JPS60103161A - Unnormalized steel bar for hot forging - Google Patents

Abstract

PURPOSE:To obtain the titled steel bar having high toughness as cooled in the air after hot forging without carrying out quenching followed by tempering by providing a specified composition consisting of C, Si, Mn, Cr, Al and Fe. CONSTITUTION:This unnormalized steel bar for hot forging consists of, by weight, 0.05-0.15% C, 0.10-1.00% Si, 0.60-3.00% Mn, 2.20-5.90% Cr+Mn, 0.01-0.05% Al and the balance essentially Fe. The steel has necessary strength and high toughness such as about 70-90kg/mm.<2> tensile strength and >= about 5kg-m/cm<2> impact value as cooled in the air after hot forging. Among said alloying components, C is required to attain said strength, yet >0.15% C makes the strength excessively high and reduces the toughness. >1.00% Si makes the strength excessively high. Mn is required to control the strength and toughness, yet >3.00% Mn deteriorates the machinability. Cr is required to attain said strength and toughness in combination with Mn, and Al is a necessary element acting as a deoxidizer.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for producing mechanical parts, etc., in which high toughness can be obtained without quenching and tempering after hot forging. The present invention relates to non-thermal steel bars for intermediate forging.

[Prior art]

In general, many mechanical parts such as automobile parts are manufactured from steel bars by hot forging, forming, quenching, tempering, (refining) treatment, and cutting. In the manufacture of such parts, for the purpose of saving energy and reducing part manufacturing costs, forging is performed by direct quenching using residual heat after hot #2 forging, or by non-thermal mediation using precipitation hardening of V, Nb, etc. These non-1. ! ! Quality # is gradually being put into practical use because it can effectively save energy by omitting the quenching and tempering processes.

However, in these non-heat treated steels using so-called macroalloying technology such as V and Nb, the base metal structure is a ferrite-pearlite structure.

In addition, due to its nature, it is left to cool after hot forging, so its crystal grains are coarse and its toughness is low, so its range of application is limited, and it is not used for suspension parts, etc., which are important safety parts. The current situation is that this is not the case. In other words, in the case of conventional non-tempered steel,
It varies depending on the forging method, the size of the item, the strength level, etc.
The impact value at 25℃ using a JIS No. 3 test piece is 5 Ky-m
A low value of /ctA or less is a convex shape. Polycrystals can be removed by completely lowering the forging heating mixture, but this will cause other problems such as the degree of filling of the mold and the life of the mold. solve the problems of
It is an object of the present invention to provide a non-temperature steel sheet for hot forging which has high toughness even after being left to cool after hot forging.

[Structure 1 of the invention] Therefore, the gist of the present invention is that a: 0.05 to 0.05 in terms of weight.
0.15%, Si: 0.10-1.00%
, Mn: 0.60-3.00%,'O
r+Mn': 2.20=5.909 et al.

At: 0.01-0.05%, the remainder being substantially F
This is a non-tempered steel bar for hot forging that provides high toughness even when left to cool after hot forging.

Prior to the detailed description of the present invention, the process of achieving the non-tempered steel bar of the present invention will be described.

First, the inventors conducted the following experiments in order to develop a high-toughness hot-forged non-heat-treated steel bar that has significantly higher toughness than conventional hot-forged non-heat-treated steel. went. That is, when the weight of the sample material is 3%, c: o, o 5 to 0.20'f+
, Mn: 0.60~3.00%, Or: 1.00~
4.00%, Si: 0.10-1.00%, A
t: 0101 to 0.05%, the rest being essentially Fe, was melted in a 300 Kq high frequency electric furnace, and forged to a diameter of 3.
It was made into a steel bar of 0 to 70 mm. A hot forging simulation test was conducted by heating the rod to 1250°C and allowing it to cool. Test specimens were taken from the materials subjected to such trials and their mechanical properties were examined.

Note that the results of such a simulation test and the results of an actual forging test as described in Examples below are in good agreement, and this simulation test is valid.

Then, Figure @1 showing the relationship between the amount of C in steel and the tensile strength after the simulation test was obtained. Since the mechanical parts targeted by the present invention have a tensile strength of 70 to 90 Kg/+u',
From FIG. 1, it was found that 0.05 to 0.15% is necessary.

Furthermore, the results of examining the effects of Or and Mn.

Or + Mn≧2.20% and the following 0 for tensile strength
We obtained a regression equation like Eq.

σB('f/*g')'=325X('10)+11X
((Or') + (%Mn) ) + 8.9...
・・・・・・・・・・・・・・・■ And from the relationship between the formula [F] and the range of C above from 0.05 to 0.151, the tensile strength is obtained from 70 to 90. is Cr + Mn ld
It has been found that it is necessary to control the ratio between 2.20% and 5.90%.

Based on the above knowledge, 8i: 0.10-1.00%.

In steel containing At: 0.01 to 0.05%, 0
:0.05~0.15'16, Or+Mn:
2.20～! 5.90%.

If the remainder is substantially Fe, it will have a tensile strength of 70 to 90 Kf/ma' and an impact value of 51 (f-
It was discovered that m/cJ or more can be obtained, and the present invention was completed.

The present invention will be explained in detail below.

0 is one of the elements that determines the strength of the product, 0.05-
If it is less than 0.05%, the tensile strength will be low, and the amount of alloying elements necessary to obtain strength will inevitably be large and uneconomical. On the other hand, if it exceeds 0.15%, the strength will become too high and the toughness will decrease, so 0.15%
'e upper limit.

Si is an element necessary for deoxidation and is required in an amount of 0.10% or more. Furthermore, even if added to Tamon, the strength would increase to more than 8%, so the upper limit was set at 1.00%.

Mn is an element that controls the strength and toughness of products together with deoxidation and Or as mentioned above, and at the same time combines with S in steel to form MIIS and prevents embrittlement during hot working of steel. Therefore, 0.60% or more is necessary. Moreover, if it exceeds 3.00%, the rigidity will decrease and manufacturing difficulties will increase, so the upper limit is set at 3.001.

Or is necessary as described above (0, along with Mn to adjust the strength and toughness of the product, and the amount of Or + MH is 2.20 to 5
．． It is necessary to add it to 90%. Or+Mn
The amount of steel must be strictly controlled to obtain the required strength and toughness. Or + MnO amount is 2.20%
If it is less than that, the toughness will decrease. Also, 0 + MnO amount is 5.9
If it exceeds 0, the strength becomes too high, so the upper limit is set to 5.9.
It was set to 0%.

At is used as a deoxidizing agent and for grain control.
0.01-0.05% is required. 0. If the amount is less than O1, it is insufficient for deoxidizing and controlling crystal grains, while adding more than 0.05% is uneconomical.
The upper limit was set as 't O, 05%.

In addition to the above-mentioned components, 40.
Pb up to 0.81% or up to 0.3% may be added.

Next, the method of using the steel of the present invention will be described. Since the composition of the steel of the present invention is designed so that the toughness of the base structure itself is high, there is no need for detailed management of the hot forging conditions, and the steel can be heated and forged under normal heating conditions.

The point to keep in mind is the cooling means. After the steel of the present invention has been forged, the parts may be allowed to cool by air or air, with care being taken to separate them one by one and cooling them, for example, on a comparer so that the parts do not overlap. Specifically, the transformation period 1 from 800°C to 400°C
Cooling may be performed at a cooling rate of 120° C. to 12° C./−.

〔Example〕

EXAMPLES The effects of the present invention will be explained in more detail with reference to Examples below.

Steel having the chemical composition shown in Table 1 was melted in a 300 Ky high-frequency electric furnace, made into a pot lump, and then forged into a steel bar with an angle of 85 mm. This steel bar was forged into the front axle of a car and allowed to cool on a conveyor (average cooling rate of 27°C/start from 800°C to 400°C). A tensile test piece and an impact test piece were taken from this front axle, and the mechanical properties were investigated, and the results shown in Table 2 were obtained. As can be seen from Table 2, steels 1 to 4 of the present invention are 70
It can be seen that it has a tensile strength of ~90 Kq/l♂ and high toughness.

In addition, the result of A5 steel of comparative example is Or+A reijo of 5.9
It has been shown that high toughness can be obtained even if the tensile strength exceeds 90 Ky/pu2 by increasing the alloying element content and making the carbon content less than 0.05%. It is too strong and uneconomical, and generally mechanical parts often have a tensile strength of 90 Kf/m or less. Comparative Example 56
It can be seen that steel has a high carbon content and extremely low toughness.

As can be seen from the above examples, the steel of the present invention is a non-tempered steel having high strength and good toughness.

〔Effect of the invention〕

According to the non-N41 quality steel bar of the present invention, after heating and forging, it is possible to achieve a yield of 70 to 90 kg/Tomo1 by simply cooling it without heat treatment.
A product with high tensile strength and high toughness can be obtained, and can be used as important safety parts such as automobile suspension parts.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between 0fl- and tensile strength. Agent Patent Attorney Masaaki Aki 2 people outside Mistake 1 Diagram C(olo)

Claims (1)

[Claims] (1) Weight ratio: 0: 0.05 to 0.15. 8i: 0.10-1.00%. Mn: 0.60-3. OO staff. Or+Mn: 2.20. -5.90%. A non-annealed steel bar for hot forging that has At: 0.01 to 0.05% and the remainder is substantially Fe, and which has high toughness even when left to cool after hot forging.