JPS5937737B2 - Steel materials for hot forging - Google Patents

Description

[Detailed Description of the Invention] The present invention is directed to a steel material for hot forging that can be used without reheating in machine structural steel that is formed by hot working, particularly hot forging. be.

Generally, hot forging of mechanical structural steel is performed at a high temperature of 1000° C. or higher.

As a result, the crystal grains become coarse, the structure after hot forging becomes coarse, and the toughness deteriorates significantly, making it unusable as is. Therefore, in order to refine the structure after hot forging,
Perform re-austenitization treatment such as standards. In order to refine the structure after hot forging, it is possible to lower the forging temperature, but this requires a forging machine with a large capacity and has significant disadvantages in terms of die life and productivity.

Experimental attempts have also been made on materials to which grain refining elements such as Nb and Ti are added, but these have not yet been put to practical use. In view of this situation, the present inventors conducted various studies in order to develop a steel that has sufficient toughness to be used without being re-austenitized after hot forging from the viewpoint of energy saving.

As a result, the conventional simple addition of Ti has no effect.
In addition to adding an appropriate amount of Ti, the amounts of S and N were found to be important factors.

In general, it is common knowledge that the lower the S'j6 and N content, the better the toughness of mechanical structural steel, but it is difficult to reduce these in actual production. However, for the above purpose, within a realistic range of S and N amounts, by adding an appropriate amount of Ti, S and N act to make S and N harmless or to compensate for the addition of Ti. , a product with excellent toughness after hot forging was obtained. The structure of such steel after hot forging is not necessarily fine. Therefore, the effect of adding Ti is not only the conventionally well-known refinement of the structure. Next, the results of experiments conducted by the present inventors in order to obtain important knowledge will be explained.

C: 0.43wt%, Si: 0.25wt%, Mn
; 0.72wt% is the basic component (S45C), Ti,
Steels with various S and N contents were melted and rolled to 60 mmf.

These steel bars were cut into 60mm lengths and upset at 1200°C to produce 15Wt7+! Forged into a thick plate. From these forged materials, 2mm TJ Notchi Shalvi test pieces were collected.
The absorbed energy (UE) of each at room temperature was determined. As a result of various investigations into the relationship between these UEs and Ti, S, and N of each steel, it was found that UE is 1 in steel, which can be summarized as 3S+N, as shown in FIG.

In the figure, ○ marks represent Ti 0.005 to 0.03wt%, mouth marks represent 0.005wt% or less, and Δ marks represent 0.03 to 0.08w.
It is a steel containing t%. The experimental ranges of S and N are 0.002 to 0.05 wt% and 0.002 wt%, respectively.
It was ~0.015 wt%. From Figure 1, 1200℃
The Charby unit value (UE) of the 5 steel forged in the steel is 0.4380 N to 1.0, and 0.00
It can be seen that a value of 5 to 0.029 wt% Ti is good.

These values are close to the Charby values of steel that was similarly hot forged and then reheated and normalized at 850°C. Note that the examples in Figure 1 are those that were hot-forged and then allowed to cool, so the same hot-forged, immediately oil-cooled, and tempered samples were also treated as Charby single value Ti (UE). When I investigated, I found that 0.4〈3s ten N〈1.0 and 0,00
Good values were found for those containing 5 to 0.029 wt% Ti.

Furthermore, 0.3 to 2.0 wt% MntO. 2~1.0w
t%Cr,O. i~0.5wt% MO,O. 4-2.0
Similar effects were found for so-called mechanical structural alloy steel containing wt% Ni.

The present invention was made based on such knowledge, and its gist is disclosed in CO. 35-0.7wt%, S
iO. l5~0.35wt%, MnO. 3-2wt%,
TiO. 05 to 0.029 wt% as a basic component, or this basic component further contains CrO. 2-1.0wt%
, MOO. l~0.5wt%, NiO. 4-2wt%
containing one or more of the following, with the remainder consisting of iron and unavoidable impurities,
A steel material for hot forging, characterized in that the S'J6 and N contents in the inevitable impurities are limited to 0.4<-Z-L-<1.03 S+N with respect to the amount of Ti added. It is in.

The present invention will be explained in detail below.

(% is Wt%) First, in the present invention, the Ti content is set at 0.005 to 0.029% because Ti is 0.0%.
If it is less than 0.05%, there is no effect of Ti, and if it is less than 0.029%
If it becomes super Ti, the toughness will worsen.

Furthermore, as is clear from Figure 1, the range of 100 is set to be more than 0.4 and less than 1.0.
Even with the above, the toughness after hot forging is not good. In this case, it goes without saying that the lower the amounts of S and N, the better, but it is not easy to lower these in actual production. However, T
For the amount i, 3S + N is within the above range, that is, 0.
005% Ti, 3S+N is 0.005 to 0.01
2%, 0.029Ti, 0.029 to 0.072
%, these S and N are less harmful or act effectively in coexistence with Ti. Other basic ingredients include CO. 35-0.7%, SiO. l5～
0.35%, MnO. Requires 3-2%.

When the carbon content is less than 0.35%, the toughness of the hot forged grain does not matter much because it is cold forged or carbonitrided.

Further, the present invention cannot be applied to materials containing more than 0.7% of C, as they are special materials such as tool steels and are handled differently from general hot forging. 0.15% or more of Si is required for deoxidation, but if it exceeds 0.35%, toughness deteriorates.

Mn is an element necessary for deoxidation, strength, and hardenability, and if it is less than 0.3%, these effects are insufficient.
On the other hand, if it exceeds 2%, it becomes a special steel with poor hot forgeability, and the present invention cannot be applied to it. In addition, the steel of the present invention has a content of 0.2 to 1.0% Cr and O depending on the usage performance. l~0.5% MO
and 0.4 to 2.0% Ni.
These are all elements necessary to improve the toughness and hardenability of steel, with Cr being less than 0.2% and MO being 0.1%.
%, and if Ni is less than 0.4%, the effect is small. on the other hand,
Steels that exceed the upper limits of each of these elements are steels for special purposes, and the present invention cannot be applied to them. Furthermore, it is important for the steel of the present invention to be sufficiently deoxidized in order for Ti to act sufficiently.
It is more desirable to deoxidize with REM or the like and an alloy thereof.

After hot forging at 1200℃, the steel material is either left to cool or directly quenched. The toughness of tempered steel is far superior to that of conventional steel, and is close to that of reheated conventional steel. Therefore, the steel of the present invention can be used without being re-austenitized after hot forging. For example, in the past, after hot forging, the material was normalized once to improve its quality.
This standardizing process can be omitted for items that have been sent to the next process. Hereinafter, the effects of the present invention will be described in more detail with reference to Examples.

Examples Steels consisting of chemical components shown in Table 1, i.e., steel types 1 to 1
4 is a commercially available conventional steel, steel types 5 to 22 are trial steels, among these, steel types 5 to 10 are comparative steels, and steel types 11 to 22 are steels of the present invention.

Note that steel type 18 was manufactured from a continuously cast steel billet. For all these steels, 1200 pieces of 60mmj x 60mm material
The material was heated to 15°C, then immediately upset and forged into a 15 mm thick disk shape. Raw forged discs are left to cool after forging, elliptical discs are quenched immediately after forging and tempered at 600°C or 650°C, and some steels are reheated and normalized after forging. A 2 mm U-notched single specimen was taken from each disc and tested at room temperature. The results are shown in Table 2. As can be seen from Table 2, the Charby values of forged steel and directly quenched and tempered steel, that is, those that are not re-austenitized after forging, are
Comparing the conventional steel and comparative steel No. 0 with the steels of the present invention of steel grades 11 to 22, it is clear that the steels of the present invention are superior.

In addition, in the steel of the present invention, when comparing steel grades 11 and 18, which have the same chemical composition, steel grade 18, that is, the one made from continuously cast billets, is superior; It can be seen that the effects of the invention can be further enhanced by manufacturing. In addition, for all steel types, the Shalby single value of the forged raw material of the inventive steel is close to the Shalby single value of the conventional steel and comparative steel that were normalized by reheating after forging. It can be seen that the invention steel does not require re-austenitization to impart toughness. As is clear from the above description, the steel of the present invention is a steel material of great industrial significance from the viewpoint of energy saving and process omission.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the 2 mm U non-chilled aluminum value (UE kg-m) and Ti/3S+N of forged steels with S45C as the basic component and variously changed Ri, S, and N.

Claims (1)

[Claims] 1 The basic components are C 0.35 to 0.7 wt%, Si 0.15 to 0.35 wt%, Mn 0.3 to 2 wt%, and Ti 0.005 to 0.029 wt%,
The balance consists of iron and unavoidable impurities, and the S and N contents in the unavoidable impurities are 0.4<T with respect to the amount of Ti added.
A steel material for hot forging characterized by limiting i/(3S+N)<1.0. 2 C 0.35-0.7wt% Si 0.15-0.35wt% Mn 0.3-2wt% Ti 0.005-0.029wt% as basic components,
Furthermore, it contains one or more of Cr 0.2 to 1 wt% Mo 0.1 to 0.5 wt% Ni 0.4 to 2 wt%, and the balance consists of iron and unavoidable impurities, and the S and N contents in the unavoidable impurities are reduced by Ti. 0.4<Ti/(3S
+N) < 1.0.