JPS61264162A - Nontempered tough steel for warm forging - Google Patents

Abstract

PURPOSE:To obtain the titled steel in which tempering heat treatment after forging is not required, by treating suitably a steel in which specified quantities of Mn and Cr are added to steel for machinery structure, to decrease a quantity of pro-eutectoid ferrite and refine pearlitic structure. CONSTITUTION:Steel composed of, by weight 0.25-0.60% C, 0.10-1.00% Si, 1.00-2.00% Mn, 0.30-1.00% Cr and the balance Fe with inevitable impurities is hot rolled or tempered or normallizing treated. In the structure obtd. thereby, denoting pro-eutectoid ferrite quantity as F%, pearlitic lamellar spacing as Dmum, the titled steel composed of ferrite and pearlite structure under F<=90-140 C% and D<=0.20mum is obtd. In the component compsn., toughness is improved by further adding <=0.1% Ti or 0.1% Nb, or machinability can be improved by adding at least one kind among <=0.15% S, <=0.30% Pb, <=0.010% Ca.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a non-thermal toughened steel for warm forging, and in detail,
The present invention relates to a non-tempered strong steel for warm forging that can produce forged products having excellent strength and toughness without performing tempering heat treatment after warm forging at a temperature below Ac, transformation point.

(Prior Art) Conventionally, forged products for machine structures are generally produced by hot forging medium carbon steel or low alloy steel material, then reheating, quenching, and tempering, that is, refining treatment. It is used after being given strength and toughness according to the requirements. However, the thermal refining treatment requires a large amount of thermal energy, and the manufacturing cost inevitably increases due to an increase in the number of processing steps, an increase in the number of products in progress, and the like.

In addition, with advances in cold forging steel and cold forging technology,
In recent years, many forged products for machine structures are being replaced by cold forged products. Furthermore, in recent years, there have been advantages such as higher dimensional accuracy than hot forging and the ability to save thermal energy, as well as lower deformation resistance of the material steel and improved deformability than cold forging. For this reason, warm forging has come to be applied to the production of various forged products.

(Purpose of the invention) Regarding the above-mentioned warm forging, research is currently being conducted on optimizing forging conditions on the premise of heat treatment after warm forging, and there have been few attempts to apply it to non-heat treated steel. Not done. Furthermore, attempts have been made to obtain strength equivalent to tempered steel by controlling the warm working conditions using conventional steel (Yuasa et al., Journal of the Japan Institute of Metals, Volume 5 (8), 788).
(1971)), in order to obtain sufficient strength using this method, a large amount of processing is required.On the other hand, in general forged products, the processing rate varies greatly depending on the part, and parts that are rarely processed In this case, sufficient strength and toughness cannot be obtained.

Therefore, in order to obtain a forged product with high strength and high toughness without performing heat treatment after warm forging, the present inventors focused on the microscopic structure of the raw steel before warm forging. As a result of extensive research on the influence of these microscopic tube structures of raw material steel on the strength and toughness after warm forging, we found that a steel made by adding predetermined amounts of Mn and Cr to machine structural steel was used as the raw material steel. In the pre-structure formed by hot-rolling or annealing or normalizing,
We discovered that by reducing pro-eutectoid ferrite I and refining the ferrite/pearlite structure, it is possible to obtain a forged product with excellent strength and toughness without heat refining after warm forging. This led to the invention.

Therefore, the present invention provides a warm forging non-woven material for machine structures that can produce a forged product with high strength and high toughness without performing tempering heat treatment after forming the desired forged product by warm forging. The purpose is to provide tempered tough steel.

(Structure of the Invention) The non-heat treated strong steel for warm forging according to the present invention contains C0.25 to 0.60%, Si 0.10 to 1.00%, Mn 1°00 to 2.00%, and Contains 0.30 to 1.00% Cr, the balance consists of iron and unavoidable impurities, and when the amount of pro-eutectoid ferrite is F (%) and the pearlite lamella spacing is D (μm), F≦90-140C % (%) (However, 0% indicates the content by weight % in steel.

) and D≦0.20 (μm).

First, conventional carbon steel for machine structures (S28C-558C"
) and steel to which predetermined amounts of Mn and Cr are added.
After normalizing treatment by heating at 50℃ and cooling in air,
A plate material with a thickness of 15 fl was produced by performing a warm forging simulation of heating at 600 to 700°C, rolling 0 to 50%, and letting it cool.The tensile strength of the test pieces obtained from these warm forging simulation treated materials was Fig. 1 shows the relationship between the resistance and the Charpy impact value. From this, it has been found that the toughness of the above-mentioned mechanical structural steel is improved by adding Mn and Cr at the same strength. Incidentally, the steel according to the present invention is
When the tensile strength is T S (kgf/mm") and the Charpy impact value is CIV (kgf-m/cm"), (TS)/(CIV) "" is 220 or more, and the strength is Figure 1 shows that it has excellent toughness and toughness.

Next, we will examine the pro-eutectoid ferrite content and pearlite lamella spacing in the microscopic tube structure of the steel before the warm forging simulation process, and the strength and strength of the warm forging simulation process material.
The relationship with toughness balance is shown in Figure 2. That is, the above-mentioned treated material whose toughness as a warm forged product has been improved by the addition of Mn and Cr has a microscopic structure before warm forging that, when the amount of pro-eutectoid ferrite is F (%), F≦90. -140C% (%) (However, 0% indicates the content in weight% in steel.

) It was found that the following conditions were satisfied and F was low.

In addition, 1. It was found that the pearlite lamella spacing was smaller than 0.20 μm.

That is, according to the present invention, the microscopic structure of a steel made by adding a predetermined amount of Mn and Cr to a conventional carbon steel for machine structural use before warm forging is as hot rolled or annealed or unsintered. Through the process, the amount of ferrite F is suppressed to below a predetermined value, and the pearlite lamella spacing is reduced to 0.20 μm.
By making the steel smaller than , when such steel is warm-forged, a warm-forged product with an excellent balance of strength and toughness can be obtained without heat refining.

In the above, before the warm forging simulation process, the steel is heated to 850°C and then air-cooled to normalize it. However, in the present invention, this heat treatment is not a wood-like treatment at all. The method of heat treatment after hot rolling does not limit the present invention in any way, as long as the steel structure satisfies the above conditions in terms of the amount of pro-eutectoid ferrite and the spacing between pearlite and lamella before warm forging. It may be subjected to normalizing treatment or annealing treatment, as shown in FIG.

Next, the reason for limiting the chemical components in the steel of the present invention will be explained.

It is necessary to add C in an amount of 0.25% or more in order to give the warm forged product manufactured from the steel of the present invention the strength necessary as a mechanical structural part. However, if too much is added, it will impair the toughness and machinability of the resulting forged product.
In the steel of the present invention, the upper limit of the amount of C added is 0.60%.

Si is an element that is necessary as a deoxidizing agent in steel manufacturing, and is also necessary to strengthen ferrite. In order to effectively obtain such effects, in the steel of the present invention, 0
．． It is necessary to add 10% or more, but if too much is added, inclusions such as SiQ□ will increase, reducing the toughness of the steel, its warm forging formability, and machinability. The upper limit of the amount is 1°00%.

As mentioned above, Mn and Cr are essential elements in the steel of the present invention in order to control the amount of pro-eutectoid ferrite and the spacing between pearlite and lamella within a predetermined range in the microstructure of the steel of the present invention before warm forging. Yes, at least 1.00% for Mn and at least 0.30% for Cr
It is necessary to add However, adding too many of these elements is not only economically disadvantageous;
When the steel of the present invention is warm-forged and subjected to induction hardening or the like, the susceptibility to quench cracking of the forged product increases. Therefore, in the steel of the present invention, the upper limits of the amounts of these elements added are 2.00% for Mn and 1.00% for Cr.

AN is 0.01 for deoxidizing steel and refining grains.
It is necessary to add 0% or more, but 0.0.0%
When the value exceeds this value, the machinability of the steel deteriorates.

Therefore, in the steel of the present invention, the amount of Aβ added is 0°oi
The range is from o to 0.0.0%.

In addition, if particularly high toughness is required for the warm forged product produced from the inventive wire, in addition to the above-mentioned elements, the inventive steel may be added as necessary to refine the crystal grains. At least one element selected from the group consisting of 'rt□, 1% or less, and NbQ, 1% or less can be added to. Adding Ti and/or Nb in amounts exceeding the above range impairs the machinability of the steel.

In addition, in order to improve the machinability of steel, the present invention network may contain at least one selected from the group consisting of S 0.15% or less, Pb 0.30% or less, and Ca 0.010% or less. It is also possible to add one type of element. However, when adding too many of these elements, toughness and warm forging formability are impaired. These elements may be added in combination with the above-mentioned Ti and/or Nb.

Next, warm forging conditions for the non-temperature toughened steel for warm forging according to the present invention will be explained.

In the present invention, the warm forging temperature is below the Act transformation point. When the warm forging temperature exceeds the Ac3 transformation point, the fine ferrite/pearlite structure is destroyed.1. This is because a sufficient balance of strength and toughness cannot be obtained in warm forged products.

(Effects of the Invention) As described above, the non-heat-treated strong steel for warm forging according to the present invention is produced by adding predetermined amounts of Mn and Cr to mechanical structural steel, and then hot rolling or annealing the steel. Or, in the pre-structure formed by normalizing treatment, the amount of pro-eutectoid ferrite is reduced and the ferrite/pearlite structure is refined, and with such steel, after warm forging, non-thermal treatment is performed. Forged products with excellent strength and toughness can be manufactured.

(Examples) Examples of the present invention are listed below, but the present invention is not limited to these Examples in any way.

Example After heating the steel having the chemical composition shown in Table 1 to 850°C,
600-700℃ after air cooling normalization treatment
A plate material with a thickness of 15+n was produced by heating the material to 0 to 50%, rolling it by 0 to 50%, and performing a warm forging simulation process in which it was allowed to cool.

Steels A, B, C, and D of the present invention are obtained by adding predetermined amounts of Mn and Cr to Comparative Steel F, which is a conventional 545C carbon steel for mechanical structures, to give the chemical composition according to the present invention. Comparative steel E has an amount of C added exceeding the range specified by the present invention, and by increasing the amount of C, pro-eutectoid ferrite is reduced and high strength is obtained.

The mechanical properties of the above-mentioned warm forging simulation treated plate materials made of the above-mentioned inventive steel and comparative steel were determined by taking JIS No. d tensile test pieces and JIS No. a impact test pieces parallel to the rolling direction from the above-mentioned sheets, and measuring Tensile and impact tests were conducted and evaluated. The results are shown in FIG. 1 and Table 2. In addition, regarding comparative steel E, 85
Table 2 also shows the mechanical properties when water quenching was performed after heating at 0°C and tempering at 600°C.

As is clear from the above results, the present invention has both superior strength and toughness compared to conventional carbon steel for mechanical structures or comparative steel made by adding a large amount of C to it. Non-thermal warm forged products can be obtained.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the amounts of Mn and Cr added in machine structural steel and the tensile strength and impact value of the obtained warm forged product. It is a graph showing the relationship between the pro-eutectoid ferrite area ratio and the minimum pearlite lamella spacing in the microscopic structure and the strength/toughness balance in the obtained warm forged product. Patent Applicant: Kobe Steel, Ltd. Representative Patent Attorney: Ittsu Makino Department Figure 2 C Gold Layer-1- ('tt%)

Claims (4)

[Claims] (1) Contains 0.25-0.60% C, 0.10-1.00% Si, 1.00-2.00% Mn and 0.30-1.00% Cr by weight, with the balance being iron and unavoidable It consists of impurities, and when the amount of pro-eutectoid ferrite is F (%) and the pearlite-lamella spacing is D (μm), F≦90-140C% (%) (However, C% is the content in weight% in steel. ) and a ferrite-pearlite structure with D≦0.20 (μm). (2) Contains (a) 0.25 to 0.60% of C, 0.10 to 1.00% of Si, 1.00 to 2.00% of Mn, and 0.30 to 1.00% of Cr in weight%; (b) Ti
Contains at least one element selected from the group consisting of 0.1% or less and Nb 0.1% or less, with the balance consisting of iron and unavoidable impurities, with the amount of pro-eutectoid ferrite being F (%) and the pearlite-lamella spacing being When D (μm), F≦90-140C% (%) (however, C% indicates the content by weight% in steel) and D≦0.20 (μm). A non-thermal toughened steel for warm forging characterized by having the following characteristics: (3) Contains (a) 0.25 to 0.60% of C, 0.10 to 1.00% of Si, 1.00 to 2.00% of Mn, and 0.30 to 1.00% of Cr in weight%; (b) S0
．． Contains at least one element selected from the group consisting of 15% or less, Pb 0.30% or less, and Ca 0.010% or less, with the balance consisting of iron and inevitable impurities, and the amount of pro-eutectoid ferrite is F (%) and pearlite.・When the lamella spacing is D (μm), F≦90-140C% (%) (However, C% indicates the content by weight% in steel) and D≦0.20 (μm) Ferrite・Non-thermal tempered strong steel for warm forging, characterized by having a pearlite structure. (4) Contains (a) 0.25 to 0.60% of C, 0.10 to 1.00% of Si, 1.00 to 2.00% of Mn, and 0.30 to 1.00% of Cr, and further, (b) Ti
at least one element selected from the group consisting of 0.1% or less, Nb 0.1% or less, and Ca 0.010% or less, and (c) S 0.15% or less, Pb 0.30% or less, and Ca 0.010% or less. and at least one element selected from the group consisting of, the remainder being iron and unavoidable impurities, where the amount of pro-eutectoid ferrite is F (%) and the pearlite-lamella spacing is D (μm), F≦ For warm forging, characterized by having a ferrite-pearlite structure of 90-140C% (%) (C% indicates the content by weight% in steel) and D≦0.20 (μm) Non-tempered tough steel.