JP2003049221A - Method for producing non-heat treated warm-forged parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing non-heat treated warm-forged parts which have little variation in strength, and can secure stable mechanical properties. SOLUTION: Steel obtained by subjecting steel having a composition containing 0.30 to 0.55% C, 0.02 to 2.0% Si, 0.1 to 2.0% Mn, 0.1 to 2.0% Cr, <=1.8% Mn(%)+Cr(%), and containing one or more kinds selected from 0.01 to 1.0% Mo, 0.001 to 1.0% V and 0.001 to 0.3% Nb, and the balance Fe with impurities to heating at 900 to 1,250 deg.C, and performing hot working at a finishing temperature of 750 to 1,100 deg.C is used as the stock. This steel is heated at 600 to 1,000 deg.C without applying cold compressive working thereto, and is forged and formed at 600 to 900 deg.C.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a non-refined warm forged part. 2. Description of the Related Art Conventionally, various non-heat treated forged parts are generally made of a rolled material of medium carbon steel or low alloy steel and hot forged to obtain a predetermined rough shape and strength. The original characteristics were secured, and thereafter, these were machined to finish the final part shape. [0003] However, in order to further reduce the cost of manufacturing parts, it is required to reduce or omit the above-mentioned machining. For this reason, a cold forging technique capable of performing machining with high dimensional accuracy has been studied. Non-refined cold-forged parts have been put into practical use for small parts. However, the deformation resistance in the case of cold forging a steel material that has been hot-rolled is generally large, and therefore it may be necessary to perform soft annealing before cold forging. In addition, large-sized components and parts that require a large degree of work during cold forging require large-scale cold forging equipment in order to form them into shapes that are extremely close to the final parts. There is also. [0004] For this reason, in recent years, the deformation resistance of the material steel has not increased as much as in cold forging, and non-finished forging has been carried out by warm forging, which does not require finish forming by machining as in hot forging. The demand for manufacturing parts has become extremely large. [0005] Generally, non-heat treated parts are manufactured by warm forging in order to improve the shape accuracy after forging, and because there is a part that remains in the material size without being subjected to compression processing by forging. In such a case, a steel material used as a material for warm forging is subjected to a process such as cold drawing. However, in the case of a non-heat treated forged part manufactured by warm forging a steel material that has been subjected to a process such as drawing in the cold state, a large variation in strength occurs depending on the portion, and stable mechanical properties cannot be secured. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to reduce the variation in strength in non-heat-treated parts even during warm forging. An object of the present invention is to provide a method for manufacturing a non-refined warm forged part capable of securing stable mechanical properties. [0007] The gist of the present invention resides in a method for producing a non-refined warm forged part as described below. That is, “in mass%, C: 0.30 to 0.30%
0.55%, Si: 0.02 to 2.0%, Mn: 0.1
To 2.0%, Cr: 0.1 to 2.0%, and Mn (%) +
Cr (%): 1.8% or less, and Mo: 0.1%
01-1.0%, V: 0.005-1.0% and Nb:
One or more of 0.005 to 0.3%, with the balance being Fe
And steel made of impurities, heated to 900 to 1250 ° C. and hot-worked at a finishing temperature of 750 to 1100 ° C. as a raw material, and without a cold compression working,
A method for producing a non-refined warm forged part characterized by heating to 00 to 1000 ° C. and forging and forming at 600 to 900 ° C. ”. [0009] The term "hot working" refers to hot forming such as hot rolling or hot forging. "Cold processing in cold" refers to forming processing to which cold compression is applied, such as cold drawing or cold forging. [0010] The present inventors have conducted various studies so that the strength variation in the non-heat-treated part is small even during warm forging, so that stable mechanical properties can be ensured. As a result, the following findings were obtained. (A) If cold forging is applied to a steel material obtained by hot working and then cold forging is performed, the strength after warm forging is greatly reduced as compared with the strength of the material as it is hot worked. I do. (B) In contrast to the above (a), if a steel material obtained by hot working under specific conditions is subjected to warm forging in a specific temperature range without performing cold compression working, The strength of the part that has been subjected to compression processing by hot forging is the same as the strength of the raw material as hot worked. (C) After cold-working a steel material obtained by hot working and then heating a specific part of the steel material to a temperature for performing the warm forging described in (a) above, The strength of a part near the heated part that is not directly heated but has increased in temperature (hereinafter referred to as the “part affected by heat”) is compared to the strength of the as-hot-processed material. To rise. (D) In response to the above (c), a specific part of the steel material obtained by hot working under specific conditions is subjected to warm forging without applying a cold compression working. When the material is heated to the temperature range, the strength at the portion affected by the heat is equal to the strength of the as-hot-processed material. The present invention has been completed based on the above findings. Hereinafter, each requirement of the present invention will be described in detail. In addition, “%” of the content of the chemical component means “% by mass”. (A) Chemical composition C of the material steel: 0.30 to 0.55% C is an element effective for increasing the strength of the non-heat treated warm forged part. However, if the content is less than 0.30%, the effect of addition is poor, and if it exceeds 0.55%, the toughness is reduced. Therefore, the content of C is set to 0.30 to 0.55%.
And Si: 0.02 to 2.0% Si is an element effective for deoxidizing steel and ensuring the strength of a non-refined warm forged part. However, if the content is less than 0.02%, it is difficult to obtain a sufficient deoxidizing effect, while if it exceeds 2.0%, the ferrite ground becomes brittle and the toughness is reduced. Therefore, the content of Si is set to 0.02 to 2.0%. Mn: 0.1 to 2.0% Mn has the effect of increasing the strength and toughness of a non-refined warm forged part. However, if the content is less than 0.1%, it is difficult to obtain the effect. On the other hand, if it exceeds 2.0%, the toughness is rather lowered. Therefore, the content of Mn is 0.1 to 2.0
%. It is important that the content of Mn be 1.8% or less in total with the content of Cr described below in order to ensure stable toughness of the non-heat treated warm forged part. Cr: 0.1-2.0% Cr has the effect of increasing the strength and toughness of a non-refined warm forged part. However, if the content is less than 0.1%, it is difficult to obtain the effect. On the other hand, if it exceeds 2.0%, the toughness is rather lowered. Therefore, the content of Cr is set to 0.1 to 2.0.
%. In order to ensure stable toughness of the non-refined warm forged part, it is important that the content of Cr be 1.8% or less in total with the content of Mn. Mn (%) + Cr (%): 1.8% or less Mn (%) + Cr which is the sum of the contents of Mn and Cr
When the value of (%) exceeds 1.8%, when the cooling rate after hot working is increased, a bainite phase is formed in the steel material, and the toughness of the non-heat treated warm forged part is reduced. Therefore,
The value of Mn (%) + Cr (%) was set to 1.8% or less in order to ensure stable toughness of the non-heat treated forged part. The lower limit of the value of Mn (%) + Cr (%) is M
0.2% when the contents of n and Cr are each 0.1%
It may be. Mo: 0.01-1.0%, V: 0.00
5 to 1.0% and Nb: at least one of Mo, V and Nb of 0.005 to 0.3%, each of which refines the structure of the raw material after hot working and makes the non-finished warm forged part Since it has the effect of increasing strength and toughness, one or more of these elements are added and contained. However, the contents of Mo, V and Nb are less than 0.01%, less than 0.005% and 0.005%, respectively.
%, The effect is difficult to obtain. On the other hand, when the contents of Mo, V, and Nb exceed 1.0%, 1.0%, and 0.3%, respectively, the toughness is rather lowered. Therefore, Mo, V
And Nb content of 0.01 to 1.0%, respectively.
005 to 1.0% and 0.005 to 0.3%, and one or more of these elements are contained. (B) Hot working of raw steel The steel having the chemical composition according to the above (A), which is a raw material of the non-refined warm forged part of the present invention, is 900 to 125
It is necessary to heat to 0 ° C. and perform hot working at a finishing temperature of 750 to 1100 ° C. If the heating temperature of the base steel is lower than 900 ° C., the deformation resistance during rolling increases, which causes a decrease in productivity. On the other hand, if the heating temperature exceeds 1250 ° C., the crystal grains become coarse. The finishing temperature of hot working is 750 ° C
If the temperature is less than 1, the deformation resistance at the time of rolling increases, causing a great decrease in productivity. If the temperature exceeds 1100 ° C., the crystal grains become coarse in the subsequent cooling process. Therefore, steel having the chemical composition described in (A) above is used in an amount of 900 to 125.
It was specified to heat to 0 ° C. and hot work at a finishing temperature of 750 to 1100 ° C. The heating temperature of the material steel is 10
00 to 1200 ° C, hot working finish temperature is 800 to 10
The temperature is preferably set to 00 ° C. (C) Warm forging of parts A steel having the chemical composition described in (A) is hot-worked under the conditions described in (B). Heat to 1000 ° C, 600-9
It is extremely important to forge and form at 00 ° C. That is, when cold forging is applied to a steel material obtained by hot working and then cold forging is performed, the strength after warm forging is greatly reduced as compared with the strength of the material as it is hot worked. In addition, the strength of the portion affected by the heat is increased as compared with the strength of the raw material that has been hot worked. For this reason, the strength variation within the non-heat-treated warm forged part becomes large, and stable mechanical properties cannot be secured. If the heating temperature for warm forging is lower than 600 ° C., the forging load may be too large to be formed into a desired shape, and the life of the mold may be shortened. On the other hand, if the heating temperature exceeds 1000 ° C., desired dimensional accuracy may not be ensured after forging. Even when the temperature for warm forging is lower than 600 ° C., the forging load may be too large to be formed into a desired shape.
The mold life is shortened. On the other hand, the temperature for warm forging is 9
When the temperature exceeds 00 ° C., the dimensional accuracy after forging is reduced. Therefore, in the present invention, a steel material obtained by hot working a steel having the chemical composition described in the section (A) under the conditions described in the section (B) can be obtained without subjecting the steel to cold compression working. It was stipulated to heat to 600 to 1000 ° C. and forge and form at 600 to 900 ° C. The heating temperature for warm forging is 800
To 950 ° C, and the temperature for warm forging is preferably 650 to 850 ° C. Hereinafter, the present invention will be described in detail with reference to examples. EXAMPLES Steels 1 to 13 having the chemical compositions shown in Table 1 were
It was melted in a 50 kg vacuum melting furnace. [Table 1] Next, these steel ingots were heated to 1100 ° C. and hot forged at a finishing temperature of 850 ° C. to have a diameter of 35 m.
m round bar. A test piece having a length of 40 mm is cut out from each round bar having a diameter of 35 mm, and the test piece is cut in a length direction including a center line, and a longitudinal Brinell hardness of a center line portion as hot forged ( HB hardness) was measured. Next, a bar having a diameter of 35 mm obtained by hot forging is peeled by a normal method, and then, steels 1 to 3 are used as material steels. Was subjected to a drawing process. Similarly, with respect to steel 4 used as a material steel, drawing was performed at room temperature at a surface reduction rate of 10.0%. Next, a 200 mm long test piece was cut out from each of the drawn round bars of steels 1-4 and each of the round bars of 30 mm diameter peeled after hot forging of steels 5-15. About 100m on one side
m is heated to 850 ° C., and the area reduction rate is 50
% Forging was performed. The test piece after the warm forging was cut in the longitudinal direction including the center line, and the longitudinal Brinell hardness (HB hardness) at the center line was measured. Table 2 shows the measurement results of the above HB hardness. In Table 2, the hardness of the “material portion” is the average value of the HB hardness measured at the five hot as-forged portions, and the hardness of the “warm forged portion” is the hot forging and compression processing. The average value of the HB hardness measured at the five points where the compression was performed, and the hardness of the “heat affected part” was the maximum value of the HB hardness measured at the five points where the compression was not applied. Show. ΔHB is the difference between the hardness of the “heat affected part” and the hardness of the “warm forged part”, and indicates the variation in HB hardness of the test piece after the warm forging. [Table 2] From Table 2, it can be seen that when hot forging was performed under the conditions specified in the present invention without applying cold compression working, both the hot forged portion and the heat-affected parts were not hot-worked. Since the value of ΔHB is small at the same HB hardness, it is clear that the strength variation in the non-heat treated part is small even when warm forging is performed, and therefore, stable mechanical properties can be secured. . On the other hand, when the temperature is out of the conditions specified in the present invention by adding cold compression working, the hardness of the warm forged portion is lower than that of the raw material as it is hot worked, on the other hand,
The hardness is increased in the part affected by the heat, and the value of ΔHB, that is, the hardness variation is large. According to the method of the present invention, the strength variation in the non-heat-treated part is small even during warm forging.
The non-refined warm forged part can be provided with stable mechanical properties.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Takatoshi Arai             1 Konomi-cho, Kokurakita-ku, Kitakyushu-shi, Fukuoka             Sumitomo Metal Kokura F term (reference) 4E087 AA10 BA02 CB02                 4K032 AA05 AA06 AA11 AA12 AA16                       AA19 AA22 AA31 AA32 AA36                       BA02 CA01 CA02 CA03 CC03                       CC04 CF02 CF03

Claims (1)

Claims: 1. mass%, C: 0.30 to 0.55%, S
i: 0.02 to 2.0%, Mn: 0.1 to 2.0%, C
r: 0.1 to 2.0%, Mn (%) + Cr (%):
1.8% or less, Mo: 0.01 to 1.0
%, V: 0.005 to 1.0% and Nb: 0.005 to
A steel material containing 0.3% or more, and the balance being Fe and impurities, is heated to 900 to 1250 ° C. and hot-worked at a finishing temperature of 750 to 1100 ° C. as a raw material. Between 600 and 10 without compression between
A method for producing a non-refined warm forged part, wherein the part is heated to 00C and forged at 600 to 900C.