-received drill rod sample.

According to an embodiment, the bainite steel as defined above or below has an Impact Toughness (IT) > 13J at room temperature when using an as-received drill rod sample.

According to one embodiment, the hardness after hardening (i.e. austenitization and water quenching) is within 56 to 62HRC (hardness 2) when performed on an as-received drill rod sample of bainitic steel as defined above or below.

The bainitic steel and drill rods made thereof as defined above or below may be manufactured by using conventional steel manufacturing and steel machining processes and conventional drill rod manufacturing and machining processes.

An object or part comprising a bainitic steel as defined above or below is austenitized, hot rolled and subjected to air cooling to room temperature, whereby the desired bainite microstructure is obtained during continuous cooling.

The mechanical properties of the surface of a part consisting of a bainitic steel as defined above or below may be further improved by induction hardening or by applying a surface treatment method such as, but not limited to, shot peening.

As described herein, the steel according to the present disclosure is intended for use in the manufacture of drill tool components, such as, for example, drill rods, such as, for example, top hammer drill rods.

The disclosure is further illustrated by the following non-limiting examples.

Examples

Example 1

All alloys in table 1 except alloy 7 were made by melting scrap and alloy in a high frequency furnace and then ingot casting using a 9 "steel die. The obtained alloy had the composition as shown in table 1. The balance being iron and unavoidable impurities.

The weight of the ingot was about 270kg. The ingot is heat-treated at 600 to 700 ℃ for 4 to 8 hours, then air-cooled to room temperature, followed by grinding the surface of the ingot. The ingot was then heated to 1100 to 1250 ℃ and hammer-forged to a rod with a circular dimension of about 130 mm. The rods were then air cooled and heat treated at 600 to 700 ℃ for 4 to 8 hours and air cooled to room temperature.

In the next step, the rod is straightened, cut, turned, drilled and inserted into the core. The round bars obtained are then hot-rolled in a rolling mill at 1100 to 1250 ℃ into hexagonal hollow bars having dimensions of 20 to 25 mm. After hot rolling, the bars were continuously air cooled to room temperature. The core is removed and the bar is cut to length and then straightened.

Example 2

Alloy 7 was produced by melting in a 75MT arc furnace and then continuously casting into 365 x 265mm billets. The alloy compositions are shown in table 1. The billet is then heated to 1100 to 1250 ℃ and hot rolled to a diameter of about 125 mm.

The rods are heat treated at 700 to 850 ℃ for 3 to 6 hours, then furnace cooled to 600 ℃, then air cooled to room temperature, then straightened, cut, turned, drilled and inserted into cores.

The round bars obtained are then hot-rolled in a rolling mill at 1100 to 1250 ℃ into hexagonal hollow bars having dimensions of 20 to 25 mm. After hot rolling, the bars were continuously air cooled to room temperature. The core is removed and the bar is cut to length and then straightened.

Example 3 mechanical testing

The results of the mechanical testing are shown in table 2.

Hardness test

Three types of hardness measurements were made at room temperature as HRC tests according to ASTM E18-19.

Hardness of the as-rolled drill rod sample after rolling,

that is, "after rolling" means after hot rolling and air cooling (hardness 1).

-the hardness of the hardened drill rod sample,

i.e. 1000 ℃ for 20 minutes, then water quenched (hardness 2)

Hardening was performed on the as-received drill pipe samples. The term "as is" means that the drill rod has been hot rolled and straightened prior to taking a sample from the drill rod.

-the hardness of the tempered drill rod sample,

i.e. 650 c for 30 minutes, and then air cooled (hardness 3).

Both as-received drill pipe samples (hardness 3 a) and hardened drill pipe samples (hardness 3 b) were tempered and reported separately.

The hardness was measured in longitudinal sections of the drill rod samples after rolling. Before the measurement, the surface was ground to a depth of 0.5 mm. Alloys 8 and 9 were tested at one drill rod position, with post-rolling hardness tested at two drill rod positions for all alloys except 8 and 9. In the hardened drill pipe samples as well as in the tempered drill pipe samples, the hardness was measured in the cross section of the drill pipe samples. All values presented are based on the average of more than three indentations in each drill rod position. No tempering test was performed on alloys 8, 9 and 10.

As can be seen from the examples, the hardness 3b is excellent for the alloys 1 to 3 and 6 to 7 of the present invention. This means that these alloys have superior resistance to softening when exposed to high temperatures compared to other alloys. Furthermore, as can be seen from the examples, the hardness 3a is also very good for these alloys. These hardness results mean that their tempering resistance will be very good both in their original state and in their hardened state, and without being bound by any theory, will also be very good both in their hardened state and in the post-rolled state. It should be emphasized that when evaluating the alloys of the examples, a combination of all results of the different mechanical tests performed has been considered.

As can be seen from table 2, all heated post-rolling hardnesses within the present invention were between 41 and 47HRC (hardness 1), which is the hardness required to have the properties optimal for the application described herein.

Tensile test

The results of the tensile test include measurements of both yield strength and ultimate tensile strength. The drill rod sample as received was tested at room temperature with sample 4 according to ASTM E8/E8M-16a, FIG. 8[ E8M ]. The values presented are based on the average of two or more samples. All alloys except alloy 10 were tested at two drill rod positions and alloy 10 was tested at one drill rod position.

Impact toughness testing (IT)

The impact toughness results are based on the total impact energy measured during the Charpy-V test (Charpy-V testing). The samples of the drill rod as such were tested at room temperature according to ISO 148-1. A10X 5X 55mm specimen with V-shaped notches was also used in accordance with ISO 148-1. The values presented are based on the average of two or more samples. All alloys except alloy 10 were tested at two drill rod positions and alloy 10 was tested at one drill rod position. As can be seen from the test results, all the alloys of the invention have good results. Although one of the reference alloys has a value close to one of the alloys of the present invention, when investigating whether the alloy is good or bad, all mechanical properties of each alloy must be considered.

Thus, as can be seen from the results of table 2, the bainitic steel of the invention will have an optimized hardness to both resist wear and reduce brittleness in drilling applications.

Furthermore, as can be seen from table 2, the bainitic steel of the present invention will have a well-balanced and optimized combination of mechanical properties such as hardness, tensile strength and impact toughness in order to withstand wear, deformation and fatigue and softening caused by the increase in surface temperature caused by frictional heat during drilling.

Table 1 composition of the alloys of the examples. Alloys 1 to 3 and 6 to 7 are alloys of the present invention and are within the scope of the claims and are marked with an "x". Alloys 4 to 5 and 8 to 10 are included as reference alloys. The balance being Fe and unavoidable impurities.

Element(s)	Alloy 1	Alloy 2	Alloy 3	Alloy 4	Alloy 5	Alloy 6	Alloy 7	Alloy 8	Alloy 9	Alloy 10
											C	0.36	0.37	0.36	0.37	0.34	0.34	0.37	0.47	0.32	0.37
Si	1.27	1.28	0.94	0.33	0.28	0.61	1.33	0.22	0.19	0.63
											Mn	0.30	0.59	0.62	0.62	0.62	0.61	0.35	0.33	0.32	0.96
P	0.004	0.004	0.005	0.005	0.005	0.005	0.007	0.005	0.005	0.004
											S	0.018	0.015	0.015	0.017	0.016	0.017	0.012	0.015	0.017	0.014
Cr	1.29	1.08	1.30	1.28	1.65	1.46	1.26	0.13	1.97	0.50
											Ni	0.19	0.50	0.50	0.49	0.81	0.50	0.19	0.47	0.45	0.21
Mo	0.68	0.49	0.51	0.67	0.30	0.48	0.68	0.57	0.27	0.72
											W	<0.01	<0.01	<0.01	<0.01	0.06	<0.01	<0.01	<0.01	<0.01	<0.01
Co	<0.010	<0.010	<0.010	<0.010	<0.010	<0.010	<0.010	<0.010	<0.010	<0.010
											V	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005
Ti	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005
											Cu	0.006	0.007	0.006	0.007	0.007	0.007	0.009	0.011	0.009	0.009
Al	0.026	0.030	0.031	0.025	0.012	0.014	0.032	0.015	0.015	0.031
											Nb	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01
N	0.012	0.007	0.009	0.017	0.007	0.006	0.008	0.009	0.008	0.010
											Ta	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005
B	<0.0004	<0.0004	0.0006	0.0007	<0.0004	<0.0004	<0.0004	<0.0004	<0.0004	<0.0004

Claims

1. A bainite steel for drilling applications, the bainite steel comprising the following composition:

c0.33 to 0.40;

si 0.60 to 1.45;

mn is 0.25 to less than or equal to 0.80;

P≤0.03；

S≤0.03；

cr 1.00 to 1.50;

0.10 to 0.60 of Ni;

mo 0.40 to 0.80;

N≤0.020；

Al≤0.05；

the balance Fe and unavoidable impurities.

2. The bainitic steel according to claim 1, wherein the content of Mn is 0.25 wt% to 0.70 wt%.

3. Bainite steel according to claim 1 or 2, wherein the content of Ni is 0.10 to 0.50 wt%.

4. Bainite steel according to any one of claims 1 to 3, wherein the content of C is 0.35 to 0.39 wt%.

5. Bainite steel according to any of claims 1 to 4, wherein the content of Cr is 1.10 to 1.50 wt%.

6. Bainite steel according to any of claims 1 to 5, wherein the content of Si is 1.00 to 1.45 wt%.

7. The bainitic steel according to claim 1, wherein the content of Ni is 0.10 to 0.40 wt%, the content of Mn is 0.25 to 0.55 wt%, and the content of Mo is 0.55 to 0.80 wt%.

8. The bainitic steel according to claim 7, wherein the content of Si is 1.00 to 1.45 wt%.

9. Use of a bainitic steel according to any one of claims 1 to 8 for the manufacture of drill components.

10. A drill component comprising a bainitic steel according to any one of claims 1 to 8.