GB2167437A

GB2167437A - Corrosion and abrasion resistant steel

Info

Publication number: GB2167437A
Application number: GB08429776A
Authority: GB
Inventors: Brian Edward Protheroe; Christopher John Heathcock; Geoffrey Graham Garrett
Original assignee: Chamber of Mines Services Pty Ltd
Current assignee: Chamber of Mines Services Pty Ltd
Priority date: 1983-09-14
Filing date: 1984-11-26
Publication date: 1986-05-29
Also published as: GB8429776D0; GB2167437B; ZA847054B; EP0225414A1

Description

1

SPECIFICATION

Anewsteet BACKGRCrUNDTOTHEIIVVEN7-ION This invention relates to a new steel.

Wear is one of the most commonly encountered problems in equipment used during mining operations. There is an increasing trend towards mechanical systems in mining. Their successto a large extent will depend on overcoming the problems of severe abrasive wear in South Africa associated with the mining and handling of extremely hard abrasive quartzitic ore. To warrantthe expense of manufactur- ing such systems their components should have as extended a wear life as possible.

In a mining environment weartakes places due to abrasion and also due to corrosion by mine waters. Thus conventional stainless steel lasts much longer in a mining environment, in the absence of extreme abrasion,than mild steel due to the corrosion resistance of stainless steel.

It is an objectof the invention to provide a new steel which is both corrosion and abrasion resistantto a greater extent than commercially available steels. SUMMARY0FTHEINVENTION

Asteel according to the invention comprises, apart from iron and incidental impurities, 0,22to 0,27% carbon,7,Oto 8,5% chromium and 2,8to 3,2% nickel, all percentages being by mass. A nominal 8% of Cr should be aimed at. Further according to the invention, if the following incidental impurities are present they should not exceedthe percentages stated below: 35 Sulphur 0,008, phosphorous 0,02, copper 0,2, tin 0,03, titanium 0,001, manganese 0,5, molybdenum 0,06 and aluminium 0,05. In the as rolled condition this steel after7 passes shows a fairly high Vickers hardness, but a relatively lowtoughness on the Charpy scale. To improve the latterthe steel should be heated to a temperature of the orderof 1 100'C and oil quenched. Tempering at a temperature of between 200 and 2500C improves the toughness still further. Afurther heattreatment does not improve thetoughness, but at some sacrifice of toughness a slight increase in hardness may be obtained. DESCRIPTION OFAN EMBODIMENT

In an example of the invention a steel was made which in addition to iron contained the following elements in the given percentages by mass: C 0,24, Cr 7,08, Ni 3,2, S 0,007, P 0,012 Si 0,027, Mn 0.02 and Mo 0,01.

A 5 kg ingot 54mrn square was rolled to a 12 mm flat bar in about seven passes. Atthe start of each pass thetemperature was 11 00'C. Thefinishing temperature was not measured.

Samples of the finished barwere cut and polished. TheVickers hardness and the toughness of a sample as rol led, and tour samples subjected to different beat treatmentswere determined. The results appear in thefollowing table.

GB 2 167 437 A 1 Sample Heat Treatment Hardness (Temperatures Longitudinal Face 50 (HY 30) A as-rolled 507 A] 1 110'C 0hr) 0Q 540 A2 1 11WC 0hr) GQ. - 533 23WC ( hr) OQ.

A3 1 1ICC (1 hr) OQ, 23WC (5 hr) OQ, 1 11WC (1 hr) OQ, 23PC (3 hr) OQ.

537 Charpy V-notch Toughness (Impact energy J) 23 37 68 64 OQ = an oil quench.

The microstructure ofthe heattreated productwas afine-grained lowcarbon martensitewith retained austenite.

Fourtons ofthe abovedescribed steelwere made bya local steelmakerand madeinto componentsfor testing. The componentswere heattreated as in sample A3. Partswere weldedtogether before heat treatment.

The components were characterised by having high strength and good ductility. The steel also shows a high hardness with good toughness. Usually hardness and toughness are mutually exclusive.

As indicated above, the limits for many impurities are fairly high so that standard steel making practices and equipment can be used.

The steel wasfound to be readily machinable and weldable so that special fabrication practices are not called for. Dueto its hardness and toughness the steel is only 40% as machinable as En9 steel.

In situations wherethe productwas exposed to the synergistic effects of corrosion and abrasion,the steel performed exceptionally well, betterthan com- mercial abrasion resistant steels. Commercial stainless steel are more corrosion resistant, but have higher coefficients of friction which makes them unsuitablefor applications involving sliding abrasion, such as shaker conveyers.

Claims

1. A method of making a steel by forming a melt comprising, apartfrom iron and incidental impurities, 0,22 to 0,27% carbon, 7,Oto 8,5% chromium and 2,8 to 3,2% nickel, all percentages being by mass, and casting the meitto form an ingot.

2. The method claimed in claim 1 in which in the melt, if the following impurities are present, they do not exceed the percentages stated below: sulphur 0.008, phosphorous 0,02, copperO,2, tin 0,03, loo titanium 0,001, manganese0,5, molybdenum 0,06 and aluminium 0,05.

3. The method claimed in either one of the above claims followed by the steps of rolling the ingot in a plurality of passes to form a steel product.

4. The method claimed in claim 3 in which the steel product is heated to a temperatue of the order of 1 100'C and is then oil quenched.

5. The method claimed in claim 4 in which the quenched product is tempered at a temperature between 200 and 250'C.

2 GB 2 167 437 A 2

6. The method claimed in claim 5 followed by a further heat treatment of heating the product to a temperature of the order of 1 100'C and oil quenching it after which it is tempered at a temperature between 5 200and250'C.

7. A method of making a steel substantially as herein described in the embodiment.

Printed in the United Kingdom for Her Majesty's Stationery Office. 8818935, 5186 18996. Published at the Patent Office, 25 Southampton Buildings, London WC2A lAY, from which copies may be obtained,