Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese

Definitions

• the present invention relates to steel used for parts such as automobiles and general machines, and more particularly to steel excellent in machinability such as tool life during cutting, cutting surface roughness and chip handling. Background art
• SUM23 and SUM24L which are called low-carbon free-cutting steels with less than 0.2% C, have been developed with emphasis on machinability. It has been known that it is effective to add machinability improving elements such as S and Pb to improve machinability. However, in recent years, Pb has tended to avoid its use as an environmental burden, and its use has been reduced.
• SUM23 Sulfur free-cutting steel which is used as a base, easily adheres to the cutting edge, causing irregularities on the cutting surface due to the falling-off of the cutting edge and the chip separation phenomenon, deteriorating the surface roughness. Therefore, from the viewpoint of machinability, there is a problem that accuracy is reduced due to deterioration of surface roughness.
• chip disposability it is considered better if chips are short and easy to separate, but simple addition of S has a large ductility of the matrix, so it was not sufficiently divided and could not be improved significantly.
• Elements other than S such as Te, Bi, and P, are also known as machinability improving elements.However, even if machinability can be improved to some extent, cracks are likely to occur during rolling and hot forging. It is said that it is desirable to have as little as possible.
• steel containing 0.2% or more of C has a relatively high strength because it contains many alloying elements such as C, Cr, and Mo.
• the problem of the formation of the cutting edge and the resulting unevenness (roughness) of the cutting surface is small, and the surface roughness is relatively good because it is originally a hard material.
• S which is a machinability improving element
• the resulting MnS will be elongated by rolling or forging, resulting in anisotropy in mechanical properties. Application to parts is greatly restricted.
• S is not added to high-strength steel to improve machinability, and in most cases, machinability is sacrificed. Disclosure of the invention
• the present invention reduces both the tool life and surface roughness of so-called low carbon steels with a C content of less than 0.15% while avoiding defects in rolling, forging, and product performance. It is an object of the present invention to provide a steel having improved and excellent machinability.
• the mechanical properties Anisotropic And steel with excellent machinability.
• Cutting is a breaking phenomenon that separates chips, and promoting it is one of the key points.
• the present inventors have conducted extensive studies and conducted extensive studies. As a result, not only increasing the amount of S but also including Zn as a basic component embrittles the matrix and facilitates blasting. It has been found that the tool life can be extended and the unevenness of the cutting surface can be suppressed.
• the present invention has been made based on the above findings, and the gist is as follows.
• a steel excellent in machinability characterized by containing A steel excellent in machinability characterized by containing.
• Ni 0.05 to 7%
• Cu 0.02 to 3% and one or two of them are contained, and when 0.3% or more is contained, Ni% ⁇ Cu% is satisfied.
• FIG. 1 is a diagram showing an outline of a plunge cutting test, in which (a) shows a plunge cutting test method, and (b) shows a tool movement.
• FIG. 2 is a view showing an Ono-type rotary bending test piece with a notch.
• Fig. 3 is a schematic diagram showing carburizing conditions, (a) is a schematic diagram showing carburizing and quenching, and (b) is a schematic diagram showing normalizing conditions.
• the basic idea of the present invention is to improve machinability without impairing mechanical properties by including Zn as an essential component of steel in addition to S.
• Zn is a particularly important element in the present invention.
• Zn has the effect of embrittlement of steel, has the effect of improving machinability, Has the effect of improving
• MnS coarse inclusions
• deterioration of mechanical properties can be suppressed to a minimum. This effect is particularly noticeable as anisotropy.
• good machinability can be obtained when Zn is added. This is thought to be because the embrittlement effect of Zn becomes significant when the temperature rises due to the cutting heat.
• a lubrication effect is created at the tool / workpiece interface.
• Zn If less than 0.001%, the effect is small. On the other hand, since Zn is very easy to evaporate during smelting, it is necessary to add a large amount of Zn in order to keep Zn in molten steel and maintain Zn content exceeding 0.5% after solidification. Since it is not industrially feasible in terms of cost, the upper limit was set at 0.5%. Therefore, the range of Zn content in the steel of the present invention is limited to 0.001 to 0.5%.
• machinability-improving elements such as Sn, B, and Te can be contained, but Sn alone does not improve machinability, and machinability is enhanced by interaction with Zn. Is improved.
• C has a significant effect on machinability because it relates to the basic strength of steel and the amount of oxygen in the steel. If the strength is increased by adding a large amount of C, the machinability decreases, so the upper limit was set to 1.5%. On the other hand, it is necessary to control the amount of oxygen appropriately to prevent the formation of hard oxides that reduce machinability and to suppress the adverse effects of solid solution oxygen at high temperatures such as pinholes during the solidification process. . If the C content is simply reduced too much simply by blowing, not only does the cost increase, but also a large amount of oxygen in the steel remains, causing problems such as pinholes. Therefore, the lower limit of 0.001% of C, which can easily prevent problems such as pinholes, was set as the lower limit. Si: 3% or less
• Mn is necessary as a deoxidizing element and to fix and disperse sulfur in steel as MnS. It is also necessary to soften the oxides in steel and make the oxides harmless. The effect depends on the amount of S added, but if it is less than 0.01%, the added S cannot be sufficiently fixed as MnS, and S becomes FeS and becomes brittle. When the amount of Mn increases, the hardness of the substrate increases, and machinability and cold workability decrease. Therefore, the upper limit was set to 3.0%.
• the upper limit of P must be set to 0.2% because the hardness of the base material increases in steel, which deteriorates not only cold workability but also hot workability and forming properties.
• the lower limit is set to 0.001%, which is an element that facilitates cutting by embrittlement and is effective in improving machinability.
• MnS improves machinability, but elongated MnS is one of the causes of anisotropy during forging. Large MnS should be avoided, but a large amount is preferable from the viewpoint of improving machinability. Therefore, it is preferable to finely disperse MnS.
• 0.0001% or more is required, and 0.001% or more is preferable.
• the content exceeds 1.2%, coarse MnS is inevitably generated, and cracks occur during production due to deterioration of the structural characteristics and hot deformation characteristics due to FeS and the like.
• N 0.0001-0.02%
• N hardens steel if it is solid solution N. In particular, in cutting, it hardens near the cutting edge due to dynamic strain aging and shortens the tool life, but also has the effect of improving the cutting surface roughness.
• BN is generated to improve machinability. If the N content is less than 0.0001%, the effect of improving the surface roughness by the dissolved nitrogen and the effect of improving the machinability by BN are not recognized, so the lower limit was set. On the other hand, if the N content exceeds 0.02%, a large amount of solid solution nitrogen is present, and the tool life is rather shortened. In addition, bubbles are generated during the production, causing flaws and the like. Therefore, in the present invention, the upper limit is set to 0.02% at which such adverse effects become remarkable.
• O is free, it becomes bubbles during cooling and causes pinholes. Control is also required to soften the oxides and suppress hard oxides that are harmful to machinability.
• oxides are used as precipitation nuclei when MnS is finely dispersed. If the O content is less than 0.0005%, MnS cannot be sufficiently finely dispersed, and coarse MnS is generated, which adversely affects mechanical properties. Therefore, the lower limit was 0.0005%. Further, if the O content exceeds 0.05%, bubbles are generated during the production and pinholes are formed.
• Sn is a soft metal, and is distributed at grain boundaries and the like in steel and embrittles the steel. This improves machinability. If the content is less than 0.002%, the effect is not recognized. If the content exceeds 0.5%, the steel is embrittled to make mirror making and rolling difficult. Therefore, the range was set to 0.002 to 0.5%.
• B is effective in improving machinability. This effect is not remarkable at less than 0.0005%, and the effect is saturated even if added over 0.05%, Therefore, if too much BN is precipitated, cracking will occur during manufacturing due to deterioration of the mirror-forming properties and hot deformation properties. Therefore, the range was 0.0005 to 0.05%.
• Cr is an element that imparts hardenability and temper softening resistance. Corrosion resistance can be obtained by adding a large amount. Therefore, it is added to steels that require high strength. In that case, it is necessary to add 0.01% or more. However, if added in large amounts, Cr carbides are formed and become brittle, so the upper limit was set at 7%.
• Mo is an element that imparts temper softening resistance and improves hardenability. The effect is not recognized at less than 0.01%, and the effect is saturated even if added over 3%, so the addition range was 0.01% to 3%.
• V forms carbonitrides and can strengthen the steel by secondary precipitation hardening. If it is less than 0.01%, there is no effect on increasing the strength, and if it exceeds 3%, a large amount of carbonitride precipitates and the mechanical properties are rather impaired, so the upper limit was set.
• Nb also forms carbonitrides and can strengthen the steel by secondary precipitation hardening. If the content is less than 0.001%, there is no effect on increasing the strength. If the content exceeds 0.2%, a large amount of carbonitride precipitates and the mechanical properties are rather impaired.
• Ti also forms carbonitrides and strengthens the steel. It is also a deoxidizing element, and it is possible to improve machinability by forming a soft oxide. You. If less than 0.001%, the effect is not recognized, and even if added over 0.5%, the effect is saturated. Also, Ti becomes a nitride even at high temperatures and suppresses growth of austenite grains. Therefore, the upper limit was set to 0.5%.
• W forms carbonitrides and can strengthen the steel by secondary precipitation hardening. If it is less than 0.01%, there is no effect on increasing the strength, and if it exceeds 3%, coarse carbonitrides are precipitated and the mechanical properties are rather impaired. Therefore, the upper limit was set.
• Ni is effective in strengthening the fly, improving ductility and improving hardenability and corrosion resistance. If the content is less than 0.05%, the effect is not recognized. Even if the content exceeds 7%, the effect is saturated in terms of mechanical properties, so the upper limit is set.
• Cu is effective in strengthening ferrite, improving ductility, improving hardenability, and improving corrosion resistance. If the content is less than 0.02%, the effect is not recognized. Even if added over 3%, the effect is saturated in terms of mechanical properties, so the upper limit is set. In addition, when Cu is added alone, the hot ductility is extremely lowered, which causes troubles such as cracking and rolling problems. When the addition amount exceeds 0.3%, it is preferable to add Ni so that Ni% ⁇ Cu% in order to avoid manufacturing trouble.
• A1 the steel in our deoxidizing element forming the A1 2 0 3 or A1N.
• This is effective for preventing the austenite grain size from becoming coarse during quenching and for improving toughness.
• the content is less than 0.001%, the effect is not recognized. If the content is more than 2%, coarse inclusions are generated, and the mechanical properties are rather deteriorated. You.
• A1 2 0 3 will cause the tool damage during cutting so hard, may promote wear. Therefore austenite coarsening effect of such grains is saturated, and the upper limit of 2% of adverse effects A1 2 0 3 becomes remarkable.
• Particularly preferred to Rukoto to 0.015% or less that does not produce a large amount of A1 2 0 3 in the case of priority the machinability is preferably 0.005% or less in the case of further prioritize softening oxide .
• Ca is a deoxidizing element that generates soft oxides and not only improves machinability, but also dissolves in MnS to reduce its deformability, and MnS shape even when rolled or hot forged Has the function of suppressing distraction. Therefore, it is an effective element for reducing anisotropy. If the content is less than 0.0002%, the effect is not remarkable. Even if the content exceeds 0.01%, not only the yield will be extremely deteriorated, but also a large amount of hard Ca0, CaS, etc. will be generated and the coating will be damaged. Decreases machinability. Therefore, the component range was defined as 0.0002 to 0.01%.
• Zr is a deoxidizing element and produces an oxide.
• the oxides serve as precipitation nuclei for MnS and are effective in fine and uniform dispersion of MnS.
• it has the function of dissolving in MnS to reduce its deformability, and suppressing the elongation of the MnS shape even in rolling or hot forging. Therefore, it is an element effective for reducing anisotropy. 0.
• the effect is less than 0,003% is not significant, not only the yield be added exceeds 5% 0.5 becomes extremely poor to generate such a large amount Zr0 2 and ZrS hard, cutting rather be Reduce the nature. Therefore, the range of components was specified to be 0.0003 to 0.5%.
• Mg is a deoxidizing element and produces oxides.
• the oxides serve as precipitation nuclei for MnS and are effective in fine and uniform dispersion of MnS. Therefore, it is an effective element for reducing anisotropy. Below 0.00002%, the effect is not noticeable However, even if added in excess of 0.02%, the yield will be extremely poor and the effect will be saturated. Therefore, the component range was defined as 0.0002 to 0.02%.
• Te is a machinability improving element.
• the formation of MnTe and the coexistence with MnS have the effect of reducing the deformability of MnS and suppressing the elongation of the MnS shape. Therefore, it is an element effective for reducing anisotropy. This effect is not observed at less than 0.001%, and saturates at more than 0.5%.
• Pb and Bi are elements that are effective in improving machinability.
• the effect is not recognized at less than 0.01%, and when added over 0.7%, not only does the machinability improvement effect saturate, but also the hot forging properties deteriorate and cause flaws. Cheap. Therefore, the respective contents were set to 0.01 to 0.7%.
• Figure 1 shows the outline of the experimental method. That is, as shown in Fig. 1 (a), the test material 2 rotating in the cutting direction 1 is cut by the tool 3, and as shown in Fig. 1 (b), the tool 3 is moved to To form Table 4 shows the cutting conditions.
• the surface roughness (10-point surface roughness Rz wm) when machining 200 grooves was measured. Specified.
• the chip has a curl shape, but if the curl is less than 5 turns and the chip breaks and short chips are generated, “ ⁇ ” indicates that The case where a long chip that does not break even when exceeding this is generated is denoted as “X”.
• Table 5 shows the chemical composition of the sample evaluated for the machinability and mechanical properties of the steel based on, and Table 6 shows the evaluation results.
• a part of each specimen was melted in a 270 t converter, then disassembled and rolled into billets, and further rolled into ⁇ 65 mm steel bars. The others were melted and rolled in a 2 t vacuum melting furnace.
• Impact value (JZ cm 2 was evaluated by preparing a U-notch specimen with a depth of 2 according to JIS.
• Table 3 shows the cutting conditions in the drilling test for the machinability evaluation of Examples 41 to 43 containing about 0.1% C.
• the machinability was evaluated at the highest cutting speed (so-called VL1000) capable of cutting up to the accumulated hole depth lOOOOmin.
• the surface roughness was evaluated by so-called plunge cutting, in which the tool shape was transferred by a parting-off tool.
• plunge cutting in which the tool shape was transferred by a parting-off tool.
• the surface roughness was evaluated by the plunge cutting shown in Table 4.
• Examples 44-46 containing about 0.3% C and Examples 47-77 with more C content the impact value and its anisotropy were shown in order to emphasize the mechanical properties.
• the impact value of the sample cut out from the cross section direction of the steel bar is shown (“C direction” column)
• (an impact value of the transverse direction sample) / (an impact value of the longitudinal sample) is shown as anisotropy.
• (Anisotropic" column) The larger the value is, the smaller the anisotropy is.
• the evaluation of the machinability of Examples 47 to 77 was carried out with the drilling property VL1000, and evaluated under the cutting conditions shown in Table 7. In these cases, the cutting surface roughness was not evaluated.
• Example 41 43 the inventive example outperformed the comparative example in VL1000 and surface roughness.
• the invention example shows a hardness HV, an impact value of the sample in the cross section direction and an impact value of the sample in the cross section direction of the comparative example containing substantially the same C and other alloying elements. Although the impact value of the sample in the longitudinal direction is almost the same,
• VL1000 is good and has excellent machinability.
• Table 8 shows examples in which a large amount of alloying elements were added to improve the hardenability of steel.
• Example 7882 a steel based on SCr420 was subjected to normalization (920 ° C x lhr ⁇ air cooling) and then subjected to a cutting test.
• the machinability was evaluated in a drilling test with the same cutting conditions as in Table 5, and the evaluation item was the highest cutting speed (so-called VL1000) that could be cut up to a cumulative hole depth of 1000 mm.
• the unit of this VL1000 is m / min. The larger the value, the better the tool life.
• an Ono-type rotary bending test piece with a notch formed with a notch of R 1.16 on a 9 mm diameter test piece was prepared, and Figs.
• Table 9 shows examples based on steel with improved hardenability by further adding a large amount of alloying elements.
• a part of the test material was melted in a 270 t converter, then disassembled and rolled into billets, and further rolled to ⁇ 50 mm. The others were melted and rolled in a 2 t vacuum melting furnace.
• the machinability was evaluated by a drilling test and the cutting conditions were the same as in Table 7, and the evaluation item was the highest cutting speed (so-called VL1000) capable of cutting to a cumulative hole depth of 1000.
• the hardness was adjusted to about HV310 by quenching and tempering using SCM440 as a base steel, and the machinability was evaluated with VL1000.
• the impact value was evaluated as a mechanical property. The impact value was measured by cutting a sample from the longitudinal direction of the bar and using a JIS3 test piece (2 mmU notch test piece).
• JIS3 test piece 2 mmU notch test piece
• the bearing steel was used as a base, and the steel was softened by spheroidizing annealing at 700 ° C for 20 hours, and the machinability VL1000 was measured.
• the invention example had almost the same hardness as the comparative example, the machinability VL1000 was large and was superior to the comparative example.

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