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
  • C22C38/02—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
• • 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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron

Definitions

• the present invention relates to a boron steel grade according to the introductory part of the attached claim 1.
• the invention also relates to a shaft made of boron steel according to the introductory part of the attached claim 6.
• Low-alloy boron steel is used inter alia for shafts which by induction hardening of a surface zone are provided with increased fatigue and static strength but also a wear-resistant surface layer.
• Induction hardening of this kind causes in the surface zone compressive stresses which counteract the occurrence of fatigue cracks in this surface zone and thereby have a positive effect on fatigue strength.
• the relationship between the magnitude of the compressive stresses and the fatigue strength is unambiguous. The greater the compressive stresses, the higher the fatigue strength.
• the compressive stresses in the surface zone are balanced by tensile stresses in central portions (the core).
• Tensile stresses in the core do not normally affect strength, since the level of stresses arising from imposed loads is low in specifically the core.
• stationary induction hardening also called single-shot hardening, i.e. a hardening operation where the total volume to be hardened is first heated to the hardening temperature and is thereafter cooled immediately or after a certain delay
• the compressive stresses in the surface zone become particularly high and the fatigue strength becomes better than is achieved by progressive induction hardening where heating and subsequent cooling are effected during continuous mutual movement between inductor/cooling shower and the workpiece which is to be hardened.
• the stresses, not least the tensile stresses in the core in the case of stationary induction hardening may become so great during the actual hardening process that cracks (central cracks) occur in the core.
• a typical and representative ratio is about 20,000 load cycles at 20 kNm torsional fatigue for progressive induction hardening as against about 80,000 load cycles at 20 kNm torsional fatigue for stationary induction hardening.
• the object of the present invention is to provide low-alloy boron steel which can be induction-hardened statically without central cracks occurring.
• Fig. 1 depicts a compilation in tabular form concerning Hie incidence of cracks as a function of composition, where primarily the molybdenum and nickel contents clearly vary
• Fig. 2 depicts in diagram form the incidence of cracks as a function of molybdenum and nickel contents
• FIG. 3 depicts in an axial section a driveshaft for which experiments with steel grades according to the present invention were carried out.
• the steel grades according to the invention are low-allow boron steel, and steel grades according to the invention with the range of composition according to the invention appear in Table 1 together with a corresponding known steel grade.
• Carbon which has a substantial influence on induction hardening characteristics, is present in contents of between 0.30 and 0.50%, resulting in desired strength after hardening. A carbon content amounting to 0.38-0.45% is preferred.
• Silicon is present in an amount of 0.15-0.40%, preferably more than 0.15% up to 0.40%, and is primarily added as a carrier for other alloying elements, but also has some strengthening effect.
• Manganese is present in an amount of 1.10 up to 1.50%, preferably more than 1.10% up to 1.50%, and has strengthening effects partly by increasing the hardenability, which, where there is great hardness depth, may affect the hardness depth in induction hardening. Manganese is also added in order to bind sulphur which would otherwise have adverse effects on impact strength.
• the phosphorus content, ⁇ 0.035%, has to be kept low to prevent brittleness and hardness cracks due to grain boundary weakening.
• MnS manganese sulphide
• Chrome is present in an amount ⁇ 0.5%, preferably more than 0.2% and less than 0.5%. Chrome increases hardenability and reduces the risk of decarburisation.
• Molybdenum in an amount of 0.030% and up to 0.15% has according to the invention proved to be able, together with certain contents of nickel as below, to prevent the occurrence of central cracks, inter alia in static induction hardening.
• the molybdenum content is normally not even specified for boron steel of this kind. It is also likely that such an addition of molybdenum in combination with nickel also reduces the risk of hardness cracks in other grades.
• Molybdenum in a quantity of 0.05 up to 0.15% is preferred.
• Nickel in an amount of 0.15% up to 0.40% has proved, together with molybdenum as above, according to the invention, to be able to prevent the occurrence of central cracks, inter alia in static induction hardening.
• the nickel content is likewise not usually specified.
• Nickel is regarded as an impurity. It is also likely that such an addition of molybdenum in combination with nickel also reduces the risk of hardness cracks in other grades.
• Nickel in an amount of more than 0.20 up to 0.40% is preferred.
• Titanium in certain contents is needed for keeping a certain content of boron in solid solution in the steel with a view to improving the hardening characteristics. Titanium should therefore be present in an amount of 0.020-0.050%. Aluminium is a deoxidant and is therefore present in low contents. Aluminium impairs the fatigue strength by forming aluminium oxide, and aluminium contents should be kept ⁇ 0.050%.
• the desirable content in solid solution is at least 0.0005%, while the total content should be limited to less than 0.004%.
• molybdenum and nickel constitute impurities which are not even specified in a standard composition.
• the composition ranges for molybdenum and nickel which result in the crack-eliminating effect according to the invention nevertheless comprise contents which clearly exceed prevailing impurity levels.
• Fig. 1 shows the incidence of cracks on a large number of driveshafts from a large number of charges with mutual varying chemical composition
• "No.” denotes the number of shafts in which cracks were detected
• “Tot.” the total number of shafts examined for each steel charge
• “Incid. %” the ratio between "No.” and “Tot”, i.e. the proportion of shafts with detected cracks.
• Fig. 2 shows the incidence of cracks, "Crack Incidence %", as a function of molybdenum content and nickel content, although for manufacturing reasons the effect of molybdenum content or nickel content would be isolated.
• the minimum contents indicated have been adjusted by a small margin to the respective content combinations of 0.035% molybdenum/0.167% nickel and 0.038 molybdenum/0.188% nickel, which resulted in no cracks.
• the preferred minimum contents have been provided with a margin upwards relative to the minimum contents extracted.
• An upper content limit has also been set for both molybdenum and nickel. This is partly for cost reasons and for preventing disadvantages, e.g. impaired machinability, which occur at increasing molybdenum and nickel contents.
• Scania boron steel TB 1639 as a low-alloy material is specified in Table 1 below.
• Low-alloy compositions are usually stated without contents of molybdenum and nickel, which substances are to be regarded as common impurities.
• a general composition according to the invention, a preferred composition and a detailed composition which in experiments resulted in lack of cracks are also specified.
• Table 1 Composition of boron steel according to the state of the art and the invention.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Articles (AREA)
• Shafts, Cranks, Connecting Bars, And Related Bearings (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=35653953

Family Applications (1)

Country Status (6)

Families Citing this family (1)

Citations (5)

Family Cites Families (4)

• 2005
  • 2005-04-12 SE SE0500812A patent/SE527221C2/sv not_active IP Right Cessation
• 2006
  • 2006-04-06 EP EP06717138A patent/EP1871917A1/en not_active Withdrawn
  • 2006-04-06 CN CN2006800116181A patent/CN101155941B/zh not_active Expired - Fee Related
  • 2006-04-06 WO PCT/SE2006/050059 patent/WO2006110100A1/en active Application Filing
  • 2006-04-06 BR BRPI0608675-6A patent/BRPI0608675A2/pt not_active IP Right Cessation
  • 2006-04-06 JP JP2008506416A patent/JP2008537982A/ja active Pending

Patent Citations (5)

Non-Patent Citations (4)

Also Published As

Similar Documents

Legal Events