JPH0470366B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION This invention relates to the heat treatment of metals, and in particular to a novel method for rapidly cooling metals. To change the physical properties of metals and their alloys,
Various heat treatment methods have been devised in which metals are heated to a certain high temperature and then cooled. Cooling generally occurs at a relatively fast rate, and such cooling is usually referred to as "quenching."
(quenching) Quenching is accomplished by immersing the metal in a liquid bath, usually water or oil. Water alone is not suitable for quenching many types of steel because it cools very quickly and causes excessive distortion, causing warping and cracking of the steel. Hydrocarbon oils provide relatively slow cooling, which is desirable for producing physical properties such as ductility in the steel. However, the slow cooling rate obtained by oil quenching does not cause excessive distortion in the metal;
It also prevents the desired hardness from developing. Therefore, it would be desirable to provide a quenching liquid that cools metal at a rate comparable to or between oil and water, yet achieves maximum hardness without warping or cracking the metal. For this purpose, various aqueous solutions and dispersions of organic compounds have been proposed as quenching agents. Such aqueous solutions and dispersions approach the quenching properties of oil, but lack the fire, smoke and fume disadvantages associated with the use of oil. For example, U.S. Pat. No. 3,220,893 discloses a liquid quenching agent comprising an aqueous solution of oxyethylene and a liquid oxyalkylene having a molecular weight of 12,000 to 14,000 having higher oxyalkylene groups. Such compounds are also called polyether polyols and poly(oxyethylene oxyalkylene) glycols. According to the patent, oxyalkylene polymers have the property that their solubility decreases as the temperature of quenching increases, such as when a red-hot metal is added. It is said to eliminate water from the bath. This polymeric layer is said to be an excellent heat transfer medium operating at high speeds and therefore its use requires relatively short quench cycle times while minimizing internal stresses and strains in the metal. Uniform hardenability of metal can be obtained. Such nonionic oxyalkylene polymer quenching agents improve the cooling of metals not only by virtue of their opposing solubility at such temperatures, but also by increasing the viscosity of the water in which they are dissolved. Adjust speed. It has therefore become customary to use large amounts of polymer, for example 10-15% by weight. In use, such relatively thick baths have the disadvantage of "drag out". That is, the polymer is removed along with the quenched metal, causing undesirable changes in bath viscosity and the effluent resulting from cleaning the quenched metal must be treated to remove adherent polymers. Very high molecular weight nonionic polyoxyalkylene glycols can be used, but the increased viscosity they result in makes them impractical. By using an organic compound that creates a vapor blanket around the metal during the quenching operation,
It has been proposed to increase the quench cycle time. An example of such an organic compound is a water-soluble polyacrylate such as sodium polyacrylate, the use of which in a quench bath is covered by a U.S. patent.
It is the subject of specification No. 4087290. One object of the present invention is to provide a new quenching method using a quench bath whose composition can be varied to obtain a wide range of quench rates from oil quench rates to water quench rates. Another object of the present invention is to provide an aqueous quench bath that can provide cooling rates comparable to those obtained with oil at relatively low bath viscosities. Another object of the present invention is to provide a new method for quenching heated metal to obtain quenched metal parts having desirable physical properties and a clean and bright metal surface. These and other objects will become apparent from the following description and appended claims. According to the present invention, a novel quenching method useful for heat treatment of metals is provided. In this method, the metal is heated to a high temperature and then the general formula (wherein, R represents an organic group that does not significantly increase the water solubility or water dispersibility and nonionicity of the polymer). Approximately 0.5
It is quenched in a bath containing an aqueous solution containing ~5% by weight.
Typically, R will be a substituent selected from the group consisting of a phenyl group or an optionally halogen-substituted alkyl group containing from 1 to 7 carbon atoms, but R is not limited to such groups and may include n is approximately
an integer such as to give a molecular weight of 5,000 to 1,000,000, preferably 50,000 to 500,000, and the substituents R on at least about 50% of said units in said polymer are 1
An alkyl group containing ~3 carbon atoms. Particularly preferred baths according to the invention have a
An alkyloxazoline polymer having a molecular weight of about
Contains 1.5 to about 3% by weight. The nonionic substituted oxazoline polymer used in the quenching bath of the novel method of the present invention provides a quenching effect similar to that of previously known oxyalkylene glycol polymer quenching agents, but the amount used is Only 1/2 of the amount used for coalescence
It was found that ~1/3. Surprisingly,
It has also been found that the quench baths used in the method of the invention have significantly lower viscosities than baths containing oxyalkylene glycol polymers for a given quench rate. As mentioned above, certain aqueous quench baths containing organic polymers are capable of reducing the initial quenching (first part of the cooling curve) of the metal.
tends to give a wide range of vapor phases. In contrast, oil quench baths provide the desirable short vapor phase and extensive convective phase. The latter is extremely important when low hardenability alloys are concerned and when soft microstructures are to be avoided. Surprisingly, the quench baths of the present invention containing substituted oxazoline polymers exhibit relatively short vapor phases and extensive convective stages similar to oil quenchers, which can be less pronounced at higher temperatures. I understand. Therefore, the quench bath of the present invention has utility where other aqueous baths containing polymers are unsatisfactory. The nonionic oxazoline polymers used in the aqueous quench bath according to the invention are water soluble or at least dispersible in water at the concentrations used in the quench process. These polymers are substituted oxazoline homopolymers or copolymers. In any case, the polymers have the general formula where R represents any organic group that does not significantly increase the water solubility or dispersibility of the polymers or render them ionic. Generally, R will be a substituent selected from the group consisting of a phenyl group or an optionally halogen-substituted alkyl group containing from 1 to 7 carbon atoms;
n is about 5,000 to 1,000,000, preferably
an integer such as to give a molecular weight of 50,000 to 500,000, and the substituents R on about 50% of said repeating units are 1
is an alkyl containing ~3 carbon atoms. The polymers used in the quenching bath may therefore be homopolymers or copolymers, depending on whether the substituents R are the same or different for all units. In the case of copolymers, they may be heteropolymers or block copolymers. If the molecular weight of the oxazoline polymer exceeds 1,000,000, it is not preferable because the cooling rate becomes slow and the viscosity of the quenching bath increases. On the other hand, it is well known to those skilled in the art that if the molecular weight of the oxazoline polymer is less than 5000, it is impractical and the difference from other polymer quenching agents becomes unclear. As mentioned above, the substituent R may be an alkyl group such as a methyl group, an ethyl group, a propyl group, an isobutyl group, and a halogenated alkyl group such as a 1-chloroethyl group or a 1-chloro-n-butyl group. Furthermore, the substituent R may be a phenyl group. Particularly preferred nonionic oxazoline polymers for use in the quench baths of this invention are from about 200,000 to about
Polyethyloxazolines having a molecular weight within the range of 500,000. Such homopolymers are thermoplastic amorphous solids that are water soluble and have low toxicity. The monomers that form the polymers used in the quench bath of the present invention are described in Chemical Reviews , which is incorporated herein by reference.
71 No. 5, pp. 483-505 (1971). The polymers used in the quenching process of the invention, whether homopolymers or copolymers, may be prepared by polymerizing monomers or comonomers in a suitable manner. According to U.S. Patent No. 3,483,141,
The monomers may be reacted in the presence of a cationic catalyst in an inert atmosphere at a temperature of about 20<0>C to about 250<0>C. Polymer Letters 4, No.
See also pages 441-445 (1966). Examples of suitable monomers include 2-methyl, 2-
Examples include ethyl and 2-isobutyl-2-oxazoline and mixtures of these monomers. The polymerization temperature is preferably in the range of about 80°C to 250°C, and the reaction time is several hours, although the reaction time will vary somewhat depending on the reactants, polymerization temperature, catalyst type and concentration, and desired molecular weight. can be done. Typical cationic catalysts that may be used in the polymerization reaction include methyl iodide, alkyl halides such as 1,4-dibromobutane, and boron trifluoride etherate.
and strong acids such as P-toluenesulfonic acid, sulfuric acid, and nitric acid. The concentration of the catalyst is such that the molar ratio of monomer to catalyst is approximately 10:1 to 60,000:
It can be changed considerably so that it becomes 1. In the quench bath used in the method of the invention, the concentration of substituted oxazoline polymer can vary from about 0.5% to about 5% by weight of the bath. If the concentration of the substituted oxazoline polymer exceeds 5% by weight, a so-called drag-out phenomenon occurs in which the polymer is removed together with the rapidly cooled metal, which is undesirable. On the other hand, it is well known to those skilled in the art that if the content is less than 0.5% by weight, it is too thin and becomes close to water, making it almost impossible to obtain a rapid cooling effect. High molecular weight polymers, e.g. 200,000~
The preferred concentration of polymer with a molecular weight in the range of 500,000 is about 1.5-3%. Advantageously, the viscosity of the quench bath does not increase appreciably with increasing polymer concentration within the above range, thus avoiding undesirable drag-out of the polymer upon quenching the metal. The quench rate generally decreases with increasing concentration of substituted oxazoline polymer. The rate also decreases as the molecular weight of the polymer increases. Additionally, the quench rate generally decreases with increasing quench bath temperature measured prior to contact with the hot metal being immersed, with the preferred range of quench bath temperatures for many practical uses being about 21-60°C (about 70-60°C).
140〓). By adjusting the above factors, i.e., the temperature of the quenching medium and the molecular weight and concentration of the substituted oxazoline polymer used in the quenching medium, a relatively wide range of cooling rates can be achieved, from oil cooling rates to rates between those of water and oil. Cooling rate can be obtained. In addition to the requisite substituted oxazoline polymers, the aqueous quench baths used in this invention may contain other additives to improve performance in certain applications.
For example, corrosion inhibitors such as sodium nitrate, ethanolamine, amine soaps to prevent corrosion of quench baths, conveyor belts and hardened parts, as well as other additives such as defoamers, disinfectants, metal deactivators, etc. agents may be added to the bath. The following examples more fully illustrate embodiments of the quenching process of the present invention, but should not be construed as limiting the scope of the invention. Test Procedures For each test measuring cooling time, the test specimen was a cylinder 500 mm long and 10 mm in diameter, made of scale-resistant austenitic steel. A microthermocouple was inserted into the center of the cylinder, and in the example case the temperature reading output of the thermocouple was recorded with a stripyard recorder (Chessell 321). In the example, the curve was plotted on a computer (Commodor) on a display (Panasonic) instead of a striptease recorder. The specimens were heated in an electric resistance furnace at a temperature of approximately 925°C (1700°C) without any atmospheric adjustment. In each test, the temperature of the specimen when immersed in the quenching agent was 849°C (1620°C).
〓) It was. The amount of quenching agent used was 0.5, and the temperature of the quenching agent was 27°C (80°C). Cooling curves were obtained using the test conditions described above and aqueous solutions of various substituted oxazoline polymers. The cooling time for the specimen to be cooled from 871°C (1600〓) to 204°C (400〓) was determined from the cooling curve. The results thus obtained are described below. Example: Six quench baths were constructed. Baths A, B, and C contained aqueous solutions of polyoxyethylene-polyoxypropylene glycol, and the concentrations of polymer in the baths were 11.7%, 5.9%, and 3.9% by weight, respectively. Bath D,
E and F are polyethyloxazoline (molecular weight
200000), each with a concentration of
They were 3.0%, 2.3% and 0.75%. Baths G, H and I are different polyethyloxazolines (molecular weight
500000), each with a bath concentration of 2.0
%, 1.5% and 0.5%. The viscosity was measured for several baths and the cooling time was determined using the procedure described above. The data obtained as a result of such tests are shown in Table 1 below. [Table] From the data in the table, if the quenching effect is measured by cooling time (normal method) and a cooling time of 12 to 13 seconds is desired, a bath concentration of 11.7% polyoxyalkylene glycol is required, and its viscosity It can be seen that the value is 8.9cSt. (See Bath A). As a control, a similar quenching effect (13.3 seconds) can be obtained with a bath containing only 3% polyethyloxazoline (molecular weight 200000), whose viscosity is only 2.7 cSt (see bath D). Using a bath containing only 2.0% polyethyloxazoline (molecular weight 500000),
A quenching time of 18.9 seconds is obtained. However, the viscosity is only 2.7 cSt (see Bath G). Therefore,
Using the quench baths of the present invention containing substituted polyoxazolines, the same quenching effect obtained with polyethylene glycol can be obtained with only 1/3 to 1/2 the amount of polymer. Equally important is that the viscosity of the aqueous baths according to the invention is considerably lower when obtaining the same quenching effect as polyoxyalkylene glycol baths. Thus, the method of the present invention is useful where aqueous baths of other polymer systems are inadequate. EXAMPLE The purpose of this example was to determine the thermal stability of the polymer used in the quench bath of the present invention in comparison to certain previously known polymer quench agents. A rectangular sheet of 1010 carbon steel approximately 7.6 cm x 12.7 cm (3″ x 5″) was placed on a heating plate and heated. Two drops of the following aqueous quench bath were placed at various locations on the metal sheet. Table: As the metal sheets heated up, the water evaporated leaving behind the respective polymers. The alkylene glycol polymer smoked, released fumes, and eventually decomposed into a crust. The oxazoline polymer did not begin to smoke until the alkylene glycol polymer was completely carbonized. Example Three quench baths were created: baths N, O and P. These are polyethyloxazolines (molecular weight ~
50,000), the concentrations of which were 3%, 2% and 1%, respectively. The viscosities of the three baths were determined by the procedure described above. The data obtained as a result of such tests are therefore presented in Table 1. [Table] The quenching bath of the present invention achieves the same quenching effect at 1/3 to 1/2 the polymer concentration required for alkylene glycol polymer baths. Thus, upon disposal, the baths used in the present invention have less negative environmental impact and require less wastewater treatment.

Claims (1)

[Claims] 1. A heat treatment of a metal that produces a desired metallurgical change in the metal by heating the metal to a high temperature and then rapidly cooling the heated metal in a bath consisting of a liquid quenching medium. A useful quenching method in which the quenching agent is an aqueous solution containing 0.5% to 5% by weight of a nonionic, water-soluble or water-dispersible substituted oxazoline polymer based on the total weight of the quenching agent; The polymer has a repeating unit represented by the following general formula, where R is a phenyl group or a halogen containing from 1 to 7 carbon atoms such that when the polymer is present at the concentration it does not significantly alter the nonionicity, water solubility and water dispersibility of the polymer. an organic group selected from the group consisting of optionally substituted alkyl groups, and at least one of the repeating units in the polymer
A quenching method, characterized in that 50% of the substituents R are alkyl groups containing 1 to 3 carbon atoms, and n is an integer giving the polymer a molecular weight of 5,000 to 1,000,000. 2. The method of item 1, wherein the polymer has a molecular weight of 50,000 to 500,000. 3. The concentration of the polymer in the quenching medium is 1.5% to 3% by weight, and the polymer is
The method of paragraph 2, having a molecular weight of 200,000 to 500,000. 4 R is C ₂ H ₅ and n is 50000 to 50000 in the above polymer.
The first is an integer that gives a molecular weight of 500,000.
Section method. 5 The concentration of the polymer in the quenching medium is 1.5% to 3% by weight, and the polymer is
The method of paragraph 4, having a molecular weight of 200,000 to 500,000.