FI95049B - Improved forging piece and its manufacturing process - Google Patents

Description

1 95049

IMPROVED FORK AND ITS MANUFACTURING METHOD -FÖRBÄTTRAT SMIDESSTYCKE OCH DESS FRAMSTÄLLNINGS-FÖRFARANDE

The invention relates to a method according to the preamble of claim 1 for producing a forging piece with advantageous strength properties and toughness, and to a forging piece made by this method.

EP 191873-B1 (= F1 72148) discloses a method for producing a direct quenched hot-rolled part with advantageous strength properties. The object of the invention is to improve this known technique so that the strength of the part, in particular the uniformity of the strength over the cross-sectional area of the part and the toughness of the part in direct quenching 10. The object of the invention is achieved as set out in claims 1 and 9.

The strength of the forging can in principle be improved by the following means: - increase in carbon content - increase in manganese content 15 - increase in chromium content - alloying with nickel - alloying with molybdenum

Increasing the carbon content effectively increases the strength, but high concentrations, especially concentrations substantially greater than 0.1%, impair toughness 20 and machinability.

Increasing the manganese content to more than 1% is useful in many cases, but manganese has a strong tendency to seep. This: easily causes quite large variations in strength over the cross-section of the part as well as between the parts in continuous production. In addition, the infiltration of manganese 25 impairs the machinability of the steel.

Increasing the chromium content by more than 2% weakens the toughness, especially when the carbon content is more than 0.06%. On the other hand, chromium has a slight tendency to seep, so that even concentrations above 1% do not impair the machinability.

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Nickel alloying is quite expensive, the operation and its effect on strength is relatively small, especially at low concentrations.

Molybdenum alloying is not a very popular operation because molybdenum is an expensive alloying agent and its strength-improving efficiency decreases with increasing concentration. In addition, molybdenum-induced bainite formation generally impairs toughness, especially if the carbon content is 0.15% or higher.

The invention is largely similar to the invention described in EP 191873-B1. An improvement over the prior art is achieved by adding small amounts of molybdenum so that the molybdenum content is 0.04 to 0.25 to 10% by weight, preferably 0.04 to 0.15% by weight.

Molybdenum alloying can effectively increase the strength of the steel according to the invention at low concentrations. This is based on the large so-called molybdenum. hardness factor and the fact that the introduction of a new alloying agent has a synergistic effect on hardening, i.e. the new alloying agent increases the hardness 15 together with other alloying elements (in this case manganese and chromium) more strongly than alone.

Molybdenum favors the formation of bainite, which can be seen, for example, in the so-called In the CCT diagram as a wide bainite area. The wide range of bainite compensates for the differences in strength between the surface and the center, since the formation of martensite on the surface 20 can be prevented and the body is made practically completely bainitic. In the steel according to the invention, molybdenum does not impair the toughness, but improves it. In addition, the wide bainite range means in practice that the extinguishing power used is not very critical, but a rather wide extinguishing power range is available. In the extinguishing of the large diameter bodies 25, the extinguishing power is forced to be relatively small, but this is not a significant disadvantage in the application of the invention.

The relatively high price of molybdenum limits its economic use to small concentrations. However, molybdenum is a much cheaper alloying agent than, for example, nickel in terms of its hardening-increasing power. In the steel according to the invention, the molybdenum content is at most 0.25% by weight and the preferred content is at most 0.15% by weight, whereby the synergistic hardening effect of molybdenum is most effective.

II

3 95049 laan. As the molybdenum content increases, the potency of the hardening effect per unit concentration decreases.

The unevenness of the strength can be improved by the extinguishing technique. By extinguishing the forging piece into water or an aqueous emulsion or solution 5, the steel according to the invention generally achieves a sufficiently uniform strength distribution over the cross-sectional area of the piece. Water is usually the most desirable extinguishing agent. Other substances may be added to the water to form an aqueous emulsion or solution. This affects the extinguishing power of the water.

The extinguishing power of the water can also be affected by adjusting its temperature. By raising the temperature of the water above room temperature, preferably above 30 ° C or 40 ° C, the best results are generally obtained in the practice of the invention. Another preferred extinguishing technique in the practice of the invention is spray extinguishing because of its excellent controllability. The power of the jet extinguishing can be easily adjusted and the extinguishing 15 can be applied to only a part of the piece. In this case, only the desired part of the part hardens, while the other parts remain soft and tough.

A particularly popular steel according to the invention contains the following weight percentages of non-ferrous substances: C 0.06%, Si 0.28%, Mn 0.91%, S 0.080%, Cr 1.11%, Al 0.038%, 20 Mo 0, 10%, Ti 0.019%, B 0.005%.

The steel billet according to the invention is well suited not only as a blank for a direct quenched hot forged part but also for cold forming, either briefly annealed or directly hot-rolled without annealing.

The steel according to the invention is also well suited for nitration. Molybdenum 25 improves emission resistance, which in nitration gives a higher interior strength. In addition, molybdenum has an anti-embrittlement effect, which gives better toughness, especially if the body is nitrated.

The forging blanks according to the invention can be cold-cut from bar-cast or hot-rolled steel and the finished guarantee can be directly extinguished from the forging temperature. The guarantees according to the invention can be machined and used without discharge.

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Forgings can also be assembled by fusion welding from several parts.

The steel according to the invention is also excellently suitable for carburizing. The advantage in this case is a higher-than-usual elongation and toughness of the interior, which is a result of the lower-than-usual carbon content of the steel. This enables the use of steel, especially in such carburized parts, which undergo major deformations and which therefore have to be rectified, for example by cold bending.

It has been found experimentally that the machinability of the steel according to the invention is clearly better than that of conventional steels (containing more carbon and often also 10 more manganese). Better machinability has been manifested in less wear on the high speed steel blade.

The strength and toughness of the part according to the invention can be improved by controlling the final hot forging temperature relatively precisely. The most popular final forging temperature is 950 ° C ... 1050 ° C. Another way to increase strength 1 5 is to map very low carbon. It is recommended that the carbon content be at least 0.07% by weight. In general, the carbon content should be so high within the limits defined by the invention that the tensile strength of the finished forged part without emission is at least 900 N / mm 2.

By adding small amounts of sulfur, at least 20 0.02% by weight, to the steel according to the invention, the machinability of the steel can be quite substantially improved. However, the sulfur content should not exceed 0.15% by weight, which impairs the mechanical properties.

The invention will now be described with reference to the accompanying drawing, the only figure of which shows the so-called CCT diagram. It shows the structure of the forging piece 25 (preferred alloy) according to the invention with different extinguishing powers.

The horizontal axis of the chart shows the time in seconds and the vertical axis the temperature in degrees Celsius. The martensitic region is indicated by the letter M, the bainitic region by the letter B, the ferritic region by the letter F, and the perlite region by the letter P. The regions are defined using different heating temperatures of the sample. 30 The solid line plot shows the situation at 1200 ° C, the dashed plot means 900 ° C heating, and the dotted line plot shows both 1200 ° C heating and sample modification with a 50% correction rate. As the diagram shows,

Claims (10)

A process for making a forging piece with advantageous pouring strength and toughness, characterized in that the material for the desired piece is made of a material which, in addition to iron and possible impurities, contains the following substances: C 0.04 ... 0, 14% by weight Si 0.05 ... 0.50 Mn 0.6 ... 1.0 Cr 1.0 ... 2.0 10 Mo 0.04 ... 0.25 S not more than 0.15 AI "0.1 B" 0.015 Ti "0.05 15 that the substance is forged at a temperature of 800 ° C ... 1300 ° C and that it in this way, a blank is transformed into a forging piece immediately after the forging phase is extinguished in water or in an aqueous emulsion or solution. Process according to claim 1, characterized in that the molybdenum content of the substance is 0.04 ... 0.15% by weight. 20 3. A process according to claim 1 or 2, characterized in that the temperature of the extinguishing liquid is poured higher than room temperature, preferably at a temperature higher than 30 ° C. 4. A process according to any one of the preceding claims, characterized in that the final temperature at the forging of the blank is 950 ° C ... 1050 ° C. Process according to any of the preceding claims, characterized in that the carbon content of the substance is at least 0.07% by weight. 6. A method according to any of the preceding claims, characterized in that the carbon content of the blank is poured so high that the tensile failure limit of the forging piece is at least 900 N / mm 2. 95049 8 Process according to any of the above claims, characterized in that the sulfur content of the substance is at least 0.02% by weight. Method according to any of the preceding claims, characterized in that the extinguishing is carried out as spray extinguishing either by extinguishing the entire forging piece or only a desired part thereof. 9. Forging piece with advantageous pour strength and toughness, characterized in that it is made of a material which, in addition to iron and any contaminants, contains the following contents of various substances expressed in weight percent: C 0.04 ... 0.14, preferably 0.07 ... 0.14 Si 0.05 ... 0.50 Mn 0.6 ... 1.0 Cr 1.0 ... 2 0. Mo 0.04 ... 0.25, preferably 0.04 ... 0.15 15. at most 0.15, preferably 0.02 ... 0.15 Al "0.1 B" 0.015 Ti 0.05 and that in the manufacture of the piece a hot forging of the piece has been carried out at a temperature of 800 ° C ... 1300 ° C with immediate extinguishing of the piece. 10. Forging piece according to claim 8, characterized in that its quenching has been carried out with the water or with an aqueous emulsion or solution, the temperature of which is preferably higher than room temperature.