US3829312A - Process for the manufacture of steel of good machinability - Google Patents

Abstract

A PROCESS FOR THE MANUFACTURE OF STEEL CAPABLE OF BEING MACHINED AT MACHINING SPEEDS RANGING FROM 60 TO 300 METERS PER MINUTE, WHICH COMPRISES DEOXIDIZING A MELT OF STRUCTURAL KILLED STEEL CONTAINING 0.1-0.6% OF CARBON, NOT MORE THAN 1.5% OF NANUGANESE, NOT MORE THAN 0.5% OF SILICON, 0.004-0.1% OF OXYGEN, AND NOT MORE THAN 0.015% OF NITROGEN, WITH A TITANIUM-CONTAINING OXYGEN COMBINING AGENT, THE QUANTITY AND COMPOSITION OF THE TITANIUM-CONTAINING COMBINING AGENT BEING SO SELECTED THAT THE INGOT AFTER THE DEOXIDATION CONTAINS 0.005-0.8% OF TITANIUM, 0.3-1.5% OF MANGANESE, 0.005-0.025% OF TOTAL OXYGEN, AND NOT MORE THAN 0.5% OF SILICON, AND DOES NOT CONTAIN MORE THAN EACH O.010% OF SOLUBLE ALUMINUM AND NITROGEN, THE BLANCE BEING IRON AND IMPURITIES, AND AT LEAST A PART OF THE TITANIUM IS PRESENT IN THE INGOT AS TIANIUM-CONTAINING OXIDE TYPE INCLUSIONS.

Description

Aug. 13, 1974 TORU ARAKI ETAL 3,3

PBOCESS FOR THE MANUFACTURE OF STEEL OF GOOD MACHINABILITY Filed Jan. 4, 1972 s Sheets-Sheet 1 F79. MI

I I DIRECTION I DIRECTION OF OF ROTATION C /;CHIPS DISCHARGE OF THE m STEEL BEING MACHINED TOOL'S CONTACT SURFACE FINISHED SURFACE 0F T L CLEARANCE MACHINED Sg STEEL ll I FLANK L! k VVFFRH T 7 CRATER WEAR DEPTH Aug. 13, 1974 TORU ARAKI H 3,829,312

PROCESS FOR THE MANUFACTURE OF STEEL OF GOOD HACHINABILITY 3 Sheets-Shoot 2 Filed Jan. 4, 1972 Fig. 2

MACHINING SPEED r o I Q m w WW 7 N P w m VM//// w m n 0 w m E W ww V/ w m 0 0 N s o F 6. U E 5 O /v/ /44/45/22,m m m m .........U 0 O. r p 343a???.W g. S o M. wmwmm mm O O O O O O E TT L MN WSW. 2 5 IE5 m w z i 6 wo m w VA F A mw |U| OO S D S C Aug. 13, 1974 TORU ARAKI ETAL 3,829,312

PROCESS FOR THE MANUFACTURE OF STEEL OF GOOD MACBINABILITY 3 Sheets-Shoot 3 Filed Jan. 4, 1972 a & V// /fi// M7//////A m m 0 m V////////////A 0 w mg m W M M MN m M m m n Z M E V///A 0, m w M m m w H AEEV IFQIS K m XZQII u O mO mm MACHINING SPEED (P/min) nited States Patent Cifice Y 3,829,312 Patented Aug. 13, 1974 US. Cl. 75-129 9 Claims ABSTRACT OF THE DISCLOSURE A process for the manufacture of steel capable of being machined at machining speeds ranging from 60 to 300 meters per minute, which comprises deoxidizing a melt of structural killed steel containing 01-06% of carbon, not more than 1.5% of manganese, not more than 0.5% of silicon, 0.004-0.1% of oxygen, and not more than 0.015% of nitrogen, with a titanium-containing oxygen combining agent, the quantity and composition of the titanium-containing combining agent being so selected that the ingot after the deoxidation contains 0.0050.8% of titanium, 0.3-1.5 of manganese, ODDS-0.025% of total oxygen, and not more than 0.5% of silicon, and does not contain more than each 0.010% of soluble aluminum and nitrogen, the balance being iron and impurities; and at least a part of the titanium is present in the ingot as titanium-containing oxide type inclusions.

This invention relates to a process for the manufacture of steel of good machinability, which is well adapted to be machined at such high speeds as from 60 meters/min. to 300 meters/min.

Conventionally known high speed machinable steels include those containing 0.0-8%0.3% of sulfur, those containing 0.1%-0.3% of lead, and those containing 0.1%- 0.3% of both lead and sulfur. Those prior art steels exhibit good machinability, when machined with high speed steel tools at a speed not higher than 100 meters/min.

Recent speeding-up of machine tool operations is remarkable, and consequently hard carbide tools are used more often for machining steel. The machining speed also is increased to such a range as 100-300 meters/min. At such super high speed machining with hard carbide tools the above mentioned sulfur and/or lead-containing steels no longer exhibit satisfactory machinability. With the view to provide a steel showing good machinability at such high machining speed as from 100 to 300 meters/ min., calcium-containing high speed machinable steel has been developed, which is manufactured by deoxidizing steel with Ca--Si alloy, and causing the formation of CaOAl SiO inclusions in such steel (H. Opits: Int. Res. in Product-Engng (1963), page 107). However, in the manufacture of this calcium-deoxidized steel, the variation in the cetilization ratio of the CaSi alloy used as the deoxidizing agent is objectionably great, and it is difiicult to control the composition of CaOAl O 4iO inclusions formed in the steel. Again, because the soluble aluminum content of such calcium-deoxidized steel is low, the steel tends to become coarse-grained, failing to meet the specifications for high quality steel.

Accordingly, the object of the invention is to provide an advantageous process for the manufacture of steel exhibiting good machinability at medium to high speed machining.

Another object of the invention is to provide an advantageous process for the manufacture of steel of excellent machinability, at high machining speeds of not lower than 100 meters/min.

The foregoing objects of the invention can be accomplished by the process of this invention which comprises deoxidizing of the melt of structural killed steel containing 0.1% to 0.6% of carbon, not more than 1.5% of manganese, not more than 0.5% of silicon, 0.004% to 0.1% of oxygen, and not more than 0.015% of nitrogen, with a titanium-containing deoxidizing agent, thequantity and composition of the titanium-containing deoxidation agent being so selected that the ingot after the deoxidation contains 0.005 to 0.08% of titanium, 0.3% to 1.5% of manganese, 0.005% to 0.025% of total oxygen, and no more than 0.5% of silicon, and does not contain more than each 0.010% of soluble aluminum and nitrogen, the balance being iron and impurities; and at least a part of the titanium should be present in the ingot as titaniumcontaining oxide type inclusions.

Thus according to the invention, titanium-containing oxide inclusions are dispersed in the ingot as a deoxidation product by titanium-deoxidizing the melt of structural killed steel. The titanium-deoxidized steel in accordance with this invention exhibits excellent machinability against high speed machining due to the action of the tita nium-containing oxide inclusions therein.

The steel melt to be titanium-deoxidized in the subject process is the structural killed steel, the oxygen content of which has been adjusted to the range of 0.004% to 0.1% by means known per se.

If the oxygen content of the steel melt is less than 0.004%, the quantity of the titanium-containing oxide inclusions formed upon the titanium-deoxidation is decreased, and their tool wear-preventing efiect is lowered. Also, the oxygen content exceeding 0.1% often proves detrimental to the ductility and toughness of the steel material.

The nitrogen content of the molten steel should not exceed 0.015%, because otherwise more titanium nitride, particularly coarse titanium nitride, than titanium oxide is formed, to accelerate abrasion of machining tools.

The steel melt employed in the invention normally contains, like ordinary structural killed steel, 0.1%-0.6% of carbon, not more than 1.5 of manganese,and not more than 0.5% of silicon. The melt steel may further contain not more than 5% of nickel, not more than 2% of chromium, and not more than 0.5 of molybdenum. In the latter case, the formed steel is a nickel-chromiummolybdenum alloy steel.

The type of deoxidizing agent employed in the invention is not critical, as long as it contains titanium, is soluble in the molten steel, i.e., has a melting point not higher than 1650 C., and forms a deoxidation product which is dispersible in the ingot'as the inclusions. Examples of such deoxidizing agent are metal titanium, sponge titanium etc., industrial titanium metals, and ferro-titanium containing no less than 5% of titanium, etc. Industrial titanium alloy scrap meets the purposes of the present invention and is a preferred material because of its ready availability. Examples of industrial titanium alloys are as follows:

As examples of useful ferro-titanium, those of the following compositions may be named.

A suitable quantity of the deoxidizing agent such as pure titanium, industrial titanium alloy, and titanium alloy scrap ranges from, at the maximum, approximately 0.4% to the minimum of approximately 0.01%, converted to titanium.

The above titanium-containing deoxidizing agents may be used in combination with other types of deoxidizing agents. Such other types of deoxidizing agents include for example, Fe-Si, Fe--Mn4i-Zr, Si--Ca alloys; pure Si, Mn, Al, Zr, etc.; Si-Ca alloys being the most preferred. Thus, the combinations of pure titanium with Si-Ca, industrial titanium alloy with Si-Ca, and ferro-titanium with Si-Ca, are the most occasionally employed.

A suitable quantity for use of the titanium containing deoxidizing agent differs depending on the composition of the specific deoxidizing agent, which can be easily determined from the required titanium content of the product ingot and the composition of the deoxidizing agent.

The titanium-deoxidized steel produced by the subject process contains, as the essential components:

titanium: 0.0050.08% manganese: 03-15% total oxygen: 0.0050.02% and silicon: not more than 0.5%

Titanium is the most important component in the steel produced by this invention, because it forms the oxide type inclusions. When more than the above-specified amount of titanium is present in the steel, the excessive titanium reacts with sulfur (if present), nitrogen (if present) and carbon in the steel, to form such inclusions as TiS, TiN, and TiC. Such inclusions which occasionally grow coarse are detrimental to the properties of the steel. Furthermore, such inclusions also accelerate abrasion of hard carbide tools. On the other hand, if the titanium content is less than the above-given lower limit, the amount of the titanium inclusions in the steel is reduced, and the intended good machinability cannot be obtained.

Manganese serves as a component of the titanium-containing oxide inclusions, and therefore the presence therepoint of inclusions, and imparts to the inclusions appropriate ductility at the machining time and prevents wear of tools. When the manganese content of the steel is less than the above-specified range, the inclusions will have excessively high melting point and insufiicient ductility.

containing silicate, which possess strong affinity to the titanium carbide and p-phase in hard carbide tools employed for machining. Consequently, during the machining a titanium-containing oxide adhesive layer is formed at the contact surface between the chip and the machining tool, as well as between the material under machining and the tool. This layer prevents the chips and the material being machined from direct attrition of the tool surface, and also prevents deterioration of tool properties by diffusion of tool components, for example, carbon, tungsten, cobalt, etc. into the chips due to the high temperature at the contact surface. Those actions of the layer are considered to inhibit the total wear.

The titanium-containing oxide type inclusions should be present in the steel in such a quantity that the titanium content of the inclusions corresponds to at least 5% of the total titanium in the inclusions.

In the steel, oxygen is present in the form of the oxidetype inclusions.

The ingot which has been titanium-deoxidized in accordance with this invention preferably contains nitrogen in an amount not exceeding 0.010%. If more nitrogen is present, the titanium in the deoxidizing agent is likely to be consumed to form titanium nitride, and consequently the amount of oxide type inclusions is reduced to achieve only insufficient improvement in the machinability of the steel product.

Absence of excess aluminum in the deoxidized ingot is again preferred but, if present, its content should not be more than 0.010%. Furthermore, the aluminum should be soluble. Soluble aluminum not exceeding 0.010% of the ingot may serve as a grain controller if aluminum is added after deoxidation and have no detrimental effect on the products machinability. However, when more than 0.010% aluminum is present, it serves to form Al-Orich inclusions of little TiO content which are objectionably hard, or forms refractory A1 0 The hard or refractory inclusions are likely to cause tool abrasion.

The process of this invention is applicable also to nickelchromium-molybdenum steel, besides ordinary structural killed steel, to impart good machinability to the products under high speed machining.

The molten steel employable in the invention contains sulfur in the quantity of a normal impurities level. However, addition of sulfur or a sulfide raising the sulfur content of the deoxidized melt up to 0.1% will further improve the machinability of the product steel at such relatively low speed machining as to '60 meters/min. As the sulfur compounds, FeS FeS, etc., may be used, but sulfur itself is most suitable for the above purpose. Similar improvement may also be obtained by adding to the deoxidized melt such metals as selenium, tellurium or compounds thereof, to cause the presence of a selenide or telluride in the steel.

According to the subject process the deoxidation of melt steel with a titanium-containing deoxidizing agent can be performed by optional known means of adding the deoxidizing agent to the molten steel.

Hereinafter the subject process will be further explained, with reference to the attached drawings and working Examples.

The drawings of FIG. 1 show, in simplified manner, the machining state, in which (A) is an enlarged three-dimensional view of the titanium-deoxidized steel of this invention under machining at a speed of meters/min, and (B) is an enlarged three-dimensional view of the steel complex-deoxidized with aluminum and silicon, under machining at a speed of again 150 meters/min.

FIG. 2 illustrates the effects of the various steels on the tool wear, the steels having been deoxidized respectively with aluminum, titanium, and silicon, after the adjustment of sulfur and oxygen contents in the molten steel.

FIG. 3 shows the state of tool wear (flank wear width) in machining the steel which is formed by deoxidizing steel melt with aluminum and titanium, with the correlation of machining speed with machining distance.

EXAMPLE 1 6 taining oxides showed a tendency to peel off the titaniumcontaining oxide layer on the contact surface of the machining tool, at speeds not exceeding 200 meters/min, which phenomenon Was not observed with the oxide layer in the steel deoxidized with titanium alone, during the machining at similar speed range. However, after the machining speed was raised to 200 meters/min. and higher, high temperatures under which even the AlgO -containing oxide started to adhere onto the tool surface were reached, and the volume of oxide layer started to increase. On the other hand, the tools clearance surfacefailed to attain the TABLE 1.THE OXIDIZED LAYER AREA ON TOOL CONIgASCIRFACE AND WEAR WIDTH ON THE TOOL CLEARANCE Length of oxidized layer Deoxidatlon agent 75 100 150 200 width (mm) Flank wear Steel composition (percent) mJmin. mJmin. m./min. m./min.

R n Amount 275 Total Solu- No. Type (percent) Tool-chips contact length (percent) mJmin. m./min. Ti Mn 0 Si ble Al N 3 10 0. 05 0. 08 0. 001 0. 43 0. 010 0. 18 0. 001' 0. 0076 8 43 0. 05 0. 07 0. 001 0. 44 0. 008 0. 15 0. 003 0. 0075 0. 67 28 0. 02 0. 04 0. 010 0. 43 0. 015 0. 16 0. 001 0. 0070 Metal TL.-. Ti 0. 03 4 d 38 56 46 48 0. 07 0. 07 0. 026 0. 0. 008 0. l9 0. 008 0. 0079 itt"- ss-s Meta 1 5 and 50 64 84 0. 03 0. 04 0. 020 0. 46 0. 014 0. 18 0. 008 0.0087 Ca-Si alloy. Ga 0.05 p

No'rE.-Machining condition:

Tool: ISO rating P10 [TiC (+TaC)28%1.

Depth of out: 1.5 mm. Feed: 0.3 mm./rev. Machining distance: 500 m.

From the above table, it can be understood that, in the runs using 0.03% of titanium metal as the deoxidizing agent, and that using 0.03% of titanium metal and 0.05% (Ca) of Ca--Si alloy as the compound deoxidizing agent, according to the present invention, the length of the oxide layer is greater and the flank wear width is less, compared with the control runs using deoxidizing agents outside the scope of this invention, i.e., Si-Mn and aluminum metal, and that using a compound deoxidizing agent containing 0.03% of titanium metal and 0.03% of aluminum metal (the aluminum content exceeding the critical upper limit of 0.010%). Concerning the above results, the following further explanations may be ofierred.

In the SiMn-deoxidized steel, Si0 -containing inclusions which were hardly deformable even during the hot forging were dispersed, which increased the flank Wear during the machining by their abrasive action, in a similar manner to the Al O -containing inclusions formed in the aluminum-deoxidized steel.

50 In contrast, in the titanium-deoxidized steel only one In the complex-deoxidized steel with titanium and aluminum, roughly two types of oxides-containing inclusions, i.e., MnO-TiOxMnO-Al O -SiO and A1 0 were formed. During machining of such steel, the Al O -conoxides produced the oxide layer on the tools contact surface even during the medium speed machining, effectively inhibiting the progress of flank wear. Under the high speed machining at 200 meters/min. and above still suflicient volume of the oxide layer was present on the contact surface, and the progress of crater and flank wear was inhibited. The last steel also had the advantage that its deoxidation could be effectively controlled.

EXAMPLE 2 One-hundred kg. of the same steel as employed as the starting material in Example 1 were melted in a high frequency induction furnace, and various deoxidizing agents were added to the melt in the similar manner to Example 1. The deoxidation was eifected with silicon metal, aluminum metal, and ferro-titanium of low carbon content (FTi Ll of HS rating), each used singly at various amounts in different runs. The ingots obtained were hot forged, normalized, and subjected to the machining test. The machining conditions were identical with those of the test given in Example 1.

The type and amount of deoxidizing agent, adjusted oxygen and sulfur contents, and the steel compositions, of each run were as shown in Table 2 below, and the test results were as shown in FIG. 2.

Aimed components.

The sulfur contents of the samples of 'Run Nos. 7 and 8 were adjusted on purpose, and also the sulfur contents and oxygen contents of Run Nos. 9 and samples were artificially adjusted. The adjustments were effected by addition of sulfur and iron oxide to the molten steels.

The chemical analysis values of Run Nos. 4, 5, and 6 samples were: sulfur content, around 0.015% in all runs, and oxygen content, in the vicinity of 0.01%, again in all runs. The steel was deoxidized, respectively, with silicon, aluminum, and titanium, in those runs. At the machining speeds ranging from 100-230 meters/min., the tools wear width with the titanium-deoxidized steel was only one-half that with the aluminum-deoxidized steel, and from one-half to one-third that with the silicon-deoxidized steel.

The chemical analysis values of Run Nos. 7 and 8 samples were: Sulfur content, around 0.01%. The steel was deoxidized, respectively, with aluminum and titanium in those runs. At the same machining speed range as in the preceding runs the wear width of the tool observed in the titanium-deoxidized steel machining was from one-half to one-third that in the aluminum-deoxidized steel machining.

The Run Nos. 9 and 10 samples both had a sulfur content around 0.023%, and the oxygen content around 0.015%. They were deoxidized, respectively, with alumium and titanium. The tools wear width in Run No. 10 was approximately one-third to one-fourth that in Run No. 9, under identical machining conditions.

Comparing Run No. 6 with Run No. 8, it could be understood that the increase in sulfide content of the steel within the range of 0.1% favorably affects the machinability of titanium-deoxidized steel.

Also from the comparison of Run No. 8 with Run No. 10, it could be understood that the increase in oxygen content favorably affects the machinability of titanium-deoxidized steel under high speed machining.

EXAMPLE 3 Two (2) tons of the same steel as employed as the starting material in Example 1 were melted in an Heroult furnace. The melt was deoxidized in a pouring ladle, respectively with aluminum metal and titanium alloy scrap (Ti-7-Al-2 alloy) used as the deoxidation agent, each producing 1 ton of ingot. The ingots were hot forged, normalized and subjected to the machinability test.

The machining conditions were identical with those in the test effected in Example 1. The tools wear widths resulting from the machining of the aluminumdeoxidized steel and titanium-deoxidized steel at various machining speeds were as compared in FIG. 3.

The type and amount of deoxidizing agent and the steel composition in each Run were as shown in Table 3 below.

ing. Thus it was confirmed that the good machinability of the titanium-deoxidized steel of the invention is still more conspicuous in longer machining duration.

EXAMPLE 4 Steels of the same composition as that employed in Example 2, except that they contained, respectively, 2% of nickel, 1% chromium, 0.3% of molybdenum, and all of those components together at respectively specified amounts, were melted in the similar manner to Example 2. The four types of melt steels were titanium-deoxidized similarly to Run No. 5 of Example 2 and the resulting ingots were hot forged and normalized.

The configurations of the titanium-containing oxide type inclusions in those samples as well as in Run No. 6 sample of Example 2 were examined with an optical microscope. The results were as shown in Table 4 below.

TABLE 4 Ti Elon- Run content getion, No. Starting steel (percent) a b" e/b 6.- Base (S35) 0. 015 12. 5 1. 1 11. 4 13. Base (S35) plus Ni, 2% 0.015 16. 5 1. 2 13. 8 14. Base (S35) plus Cr, 1% 0. 015 14. 0 0. 9 15. 6 15---. Base (S35) plus M0, 0.3 0. 015 15. 6 1. 0 15. 6 16.--. Base (S35) plus Ni, 2%; Cr, 1%; 0. 015 11.0 0. 8 13. 8

a=statistically determined length of inclusions paralleling the forged surface t).

b=Statistically determined thickness of inclusions perpendicular to the forged surface (n).

In all samples, the forging ratio was 16. From Table 4 above, it can be understood that the hot elongations of the itanium-containing oxide type inclusions in the steels of Runs Nos. 13 through 16 were slightly higher than that of the base steel containing none of the additional metal element (Run No. 6). This fact indicates that the former steels exhibit good plasticity under high speed machining, during which the tool surface tempeature reaches to substantially the same level as that of the hot forging temperature of the sample steels. Thus, low alloy steels containing such additional metal element or elements can be imparted with equally good, or even better, machinability than that of titanium-deoxidized S350 steel, for high speed machining, when similarly titanium-deoxidized.

We claim:

1. A process for the manufacture of steel capable of being machined at machining speeds ranging from to 300 meters per minute, which comprises providing a melt of structural killed steel containing 0.l-0.6% of carbon, not more than 1.5% of manganese, not more than 0.5% of silicon, 0.0040.1% of oxygen, and not more than 0.015% of nitrogen, adding about 0.01-0.4% of titanium as a titanium-containing oxygen combining agent, cooling the melt and manufacturing the killed steel ingots, the

ingot after solidification containing 0.005-0.08% of titanium, 0.3-1.5% of manganese, 0.005-0.025% of total oxygen, and not more than 0.5% of silicon, and does not contain more than each 0.010% of soluble aluminum and nitrogen, the balance being iron and impurities; and at least 5% of the titanium is present in the ingot as complex oxide inclusions of titanium and manganese.

2. The process of Claim 1, wherein the melt of the structural killed steel as well as the ingot after solidification further contain not more than 5% of nickel, not more than 2% of chromium, and not more than 0.5 of molybdenum.

3. The process of Claim 1, wherein sulfur, selenium, tellurium or mixture thereof is added to the steel melt, so that the ingot after solidification should further contain not more than 0.1% of sulfur, selenium, tellurium or mixture thereof.

4. The process of Claim 1, wherein said titanium-containing oxygen combining agent is pure titanium.

5. The process of Claim 1, wherein said titanium-containing oxygen combining agent is ferro-titanium containing not less than of titanium.

6. The process of Claim 1, wherein said titanium containing oxygen combining agent is titanium alloy scrap.

7. The process of Claim 1, wherein said titanium-containing oxygen combining agent is a mixture of pure titanium with a calcium-containing alloy.

8. The process of Claim 1, wherein said titanium-containing oxygen combining agent is a mixture of alloy containing not less than 5% of titanium and a calcium-containing alloy.

9. The process of Claim 1, wherein said titanium-containing oxygen combining agent is a mixture of titanium alloy scrap with a calcium-containing alloy.

References Cited UNITED STATES PATENTS 3,575,695 4/1971 Miyashita -57 1,959,399 5/1934 Whiteley 75-53 3,644,144 2/1972 Timofeev 148-26 3,405,005 10/1968 Feldman 148-26 3,554,792 1/ 1971 Johnson 148-2'6 3,645,782 2/ 1972 Johnson 148-26 2,915,386 12/1959 Strauss 75-53 3,467,167 9/1969 Mahin 75-58 L. DEWAYNE RUTLEDGE, Primary Examiner P. D. ROSENBERG, Assistant Examiner US. Cl. X.R. 75-53, 57

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