JPH02163315A - Manufacture of homogeneous high carbon steel - Google Patents

Abstract

PURPOSE:To manufacture a homogeneous high carbon steel free from segregation and having uniform internal quality by successively subjecting a continuously cast high carbon steel slab or a high carbon steel billet to primary hot working under specified conditions and diffusion treatment by soaking, removing the decarburized surface with a solvent and carrying out reheating and secondary hot working. CONSTITUTION:A continuously cast high carbon steel slab or a high carbon steel billet contg., by weight, 0.25-0.61% C, 0.15-0.35% Si, 0.60-0.90% Mn, <0.030% P, and <0.035% S is subjected to primary hot working at 1,000-1,300 deg.C and 18-30% draft to press the internal pores and to diffuse the segregated components. The hot worked slab or billet is held at 1,250-1,300 deg.C for >=10hr to sufficiently diffuse the segregated components by soaking and the decarburized surface layer is removed with a solvent, e.g. by 2-3mm thickness. The slab or billet is then heated again to 1,000-1,300 deg.C and subjected to secondary hot working. A homogeneous high carbon steel having uniform internal quality is manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing homogeneous high-carbon steel, and more specifically, to reduce segregation of sea bream slabs or steel slabs, and to produce homogeneous high-carbon steel having uniform internal quality. This invention relates to a method for manufacturing high carbon steel.

[Prior Art] Conventionally, as a technique for removing or reducing the segregation of alloying elements and impurity elements existing in steel slabs or steel slabs by heating and hot working, for example, JP-A-58
Publication No. 001210 discloses that the slab or steel slab is subjected to primary hot working with a cross-section reduction rate of 20% or more, and then reheated continuously or below the temperature at which the primary hot working ends. A method for maintaining the center temperature of 1000° C. or more for 30 minutes or more is disclosed.

However, with this method, in the case of flat slabs with large cross sections and high carbon steel, the problem is that short-time soaking diffusion is insufficient to reduce segregation, and locally dense segregation remains. There is.

Generally, high carbon steel is used for machine parts and mold members, but there are problems such as cracking due to localized dense segregation, poor machining accuracy during machining, and early tool wear. In recent years, poor appearance of the machined surface has become a focus of attention, and resolving this issue is a major issue.

[Problems to be Solved by the Invention] In view of the segregation and poor appearance in the conventional high carbon steel explained above, the present inventor has conducted extensive research, and as a result, the present invention has been made to solve the problem of steel, particularly high carbon steel slabs. Alternatively, they developed a method for producing high carbon steel that reduces local segregation of steel slabs and has uniform internal quality.

[Means for Solving the Problems] The method for producing homogeneous high carbon steel according to the present invention is characterized by: C0.25 to 0.61 wt%, Si 0. f5~0.
35wt%, Mn 0.60-0.90wt%, P 0
．． A steel slab or slab containing 0.030 wt% or less, S 0.035 wt% or less, and the balance consisting of Fe and unavoidable impurities is subjected to primary hot working at a reduction rate of 18 to 30%, and then heated at 1250 to 1300°C. 1 at temperature
After removing the decarburized layer by performing soaking diffusion treatment for 0 hours or more, reheating is performed to perform secondary hot working.

The method for producing homogeneous high carbon steel according to the present invention will be described in detail below.

First, in the method for producing homogeneous high carbon steel according to the present invention,
The components and component ratios of the steel used will be explained.

C is an element that is included to ensure strength, and if the content is less than 0.25 wt%, the strength will be insufficient;
If the content exceeds wt%, thermal handling becomes complicated. Therefore, when used for machine parts, mold parts, etc., C.
The content is 0.25 to 0.61 wt%.

StSMn is an element contained for deoxidation, and
Contains 1￥1 less than 0.15wt%, Mn content is 0.60
If the Si content exceeds 0.35 wt% and the Mn content exceeds 0.90 wt%, they will be contained as non-metallic inclusions, which will be harmful in practice. Therefore, the Si content is 0.15 to 0.35wt
%, and the Mn content is 0.80 to 0.90 wt%.

P%S is an impurity element, and the P content is 0.030wt
%, and if the S content exceeds 0.035 wt%, the internal quality will deteriorate. Therefore, the P content is Q, 030
wt % or less, and the S content is 0.035 wt % or less. Next, a method for producing homogeneous high carbon steel according to the present invention will be described.

In the method for producing homogeneous high carbon steel according to the present invention, the primary hot working with a reduction rate of 18 to 30 is performed to effectively remove segregated elements by compressing the internal porosity of the steel slab or steel slab. This is to diffuse the
The reason why it is set at ~30% is that the higher the rolling reduction rate, the greater the porosity compression effect, but in order to diffuse the segregated elements, the rolling reduction rate must be at least 18%, so the lower limit is 18%. %, and if the reduction rate exceeds a certain value, the effect of diffusion of segregation will be saturated, and if the reduction rate is too large, the steel slab or steel billet will become isolated. Since the weight is reduced and the manufacturing dimensions of the product are subject to significant restrictions, the upper limit of the rolling reduction is set at 30%.

- In hot working, it is necessary to heat the steel slab or steel billet, and in the case of continuously cast slabs, hot working may be performed during the cooling process after solidification.

Considering the diffusion effect of segregated elements caused by heating before hot working, the higher the temperature, the better, but in order to prevent softening of slabs or steel slabs and to suppress the formation of scale, it is recommended to set the temperature to 1300℃ as the upper limit. Moreover, the diffusion effect of the segregated elements due to heating before hot working is less effective at temperatures below 1000°C, so 1000°C is set as the lower limit.

After the primary hot working is completed, holding the temperature at 1250 to 1300°C for 10 hours or more is because the higher the soaking temperature and the longer the soaking time, the more effective it is for diffusing segregated elements. However, if the soaking temperature is low, the soaking time will be longer.
Since there are problems in mass production, it is advantageous for mass production to make the soaking temperature as high as possible and shorten the soaking time.

From this, the above effects cannot be expected unless the soaking temperature is at least 1250°C or higher, and
13 as a temperature that does not cause fusion of steel slabs or steel slabs
The upper limit was 00°C.

In order to avoid deteriorating the appearance of the machined surface at a soaking temperature of 250°C, a soaking time of at least 10 hours is required; if the soaking time is less than 10 hours, locally concentrated segregation will remain, and the workpiece surface will deteriorate. The soaking time should be set to 10 minutes to prevent appearance defects.
It should be more than an hour.

Furthermore, the above-mentioned soaking/diffusion treatment requires high temperatures and long periods of time.
Since decarburization occurs on both the front and back sides and sides of a steel slab or steel slab, causing softening, it is necessary to remove the decarburized layer before secondary hot working.

This decarburized layer is removed by 2 to 3 mm using a hot scarf.
It is best to use a solvent with a thickness of .

Secondary hot working is performed after removing the decarburized layer.

To explain the rolling reduction ratio and temperature in this secondary hot working, in order to completely compress the internal porosity, the total rolling reduction ratio must be 4 or more, and - the maximum rolling reduction ratio in the hot working process. When 30% is applied, in order to ensure a total reduction ratio of 4, the reduction ratio in the secondary hot working is 64.3% or more. Therefore, the reduction ratio in the secondary hot working needs to be 64% or more.

Further, the temperature in the secondary hot working is set at 1000 to 1300°C for the same reason as in the primary hot working.

[Example] An example of the method for producing homogeneous high carbon steel according to the present invention will be described.

Example 1 A steel plate having a thickness of 30 mm was produced by continuous casting of steel having the components and proportions shown in Table 1.

Table 2 shows - Hot working conditions, namely rolling reduction, heating temperature, soaking conditions, soaking temperature, soaking time, secondary hot working conditions, rolling reduction, heating temperature, plate thickness. and the results of visual inspection of the machined surface.

For the appearance inspection of the cut surface, the cut steel plate was processed into a large surface using a milling machine, and the quality of the appearance was determined by visual inspection.

Example 1 is a case where soaking and diffusion treatment is not performed.

Examples 2 and 3 are cases where the rolling reduction ratio under the -fire hot working conditions is small.

In Examples 4 to 6, the reduction rate under the -fire hot working conditions was 18% or more, so the appearance of the machined surface was good.

Examples 7 and 8 are cases where the soaking temperature is low, and Examples 9 and 1O are cases where the soaking time is short, and the appearance of the machined surface is poor in both cases.

As is clear from Table 2, according to the method for producing homogeneous high carbon steel according to the present invention, the segregation present in the scrap slab can be sufficiently reduced, and the appearance of the machined surface is also good. It can be seen that it is.

Example 2 A steel plate having a thickness of 30 mm was produced by casting steel having the components and proportions shown in Table 3 using a continuous casting method.

Table 4 shows the primary hot working conditions, namely rolling reduction rate, heating temperature,
The soaking conditions, that is, the soaking temperature, the soaking time, and the secondary hot working conditions, that is, the rolling reduction ratio, heating temperature, plate thickness, and the results of the appearance inspection of the machined surface are shown.

For the appearance inspection of the cut surface, the cut steel plate was processed into a large surface using a milling machine, and the quality of the appearance was determined by visual inspection.

Example 11 is a case where soaking and diffusion treatment is not performed.

Example 12 is a case in which the rolling reduction ratio of the primary hot working conditions is small, and the appearance of all machined surfaces is poor.

In Examples 13 and 14, the rolling reduction ratio under the primary hot working conditions was 18% or more, so the appearance of the machined surface was good.

Example I5 is a case where the soaking temperature is low, and Example 16 is a case where the soaking time is short, and in both cases, the appearance of the machined surface is poor.

[Effects of the Invention] As explained above, since the method for producing homogeneous high-strength steel according to the present invention has the above configuration, alloying elements and impurities are not segregated in the center of the cross section of the steel slab or steel slab. It has the excellent effect that it does not produce an alloy state that is different from the content and proportion of the initial steel, and the appearance of the machined surface is also good.

Claims (1)

[Claims] C0.25-0.61wt%, Si0.15-0.35
wt%, Mn0.60-0.90wt%, P0.030
wt% or less, S0.035wt% or less, and the balance consists of Fe and unavoidable impurities, primary hot working is performed at a reduction rate of 18 to 30%, and then at a temperature of 1250 to 1300 ° C. In 1
A method for producing homogeneous high carbon steel, which comprises performing soaking diffusion treatment for 0 hours or more to remove a decarburized layer, and then reheating and performing secondary hot working.