JPS62180011A - Thermo-mechanical treatment of steel - Google Patents

Abstract

PURPOSE:To easily obtain a steel material having high elongation in a specified temp. range and showing superplastic characteristics at a low cost by subjecting a hypoeutectoid steel to heating, hot working and reheating under specified conditions. CONSTITUTION:A hypoeutectoid steel is heated to the AC3 point +100 deg.C - the AC3 point -200 deg.C and hot worked at >=20% working rate and a working finish temp. which is below the heating temp. by <=50% of the heating temp. the steel is then reheated to the AC1 point - the AC3 point to form a fine alpha+beta two-phase structure and to produce superplasticity. Thus, a hypoeutectoid steel having considerable high elongation in a specified temp. range and showing superplastic characteristics is obtd. by such relatively simplified thermo- mechanical treatment.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) This invention is applicable to, for example, automobiles, ships, and industrial machinery.

The present invention relates to a process heat treatment method for steel that is used to significantly improve the elongation in a specific temperature range of steel materials used as materials for various mechanical structures such as agricultural machinery, aerospace equipment, and office equipment.

(Prior Art) Conventionally, there have been superplastic alloys that significantly improve the elongation of metal materials, and zinc-based superplastic alloys (SPZ) and aluminum-based superplastic alloys (SPA) have been developed.For example, Zn-22 Some weight % An co-refracting alloys have been put into practical use. In addition, nickel-based super heat-resistant alloys (for example, lN-100
) have also been incorporated into jet engine parts by utilizing their superplasticity.

(Problem to be solved by the invention) However, conventional superplastic alloys are alloys with low mechanical strength such as the above-mentioned zinc-based or aluminum-based alloys, or special alloys such as nickel-based superheat-resistant alloys. It is a very expensive alloy, and it has been desired to apply this type of Itfl plasticity phenomenon to steel materials as well. In response to such demands, the development of iron-based Miffle materials is gradually progressing, and further improvements are being sought.

This invention was made in view of the above-mentioned conventional trends, and provides a processing heat treatment method that makes it possible to easily and at low cost obtain a steel material exhibiting superplastic properties with large elongation in a specific temperature range. is intended to provide.

[Structure of the Invention] (Means for Solving the Problems) The method for processing and heat treating steel according to the present invention is to process hypoeutectoid steel at Ac3 points +100'0 as shown in the pattern illustrated in FIG.
- After heating in the range of 3 Ac -200℃, the processing rate is 20
% or more and the finishing temperature is at least 50% lower than the heating temperature, then Ac, point ~ Ac
It is characterized in that it is reheated to a range of three points to develop superplasticity as a fine α+γ two-phase structure.

In this processing heat treatment method, the heating temperature of the hypoeutectoid steel is set to A
The reason for setting the range from c3 point +100℃ to Ac3 point -200℃ is because if the temperature is lower than this, it will be difficult to perform machining at a predetermined machining rate by the predetermined machining end temperature. This is because if the content is too high, there is a risk of coarsening of the tissue. Further, the reason why the total processing rate is set to 20% or more is because fine crystals of, for example, 10 gm or less cannot be obtained after processing, and the processing rate is more preferably set to 50% or more. In addition, the reason why the processing end temperature is set to a temperature that is 50% lower than the initial heating temperature is because if the temperature is lower than this, it becomes difficult to perform processing to obtain a predetermined processing rate. The processing end temperature is set to a temperature that is 40% lower than the initial heating temperature or higher.

Furthermore, after performing the above processing, it is reheated to a range of Ac1 point to Ac3 point to develop superplasticity as a fine α + γ two-phase structure, but in this case, the reheating temperature is Ac
If it is lower than the Ac3 point, good Itfl plasticity cannot be expressed, and if it is higher than the Ac3 point, good superplasticity cannot be expressed either.

In addition, in the processing heat treatment method according to the present invention, after performing the predetermined processing, it takes a relatively long time to reheat to the range of Ac, point to Ac3 point, for example, due to production or transportation reasons. This also includes cases where a long period of time has passed.

In one embodiment of the present invention, the processing performed after heating the hypoeutectoid steel to a temperature in the range of Ac3 point +100°C to Ac3 point -200°C is performed at a processing rate of 5 to 3 while the temperature decreases by 10%.
The processing can be carried out at a rate of 0%, so that the total processing rate is 20% or more and the processing end temperature is 50% lower than the heating temperature or more. In this case, if the processing rate of processing performed while the temperature decreases by 10% is less than 5%, fine crystals may not be obtained, and if it is more than 30%, the amount of processing at high temperature increases and the processed structure deteriorates. This is because it becomes longer and less likely to have an equiaxed load.

FIG. 5 shows an example of a processed evaporation turn according to this embodiment, and Table 1 illustrates the relationship between temperature and processing rate.

Table 1 In this case, the total processing rate should be 20% or more, more preferably 50% or more, and the processing end temperature should be 50% higher than the heating temperature.
More preferably, the temperature is lowered by 40% or higher. Further, it is more desirable that the processing speed is between 0.1%/min and 50%/min.

In another embodiment of this optical IJI, after the above-mentioned processing is performed, an IJI like the pattern illustrated in FIG.
＾ ＾ 、One piece to ＾ ＾ ＾ ＾ ＾ ＾ ＾ ＾
80I+I/rS Bamboo opening jji hn After holding the shaft, it is cooled to form a fine structure, and then Ac1 point ~ Ac3
By applying ILT heating to a point range, a fine α+γ two-phase structure can be formed.

In this case, the reason why the heating is maintained in the range of Ac3 point to Ac3 point +50°C is to obtain a fine structure after cooling. It is also desirable to obtain a fine martensitic structure.

In other words, after the above processing, the crystals have a shape that is elongated in the forging (rolling) direction, but by applying such heat treatment, it is possible to make them relatively equiaxed crystals, which reduces elongation. It will be possible to increase it further. After this heat treatment, Ac
If necessary, it is also desirable to reheat the material to a temperature in the range of , to Ac3 point to develop superplasticity as a fine α+γ2 phase structure.

In yet another embodiment of the present invention, prior to heating the hypo-eutectoid steel to a range of 3 points Ac + 100°C and 3 points Ac - 200°C, as in the pattern illustrated in FIG. It is also possible to heat and maintain the temperature in the range of 300° C. on the Ac3 point scale and then allow it to cool.

This kind of heat treatment before processing removes and adjusts the non-uniformity of the structure and crystals that occur when forging or rolling large continuously cast slabs or large ingots.
This is effective in reducing material non-uniformity to some extent at the end of machining, and it is also good to employ this pre-machining heat treatment if necessary.

In yet another embodiment of the present invention, prior to heating the hypoeutectoid steel to a temperature in the range of Ac3 point +100°C to Ac3 point -200°C, as in the pattern illustrated in FIG. It is also possible to heat and hold in the range of Ac3 point + 300°C and then let it cool, then heat and hold in the range of Ac3 point to Ac3 point + 100°C and then rapidly cool it.

In this way, if the pre-processing heat treatment shown in Fig. 3 is followed by rapid cooling after heating and holding in the range of AcB point to Ac3 point + 100°C as shown in Fig. 4, the heating temperature during processing can be reduced to Ac3. If the temperature is below (Ac3 point - Ac3 point -200℃), the refined crystals will be processed without much growth during processing, so it will be effective in refining the crystal grains. It is also good to adopt such a pre-processing heat treatment.

The processing heat treatment method according to this invention has a carbon content of 0.6
It is applicable to hypoeutectoid steel containing 5% by weight or less, and can be applied to carbon steel and alloy steel included in hypoeutectoid steel, and is not particularly limited, but the following:
Several examples of hypo-eutectoid steel to which this invention is applied are shown below.

That is, in the embodiment of the present invention, the hypoeutectoid steel has, in weight percent, C: 0.08 to 0.65%, Si: O, 15 to
1.0%, Mn:O, 1 to 2.5%, and the balance may be carbon steel or manganese steel containing Fe and impurities.

The analyzed steel is in weight%, C: 0.08-0.65%, Si: 0
．． 15-1.0%, Mn: 0.1-2.5%, Cr
:0.2 to 1.0%, the balance being Fe and impurities, such as chromium steel or manganese chromium steel.

Furthermore, in another embodiment of the invention, the hypoeutectoid steel has a weight percentage of C: 0.08-0.65%, Si:O, 15%.
~1.0%, Mn: 0.1~2.5%, Cr: 0
, 2-3, 0%, MO=0.1-1.0%, balance Fe
and chromium-molybdenum steel containing impurities.

Furthermore, in another embodiment of the invention, the eutectoid steel has c:o, os~0.65%, Si:0.
15-1.0%, Mn: 0.1-2.5%, Ni: 0.
It can be a nickel-chromium steel containing 2 to 1.5%, Cr: 0, 2 to 3, 0%, and the balance Fe and impurities.

Therefore, hypoeutectoid steel has heavy h(%, C: 0, 08~0.6
5%, Si: 0.15-1.0%, Mn: 0.1-2.
5%, Ni: 0.2-1.5%, Cr: 0, 2-
It can be a nickel-chromium-molybdenum steel-based steel consisting of 3.0%, Mo:O, 1.0%, and the remainder Fe and impurities.

Furthermore, in another embodiment of the present invention, the hypoeutectoid steel contains W: 0.1 to 1.0% in the balance Fe, or Nb+Ta: 0.1% in the balance Fe.
05-2.0%, v: 0.05-2.0%, Ti:
0.0%, 0.05% to 2.0% and A text: 0.05% to 1.0%.

In the above-mentioned hypoeutectoid steel, if the C content is low, the necessary strength cannot be ensured, and if it is high, the toughness will decrease, so it is more desirable to set it to 0.08 to 0.65%. Si acts as a deoxidizing agent and increases strength, and
3 points to make processing at high temperatures easier, but if too much, the toughness deteriorates, so it is more desirable to set it at 0.15 to 1.0%, and Mn acts as a deoxidizing agent and a desulfurizing agent. Cr also improves hardenability and increases strength, but if it is too much, workability and machinability decrease, so it is more desirable to set it at 0.1 to 2.5%. Cr improves hardenability and corrosion resistance. It improves the AcA point and facilitates processing at high temperatures, but if it is too large, it reduces workability and toughness at room temperature, so it is more desirable to set it to 0.2 to 1.0%. M
o improves hardenability and tempering resistance, improves strength, and raises Ac3 point to facilitate processing at high temperatures, but too much will impair workability and toughness at room temperature, so o It is more desirable to set it to .1 to 1.0%, and although Ni is effective in increasing the strength of steel, too much Ni reduces toughness, so it is more desirable to set it to 0.2 to 3.5%. .

Further, although W increases the Ac3 point and facilitates processing at high temperatures, too much W impairs toughness, so it is more desirable to have a content of 0.1 to 1.0%, and Nb.

Ta, V, Ti, and AM are effective in refining crystal grains,
V increases the Ac3 point and facilitates processing at high temperatures, but too much V impairs workability and toughness at room temperature, so Nb
+Ta (either one may be 0) is 0.05
~2.0%, ■0.05~2.0%, Ti 0.05
It is more desirable to set the content to 2.0% and AM to 0.05 to 1.0%. In addition, aging improves strength and improves corrosion resistance.
1. Cu may be added in an amount of 0.2 to 2.0% to improve weather resistance; 1. CO may be added in an amount of 0.3 to 1.5% to improve strength; and other desired effects may be added. Elements obtained can also be added.

(Example 1) Hypoeutectoid steels having the chemical compositions shown in Table 2 were melted to obtain test steels of i94101. , Fig. 6, Fig. 7(a)(b), Fig. 8
Process heat treatment was performed on each sample steel at the temperatures and processing rates shown in Table 3 in the patterns shown in Figures (a) and (b) and Figures 9 (a) and (b).

Next, a tensile test (plastic working) was conducted at the superplastic working temperature shown in Figure 2, with an infrared radiation image furnace installed.
Similarly, the elongations shown in Table 3 were obtained.

As shown in Table 3, it is possible to obtain a considerably large elongation even when processing heat treatment is performed using a significantly simplified pattern that does not involve the quenching shown in Fig. 6.
By performing quenching (H2) after finishing the processing using the patterns shown in FIGS. 7(a) and 7(b), more equiaxed loading is possible, and therefore the elongation is further increased. Also, Figure 8 (
By adding a heat treatment of heating and cooling before machining with the patterns shown in a) and (b), it is possible to weaken the material non-uniformity at the end of machining to some extent, further increasing the elongation, as shown in Figure 9. (&) By adding heating and cooling and quenching (H+) before processing with the pattern shown in (b),
It is possible to further increase the elongation, as shown in Figure 7 (b
), FIG. 8(b), and FIG. 9(b), it was confirmed that large elongation could be obtained even when the heating temperature during processing heat treatment was set to 3 Ac points or less.

(Example 2) Test steels were prepared by melting hypo-eutectoid steels having the chemical composition shown in Table 4, and the test steels were prepared as shown in Figs. 10(a)(b) and 11(a).
(b), Fig. 12 (a) (b) and Fig. 13 (
a) Machining each sample steel using the patterns shown in (b) at the processing rates shown in Table 5 (I, II, and I in the table correspond to regions T, u, and m in each figure, respectively) and at the temperatures shown in Table 5. Heat treatment was performed.

Next, using an Instron type tensile testing machine equipped with an infrared radiation image furnace, a tensile test (plastic working) was conducted at the superplastic working temperature shown in Table 5. Elongation was obtained.

As shown in Table 5, it is possible to obtain a considerably large elongation even when processing heat treatment is performed using the simplified pattern shown in Figs. 10(a) and (b) without quenching, and as shown in Fig. 11. By performing quenching (H3) after processing using the patterns shown in (a) and (b), it is possible to make the crystals that are elongated in the forging (rolling) direction relatively equiaxed. Therefore, the elongation increases further. Also,
By adding a heat treatment of heating and cooling before machining using the patterns shown in Figures 12(a) and (b), it is possible to remove to some extent the non-uniformity of the material that exists at the end of machining, especially in large materials. Therefore, the elongation further increases, and it is possible to further increase the elongation by adding heating and cooling and quenching before processing with the patterns shown in Fig. 13 (a) and (b). b) As shown in Fig. 11 (b), Fig. 12 (b), and Fig. 13 (b), it was confirmed that large elongation could be obtained even when the heating temperature during processing heat treatment was set to 3 Ac or less. [Effects of the Invention] As explained above, according to the steel processing heat treatment method according to the present invention, hypoeutectoid steel can be heated at Ac3 points +100°C to Ac
After heating in the range of 3 points - 200'O, perform processing at a processing rate of 20% or more and a processing end temperature of 50% lower than the heating temperature or higher to obtain a temperature in the range of 1st point Ac to 3 points Ac. By reheating the steel to form a fine α+γ two-phase structure, it is possible to obtain a hypoeutectoid steel that exhibits superplastic properties with considerably large elongation in a specific temperature range through relatively simple processing heat treatment. This has the remarkable effect of providing a structural steel suitable as a material for manufacturing complex-shaped mechanical structural parts such as gears by plastic working such as forging.

[Brief explanation of drawings]

Figures 1 to 4 are explanatory diagrams showing processing and heat treatment patterns for steel according to each embodiment of the present invention, and Figure 5 is a diagram showing the procedure when processing after heating is divided into multiple stages in an embodiment of the present invention. Explanatory diagrams illustrating FIGS. 6 and 7 (a)
(b), Fig. 8(a)(b) and Fig. 9(a) (
b) is an explanatory diagram showing the working heat treatment pattern of steel adopted in Example 1 of the present invention, FIGS. 10(a) and (b)
, FIG. 11(a)(b), FIG. 12(a)(b), and FIG. 13(a)(b) are explanations showing the working heat treatment pattern of steel adopted in Example 2 of the present invention. . Patent applicant Daido Steel Co., Ltd. Patent attorney Yutaka Oshio Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 7 (b) Figure 8 (G) Figure 8 Figure (b) Figure 9 Figure 9 (b) Figure 1O Figure 10 (b) Figure 11 Figure 11 (b) Figure 12 Figure 12 (b)

Claims (13)

[Claims] (1) Hypoeutectoid steel at Ac_3 points +100℃ ~ Ac_3 points -
After heating to a temperature in the range of 200°C, processing is carried out at a processing rate of 20% or more and the finishing temperature is at least 50% lower than the heating temperature, and then reheated to a range of Ac_1 point to Ac_3 point to form fine particles. A method for processing and heat treating steel, which is characterized by expressing superplasticity as an α+γ two-phase structure. (2) Hypoeutectoid steel from Ac_3 points +100℃ to Ac_3 points -
Processing performed after heating to a range of 200°C is performed at a processing rate of 5 to 30% while the temperature decreases by 10%, and the total processing rate is 20% or more and the processing end temperature is 50% higher than the heating temperature. The method for processing and heat treating steel according to claim 1, wherein the temperature is lower than or equal to the lowered temperature. (3) After processing, Ac_3 points ~ Ac_3 points +5
After heating and maintaining it in the range of 0℃, it is cooled to form a fine structure,
The method for processing and heat treating steel according to claim 1 or 2, wherein the steel is then reheated to a temperature in the range of Ac_1 point to Ac_3 point to form a fine α+γ two-phase structure. (4) Hypoeutectoid steel from Ac_3 points +100℃ to Ac_3 points -
Prior to heating to 200℃ range, Ac_3 points ~
Claims (1) to (3) characterized in that the product is heated and held in the range of Ac_3 points +300°C and then allowed to cool.
A method for processing and heat treating steel according to any one of paragraphs. (5) Hypoeutectoid steel at Ac_3 points +100℃ ~ Ac_3 points -
Prior to heating to 200℃ range, Ac_3 points ~
Claim No. (1) characterized in that the product is heated and held in the range of Ac_3 point + 300°C and then allowed to cool, and then heated and held in the range of Ac_3 point to Ac_3 point + 100°C and then rapidly cooled.
The method for processing and heat treating steel according to any one of items 1 to 3. (6) Hypoeutectoid steel at Ac_3 points +100℃ ~ Ac_3 points -
After heating to a range of 200°C, processing is carried out at a processing rate of 50% or more and a processing end temperature of 40% lower than the heating temperature or more. The method for processing and heat treating steel according to any of item (5). (7) Hypoeutectoid steel is C: 0.08 to 0.65% by weight
, Si: 0.15-3.0%, Mn: 0.1-2.5%
, the remainder being Fe and impurities. (8) Hypoeutectoid steel is C: 0.08 to 0.65% by weight
, Si: 0.15-3.0%, Mn: 0.1-2.5%
, Cr: 0.2 to 3.0%, the balance being Fe and impurities.
) to (6). (9) Hypoeutectoid steel is C: 0.08 to 0.65% by weight
, Si: 0.15-3.0%, Mn: 0.1-2.5%
, Cr: 0.2 to 3.0%, the method for processing and heat treating steel according to any one of claims (1) to (6). (10) Hypoeutectoid steel is C: 0.08 to 0.65 in weight%
%, Si: 0.15-3.0%, Mn: 0.1-2.5
%, Ni: 0.2-3.5%, Cr: 0.2-3.0%
, the remainder being Fe and impurities. (11) Hypoeutectoid steel is C: 0.08 to 0.65 in weight%
%, Si: 0.15-3.0%, Mn: 0.1-2.5
%, Ni: 0.2-3.5%, Cr: 0.2-3.0%
, Mo: 0.1 to 1.0%, the balance being Fe and impurities.
) to (6). (12) The hypoeutectoid steel contains W: Mo: 0.1 to 1.0%, the balance Fe and impurities in any one of claims (7) to (11). A method for processing and heat treating steel as described in . (13) Hypoeutectoid steel has Nb+Ta:0.
05-2.0%, V: 0.05-2.0%, Ti: 0.
05-2.0%, Al: 1 of 0.05-1.0%
The method for processing and heat treating steel according to any one of claims (7) to (12), characterized in that the method contains one or more types.