JPS62139817A - Production of steel wire enabling quick spheroidization treatment - Google Patents

Abstract

PURPOSE:To quickly and effectively execute spheroidizing annealing to be executed prior to cold working by executing a hot rolling stage and subsequent heat treatment under specific conditions in the stage of producing a steel wire by hot rolling. CONSTITUTION:A solid round billet of a steel contg., per weight %, 0.15-0.70% C, <0.35% Si, 0.30-1.80% Mn, <0.005% O, and <0.015% S is worked to the steel wire by rough rolling, intermediate rolling and finish rolling at hot. The rolling temp. is so controlled in this case that the finish rolling start temp. is made 650-850 deg.C and that the finish rolling end temp. is made <=950 deg.C. The steel wire is quickly cooled down to a 650-750 deg.C region right after the end of rolling and is coiled to a non-concentrical state. The steel wire is then cooled at a cooling rate of >=0.5 deg.C/sec down to 500 deg.C to form a specified level or above of fine ferrite pearlite structure. The time for the spheroidizing annealing to be executed prior to the subsequent cold forging is thus shortened and the productivity and energy conservation effect are improved.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a method for producing steel wire rods by hot rolling, and in particular, by controlling the process of hot rolling steel wire rods, the method can be used to produce steel wire rods prior to cold working. The results of research and development to enable rapid and effective spheroidization annealing are described below.

After hot rolling, the steel wire rod is drawn again, cut,
Although hot-rolled materials are subjected to cold processing such as cutting and forging, they lack the deformability to withstand cold processing and have high deformation resistance, so they are not used as hot-rolled materials. and not subjected to cold working.

Therefore, prior to cold working, spheroidizing annealing is performed for the purpose of improving the deformability of hot rolling and reducing the deformation resistance. Spheroidizing annealing achieves the above objective by heating and cooling a hot-rolled material under specific conditions to change the microstructure of the steel to one in which spherical or near-spherical carbides are uniformly dispersed in the ferrite matrix. This is heat treatment to make it compatible.

However, this heat treatment usually requires high-temperature heating and long-term holding, requiring heat treatment equipment such as expensive heating furnaces, and continued heating for long periods of time can cause problems such as scale adhesion and decarburization, resulting in reduced resource energy and cost costs. This also resulted in a large loss in terms of productivity.

(Prior art) Here, Japanese Patent Publication No. 55-31165, Japanese Patent Publication No. 56-372
The proposals disclosed in Japanese Patent Publication No. 88 and Japanese Patent Publication No. 59-29645 involve hot rolling carbon steel or manganese steel, cooling it under specific conditions, changing the microstructure of the steel to an intermediate structure, and then rolling the carbon steel or manganese steel into an intermediate structure. The main idea is to perform spheroidizing annealing below the transformation point to reduce the loss that occurs during conventional spheroidizing annealing.

(Problems to be Solved by the Invention) According to research by the inventors, if the structure before spheroidizing annealing is made into an intermediate structure, the dispersibility of carbides after spheroidizing annealing is improved and the deformability is improved. , the deformation resistance does not decrease much,
It has been found that if the deformation resistance is to be lowered to the conventional level, the spheroidizing annealing time must be extended, which leaves a drawback.

Furthermore, if the previous structure is simply a ferrite/pearlite structure, the deformation resistance decreases quickly, but the dispersibility of carbon substances is poor, and as a result, the deformability is significantly deteriorated.

The inventors have overcome these problems to create a hot rolled steel that can significantly promote spheroidization during spheroidizing annealing, has high deformability after spheroidizing treatment, and has low deformation resistance. After extensive research aimed at creating wire rods, we found that if the structure before spheroidization is a ferrite/pearlite structure that is finer than a certain level, spheroidization progresses quickly, and the deformability and deformation resistance after spheroidization are high. It was found that the value was low.

It is clear that it is effective to finish hot finish rolling at a low temperature in order to obtain such a fine ferrite/pearlite structure after hot rolling. This is because by terminating the rolling process, the γ grain size after rolling becomes fine, leading to an increase in the number of deformation nuclei during T→α deformation.

However, in continuous rolling at high speed and with extremely short pass intervals, such as wire rod rolling, the temperature rise due to heat generation during processing is extremely large, and it is generally difficult to finish hot rolling at a low temperature. On the other hand, if low-temperature finishing is to be performed, rolling must be performed at low speed, which inevitably leads to a decrease in productivity.

(Means for solving the problem) The inventors conducted further research in order to achieve the target fine ferrite/pearlite structure in wire rolling without reducing the rolling speed, and as a result, they found that rapid cooling after finishing rolling is effective. It was further discovered that

In other words, in wire rod rolling, the 7 grain size immediately after rolling is extremely fine due to dynamic recrystallization, but due to rapid grain growth, γ becomes coarse during T→α transformation, resulting in This results in a coarse ferrite/pearlite structure.

On the other hand, by suppressing the rolling end temperature below a certain limit and also using rapid cooling after rolling, it becomes possible to cause γ→α transformation from a single fine grain, which reduces the rolling speed. It is possible to advantageously obtain the target fine ferrite/pearlite structure.

That is, in this invention, C: 0.15 to 0.70 wt%.

Si: less than 0.35 wt%, ! , In: 0.30 to 1.3 wt%.

0:0.005wt% or less, s:o, less than 015wt% and the balance is Fe and unavoidable impurities when producing a steel wire rod through rough rolling, intermediate rolling and finishing rolling. The rolling start temperature is 650 to 850°C, and the finish rolling end temperature is 95°C.
Control the temperature below 0℃, and immediately after rolling the temperature is 650-750
The steel wire is rapidly cooled to a temperature range of ℃ and wound in a non-concentric manner.
This is a method for manufacturing a steel wire rod that can be rapidly spheronized, which is characterized in that the steel wire rod is then cooled to 500° C. at a rate of 0.5° C./S or more to form a fine ferrite/pearlite structure.

(Function) C: 0.15 to 0.70 wt% (hereinafter simply referred to as 96) From the viewpoint of processing 1, it is desirable that C is low as long as hardenability is not inhibited, but if it is less than 0.15%, A problem arises in hardenability, and the characteristics essential for a 1 m long part cannot be secured. On the other hand, if it exceeds 0.7%, extremely coarse cementite particles will be locally formed due to spheroidizing annealing and impede cold workability, so it is limited to 0.70% or less.

S+: less than 0.35%.

In addition to reducing the ductility by solid solution in ferrite (e), it also raises the transformation point and promotes the growth of pro-eutectoid ferrite grains, making it impossible to obtain a fine ferrite/pearlite structure. Since it is an element that has an adverse effect, it is limited to a range where this effect is small, that is, less than 0.35%.

\ln: 0.30 to 1.8 wt%.

Along with C, Mn is not only indispensable in ensuring hardenability, but is also effective in promoting finer structure by lowering the transformation temperature, and these effects are remarkable at 0.30% or more. However, if it exceeds 1.8%, cementite is stabilized and spheroidization is inhibited.

S: 0, Q less than 15wt%.

After hot rolling! j n 0.015% because it exists as an inclusion bent in the rolling direction of the S system and inhibits cold workability.
The content should be less than 0.005%, especially about 0.005% or less.

○: 0. QQ 5wt% or less. Similar to sulfides, oxide-based inclusions seriously impede cold workability, so the upper limit is set at 0.005%.

Next, controlling the finish rolling end temperature to less than 950°C is as follows:
This is because at temperatures above this temperature, γ grains become coarse and it is difficult to obtain a fine ferrite/pearlite structure.

In addition, the finish rolling start temperature was set at 650 to 850°C because
If the temperature is lower than 650°C, the deformation resistance will be excessive and rolling will be difficult, while if it exceeds 850°C, it will be difficult to control the finish rolling end temperature to below 950°C without reducing the rolling speed. The temperature was below ℃.

Also, the coiling temperature was set in the range of 650 to 750°C.
If the temperature is below 0℃, there is a risk of the formation of bainite or martensitic structures, which may lead to breakage during winding, while if the temperature exceeds 750℃, it will not be effective in suppressing the growth of a single grain after rolling, and fine ferrite will be produced. - This is because pearlite structure is difficult to obtain.

The reason why the cooling rate up to 500° C. is set to 0.5° C./S or more is because if the cooling rate is lower than this, pro-eutectoid ferrite will grow and it will be difficult to obtain the target fine ferrite/pearlite structure.

3 45 is a representative steel type of JIS mechanical structural carbon steel.
After melting C in a converter, it is made into 300X40 by continuous casting.
After forming a bloom of 0 +n+n, it was rolled into a 150 mm billet, and then wire rolled into a 11 m billet.
It was made into mφ wire rod. Table 1 shows the chemical composition of the billet.

Table 1 Chemical composition (wt%) Table 2 shows the wire rod rolling conditions. Out of the 114 test specimens, wire rods with level Nos. 3 to 111 manufactured under the conditions of this invention had ferrite grain sizes. It has an extremely fine ferrite/pearlite structure of about 2 to 6 microns.

Further, the results of spheroidizing annealing performed on the materials manufactured under the conditions shown in Table 2 are shown in FIG. As shown in this figure, the wire rod manufactured under the rolling conditions of the present invention undergoes extremely rapid spheroidization, and as shown in Figure 2, the strength decreases quickly and the ductility is also extremely high after spheroidizing annealing. It has a high value.

(Effect of the invention) By applying this invention, it becomes possible to shorten the time of spheroidizing annealing performed prior to cold forging,
The productivity improvement and energy saving effects are extremely impressive.

[Brief explanation of drawings]

FIG. 1 is a graph of the relationship between the ferrite grain size of the rolled material and the spheroidization rate, and FIG. 2 is a graph of the relationship between the ferrite grain size of the rolled material, the strength after spheroidization, and the reduction of area. Figure 1 ferrite

Claims (1)

[Claims] 1. C: 0.15 to 0.70 wt%, Si: less than 0.35 wt%, Mn: 0.30 to 1.8 wt%, O: 0.005 wt% or less, S: 0. When manufacturing a steel wire rod from a solid round billet containing less than 15 wt% of Fe and the remainder consisting of Fe and unavoidable impurities through rough rolling, intermediate rolling and finish rolling, the finish rolling start temperature is set at 650 to 850°C and the finish rolling is completed. The temperature is controlled to less than 950°C, and immediately after rolling is completed, the steel wire is rapidly cooled to a temperature range of 650 to 750°C, and the steel wire is wound non-concentrically, and then cooled to 500°C at a rate of 0.5°C/S or more. A method for producing a steel wire rod that can be rapidly spheronized, characterized by forming the steel wire rod into a fine ferrite/pearlite structure.