JP2007530780A - Steel for mechanical parts, method for producing mechanical parts from the steel, and mechanical parts obtained by using the steel - Google Patents

Abstract

A steel material suitable for manufacturing a mechanical element, a method for manufacturing the mechanical element, and a mechanical element are provided.
SOLUTION: 0.19% ≦ C ≦ 0.25%; 1.1% ≦ Mn ≦ 1.5%; 0.8% ≦ Si ≦ 1.2%; 0.01% ≦ S ≦ 0.09 %; Trace amount ≦ P ≦ 0.025%; Trace amount ≦ Ni ≦ 0.25%; 1% ≦ Cr ≦ 1.4%; 0.10% ≦ Mo ≦ 0.25%; Trace amount ≦ Cu ≦ 0 0.010% ≦ Al ≦ 0.045%; 0.010% ≦ Nb ≦ 0.045%; 0.0130% ≦ N ≦ 0.0300%; optionally, trace amount ≦ Bi ≦ 0. 10% and / or trace amount ≦ Pb ≦ 0.12% and / or trace amount ≦ Te ≦ 0.015% and / or trace amount ≦ Se ≦ 0.030% and / or trace amount ≦ Ca ≦ 0.0050% The balance consists of iron and impurities, and the average values of J Jom test of 5 times J _3m , J _11m , J _15m , and J _{2 5m} is: α = | ≦ 2.5HRC | J 11m -J 3m × 14/22-J 25m × 8/22; to use and β = J _3m -J _15m ≦ 9HRC become steel.
[Selection] Figure 1

Description

  The present invention relates to the field of steel metallurgy, and more particularly to a steel material for mechanical elements such as pinions.

  Steel for gear production has a high level of contact metal fatigue resistance. In most cases, carburizing treatment or carbonitriding treatment is performed on machine elements manufactured from these steel materials. Due to the carburizing or carbonitriding treatment, the machine element has a high level of surface hardness and mechanical strength, at the same time, in particular with a carbon content in the range of only 0.10 to 0.30%. It is applied while maintaining the core strength. The upper limit of the carbon content of the carburized layer is approximately 1%.

  Various documents describe steel materials for gear production for the purpose of carburizing. These documents include Patent Document 1, which contains relatively low Si and Mn contents (0.45 to 1%, respectively) in order to avoid grain boundary oxidation during the carburizing process. And 0.40 to 0.70%). Patent Document 2 describes a steel material for gear production that is carburized using plasma or under reduced pressure and then shot blasted, and the contents of Si and Mn in the steel material are described in the above-mentioned US patent. It is described that it can be higher than the case of. These steel materials have a high level of resistance to the surface pressure generated in the pinion, thereby improving the lifetime of the pinion.

  Patent Document 3 proposes a steel material for mechanical elements such as pinions, the composition of which is: 0.12% ≦ C ≦ 0.30%; 0.8% ≦ Si ≦ 1.5%; 1 0.0% ≦ Mn ≦ 1.6%; 0.4% ≦ Cr ≦ 1.6%; Mo ≦ 0.30%; Ni ≦ 0.6%; Al ≦ 0.06%; Cu ≦ 0.30% S ≦ 0.10%; P ≦ 0.03%; Nb ≦ 0.050%. This steel material has the advantage that plastic deformation during driving is minimized, in particular as a whole element, due to a sensible balance of silicon and manganese contents. The carburizing or carbonitriding treatment should preferably be carried out under non-oxidizing conditions, for example under reduced pressure, in order to prevent grain boundary oxidation from being induced by the relatively high silicon and manganese content. I must.

  Generally, the carburizing process or the carbonitriding process is performed in a temperature range of 850 to 930 ° C. Recently, however, this process tends to be attempted to be performed at higher temperatures (high temperature carburizing or high temperature carbonitriding) ranging from 950 to 1050 ° C. By such an increase in the processing temperature, the length of the processing time for obtaining the same carburizing depth is shortened, or the carburizing depth within the same processing time is increased. Therefore, the manufacturer has a choice between improving installation productivity or improving the performance of the target product.

US Pat. No. 5,518,685 JP-A-4-21757 International Publication WO-A-03 012 156 Pamphlet

  However, when the above-mentioned known steel material is subjected to high temperature carburizing treatment or high temperature carbonitriding treatment, many problems occur. The first problem is that high temperatures induce an increase in poorly controlled particles that are detrimental to the mechanical properties of the machine element. The next problem is that deformation occurs in the machine element in the quenching process, which is the next process of the carburizing process or the carbonitriding process. When these problems occur, the machine elements need to be reworked or, in the worst case, must be discarded. These problems are more pronounced when the quenching process is performed on elements immediately after being subjected to carburizing or carbonitriding at high temperatures rather than at standard temperatures.

  The object of the present invention is to solve the above-mentioned problems while simultaneously maintaining the required mechanical properties for steel metallurgists performing high temperature carburizing or high temperature carbonitriding on mechanical elements, in particular pinions. A further object is to provide a steel material that is characteristically equivalent to the steel material that has been subjected to the carburizing or carbonitriding treatment at a more standard temperature.

In order to solve the above-mentioned problems and achieve the object, the steel material for mechanical elements according to the present invention has a composition in weight percentage:
0.19% ≦ C ≦ 0.25%;
1.1% ≦ Mn ≦ 1.5%;
0.8% ≦ Si ≦ 1.2%;
0.01% ≦ S ≦ 0.09%;
Trace amount ≦ P ≦ 0.025%;
Trace amount ≦ Ni ≦ 0.25%;
1% ≦ Cr ≦ 1.4%;
0.10% ≦ Mo ≦ 0.25%;
Trace amount ≦ Cu ≦ 0.30%;
0.010% ≦ Al ≦ 0.045%;
0.010% ≦ Nb ≦ 0.045%;
0.0130% ≦ N ≦ 0.0300%;
Optionally, trace amount ≦ Bi ≦ 0.10% and / or trace amount ≦ Pb ≦ 0.12% and / or trace amount ≦ Te ≦ 0.015% and / or trace amount ≦ Se ≦ 0.030% and / or Or trace amount ≦ Ca ≦ 0.0050%;
The balance obtained from the manufacturing operation consists of iron and impurities, and the chemical composition has the average values J _3m , J _11m , J _15m , and J _{25m of} five Jomini tests:
_{α = | J 11m -J 3m ×} 14/22-J 25m × 8/22 | ≦ 2.5HRC; and β = J _3m -J _15m ≦ 9HRC As will be characterized in that it is adjusted.

Preferably, the composition is
β = J _3m −J _15m ≦ 8HRC is adjusted.

Preferably, the composition is:
0.19% ≦ C ≦ 0.25%;
1.2% ≦ Mn ≦ 1.5%;
0.85% ≦ Si ≦ 1.2%;
0.01% ≦ S ≦ 0.09%;
Trace amount ≦ P ≦ 0.025%;
0.08% ≦ Ni ≦ 0.25%;
1.1% ≦ Cr ≦ 1.4%;
0.10% ≦ Mo ≦ 0.25%;
0.06% ≦ Cu ≦ 0.30%;
0.010% ≦ Al ≦ 0.045%;
0.015% ≦ Nb ≦ 0.045%;
0.0130% ≦ N ≦ 0.0300%;
Optionally, trace amount ≦ Bi ≦ 0.07% and / or trace amount ≦ Pb ≦ 0.12% and / or trace amount ≦ Te ≦ 0.010% and / or trace amount ≦ Se ≦ 0.020% and / or Or trace amount ≦ Ca ≦ 0.045%;
The balance obtained from the manufacturing operation consists of iron and impurities.

Most preferably, the composition is:
0.20% ≦ C ≦ 0.25%;
1.21% ≦ Mn ≦ 1.45%;
0.85% ≦ Si ≦ 1.10%;
0.01% ≦ S ≦ 0.08%;
Trace amount ≦ P ≦ 0.020%;
0.08% ≦ Ni ≦ 0.20%;
1.10% ≦ Cr ≦ 1.40%;
0.11% ≦ Mo ≦ 0.25%;
0.08% ≦ Cu ≦ 0.30%;
0.010% ≦ Al ≦ 0.035%;
0.025% ≦ Nb ≦ 0.040%;
0.0130% ≦ N ≦ 0.0220%;
Optionally, trace amount ≦ Bi ≦ 0.07% and / or trace amount ≦ Pb ≦ 0.12% and / or trace amount ≦ Te ≦ 0.010% and / or trace amount ≦ Se ≦ 0.020% and / or Or trace amount ≦ Ca ≦ 0.045%;
The balance obtained from the manufacturing operation consists of iron and impurities.

  The subject of the invention also relates to a method for producing mechanical elements from carburized or carbonitrided steel, which is intended for producing mechanical elements from the aforementioned type of steel. It is characterized in that a machining process, a carburizing process or a carbonitriding process is performed, followed by a quenching process.

  The carburizing or carbonitriding process is preferably performed at a temperature of 950 to 1050 ° C.

  The subject of the invention also relates to a steel mechanical element, such as a gear element, characterized in that it is manufactured by the method described above.

  As is apparent from the above, the present invention is based on the precise adjustment of the main alloying elements and the content ranges of aluminum, niobium and nitrogen with a coexisting content and a clear content.

  The desired result is roughly divided into two.

  First, the content of the main alloying element is selected to achieve a Gemini curve that shows no inflection points. Such conditions make it possible to minimize deformation during the quenching process. From such a viewpoint, the carburizing process or the carbonitriding process performed at a high temperature is particularly important as described above.

It should be noted that the Gemini curve of steel produced using conventional standard tests indicates the quenchability of the steel. This curve is created by measuring the hardness of a cylindrical specimen that has been quenched by jetting water onto one end along one length of its generatrix using a jet stream. The hardness is measured at a point some distance x (in mm) away from the end where the water was jetted, and its corresponding value is designated J _x . J _xm represents an average value of values obtained in five tests for measuring the hardness at the distance x.

As disclosed in European Patent Publication No. 0 890 653 (which allows the reader to refer to further details), the Applicant has identified a steel material exhibiting a Gemini curve with no inflection points. It clearly demonstrates that the composition is useful for significantly reducing deformation in the quenching process that follows the carburizing or carbonitriding process. Such Gemini curves without any inflection points have the following relations with the values J _11m , J _3m , J _25m and J _15m :
α = | J _11m −J _3m × 14 / 22−J _25m × 8/22 | ≦ 2.5HRC;
β = J _3m −J _15m ≦ 9 HRC, or preferably ≦ 8 HRC
Is generated when the above is satisfied.

  Therefore, the composition of the steel material according to the present invention is adjusted so that the relationship is also generated in the present invention.

  In addition, the composition of the steel material of the present invention has a distinct size, particularly when aluminum, niobium and nitrogen are contained, so that the particle size can be reduced even when carburizing or carbonitriding is performed at a high temperature. Is adjusted so that it can be controlled.

  Finally, the steel composition must of course provide the desired mechanical properties. Among other things, the criteria to be specifically monitored include the carburization depth (conventionally defined as the carburization depth at the point where the measured hardness is 550 HV), between the surface of the carburized machine element and the core. Hardness deviation, and core hardness. The deviation in hardness between the carburized steel surface and the core should be as small as possible to minimize deformation during the quenching process. Also, the core hardness must be high in order for the machine element to react effectively to driving strain, and thus for the machine element to have a high level of strength with respect to durability and metal fatigue.

  The steel material according to the present invention is optimal for high-temperature carburizing treatment, and can reduce carburizing time, improve productivity, and reduce carburizing cost without reducing mechanical properties after carburizing treatment. Particularly suitable for producing mechanical elements such as pinions.

  Hereinafter, the present invention will be further described with reference to the accompanying drawings showing the four comparative steel materials and the Gemini curves of the three steel materials according to the present invention. The present invention will be better understood by reading the following description.

  The steel material according to the present invention is primarily intended to produce mechanical elements that are exposed to high levels of strain, such as gear elements. The element is at both a standard temperature of approximately 850-930 ° C. and a high temperature in the range of 950-1050 ° C. (preferably under low pressure or in a non-oxidizing atmosphere to prevent oxidation of the most oxidizable elements) Below, it is intended to be carburized or carbonitrided. These elements must have a high level of fatigue resistance, high strength, and there should be very little deformation during heat treatment such as quenching after carburizing or carbonitriding. I must. The steel of the present invention has the following composition (all percentages are percentages by weight).

  The carbon content of the steel according to the present invention is between 0.19% and 0.25%. These contents are standard amounts in gear manufacturing steel. Furthermore, by setting to this range, it is possible to adjust the content of the remaining elements, thereby making it possible to make the Gemini curve into a desired shape. Further, the lower limit of 0.19% is set from the core hardness obtained by the quenching process. If it exceeds 0.25%, the hardness becomes so high that the necessary machining for the steel material may be difficult. A suitable range is 0.20 to 0.25%.

  The manganese content of the steel according to the invention is between 1.1% and 1.5%. This lower limit value is set in correlation with the content of the remaining elements in order to generate a necessary Gemini curve. If it exceeds 1.5%, segregation occurs, and banding may occur during the quenching process. Furthermore, such high contents result in excessive corrosion of the heat-resistant coating of the steel ladle during its manufacturing operation. It is not necessary to further limit the content range. This is because it is very difficult to produce such an accurate product at a steel mill. A suitable range is 1.2 to 1.5%, more preferably 1.21 to 1.45%.

  The silicon content of the steel material according to the present invention is between 0.8% and 1.2%. By setting to this range, the required shape of the Gemini curve can be obtained in correlation with the content of the remaining elements. The lower limit of 0.8% is set in order to obtain a necessary core hardness and to limit the hardness deviation between the surface after the carburizing or carbonitriding treatment and the core. If it exceeds 1.2%, silicon (which slightly segregates itself) tends to promote segregation of other elements, so that excessive segregation may occur. Moreover, there exists a possibility of increasing the oxidation during a carburizing process or carbonitriding process. The preferred range is 0.85 to 1.20%, and more preferably 0.85 to 1.10%.

  The sulfur content of the steel material according to the present invention is between 0.01% and 0.09%, and the lower limit is set to obtain appropriate machinability. If it exceeds 0.09%, the heat forgeability may be considerably lowered. A preferable range is 0.01 to 0.08%.

  The phosphorus content of the steel material according to the present invention is between the trace amount and 0.025%. In general, standards in force tend to require maximum phosphorus content in this range. Further, exceeding this value may interact with niobium and cause the steel to become brittle in the process of thermoforming into the shape of a bloom or billet and / or subsequent casting processes. The phosphorus content is preferably an upper limit of 0.020%.

  The nickel content of the steel material according to the present invention is between the trace amount and 0.25%. This element is deliberately introduced in a higher content, but unnecessarily increases the cost of this metal. In practice, the nickel content naturally obtained from the melt of the forging raw material is sufficient without elaborate addition. A suitable range is 0.08 to 0.20%.

  The chromium content of the steel according to the present invention is between 1.00% and 1.40%. By setting to this range, the desired shape of the Gemini curve can be obtained by correlation with the content of the remaining elements. Furthermore, by setting the lower limit to 1.00%, the core hardness of the product can be maintained at a high level. If it exceeds 1.40%, the production cost will increase unnecessarily. The preferred range is 1.10 to 1.40%.

  The molybdenum content of the steel according to the present invention is between 0.10% and 0.25%. By setting within this range, the desired shape of the Gemini curve and the core hardness can be obtained by correlation with the content of the remaining elements. The preferred range is 0.11 to 0.25%.

  The copper content of the steel material according to the present invention is between the trace amount and 0.30%. As with the nickel, it is generally kept pure and simple by the nickel content obtained after melting the raw material. If it exceeds 0.30%, the malleability and the core strength of the product are lowered. A preferred range is 0.06 to 0.30%, and in order to optimize the shape of the Gemini curve and the hardness after quenching, it is preferably 0.08 to 0.30%.

  The content of aluminum, niobium and nitrogen in the steel material according to the invention must be controlled within precise limits. These are elements that enable the fineness of metal particles to be controlled by mutual reaction. This fineness is necessary to maintain the strength in the carburized layer or the carbonitriding layer at a high level, to maintain the fatigue resistance at a high level, and to reduce variation in deformation during the quenching process. Furthermore, it is important to obtain the required shape of the Gemini curve. The control of the particle size is especially important in the description of the present invention. This is because the steel material of the present invention must be capable of being subjected to high temperature carburizing or carbonitriding without causing an excessive increase in particle size.

  This particle size control is performed substantially by precipitation of aluminum and / or niobium nitride and carbon nitride. Therefore, in order to perform such control, it is necessary that a significant amount of these two elements is contained, and at the same time, the nitrogen content is generally obtained from a manufacturing process carried out under standard conditions. It needs to be significantly higher than that.

  The aluminum content should be between 0.010% and 0.045%. In addition to the aforementioned particle size control factor, this element controls the purity of the steel material related to deoxygenation and oxide content of the steel material. If the content is less than 0.010%, the effect is insufficient from the viewpoint described above. If it exceeds 0.045%, the purity related to the oxide content may be insufficient for the main target product. A suitable range is from 0.010 to 0.035%.

  The niobium content should be between 0.010% and 0.045%. When the content is less than 0.010%, particularly when the aluminum content is the lowest, the effect of controlling the particle size becomes insufficient. If it exceeds 0.045%, as mentioned above, cracks may occur during continuous casting of the steel material, particularly when interaction with phosphorus can occur. A suitable range is 0.015-0.045%, More preferably, it is 0.015-0.040%.

  In the aforementioned correlation between aluminum and niobium content, the nitrogen content should be between 0.0130% and 0.0300% (130-300 ppm). Thereby, the desired adjustment of the particle size and the desired shape of the Gemini curve are obtained. A preferable range is 0.0130 to 0.0220%.

  If necessary, one or more known elements, in particular lead, tellurium, selenium, calcium, bismuth, may be added to the steel of the present invention in order to improve machinability. The maximum content is 0.10%, preferably 0.07% for Bi, 0.12% for Pb, 0.015% for Te, preferably 0.010%, 0.030% for Se, preferably It is 0.020% and in Ca is 0.0050%, preferably 0.0045%.

  The remaining elements are contained in the steel material as impurities generally introduced from the manufacturing operation, and are not intentionally added. In particular, the titanium content should not exceed 0.005%. Since the steel material according to the present invention has a very high nitrogen content, when this content is exceeded, coarse titanium nitride and / or carbon nitride is formed (which can be confirmed with a microscope), reducing fatigue strength, There is a possibility that workability is impaired. Furthermore, because titanium supplements nitrogen, nitrogen is no longer useful for particle size control.

  Examples of the present invention will be described below. In the accompanying drawings, Gemini curves of four steel materials are shown. Table 1 shows the compositions of these steel materials. Steel materials A, B, C and D are comparative steel materials. Steel materials E, F and G are steel materials according to the present invention.

試料Ａでは、前記定義のサイズαは８．７であり、前記定義のサイズβは１９．１である。したがって、これらは、本発明が要求する最大値を超えている。そのジェミニ曲線が非常にはっきりした変曲点を有していることが確認できる。

In sample A, the defined size α is 8.7 and the defined size β is 19.1. Therefore, these exceed the maximum values required by the present invention. It can be confirmed that the Gemini curve has a very clear inflection point.

  In sample B, α is 2.38 and β is 11.1. Therefore, β does not meet the requirements of the present invention, and its Gemini curve has a clear inflection point, although this steel material has niobium and nitrogen within the aforementioned limits. ing. The main reason is that the silicon content of the steel material is insufficient.

  In sample C, α is 3.38 and β is 10.7. Both α and β are within the aforementioned limits, and the Gemini curve has a clear inflection point. Cr and Mn are slightly below the required minimum values, and the nitrogen content is particularly insufficient.

  In sample D, α is 2.845 and β is 9.5, which is outside the above-mentioned limitation. The Gemini curve has a clear inflection point due to the lack of Cr and nitrogen content.

  However, in the sample E according to the present invention, α is 0.41 and β is 2.7. The required conditions are met and the Gemini curve is almost straight and has no inflection points.

  Similarly, in the sample F according to the present invention, α is 0.23 and β is 3.7. Even in this sample, the Gemini curve is almost linear and has no inflection point.

  Similarly, in the sample G according to the present invention, α is 0.83 and β is 6.6. The Gemini curve is almost straight and does not have a clear inflection point.

  The characteristics of the steel materials A, B and E during carburizing treatment shown in Table 1 are similarly measured under standard temperature conditions and high temperatures.

  Carburizing treatment at a standard temperature (930 ° C.) was performed under a low pressure under the same conditions using a cylindrical sample in order to obtain a carbon content of 0.75% on the carburized surface. . Following these carburizing treatments, in a gaseous medium (nitrogen was used in this test, but a nitrogen / hydrogen mixture containing, for example, 10% hydrogen can also be used), two pressure conditions: 5 Quenching was performed under pressure conditions of bar and 20 bar. This test was conducted for the purpose of obtaining a surface hardness of 700 to 800 HV and a carburization depth of 0.50 mm (that is, a carburization depth at a location where the hardness is 550 HV). The results are shown in Table 2 (test at 5 bar) and Table 3 (test at 20 bar).

これらの試験が示すように、比較の鋼材Ａは、所望の浸炭深さを容易に実現し得ない。それは、焼き入れ可能性が欠如しているためである。

As these tests show, the comparative steel A cannot easily achieve the desired carburization depth. This is due to the lack of quenchability.

  All of the three steel materials of the comparative steel materials B and C and the steel material E according to the present invention have obtained the desired carburization depth under the standard temperature conditions for carburization.

  In the quenching medium at 5 bar, the deviation ΔHV between the surface hardness and the core hardness of the comparative steel B and the steel E according to the present invention is approximately the same (ΔHV = 352 and 354), and the comparative steel A ( It is lower for ΔHV = 497). However, in the quenching medium at 20 bar, the ΔHV of the comparative steels B and C is considerably unsuitable compared to the ΔHV of the steel E of the present invention (ΔHV = 297, 330 and 226, respectively). As a result, it has been confirmed that the residual strain caused by these hardness deviations, which causes deformation when the carburized element is quenched under severe conditions, can be minimized by using the steel material of the present invention. It was done.

  Finally, the highest level of core hardness is obtained with the steel E according to the invention. Thus, a gear element that is exposed to a high level of strain during driving and outweighs the strain applied to the driving element in order to maintain a high level of fatigue resistance during driving (particularly There is a need for an element with a high level of mechanical properties (in that the hardness of the lower and core parts of the carburized layer is at a high level), and the steel according to the present invention is It is most suitable for those with a high level of fatigue resistance during driving.

  Further, the carburization test was performed at a high temperature (980 ° C.) on the above-described comparative steel materials A and D and the cylindrical sample of the steel material E according to the present invention. In this example, the carbon content of the carburized surface was again 0.75%. In the two examples, the surface hardness was measured as 700 to 800 HV, and the carburization depth was 0.50 mm at a location where the hardness was 550 HV. The quenching in the gaseous medium (nitrogen), performed after the carburizing treatment, was performed at a pressure of 20 bar for steels A and D and for steel E only at 1.5 bar. It was. The results are shown in Table 4. The particle size was evaluated according to the ASTM standard.

９３０℃の標準の温度での浸炭処理では、前記２例の鋼材は、目的の表面硬度を達成している。

In the carburizing process at a standard temperature of 930 ° C., the steel materials of the two examples achieve the target surface hardness.

  Although comparison A is quenched under more severe conditions known to increase the carburization depth and all others to be the same, in the present invention, the carburization depth is significantly greater than that of comparison A. I can get it.

  The hardness deviation between the surface and the core is considerably less for the present invention than for comparisons A and D (ΔHV = 240 (sample E), 428 (sample A) and 274 (sample D), respectively)). The aforementioned advantages regarding deformation during the quenching operation that follows the carburizing process are also further improved in this example.

  The core hardness is higher in the present invention than in the comparative example, despite the lower pressure of the quenching medium. In addition, in this example, the result relating to the improvement of the fatigue resistance during the driving although being quenched at the standard temperature is the same as the above.

  Finally, in both the carburized region and the region outside the carburized region, the steel material according to the present invention has a fine ASTM particle size as compared with the comparative steel materials A and D. Therefore, there is less risk that the particle size will increase during the carburizing process at high temperature. This is a very important advantage. This is because increasing the particle size of the carburized element has a very detrimental effect on the fatigue resistance and strength of the root of the carburized element. Therefore, the steel material according to the present invention is perfectly suitable for use in the production of gear elements (or all other elements that require similar properties) that are carburized or carbonitrided at high temperatures. And its properties can be achieved economically without sacrificing all the properties of the element.

  Further, other carburization tests were performed on the comparative steel material A and the steel material E according to the present invention at low pressure.

  Low-pressure carburizing treatment was performed on steel A at 930 ° C., and then gas quenching was performed at 20 bar. In order to obtain a target carburization depth of 0.50 mm at HV = 550, A 72 minute carburization treatment was required. Using the steel material E according to the present invention, low-pressure carburizing treatment was performed at 930 ° C., and then gas quenching (with the same gas as in the case of the steel material A) was performed, but the carburization depth at the same HV = 550 was 0. In order to obtain 50 mm, carburizing treatment for 30 minutes was sufficient.

  Low-pressure carburizing treatment was performed on steel A at a high temperature of 980 ° C., and then gas quenching was performed at 20 bar. In order to obtain a target carburization depth of 0.50 mm at HV = 550 , Carburizing treatment for 30 minutes was necessary. In steel E according to the present invention, in order to obtain a carburization depth of 0.50 mm at the same HV = 550, a low-pressure carburization treatment at 980 ° C. for 20 minutes and a gas quenching treatment at a pressure of only 1.5 bar. It was enough. The quenching gas used for the steel materials A and E was naturally the same.

  This means that in the steel material E according to the present invention, the carburizing time is shortened at both the standard carburizing temperature (930 ° C.) and the high temperature (980 ° C.), thereby reducing the carburizing cost (the amount of carburizing gas, This shows that the carburizing time,...) Can be reduced, and the productivity for obtaining the carburized element can be improved.

  In addition, since the steel according to the present invention can control the quenchability, the pressure of the quenching gas can be reduced to obtain an ideal carburizing depth, thereby further reducing the deformation of the carburizing element. It can be reduced or eliminated, and labor saving and simplification can be realized regarding the technology in the quenching gas components in the chamber of the gas quenching furnace.

Moreover, the carburizing process was implemented at high temperature (980 degreeC) with respect to the impact strength sample (dimension: L = 55mm, cross section 10x10mm) without a notch in low pressure. For the comparative steel A, it is carried out before the gas quenching process under a pressure of 20 bar, whereas for the steel E according to the invention, in this example it is only 1.5 bar. It was performed before the gas quenching process under pressure. The intended carburization depth was the same as the quenching gas type. The sample thus carburized and quenched was then destroyed by impact at ambient temperature. The destruction energies obtained by this method are:
In comparative steel A, it is 19 joules,
In the steel material E according to the present invention, it was 29 joules.

  At the same time, the impact strength sample of the comparative steel material A was carburized at a standard temperature (930 ° C.) under a low pressure in order to obtain the same carburization depth as before. They were then carburized with the same gas under a pressure of 20 bar. These samples were then destroyed at ambient temperature as described above, and the fracture energy obtained by measuring in the same manner was 17 joules. This breaking energy is very low compared to the steel material E according to the present invention that has been carburized at a high temperature.

  This shows that the comparative steel A was carburized at a high temperature despite having a core strength (312 HV) lower than the core hardness (500 HV) of the steel E according to the present invention. That is, the hardness of the steel material E is higher than the hardness of the comparative steel material A having the same final carburization depth carburized at a high temperature or a standard temperature. That is, when the steel material according to the present invention is used to perform the high temperature carburizing process for the purpose of obtaining a specific carburizing depth, the hardness of the carburized element obtained from this steel material is actually the same It does not decrease compared to the case of using a comparative steel material that has been carburized at high or standard temperature to obtain depth. The difference regarding the core hardness between the two steel materials is not detrimental in this respect. In addition, this shows that the steel material according to the present invention is particularly suitable for carburizing treatment at high temperature, shortening the carburizing time, improving productivity, and carburizing at standard temperature or high temperature. It is suitable for both reducing the carburizing cost compared to the known steel being processed. Properties such as hardness obtained by using these elements are not deteriorated as compared with the case of using a comparative steel material.

  Further, under the above-described conditions, a bending fatigue sample of steel E according to the present invention (a wide U-shaped notch was formed at the center of the sample) was carburized at a high temperature (980 ° C.) under a low pressure. Processed. After the carburizing treatment, gas quenching was carried out under a pressure of only 1.5 bar, in the same way as with the impact strength sample with the desired carburization depth and quenching gas type. Similarly, in order to realize the same carburization depth at the standard temperature of 930 ° C. for the steel material A according to the prior art and the same bending fatigue sample of the steel material E, the gas carburizing treatment is performed Went to. After the carburizing treatment, the sample was subjected to an oil quenching treatment in order to improve the hardness and strength with respect to the bending fatigue of the steel material A. Next, the fatigue limits of two sample batches of steel materials E and A that were similarly carburized were compared with respect to bending fatigue at four points (the load related to bending fatigue is concentrated in the wide U-shaped notch). This bending fatigue test was performed up to 10 million times for each of the steel materials A and E which were carburized and quenched under the above conditions.

  Under these conditions, the fatigue limit of the steel material E according to the present invention of 10 million times was 1405 MPa, and that of the steel material A was only 1165 MPa.

  These show that when steel materials according to the present invention are used to perform a high temperature carburizing process aimed at obtaining a specific carburizing depth, the strength related to bending fatigue does not decrease and the conventional technology It is very beneficial compared to conventional carburizing processes performed at standard carburizing temperatures on steel. In order to improve the strength related to bending fatigue, the steel materials of the prior art are carburized at the same depth and similarly quenched in oil.

  What should be added to this point is that these bending fatigue tests are intended to simulate the fatigue strength of gear teeth, gear mechanisms or gear elements in an automobile gearbox. As mentioned earlier, this indicates that the steel according to the present invention is optimal for high temperature carburizing treatment, and carburized pinion or gear mechanism teeth obtained using these elements. Reducing the carburizing time without reducing the strength related to bending fatigue, and improving productivity and reducing the carburizing cost compared to known steel materials carburized at standard temperature. It is preferred for both.

  As described above, the steel material according to the present invention is optimal for high-temperature carburizing treatment, and without reducing the mechanical properties after carburizing treatment, shortening the carburizing time, improving productivity, and carburizing treatment cost. And is particularly suitable for manufacturing mechanical elements such as pinions.

It is a figure which shows the gemini curve of four comparative steel materials and three steel materials which concern on this invention.

Claims (8)

Its composition is in weight percentage:
0.19% ≦ C ≦ 0.25%;
1.1% ≦ Mn ≦ 1.5%;
0.8% ≦ Si ≦ 1.2%;
0.01% ≦ S ≦ 0.09%;
Trace amount ≦ P ≦ 0.025%;
Trace amount ≦ Ni ≦ 0.25%;
1% ≦ Cr ≦ 1.4%;
0.10% ≦ Mo ≦ 0.25%;
Trace amount ≦ Cu ≦ 0.30%;
0.010% ≦ Al ≦ 0.045%;
0.010% ≦ Nb ≦ 0.045%;
0.0130% ≦ N ≦ 0.0300%;
Optionally, trace amount ≦ Bi ≦ 0.10% and / or trace amount ≦ Pb ≦ 0.12% and / or trace amount ≦ Te ≦ 0.015% and / or trace amount ≦ Se ≦ 0.030% and / or Or trace amount ≦ Ca ≦ 0.0050%;
The balance obtained from the manufacturing operation consists of iron and impurities, and the chemical composition has the average values J _3m , J _11m , J _15m , and J _{25m of} five Jomini tests:
_{α = | J 11m -J 3m ×} 14/22-J 25m × 8/22 | ≦ 2.5HRC; such that and _{β = J 3m -J 15m ≦ 9HRC} , characterized in that it is adjusted mechanically Steel material for structural elements. The composition is
The steel material for a mechanical element according to claim 1, wherein β is adjusted so as to satisfy J = J _3m −J _15m ≦ 8HRC. Said composition is:
0.19% ≦ C ≦ 0.25%;
1.2% ≦ Mn ≦ 1.5%;
0.85% ≦ Si ≦ 1.2%;
0.01% ≦ S ≦ 0.09%;
Trace amount ≦ P ≦ 0.025%;
0.08% ≦ Ni ≦ 0.25%;
1.1% ≦ Cr ≦ 1.4%;
0.10% ≦ Mo ≦ 0.25%;
0.06% ≦ Cu ≦ 0.30%;
0.010% ≦ Al ≦ 0.045%;
0.015% ≦ Nb ≦ 0.045%;
0.0130% ≦ N ≦ 0.0300%;
Optionally, trace amount ≦ Bi ≦ 0.07% and / or trace amount ≦ Pb ≦ 0.12% and / or trace amount ≦ Te ≦ 0.010% and / or trace amount ≦ Se ≦ 0.020% and / or Or trace amount ≦ Ca ≦ 0.045%;
3. The steel material for a mechanical element according to claim 1, wherein the balance obtained from the manufacturing operation is made of iron and impurities. Said composition is:
0.20% ≦ C ≦ 0.25%;
1.21% ≦ Mn ≦ 1.45%;
0.85% ≦ Si ≦ 1.10%;
0.01% ≦ S ≦ 0.08%;
Trace amount ≦ P ≦ 0.020%;
0.08% ≦ Ni ≦ 0.20%;
1.10% ≦ Cr ≦ 1.40%;
0.11% ≦ Mo ≦ 0.25%;
0.08% ≦ Cu ≦ 0.30%;
0.010% ≦ Al ≦ 0.035%;
0.025% ≦ Nb ≦ 0.040%;
0.0130% ≦ N ≦ 0.0220%;
Optionally, trace amount ≦ Bi ≦ 0.07% and / or trace amount ≦ Pb ≦ 0.12% and / or trace amount ≦ Te ≦ 0.010% and / or trace amount ≦ Se ≦ 0.020% and / or Or trace amount ≦ Ca ≦ 0.045%;
The steel material for a mechanical element according to claim 3, wherein the balance obtained from the manufacturing operation is made of iron and impurities. A method of manufacturing a mechanical element from a steel material subjected to carburizing or carbonitriding,
The steel material according to any one of claims 1 to 4 is used for the purpose of producing a mechanical element, and a machining process, a carburizing process or a carbonitriding process is performed, and then a quenching process is performed. A method for manufacturing a mechanical element.   The manufacturing method according to claim 5, wherein the carburizing process or the carbonitriding process is performed at a temperature of 950 to 1050 ° C. 6.   A steel mechanical element manufactured by the manufacturing method according to claim 5 or 6.   The mechanical element according to claim 7, wherein the mechanical element is a gear element.

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