JP4263648B2 - Ti-added high strength steel with excellent machinability - Google Patents

Description

  The present invention relates to steel for high-strength parts that transmits power, such as automobile shafts and gears, and that requires cutting work.

  In general, in order to cope with miniaturization and weight reduction and high output of automobiles, it is necessary to increase the strength of components that transmit power such as shafts and gears.

  Therefore, Ti-added steel is available as a means for increasing strength from material chemical components (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4). These prior technologies are premised on surface treatment similar to that of conventional steel, for example, heat treatment such as tempering, non-tempering, carburizing, carbonitriding, etc. Since a larger amount of Ti was added than steel for steel, the strength could be improved by the dispersion strengthening by the large amount of finely precipitated TiC or the effect of finely stabilizing the crystal grain size.

  However, as a negative effect when adding a large amount of Ti, the tool life during cutting may be reduced depending on the cutting conditions compared to conventional steel, or the chips may not be finely divided, causing troubles around the tool. There is.

  And in the conventional Ti mass addition steel, the steel which added Ca for the purpose of machinability improvement is developed (for example, refer patent document 5 and patent document 6). However, even if Ca is simply added, the effect does not always appear sufficiently.

Japanese Patent Laid-Open No. 10-251806 JP-A-11-302727 Japanese Patent Laid-Open No. 11-71630 JP 2002-266053 A Japanese Patent Laid-Open No. 10-324952 Japanese Patent Laid-Open No. 10-152752

  The problems to be solved by the present invention are steels for high-strength parts that transmit power, such as automobile shafts and gears, such as SC, SMn, SCr, SCM, SNC, SNCM, and B, V, It is intended to improve the machinability of steel for high strength parts formed by adding Ti to steel added with strengthening elements such as Nb or free cutting elements such as Pb, Bi and Mg. .

  Steel added with a large amount of Ti has poor machinability due to the increase in hard Ti-based carbonitrides and the modification of sulfides, which are free-cutting materials. it is conceivable that. For general structural steels such as JIS standard SC, SMn, SCr, SCM, SNC, SNCM, and steels to which free cutting elements such as B, V, Nb or Pb, Bi, Mg are added In addition, MnS is contained as an inclusion. This MnS has an effect of improving machinability by becoming a stress concentration source during cutting and promoting crack generation and propagation. However, when a large amount of Ti is added to increase the strength, Ti sulfide or Ti carbon sulfide is generated without generating MnS. Since these Ti sulfides and Ti carbon sulfides are smaller and harder than MnS, there is a drawback that the effect of improving machinability is weak.

  However, the inventors have found that even with the same amount of S, the machinability is greatly improved by adjusting O of Ti-added steel to a certain amount and adding a specific range of amount of Ca. It was. This is due to the combined effect with Ca-based oxides that are generated simultaneously with the modification of the Ti sulfide composition or Ti carbon sulfide composition because Ca has a higher sulfide generation capacity than Ti. This is because, when Ca is added under a constant oxygen amount and Ti amount, since the Ca-based sulfide and Ca-based oxide effective for machinability can coexist, the machinability increases. is there.

Therefore, in the means of claim 1 of the present invention for solving the above-mentioned problems , C: 0.10 to 1.20%, Si: 0.05 to 1.25%, Mn: 0.30 in mass%. To 1.50%, P: 0.035% or less, S: 0.003 to 0.070%, Al: 0.005 to 0.050%, Ti: 0.10 to 0.30%, N: 0 0.15% or less, Ca: 0.0005 to 0.01%, O: 0.0005 to 0.01%, consisting of the balance Fe and inevitable impurities, 100 × Ti × O / Ca = 1 to 100 ...... Steel that satisfies the formula of (1), and is made of mechanical structural steel containing Ca-based sulfides or Ca-based oxides produced by Ca treatment. It is a strength steel.

According to the second aspect of the present invention, the mechanical structural steel is, in addition to the steel components of the first aspect, in mass%, further Cr: 0.1 to 3.0%, Mo: 0.15 to 1.5. %, Ni: 0.25 to 3.0%, B: 0.0003 to 0.0080%, Nb: 0.01 to 0.15%, V: 0.03 to 0.30% or one type Ca-based sulfide containing two or more types, balance Fe and inevitable impurities, and satisfying the formula of 100 × Ti × O / Ca = 1 to 100 (1), and formed by Ca treatment Alternatively, it is a Ti-added high-strength steel excellent in machinability, characterized by comprising a mechanical structural steel containing a Ca-based oxide .

According to the third aspect of the present invention, in addition to the steel components of the first or second aspect, the mechanical structural steel is, in mass%, Bi: 0.01-0.30%, Pb: 0.01-0. 30%, Mg: contains one or more of 0.0005 to 0.01%, consists of remaining Fe and inevitable impurities, 100 × Ti × O / Ca = 1 to 100 (1) The Ti-added high-strength steel excellent in machinability, characterized in that it is made of a steel for mechanical structures containing a Ca-based sulfide or Ca-based oxide produced by Ca treatment .

  The reason for adding the component elements of the Ti-added high-strength steel will be described below. In addition,% shows the mass%.

C: 0.10 to 1.20%
C is an element necessary for ensuring strength. However, if too much, machinability is hindered. Therefore, C is 0.10 to 1.20%, preferably 0.15 to 0.65%.

Si: 0.05-1.25%
Si is an element necessary as a deoxidizing material. However, if too much, machinability is hindered. Therefore, Si is set to 0.05 to 1.25%, preferably 0.10 to 1.00%.

Mn: 0.30 to 1.50%
Mn is an element necessary for ensuring hardenability. However, if too much, machinability is hindered. Therefore, Mn is 0.30 to 1.50%, preferably 0.35 to 1.00%.

P: 0.035% or less P is contained as an impurity, but if it is too much, the impact strength is lowered. Therefore, P is set to 0.035% or less, preferably 0.030% or less.

S: 0.003-0.070%
S is an element that generates sulfide and improves machinability. However, when the amount is too large, the hot workability and impact strength are lowered. Therefore, S is 0.003 to 0.070%, preferably 0.005 to 0.045%, and more preferably 0.010 to 0.030%.

Al: 0.005 to 0.050%
Al is an element necessary as a deoxidizing material. However, the upper limit is the normal electric furnace level at the time of melting by an electric furnace. Therefore, Al is made 0.005 to 0.050%, preferably 0.005 to 0.035%.

Ti: 0.10 to 0.30%
Ti is an element necessary for preventing grain coarsening due to TiC. However, if it is too much, the production is reduced. Therefore, Ti is 0.10 to 0.30%, preferably 0.11 to 0.20%.

N: 0.015% or less N is contained as an impurity, but if it is too much, TiN is generated and machinability is lowered. Therefore, N is set to 0.015% or less, preferably 0.010% or less.

Ca: 0.0005 to 0.01%
Ca is an element that generates a Ca-based sulfide and a Ca-based oxide to ensure machinability. Therefore, in the steelmaking stage, Ca treatment is performed by adding an alloy containing Ca in the molten steel in a lump or wire. Although the sulfide and oxide are modified by Ca treatment and an effect of improving machinability appears, the effect becomes clear when contained in steel by 0.0005% or more. However, if the amount is too large, the cost is increased, and the strength characteristics are adversely affected by the generation of large-scale CaO. Therefore, Ca is 0.0005 to 0.01%, preferably 0.001 to 0.005%.

O: 0.0005 to 0.01%
O couple | bonds with Ca and produces | generates Ca type | system | group oxide and improves machinability. However, if the amount is too large, the strength decreases due to the formation of large oxides. Therefore, O is set to 0.0005 to 0.01%, preferably 0.001 to 0.005%.

Cr: 0.1-3.0%
Cr is an element necessary for ensuring hardenability. However, if too much, machinability is hindered. Therefore, Cr is set to 0.1 to 3.0%, preferably 0.6 to 2.0%.

Mo: 0.15-1.5%
Mo is an element necessary for ensuring high-temperature hardness and hardenability. However, if the amount is too large, the machinability is lowered, which is disadvantageous in terms of cost. Therefore, Mo is set to 0.15 to 1.5%, preferably 0.25 to 1.0%.

Ni: 0.25 to 3.0%
Ni is an element necessary for ensuring the root bending fatigue strength of gears and the like. However, if the amount is too large, the machinability is lowered, which is disadvantageous in terms of cost. Therefore, Ni is set to 0.25 to 3.0%, preferably 0.3 to 1.0%.

B: 0.0003 to 0.0080%
B is an element necessary for ensuring hardenability. However, when the amount is too large, the strength decreases due to precipitation of borocarbides. Therefore, B is 0.0003 to 0.0080%, preferably 0.0010 to 0.0030%.

Nb: 0.01 to 0.15%
Nb is an element that improves the bending fatigue strength by stabilizing the crystal grains. However, too much is disadvantageous in cost. Therefore, Nb is set to 0.01 to 0.15%, preferably 0.02 to 0.10%.

V: 0.03-0.30%
V is an element necessary for ensuring high-temperature hardness. However, too much is disadvantageous in terms of cost. Therefore, V is 0.03 to 0.30%, preferably 0.10 to 0.25%.

Bi: 0.01-0.30%
Bi is an element necessary for improving machinability. However, when too much, hot workability will fall. Therefore, Bi is set to 0.01 to 0.30%, preferably 0.03 to 0.25%.

Pb: 0.01-0.30%
Pb is an element necessary for improving machinability. However, when too much, hot workability will fall. Therefore, Pb is set to 0.01 to 0.30%, preferably 0.03 to 0.25%.

Mg: 0.0005 to 0.01%
Mg is an element that improves machinability by controlling sulfides and oxides. However, too much is disadvantageous in terms of cost. Therefore, Mg is 0.0005 to 0.01%, preferably 0.001 to 0.005%.

  Further, in the above components, Ti, O, and Ca satisfy the formula of 100 × Ti × O / Ca = 1 to 100 (1). When satisfied, a machinability improving effect is obtained. The value of the above expression (1) is preferably 1 to 25.

  In the invention of the present application, a Ca-based sulfide or a Ca-based oxide is added by adding Ca as a steel component to a steel for high-strength parts that transmits power such as a shaft or gear for automobiles containing Ti as a means for increasing the strength. The machinability of Ti-added steel, which has been difficult in the past, is greatly improved by defining the steel composition of the present application and further defining the relation of the proportions of Ti, O, and Ca in the composition within a certain range. Therefore, an excellent effect is obtained in that a steel for high-strength parts that can be easily machined can be obtained.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described by way of examples through a machinability test described below.

  In the 100 kg vacuum melting furnace, the steel of the present invention having the chemical composition shown in Table 1 produced by adding a Ca—Si alloy to molten steel and the steel of comparative steel were melted to obtain a steel ingot. The obtained steel ingot was forged into a steel bar having a diameter of 40 mm at 1250 ° C. Then, after hold | maintaining at 920 degreeC for 1 hour, it air-cooled and used for the machinability test.

  In Table 1, the value of 100 × Ti × O / Ca in formula (1) is rounded off to the first decimal place. Furthermore, even if Ca was less than 0.0001 mass%, it was calculated at 0.0001 mass%. The shaded portion is outside the scope of the claims of the present invention.

  As the machinability test, 1) a turning carbide tool life test, 2) a drill life test, and 3) a chip disposal test were performed. Table 2 shows the machinability test results.

  1) Turning carbide tool life test uses a P20 tool as a carbide tool, cutting speed: 200 m / min, feed: 0.1 mm / rev, depth of cut: 0.5 mm, evaluation method: dry type flank wear Evaluation was made by the time required to reach VB = 0.2 mm.

  2) The drill life test was performed using a φ5 mm high-speed drill, cutting speed: 25 m / min, feed: 0.1 mm / rev, hole depth: 15 mm, evaluation method: dry method, and the number of drilled holes until drill breakage.

  3) Under the condition of the chip disposal test and 1) above, turning was performed while changing the feed to 0.1, 0.15, 0.20 mm / rev, and the chips obtained at that time were collected to obtain chips 1 The number of chips per piece was evaluated.

  In Table 2, the machinability test results are as follows. 16 to 18 are shown as relative steels as relative steels. No. 1-5 and no. 13, no. 14 is No.14. No. 17, no. 6-10 and no. 15 is No.15. No. 18, no. 11, no. No. 12 is No. 12. Each of the 16 machinability test results is 1. The shaded portion indicates less than 2. The target value is 2 or more.

  No. of invention steel of Table 2 in a machinability test result. 1 to 12 relate to the claimed steel of the present invention. The machinability of the steel of the present invention shows a high index of 2 or more in any of the drill life, the carbide tool life, and the chip disposal. On the other hand, No. of comparative steel. Among the six cases 13 to 18, those showing an index of 2 or more were No. in drill life. No. 13 in No. 13 has no carbide tool life, and the chip disposal is No. 13 and no. Only two of 15 examples, none of them reached 2, indicating that the present invention is extremely excellent in machinability.

Claims (3)

Steel for machine structure is mass%, C: 0.10 to 1.20%, Si: 0.05 to 1.25%, Mn: 0.30 to 1.50%, P: 0.035% or less , S: 0.003-0.070%, Al: 0.005-0.050%, Ti: 0.10-0.30%, N: 0.015% or less, Ca: 0.0005-0. 01%, O: 0.0005-0.01% in steel, balance Fe and inevitable impurities, satisfying the following formula (1), Ca-based sulfide or Ca-based produced by Ca treatment A Ti-added high-strength steel excellent in machinability, characterized by comprising mechanical structural steel containing an oxide.
100 × Ti × O / Ca = 1 to 100 (1) In addition to the steel components according to claim 1, the steel for machine structure is in mass%, and Cr: 0.1 to 3.0%, Mo: 0.15 to 1.5%, Ni: 0.25 ~ 3.0%, B: 0.0003 to 0.0080%, Nb: 0.01 to 0.15%, V: 0.03 to 0.30% of one type or two or more types, A steel comprising the balance Fe and unavoidable impurities and satisfying the following formula (1), comprising a steel for mechanical structure containing Ca-based sulfide or Ca-based oxide produced by Ca treatment. Ti-added high-strength steel with excellent machinability.
100 × Ti × O / Ca = 1 to 100 (1) In addition to the steel components according to claim 1 or 2, the steel for machine structure is in mass%, Bi: 0.01 to 0.30%, Pb: 0.01 to 0.30%, Mg: 0 A steel containing one or more of 0.05 to 0.01%, the balance being Fe and inevitable impurities, and satisfying the following formula (1): A Ti-added high-strength steel excellent in machinability, characterized by comprising a mechanical structural steel containing a Ca-based oxide.
100 × Ti × O / Ca = 1 to 100 (1)