US3117042A

US3117042A - Heat-treatment of metals

Info

Publication number: US3117042A
Application number: US706557A
Authority: US
Inventors: Blechner Heinrich
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-01-04
Filing date: 1958-01-02
Publication date: 1964-01-07
Anticipated expiration: 1981-01-07

Description

United States Patent 3,117,042 HE.- T-TREATMENT 0F fv/ETALS Heinrich Bleehner, .lauresgasse 1/ 12a, Vienna iii, Austria No Drawing. Filed fan. 2, i953, Ser. N 706,557 Claims priority, application Austria Jan. 4, 1957 1 Claim. (ill. 143-452) This invention relates to the production of heat-treated workpieces of metal, particularly of steel.

It is an object of the invention to provide a method of heat-treating workpieces of steel to produce a substantially austenitic structure at room temperature.

It is another object of the invention to provide a hardened, fine-grained steel structure which is superior in hardness, wear resistance, elasticity, and resistance to corrosion to martensitic and hardenitic structures of the same composition.

It is a further object of the invention to provide an improved method of heat-treating workpieces by contacting them with a tool moved relative to the workpiece.

It is a further object of the invention to provide an improved method of shaping metal workpieces with a tool whereby the costs of tools and the costs of tool trueing are substantially reduced compared to shaping treatments carried out according to conventional practice.

It is a further object of the invention to provide a method of treating metal workpieces with a tool and simultaneously trueing the tool.

It is a further object of the invention to provide a method of surface-finishing metal workpieces which enables the production of a high finished at a fraction of the cost involved in a conventional methods.

It is a further object of the invention to provide an improved method of hardening and surface-finishing workpieces of steel in one operation.

It is a further object of the invention to provide an improved method of hardening and shaping workpieces of steel in one operation.

It is a further object of the invention to provide an improved method of shaping and surface-finishing work pieces of metal in one operation.

It is a further object of the invention to provide an improved method of shaping, hardening and surface-finishing workpieces of steel in one operation.

It is a furhter object of the invention to provide an improved method of profiling workpieces of metal, which can be combined in a single operation with surface-finishing and, in the case of workpieces of steel, with hardening and/ or surface finishing.

It is a further object of the invention to provide an improved method of welding metal workpieces.

Additional objects and advantages of the invention will become apparent as the specification proceeds.

According to one aspect of the invention, heat-treated workpieces of steel are produced by successively subjecting fractional portions of the workpiece to a temperature rise above its critical range and causing each of said portions immediately after it has been subjected to said temperature rise to cool below the martensite line at a rate sufiiciently high to retain a substantially austenitic structure.

A preferred mode of carrying out this method is offered by a method of producing heat-treated workpieces of metal, which comprises successively contacting frac-v tional surface portions of the workpiece wtih a tool member at a pressure and relative speed sufficient to subject each of said portions while thus contacted to a temperature rise above the critical range in the case of workpieces of steel or above the melting point in the case of workpieces of a metal other than steel, and causing each of said portions of the workpiece immediately after it has thus 3,11 1%? Patented Jan. 7, 1964 "ice been contacted to cool substantially to room temperature.

In this specification, the term fractional surface portion defines a surface portion which can be subjected to a temperature rise above the critical range in the case of workpieces of steel or above the melting point in the case of workpieces of a metal other than steel and which due to its small size will immediately return to the temperature of the rest of the workpiece and of the ambient atmosphere, even if the same are substantially at room tem- 0 perature, as soon as said portion is no longer subjected to the conditions which caused said temperature rise. In connection with the production of the fine-grained hardened steel structure mentioned hereinbefore, the term fractional surface portion defines a surface portion which can be subjected to a temperature rise above the critical range of steel and which due to its small size will be cooled to a temperature below the martensite line at a rate sufficiently high to retain a substantially austenitic structure, by a dissipation of heat to the remainder of the workpiece and to the ambient atmosphere, which are maintained substantially at room temperature, when said portion is no longer subjected to the conditions which caused said temperature rise.

In this specification and the appended claim, the term steel is used to describe a metal which shows a behavior similar to steel when subjected to a hardening and tempering treatment as is usual for steel.

It is usual to machine or work workpieces with vari ous tools. Tools are known which are used for dividing or cutting only by virtue of their high cutting speed. This gives rise to irregular hard portions at the cut surfaces and it is necessary to remove these hard portions before the subsequent processing of the workpiece. In order to increase the wear resistance of the usual workpieces a surface treatment is adopted. All these operations require a great expenditure of labor, time and energy. The results, particularly those achieved in heattreating relatively small workpieces, are often fairly irregular. For this reason it has been attempted to effect the heat treatment of the workpieces more quickly and more uniformly in automatic hardening plants, which may be gas-fired or high frequencyor resistance-heated or the like and to which the workpieces are fed immediately after the mechanical treatment. In all these methods of hardening, the quenching treatment gives rise to dangerous internal stresses, which must be removed by a so-called tempering treatment.

It has been found that when steel is first heated con siderably above the upper limit of the critical range, preferably to or above the fusion point, by a supply of energy in any desired form, and is then subcooled at the highest rate, the austenite, which in other cases is stable only at elevated temperatures, can be retained in a stable form in large quantities (e.g., up to 98%) even at room temperature. This is followed by a mechanical or other influence, particularly by a shock action caused by shaking, impact, machining or by the use of the workpiece itself, or by temperature, electrical or other influences, whereby a sudden conversion in structure is caused which provides a structure which is superior to the previously known martensitic or hardenitic structures by a much higher hardness, higher wear resistance, higher elasticity and resistance to corrosion, improved surface finish and other properties. This structure has only low internal stresses even without additional heat-treatment. For this reason it does not split or crack, remains firmly bonded to the underlying material and retains its brightness. By this method, carbon and alloy steels are given the desirable properties of austenitic steels. The method is applicable with extreme ease due to the simplicity of the procedure and of the tools required.

For instance, the use of a tool which has been treated by the method of the invention will be sufficient to initiate the hardening process immediately, whereby the tool is given an extremely high hardness. The intense, brief temperature rise and the quick cooling produced by the method according to the invention do not give rise to stresses in the tool and workpiece. The resulting surface layer has a uniform smoothness, is free of cracks, has no tendency to scale, remains bright, is resistant to corrosion and can be controlled in its thickness. On the other hand, the thickness of the layer and its depth of roughness remain constant under constant operating conditions. In conection therewith the core of the material to be hardened according to the invention may be subjected to any desired heat treatment. For instance, a core of particularly high elasticity may be provided with a surface layer of particularly high hardness and wear resistance, which surface layer is firmly bonded to the core and does not peel off or detach. The energy required for intense heat ing and high-speed cooling may be produced by mechanical treatment without involving an expenditure of additional energy for this purpose. It is sufficient to increase the speed of the tool to produce a relative speed of at least 80 meters per second between the workpiece and the tool at the point of contact. This speed is limited particularly by the need to ensure the safety of the operator. The method of the invention has been carried out in practice with relative speeds up to 260 meters per second between the workpiece and the tool. The working conditions such as the working pressure between the tool and the workpiece, the time of treatment of the workpiece, the initial hardness or artificial hardness of the workpiece, its carbon content, its content of alloying constituents, the nature of the material, the feed rate, and the exact adjustment and/ or matching of these conditions are of special importance in view of the very high rela tive speed between tool and workpiece. For this reason it is essential that the devices for adjusting and matching the various working conditions are constructed for perfect rigidity and freedom of shake and that their coaction can be adjusted most precisely and can be maintained constant. When all these requirements are fulfilled, highest qualities can be achieved, which were previously attained only with very high expenditure.

Another factor which can be varied is the feed movement of the tool and/or workpiece. These movements may take place in different directions. The tool and/or the workpiece may be caused to reciprocate, oscillate, roll, e.g., on a surface, revolve on an arm, etc.

The tool used may consist for these high relative speeds of a round member, formed simply on the lathe, particu larly as a disc, and has a service life which is a multiple of the service lives of previously usual tools. The expenditure of energy, time, labor and supervision are minimized.

Whereas a thin disc about 100 mm. in diameter and having an edge bevelled at an angle of about 45 has proved most satisfactory in carrying out the method of the invention, it may be replaced by a great variety of other tool member such as plain or profiled members in the form of discs, rolls, cones, or balls.

The extremely high ultimate tensile stress of tools of steel enables speeds which would cause immediate fracture of the urual ceramic or other grinding wheels.

The method of the invention may be adopted to perform shaping treatments similar in eifect to milling, reaming, profiling, spinning, drawing, trueing, as well as for surface-finishing treatments similar and in many cases superior in effect, e.g., to grinding, press-polishing, honing and lapping. Surface-finishing treatments may be combined with shaping treatments. When performed on workpieces of steel, these shaping and/ or surface-finishing treatments can be combined with the hardening of the workpiece. For instance, surface layers having a highfinishing and extremely high hardness may be produced on cutting parts of knives, surgical instruments and the like, on toothed wheels, bevel wheels, spur gears. worm wheels and spiral gears and on the points of needles and of shafts. Profiling operations which can be performed by the method of the invention include, e.g., the cutting of teeth on saws, wheels, the cutting of threads on screws, the forming of flutes on twist drills. The method enables even the profiling of very small precision parts such as for watches. These parts may be cut from solid stock, hardened and finished in a single operation.

The tool may contact the workpiece with a profiled portion in a direction at right angles to the axis of rotation of the tool or with a surface which extends parallel or at right angles or at any other angle to the axis of rotation of the tool.

For profiling operations, guides for the feed movement of the tool and/ or workpiece may be employed.

The maintenance of the tools used in the method of the invention is panticularly simple and inexpensive. It is sufficient to true them by hand or semior fully automatically by a hardened and tempered smooth steel rod held against the tool. This true-ing can be controlled to smoothen, temper, grind and/or polish the tool and provide it with an extremely hard layer. The trueing operation may be performed continuously or periodically while the tool itself is in operation. Tools having polished surfaces can be used to produce on the work-piece a particularly thin hardened layer (0.001 mm. or less) having a particularly high surface finish.

Tools which are stationary in operation may be periodically trued by treating them for a short time according to the method of the invention with a tracing tool rotating at high speed. In this way the tools can be provided with particularly nicely ground, extremely sharp cutting edges and extremely hard points. These edges and points have a very long service life.

As a result, stocking problems are simplified and the tool account is reduced. Above all, the use of extremely for any subsequent heat treatment such as quench-hardening and tempering. The machines in which such tools are used at high and very high relative speeds with respect to the workpiece are inexpensive in construction and simple in attendance. They are particularly suitable for full automation. Surfaces or hardened structures produced by such tools are smooth, can be given particularly high degrees of hardness, have a particularly high resistance to wear and resistance to corrosion, they do not split or tear, they do not separate from the core, they are practically free of stresses, they do not scale but remain bright. The temper of the core is not influenced. The exact, reliable and shake-free devices which should be provided for adjusting and matching the other operating conditions enable, e.g., the adjustment of any desired thickness of the hardened layer by a change of working conditions or the maintenance of a given thickness of the hardened layer for longest periods with a fixed setting. This enables full automation, particularly of the hardening treatment according to the invention. For instance, when it is desired to form a particularly smooth surface, having a depth of roughness of less than 0.1 on a small shaft, the workpiece is given a high speed relative to the shaft (120 meters per second). As a result, the shaft in slight contact with the tool is given a speed of 2OG,OO0 rotations per minute. In this case the working pressure between the tool and workpiece amounts only to a few grams. On the other hand, these operating conditions can be changed so as to cause a. plastic deformation of the workpiece or to weld two workpieces together or perform other machining or other treatments thereon.

The following results, described by way of example, have been obtained with experimental set-ups:

(1) A particularly simple experiment resides in moving a thin cylindrical steel disc, rotating at a peripheral speed of 120 meters per second, in the longitudinal direction, e.g., at mm./sec. over a gripped, pre-hardened steel strip, against which the disc is urged under low pressure, e.g., of 50 grams. By this treatment the steel strip is ground to a very low depth of roughness, eg of 0.2/,u., and hardened. The surface of the resulting hardened layer is bright and resistant to corrosion. Due to the moving small working area and the relatively large mass of the workpiece and the air entrained by the high-speed tool it is not necessary to provide an additional coolant. Blued steel strip having a carbon content of about 0.8% and a core having a micro-hardness of 450-500 kg./ sq. mm., can be ground and finished in this way to attain a surface having a micro-hardness of 1100-1200 kg./sq. mm., measured under a load of 25 gram. The depth of grinding under a working pressure of 500 grams is 0.1 mm., the thickness of the layer is 0.05 mm.

Blued Steel Strip, 0.6 mm. Thick Absolute speed of tool 120 meters/sec. Feed rate of tool 0. Pressure between tool and workpiece Approx. 20 grams/sq. mm.

(2) Teeth produced in narrow, thin strip by reaming were given at the same time a hardened layer 0.08 mm. thick. This layer was uniformly formed on the cutting and rear faces and at the tip of the teeth. The layer is inseparably bonded to the rest of the material; it will not crack or peel, is resistant to corrosion, has an extremely high resistance to corrosion and attains a micro-hardness of 1150-1250 kg./sq. mm. under a load of 25 grams/sq. mm. The micro-hardness of the rest of the material amounted to about 600-650 kg./ sq. mm. under the same load. Such saws will readily cut hardened steel; the tips of the teeth will remain intact even after prolonged use.

Saw Blading Absolute speed of tool 120 meters per second. Feed rate of tool, three reversals- 9.2 cm./ sec. Pressure between tool and Workpiece Approx. 500 grams. Absolute speed of workpiece.. Approx. 1.7 mm./ sec. Initial hardness of blading (micro-hairdness under a load of 25 grams/sq. mm.) 700 kg./sq. mm. Carbon content 0.9%. Micro-hardness under a load of 25 grams/sq. mm. after the treatment 1100-1500 kg./ sq. mm. Thickness of hardened layer 0.05-0.1 mm.

(3) Using a parting tool which had been ground and hardened according to the invention, 1350-1450 rings were cut from steel tubing whereas only 950 rings, at most, could be cut trom the tubing with parting tools of steel tempered by ordinary methods.

6 Grinding a Parting Tool Absolute speed of tool 120 meters/ sec. Feed rate of tool 0. Pressure between tool and 'workpiece Approx. 5-10 gra-ms/ sq. mm.

Absolute speed of workpiece 0. Initial hardness of workpiece (micro-hardness under a load of 25 grams/sq. mm.) 700 kg./sq. mm. Carbon content 0.9%. Micro-hardness under a load of 25 grams/ sq. after the treatment 1050 kg./sq. mm. Thickness of hardened layer 0.01-0.02 mm.

(4) A shaft is rotatably carried between centers. By means of the disc, this shaft is given a speed which is lower or higher than or equal to the speed of 120 meters/ sec. of the disc. The thickness of the resulting hardened surface layer depends on the working pressure between the tool and the workpiece. The depth of roughness does not exceed 0.2,u.

Surface Treatment of Round Shaft, 5 mm. in Diameter Absolute speed of tool 120 meters/ sec. Feed rate of tool 0. Pressure between tool and workpiece Slight pressure. Absolute speed of workpiece, driven by tool 100,000 r.p.m. Initial hardness of workpiece (microhardness under a load of 25 grams/ sq. mm.) 800 kg./sq. mm. Carbon content 0.9-1.1%. Micro-hardness under a load of 25 grams/sq. meter after the treatment 1100 kg./ sq. mm. Thickness of hardened layer 0.01 mm.

(5) A steel disc having a working edge termed in accordance with the desired profile of a screw thread and rotated at high speed is caused to contact a bolt, which is axially fed and rotated at the same time. This results in the formation of a screw thread, the sides of which are shaped, tempered and hardened at the same time.

*(6) Plastic deformation will result if the working pressure between the tool and the workpiece is substantially increased in Example 6.

(7) When two or more wires or metal sheets are contacted under an appropriate pressure by a disc which rotates, e.g., at 120 meters per second and is moved, e.g., in the longitudinal direction of the wires or sheets, this will result in a very uniform and durable welded joint.

It is emphasized that all examples can be carried out with a simple tool rotating at high speed.

I claim:

A process for the treating of surfaces of hardened steel, especially tools, for the purpose of hardening the surtace, comprising heating with a fast rotating steel disk having a peripheral speed beyond meters per second to the hardening temperatures by :friction, then quenching by the deeper located cool layers of the steel, said heating progressing over the surface to or beyond the melting point with simultaneously quenching.

References Cited in the file of this patent UNITED STATES PATENTS 974,099 Sundborg Oct. 25, 1910 1,799,614 Coberly Apr. 7, 1931 2,424,794 Brown July 29, 1947 2,670,528 Brunberg Mar. 2, 1954 2,935,364 Smith May 3, 1960