US3454432A - Process for strengthening a low carbon high strength steel - Google Patents

Process for strengthening a low carbon high strength steel Download PDF

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Publication number
US3454432A
US3454432A US546764A US3454432DA US3454432A US 3454432 A US3454432 A US 3454432A US 546764 A US546764 A US 546764A US 3454432D A US3454432D A US 3454432DA US 3454432 A US3454432 A US 3454432A
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steel
strain
high strength
low carbon
strengthening
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US546764A
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English (en)
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Chiaki Asada
Toshiyuki Watanabe
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Daido Steel Co Ltd
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Daido Steel Co Ltd
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    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment

Definitions

  • This invention relates to a novel process for strengthening a low carbon high strength steel to obtain the strengthened steel of which yield point or proof stress is equal to or higher than that of a medium carbon high strength steel, without decreasing the original toughness and ductility of the low carbon high strength steel.
  • this invention relates to a novel process for strengthening a low carbon high strength steel compris-l ing 0.10 to 0.25% by weight of carbon, not more than 7% by Weight in total of at least one kind of metal selected from the group consisting of silicon, manganese, nickel, chromium, molybdenum, vanadium, titanium and the alloying elements, and, the balance, iron including incidental impurities and having the martensitic structure as quenched or as tempered at a temperature not higher than 350 C.
  • the low carbon high strength steel it is more desirable for the low carbon high strength steel to contain at least two kids of metals than to contain only one kind of metal selected from said group, from the view-point of the hardenabjllity of said starting steel as well as the mechanical properties and production cost of a strengthened steel to be obtai'ed from said starting steel.
  • the steel produced by the process of this invention can be used as a material of, for example, bolts, gears and axles.
  • a common structural steel there are two different ways to allow a common structural steel to have more than 100 kgJmm.2 of tensile strength.
  • One way is to make a sorbitic steel of the common structural steel by adding thereto elements such as molybdenum, vanadium andthe like which will provide tempering resistance and secondary hardening, and the other one is to make a tempered martensitic steel of a low-alloy or medium-alloy 'steel by tempering at a lower temperature. It is generally known that such a tempered martensitic steelhaving a specially lower carbon content has excellent toughness 'and ductility even when the steel is high in strength.
  • a low carbon martensitic steel may be comparatively easily given therein a strain uniformly, because said steel does not show its own definite yielding phenomena like an austenite steel.
  • An object of this invention is to provide a novel strengthened steel product having an improved yield point or proof stress without any decrease in the usual toughness and ductility of a low carbon martensitic steel.
  • Another object of this invention is to provide a novel process for strengthening a low carbon high strength steel to produce the novel strengthened steel.
  • FIG. 1 shows relations between mechanical properties and carbon contents of a low carbon high strength steel such as a 0.8 Si-1.2 Mn-l.5 Cr steel;
  • FIG. 2 relations between mechanical properties and tempering temperatures of the said Si-Mn-Cr steel
  • FIG. 3 relations between mechanical properties and low-temperature tempering times of the steel in which a permanent strain has been created after the quenching of the steel;
  • FIG. 4 relations between notch strength ratios and the permanent strains of the same steel
  • FIG. 5 relations between mechanical properties and not more than 1% permanent strains of the steel further tempered
  • FIG. 6 relations between hardness, Charpy impact 3 values and permanent strains of the same steel as represented in FIG. 6;
  • FIG. 7 the stress-strain diagram of the same steel at different strain levels.
  • FIG. 8 relations between mechanical properties and not more than permanent strains of the same steel.
  • FIGS. 3-8 are specially intended for the illustration of the effects of this invention.
  • FIG. 1 in which there are shown relations ⁇ between the mechanical properties and carbon contents of 0.8 Si-1.2 Mn-l.5 Cr steel (as one example of low carbon high strength steel) which has been tempered at 300 C. after the oil quenching at 880 C. (880 C. O.Q.), the tensile strength and proof stress of the steel remarkably increase in a linear way and the yield ratio of the steel also increases with the increase of the carbon content thereof, While the yield ratio will decrease to less than 0.8 in lower carbon range in which the toughness (elongation and impact value) of the steel may still be kept at a satisfactory level.
  • FIG. 2 in which relations between the mechanical properties and tempering temperatures of said Si-Mn-Cr steel are shown by curves indicates that, in the same way as in FIG. 1, the proof stress of the steel increases very sharply as the tempering temperature rises up, reaches the maximal value of about 125 kg./mm.2 at about 300 C. and then begins to decrease gradually as the tempering temperature rises.
  • the yield ratio gradually increases with the rising of the tempering temperature, While the yield ratio obtainable in the range of tempering temperatures (275-325 C.) is no more than a value of 0.80-083, which is somewhat lower than the yield ratio 0.9 of a tempered sorbitic steel obtained by tempering it at about 500 C.
  • a low carbon high strength steel (0.19 C-0.76 Si-1.29 Mn1.52 Cr*0.08 Ti), similar in composition to the preceding one, which has been tempered at 200 C. for not more than 5 hours after the creation of 0.2% permanent strain in the steel by tension at ambient temperature will be remarkably improved in 0.2% offset proof stress and U notch Charpy impact value simultaneously with tensile strength, reduction of area and elongation being left unchanged, as compared with one which has been treated in the same way as the above except for the creation of the permanent strain.
  • This fact therefore, means the yield ratio of the former steel has been strikingly enhanced.
  • test pieces each having a notch of stress concentration factor 4.0 Were subjected to a tension test after they had given not more than 1.0% permanent strain in order to investigate the effect of the notch on a strain aging.
  • the results are that the 0.2% proof stress is remarkably enhanced and that the notch strength ratio can be kept at a level as high as about 1.3.
  • FIG. 7 The effect of this invention is clearly seen in FIG. 7 in which the stress-strain diagrams of the same steel at different strain levels are represented.
  • test pieces for tension test subjected to the treatments of this invention were so broken that the fracture looked like a shallow cup in the same way as in a sorbite steel. This means that the pieces will not easily cause brittle fracture in spite of their high yield ratio.
  • the magnitude of a permanent strain given in a steel should be a value of 3.0% and below, in order to obtain a satisfactory effect of the strain on the steel; while a permanent strain of a value of more than 3% is not desirable, because such strain will be far less effective to increase yield point and will, on the contrary, decrease toughness and ductility as well as impact value.
  • O.Q. Oil quenching
  • Tempel-ing time (hr.) 0 0. 5 1. 0 1. 5 3.0 5.0
  • Group A (Strain given) 142. 8 135. 7 133. 0 132. 2 Group B (No strain given) 97. 7 114.3 113. 5 115. 2 116. 5 118. 0
  • Tempering time (hr.) 0 0. 5 1. 0 1. 5 3. 0 5.0

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Articles (AREA)
US546764A 1965-05-07 1966-05-02 Process for strengthening a low carbon high strength steel Expired - Lifetime US3454432A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP40026369A JPS5112446B1 (es) 1965-05-07 1965-05-07

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US3454432A true US3454432A (en) 1969-07-08

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US (1) US3454432A (es)
JP (1) JPS5112446B1 (es)
DE (1) DE1508383B1 (es)
GB (1) GB1115584A (es)

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3388011A (en) * 1965-10-08 1968-06-11 Atomic Energy Commission Usa Process for the production of high strength steels

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE566660C (de) * 1926-06-05 1932-12-22 Wilhelm Puengel Dr Ing Verfahren zur Verbesserung der Festigkeitseigenschaften von kaltgezogenen Stahldraehten
DE884955C (de) * 1945-01-03 1953-07-30 Oberhuetten Vereinigte Obersch Verfahren und Vorrichtung zur Herstellung von Stabstahl

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3388011A (en) * 1965-10-08 1968-06-11 Atomic Energy Commission Usa Process for the production of high strength steels

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DE1508383B1 (de) 1970-04-16
JPS5112446B1 (es) 1976-04-20
GB1115584A (en) 1968-05-29

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