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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten

Definitions

• One object of my invention is to provide a steel that is capable of being hardened to a relatively high hardness level, such as Rockwell C 64 or 65.
• a relatively high hardness level such as Rockwell C 64 or 65.
• prior to my invention it has been generally believed that such hardnesses could be obtained dependably with high temperature tempering only in the relatively expensive high-speed tool steels, steels containing molybdenum and/ or tungsten in substantial quantities, e.g., having a molybdenum equivalent (content of molybdenum plus one half the content of tungsten) in the range of 4.5 to percent, usually at least 7 percent.
• Certain hot-work steels are known that cost about half as much as the above-mentioned highspeed tool steels and can be heat-treated by secondaryhardening to a maximum achievable hardness of about Rockwell C 59, but it is generally accepted in the tool steel industry that such steels are not suitable for the applications mentioned above. Accordingly, it is one object of my invention to provide a steel suitable for the above-mentioned cutting applications, yet about one-half the cost of the high-speed tool steels.
• tool steels for knives, such as in high-temperature shears, slitters, and cold-metal shears.
• knives such as in high-temperature shears, slitters, and cold-metal shears.
• tool steels hardened to Rockwell C 58 to 60.
• the versatile new steel of the present invention competes in this respect with a large number of hotwork die steels and high-temperature alloys.
• Another object of my invention is to provide a steel exhibiting the properties indicated above, along with the capability of being sulfurized to improve free-machining properties.
• Still another object of my invention is to provide a steel having, in combination with the above-mentioned properties, the ability to be rolled to the form of sheet or strip, which may be subsequently treated to high strength for such applications as hack saw blades and band-saw strip.
• the invention consists in adding small amounts of tungsten, such as about 0.20 percent, to semi-high-speed steel, particularly such steel containing under 1.5 percent vanadium and over about 1.5 percent silicon, to avoid grain coarsening of the steel during austenitization and the consequent embrittlement that has hitherto prevented semi-high-speed steel from finding extensive use.
• tungsten such as about 0.20 percent
• I provide a semi-high-speed steel with a critical and substantial content of silicon, about 2 percent, sufficient to improve the as-tempered hardness but not enough to cause grain coarsening.
• the invention comprises steels of the character above-indicated with small additions of titanium and/or sulfur, for purposes hereinafter stated.
• the steel exhibit substantial wear resistance, and accordingly it is highly desirable that the steel contain at least about 0.75 percent, preferably 1.0 percent, of vanadium, since lower wear resistance is observed if the vanadium content is less.
• the steel becomes rather difficult to grind if the vanadium content exceeds the upper limits specified above, but the board idea of adding tungsten in small amounts for grain refinement is applicable with steels containing up to about 2 percent of vanadium.
• Steels containing more than 2 percent vanadium usually have sufi'lcient alloy carbides that the formation of coarse grains upon austenitization is not a serious problem.
• the secondary hardness (hardness after quenching and tempering) is low.
• my invention is applicable with steels containing as much as 5 percent of molybdenum, but with molybdenum contents greater than about 3 percent, the benefits obtained do not usually justify the added cost.
• titanium are not absolutely necessary, it is preferred to add about 0.20 percent of titanium or slightly more, to add to the wear resistance and reinforce the resistance to the formation of coarse grain structure upon austenitization. It is also preferred, however, not to add more than the upper limit of titanium specified above, because at that point the addition of the titanium becomes difficult to control, and the addition of further quantities is without substantial benefit to the properties justifying theaddition. For bearing applications, a vacuum-melted titanium-free steel is preferred.
• Usual steelmaking impurities or tramp elements such as sulfur, phosphorous, nickel, copper, tin, arsenic, hydrogen, etc. may be present in usual amounts not inconsistent with good steelmaking practice, and otherwise the balance of the steel is iron.
• the heat treatment to be used with the steel of this invention will depend upon a variety of factors, including (1) the intended use of the steel, (2) the section size, (3) the hardness to be de veloped and (4) the exact chemical composition of the steel.
• the steel is heat-treatable to maximum hardness by using an austenitizing temperature in the range about 1950" F. to '2050 F., preferably about 2000 F., followed by a double or triple temper, about 2+2 hours or 2+2+2 hours, at a temperature of about 950 F. to 1025 F., preferably about 975 F. or 1000 F.
• higher austenitizing temperatures such as 2075 F.
• the response to tempering of a steel in accordance with my invention is indicated in Table I below.
• the steel had the following chemical composition: 1.12 percent carbon,-0.3 percent manganese, 1.95 percent silicon, 3.87 percent chrominum, 1.09 percent vanadium, 0.30 percent tungsten, 2.59 percent molybdenum, 0.15 percent titanium and the balance iron except for incidental impurities.
• Laboratory-size speciments (about inch square by /2 inch long) were prepared from a 2,000-pound air induction-furnace heat of the steel. The specimens were austenitized for four minutes at the indicated temperature, air-cooled to room temperature, tested for hardness and grain size, tempered as indicated, and again tested for hardness.
• the as-tempered hardnesses at a given austenitizing temperature are essentially the same, whether the steel is aircooled (as is usual for such applications as rolls or threadrolling dies) or oil-quenched (as is usual for cutting tools).
• the steel of this invention performs satisfactorily in many cutting applications not so stringent as to require the use of high-speed steel.
• Machining AISI Type 4340 steel at Rockwell C 20 at 70 surface feet per minute, other conditions the same, the tool exhibited a life of 37.3 minutes.
• my new steel is capable, when properly heat-treated, of developing the high hardenss required (about Rockwell C 63 to 65) for use in cutting-tool applications requiring less than the very high hardnesses (R 66 and over) achievable only with the expensive high-speed steels.
• My new steel also meets the requirements of fine grain size, freedom from retained austenite, and adequate impact strength, and as shown above, it affords in certain applications a tool life sufficient to reduce the cost of certain cutting operations where conventional high-speed steels have hitherto been used.
• My new steel is also useful for applications requiring a steel exhibiting a high compressive yield strength, such as about 400,000 p.s.i. or more at 0.2 percent offset, when heat-treated to a hardness in the range Rockwell C 62 to 64. Specimens 0.500 inch in diameter by 1.500 inch long were prepared, heat-treated as indicated below, and tested, the results being presented in Table III.
• the observed yield-strength values are good, greatly exceeding values of 240,000 to 340,000 p.s.i. obtained with the air-hardening AISI Type A2 and D2 steels, respectively, heat-treated to about Rockwell C 63 in the manner conventional for such steels, and approaching the values of 420,000 and 413,000 p.s.i. for conventionally hardened AISI Types M1 and M2 steels, respectively.
• This invention 63 5 AISI Type M-ZH AISI Type D2 AISI Type M-l- AISI Type A-2- :ooooueo ocozroo Tests were conducted to investigate the machinability of the steel of this invention, both plain and sulfurized to improve machinability, in comparison with that of other high-speed and air-hardening steels.
• the test specimens were annealed bars of the steel inch thick, and the time required to penetrate the steel At-inch using a 4-inch drill, ISO-pound thrust, 460 r.p.m., was observed in each case.
• AISI Type M steel was taken as a standard, and in each case the observed time was divided into the time required for penetration of Type M2 steel and then multiplied by 100 to afford a Machinability Rating.
• the semi-high-speed steels known prior to this invention have the drawback that to avoid undesirable .grain coarsening during austenitizing, they must be austenitize-d at temperatures below those which yield the highest as-tempered hardnesses.
• Roberts et 'al. attribute the rapid grain coarsening of such steels to their having a lower alloy carbide content than the true high-speed steels, and they suggest no way of overcoming this disadvantage, which has prevented known semi-high-speed 8 steels from having broad usefulness.
• a further unexpected teaching is that contrary to the general belief that higher silicon contents in such steels would be detrimental as respects cleanliness and tendency to decarburize and without compensating benefits, I have discovered that a tungstentreated semi-hi-gh-speed steel can be improved in respect to hardness attainable after tempering by the addition of a substantial amount of silicon, such as 1.5 to 2.5 percent.
• semi-high-speed steel will be understood as meaning a steel having all the following characteristics:
• Tungsten More than 0.15% and up to 0.50%.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Articles (AREA)
• Powder Metallurgy (AREA)

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Cited By (18)

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Citations (2)

• 1964
  • 1964-04-30 US US363980A patent/US3295966A/en not_active Expired - Lifetime
• 1965
  • 1965-04-14 GB GB16104/65A patent/GB1088317A/en not_active Expired
  • 1965-04-27 ES ES0312296A patent/ES312296A1/es not_active Expired

Patent Citations (2)

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