JPH04350145A - High carbon steel for refining excellent in toughness and fatigue resistance and its production - Google Patents

Abstract

PURPOSE:To obtain a high carbon steel good in workability and satisfying the whole of strength, toughness and fatigue resistance only by simple heat treatment after working by using the conventional Cr-Mo steel as a base, reducing the content of Cr and Mo and adding specified amounts of Ni, Ti and Nb thereto. CONSTITUTION:A steel contg., by weight, 0.40 to 0.08% C, <=0.30% Si, 0.2 to 1.0% Mn, 0.3 to 1.0% Cr, 2.0 to 5.0% Ni, 0.1 to 0.5% Mo, <=0.06% sol.Al, <=0.0080% N, <=0.030% P and <=0.010% S, furthermore contg 0.01 to 0.20% Ti and/or 0.0l to 0.20% Nb and the balance Fe is used. In this steel, hot rolling is completed at >700 deg.C, and after that, it is coiled at 500 to 700 deg.C. After the above hot rolling, the steel is furthermore subjected to spheroidizing or, before this spheroidizing, it is cold-rolled, or moreover, before this cold rolling, softening is executed. Furthermore, at the time of adding 0.1 to 0.5% V to the above steel, its fatigue properties in a low cycle area where large loads are repeatedly applied can remarkably be improved.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to high carbon steel that exhibits excellent toughness and fatigue resistance through relatively simple heat treatment, and is particularly applicable to high carbon steels that require wear resistance and impact resistance. The present invention relates to a high carbon steel material for thermal refining that is suitably used as chain material, machine parts, etc., and a method for producing the same.

0002

[Prior Art] In general, tempered carbon steel materials used after undergoing heat treatment processes such as quenching and tempering are high carbon steels containing at least 0.4 wt% (hereinafter simply referred to as "%") of C. is used. Such high carbon steel has high hardness and excellent strength and wear resistance, so it is widely used in the fields of mechanical parts such as chains and gears, cutlery, and springs.

The general properties required of these high carbon steels are mainly: (1) good workability before quenching, (2) ability to obtain desired hardness and high toughness through quenching and tempering treatments, and (2) good workability before quenching. There are three points: high fatigue strength. Among these, the workability before quenching mentioned above is controlled by the shape of carbides in the steel, and it is desirable that the steel be completely spheroidized by annealing. Furthermore, the hardness and toughness after quenching and tempering described in (2) above tend to contradict each other, and special measures are required to obtain high toughness with high hardness. For example, the most common method is to add a large amount of Cr or Mo, but if a large amount of Cr or Mo is added, it is difficult to form a ball, and this method makes it difficult to ensure workability, which is the first required performance. On the contrary, it becomes difficult. Therefore, in order to improve the workability of Cr-Mo steel, we suppressed the amount of Si and C, and added Ni,
Method of adding Ti, Nb, B (Japanese Unexamined Patent Publication No. 57-4
3959 Publication) and a method of adding Mn, Ti, and B to reduce or eliminate Cr and Mo (
JP-A-1-100244) and the like have been proposed.

0004

[Problems to be Solved by the Invention] However, all of these conventional methods lack a perspective on "fatigue resistance", which is the performance required in (2) above. From this,
The reality is that there is a strong demand in this field for the development of materials that satisfy both of the above characteristics (1) to (2).

[0005]

[Means for Solving the Problems] In view of the above-mentioned problems observed in conventional high carbon steel sheets, the inventors have developed a method that not only provides good workability but also improves strength and toughness by simply applying a simple heat treatment after the processing. In order to provide a high carbon steel sheet that satisfies all requirements for fatigue resistance, we conducted various studies, obtained the following findings, and developed a high carbon steel material for tempering according to the present invention. The idea of the present invention is characterized by the following points.

[0006] Based on conventional Cr-Mo steel, when a steel plate with reduced Cr and Mo and Ni added is quenched and then tempered at a low temperature, it becomes the same as the conventional Cr-Mo steel.
It is possible to obtain strength equal to or higher than that of steel, and its toughness and fatigue resistance are significantly superior to conventional Cr-Mo steel. ■ When V is added to the above steel, other properties are sacrificed. The fatigue properties in the so-called low cycle range where large loads are repeatedly applied are significantly improved without causing any loss of strength. Fatigue resistance should be further improved.

The present invention is based on the above-mentioned findings, and is characterized by C: 0.40-0.
80%, Si: 0.30% or less, Mn: 0.2
~1.0%, Cr:0.3 ~1.0%, N
i:2.0~5.0%, Mo:0.1~
0.5%, sol. Al: 0.06% or less, N:
0.0080% or less, P: 0.030% or less, S
:0.010% or less, and further contains Ti:0.01%
~0.20% and any one or two of Nb:0.01~0.20%, or further contains V:0.
1 to 0.5%, and the remainder is substantially F.
By having a composition consisting of E and unavoidable impurities, it exhibits good workability and ensures sufficient hardness (strength) and excellent toughness and fatigue resistance with a relatively simple heat treatment. We have made it possible.

[0008] The present invention also provides that the steel having the above-mentioned composition is heated to Ac3 point or higher, hot rolling is completed at a temperature of 700°C or higher, and then coiled at a temperature range of 550 to 700°C. Alternatively, the hot rolling is followed by spheroidizing annealing, or the hot rolling is followed by cold rolling with a reduction ratio of 10% or more and then spheroidizing annealing is performed, or the cold rolling is followed by spheroidizing annealing. A high carbon steel material for heat treatment that exhibits good workability by annealing beforehand, and can ensure sufficient hardness (strength) as well as excellent toughness and fatigue resistance by applying a relatively simple heat treatment. We propose a manufacturing method that is characterized in that it can be manufactured at low cost.

As described above, the present invention exhibits good punching workability and molding workability, and furthermore, after these processes, oil quenching is performed at about 800 to 900°C, and tempering treatment is performed at a temperature lower than 300°C. The present invention relates to a high carbon steel material that exhibits high strength, excellent toughness and fatigue resistance by applying the above-mentioned methods, and a method for manufacturing the same. The reason is as follows.

C: C is a necessary component to ensure strength, but if it is less than 0.40%, sufficient strength will not be obtained after quenching and tempering, but if it is contained in excess of 0.80%, it will not be possible to obtain sufficient strength. and coarse pro-eutectoid cementite is formed, leading to deterioration of toughness and fatigue resistance. Therefore, the C content is 0.40-0.8
It was set to 0%. Si: Si is an element used for deoxidation and is also a strengthening element at the same time. However, if the content exceeds 0.30%, the formability of the steel sheet will deteriorate. Therefore, the Si content was set to 0.30% or less. Mn: Like C, Mn is effective in securing strength and improving hardenability, but if its content is less than 0.2%, the desired effect cannot be obtained by the above action, while if it exceeds 1.0% If it is contained, cold workability will deteriorate. Therefore, M
The n content was 0.2 to 1.0%. Cr: Cr has the effect of preventing the formation of graphite, improving the hardenability of the steel sheet, and increasing the strength, so it is a component added when it is necessary to improve the properties by these effects. If the content is less than 0.3%, the above effects will not be sufficient, while if it exceeds 1.0%, spheroidization will become difficult. Therefore, the Cr content is 0.3-1.0
%.

Ni: The addition of Ni has the most important meaning in the present invention. That is, the addition of Ni dramatically improves toughness and fatigue resistance without sacrificing other properties. However, if the Ni content is 2.0% or less, the above effects cannot be obtained, and on the other hand, if it is added in excess of 5.0%, the effect is saturated. Therefore, the Ni content is 2.0~
It was set at 5.0%. Mo: Mo is an element that increases the softening resistance during tempering and is also effective in improving toughness, but if the content is 0.
If it is less than 1%, the above effect will not be sufficient; on the other hand, if it is 0.5%
If the Mo content exceeds 0.1, it is difficult to form spheroids.
~0.5%. V: V is an element effective in improving fatigue properties in the low cycle range, but if its content is less than 0.1%, the above effects are not sufficient, while if it exceeds 0.5%, residual carbide may be formed during quenching. The V content is set to 0.1 to 0.5% because it tends to remain and causes deterioration of toughness and fatigue resistance.

Ti: Ti has the effect of fixing solid solution N and improving cold workability, as well as suppressing grain coarsening during quenching and heating and improving toughness after tempering. If the amount is less than 0.01%, the above effects will not be sufficient;
When the content exceeds 0.20%, hardenability decreases and toughness deteriorates due to coarse TiC. Therefore, the Ti content was set to 0.01 to 0.2%. Nb: Like Ti, Nb also has the effect of suppressing grain coarsening during quenching and heating and improving toughness after tempering. If the content is less than 0.01%, the above effects will not be sufficient;
．． If the Nb content exceeds 20%, the hardenability will decrease and the toughness will deteriorate due to coarse NbC, so the Nb content should be 0.
01-0.2%. sol. Al: sol. Al is a deoxidizing agent added to prevent the formation of oxide inclusions, and as long as Al is sufficiently deoxidized, it does not necessarily have to remain in the steel sheet. However, sol. If the Al content exceeds 0.06%, ductility during cold working will decrease. Therefore, sol. A
The l content was set to 0.06% or less. N: Mainly exists in the form of AlN and is useful for refining crystal grains, but if it is contained in a large amount, hot workability and cold workability are reduced. Therefore, the N content was set to 0.0080% or less. P: The lower the P content, the better for improving toughness. In particular, when the P content exceeds 0.03%, P segregates at grain boundaries, making it easy to cause grain boundary embrittlement. Therefore, the P content is 0.0
It was set to 3% or less. S: Like P, the lower the toughness, the more preferable it is, but the presence of MnS has a significant effect on toughness deterioration, especially when the steel has high strength like the steel of the present invention. Therefore, the S content is 0.01%
The following was made.

Next, the manufacturing conditions of the high carbon steel material for thermal refining according to the present invention will be explained. a. Heating temperature: In order to make the structure before processing into uniform austenite, it was decided to heat to Ac3 point or higher. b. Hot rolling finishing temperature: Since the steel with the composition according to the present invention contains elements that suppress pearlite transformation, in order to stably transform pearlite, it should be rolled at the lowest temperature possible to increase the driving force for transformation. This is desirable. However, when the temperature is below 700°C, the deformation resistance increases rapidly and rolling becomes difficult, so the hot rolling finishing temperature was set to exceed 700°C. c. Coiling temperature: Ni, Cr, M like the steel of the present invention
When steel containing O is rolled up at 400 to 550°C, an abnormal structure consisting of coarse amorphous carbides is produced. Also, 4
If winding is performed at a temperature below 00°C, a hard phase such as bainite is generated, making winding substantially difficult. However, 550℃
If the coiling temperature is above 700°C, normal pearlite will be produced, but if the coiling temperature exceeds 700°C, the effects of decarburization cannot be ignored. Therefore, in the present invention, the winding temperature is set at 550 to 700°C.

In order to ensure even more workability than the basic manufacturing method described above, the present invention may include a method in which spheroidizing annealing is performed after completion of hot rolling, and the conditions for this treatment are as follows: Normal range (600~700℃ x 2~24h
r) is carried out within. Furthermore, the present invention may be a method of performing cold rolling at a rolling reduction of 10% or more prior to the spheroidizing annealing. By performing cold rolling and spheroidizing annealing in this manner, a great effect is shown in promoting spheroidization. That is, in the present invention, after hot rolling, cold rolling with a rolling reduction of 10% or more is performed prior to spheroidizing annealing. Furthermore, in the present invention, when the material is hard and difficult to cold-roll, annealing for softening may be performed before the cold-rolling. The conditions for this softening annealing are in the normal range (
600 to 700°C x 2 to 24 hours) as appropriate.

[0015]

【Example】

Example 1 Each slab (200 mm thick) with the component composition shown in Table 1
was produced through a manufacturing process according to conventional methods. Next, each of these slabs was heated to 1200°C for 30 minutes, then hot rolled at a finishing temperature of 870°C to form a hot rolled steel plate with a thickness of 4mm, cooled to 650°C on a hot run table, and then rolled. I took it. Each hot-rolled steel sheet produced under these conditions was subjected to a quenching process in which it was heated and held at 850°C for 30 minutes, then rapidly cooled in an oil bath, and then tempered at 200°C and 300°C for 2 hours. Ta. "Hardness", "impact absorption energy", "fatigue limit", and "notch fatigue strength" were measured for the samples obtained through such a manufacturing process. Among the measured values, notch fatigue strength is determined by notch radius 0
．． 3 on a test piece of the shape shown in Figure 1 with 5 mm notches on both ends.
A stress of 0 kg/mm2 is applied and the number of breaks is compared. The results are also shown in Table 1. As is clear from Table 1, it was found that the steel plate manufactured according to the present invention has excellent impact resistance and fatigue resistance.

Example 2 Slabs (200 mm thick) having the component compositions shown in Table 2
was produced through a manufacturing process according to conventional methods. Next, each of these slabs was heated to 1200°C for 30 minutes, then hot rolled at a finishing temperature of 870°C to form a hot rolled steel plate with a thickness of 4mm, cooled to 650°C on a hot run table, and then rolled. I took it. Each hot-rolled steel sheet produced under these conditions was subjected to a quenching process in which it was heated and held at 850°C for 30 minutes, then rapidly cooled in an oil bath, and then tempered at 200°C and 300°C for 2 hours. Ta. "Hardness", "impact absorption energy", "fatigue limit", and "notch fatigue strength" were measured for the samples obtained through such a manufacturing process. Among the measured values, notch fatigue strength is determined by notch radius 0
．． 3 on a test piece of the shape shown in Figure 1 with 5 mm notches on both ends.
A stress of 0 kg/mm2 is applied and the number of breaks is compared. The results are also shown in Table 2. As is clear from Table 1, it was found that the steel plate manufactured according to the present invention has excellent impact resistance and fatigue resistance.

Example 3 Each slab (200 mm thick) with the component composition shown in Table 3
was produced through a manufacturing process according to conventional methods. Next, each of these slabs was heated to 1200°C for 30 minutes, then hot rolled at a finishing temperature of 850°C to form a hot rolled steel plate with a thickness of 4mm, and rolled on a hot run table to each coiling temperature shown in the table. It was cooled and then rolled up. After cooling to room temperature, cold rolling is performed at various reduction rates, and then these cold rolled steel sheets are
Spheroidizing annealing was performed in a nitrogen atmosphere at 680°C. Table 4 shows changes in hardness depending on cold rolling reduction and annealing time. As is clear from Table 4, when cold rolling is performed at a predetermined rolling reduction during spheroidizing annealing, the spheroidization of cementite is further promoted, and a steel sheet with better workability can be obtained.

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[Effects of the Invention] As explained above, according to the present invention,
Steel materials with excellent thermal shock resistance, fatigue resistance, and wear resistance can be obtained. Therefore, it is very suitable as a material for chains and machine parts, which require excellent properties in both of these properties. Moreover, the method of the present invention can stably supply high carbon steel for tempering which has such excellent properties.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a notch fatigue strength test piece.

Claims (6)

[Claims] [Claim 1] C: 0.40 to 0.80 wt%,
Si: 0.30wt% or less, Mn: 0.2 to 1.
0 wt%, Cr: 0.3 to 1.0 wt%,
Ni: 2.0 to 5.0 wt%, Mo: 0.
1 to 0.5 wt%, sol. Al: 0.06wt%
Below, N: 0.0080wt% or less, P: 0.03
0 wt% or less, S: 0.010 wt% or less, and further contains any one or two of Ti: 0.01 to 0.20 wt% and Nb: 0.01 to 0.20 wt%. A high carbon steel material for tempering with excellent toughness and fatigue resistance, with the remainder essentially consisting of Fe and unavoidable impurities. [Claim 2] C: 0.40 to 0.80 wt%,
Si: 0.30wt% or less, Mn: 0.2 to 1.
0 wt%, Cr: 0.3 to 1.0 wt%,
Ni: 2.0 to 5.0 wt%, Mo: 0.
1 ~ 0.5 wt%, V: 0.1 ~ 0.5 wt%
, sol. Al: 0.06wt% or less, N: 0
．． 0080wt% or less, P: 0.030wt
% or less, S: 0.010 wt% or less, Ti: 0.01 to 0.20 wt% and Nb: 0.01
~0.20wt% of any one or two types,
A high carbon steel material for thermal refining with excellent toughness and fatigue resistance, with the remainder essentially consisting of Fe and unavoidable impurities. 3. The steel according to claim 1 or 2 is made of Ac
A high carbon steel material for tempering with excellent toughness and fatigue resistance, which is heated at three or more points to complete hot rolling at a temperature of over 700°C, and then coiled at a temperature range of 550 to 700°C. manufacturing method. 4. The steel according to claim 1 or 2,
Complete hot rolling at a temperature of over 700°C by heating at three or more points, then winding at a temperature range of 550 to 700°C,
A method for producing a high carbon steel material for thermal refining with excellent toughness and fatigue resistance, which is characterized by successively subjecting it to spheroidizing annealing. 5. The steel according to claim 1 or 2 is made of Ac
Complete hot rolling at a temperature of over 700°C by heating at three or more points, then winding at a temperature range of 550 to 700°C,
A method for producing a high carbon steel material for thermal refining with excellent toughness and fatigue resistance, which comprises successively cold rolling with a rolling reduction of 10% or more and then spheroidizing annealing. 6. The method for producing a high carbon steel material for tempering with excellent toughness and fatigue resistance according to claim 4, characterized in that annealing is performed before cold rolling.