Steel R18 Research Articles

Kinetics of the decomposition of supercooled austenite in high-speed steels R6M5, R6M5K5, and R18

1. The kinetics of the decomposition of supercooled austenite was studied and the effect of slight differences in the composition (within the nominal limits) of steels R18, R6M5K5, and R6M5 on the stability of supercooled austenite was determined. 2. Methods of mathematical statistics were used to establish the variation of austenitic and pearlitic transformation times with the chemical composition of steel R18. For the minimal concentration of carbon and carbide-forming elements the time for the austenitic and pearlitic transformations is 2–3 and 3–4 h, respectively; it is 6–7 and 11–12 h for the maximum concentration. 3. Isothermal annealing conditions were established in relation to the chemical composition of steel R18 in chamber furnaces with a given ratio of austenitic and pearlitic transformation times. 4. By taking into account the chemical composition of the heat it is possible to improve greatly the productivity of furnace equipment and the quality of annealing of high-speed steels.

Increasing the durability of cutting tools

It is well known from the theory of cutting that slide friction plays the dominating role in the wear of the cutting tool. The shaving, running off the part, rubs continuously and with great force against the front edge of the cutting tool, the edges of the spiral grooves of drills, taps, and milling cutters, and heats the metal, thus reducing its resistance towards the cutting stresses and accelerating wear. Modern cutting is characterized by an increased automation of metal-cutting machines, by increased speeds, loads, and temperatures, andbyhigh requirements with regard to the precision and quality of the machine parts manufactured. For this reason the increase in productivity in the cutting of many metals is directly connected with an increase in the strength and wear resistance of the cutting tool. Wear-resistant and antifriction coatings have recently become widely used for the purpose of improving the durability of cutting tools. Thus, for instance, eiectrolytie chromium plating forms a surface layer with a high corrosion resistance, a low friction coefficient, high hardness, and wear resistance. The practice shows, however, that chromium plating is efficient only on cutting tools made of fast-cutting and carbon cutting steels (thread and gear cutting tools, etc.) where relatively low quantities of heat are created at the cutting edges, i.e., at relatively low cutting speeds (25-30 m/min) and pressures, and at cutting temperatures below 500 ~ since chromium begins to oxidize above 500 ~ and loses its hardness. It has been found [1] that the durability of a chromium-plated metal cutting tool increases as follows when working on steel and cast iron: in the case of drills by a factor of 3, of milling cutters by a factor of 2.53.5, of twist drills by a factor of 3, of thread cutters by a factor of 3-4, of cutting dies by a factor of 2.5, and in the case of slot hob cutters by a factor of 3. Significant developments have taken place in the chromium plating of tools (chromium plating in cold, tetrachromate, self-adjusting electrolytes, in an ultrasonic field, etc.). Nevertheless, the process is very laborious and expensive. For this reason, in an effort to improve the durability ofcuttingtools, great attention is paid to coatings of other metals and alloys. It has been found that the inclusion of other substances in the galvanic platings increases their hardness, thus increasing to some extent the wear resistance of the tool. It has been shown experimentally that the service life of hard-alloy blades can be increased significantly by coating their surface with a very thin layer of highly wear-resistant metal carbides [2]. Investigations of the durability of cutting tools with an electrochemicall y applied layer containing nickel and phosphorus, and of the effect of this coating on the cutting forces and the durability of cutters made of hard alloys, and of drills made of fast-cutting steels,have shown that the working properties of ha rd-alloy blades can be improved by the application of a nickel-- phosphorus coating on working surfaces that had been deeply etched. This pretreatment enhances the penetration of the coating material to greater depths, thus ensuring the presence of a lubricant on the toot surface for long periods of time. The durability of cutters with blades made of T15K6 alloy for the turning of steels that are difficult to machine, with a tensile strength of 82-84 kgf/mm 2, is increased by a factor of 1.6-2.2 and in the ease of drills made of R18 and I16M3 steels by a factor of 3-5 [3, 4]. With the aim to introduce cutting tools with anttfriction coatings in the fittings industry, the efficiency of the existing methods for the increase in durability of toots was analyzed at the VNIITarmaturoi. The following requirements were taken into consideration: The durability (service life) of the tool must be stable, the methods (of increasing the durability) must be efficient, relatively simple and inexpensive, and the tools should fit in the existing conditions of production with minimum capital expenses. Having in mind that the wear resistance of tools made of hard alloys is relatively high and that methods of further increasing the durability are complex, and that they require special equipment, tools made of

Effect of annealing on the properties of high-speed steels

1. Annealing (at 825–900°) for 24 h for hot-rolled and 15–18 h for cold-rolled high-speed steel lowers the quench hardness, secondary hardness, and red hardness. These properties are much more impaired after annealing at 900° than at 825°. 2. The effect of annealing depends on the amount and composition of M6C carbide, i.e., the chemical composition of the high-speed steel. The properties are most impaired for steel R18, where the carbide contains more tungsten, and less impaired for steels R12 and R6M5. 3. It is recommended that the annealing temperature not be higher than 850–860°, that the load in the furnace be limited so that the annealing time at temperatures over 800° does not exceed 10–18 h, and that the annealing time be still shorter for cold-rolled steels.

Investigation of carbide phases in high-speed steels R18 and R6M5

Investigation of carbide phases in high-speed steels R18 and R6M5

Carbide transformation in cast steel R6M5 during high-temperature treatment

1. Heating of steel R6M5 in the manufacturing process leads to transformation of eutectic carbides and also division, spheroidization, and coalescence of carbide particles. The carbide in the lamellar eutectic is transformed to M6C and VC; VC is also formed in hexagonal and skeleton eutectics. 2. In steel R6M5, unlike steel R18 [1], the carbide transformation occurs at relatively low temperatures and short heating times. 3. In steel R6M5 modified with nitrogen and zirconium the rate of the carbide transformation increases, while the rate of the change in the shape of the carbide particles decreases. The difference in the structure of steel R6M5 modified with zirconium or nitrogen and the standard heat after heating under identical conditions indicates the necessity of correcting the heating conditions for ingots of modified steel R6M5 before rolling.

Kinetics of induction heating of steel parts in a salt bath with a graphite crucible

1. Heating of steel parts in a high-temperature induction salt bath with a graphite crucible results not only from the heat from the surrounding fused salts but also from the electromagnetic field that occurs in the crucible. 2. The heating curves for steel parts in induction and electrode salt baths are of the same shape in the initial and middle sections. A difference in the curves is observed in the last stage of heating. In an induction salt bath the temperature in the center of the piece reaches the temperature of the fused salts, while in an electrode salt bath it remains 10–15° below the temperature of the fused salts. 3. The through heating time for steel parts is 30–50% smaller in an induction salt bath with a graphite crucible than in an electrode salt bath. 4. The effect of preliminary heating and the temperature of the salts is the same in both baths — the through heating time decreases as they increase. 5. The through heating time for samples of steels R6M5, R12, and R18 is practically the same with an identical temperature of the fused salts.

X-ray study of steel R18 irradiated with fast electrons

Radiation effects on highly alloyed C steels were investigated. It was found that changes in the crystal structure of martensite and retained austenite in irradiated steel R18 cannot be due to any cause not associated with radiation defects (heating in the process of irradiation, for example). As in irradiated carbon steel, it is an irradiation effect. With a high density of radiation point defects in the crystal lattice of martensite the carbon is redistributed in the ..cap alpha.. solid solution at a high rate (at low temperatures) not only in carbon steels but also in alloy steels. In alloy steels, as in carbon steels, irradiation is responsible for a new condition of martensite characterized by unordered distribution of carbon in the lattice. It may be that this change in the character of the carbon distribution in the lattice of martensite also entails a change in some properties of the material.

Size of excess carbides in high-speed steels

1. The number of large carbides (over 9 μ), commensurate with the radius of curvature of the cutting edge, increases with the weight of the ingot, especially in the case of high-tungsten steel R18, which is the result of the solidification conditions. 2. Reducing the tungsten content and adding molybdenum induce refining of the carbides. In deformed tungsten-molybdenum steel R6M5 the number of large carbides is only half that in steel R18. Nevertheless, the number of large carbides remains substantial in steel R6M5 obtained from large ingots (550 kg and larger). 3. The degree of deformation, which has a large effect on the distribution of carbides (carbide heterogeneity), has almost no effect on the size of carbides. 4. For the production of high-speed steels rolled to small sections (diameter up to 20 mm) it is recommended that the ingot weigh 100–150 kg.

Structure formation in titanium carbide-steel alloys produced by the infiltration process

1. The temperature at which the porous carbide skeleton of a Ferro-TiC alloy is sintered plays an important part in the evolution of the structure and properties of the alloy. 2. The higher the sintering temperature and the starting porosity of the carbide skeleton, the greater is the sintering shrinkage, which must be allowed for the design of casting molds for thermoplastic slips. 3. Use of carbide skeletons sintered at a high temperature, e.g., 2000° C, ensures strain-free infiltration with an even distribution of carbides, enabling nonporous alloys to be produced possessing high strength properties. 4. The disappearance of the ledeburitic eutectic in R18 and R9K5 steels after the infiltration of porous carbide skeletons sintered at 1500° C is linked with depletion of the alloying elements in the steels and their dissolution in the titanium carbide.

Rectification of salt baths for quenching tungsten-molybdenum and tungsten-molybdenum-cobalt high-speed steels

1. The susceptibility to decarburizing of the steels investigated increases in the following order: R6M5, R9M4K8, R6M5K5. 2. To prevent decarburizing of tools made of steels R6M5, R9M4K8, and R6M5K5 the minimal carbon content of control samples (bands of steel 13Kh) after heating at standard quenching temperature for 1 min should be 0.95–1%, as compared with the 0.85% required for quenching of steel R18. 3. The effect of the rectifiers tested increases in the following order: borax, ferrosilicon, magnesium fluoride. With periodic use of high-temperature salt baths one must add at least 0.6–0.8% borax and 0.35–0.50% ferrosilicon twice during the working shift and 0.6–0.8% magnesium fluoride once during the shift. in view of the low effectiveness of borax as a rectifier, it should be used only for quenching of tools heated for a short time. 4. Periodic additions of magnesium fluoride are possible in the absence of prepared mixtures of magnesium fluoride with barium chloride.

Effect of the structure on the mechanical properties of steel R18

1. High-speed steel R18 as-cast, with a fine crystalline structure, has, under all conditions, rates and temperatures of deformation, a ductility consderably lower than that for the wrought steel. 2. The cast steel is sensitive to the deformation rate. With static compression it is more ductile than with dynamic compression. At 800–1250° eCst/Cdyn. The wrought steel is less sensitive to the deformation rate. 3. The ductility in tension, compression, and torsion, and also the impact toughness, reach their highest values at temperatures 50–100° higher for the cast steel than for the wrought steel. 4. Heating of cast steel R18 before pressing and heat treatment at 20–800° and cooling from 800 to 20°, and also at 20 to 500° and 500 to 20° for the wrought steel, should be slow.

Low-temperature cyaniding of tool steels

1. It is expedient to use low-temperature cyaniding to increase the service life of tools manufactured from steels 4Kh4M2VFS, 3Kh2V8F, Kh12M, R18, R6M3, and R6M5. 2. The following cyaniding conditions are recommended for high-alloy tool steels: 560\2-600\dg for 1\2-3 h for steels 3Kh2V8F and 4Kh4M2VFS (DI-22); 540\2-560\dg, 1\2-3 h, for steel Kh12M; 560\2-580\dg, 5\2-60 min, for steels R18 and R6M3. Cyaniding under these conditions makes it possible to obtain a high-quality case 0.030–0.15 mm deep with a surface hardness H200=1075–1400. 3. Tests of the wear resistance, scoring resistance, heat resistance, red hardness, and fatigue resistance showed substantial improvements in these properties after cyaniding.

Heat treatment of high-speed steel R6M5

1. To obtain a higher hardness (>HRC 63) and heat resistance (>HRC 59 at 620°C for 4 h) the holding time for quenching steel R6M5 should be 25% longer than for steel R18. The optimal quenching temperature, producing a grain size of grade 11–10, is 1220–1240°C. 2. Steel R6M5 must be protected against decarburizing during heating to quenching temperature. The salt bath should be rectified (deoxidized) with magnesium fluoride or borax. 3. The optimal tempering conditions for the highest hardness and mechanical properties are tempering at 350° and double tempering at 560–570° for 1 h. For tools subject to attrition (without impact) it is recommended that tempering be conducted at 540–550° twice or three times for 1 h to provide higher hardness and heat resistance. The heat treatment recommended for steel R6M5 increases the durability of tools by 25–30%.

Increasing the ductility of annealed tool steels

1. To improve the ductility of previously annealed steel, the annealing temperature can be lowered from 730°C [2] to 630°C, which results in the cleanest surface. 2. Tool steels should be cooled rapidly from 630°C in water or oil. 3. To improve the ductility of steels R18, R6M3, and Kh12 it is recommended that they be annealed at 630°C with cooling in water, and that steel 9KhS be annealed at 800°C and cooled in oil from 630°C.

Technological and cutting properties of high-vanadium high-speed steels

1. Economically alloyed high-speed steels with a high vanadium content (8%) and low tungsten content (2.5%) are superior to steel R18 in heat resistance (by 10–15°C) and in cutting properties. 2. The wear resistance of blades of high-vanadium steels R2M3F8 and R2M4F8K5 in gear cutting at rates over 60 rev/min and feeds of 0.25–0.75 mm/rev is 1.5–3.0 times higher than that of steel R18. 3. High-speed steels with a high vanadium content (8%) and low tungsten content (2.0–2.5%) can be quenched to a smaller grain size (grade 11). 4. An increase of the chromium content from 4% to 6% in steel R2M3F8 is inadvisable, since it does not improve the durability of cutting tools. 5. High-vanadium steels can be recommended for tools with minimal grinding or no grinding.

High-temperature multistage hardening of high-speed steel

1. Raising the temperature of the quenching bath from 400–550°C to 600–675°C with brief holding (up to 30 min) of high-speed steel R18 causes no changes in the structure or physical, mechanical, or cutting properties. 2. Raising the temperature of the quenching bath above 675°C is inadvisable, since prolonged holding may lower the red hardness, strength, and cutting properties. 3. Quenching at 600–675°C with holding for no more than 30 min and cooling in air can be recommended for wide use in heat treating various tools of high-speed steel. It prevents cracks, substantially reduces deformation (warping, changes in dimensions, etc.), and eliminates the possibility of corrosion. 4. It is recommended that high-speed steel be quenched in a bath of BNK-1 salt, containing 50% BaCl2+25% NaCl+25% KCl, with a melting temperature of 590°C and operating temperature of 610–900°C.

Properties of steel R18 deformed at high rates

1. At 900–1180°C and deformation rates of 15–110 m/sec the carbide heterogeneity after upsetting and, particularly, after pressing is one to three grades smaller than in the original material. The grain size is grade 10–12. 2. The bending strength is highest for samples deformed at the rate of 50 m/sec.

Structure and properties of sintered R18 steel

1. In the manufacture of sintered R18 steel by DHP, the optimum process parameters are: treatment temperature 1250–1280°C, specific work of pressing 25–30 kg−m/cm3, and holding time 10 min. 2. Sintered steel produced by this method has a homogeneous, fine-grained structure free from carbide segregation. 3. The useful life of sintered steel tools is twice that of tools made in standard steel.

Impact-abrasive wear of nitrided tool steels

1. The wear resistance of the nitrided case under impact loading conditions is higher than under static loading conditions and depends on the strength and toughness of the case, which is determined by the composition of the steel and the structure of the case. 2. With increasing depth of the case the wear resistance first increases and then decreases. The case depth at which the wear resistance is highest differs for steels with different types of structures. 3. With a high hardness (HV 1340) the wear resistance is higher with a deep case −0.015–0.02 mm for high-speed steels R18 and R12, 0.065–0.075 mm for high-chromium steel Kh12M, and 0.12–0.13 mm for chromium — tungsten steels 3Kh2V8F and 4Kh5V2FS. 4. The recommended nitriding conditions are 520°C for 1 h (or 560°C for 20 min) for high-speed steels, 520–540°C for 6 h for high-chromium steels, and 520–540°C for 6 h (or 540–560°C for 4 h) for chromium — tungsten steels.

Electron microscopic investigation of the structure of steel R18

Electron microscopic investigation of the structure of steel R18