GB2132638A - Aqueous agent for quenching ferrous alloy based on high-viscosity oxyalkylene glycol - Google Patents

Abstract

An aqueous agent for quenching components of ferrous alloys, in particular carbon steels and alloy or slightly alloyed steels, which makes it possible to achieve substantially homogeneous hardness throughout the thickness of the quenched components, while providing a transition temperature theta 2 between nucleate boiling and convection, that is at least equal to 260 K, comprises from 0.5 to 20% by weight of a polyoxyalkylene glycol ether having a viscosity at 20 DEG C that is at least equal to 100,000 and preferably at least equal to 150,000 mPa.s. It is also possible to introduce various additives and in particular borax, in a concentration of from 0.2 to 5% by weight. In many cases, the aqueous agent may replace quenching oils.

Description

SPECIFICATION Aqueous agent for quenching ferrous alloy based on high-viscosity oxyalkylene glycol The present invention relates to quenching in an aqueous agent and more particularly concerns an aqueous quenching agent for ferrous alloys and more particularly for carbon steels and alloy steels.

It is known that optimum mechanical characteristics are achieved in steels only after the steel has been heated at elevated temperature and quenched. The rate and the conditions of cooling of the steel during the quenching operation have a crucial influence on the mechanical properties of the steel. If these conditions are not observed, the result may be deformation and even shrinkage cracking of the quenched components.

Quenching is generally carried out in a liquid or other fluid agent. Depending on the desired rate of cooling, the liquid agent may be of the aqueous, oily or igneous (molten salt) type. The theory and practice of quenching steels are set out for example in the chapter entitled 'Quenching of steel' on pages 1 5 to 36 of volume 2 of the 'Metals Handbook' 8th edition, edited by the American Society of Metals.

When a steel component that has been previously raised to a high temperature, for example 8500C, is quenched in water, cooling takes place in three distinct stages.

The first stags, viz, calefaction, corresponds to the temperature range of from 8500C to about 5000 C. In this stage the component is encased in a layer of water vapour which insulates it from the liquid water and reduces the rate of cooling.

The second stage, viz. nucleate boiling, approximately corresponds to the temperature range of from 5000C to 1 500 C. In this stage bubbles of water vapour appear at a large number of points on the component.

The third stage involves cooling by conduction and convection, by virtue of direct contact between the liquid water and the component.

Moreover, it is known for different additives to be added to the water used as the quenching agent in order to regularise their action and to shift the transition between the calefaction phase and the nucleate boiling phase in the desired direction and as far as may be possible.

In 1960, in a marketing brochure, Wyandotte Chemical Co. recommended the use of polyoxyalkylene glycols as additives for quenching agents. The substance identified by the registered trade mark Pluracol V 10 had a moiecular weight of from 25,000 to 35,000.

The above quoted 'Metals Handbook' states that the addition of 0.01% of polyvinyl alcohol to the quenching water substantially increases the rate of cooling during the calefaction phase.

French Patent FR-A-1 384 244, which is equivalent to U.S. Specification No. 3,820 893 describes aqueous agents based on polyoxyalkylene glycols with the addition of anti-corrosion agents such as nitrites or borates, in proportions that are not clearly defined but that are certainly low.

However, systematic tests carried out with polyoxyalkylene-glycol-based aqueous agents gave results that were still greatly different from those produced with mineral oils. In particular, the calefaction phase, at least in a quenching agent that is not agitated or that is only slightly agitated, is unstable and difficult to reproduce, while the point of transition, referred to as 02, between the nucleate boiling phase and the convection phase occurs at an excessively low temperature (about 130 to 1 800 C), whereas, in the ideal situation, it should occur at about 3500 C. This temperature substantially corresponds to the point, referred to as Ms, at which martensitic transformation of most steels commences.

Furthermore, when using agents based on water-soluble polymers, in particular polyoxyalkylene glycols, it has been found that, when quenching a relatively thick steel component, for example a cylindrical testpiece from 20 to 30 mm in diameter, the core hardness is substantially less than the surface hardness, and that is generally unacceptable.

Surprisingly, it was found that quenching agents based on polyoxyalkylene glycol ethers behaved in a totally different manner as soon as the polyoxyalkylene glycol ethers had a viscosity of higher than 100,000 mPa.s and preferably higher than 1 50,000 mPa.s.

The present invention therefore provides an aqeous agent for quenching components of ferrous alloys and in particular carbon steels and alloyed or weakly alloyed steels, which makes it possible to achieve substantially homogeneous hardness throughout the thickness of the quenched components, while providing a transition temperature difference 02 between nucleate boiling and convection that is at least equal to 260K, comprising an aqueous solution containing from 0.5 to 20% and preferably from 5 to 10% by weight of a polyoxyalkylene glycol ether that has a viscosity at 200C at least equal to 100,000 and preferably at least equal to 150,000 mPa.s.

The quenching agent according to the invention may also comprise various additives which enhance its efficiency, in particular from 0.2 to 5% of a sodium salt. Borax (Na2B407) has shown itself to be particularly effective. Other additives of known type may be added such as anti-corrosion agents or biocides to prevent biodegradation of the quenching agent in the course of prolonged storage.

For the purposes of carrying the invention into effect, use is conveniently made of high-viscosity polyoxyalkylene glycol ethers which are manufactured and marketed by PCUK, Produits Chimiques Ugine Kuhlmann, under the registered trade mark Emkarox. Those substances are characterised by an ethylene oxide/propylene oxide ratio that is substantially equal to 3.

In order to demonstrate the effectiveness of the novel quenching agent and its superiority over the known agents based on polyoxyalkylene glycols of lower viscosity, the following tests were carried out: As comparative substances, the following quenching agents were used (viscosities are expressed in terms of mPa.s.): 1 water at 200C 2 Commercially available mineral oil at 500C 3 Emkarox FC 31, viscosity 19,500, at 5%, in water at 200C 4 Emkarox FC 31, viscosity 45,000, at 5%, in water at 200C 5.Emkarox FC 31, viscosity 45,000, at 5%, in water at 200C with the addition of 1.5% borax 6 Emkarox FC 31, viscosity 105,000, at 5%, in water at 200C 7 Emkarox FC 31, viscosity 1 65,000, at 5%, in water at 200C 8 Emkarox FC 31, viscosity 165,000, at 5% in water at 20"C with the addition of 1.5% of borax Although it is not possible to establish strict correspondence between the viscosity of the Emkaroxes used and their mean molecular weights, the following values can be given by way of indication: Approximate mean molecular weight FC 31/19 500 12,000 FC31/45000 24,000 FC 31/105 000 28,500 FC 31/165 000 29,000 The testpiece for the thermal tests is a silver cylinder 16 mm in diameter and 48 mm in length, provided with a thermocouple and heated at 8500C for 20 minutes.

The testpieces for the mechanical tests are cylinders made of steel 38 C2 (carbon 0.9%, chromium 0.51%) of the same size (1 6x48 mm), which are heated at 8500C and fitted with two thermocouples disposed halfway along, one at the core and the other under the surface.

Quenching tests were effected, with the liquid being injected under a pressure of 2 bars by means of a hypodermic syringe opening at the bottom of the testpiece, so as to eliminate the calefaction phase, as far as possible, and the position of point 62 (the transition between nucleate boiling and convection) was noted.

For the mechanical tests (taking measurements in respect of hardness and deformation), the procedure involved performing quenching tests with agitation in a rectangular stainless steel tank with a capacity of 3 litres, which is separated into two compartments by an internal partition disposed 2 cm from the bottom and not projecting above the surface of the liquid. A screw agitator rotating at 2000 rpm is disposed in one compartment and the testpiece to be quenched is introduced into the other.

By virtue of that arrangement, the quenching agent follows a circular path in its agitation movement.

Taking the steel testpieces after treatment in that way, measurements were taken in respect of Rockwell C hardness, under a load of 1 50 kg, on a cross-section produced after cutting, without heating, along a plant perpendicular to the axis and at a halfway point. The measurements in respect of hardness were taken at the surface, at a distance of 1 mm under the surface, at half-radius and at the core. Measurements were also taken in respect of deformation ofthetestpieces by comparison, art a temperature of 200C, of their diameters at the top, the middle and the bottom, along two perpendicular planes before and after quenching.

The results of those tests, in which the Emkarox was always used at a concentration of 5% by weight in water and a temperature of 200 C, are set out below.

1. Thermal tests, position of point 62 Agent No. Composition OC 1 water at 200C 100 2 oil at 500C 375 3 Emkarox FC 31 19500 130 4 Emkarox FC 31 45 000 155 5 Emkarox FC 31 45 000+1.5 wt.% borax 160 6 Emkarox FC 31 105000 195 7 Emkarox FC 31 165000 260 8 Emkarox FC 31165 000+1.5 wt.% borax 325 The table shows on the one hand the substantial increase in 62 when using Emkarox 1 65 000 and, on the other hand, the effect of adding borax, the influence of the latter being relatively small with regard to the substance having a viscosity of 45,000 and very substantial with regard to the substance having a viscosity of 165,000.

2. Mechanical tests: Rockwell C hardness 150 kg, of the steel 38 C 2 testpiece A Core Agent No. Surface 1 mm R/2 Core surface Comparative tests 1 58 56 52 51 7 2 49.5 49 47 45 4.5 3 57 56 54 51 6 4 56 55 53 51 5 5 55 54 52 50 5 6 54 53.4 51 49.5 4.5 Invention 7 50 49.5 49 48 2 8 50 49.5 49 48.5 1.5 9 49.5 49 48.5 48 1.5 Agent No. 9: Emkarox FC 31-165 000, 10%+borax 1.5% It is noted that, in the last three tests (according to the invention) (Emkarox 1 65 000), the curve in respect of hardness in a transverse direction is virtually flat (a difference of 1.5 to 2 points on the Rockwell scale between the core and the surface), which is a result that oil itself cannot achieve (a difference of 4.5 points) in the present case.The addition of borax is also favourable (a gain of 0.5 point), and likewise in regard to the increase from 5 to 10% of the concentration of Emkarox in the agent.

3. Mechanical tests: deformation of the testpiece Deformation of the testpieces, expressed in micrnmeters (shown are the limit figures measured and, below, the mean) Plane through the orifice Plane perpendicular to of the thermocouple the previous plane Quenching agent Top Middle Bottom Top Middle Bottom Water at 200C +7/+13 --3/+10 0/+10 0/+10 +10/+15 +2/+12 (Heterogeneous, insignificant) (Heterogeneous, insignificant) Oil at 500C +7/+10 0/+15 +6/+12 +3/+10 +0/+5 5/+10 +8 +7 +8 +6 +3 +7 Emkarox FC 45 000 +18/+20 +12/+24 +20/+20 +20/+20 +20/+20 +22/+27 5%+1.5% of borax +19 +18 +20 +20 +20 +25 Emkarox FC 45 000 +7/+13 +7/+15 +12/+17 +8/+13 +10/+13 +12/+17 10%+1.5%ofborax +10 +12 +14 +10 +11 +14 Emkarox FC 165 000 +9/+ 12 +8/+12 +9/+11 +8/+13 +10/+13 +10/+12 5%+borax (1.5%) +11 +10 +10 +11 +11 +11 Only the last test is in accordance with the present invention Attention is directed to the remarkabie degree of homogeneity and the low level of deformation produced in Emkarox 165 000, in a proportion of 5 wt.% with 1.5 wt.% of borax, which compares very favourabiy with the deformation which occurs when using oil.

Therefore, in most cases, the quenching agent according to the present invention may replace quenching oils, with all the resulting advantages: no smell, no pollution, no danger of fire and easy cleaning of the quenched components.

Claims (7)

Claims

1. An aqueous agent for quenching components of ferrous alloys that makes it possible to achieve substantially homogeneous hardness throughout the thickness of the quenched components, while providing a transition temperature difference 62 between nucleate boiling and convection, that is at least equal to 260 K, comprising an aqueous solution containing from 0.5 to 20% by weight of a polyoxyalkylene glycol ether having a viscosity at 200C that is at least equal to 100,000 mPa.s.

2. An aqueous agent as claimed in Claim 1, in which the said viscosity is at least 150,000 mPa.s.

3. An aqueous agent as claimed in Claim 1 or 2 comprising from 5 to 10% by weight of the polyoxyalkylene glycol ether.

4. An aqueous agent as claimed in any preceding claim further comprising from 0.2 to 5% by weight of a sodium salt.

5. An aqueous agent as claimed in Claim 4 in which the sodium salt is borax.

6. An aqueous agent as claimed in Claim 1, substantially as hereinbefore described.

7. A method of quenching a ferrous alloy in which the quenching agent is an aqueous agent as claimed in any one of Claims 1 to 6.