JPS61153230A - Production of low-alloy steel wire rod which permits quick spheroidization - Google Patents

Abstract

PURPOSE:To eliminate the need for softening and to obtain a titled low-alloy steel wire rod in the considerably reduced treatment time for spheroidization by subjecting the low-alloy steel having the prescribed component compsn. to rough rolling and intermediate rolling after soaking then to finish rolling at the controlled draft in a specific temp. range then cooling the rolled steel at the prescribed cooling rate. CONSTITUTION:The low-alloy steel contg., by weight %, 0.13-0.43% C, 0.15-0.35% Si, 0.30-1.20% Mn, 0.75-1.20% Cr, 0.15-0.45% Mo and >=0.10% Al and consisting of the balance substantially Fe is treated in the following manner: The low-alloy steel is subjected to the rough rolling and intermediate rolling after soaking at 900-1,150 deg.C then to the finish rolling at >=20% in a 650-900 deg.C range by which the fine structure is obtd. The low-alloy steel after the finish rolling is cooled down to 600-550 deg.C at 0.05-0.5 deg.C/S cooling rate and the intended low-alloy steel wire rod which permits quick spheroidization is obtd.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for producing a low-alloy steel wire rod that can be rapidly spheroidized, and particularly to a method for producing a low-alloy steel wire rod for cold forging prior to cold forging. The purpose is to make it possible to omit softening annealing and annealing as pre-treatments and to shorten the processing time in spheroidizing annealing.

(Conventional technology) Used for automotive bolts, nuts, rods, etc.
The low-alloy steel is subjected to softening annealing and spheroidizing annealing before being formed into the above-mentioned shapes by cold forging. This is because low-alloy steel as mentioned above has high hardness in the hot-rolled state, which results in a shortened tool life. This is to improve the deformability of the tool, extend the tool life, and at the same time prevent the occurrence of cracks.

However, such heat treatment requires holding at a high temperature for a long time, and therefore requires heat treatment equipment such as a heating furnace and a large amount of thermal energy. Furthermore, because one-scale loss and decarbonization were unavoidable, there were large losses in terms of resources, energy, costs, and productivity.

As a solution to this problem, various methods and devices have been proposed for softening the #1 wire by utilizing the heat retained during hot rolling (US Pat. No. 82814.92, Patent No. 82814.92, Publication No. 56-2!8978, No. 59-81578, JP-A-56-41324, No. 5
No. 6-84424, No. 56-86619 and No. 1
(Refer to each publication No. 56-86620).

The technologies disclosed in the above-mentioned publications all disclose methods and equipment for controlling the heat retained in the wire rod after hot rolling at high speed, and also the cooling required to soften the steel wire after hot rolling. This is an outline of a method that advantageously achieves optimization of speed.

(Emphasis to be Solved by the Invention) However, in the above method, although softening can be achieved, it deteriorates the spheroidizing annealing characteristics in the next step of spheroidizing treatment, especially for the above-mentioned low alloy steel par. The problem is that the deterioration is so significant that the spheroidizing annealing time has to be extended compared to the conventional method.The problem is that the energy cost and productivity of the heat treatment process as a whole are not much different from the conventional method. was left behind.

(Means for Solving the Node Point) As a result of intensive research to solve the above problem, the inventors have found that the deterioration of the spheroidizing annealing properties is caused by the softening treatment causing the steel structure to become coarse ferrite. It was found that 1" was caused by the formation of a two-phase structure of pearlite.

That is, I) coarsening of ferrite grains reduces the grain boundary area and increases C
(1) Suppressing the grain boundary diffusion of atoms; (1) Also, coarsening of pearlite grains delays fragmentation and agglomeration of cementite in pearlite parts during spheroidizing annealing, (111) and these act synergistically. As a result, they discovered that the spheroidizing annealing properties deteriorated. −□
``Therefore, with the aim of improving the microstructure of low-alloy steel wire rods, the inventors conducted numerous experiments and studies on rolling and cooling conditions, and as a result, they changed the steel structure to a fine ferrite-pearlite two-phase structure and applied softening annealing. They developed a new method for producing steel wire that makes it possible to omit the spheroidization process and shorten the time required for the spheroidization process, thereby completing the present invention.

That is, in this invention, C: 0.13 to 0.43 wt
% (hereinafter simply indicated by the section), Si: 0.15 to 0.
8ti%, Mn: 0.30-1.20%, Cr:
0.75~1.20%, 10M0! 0.15～
0.45% and l: 0.10% or less,
The remainder is made of low alloy steel with a composition of substantially Fe, 900~
After soaking at 1150°C, rough rolling and intermediate rolling were performed, and then finish rolling was performed 15 times at a rolling reduction of 20 coefficients or more in the temperature range of 650 to 900°C, and then 0.05 to 0.
．． This is a method for manufacturing a low alloy #4 wire rod capable of rapid spheroidization, which comprises cooling to 600 to 550°C at a cooling rate of 5°C/S.

(effect) This invention will be explained in detail below.　　　　′.

First, in this invention, the reason why the material components are limited to the above range 1 will be explained.

Oj 0.13 to 0.43 If O is less than 0.13%, sufficient strength as a structural member cannot be obtained, while if it exceeds 0.43%, softening 5 becomes difficult. It was limited to a range of 0.43%.

Si + 0.15~0°35% Sl has poor deoxidizing effect when it is less than 0.15%;
．． If it exceeds 35%, the impact value will decrease, so increase the value by +00%.
．． It was limited to a range of 15 to 0.35%.

Mn: 0.30 to 1.2o% In is less than 0.8%, which causes deterioration in hardenability, while when it exceeds 1°2, it causes an increase in strength, so 0.3
It was limited to a range of 0 to 1.2 inches.

Cr: 0.75-1.20% If Cr is less than 0.75%, the effect of refining pearlite crystal grains will be poor, while if it exceeds 1.201, the sag will increase. .20% range.

No? 0.15 to 0.45 The relation number is 0.
If it is less than 15%, sufficient strength cannot be obtained;
If it exceeds 5%, the strength will increase excessively, so O, ]J
It was limited to a range of 0.45%.

Il: 0.10% or less l effectively contributes to refinement of pearlite crystal grains, but
If it exceeds 0.10%, the toughness will deteriorate, so it was decided to contain it in a range of 0.10% or less.

Next, we will explain the reasons for limiting the rolling and cooling conditions.
This is because if it is less than C, hot rough rolling becomes difficult, while if it exceeds 1150°C, austenite grains become coarse and it is difficult to obtain a fine structure. 15 Finish rolling temperature 65
The reason why the rolling temperature is 0 to 900°C is that it is difficult to perform finish rolling at a temperature lower than 650°C, whereas a fine structure cannot be obtained when the temperature exceeds 900°C.

The reason why the reduction ratio in finish rolling is set to 20% or more and 2L' is that if the reduction ratio is less than this value, it is difficult to obtain the desired fine structure.

Furthermore, regarding the cooling rate, if it is less than 0°05°C/s, it will take a long time to cool down, which is a significant disadvantage of reducing productivity, while if it exceeds 0.5°C/s, bainite will be generated. This is because the strength increases excessively. Here, the cooling stop temperature is limited to the range of 550 to 600'C.
If the temperature is below 600°C, it will have little effect on softening, and the cooling time will become longer, which is unfavorable from a productivity standpoint.On the other hand, if the temperature exceeds 600°C, 1-paveinite will be generated, leading to an excessive increase in strength, resulting in soft This is because it becomes a firm statement.

(Example) Embodiments of the present invention will be described below in comparison with conventional examples.

#4 wire material having the component composition shown in Table 1 was rolled and cooled to produce a wire rod under the conditions shown in Table 2 according to the Kenki method and the method of this invention. Table 8 shows the results of examining the structure and strength of each wire thus obtained. Especially regarding conventional example a,
The strength after softening annealing according to the heat pattern 15 shown in FIG. 1 was also investigated, and the results are also listed in Table 8.

Then, a second
A spheroidizing annealing treatment was performed according to the heat pattern shown in the figure, and the relationship between the spheroidization time and the spheroidization rate was as shown in FIG. - Now, as is clear from the results shown in Clothing 8 above, in the conventional example and the preferred example C, softening annealing can be omitted. However, as is clear from the results shown in FIG. 8, the wire rod obtained according to the conventional example has the disadvantage that it takes a long time to spheroidize it. In contrast, the preferable example obtained according to the present invention In this case, not only can softening annealing be omitted, but also rapid spheroidization can be achieved.

(Effects of the Invention) Thus, according to the present invention, the softening annealing and the long-term spheroidization treatment are omitted and the spheroidization treatment is performed on low-alloy steel wire rods, which conventionally required softening annealing and long-term spheroidization treatment prior to cold forming. It is also possible to realize a significant reduction in time, and therefore a significant reduction in energy costs and a dramatic improvement in productivity.

[Brief explanation of drawings]

Figure 1 is a heat pattern diagram for softening annealing, Figure 2 is a heat pattern diagram for spheroidizing annealing, and Figure 8 is a wire rod a'
, b and C are graphs comparing the relationship between the spheroidization time and the spheroidization rate.

Claims (1)

[Claims] 1. C: 0.13 to 0.43 wt% Si: 0.15 to 0.35 wt% Mn: 0.30 to 1.20 wt% Cr: 0.75 to 1.20 wt% Mo: A low alloy steel containing 0.15 to 0.45 wt% and 0.10 wt% or less of Al, with the remainder being substantially Fe, is soaked at 900 to 1150°C, then subjected to rough rolling and intermediate rolling. and then heated for 20 minutes in a temperature range of 650-900℃.
After finish rolling with a rolling reduction of 0.05% or more,
A method for producing a low-alloy steel wire rod capable of rapid spheroidization, characterized by cooling to 600 to 550°C at a cooling rate of 0.5°C/S.