CA2848823A1

CA2848823A1 - Hardening steel for lifting, fastening, clamping and/or lashing means and connecting elements, component for lifting, fastening, clamping and/or lashing technology, connecting element and method of production thereof

Info

Publication number: CA2848823A1
Application number: CA2848823A
Authority: CA
Inventors: Rolf Sinz
Original assignee: RUD Kettenfabrik Rieger und Dietz GmbH and Co KG
Current assignee: RUD Kettenfabrik Rieger und Dietz GmbH and Co KG
Priority date: 2011-10-26
Filing date: 2012-10-24
Publication date: 2013-05-02
Anticipated expiration: 2032-10-24
Also published as: PL2732060T3; DE102011054840A1; JP6147264B2; EP2732060B1; RU2579854C2; JP2015501384A; CA2848823C; ZA201402725B; EP2732060A1; BR112014009280B1; CN103930581B; RU2014121002A; DE202011052154U1; BR112014009280A2; CN103930581A; WO2013060724A1; ES2653665T3

Abstract

The invention relates to a hardening steel of quality class 8 and above for lifting, fastening, clamping and/or lashing means. The invention further relates to a connecting or structural element made from this steel for lifting, fastening, clamping and/or lashing technology. The invention further relates to a method for producing a connecting element or a structural element. Cost-effective production of connecting and structural elements that are resilient at low temperatures is achieved through use of the steel according to the invention, said steel having the following composition in weight percent: carbon 0.17 to 0.25, preferably 0.20 to 0.23; nickel 0.00 to 0.25, preferably 0.00 to 0.10; molybdenum 0.15 to 0.60, preferably 0.30 to 0.50; niobium 0.01 to 0.08 and/or titanium: 0.005 to 0.1 and/or vanadium: = 0.16, wherein the content of niobium can preferably be between 0.01 and 0.06; aluminium 0 to 0.050, preferably 0.020 to 0.040; chromium 0.01 to 0.50, preferably 0.20 to 0.40; silicon 0.1 to 0.3, preferably 0.1 to 0.25; manganese 1.40 to 1.60; phosphorus less than 0.015; sulphur less than 0.015; copper less than 0.20 and nitrogen 0.006 to 0.014, the remainder consisting of iron and unavoidable impurities.

Description

Hardening steel for lifting, fastening, clamping and/or lashing means and connecting elements, component for lifting, fastening, clamping and/or lashing technology, connecting element and method of production thereof The invention relates to a hardening steel for lifting, fastening, clamping and/or lashing means of quality grade 8 and above. In particular the invention relates to the use of said steel for lifting, fastening, clamping and/or lashing means, especially for chains and chain links, and for connecting elements, for example bolts. Further the invention relates to a connecting element, like a bolt, and component of the lifting, fastening, clamping and/or lashing technology made from said steel. Also the invention relates to a method for the production of such a connecting component, particularly the treatment of steel in a chain molding process and hardening process.
A plurality of compositions for steel is already known, also for steels that are used in lifting, fastening, clamping and/or lashing means. Under high safety requirements lifting, fastening, clamping and/or lashing means must lift or lash heavy loads or must enable fastening or rather securing of the lifting, fastening, clamping and/or lashing means at the load or at fixing devices.
According to their mechanical resilience the lifting, fastening, clamping and/or lashing means are divided into different quality classes or grades. The quality classes or grades are mostly standardized, for example quality grade 8 according to ISO 3076, 3077 or in Germany DIN-EN
818-2, 818-7 and quality grade 10 according to PAS 1061.
The higher a quality grade the heavier loads can be carried by the lifting, fastening, clamping and/or lashing means of identical cross sectional area. Hence a lifting, fastening, clamping and/or lashing means having a higher quality grade can, at identical weight, carry a heavier load than a lifting, fastening, clamping and/or lashing means having a lower quality grade and is thus easier to handle in operation.
For example, a quality grade 8 steel chain measuring 0 16 mm x 48 mm must have a minimum breaking force (BF) of 320 kilonewton, a corresponding chain of quality grade 10 must have a minimum breaking force of at least 400 kilonewton. The same applies to the classification into "grade 8" and "grade 10" according to US standards.
For such structural elements of quality grade 8 and above previously steels containing nickel have been used. For example US 2007/0107808 Al discloses such steel. However, since nickel is expensive it is sensible from an economic point of view to avoid the use of nickel or reduce the

2 nickel content. In the light of the mechanical requirements defined for the quality grades with respect to the tempering resistance and the low temperature ductility the avoidance of nickel is not unproblematic. Nickel is particularly considered essential for steels for lifting, fastening, clamping and/or lashing means because the notched impact strength of nickel alloyed steels (Ni > 0.8 % by weight) is high enough that the strength is hardly impaired by surface damages like notches occurring in extreme use.
An annealed connecting element is known for example from DE 10 2008 041 391 Al. This bolt attains its high strength as a result of a bainite structure. It is disadvantageous that such a microstructure can be formed only in accurately controlled cooling and isothermal transformation processes. DE 28 17 628 C2 relates to steel alloys having a bainite structure.
Other high-strength bolts are known for example from EP 1 728 883.
These known connecting elements are of high strength, however, at low temperatures they are very brittle. Thus they are unsuitable for use at a low temperature range, for example in outdoor use in mountain, winter or polar regions.
It is the object of the invention to provide a steel composition having a low nickel content or avoiding nickel that fulfils the requirements of quality grade 8 or above with respect to the mechanical properties. Particularly a steel is to be provided having a high notch impact energy at low temperatures, for example of -40 C, and at high temperatures, e.g. of +400 C, and at the same time an adequate strength as well as tempering resistance. Since the components of the lifting, fastening, clamping and/or lashing technology possess surfaces prone to wear the steel must also be hardenable. Furthermore it should be forgeable in order to produce particularly resilient structural elements cost-effectively.
It is a further object of the invention to improve the connecting element referred to above in such a way that at a high resilience, i.e. a high tensile strength, at low temperatures no brittle fracture behaviour occurs.
This object is achieved with the low-alloy steel according to the present invention having the composition below in weight percentage:
carbon 0.17 to 0.25, preferably 0.20 to 0.23, nickel 0.00 to 0.25, preferably 0.00 to 0.15 or 0.10, molybdenum 0.15 to 0.60, preferably 0.30 to 0.50,

3 niobium 0.01 to 0.08 and/or titanium: 0.005 to 0.1 and/or vanadium: 5 0.16 wherein the content of niobium can preferably be between 0.01 and 0.06, aluminium 0 to 0.050, preferably 0.020 to 0.040, chromium 0.01 to 0.50, preferably 0.20 to 0.40, silicon 0.1 to 0.3, preferably 0.1 to 0.25, manganese 1.40 to 1.60, phosphorus less than 0.015, sulphur less than 0.015, copper less than 0.20, nitrogen 0.006 to 0.014, remainder of iron and unavoidable impurities.
The present steel fulfils in chains the mechanical requirements of quality grade 8 and above, especially of quality grades 8 and 10, with regard to the tensile strength and the notch impact energy. Thus experiments performed by the applicant have shown that a component having a diameter of 16mm, that has been kept at approximately 880 C for about half an hour, quenched and subsequently kept at approximately 450 C for about half an hour, in a tensile test possessed values of Rm (tensile strength) of just above 1200 MPa, A5 of about 14%
(breaking elongation), Z of about 65 % (area reduction). The component has a notch impact energy of approximately 140 Joule at room temperature.
A connecting element made of this steel possesses very high strengths and at the same time an extremely high low temperature ductility thus providing high safeties even in a damaged condition at very low temperatures.
The known bolts of the highest property classes 14.8, 15.8 and/or 16.8 even at room temperature mostly exhibit a low ductility. Inevitably at low temperatures below the freezing point they tend to exhibit brittle failure. This fracture behaviour is not tolerable for a number of applications, especially for bolts for fastening, lifting and lashing means, because they are frequently applied under very extreme climatic conditions as for example on boats in the polar region or for the transport of goods in mountain regions. Small damages can thus result in an immediate failure of the connecting element. This hazard is significantly reduced with a connecting element according to the present invention.
The steel can also be used for components of the fastening, lifting and lashing technology, especially chain links, and also for components of the connection technology, i.e. for connecting elements. This appears not readily obvious because the relevant standards for connecting

4 elements, e.g. ISO 898, require a carbon content of at least 0.28 weight percent and the loads of chain links and connecting elements, especially bolts, are different.
By means of the low material inventory of nickel or respectively the complete avoidance of nickel the present steel is cost-effective.
The steel according to the invention is particularly suitable for use in components and work parts that on the one hand must have high tensile strengths and at the same time are exposed to abrupt hard mechanical strains like shocks or impact occurrences, especially when exhibiting operational notches. These are in particular the already mentioned lifting, fastening, clamping and/or lashing means like for example steel chains or profile chains, chain spanners, stop points, hooks, etc., as well as in particular driving force transferring elements in conveying systems and conveying plants. These strains are dominated by high ductility values.
A steel chain measuring 0 16 mm x 48 mm, according to own experiments for example, possesses a breaking force of 320 kilonewton required for the quality grade 8 even after a tempering treatment at a temperature of up to 550 C for one hour. Experiments by the applicant at 400, 450, 500 and 550 C have confirmed this. The present steel is denoted 20MnMoCrNb6-4.
From the state of the art a pressure vessel steel 18MnMo4-5 (EN 10028-2) is known. This refers to a coarse grained, heat-resistant steel that is used in a field which is totally different from lifting, fastening, clamping and/or lashing means and that does not fulfill the requirements of the quality grade 8 and above. Due to the requirement profile and coarseness of grains at a high ductility only low tensile strengths are attainable.
In particular a component made from the present steel can be treated in different sections, for example tempered, so that in these different sections different hardnesses, ductilities and/or notch impact energies are present.
In the following some preferred embodiments of the invention are exemplified.
The additional features of these embodiments can be employed each individually or together with the features of other embodiments in arbitrary combination.
In a first preferred embodiment the content of nickel in weight percent is less than 0.15 or 0.10%.
Since nickel is very expensive it is desirable to keep the nickel content in the steel as low as possible. By means of a content of 0.10% or less it is thus possible on the basis of the remaining alloy composition to further reduce the costs. It is possible in particular to produce steel that irrespective of impurities does not contain any nickel. Such a nickel-free steel furthermore saves the additional working stage of adding nickel.
According to another preferred embodiment the content of carbon in weight percent is between 0.20 and 0.23 /0. Due to a higher content of carbon the steel becomes harder however with an increase in carbon content the ductility decreases. Therefore the preferred range of the carbon content is restricted to the present range.
In a further preferred embodiment of the invention the content of molybdenum in weight percent is between 0.30 and 0.50 %. This range is particularly advantageous for obtaining the desired tempering resistance at low costs.
In a further preferred embodiment of the invention the content of niobium in weight percent is between 0.01 and 0.06 %.
In a further preferred embodiment of the invention the content of aluminium in weight percent is at least 0.020 and/or at most 0.040 %.
In a further preferred embodiment the content of chromium in weight percent is between 0.20 and 0.40 % Chromium increases the tensile strength, however, it reduces the notched impact strength. For the entire range these two effects are well balanced.
Preferably the content of silicon in weight percent is between 0.1 and 0.25 %.
It is of particular advantage if the sum of the doubled content of nickel or niobium, the approximately 1.6-fold content of titanium and/or the one-fold content of vanadium is at most approximately 0.16 % (each in weight percent).
In a particularly advantageous embodiment the steel having the composition according to the present invention is of an extremely fine grained form having a grain size finer than 7. Fine grained steel has a higher low temperature ductility together with a higher tensile strength.
Preferably the present steel and respectively the present component has a grain size of 9 to 10.
In a further advantageous embodiment for the production of a component from the steel according to the present invention this production comprises optionally repeated hardening and/or tempering.
In a further advantageous embodiment of the present steel a lifting, fastening, clamping and/or lashing means made from said steel possesses a tensile strength of at least 800 N/mm2, more preferably at least 1200 NI/mm2 at the ductility required for chains in the respective quality grades. By accepting a lower low temperature ductility, for example because the steel is used only at higher temperatures, higher tensile strengths can also be attained with the present steel.
In a further advantageous embodiment the steel or a component made from the steel possesses a hardness of 400 to 450 HV30.
In a further advantageous embodiment the steel or, respectively, a component made thereof have in different sections a hardness difference of 80 to 120 HV30.
In a particularly advantageous embodiment the steel or a component made from the steel essentially retains its hardness at 380 C, even better at 400 C and even better still at 410 C for 1 h.
The steel or, respectively, a component made from said steel possesses in a preferred embodiment a notch impact energy of at least 30 Joule, preferably at least 45 Joule, more preferably from about 120 to 140 Joule at -40 C. This low temperature ductility guarantees that the component exhibits sufficient safeties even in cold surroundings. At -60 C
the notch impact energy is at least about 50 Joule.
In a particularly advantageous embodiment of the method a component, for example a chain link, made from the present steel is treated differently in different sections. In particular a hardened component can be treated in different sections with different tempering temperatures.
A chain link for example can be treated in the section of its limb with another temperature than in the section of the bow. By means of such a method sections having different degrees of hardness and ductility are produced. The harder sections constitute wear surfaces while the less hard but more ductile sections possess a particularly high resistance against operational failure.
In a particularly advantageous embodiment of the method for the production of a component, a chain link especially, the chain link is treated in such a way that it possesses in at least one section a hardness of about 400 to 450 HV30 and in at least one other section a hardness of about 365 to 390 HV30 and at the same time fulfils the requirements of the quality grade 8 with respect to breaking force and breaking elongation. The sections having different properties are preferably connected, i.e. they are linked to one another.
According to another advantageous embodiment the difference in hardness of two different sections of a present component can be approximately 90 to 110 HV30. A chain consisting of such chain links has particularly advantageous properties. At sections exposed to an increased frictional and/or shock load, for example at the bows, the chain can exhibit an increased hardness. In sections that are mainly exposed to mechanical tensile strain or bending strain when in operation, for example at the limbs, the chain link can exhibit an increased resistance to failure even under unfavourable conditions.
In a particularly advantageous embodiment a chain link has a hardness of about 430 to 470 HV30 in one section and of about 380 to 395 HV30 in another section and at the same time fulfils the requirements of quality grade 10.
The steel is particularly suitable for use in a component of the lifting, fastening, clamping and/or lashing technology, especially in a chain or a chain link, and/or in a connecting element, for example a bolt.
The treatment of the present steel in a cold working and hardening process for the production of a connecting element and/or a component having the aforementioned properties is of particular advantage.
According to a further advantageous embodiment the present connecting element can contain lath martensite having lancet packets within its structure. Lath martensite induces a high strength and contrary to other martensites, like mixed martensite or plate martensite, does not affect the low temperature ductility. Lath martensite is formed in the course of the hardening and tempering on abrupt quenching from a temperature above the AC3 point with subsequent tempering temperatures that remain below the temperature above which E-carbide (transition carbide Fe2C) decomposes. Consequently it is advantageous if in the production of the connecting element the tempering temperature lies below the decomposition temperature of E-carbide.
In a cross-section through the connecting element the area percentage of the lath martensite can be at least 85%, preferably at least 90 %. It should be hardly possible to achieve area percentages of more than 98 % of lath martensite in a cross-section so that this value can be considered the upper limit of the lath martensite percentage.
The tempering temperature in the course of the quenching and tempering of the connecting element can be between 180 C and 220 C, preferably around or exactly 200 C. At these tempering temperatures particularly advantageous combinations of a high low temperature ductility with a high tensile strength are obtained.

The connecting element can contain cold-worked sections, for example one or more shaped or rolled thread sections. Preferably cold forming is performed before quenching and tempering.
On the basis of the aforementioned steel alloy, compared to the known connecting elements the present connecting element is characterized by special combinations of mechanical parameters that can be adjusted essentially by means of the tempering temperature. It appears to apply to the present steel alloy at tempering temperatures up to a maximum of 250 C
that the higher the tempering temperature is the lower the attainable tensile strength and the higher the low temperature ductility will be. In the following the notch impact energy KV
serves as a parameter for the low temperature ductility, as determined for example with a notch bar impact test on V-notch samples according to ISO 148-1.
According to an advantageous embodiment at a temperature of -40 C the notch impact energy KV is at least 55 Joule with a tensile strength Rm of at least 1400 N/mm2. An upper limit of the notch impact energy KV at a temperature of -40 C and a tensile strength of at least 1400 N/mm2 can be 70 J.
The notch impact energy KV at even lower temperatures, especially at -60 C, and at least 1400 N/mm2 can be at least 45 J. An upper limit of the notch impact energy KV at -60 C can be 60 J.
At a notch impact energy KV of at least 55 J at -40 C, and preferably no more than 70 J at -40 C, the tensile strength Rm can preferably be between 1500 and 1600 N/mm2.
The present connecting element can possess a hardness of 450 to 480 HV30.
The connecting element preferably has a fine grained microstructure having a grain size of 9 or finer. The grain size can preferably be 10. The grain size can be determined for example according to ASTME E 112.
According to a most preferred embodiment the connecting element is manufactured preferably from steel 20MnMoCrNb6-4.
In order to guarantee a sufficient hardness characteristic, in one embodiment the diameter of the present connecting element is at most between 20 and 25 mm, corresponding to bolt diameters of at most M20 to M25.
Most preferably the connecting element is a bolt, preferably for a fastening means, of property classes 14.8, 15.8 and/or 16.8.

The tempering resistance, as required for example in PAS 1061 for chains, can be over 1 hour at a tempering temperature of at least 380 C, preferably at least 400 C, more preferably at least 410 C. At such tempering temperatures, however, the tensile strength required for connecting elements of property class 14.8 and above can no longer be achieved.
The invention also relates to the use of steel having one of the above-mentioned compositions for the production of a quenched and tempered connecting element and preferably a connecting element at least tempered in sections, preferably a bolt.
The invention further relates to a method for the production of a connecting element, preferably a bolt, from such steel comprising the additional step of quenching and tempering. As already described above, in the course of the quenching and tempering the connecting element can be tempered at temperatures between 180 C and 220 C, preferably around or at 200 C.
In the following the invention is exemplarily described by means of one example. In the light of the above explanations, the embodiments described in connection with this example can be arbitrarily combined with one another or be omitted if the advantage linked with the respective feature should not matter in one embodiment.
It is shown by:
Fig. 1 a schematic diagram of a chain link that has been made from the steel according to the present invention, Fig. 2 a schematic diagram of a connecting element according to the present invention, Fig. 3 a schematic, qualitative diagram of the results of a tension test with a round sample, Fig. 4 a schematic, qualitative diagram of the results of a static bending test with stud-bolts of different property classes, Fig. 5 a schematic, qualitative diagram of the notch impact energy KV at -40 C for bolts having different property classes, Fig. 6 a schematic, qualitative diagram of the energy absorbed on breaking threaded bolts M20 at a temperature of -40 C, Fig. 7 a schematic, qualitative diagram of the results of tension tests (SOD tests) with slotted head screws of different property classes with two different slot depths at -40 C, Fig. 8 a schematic qualitative diagram of the breaking force and breaking nominal voltage after the tension tests (SOD tests) with slotted head screws according to the present invention at -40 C and at -60 C as a function of the slot depth.
Representative for components of the lifting, fastening, clamping and/or lashing technology, in Fig. 1 a chain link 1 is shown that is made from the present steel. It can be, for example, a steel chain link. The chemical composition that can be determined for example by chemical analysis of the melt, according to the invention is as follows in weight percent:
carbon 0.17 - 0.25 %, nickel 0.00 - 0.25 `)/0, molybdenum 0.15 -0.60 %, niobium 0.01 -0.08 % and/or titanium 0.005 -0.1 % and/or vanadium 5. 0.16 %, aluminium 0.020 - 0.050 %, chromium 0.10 -0.50 %, silicon 0.1 - 0.3 %, manganese 1.40 - 1.60 %, phosphorus < 0.015 %, sulphur <0.015 %, copper <0.20 %, nitrogen 0.006 - 0.014 %, remainder of iron and unavoidable impurities.
Preferably the nickel content can be smaller than 0.10 weight percent, the carbon content between 0.20 and 0.23 weight percent, the molybdenum content between 0.30 and 0.50 weight percent, the niobium content between 0.01 and 0.06 weight percent, the aluminium content between 0 or respectively 0.020 and 0.040 weight percent, the chromium content between 0.20 and 0.40 weight percent and/or the silicon content between 0.1 and 0.25 weight percent.
In particular the sum of the doubled content of nickel (in weight percent), the approximately 1.6-fold content of titanium (in weight percent) and/or the one-fold content of vanadium (in weight percent) should be at most approximately 0.16 % weight percent.
The chain link 1 made from the present steel exhibits mechanical properties constituting a good compromise of tensile strength and notch impact energy. As is shown by the experimental runs, the present steel fulfills the requirements of quality grades 8 and 10 without any difficulty. The production is cost-effective due to the low content of nickel or the avoidance of nickel in the production process because nickel is expensive. Especially the present steel can possess a high notch impact energy at a low temperature range, for example at -40 C, and a high tempering resistance at high temperatures, for example at 400 C.
In order to determine the properties of the steel, as required by the relevant steel standards, e.g.
DIN 17115, firstly a 0 16mm cylinder was examined as a reference. After annealing at 880 C for about 1/2 h it was quenched in water and subsequently tempered at 450 C for 1 h and cooled in air. Thereafter the sample had an Rm value of 1213 MPa, an A5 value of 13.1%
and a Z value of 64%. At room temperature it had a notched impact strength of about 140 J.
A sample that had been heat-treated at 930 C for approximately 4 h and quenched in water possessed a grain size of 8-9. Hence the steel is fine grain stable.
In order to demonstrate that components made of the present steel meet the requirements of different quality grades the applicant has carried out various experiments.
All experiments were conducted using a steel chain measuring 0 16 mm x 48 mm. The results for the steel chains can be transferred to other typical fastening, lashing and lifting means as for example stop points, clamps, chain locks etc.
Test series 1 In a first part, a chain was tempered after hardening from a temperature above the critical point AC3 of the iron carbon diagram and then tempered for about one hour at various temperatures.
Here, after various tempering temperatures for one hour each, the chain exhibited the values of tensile strength and breaking elongation shown in Table 1.
Table 1 T in C Fma, in kN A in %
450 372.8 26.1 500 354.8 28.6 550 346.3 30.2 The tempering experiments demonstrate that the mechanical properties required in quality grade 8 are maintained also at high temperatures up to the beginning of the creep range. At a tempering temperature of 400 C for approximately one hour it possessed a notch impact energy of about 130 j at -40 C. The present steel consequently is both low temperature ductile and creep resistant.

Hence, according to Table 1, the chain achieves the minimum breaking force of 320 kN and minimum breaking resistance of 800 N/mm2, respectively, required for such a steel chain for quality grade 8.
According to this test series a chain made from the present steel meets the mechanical requirements of quality grade 8 according to ISO 3076 and DIN EN 818-2.
Test series 2 The chain was hardened from a temperature above AC3, tempered and subsequently tempered again at 380 C for about one hour. Thereby a tensile strength of approximately 435 kN was attained at a breaking elongation of 31 %. Thus the chain exhibits the required minimum breaking strength of 400 kN and 1000 N/mm2, respectively, after reheating.
Test series 2 demonstrates that a chain made of the present steel also meets the requirements of PAS 1061 and thus it is suitable for chains having the quality grade 10.
Test series 3 In a third test series a chain link was tempered at a temperature between 180 C and 220 C after hardening from a temperature above AC3. A chain link treated that way had a notched impact bending energy of more than 50 J at -40 C and of about 50 J at -60 C. The minimum breaking force was significantly higher than 420 kN at just above 490 kN. Hence such a chain link can be used for applications at very low temperatures.
Figure 2 shows in an exemplary way a connecting element 10 in the form of a bolt. The bolt is fitted and annealed with a cold-formed, especially rolled thread section 20.
The connecting element 10 is made from steel having the following alloy components:
carbon: 0.15 to 0.25 % by weight, preferably 0.20 to 0.23 % by weight, nickel 0.00 to 0.25 % by weight, preferably 0.00 to 0.10 % by weight, molybdenum: 0.15 to 0.60 % by weight, preferably 0.30 to 0.50 A by weight, niobium: 0.01 to 0.8 % by weight and/or titanium: 0.005 to 0.01 % by weight and/or vanadium: 0.16%, wherein niobium can preferably be from 0.01 to 0.06% by weight, aluminium: 0 to 0.050 % by weight, preferably 0.020 to 0.040 % by weight, chromium: 0.10 to 0.50% by weight, preferably 0.20 to 0.40% by weight, silicon: 0.1 to 0.3 % by weight, preferably 0.1 to 0.25 % by weight, manganese: 1.40 to 1.60 % by weight, phosphorus: <0.015 % by weight, sulphur: <0.015 A) by weight, copper: <0.20 % by weight, nitrogen: 0.006 to 0.14 % by weight.
The remainder of the steel is iron and unavoidable impurities.
The sum of the doubled content in weight percent of nickel, the approximately 1.6-fold content of titanium and/or the one-fold content of vanadium, in weight percent respectively, should preferably be at most approximately 0.16% by weight.
The first test series with that steel was conducted with regard to its suitability for the production of chain links. These tests also suggest the suitability for the production of connecting elements 10.
Experiment 1.1 Firstly according to DIN 17115 as a reference a cylinder having a diameter of 16mm made from the steel described above was examined. After annealing at 880 C for about half an hour the cylinder was quenched in water and subsequently tempered at 450 C for one hour and cooled in air. Thereafter this sample had a tensile strength 13, of 1213 N/mm2, a value of A5 of 13.1% and a value of Z of 64%. At room temperature the sample possessed a notched impact strength of about 140 J.
It can be concluded from that experiment that at a tempering temperature of between 180 C an 220 C, preferably around 200 C, significantly higher values of the tensile strength 13, are achieved. The tensile strength at such a tempering temperature should be at least 1400 N/mm2, especially above 1500 N/mm2 up to about 1600 N/mm2, possibly slightly above, so that bolts having a property class of 14.8, 15.8 and 16.8. can be obtained.
Experiment 1.2 A sample that had been heat-treated at 930 C for about four hours and quenched in water showed an ASTM grain size of 8 to 9. Therefore, the steel is fine grain resistant.
At tempering temperatures of 180 C to 220 C and shorter tempering periods, of for example one hour, even finer grain sizes, about ASTM 10, are anticipated. Grain sizes of about ASTM 10 are also attainable with a heat treatment at lower temperatures and/or a shorter period.

Experiment 1.3 In order to demonstrate that steel chains and other typical fastening, lashing and lifting means, as for example stop points, clamps, chain locks etc., made from the above steel meet the relevant quality grades for these components, further tests have been carried out. These experiments were conducted using a steel chain measuring 0 16 mm x 48 mm.
Test series 1.3.a In a first series of tests after hardening the steel chain 16 x 48 was annealed at a temperature above the critical point AC3 of the iron carbon diagram and thereafter tempered for approximately one hour at various temperatures. Here, after various tempering temperatures, the chain had the values shown in Table 2 with respect to tensile strength and breaking elongation.
Table 2 T C Frna, in kN Ar %
450 372.8 26.1 500 354.8 28.6 550 346.3 30.2 The tempering experiments demonstrate that the steel is creep resistant (heat-resisting). Since at a tempering temperature of 400 C for about one hour a notch impact energy of about 130 J at -40 C could be verified the above steel for the connecting element 1 is both low temperature ductile and creep resistant. As is proved by Table 2, the breaking load increases with a decrease in tempering temperature while the breaking elongation decreases.
Within the chain link a minimum breaking strength of 800 NI/rnm2 is achieved.
Test series 1.3.b The chain was hardened from a temperature above AC3, tempered and subsequently tempered again at 380 C for about one hour. Here the chain link showed a tensile strength of about 435 kN at a breaking elongation of 31%. Thus on reheating the chain has a minimum breaking strength of 1000N/mm2.
Test series 1.3.c In a third series of tests a chain link was tempered at a temperature between 180 C and 220 C
after hardening from a temperature above AC3. A chain link treated that way had a notched-bar impact energy KV according to DIN EN 10045 of more than 50 J at -40 C and of about 50 J at -60 C. The minimum breaking strength was just above 490 kN within the chain link. Also from this a tensile strength Rm of more than 1400 N/mm2, especially between 1500 N/mm2 and 1600 N/mm2, can be concluded for a connecting element like a bolt if one allows for the more multidimensional stress condition of the connecting element.
In a second series of tests the steel was quenched from a temperature above the AC3 point and then tempered between 180 C and 220 C. After this quenching and tempering, in a cross section or micrograph, respectively, the samples possessed a lath martensite area percentage of between 85% or 90%, respectively, and 98%.
Starting material for all samples was a threaded bolt M20.
Experiment 2.1.a A tensile test according to ISO 6892-1 at a temperature of 20 C with the round specimen turned off from the threaded bolt M20 having an outside-diameter of 15 mm qualitatively results in the distribution shown in Fig. 2.
The tensile elastic limit Rp0,2 of the turned off round specimen thus is between 1250 and 1350 N/mm2. The tensile strength Rm is above 1400 N/mm2, between 1500 and 1600 N/mm2.
The breaking elongation A5 is from above 13 % to a maximum of 18%, in the region of about 15%. The area reduction Z is higher than 48% up to about 55%, in the region of 51%.
Experiment 2.1.b If a round specimen having an outside diameter of 15 mm turned off from the stud bolt M20 was tempered at about 200 C in order to obtain a high tensile strength Rm, the following values would be obtained: Rm = 1550 ... 1600 N/mm2, Rp0,2= 1300 ... 1350 N/mm2, A5 = 8 ...
12%, Z = 40 ...
50%.

From the results of the tensile test according to Figure 3 it can be concluded that the connecting element according to the present invention exhibits a very high tensile strength and at the same time a high ductility at room temperature. In the light of the results of the tensile test, as far as hereinafter tests are carried out with a stud bolt according to the present invention, it is assigned to property class 15.8.
Experiment 2.1.c In a further experiment, after a tempering temperature of 300 C a further round specimen equally cut from a bolt M20 made from the present steel had an area reduction Z in the range of 60 ... 70%. Due to the high tempering temperature the tensile strength Rm was 1425 ... 1475 N/mm2.
Experiment 2.2 In Figure 4 the results of a static bending test with stud bolts M20 of property classes 8.8, 10.9, 12.9 and 15.8 are presented qualitatively and, on the bottom right, the samples at the end of the experiment are shown. The connecting element according to the present invention of property class 15.8 has been compared with commercial connecting elements of property classes 8.8, 10.9 and 12.9.
The bending test has been carried out using 120 mm long stud bolts and a steel prop having a radius of 20 mm. The stud bolts rested on the inclined plane of a 90 prism.
It turns out that not only can the connecting element according to the present invention absorb a significantly higher bending load, but also the deformability of the present connecting element exceeds the deformability of the bolts of the lower property classes 12.9 and 10.9. Thus a bolt M20 according to the present invention survives a bending deformation of 24mm.
At that deformation the bolts of property classes 12.9 and 10.9 had already broken.
Experiment 2.3 In further experiments the low temperature ductility of a threaded bolt M20 according to the present invention was examined. For that purpose at -40 C a notched-bar impact test according to ISO 148-1 was carried out. The qualitative results, again in comparison with connecting elements of lower property classes, here 10.9 and 12.9, are shown in Figure 5.
The notch impact energy KV at -40 C of above 60 J up to about 69 J obtained according to these experiments with the present connecting element 15.8 is significantly above the values of the notch impact energy KV for the otherwise identical ISO-V-samples of the stud bolts of property classes 10.9 and 12.9.
The connecting elements according to the present invention thus possess a high low temperature ductility that exceeds the low temperature ductility of the lower property classes.
Experiment 2.4 The high low temperature ductility of a present connecting element which despite a significantly higher strength exceeds the low temperature ductility of lower property classes, can also be seen from Figure 5. Figure 6 shows qualitatively the absorbed energy when breaking threaded bolts M20 at a test temperature of -40 C.
Hence at -40 C a present threaded bolt M20 absorbs significantly more energy than the threaded bolts M20 of the property classes 10.9 and 12.9. At low temperature applications the excess of absorbed energy of the connecting element according to the present invention provides higher safety in operation.
Experiment 2.5 In a further series of tests the ductility behavior of present connecting elements was examined in comparison with commercial connecting elements of lower property classes at -40 C by means of SOD experiments.
In SOD ("Slit Opening Displacement") experiments a slot parallel to the secant, in some samples having a depth of 3.4mm and in other samples having a depth of 6.8 mm measured from the core depth of the thread, is driven into the bolts M20 (see Fig. 6). The slot depth thus corresponds to 20% (slot depth 3.4 mm) and 40% (slot depth 6.8 mm), respectively, of the diameter. Subsequently the bolts are strained under tension. Via a strain gauge at the outer diameter opposite to the deepest point of the slot the opening of the slot with an increase in tensile strain is monitored.
The result of the SOD experiments is qualitatively shown in Figure 7.
It can be seen that in comparison to the bolts 10.9 and 12.9 up to the breakage of the bolt the highest absolute energies can be absorbed by the present connecting element.
Further it can be seen from the test results in Figure 7 that breakage occurs with the present connecting elements only after the slot has been considerably widened. While a bolt M20 of property class 12.9, more or less regardless of the slot depth, breaks after widening of the slot by about 0.3 mm and a bolt of property class 10.9, equally more or less regardless of the slot depth, breaks at a slot widening by about 0.5 mm, a connecting element according to the present invention made from the steel above tolerates a widening of the slot by significantly more than 0.5 mm, namely up to more than 0.7 mm.
It can be concluded from the SOD experiments that even at a temperature of -40 C a connecting element according to the present invention will not fall below the admissible working load limit WLL for stop bolts even at -40 C and when damaged. Thus a safety factor of 6 applies to stop bolts with respect to the tensile strength for being an admissible working load limit. A bolt of property class 15.8 with a tensile strength of 1500 kN when used as stop bolt consequently must be loaded at most with only 1500 kN/6 = 250 kN. However, at -40 C the connecting element according to the present invention has a more than three-fold remaining safety with respect to the working load limit. This safety exists even at -60 C. In Figure 8 the tensile strength, the working load limit WLL and the three-fold working load limit are marked by chain dotted lines.
All of the experiments show that the connecting element according to the present invention combines an extremely high strength with an extremely high low temperature ductility. With regard to bending strength as well as notch impact energy and breaking strength of the SOD
samples, the present connecting elements are superior to the known connecting elements.

Claims

1. Hardening steel for lifting, fastening, clamping and/or lashing means of quality grade 8 and above having the following composition in weight percent:
carbon 0.17 - 0.25 %
nickel 0 00 - 0 25 %
molybdenum 0 15 - 0.60 %
niobium 0.01 - 0.08 % and/or titanium 0.005 - 0.1 % and/or vanadium <=
0.16 %
aluminium 0 - 0.050 %
chromium 0.10 - 0.50 %
silicon 0.1 - 0.3 %
manganese 1.40 - 1.60 %
phosphorus < 0.015 %
sulphur < 0.015 %
copper < 0.20 %
nitrogen 0 006 - 0.014 %
remainder of iron and unavoidable impurities.

2. Steel according to claim 1 characterized in that the nickel content in weight percent is less than 0.15 %.

3. Steel according to claim 1 or 2 characterized in that the carbon content in weight percent is between 0 20 and 0.23 %.

4. Steel according to any one of claims 1 to 3 characterized in that the molybdenum content in weight percent is between 0.30 and 0 50 %

5. Steel according to any one of claims 1 to 4 characterized in that the niobium content in weight percent is between 0.01 and 0.06 %.

6 Steel according to any one of claims 1 to 5 characterized in that the aluminium content in weight percent is at least 0.020 and/or at most 0.040 %.

7. Steel according to any one of claims 1 to 6 characterized in that the chromium content in weight percent is between 0.20 and 0.40 %.

8. Steel according to any one of claims 1 to 7 characterized in that the silicon content in weight percent is between 0.1 and 0.25 %.

9. Steel according to any one of claims 1 to 8 characterized in that the sum of the doubled content (in weight percent) of nickel, the approximately 1.6-fold content of titanium (in weight percent) and/or the one-fold content of vanadium (in weight percent) is at most about 0.16 % by weight.

10. Connecting element and/or component, especially a bolt or a chain link for lifting, fastening, clamping and/or lashing means, characterized in that it is at least partially made from a steel according to any one of claims 1 to 9.

11. Connecting element or component according to claim 10 characterized in that the steel has in different, connected sections different hardnesses and/or strengths and/or notch impact energies.

12. Connecting element or component according to claim 10 or 11 characterized in that it has a hardness of 400 to 480 HV30

13. Connecting element or component according to any one of claims 10 to 12 characterized in that it has in different sections a difference in hardness of 80 to 120 HV30.

14. Connecting element or component according to any one of claims 10 to 13 characterized in that it has a minimum breaking stress of at least 800 N/mm2, preferably at least 1200 N/mm2.

15 Connecting element or component according to any one of claims 10 to 14 characterized in that it has a notch impact energy of at least 30 J, preferably at least 45 J, at -40°C and/or a notch impact energy of at least 50 J at -60°C.

16. Connecting element or component according to any one of claims 10 to 15 characterized in that it has a tempering resistance of more than one hour at a tempering temperature of at least 380°C, preferably at least 400°C, even more preferably at least 410°C.

17. Connecting element or component according to any one of claims 10 to 16 characterized in that it is fine grained, especially that it has grain size 9 or finer, in particular grain size 10.

18. Connecting element according to any one of claims 10 to 17 characterized in that it has a notch impact energy KV of at least 55 J at -40°C and a tensile strength R m of at least 1400 N/mm2.

19. Connecting element according to any one of claims 10 to 18 characterized in that the notch impact energy KV is at most 70 J at -40°C and at a tensile strength of at least 1400 N/mm2.

20. Connecting element according to any one of claims 10 to 19 characterized in that the notch impact energy KV is at least 45 J at -60°C and at a tensile strength R m of at least 1400 N/mm2.

21. Connecting element according to any one of claims 10 to 20 characterized in that the notch impact energy KV is at most 60 J at -60°C.

22. Connecting element according to any one of claims 10 to 21 characterized in that it is annealed at a tempering temperature of between 180°C and 220°C.

23. Connecting element according to any one of claims 10 to 22 characterized in that the tensile strength R m is between 1500 and 1600 N/mm2.

24. Connecting element according to any one of claims 10 to 23 characterized in that it has a fine grained microstructure with a grain size of 9 or finer according to ASTM.

25. Connecting element according to any one of claims 10 to 24 characterized in that in a cross-section of the connecting element the area percentage of lath martensite is at least 85%.

26. Connecting element according to any one of claims 10 to 25 characterized in that it has a cold-formed section.

27. Connecting element according to any one of claims 10 to 26 characterized in that the connecting element is a bolt of property grade 14.8, 15.8 or 16.8.

28. Treatment of a steel according to any one of claims 1 to 9 in a cold forming and hardening process for the production of a component according to any one of claims 10 to 17 or a connecting element according to any one of claims 10 to 27.

29. Use of the steel according to any one of claims 1 to 9 for a connecting element, especially a bolt, or a component of the lifting, fastening, clamping and/or lashing technology, especially a chain or a chain link.